tungsten inert gas welding - techav

TUNGSTEN INERT GAS

WELDING (TIG)

Learner Guide

TABLE OF CONTENTS INTRODUCTION PAGE 1 PROGRAMME 1 - (THE TIG PROCESS - AN INTRODUCTION) RESOURCE NOTES - PROGRAMME NO. 1 PAGE 3 SELF-TEST NO. 1 - TIG PRINCIPLES AND SAFETY PAGE 9 PROGRAMME 2 - (BASIC EQUIPMENT) RESOURCE NOTES - PROGRAMME NO. 2 PAGE 13 SELF-TEST NO. 2 - TIG EQUIPMENT PAGE 19 PROGRAMME 3 - (TIG EQUIPMENT SETTING UP PROCEDURES) RESOURCE NOTES - PROGRAMME NO. 3 PAGE 22 SELF-TEST NO. 3 - EQUIPMENT PREPARATION PAGE 33 PROGRAMME 4 - (TIG WELDING PROCEDURES AND PROCESSES) RESOURCE NOTES - PROGRAMME NO. 4 PAGE 36 PRACTICAL EXERCISES - PROGRAMME 4 PAGE 41 EXERCISE #1 - FUSION PROCESS ("PUDDLE WELD") PAGE 42 CRITERION CHECK LIST #1 (FOR A "FUSION RUN") PAGE 44 EXERCISE #2 - STRINGER BEAD PAGE 45 CRITERION CHECK LIST #2 (FOR STRINGER BEAD) PAGE 47 EXERCISE #3 - BUTT JOINT PAGE 48 CRITERION CHECK LIST #3 (FOR "BUTT-JOINT") PAGE 50 EXERCISE #4 - CORNER JOINT PAGE 51 EXERCISE #4.1 - OUTSIDE CORNER JOINT PAGE 53 CRITERION CHECK LIST 4.1 (FOR SIS OUTSIDE CORNER JOINT) PAGE 55 EXERCISE 4.2 - INSIDE CORNER JOINT PAGE 56 CRITERION CHECK LIST 4.2 (FOR SIS INSIDE CORNER-JOINT) PAGE 58 ALUMINIUM WELDING (LAP JOINT) PAGE 59 EXERCISE 5.1 - BASIC EXERCISES WITH ALUMINIUM PAGE 60 CRITERION CHECK LIST 5.1 (FOR ALUMINIUM-BEADS) PAGE 61 LAP JOINT PAGE 62 EXERCISE 5.2 - ALUMINIUM LAP JOINT PAGE 64 CRITERION CHECK LIST 5.2 (FOR ALUMINIUM-LAP JOINT) PAGE 65

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INTRODUCTION This learning aid, consisting of you "Learners Guide" and 4 video programmes, has been designed to assist you to learn the BASIC SKILLS and KNOWLEDGE involved in "Tungsten Inert Gas" welding processes. OBJECTIVES (PURPOSE OF THIS MATERIAL) This series serves to assist you, the "Learner", in achieving a "Learnership" in any of the engineering fields where TIG welding is stated as being a "unit of learning". PURPOSE STATEMENT (WHAT YOU WILL LEARN) During this learning programme you will learn:

o To describe the TIG welding process. o To identify, by name, the equipment, components, accessories and consumables

used in typical TIG processes. o To set up and prepare for welding. o To use TIG equipment to produce "flat welds" on thin metal, including steel, stainless

steel and aluminium. LEARNING ASSUMED TO BE IN PLACE (WHAT YOU SHOULD ALREADY KNOW)

o A working knowledge of Industrial Safety and Arc welding PPE. o Identify common metals and "alloys". o An understanding of AC and DC current. o Use SMAW equipment. o Use "oxy / fuel" welding equipment.

LEARNING OUTCOMES (WHAT YOU WILL BE ABLE TO DO AFTER COMPLETING THE TIG MODULE)

o Prepare a TIG outfit for welding. o Make down hand "stringer beads" on thin steel plate. o Weld common joints on m/s plate, stainless plate and aluminium stock.

LEARNERS INSTRUCTIONS (HOW TO USE THIS LEARNING AID) Step1 - Read the Resource Notes and follow any written instructions. Step 2 - View the relevant video section (where applicable). Step 3 - Complete any "Self-Test Exercise" (as applicable). Step 4 - Perform a practical exercise (as applicable). Step 5 - Have your mentor/facilitator assess your work.


PROGRAMME 1 - THE TIG PROCESS - AN INTRODUCTION THE BASIC TIG PROCESS In this section you will learn: 1.1. To describe the concept / principles of TIG. 1.2. Describe the equipment and consumables used in TIG process. 1.3. Describe types of welding currents. 1.4. Describe the necessary PPE and safety factors involved in TIG welding processes.

BEGIN THIS SECTION OF LEARNING BY READING THE RESOURCE NOTES BEGINNING ON THE NEXT PAGE.


RESOURCE NOTES - PROGRAMME NO. 1 1.1. PRINCIPLES OF TIG The acronym "TIG" stands for "Tungsten Inert Gas". The more "technical" term for this process is "Gas Tungsten Arc Welding" or "GTAW'. Both describe the principle elements used in the welding process, which are:

o An inert "shielding-gas" (normally Argon). o A "non-consumable electrode", made of "Tungsten" or a tungsten "alloy".

Tungsten inert gas (TIG) welding was developed in the 1940's primarily for welding Magnesium alloys and aluminium, both of which were considered to be "difficult" to weld before that time. Using an inert gas shield instead of slag to protect the weld- pool, the TIG process was a highly attractive alternative to gas (oxy / fuel) and manual metal are welding (SMAW). TIG has played a major role in the acceptance of aluminium for high quality welding and structural applications. TIG welding is a process in which an arc is generated between a tungsten electrode and the base metal to be welded. The electrode does not melt or become part of the weld and this is why the electrode is referred to as being "non-consumable". When the arc is struck the electrode, and the molten weld-pool, must be protected from the atmosphere to prevent "oxidation". In order to achieve this protection an "inert gas" is used to surround or "shield" the weld area. An inert gas is one that will not react with the electrode, the arc or the molten base-metal. The most common gas used with TIG is "argon" although, depending on the base metal type, other gases may also be used. The most usual "alternative gas" is "helium". The TIG process is well suited for welding many types of metal including: aluminium, magnesium, stainless-steel, brass, copper, cast-iron and low carbon-steel.

1.2. THE BASIC EQUIPMENT (TIG) The equipment needed to operate a TIG (GTAW) welding station comprises:


o A "Power Source" or "Welding Machine". This unit generates the "welding-current" required to cause an arc between the electrode tip and the base metal.

o A "shielding-gas" supply system. This is necessary to "shield the arc" from the atmosphere.

o A "Torch" which is the device used to direct the arc onto the base metal. o Welding Lead (cables) that carry the welding-current to the torch and back to

the power source in order to "complete" the welding circuit.

1.3. WELDING CURRENTS AND THEIR EFFECTS IN TIG WELDING In any electrical circuit electrons, which are "negatively charged", flow from a "negative pole", through the circuit, and back to the "positive pole" of a power source. In a "Welding Circuit" electrons move from the negative pole and are forced to "jump" across a small "air-gap" in order to reach the positive pole. This action (of the electrons) results in the "welding-arc". The heat generated in the "welding arc" causes the shielding gas to "ionise". Gas ions are "positively charged" particles and they move in the opposite direction to electrons. The heat developed in the arc is the product of the arc-current times the arc-voltage. Electrons effectively carry about 70% of the "arc-heat" and place this onto the positive pole of the arc. (Gas) Ions effectively carry about 30% of the arc-heat and place this heat onto the "negative pole" of the arc. Polarity Welding circuits may be configured in the following ways:

Direct Current - Straight Polarity. Direct Current - Reverse Polarity, and


Alternating Current. Straight polarity means that the "ELECTRODE" is connected to the "NEGATIVE" connection of the power source. The base-metal is connected to the positive connection. This configuration is also known as "DCEN", meaning: "Direct current-electrode negative". In this configuration, the electrons move across the gap from the "negative electrode" and into the "positive" base metal. The gas-ions, being "positively charged", move in the opposite direction, to the electrode. Straight-Polarity results in a weld with deep penetration because the majority of the arc-heat is concentrated at the positive terminal of the arc that is the base metal. Straight Polarity is the most USUAL Polarity for TIG welding with DC current. Reverse Polarity, not surprisingly, is the opposite of Straight Polarity. Here the electrode is connected to the "POSITIVE" connection of the power source and the base metal to the negative. Reverse polarity is also known as DCEP, meaning: Direct current, electrode positive. With reverse-polarity 70% of the heat moves to the ELECTRODE which is why the use of reverse polarity is limited to relatively LOW welding currents. Reverse Polarity is best suited for thin metal as it results in a weld with shallow penetration. One advantage with "DCEP" is the "cleaning action" it has upon metal surfaces. Let's explain this. CLEANING ACTION (DCEP) On some metals a layer of "oxide" will develop in the area ahead of the weld pool. This "oxide layer", if not removed, will prevent the weld-pool from flowing smoothly along the joint to be welded. In the "reverse-polarity mode" gas ions are attracted to the base metal where they literally "bombard" the metal like the pellets of a shotgun. This "bombardment" of ions breaks away the oxides leaving a "clean surface" onto which the molten "weld- pool" will flow. It must be noted that with "Straight-Polarity" there is NO cleaning action. NOTE: The major disadvantage of DCEP is that the greater portion of heat is developed at the positive electrode. This means that in order to obtain a "deep


penetration" and benefit from the "cleaning action", the current must be increased about 3 times greater than that used with "Straight polarity". This current increase, plus the fact that more heat is developed at the positive electrode, means that an electrode operating on Reverse Polarity must dissipate about five times as much heat as an electrode operating on Straight polarity. Usually an electrode for reverse polarity is about four times the diameter of an electrode used on straight polarity. DCEP results in relatively "shallow penetration". AC (WITH HIGH FREQUENCY) The 3rd current selection used with TIG is "Alternating Current". It must be made clear, right here at the beginning of this discussion, that an AC welding current (as used with TIG) must be "stabilised' using "High Frequency" voltage. When the electrode is connected to an AC supply the polarity changes continuously at a frequency of 50 times per second, between positive and negative polarity. It is for this reason that, in the AC mode, the desirable features of both DCEN and DCEP are obtained. Alternating current provides both the "penetration" of a negative electrode and the cleaning action of a "positive electrode". For practical purposes you should use AC-HF for all "aluminium" and "magnesium alloy" work. AC produces "medium penetration" in a weld.


1.4. PERSONAL PROTECTIVE EQUIPMENT AND SAFETY Any person who is involved in using TIG equipment must wear the correct Personal Protective Equipment (PPE) and be aware of "safety related" issues. PERSONAL PROTECTIVE EQUIPMENT Those of you who have already completed the TECH AV series "SMAW' will be aware of the need for PPE. The primary items of clothing and protective devices are the same in TIG processes namely:

o Protection of the eyes against "flash" (arc eye). o Protection of the skin against "flash burns". o Protection of other workers around you from "eye flash".

A notable difference between TIG welding and SMAW processes is the absence of "slag" and the need to "chip" a weld bead after it has cooled. For this reason it is really unnecessary to wear spats and a welding cap. Of course these items may be worn if you think they are necessary. Although the arc in a TIG process appears to be less "intense" than with the SMAW arc it is nevertheless still dangerous to the "naked eye" owing to the "radiation" of "infra-red" and "ultra-violet" rays. It is for this reason that you must wear a "Welding Hood or mask" fitted with a darkened glass "filter lens". Filter lens are available in various "shades" ranging between "shade number 9" up to "shade number 14". The higher the number, the higher the "protection". As a guide to the selection of a suitable shade-number the following recommendations are offered:

Shade Number Welding Current (Amps)

9 Below 20

10 20 – 40

11 40 – 100

12 100 – 175

13 175 – 250

14 250 – and over Table 1 - Welding Lens selection

Skin protection is also an important factor in the TIG process. Prolonged "unprotected" exposure to arc rays will result in "arc burn", a similar condition to sunburn. The most "vulnerable" parts of your body are your hands, your face and your neck area. Special "welding gloves", made from soft leather (pigskin), are usually worn by experienced TIG operators. These gloves offer protection from the arc rays yet they also permit "flexibility" if your fingers whilst inside the gloves. Standard "welding gauntlets" are seldom used because they are too "stiff' and cumbersome for the "delicate" handling of a TIG torch. It must be noted that "pig


skin" gloves are NOT heat resistant and for this reason do not handle "hot metal" whilst you are wearing them. A welder’s helmet (hood) will offer the necessary protection for your face. In order to protect your neck area, and any other part of your body too, it is recommended that you wear proper "overalls" (coveralls) and have all the buttons (or zipper) done up. The sleeves should be rolled down too! People working around you should be protected from the arc. Ideally you should erect "flash screens" around your welding bay, or around the area in which you are working. People around you who are exposed to "reflected rays" (bouncing off a white wall or off glass etc.)should wear "anti-flash goggles". The welder (operator) should "discourage" anyone from "watching" a weld. Anyone who looks directly at the arc MUST wear a "welding hood". BASIC SAFETY

As can be expected, there are some basic "safety rules" applicable to TIG processes. The following "considerations" apply:

o Always use and wear the applicable PPE. o Do not weld in "confined areas" as the risk of "oxygen deficiency" is high

owing to the "oxygen displacing" nature of the "shielding gases". Always ensure an adequate flow of "fresh air".

o Be careful regarding "fumes". Certain metals and alloys may produce toxic fumes when molten. Always have your Mentor / Facilitator advise you concerning this issue:

o Ensure that gas cylinders are securely "chained" in the upright position. A falling cylinder can cause tremendous damage.

o Never stand "facing" the discharge side of a cylinder whilst "blowing out' or when opening the cylinder valve.

o Remove all "combustible materials" from around the welding area before you commence work.

o Observe the necessary rules for working on or around "electrical machinery" and never operate the equipment in wet conditions.

o Observe all "general safety rules" that apply to your industry or plant area.

NOW VIEW THE VIDEO (TIG -1) AND THEN COMPLETE THE SELF -TEST EXERCISE ON THE NEXT PAGE.



SELF-TEST NO. 1 – TIG PRINCIPLES AND SAFETY INSTRUCTIONS Complete the following exercise without reference to your notes or the video. When you have completed the exercise check your answers / responses by:

o Referring to the notes. o Reviewing the video material. o Asking your Facilitator / Mentor.

QUESTIONS YES NO

1. What do the letters “TIG” mean? ANS: _________________________________________________

2. What other letters also describe the TIG process? ANS: _________________________________________________

3. For which metal type is TIG particularly useful? ANS: _________________________________________________

4. Which component in the TIG system contains the metal "Tungsten"? ANS: _________________________________________________

5. What does the "Inert Gas" do in the process? ANS: _________________________________________________ _____________________________________________________

6. What type of gas is most commonly used in the TIG process? ANS: _________________________________________________

7. List those units required to make up a full TIG welding system: i) _______________________________________________ ii) _______________________________________________ iii) _______________________________________________ iv) _______________________________________________


8. The electrons in an arc move in which direction? (tick applicable answer) a) From negative to positive pole. b) From positive to negative pole. c) In both directions.

9. Approximately how much of the "arc-heat" is deposited by electrons onto the pole? (Tick applicable answer) a) 30%. b) 70%. c) 100%.

10. Straight Polarity (DCSP) means what? (Tick applicable answer) a) Electrode positive. b) Electrode negative. c) Alternating current.

11. Reverse Polarity (DCRP) means what? (Tick applicable answer) a) Electrode negative. b) Electrode positive. c) Alternating current.

12. Which DC polarity would you use for maximum cleaning action? ANS: _________________________________________________

13. What factor in the TIG arc is responsible for the "cleaning action"? ANS: _________________________________________________

14. What "desirable features" does AC welding current provide? ANS: _________________________________________________

15. What are considered "essential" items of PPE when using TIG? i) _______________________________________________ ii) _______________________________________________ iii) _______________________________________________

16. What makes the TIG process “hazardous" in a confined space? ANS: _________________________________________________


17. What "General Safety rule" applies when using TIG? ANS: _________________________________________________

MOVE ON TO PROGRAMME #2.


PROGRAMME 2 - BASIC EQUIPMENT In this programme you will learn to identify the basic components that make up a typical TIG welding system. You will learn to describe the purpose and function of each major component in the system namely: 2.1. Welding Machines (Power Sources) and Welding leads. 2.2. TIG Torches and electrodes. 2.3. Shielding Gas supply system. 2.4. Filler rods (Filler material).

READ THROUGH THE NOTES THAT BEGIN ON THE NEXT PAGE.


RESOURCE NOTES - PROGRAMME NO. 2 2.1. WELDING MACHINES (POWER SOURCE) Welding Machines for TIG processes must be of the "constant current" type. Most AC / DC "SMAW' welding machines can also be used for TIG. Some machines are produced specifically for TIG operations and these types offer every feature you will need in order to perform any TIG weld. With the exception of aluminium, virtually all metals are welded using Direct Current (DC) and for this reason it is most important that you have a machine that offers this feature. More specifically, you will need "DC Straight Polarity" (DCEN) more than "reverse polarity" (DCEP) as reverse polarity with TIG is rarely used. If you have to weld aluminium then you will need a machine that offers an AC output with "High Frequency" (HF). Without launching into a complicated theoretical explanation, suffice it to say that, without the HF factor, the arc will not be "stable". AC with HF offers the "best" results on aluminium owing to the excellent "cleaning action" of AC. You can weld aluminium using DC Reverse Polarity (DCEP) but the results (quality) do not match AC-HF. An "ideal machine" (power source) for a TIG operation should include the following features:

o Selection between current types (ACHF and DCEN at least). o Selection of current ranges (from around 20 up to 250 amps or more) with

"fine control" adjustment. o A "High Frequency" start facility for DC operations. o High Frequency "continuous" control for AC-HF operations. o "Tapering Current control", either on a "foot control" or "thumb switch

control". o "Remote control" and "Panel" selection facility (External or Internal Control). o Shielding-gas control, specifically "post flow" setting control. o "Quick-coupling" connections for the welding leads. o Torch cooling facility (water cooling) on machines rated above 200 amps

(welding current).


Typical combination TIG and SMAW power source

Unfortunately a power source with all the TIG functions is very expensive and therefore not found in every workshop. It is very likely that your company, where the need for TIG welding arises, will utilise a "combination welding machine" (AC / DC unit). As mentioned, this type of machine can be used for both TIG and SMAW welding operations thus making them more suitable for "general purpose" work. All that is required in order to set up your ACIDC welding machine for TIG is:

o A TIG torch attached to a suitable "electrode cable" (to suit your machines output connection).

o Shielding gas supply and regulator. 2.2. WELDING LEADS (WELDING CABLES) Welding leads are connected to the welding machines' "output connections". Welding leads carry the "welding current" out of the machine, through the work, and back into the machine thus completing the "welding current circuit'. One lead carries current to the "electrode" and hence it is called the "electrode lead" (or electrode cable). The second lead, called the ground lead (or work lead), carries the "return current" to the machine. Both leads are connected into the machines' "welding connector sockets", and depending on the type of machine, these may be labelled in the following ways:

o “+” and “–”. o “Electrode” and "Work” or sometimes "Ground"/

2.3. TIG TORCHES AND ELECTRODES THE TORCH TIG torches can be obtained in many shapes and sizes and the selection of any particular type is normally made according to the type, and the position of the work that has to be done. A torch serves 4 main functions, namely:


o It holds the "electrode", enabling the operator to place the electrode tip where it’s needed.

o Makes electrical connection with the electrode. o Directs the "shielding gas" around the electrode and onto the weld area. o Insulates the operator from electrical shock.

A typical torch comprises the following:

o Torch Body. o Nozzle (also called a "cup"). o Collet Body. o Collet. o End Cap and "O-Ring" (seal). o Gas flow-control (on manual types). o A "thumb switch" (on remote types).

The torch body contains the "electrical connection" to an "electrode", the shielding gas and, on liquid cooled types, the cooling water. The "nozzle" (also called the "cup") is used to direct the shielding gas onto the weld" Nozzles are available in various sizes (diameters). The nozzle size selection is made, amongst other reasons, by the "volume of gas" required for a given weld. Nozzles are (usually) made from "ceramic" material (e.g. "Alumina") that can withstand extremely high temperatures. The collet-body (sometimes known as a "guide") and a "split-collet" fit into the torch-head. The collet assembly provides a firm grip, and electrical-connection, upon the selected "electrode" which is inserted through the split-collet. An end-cap (also called a "back-cap") is threaded into the torch head, over the projecting electrode. The end-cap has a "gas-seal", usually in the form of an "O- Ring", in order to prevent the leakage of "shielding-gas".


2.3. TUNGSTEN ELECTRODES Tungsten is used to manufacture TIG electrodes because it (tungsten) has the highest melting point of all metals (3,400 degrees C). Tungsten remains "hard" even when it is at "red heat". If used correctly a tungsten electrode should last almost indefinitely. Electrodes are available in various types, diameters (size) and lengths. The standard electrode length is nearly 150mm. Standard "electrode-sizes (diameters)" range from as small as 0.5mm and go up to 6,35 mm. The two most commonly used types of electrode (in SA) are alloyed with either Thorium or Zirconium. These elements improve the "arcing characteristics" of electrodes under certain conditions. "Thoriated Electrodes" are colour coded "red" and are best suited for DC current. "Zirconiated Electrodes" are colour coded "white" and are best suited to AC-HF current. A new electrode has to have its "tip" prepared, usually by grinding, into a specific shape before it can be put into use. We will cover this aspect in a later session. 2.4. SHIELDING GAS Shielding gas, most commonly "argon", is stored in a "gas cylinder", similar in construction to the "oxygen cylinder" of an "oxyacetylene set". Shielding gas is stored at very high pressure, (approx. 200 kg/cm2 or 200 bar). This pressure is far too high for direct use in the welding system, but necessary in order to store sufficient volume within the cylinder. The delivery pressure (pressure supplied to the torch) is around 2 bar (2.1 kg/cm2), and this is achieved through a "Regulator / Flow-meter". The "regulator is attached to the delivery-valve situated on top of the cylinder. The delivery-valve is controlled (opened or closed) by a "hand-wheel". When the "delivery valve" is opened gas from the cylinder flows through the regulator. A "pressure gauge", attached to the regulator, indicates the "remaining pressure" within the cylinder. When the pressure gauge shows a low pressure (approximately 2kg/cm2) then the cylinder must be "refilled" by your local gas- supplier. A flow meter controls the rate at which gas passes through the "gas line" and into the torch. This (flow rate) can be "adjusted" by the operator to suit the welding requirement. The "flow rate" of gas is measured in "litres per minute" (Lpm).


Most regulators and flow meters are housed together as an "assembly".

Note: The pressure-gauge does NOT indicate the pressure in the gas-line (to the torch).

Typical regulator and flow meter

The gas cylinder is most usually situated directly behind the welding machine and frequently you will find that the cylinder is carried on the same "frame or chassis" that supports the welding machine. 2.4.1 HANDLING CYLINDERS Cylinders, especially FULL cylinders, must be handled very carefully and kept UPRIGHT. If a cylinder is allowed to fall, or drop, there is the danger of the delivery- valve breaking off. Should this happen, the cylinder will take off like a jet causing tremendous damage and even death to anyone in its path! A cylinder must always be secured (to a solid structure) with a strap or a chain to prevent it from toppling over. Many welding machines have a special cylinder platform onto which the gas cylinder is positioned and chained. As a rule you should never open the delivery valve and allow the gas to discharge freely into the atmosphere. The pressure of the gas can cause any solid particles (dust etc) to be propelled at tremendous speed and result in serious injury should they strike a person. 2.5 FILLER RODS Whenever a weld has to be "reinforced" we must add "filler material" into the molten "weld-pool". Reinforcement is achieved using a "filler rod" (sometimes called "filler-wire").


Filler rods are made of solid "wire" and may be obtained in pre-cut lengths (approximately 900mm) or on "reels". The material from which the rods are made is normally an "alloy" of "compatible metals" (similar to the base metal). TIG filler rods must NOT be confused with "Gas Welding Rods" which are not suitable for use with shielding gases. Filler rods are most usually identified by an identification code that is stamped onto each rod. (Note that some rods, notably "mild steel rods" may not be marked. Always make sure that your supplier provides you with "suitable TIG rods).

BASE METAL FILLER METAL (identity)

Aluminium ER1100, ER4043, ER5356

Copper & Copper Alloys ERCu, ERCuAI-A1

Magnesium ERAZ61A, ERAZ92A

Nickel & Nickel Alloys ERNi-1, ERNiCr-3, ERNiCrMo-3

Carbon Steel (Mild Steel) ER70S-3, ER70S-6

Low Alloy Steel ER80S-B2, ER80S-D2

Stainless Steel ER308, ER308L, Er316, ER347

Titanium ERTi-1

Zirconium ERZr-2 Table 2 -Filler rod material and identification

NOW VIEW THE VIDEO (TIG-2) AND THEN COMPLETE SELF-TEST EXERCISE NO. 2.



SELF-TEST NO. 2 - TIG EQUIPMENT INSTRUCTIONS Complete the following exercise without reference to your notes or the video. When you have completed the exercise check your answers / responses by:


QUESTIONS YES NO

1. What two features must a welding machine have if you want to use it with TIG? i) _______________________________________________ ii) _______________________________________________

2. When connecting the welding leads to a DC machine to which "output connection" would you "normally" connect the "electrode lead"? ANS: _________________________________________________

3. When you have connected the electrode lead as answered in question 2 then you have set the welding current to what? (Tick the answers that relate) a) DCRP. b) DCSP. c) DCEN. d) DCEP.

4. Which type of welding current is normally used when welding Aluminium? ANS: _________________________________________________

5. What are the 4 main functions of a TIG welding-torch? i. _______________________________________________

ii. _______________________________________________ iii. _______________________________________________ iv. _______________________________________________


6. Name the main parts of a typical TIG torch. 1) _______________________________________________ 2) _______________________________________________ 3) _______________________________________________ 4) _______________________________________________ 5) _______________________________________________ 6) _______________________________________________ 7) _______________________________________________

7. In this country (South Africa) you will usually obtain electrodes colour coded red or white. What do these colours indicate? a) White electrodes are used with ___________________ . b) Red electrodes are used with ____________________ .

8. What is the purpose of a "regulator/flow-meter"? ANS: _________________________________________________

9. Filler rods (or wires) suitable for TIG welding can be identified how? (give 2 answers) 1) _______________________________________________ 2) _______________________________________________

CHECK YOUR ANSWERS BEFORE PROCEEDING TO PROGRAMME #3.


PROGRAMME 3 - TIG EQUIPMENT SETTING UP PROCEDURES In this programme you will learn to prepare the following for use:

o Typical Welding machines. o Shielding Gas apparatus. o A typical TIG torch.

And then:

o Set-up for welding.

BEGIN THIS SECTION OF LEARNING BY FIRST READING THE RESOURCE NOTES BEGINNING ON THE FOLLOWING PAGE.


RESOURCE NOTES - PROGRAMME NO. 3 INTRODUCTION As in any welding operation it is important that your TIG equipment is correctly installed, connected and set-up. The following items are those which we shall be "attending to" in this module:

o Pre-Inspection of the welding-set. o Connecting of welding leads or "cables". o Connection of shielding gas accessories. o Torch Preparation. o Machine Setting. o Work station preparation.

We shall explain each point using "typical" equipment. It must however be noted that for "specific instructions" you must refer to the "Operators Manual" for the machine or system that you will be using. NOTE: This series of instruction assumes that the power source is "mains powered" as opposed to "engine driven" welding sets. 3.1. PRE-INSPECTION OF THE WELDING-SET The power source must be in "safe working order" and your first task should be to check the power source, and the attachments, to ensure that they are "safe" to use. The following items should be inspected visually and all faults reported to a supervisor prior to connecting the machine to the mains.

o The "general condition" of the welding set. o The mains supply cable to the machine. o The welding leads and terminal connections. o The shielding gas components.

A welding machine, and its accessories, in poor general condition is probably an "electrical hazard" too! Check the following items and if they are damaged, missing or in an "unsafe-condition" DO NOT USE the set.

o Covers and panels must surround the "internal electrical components". The covers must be secured with all the fasteners intact.

o The incoming Power Cable or "supply cable" must be in a safe "electrical condition". Any damage to the insulation or exposure of conductors constitutes an "UNSAFE CONDITION". Inspect the cable along its entire length from the machines' "entry point" right up to the "connector plug". Make sure that the connector plug is securely attached to the cable and that its electrical contacts are clean and "bright".

o The welding leads must also be "electrically safe". Damage to the cable insulation, exposure of conductors and loose or poorly fitted "connecting lugs" all constitute "electrical hazards". Note that the electrode lead is usually


"sheathed" in order to contain the gas line to the torch and water lines where applicable. If the sheath is in good condition then the electrode lead to the torch is likely to be in good condition as well.

o Check the welding lead connection terminals. "Stud type terminals" should be secure and not "floppy". If these are loose then secure the "retaining nuts" using a spanner (not pliers!).

o Inspect all the "panel control devices". Loose and broken switches, broken control knobs, missing knobs and "jury rigged" shear pins (on selector levers for example) all contribute to an "unsafe machine".

o All "decals" or "instructional notices" must be "readable". If a switch or controller does not have a label then the chances are you'll be GUESSING what that control is for.

o The Shielding Gas Cylinder is usually carried in the same "base" as the machine. Check that the cylinder is properly positioned on its "platform" and that it is secured with a chain or a strap.

o All gas cylinders must be fitted with a pressure-regulator/flow meter unit. Make sure that this is in good condition and properly installed. (We cover this aspect in the module). The pressure gauge must be undamaged and "readable".

o Make sure that the set is "stable" and not likely to topple. Check that the "castors" or wheels on the trolley are in good condition and not loose, broken or "about to fall off'. It is very dangerous to move a set on a "wobbly base".

NOTE: Make sure that the machines" "isolation switch" (ON / OFF) is in the OFF position before you make the connection to the "mains supply". 3.2. CONNECTING THE WELDING LEADS (CABLES) SAFETY NOTE: It must always be kept in mind that the connecting of any current conducting apparatus is a hazardous operation and safety-rules apply. In the case of welding cables the following rule must be observed:

o NEVER connect or disconnect a cable when the machine is switched ON! Always ISOLATE (Switch OFF) the machine at the ON / OFF switch whenever performing this task.

Welding cables are connected to machines either with "lugs" or with "pin connectors" (also known as "bayonet" connectors). As with any electrical connection it is important that the connecting metal parts are "shiny clean" in order to create a good, resistance free, electrical contact. Dirty or corroded contacts will result in damage to both the contacts and to electrical components in the power source. Lugs are secured to threaded contactor-studs (terminals) with nuts. The nut must be tightened firmly with a spanner of the appropriate size. The use of a "shifting spanner", water-pump pliers or any tool other than the spanner is not recommended as these tools will cause damage to the nut and the terminal. Do NOT


over-tighten the nuts as this can result in the stud rotating and this will cause an internal disconnection. Pin, or "bayonet" connectors should be inserted into their sockets and then twisted fully to the right in order to "lock" the connection. This "twisting action" also ensures a tight "electrical connection". Failure to do this can result in "arcing" between the pin and socket when the welding current flows. In the last module you learnt that welding leads, on certain power sources, may be connected according to the "polarity" required. Always make sure that you have the leads connected to the correct machine points. If the machine has "switch-able polarity" then the welding leads remain in their original "designated" positions. The "work lead" should be connected to the "work-piece" or to your welding bench. The ground clamp MUST be connected to "bright metal". Rust, paint, oil or any substance that might cause a "resistance" to current flow must be removed from the point of contact with the ground clamp. 3.3. CONNECTION AND PREPARATION OF SHIELDING GAS In this section we assume that you will be starting the process of preparing the gas supply from the time of fitting a "refilled cylinder". 3.3.1 INSTALLING A REGULATOR Before installing a regulator assembly it is wise to "blowout" any dirt from the delivery valve (thus preventing it from entering and damaging the delicate parts in the regulator). To do this, make sure that the valve is pointing away from you and anyone else and then quickly open and then close the cylinder valve. The regulator assembly is now attached (threaded) to the valve and secured using a "correct fitting spanner". (Do not use shifting spanners or pliers etc. as these can damage the regulator nut). Make sure that the flow meter is in the vertical position (upright) when the nut is tight. Connect the "gas-line" to the output connection on the flow meter. Make sure that the control valve on the flow meter is closed before you open the cylinder delivery valve. Always open the delivery valve SLOWLY to avoid a sudden "shock load" on the regulator. SAFETY: When opening the delivery valve always stand to the side of the apparatus, in other words DO NOT FACE the gauges. Open the valve SLOWLY to prevent a sudden rush of pressure into the regulator and the pressure gauge. (Gauges have been known to "explode!")


3.3.2 SETTING THE GAS FLOW When the gas line has been connected to the regulator, and the delivery valve has been opened, we can set the desired gas-flow. The commonest type of flow-meter is the "floating-ball" type and this is the type that we will explain. In order to set the desired flow rate the gas must be "flowing" through the system. When the gas is connected directly to the torch (basic system) we simply open the torch valve in order to get the gas to flow. If the gas is "machine controlled" then we need to connect the machine and turn it on. Set the gas "post flow timer" to its maximum time setting for purposes of setting the flow rate. Keeping the torch away from "ground", activate the "thumb switch". This should trigger the gas control solenoid in the machine and gas will flow to the torch. Check the hose (gas line) for any damage between the machine and the regulator. Check that the connections at both ends of the line are secure and that there are no leaks. While the gas is flowing adjust the flow-rate in the following manner:

o Turn (open) the flow control-knob at the regulator, until the ball "floats". Read the flow by comparing the TOP of the ball against the calibrated scale on the gauge-glass. Read the scale at "eye-level" to obtain an accurate reading. Adjust the flow, up or down, by turning the control knob in or out until the flow (in litres per minute) matches the "specified" or the "desired" rate.

o Close the torch-valve (if applicable) when the desired rate has been set, or o Wait for the post flow timer to "time out" and shut off.

The gas flow will now remain at the "pre-set value" each time the torch valve (or gas solenoid valve) is opened.

Read at "eye level" to top of ball


3.3.3 SETTING "POST FLOW" TIMER The "post flow timer", on machines so equipped, is set according to the welding current ("amperage"). The post flow control is nearly always situated on the control panel of the machine. The control knob will have markings to indicate time (in seconds) commonly from zero to 30 seconds. As a "general rule of thumb" allow 1 second "post flow" for every 10 amps of welding current. This is normally sufficient to cool the electrode and prevent the tungsten from oxidising at the end of a weld run. By way of example: If the welding current is 100 amps then set the post flow to (100 + 10) = 10 seconds. 3.4 PREPARE THE TORCH In the normal course of TIG welding it will be necessary for you to prepare your torch for whatever welding function you are attending to. In this section you will learn the basic preparatory steps for:

o Selecting and Preparing an electrode for DC and for AC applications. o Selecting a suitable "nozzle" for the job in hand. o Assembling the torch and setting the electrode protrusion.

3.4.1 SELECTING AND PREPARING AN ELECTRODE When selecting an electrode you need to know what current type and what current "value" you will be using for the particular weld. If you are using DC current then select a "thoriated" or "red" electrode. If you are using AC current then select a "Zirconium" or "white" electrode. Thereafter we are concerned only with the "welding current", or "amperage" that we'll be using in order to select a suitably sized electrode. Tables 3, 4 and 5 in this "learners guide" will enable you to make your selection based on several "parameters including material type, thickness and welding currents. When you have selected the appropriate electrode the next step will be to prepare it for welding purposes. You will notice that "new electrodes" have "blunt tips" therefore, before we can use the electrode, the tip will need to be "shaped". The tip shape is determined by the "current type". If the current is DC then the tip is pointed. The length of the pointed section is approximately twice the electrodes' diameter. If the current being used is AC then the tip shape is "rounded". In preparation for an AC electrode the tip is first sharpened to a shallow point. The length of the point is


approximately ¼ to 1/2 half the electrode diameter. The "ball shape" is formed upon striking the arc on a piece of clean steel or copper plate. Electrode tips are shaped using an "emery wheel" or "grind-stone". Tungsten is the hardest of all known metals; therefore the grinding-wheel must be "hard" and have a "fine-grit". A "silicon carbide" wheel is the most suitable for the dressing of electrodes. The face of the wheel must be clean, free of embedded material and properly dressed (to present a "flat" grinding surface). "Electrode tips" must be ground "longitudinally" in order to achieve desirable welding results. Do NOT grind a tip "horizontally' as this will result in "radial grooves" which in turn result in the arc becoming unstable.

3.4.2 SELECTING NOZZLES (CUPS) There are many sizes and shapes of nozzles. The size of a nozzle is determined by the "inside diameter" of the orifice, and this in turn, determines the volume of "shielding gas" that will surround the weld pool. Sometimes you will see "numbers" printed on nozzle bodies. The number is a "code" NOT the actual size. For example a NO.6 nozzle has an "inside diameter" of 9.5 mm. Table 3 lists commonly used nozzles and give their "inside-diameters".

Nozzle No.

Actual I.D (mm)

4 6.5 5 8.0 6 9.5 7 11.0 8 12.5 9 14.3

10 16.0 Table 3 - Nozzle numbers and sizes


The selection of a nozzle size is normally based upon the "width" of the weld bead. Naturally it follows that a wide bead requires a large diameter nozzle. As a "rough guide" one would select a nozzle that is between 3 - 4 mm larger (inside diameter) than the bead width or approximately 4 times the electrode size. The type of joint will also affect the selection of a nozzle. For example if you need to weld deep inside a groove root joint then you will need to select a "tapered nozzle" that will allow you access.

Typical application for a "wasted nozzle"

When fitting a nozzle that has been used always check that it is in good condition. Ceramic material is very brittle and can break easily if not carefully handled. A chipped, cracked or broken ceramic will not provide the necessary "gas envelope" and a weld of inferior quality will result. Check the inside of the nozzle as well. The inside must be clean and free of adhering "slag" that will affect the flow. If there is slag inside the nozzle tip then you will have to find another nozzle. Do not attempt to scrape out slag as it will be very ' permanently stuck" and you will end up breaking the ceramic in your efforts! (Both ways the nozzle must be discarded) 3.4.3 ASSEMBLE A TORCH The assembly procedure for a torch is not difficult and requires NO TOOLS. The torch will need to be assembled whenever you change the size of the electrode as this also involves the fitting of an appropriate collet and collet-body. Assuming that your torch is dismantled to begin with, follow this procedure:

o Select a collet, and a collet body to match the selected electrode (in terms of size). You will see size markings on the collets. (Use a magnifying glass if necessary).

o Thread the collet body into the torch body and secure it with your hand. Do NOT over tighten this.

o Select the desired nozzle (ceramic) and thread this fully onto the collet body. o Slip the "split-collet" together with the electrode into the torch body. Be sure

that the "tapered end" of the collet enters the back of the collet body. o Check that the rubber "O-Ring" on the back-cap (end-cap) is in good

condition and properly fitted.


o Fit the back-cap into the torch body .but don't tighten it at this point. o Get the electrode's tip to protrude past the end of the nozzle. The actual

protrusion should never be greater than the nozzles' "internal diameter". The minimum protrusion is 3 mm.

o Tighten the back-cap, by hand, to secure the electrode in its collet. Make sure that the back-cap is fully seated against the torch body to ensure a proper gas-seal.

3.4 MACHINE SETTINGS Prior to beginning any welding operation it will be necessary to set up the welding machine for "optimum" operation. In order to make these "optimum settings" you need to know the following:

o What type of metal is to be welded? o How thick is the metal? o What type ofjoint is being welded? o What welding position will be used?

From the "type of metal” you will select the "type of current' namely, DCEN, DCEP or AC with HF. From the thickness of metal you will set the "amperage" for welding. From the type of joint you will select the torch nozzle and the gas flow. From the welding position you will "adjust" all parameters. Note that in this basic course we are concerned only with "flat" or "down-hand" welding positions. In more advanced modules we shall deal with "out of position welding" such as you will experience when welding pipe joints etc.

For purposes of this module we need set the following parameters at the welding machine (power source):

o Current type and Polarity. o Welding Current (Amperage). o Shielding Gas flow-rate.


Please consult Tables 4 - 5 and 6 for "nominal settings" of common materials.

MILD STEEL - DCEN THICKNESS

MM JOINT WELDING (AMPS)

ELECTRODE SIZE mm

FILLER WIRE SIZE mm

GAS FLOW (Lpm)

1.6

Butt Lap

Corner Fillet

60 - 70 70 - 90 60 - 70 70 - 90

1.59 1.59

5 5 5 5

3.18

Butt Lap

Corner Fillet

80 - 100 90 - 115 80 - 100 90 - 115

1.59 – 2.38 2.38

7 7 7 7

4.76

Butt Lap

Corner Fillet

115 - 135 140 - 165 115 - 135 140 – 170

2.38 3.18

9 9 9 9

6.35

Butt Lap

Corner Fillet

160 - 175 170 - 200 160 - 175 175 - 200

3.18 4.0

9 14 9

14 Table 4 - Nominal Settings Mild Steel

STAINLESS STEEL - DCEN

THICKNESS MM JOINT WELDING

(AMPS) ELECTRODE

SIZE mm FILLER WIRE

SIZE mm GAS FLOW

(Lpm)

1.6

Butt Lap

Corner Fillet

40 - 60 50 - 70 40 - 60 50 – 70

1.59 1.59

3 – 4 5

3 – 4 5

3.18

Butt Lap

Corner Fillet

65 - 85 90 - 110 65 - 85

90 – 110

2.38 2.38

5 7 5 7

4.76

Butt Lap

Corner Fillet

100 - 125 125 - 150 100 - 125 125 – 150

2.38 3.18

7 9 7 9

6.35

Butt Lap

Corner Fillet

135 - 160 160 - 180 135 - 160 160 - 180

3.18 4.0

9 9 9

9 - 14 Table 5 - Nominal Settings Stainless Steel


ALUMINIUM – AC/HF THICKNESS

MM JOINT WELDING (AMPS)

ELECTRODE SIZE mm

FILLER WIRE SIZE mm

GAS FLOW (Lpm)

1.6

Butt Lap

Corner Fillet

60 - 85 70 - 90 60 - 85

75 - 100

1.59 1.59

5 5 5 7

3.18

Butt Lap

Corner Fillet

125 – 150

130 - 160 120 - 140 130 - 160

2.38 3.18 2.38 3.18

2.38

9 9

12 12

4.76

Butt Lap

Corner Fillet

180 - 225 190 - 240 180 - 225 190 - 240

2.38 4.0

3.18 4.0

3.18

14 14 14 14

6.35

Butt Lap

Corner Fillet

240 - 280 250 - 320 240 - 280 250 - 320

4.0 4.76 4.0

4.76

4

14 14 14 14

Table 6 - Nominal Settings Aluminium 3.5. PREPARATION OF THE WORK STATION Welding operations may be done "on site" or at your "welding bay" but either way you must make this area safe for welding. Apart from erecting flash screens you should also make every effort to keep the area clean, dry and clear of obstacles. Set out your welding leads in such a way that they are "free" to extend to your work. You don't want the leads to "snag" as you are attempting to make a weld. Work on a clean and dry surface. Take the time to wipe down the welding bench (where applicable) and remove unnecessary "clutter" from the area. Make sure that you are equipped with all necessary PPE and, where applicable, run the extractor fan. THE FULL SET-UP (IN SUMMARY) So far we have covered individual items and described various procedures necessary to "prepare" that item for a welding operation. Let us now look at the actual "set-up procedure" that you would normally take when preparing to start a welding operation. Procedure in steps:

1. Prepare the power source for the work-piece to be welded. 2. Prepare your torch with the correct electrode and nozzle.


3. Prepare and connect the welding leads. 4. Set the shielding gas flow rate. 5. Obtain the necessary "filler wire" (If applicable). 6. Make sure you are wearing the necessary PPE. 7. Prepare your work area (make it safe). 8. Get started!

NOW VIEW VIDEO TIG-3 THEN COMPLETE THE SELF-TEST EXERCISE NO. 3.



SELF-TEST NO. 3 - EQUIPMENT PREPARATION INSTRUCTIONS Complete the following exercise without reference to your notes or the video. When you have completed the exercise check your answers / responses by:


QUESTIONS YES NO

1. If you discover any fault with your welding equipment during the "pre-inspection", what must you do? ANS: _________________________________________________

2. Before you fit or swap the welding-cables what must you be sure to do? ANS: _________________________________________________

3. Why must "pin type connectors" be fully turned or twisted into their sockets? ANS: _________________________________________________

4. What is important when connecting the work-lead clamp to the work or a welding-bench? ANS: _________________________________________________

5. When "reading" a floating-ball type flow-meter the reading must be taken where? ANS: _________________________________________________

6. What "rule of thumb" is used when setting the "post-flow"? ANS: _________________________________________________

7. What type of electrode must you fit when you are using DC welding current? ANS: _________________________________________________


8. What type of electrode must you fit when you are using AC welding current? ANS: _________________________________________________

9. How do you determine the nozzle-size for a weld? ANS: _________________________________________________ _____________________________________________________

10. Why must you not fit or use a nozzle that is cracked or has slag" inside it? ANS: _________________________________________________

11. How much protrusion, normally, must you allow the electrode beyond the nozzle? ANS: _________________________________________________

CHECK YOUR ANSWERS BEFORE MOVING ON TO PROGRAMME #4.


PROGRAMME 4 - TIG WELDING PROCEDURES AND PROCESSES In this programme we shall demonstrate (and explain) the procedures for:

o Creating a "fusion weld". o Running a "stringer bead". o Welding a "Butt Joint". o Welding a Corner Joint. o Welding a "Lap joint".

NOTE: The above exercises may be affected on mild-steel, stainless steel and aluminium

thin plate (maximum 3 mm). OBJECTIVES In this programme you will learn the following essential elements:

o Prepare mild steel, stainless steel and aluminium plates for TIG welding. o Strike an arc using the "touch strike method". o Strike an arc using "lift-arc" method. o Strike an arc using HF start method. o Run a fusion bead on mild steel plate. o Run a stringer bead on mild steel plate. o Weld a straight butt-joint on mild steel plate. o Weld an inside corner joint on stainless steel plate. o Weld a Lap Joint on aluminium.

BEGIN THIS SECTION OF LEARNING BY READING THE RESOURCE NOTES STARTING OVER PAGE.


RESOURCE NOTES - PROGRAMME NO. 4 TIG WELDING PROCEDURES AND PROCESSES

INTRODUCTION In this programme you will be shown the most important basic elements of TIG welding. When you have successfully completed this programme you will be able to attempt most (not all) TIG welding projects with a reasonable degree of confidence. As with any "hand-skill", TIG welding involves hand to eye co-ordination and full concentration toward the job. Do not be disappointed if your first attempts are failures. Be assured that even the best of welders began with many failures. The key to producing a "successful weld" is PRACTICE, and then more practice! The information offered in this programme is intended to help you over the problems that many learners encounter. THE BASIC OF BASICS! With the TIG process of welding there is one major rule and if you don't obey this rule you will NEVER produce a successful weld! The rule is simple and it goes like this: "The only joint that can be welded with the TIG process is a CLEAN JOINT" The above statement is not a "man-made rule", it is a "Scientific FACT ". Any "foreign matter" in the weld zone must be removed or the weld will be "sub-standard". Matter (substances) that must be removed include:

o A layer of "oxide". o Oil and grease. o Workshop dust and dirt. o Wax (polishes). o Chalk and marking pen ink. o Foot marks made from shoes and boots on the plate metal. o Deposits from exhaust systems etc.

4.1. METAL PREPARATION MILD STEEL Apart from the Substances already mentioned, rust, corrosion, mill-scale and other substances will all adversely affect the quality of a weld and must therefore be removed. Even the cleanest looking piece of steel will have a layer of "oxide" on its surface. Oxides cannot be removed with "degreasers" they must be "abraded" (ground, filed or sanded).


Mild-Steel should cleaned in the following way: 1. Remove all traces of grease, oil or other "oily substances" with a good chemical

de-greasing agent. The ideal agent is "acetone" for the removal of oily and waxy deposits.

2. Ask your Facilitator / Mentor to explain what degreasers are to be used in your organisation.

3. Use a sander or an angle grinder to remove all "oxides" (rust and mill-scale) from the weld area. When the metal is "bright" then it is ready to be welded.

STAINLESS STEEL Stainless steel does not require such harsh treatment as its cousin "mild steel" owing to the nature of its structure (chemical / molecular). Rust or mill-scale does not form on the surfaces but other substances, including certain "oxides", may adhere to them. A thorough wiping of the surfaces with a "solvent soaked cloth" will normally produce a clean and "weld-able surface". Where the surfaces require more vigorous cleaning (for example, over a welded section) then use either a "stainless steel brush" or a "fresh piece of CLEAN emery cloth". NOTE: When working with "stainless steel" do not use materials / tools (files, emery cloth etc.) which have been used on mild steel as this will result in contamination. ALUMINIUM The surfaces of aluminium plate are nearly always coated with "oxides" especially if the material has been standing in the atmosphere for any length of time. Aluminium oxide has a melting temperature several hundred degrees higher than plain aluminium. The oxides, although only a few "microns" thick, will seriously affect welding results. Removal of the oxide layer is best made using a "sanding disc" (rotary disc). It must be noted that aluminium tends to clog normal abrasive-wheels and discs and that a clogged disc (and wheel) may "explode". For this reason it is very important that you use only discs rated, or recommended, for use with aluminium. Wipe all surfaces, after sanding, with acetone and do not handle these surfaces thereafter. 4.2. TORCH HANDLING Handling the torch is an essential skill in the process of TIG welding. The torch is very light and need not be gripped with great force! The more "relaxed" you are the better control you will have when you handle and guide the torch. HOLDING THE TORCH Every welder has his (or her) preference on how to hold the torch, but for most beginners the "pencil grip" is perhaps the best starting point.


Method of "down hand" holding and supporting the torch

o When welding in the "down-hand" (flat) position you can usually maintain

good control over the "arc length" by using one finger to act as a guide upon the surface of the work-bench (or the plate being welded).

o The torch is (most usually) held so that the electrode tip is at an angle of about 60 to 75 degrees to the work surface (15 to 30 degrees off vertical). The tip is pointed in the direction of travel. This angle can alter depending on the joint, the main thing is that a "steady arc" is difficult to maintain at other angles.

4.3. STRIKING AN ARC We now come to the most fundamental skill of all, striking an arc! The manner in which this is done depends on two factors namely, the equipment you are using and the type of current you have selected. The two common methods of striking an arc are, "touch striking" (also called "scratch start") and "High Frequency striking". We will describe both methods. TOUCH STRIKING (SCRATCH START) This method is also called "short circuiting" and is used ONLY with a DC welding current. Do NOT use this method if you have selected AC or serious damage to the electrode will result. Follow this recommended procedure:

o Make sure that shielding gas is flowing through the torch. o Hold the torch "flat" and bring it down onto the work so that the ceramic

section contacts the metal (not the electrode). o Align the electrode so that it is parallel, and above, the weld seam (or line)

and drop your welding mask over your eyes. o Carefully tilt the torch (pivot) so that the electrode just makes contact with

the metal. o Immediately tilt the torch back to "break the contact". At this moment the

arc will begin.


o Wait until the arc becomes "stable" (continuous) then move the torch into the standard 60 - 75 degree position.

o "Adjust" the arc-length, by lifting or lowering the torch, until the gap is approximately 2 or 3 times the electrode thickness (5 - 7 mm).

When the arc is stable the next step (usual) would be to wait a few seconds until a "weld pool" develops and then move off in the direction of "welding". However as this exercise is (intended) purely to enable you to practice the skill of "striking" we will now "break the arc". This process is done at the end of each weld section. The "ideal way" to break an arc is to shut off (or taper off) the welding current. Triggering the "remote control" will result in the welding current "tapering off' to zero, over a pre-set time on welding machines' so equipped. Where this function is not available, the arc is broken by lifting the torch upward and away from the base-metal. The arc will stop as soon as the gap is too big for the arc to "jump", but we now have a problem. With the nozzle tip pointing sideways the shielding gas is no longer being directed onto the hot weld area. This means that the weld is free to react with oxygen (air) and this in turn means that "oxidation" will result. The point being made is that unless the nozzle is twisted back over the weld, very smartly, the weld will oxidise. Using this method it is advisable to tack a "run-off tab" to the end of the work- piece. The arc is then "broken" on this tab where no harm is caused to the main weld bead. LIFT ARC METHOD The "lift arc" technique is very similar to a scratch start in that the electrode is "touched" onto the base metal and then pulled away to break the circuit and cause a spark to occur. The difference is that the power-source automatically reduces the "starting current" so that the electrode won't "stick" to the metal when contact is made. Machines that incorporate a function-switch labelled "Liftig" or "Liftarc" will offer this feature. HIGH FREQUENCY STRIKE This method is the most effective and the least destructive way to strike an arc. Unfortunately this method is only possible if your welding machine has a "High Frequency Start" function. NOTE: Always follow the instructions given in the Operators Manual (Instruction Manual) for the power source that you are working with. The "Normal Procedure" for HF strike is as follows:

o Ensure that the power source is set up for the work, set to DC current (DC EN) and powered up.


o Select the "HF Start-position" on the control panel. (Normally a toggle-switch).

o Make sure that the "contactor" is set to the "remote" position. o Assuming that your work is correctly set up and the welding leads are

connected; bring the torch to the work. Hold the electrode tip about 3 to 4mm from the work surface.

o Drop your welding hood / visor and activate the thumb-switch on the torch (or the foot control). You will see (and hear) a "crackling arc" jump across the gap between the tip and the work; this is the "High Frequency Arc".

o As soon as this arc has stabilised the DC current will start to flow "across the HF". When the DC arc has stabilised the HF will cut out. (All this takes less than 2 or 3 seconds to accomplish!)

o When the DC arc is "stabilised" you can continue welding in the normal way. As we have not yet begun running a bead we will simply break the arc.

o To break the arc, activate the thumb-switch (or release the foot control) in order to stop the welding current. Hold the torch over the weld for a few seconds to allow the shielding gas to cool the weld and the electrode tip. If your machine has a "post flow" function, the gas will stop flowing after the "pre-set time" has lapsed. (Post flow "pre-set" is a setting made by the Operator) 2.2.3 High Frequency AC arc.

Most (if not all) AC welds using TIG require HF to "maintain the arc" (keep it going). To strike the arc when you are using AC follow the same procedure as for DC. Note that the HF switch should be set to the "Continuous" position.

WATCH THE VIDEO DEMONSTRATIONS 4.1 AND 4.2 AND THEN PERFORM THE PRACTICAL EXERCISES.



PRACTICAL EXERCISES - PROGRAMME 4 THE WELDING PROCESSES The following exercises are intended to offer you both "visual demonstration" and "practical tips" in the following:

o Exercise #1 - Run a "puddle weld" or making a "fusion weld". o Exercise #2 - Run a "stringer bead", or "adding filler material to the fusion weld. o Exercise #3 - Weld a "Butt Joint".

NOTE: The first 3 exercises will be demonstrated using 3 mm mild steel plate. o Exercise #4 - Weld a "Corner joint" on 2 mm stainless steel plate. o Exercise #5 - Weld a "Lap Joint" on 3 mm Aluminium plate.


EXERCISE #1 FUSION PROCESS ("PUDDLE WELD")

OBJECTIVE The purpose of this exercise is primarily to offer you the practical experience of using your TIG torch. In this exercise you will experience several factors, namely:

o Maintaining your torch at the correct angle. o Maintaining a correct weld-pool moving.

MATERIAL REQUIRED For this basic exercise we suggest that you use 3 mm mild steel "cold rolled plate". Cut or obtain a piece of plate approximately 50 x 200 mm. INSTRUCTIONS (DEMONSTRATION)

1. Watch the video demonstration for Exercise #1 on video No. 4. 2. Attempt to do the task yourself in your training area. 3. Check your work against Criterion Check-list #1 on the following page.

REMEMBER THE FOLLOWING POINTS

1) Clean the entire surface on both sides using an angle grinder or a belt-sander. Obtain a "bright clean surface".

2) Scribe "welding lines" along the plate spaced approximately 20 mm apart. These will be used as guides when you make your runs. Note that you should not use chalk, or a "koki-pen" to make these lines as the chalk and the ink will "contaminate" the weld. Set the current and the gas flow according to the metal thickness and electrode size.

3) Strike the arc and hold the torch steady until the weld-pool has developed properly. 4) Keep the torch at the correct angle. 5) Use your fingers to help keep the torch steady and the arc-length consistent. 6) Move (travel) at a speed that keeps the pool moving but does not "dry up".

Remember not to move too slowly or you will burn a hole through the plate. 7) Stay "relaxed". If you "over concentrate" you will "stiffen up" and find it impossible

to control.

VIEW VIDEO DEMONSTRATION #1 AND THEN PRACTICE THE PROCEDURE.



As you watch the video demonstration, keep your eye on the "steadiness" of the torch as the welder move the electrode forward. Notice the torch angle and how this never varies as the torch moves ahead and that the "arc length" remains constant. All of these features are essential to the creation of an "acceptable weld". It takes a great deal of practise to achieve this degree of "competency" and skill, so don't give up!


CRITERION CHECK LIST #1 (FOR A "FUSION RUN")

INSTRUCTIONS When you have made a "successful" fusion run (bead) on 3 mm mild steel plate use the checklist below in order to assess the quality of your work.

CRITERIA YES NO 1. The run(s) follows the marked lines. 2. Runs are “clean” in appearance – no inclusions of oxide. 3. Uniform width (approximately 6 mm wide). 4. “Ripples” are uniformly spaced along the run. 5. Beads follow the scribed lines.

The above check-list does not take into account your "method" of producing the run, in other words it simply assesses the "finished work". If however you find that you cannot produce a bead meeting the "standard" required then perhaps your method requires looking at. Use the check-list below to assess your operating method and other criteria that will affect the bead.

CRITERIA YES NO

1. Are the “optimum settings” of the welding equipment correct?

2. Is the metal sufficiently clean for TIG welding?

3. Is the electrode tip clean and the correct shape?

4. Are you able to maintain a “consistent” arc-length?

5. Is the torch angle correct at 60 - 75 degrees?

6. Is the gas flowing?

7. Are you moving at the correct travel speed?

8. Are you following the scribed lines?

HAVE YOU FACILITATOR CHECK YOUR WORK AND THEN MOVE ON TO THE NEXT EXERCISE.


EXERCISE #2 - STRINGER BEAD OBJECTIVE The purpose of this exercise is primarily to offer you the practical experience of using your TIG torch in conjunction with a filler rod (wire). In this exercise you will experience new factors, namely:

o Maintaining a weld-pool whilst introducing filler material. o Controlling the wire feed action.

MATERIAL REQUIRED For this basic exercise we suggest that you use 3 mm mild steel "cold rolled plate". Cut or obtain a piece of plate approximately 50 x 200 mm. Obtain a length of mild steel filler wire. INSTRUCTIONS (DEMONSTRATION)

o Watch the video demonstration for Exercise #2 on video No. 4. o Attempt to do the task yourself in your training area. o Check your work against Criterion Check-list #2 on the following page.

REMEMBER THE FOLLOWING POINTS:

1) Cut the filler wire to a convenient or "manageable length". 2) Using emery cloth, clean the filler wire to remove any residual oxides. 3) Proceed in the same manner as in exercise 1 to strike the arc and form the welding

pool. 4) Hold the tip of the wire in the gas shield at all times. If you remove it then it will

become contaminated with oxide that will enter into the weld pool. 5) Maintain the filler wire at an angle of 15 - 20 degrees thus forming a 90 degree angle

with the electrode. 6) Dip the tip of the wire into the front edge of the weld pool, not into the path of the

arc. 7) Introduce the filler material quickly. Do not hold the wire in the pool as this will

"freeze" the weld and cause the wire to stick. 8) Maintain a constant forward motion along the weld line. 9) When you approach the end of the weld run speed up your movement as the metal

will be hotter now. If you have remote current control, then reduce the current gradually. (Activate the down-slope with the torch thumb-switch, or, lift up your foot on the foot-control pedal).

10) At the end of the run break the arc or stop the current. Hold the nozzle over the weld pool until the weld has cooled. Allow about 10 seconds of "post flow" shielding to prevent the bead from "oxidising".

11) Allow the metal to cool and then inspect your work.


NOTE: During the process you may experience difficulty with handling the filler wire. Observe how the demonstrator uses the wire (in DVD). Note the manner in which he "feeds the wire" through his fingers thereby managing to keep his hand out of the "hot area". Avoid "resting" the wire onto the metal as this will result in it sticking. In the video demonstration you will be able to see very clearly how the welder operates both the torch and the filler wire. Pay particular attention to the "technique" that the welder applies to the introduction of the wire into the weld pool. You will see that the wire (tip) is kept well inside the "gas shield" at all times. You will observe that the introduction of filler is made rapidly and that the wire does not get chance to "rest" in the pool. If it did then it would "pull heat" from the pool resulting in the pool "freezing" and the wire sticking. The result of a good "stringer" is a neat, clean looking bead. The "C shaped" ripples in the bead are evenly spaced and the overall bead width is "uniform". As we are working with 3 mm plate and "Straight Polarity" we might expect fairly deep penetration of heat into the metal. By observing the reverse side of the work after completion you should notice a definite "root bead". This proves that the welding current is correct for the plate thickness. If the "root bead" is uniform in width then you can be assured that you have travelled at a "good speed" and maintained a constant "arc-length".

VIEW VIDEO DEMONSTRATION #2 AND THEN PERFORM THE PRACTICAL EXERCISE.



CRITERION CHECK LIST #2 (FOR STRINGER BEAD)

INSTRUCTIONS When you have made a "successful" stringer-bead on 3 mm mild steel plate, use the checklist below in order to assess the quality of your work.

CRITERIA YES NO

1. The bead is of uniform width @ approximately 6mm wide.

2. The bead is of uniform height.

3. The ‘ripples’ are consistent (evenly spaced).

4. The beads are on the line (straight).

5. Beads are free of contamination (oxide). The above check-list does not take into account your "method" of producing the run, in other words it simply assesses the "finished work". If however you find that you cannot produce a bead meeting the "standard" required then perhaps your method requires looking at. Use the check-list below to assess your operating method and other criteria that will affect the bead.

CRITERIA YES NO

1. Metal has been sufficiently “cleaned” for TIG process?

2. Torch and filler wire angles correctly maintained?

3. Consistent arc-length maintained?

4. Filler wire tip always kept within the gas-shield?

5. Filler wire kept clear of the electrode?

6. Filler material added “consistently” (results in even ripples)?

7. Adequate gas-flow provided?

8. Post flow gas held over during arc break?

HAVE YOUR FACILITATOR CHECK YOUR WORK AND THEN PROCEED TO THE NEXT EXERCISE.


EXERCISE #3 - BUTT JOINT OBJECTIVE The purpose of this exercise is primarily to offer you the practical experience of producing a basic weld in the "down-hand" or "flat position". Although several "setting up" factors tend to come into play in this exercise we must stress that the main objective is that you are able to perform the actual "welding process". In this exercise you will gain experience in / with:

o Setting up (preparing) flat plates to produce a "butt joint" to obtain a root-gap. o Maintaining the electrode (arc) in the centre of the weld joint. o Introducing the required amount of filler material into the joint. o Holding the filler wire in line with the weld joint. o Producing a "neat" weld bead with good penetration.

MATERIAL REQUIRED For this basic exercise we suggest that you use 3 mm mild steel "cold rolled plate". Cut or obtain 2 pieces of plate approximately 50 x 200 mm. Obtain a length of mild steel filler wire INSTRUCTIONS (Demonstration)

o Watch the video demonstration for Exercise #3 on video No. 4. o Attempt to do the task yourself in your training area. o Check your work against Criterion Check-list #3 on the following page.

REMEMBER THE FOLLOWING POINTS

1) Ensure that all the surfaces to be welded are properly cleaned. Do not overlook the cleaning of the "inside edges" of the metal.

2) Set the metal work-pieces upon a clean and flat surface (welding bench). 3) Create a "root-gap" between the plates. The root gap must be the same width as the

filler wire thickness. 4) Make a short "tack weld" at one end of the work. Make sure that, when you do this

the arc is held in the centre of the joint. (The weld pool must spread equally across both edges).

5) Stop and check the root gap. The gap must remain "parallel". As a rule the gap will tend to open owing to the contraction of the weld. Use your filler wire as a "gauge" and reset the gap by tapping the metal. (Take care to avoid holding the hot weld!) Tack the opposite end of the work and then place a tack in the centre of the piece.

6) Check for "flatness". The work will now require "pre-setting" to allow for pulling when the weld cools. Lay the work reverse side up over two plates. Tap the joint so that the plates "bend up" slightly. (You need to judge the actual amount)

7) Reposition the work (correct side up) onto the welding surface.


8) Commence welding along the joint in exactly the same manner as you practised in the last exercise (stringer bead). The primary difference now is that you will require more filler material in order to fill the "root gap" therefore the travel speed will tend to be slower than for a "fusion weld".

9) Do not try to "speed up" the process. TIG is a slow process on steel. The key to a successful weld is to maintain a good weld pool and keep it on the move all the time.

As you watch the video demonstration of a butt joint being welded take particular notice of the manner in which the welder keeps the weld pool "wet" but always moving ahead. Watch carefully how the filler material is introduced into the root and how the wire is always fed into the front section of the pool, never directly into the arc. It must always be remembered that when welding of small work-pieces, and especially relatively thin material, there will be a considerable accumulationofheat in the metal. Toward the end of a run this heat accumulation effectively means that less heat is needed from the torch to cause melting. If we don't reduce the heat input then a "hole" will be blown into the joint and the weld will be ruined. The only way to generate less heat from the torch is to decrease the welding current (amperage). To reduce amperage, without current control, the arc length should be increased butthere are limitations to this "trick". If you increase the arc length excessively the weld pool will tend to "crystallise" and become "brittle". We need mention that knowing just how much to "speed up" and "increase arc length" is a matter of 'judgement and "experience". After completion of the weld you can "read" the quality of your work by observing both sides of the joint. A good weld, on the welded side, will reveal a consistent bead of correct width and with uniform "ripples". On the "reverse side" you must observe a root-bead of uniform width and "protrusion".

NOW VIEW VIDEO SECTION #3 AND THEN PERFORM THE PRACTICAL EXERCISE.



CRITERION CHECK LIST #3 (FOR "BUTT-JOINT")

INSTRUCTIONS When you have welded your butt-joint on 3 mm mild steel plate use the checklist below in order to assess the quality of your work.

CRITERIA YES NO

1. The weld-bead is ‘uniform’ in width and height along the joint?

2. The ‘ripples’ are consistent (uniform) in shape and spacing?

3. The plates are ‘level’ (owing to the pre-set)? 4. Penetration (root bead) can be seen along the full-length

(reverse side)?

5. Penetration bead is uniform in width and protrusion. The above check-list does not take into account your "method" of producing the run, in other words it simply assesses the "finished work". If however you find that you cannot produce a bead meeting the "standard" required then perhaps your method requires looking at. Use the check-list below to assess your operating method and other criteria that will affect the bead.

CRITERIA YES NO

1. Metal plates are properly cleaned for TIG process?

2. Root gap is set to filler wire width?

3. A pre-set was allowed after tracking?

4. Torch and wire angles maintained correctly?

5. Weld pool maintained evenly across the root gap?

6. Travel speed of torch and wire maintained correctly?

7. Arc-length maintained steady (consistent)?

8. Allowance made for heat build-up toward end of run?

HAVE YOUR FACILITATOR CHECK YOU WORK AND THEN PROCEED TO EXERCISE #4.


EXERCISE #4 - CORNER JOINT In the following exercises you will gain experience in welding corner joints. As a further opportunity to gain experience we shall be working with Stainless Steel. STAINLESS STEEL (SIS) The term "Stainless Steel" refers to a group of "steel-alloys" that contain "chromium" and "nickel" in their basic structure. Stainless steels are produced, primarily, to resist corrosion. Corrosion is the "chemical reaction" and subsequent deterioration of metal upon contact with certain substances. There are various types of stainless steel, not all are "weldable" using TIG processes. It is virtually impossible to identify a type of stainless steel simply by "looking at it". The type or grade of steel is normally only identifiable by observing the sheet metal identification label when it is supplied from the merchant. If you are contemplating any welding on stainless steel always ask your Facilitator or Supervisor for advice on the welding process. One thing that is particularly important when welding sis is "contamination" during the welding process. SIS is easily contaminated if it comes into contact with certain metals, especially "mild steel". For this reason it is important that you understand a few basic "rules, namely:

o Never weld stainless steel upon a "Mild Steel surface". Use copper or stainless steel as the "backing" for welding SIS.

o Always use "stainless steel" instruments to clean stainless steel work. Never use "mild steel".

o Always "match" the filler wire (AWS specification) to be used with the "type" of stainless to be welded. You must consult your supplier for this information.

o Always use the lowest heat possible when welding. This basically means "keep the welding currents as low as you can".

o The weld area must be clean and totally free of any contamination, including finger "oils".

CORNER JOINTS There are basically two methods of welding corner joints namely:

o Outside weld. o Inside weld.

An "outside corner weld" is very often made without filler, especially on thin plate. When welding without filler, the weld is affected by "fusing" the two base metals together. An "inside corner weld" is made in the same manner as a "fillet weld". These welds are most usually reinforced with filler material.


NOW VIEW THE VIDEO SECTIONS 4.1 AND 4.2 THEN PERFORM THE EXERCISES ON THE FOLLOWING PAGES.



EXERCISE #4.1 - OUTSIDE CORNER JOINT OBJECTIVE OF THIS EXERCISE The main objective is that you obtain experience with welding stainless steel as you weld a corner joint. You will learn the process of welding an outside corner joint on 2 mm stainless steel plate. MATERIALS REQUIRED

o 2 pieces of 2 mm SIS plate approximately 200 x 50 mm. o 2 mm Filler wire code ER 316L. o NEW 1.6 mm red electrode (or an electrode that has been used only with SIS). o Cleaning fluid (acetone) and clean cloth or rag.

INSTRUCTIONS FOR "OUTSIDE CORNER WELD"

o Prepare (clean) the metal for welding in the manner described using correct tools. o Set up the plates (using a jig) as demonstrated to create a corner joint. o Set the power source as per recommendations. o Tack weld the plates. o Weld the corner joint. o Inspect the completed weld.

BASIC (OPTIMUM) SETTINGS (FOR 2 MM PLATE)

o Welding Current - DCEN. o Current setting - 50 amps. o Gas flow - 4 to 5 Lpm. o Post flow - 5 seconds (min). o Nozzle (ceramic) - No. 6 (9.5 mm). o Electrode - 1.6 mm (red).

GENERAL PROCEDURE In preparation for welding this joint the two plates should be set up in a support frame or "jig" so that they can be "tack welded". One very important fact that must be "re-emphasised' is that the jig and any other surface against which your SIS work-pieces are placed must be made of SIS or Copper and never ordinary "ferrous metal" (such as mild steel). The following steps are outlined and demonstrated in the DVD section and are listed here for easy reference:


PREPARATION AND SET UP o Prepare (clean) the metal surfaces, including the filler-wire, using acetone or an

"approved solvent". o Set up and secure the metal sections in a suitable copper or stainless steel jig. The

"apex" of the corner must form a "V-section". o Make sure that the electrode is prepared for DC. Use only a new electrode or one

that has NOT been used on material other than stainless steel. o Set and adjust your equipment to the "optimum settings" (See above).

TACK WELD

o The first tack should be made in the centre of the joint. Strike the arc inside the "V" of the apex. Wait until a small weld-pool develops and then run the pool for about 4 mm along the apex. Stop the arc and maintain shielding gas flow until the weld-pool cools.

o Check that the metal plates have not moved as a result of the cooling metal "pulling". Reset the corner "apex" if necessary.

o Tack the ends of the join. Place the tacks slightly inside the joint, which will reduce the risk of burning the edges.

o Note that after tacking you can either leave the work on the jig, or remove it. If you decide to remove it then make sure that you set it down onto a "stainless steel surface" for the remainder of the welding process.

MAIN WELD NOTE: The work may remain on the jig, or if you prefer, it may be placed onto a stainless steel surface for the main weld. Proceed with the main weld as follows:

o Strike the arc inside the right hand edge and then draw the arc to the edge. Establish a weld-pool within the "V section" of the joint.

o Maintain the torch angle at 60 to 75 degrees and proceed to move along the joint. o Keep the arc length constant as you move the weld-pool along the joint and do not

"weave" the torch as this will cause the bead to "spill" over the edges. o When you reach the end of the run break the arc and run back onto the bead (until

the current tapers off).


CRITERION CHECK LIST #4.1 (FOR S/S OUTSIDE CORNER JOINT)

INSTRUCTIONS When you have welded your Outside Corner on 2 mm stainless steel then use the checklist below in order to assess your work.

CRITERIA YES NO

1. The weld is straight and neat in appearance.

2. The weld is free of contamination, craters etc.

METHOD

1. Metal has been sufficiently “cleaned” for TIG process?

2. Torch angle correctly maintained?



5. Post flow gas held over pool during arc break?

HAVE YOUR FACILITATOR CHECK YOUR WORK THEN MOVE ON TO THE NEXT EXERCISE.


EXERCISE 4.2 - INSIDE CORNER JOINT OBJECTIVE OF THIS EXERCISE The main objective is that you obtain experience with welding stainless steel as you weld a corner joint. You will learn the process of welding an inside corner joint on 2 mm stainless steel plate. MATERIALS REQUIRED

o 2 pieces of 2 mm SIS plate approximately 200 x 50 mm. o 2 mm Filler wire code ER 316L. o NEW 1.6 mm red electrode (or an electrode that has been used only with SIS). o Cleaning fluid (acetone) and clean cloth or rag.

INSTRUCTIONS FOR "INSIDE CORNER WELD"

o Prepare (clean) the metal for welding in the manner described using correct tools. o Set up the plates (using a jig) as demonstrated to create a corner joint. o Set the power source as per recommendations. o Tack weld the plates. o Weld the corner joint. o Inspect the completed weld.

BASIC SETTINGS Set up your TIG equipment to the following recommendations:

o Welding Current - DCEN. o Current setting - 50 amps. o Gas flow - 4 to 5 Lpm. o Nozzle (ceramic) - No. 6 (9.5 mm). o Electrode - 1.6 mm (red).

WELDING PROCEDURE For purposes of this exercise the process begins in exactly the same manner as you did with the outside corner joint. This exercise will commence from the point where your two plates have been tack-welded upon the setting-jig. The following steps are outlined and demonstrated in the video section and are listed here for reference:

o Remove the tacked work from the jig and place it upon a stainless steel "backing plate". Remember that you must not weld stainless steel if it is placed directly upon "carbon steel".

o If necessary, clamp the work in order to hold it firmly in position, and to ensure a good "electrical connection" with the work-lead.


o Strike the arc slightly inside the right hand corner and then draw the arc back to the edge in order to form the weld-pool.

o Hold the torch at 65 – 70 degrees to the line of travel keeping the body in line with the weld bead axis.

o Keep the arc directed into the “root” of the joint by holding the torch at a 45 degree angle. You will find that the vertical plate tends to get hotter than the lower section. This is because the lower section absorbs more heat as a result of the “bench metal and backing”. For this reason, in practise, the arc is normally pulled slightly to the lower section and the filler material introduced onto the lower plate.

o Continue welding at a speed that maintains the weld-pool at the correct size. You will need to decrease the current or increase the welding speed as you approach the end of the run to compensate for the heat build-up on this small work-piece.

o Remember to maintain the post gas flow on the weld when the arc is broken.

CHECK YOUR WORK USING THE CRITERIA CHECK-LIST ON THE FOLLOWING PAGE.


CRITERION CHECK LIST #4.2 (FOR S/S INSIDE CORNER-JOINT)

INSTRUCTIONS When you have welded your Inside Corner on 2 mm stainless steel then use the checklist below in order to assess your work.

CRITERIA YES NO

1. The weld is straight and neat in appearance.

2. The weld is free of contamination, craters etc.

METHOD

1. Metal and filler-wire has been sufficiently “cleaned” for TIG process?

2. Torch and filler-wire angle correctly maintained?

3. Filler-wire not removed from the gas shield?



6. Post flow gas held over pool during arc break?

PROCEED TO EXERCISE 5 (ALUMINIUM WELDING).


ALUMINIUM WELDING (LAP JOINT) In the following exercises you will gain experience in the welding of aluminium. The practical exercise involves the welding of a "lap-joint" but the main objective is that you receive experience with the use of TIG equipment when welding aluminium plate. Aluminium is not a difficult metal to weld using the TIG process. However before attempting to weld a joint we need first explain a few basic pointers.

o To avoid contamination, welding in the flat position should be done upon a stainless steel plate, not directly upon a steel welding bench.

o The weld zone, on all surfaces, front, back and the edges, MUST be sanded to remove the "oxide layers" and then "cleaned" (using acetone) to remove any soluble matter such as grease, oil wax etc.

o Always use an AC welding current with TIG, especially if you are welding thin plate (up to 4 mm).

o Always use High Frequency. Set this control to "Continuous". o Use a "Zirconiated" (white) tungsten-electrode. o Do NOT allow the electrode tip to contact the metal when you strike the arc. o It is often advisable, especially when "flat-position welding" on thin plate, to use

"run-on and run-off tabs". BASIC WELDING PROCEDURE There is very little difference, in the actual welding procedure, from "steels". You will observe that the metal does not produce a bright red weld pool but rather a "watery looking pool". Once you get used to this you will have no difficulty with the weld. Aluminium is a very good conductor of heat and for this reason you will find that it is easy to "overheat" the metal. A condition known as "hot shortness" will occur if you apply too much heat to the weld zone, and more especially if you do not use a "backing plate" (made of copper or stainless steel). Hot shortness, in practical terms, results in the heated weld metal sagging and then literally dropping off resulting in a "blow-hole" appearing. It does this very suddenly and for this reason you will need some "hands on experience" in welding the metal and getting used to its "differences".

NOW VIEW THE VIDEO SECTIONS 5.1 AND 5.2 AFTER WHICH PERFORM THE EXERCISES ON THE FOLLOWING PAGES.



EXERCISE 5.1 - BASIC EXERCISES WITH ALUMINIUM OBJECTIVE OF THIS EXERCISE The main objective is that you obtain experience in the running of beads on 3 mm aluminium plate. MATERIALS REQUIRED

o 3 mm aluminium plate approximately 200 x 50 mm. o 2 mm Filler wire for aluminium. o 2.4 mm zirconium (white) tungsten-electrode. o Rotary cleaning disc (rated for stainless steel). o Cleaning fluid (acetone) and clean cloth or rag.

The first exercise you should attempt, just as you did with mild-steel, is to make a few "fusion weld runs" on pieces of scrap material. Once you are comfortable with fusion-runs, make a few "stringer beads" using filler wire. Note that you must use the correct wire type (for aluminium) and ensure that it is wiped clean , using acetone before you introduce it into the weld pool.

CHECK YOUR COMPLETED WORK USING THE CHECKLIST ON THE FOLLOWING PAGE.


CRITERION CHECK LIST 5.1 (FOR ALUMINIUM-BEADS)

INSTRUCTIONS When you have completed the exercise on your practice plates, check your work against the checklist below.

CRITERIA YES NO

1. Fusion beads are straight and clean. (No holes or contamination)

2. Stringer beads are straight and ‘uniform’ in width.

3. Ripples are consistent and uniform along the bead.

4. Beads are free of contamination and craters.

METHOD

1. Weld zone has been properly sanded and cleaned?

2. Torch angle and arc length correctly maintained?

3. Weld pool size maintained during the weld process?

HAVE YOUR FACILITATOR CHECK YOUR WORK AND THEN PROCEED TO THE NEXT EXERCISE.


LAP JOINT A lap joint is a common type of joint used with aluminium fabrication work (thin plate) and this is why we have elected to use it for the exercise. The material that we suggest you use is 3 mm aluminium plate cut into sections 50 x 200 mm. As with most other exercises the task can be divided into 3 main sections:

1. Prepare the metal for welding. 2. Set-up the work on the welding-bench. 3. Run the weld.

PREPARE THE METAL This we have covered in some detail, and by now you must be a little tired of being told to do this! But, if you don't follow this advice, you could end up with a poor weld. Remember to sand (grind) all the surface areas that will be involved in the weld. Then clean all these areas with acetone before commencing the weld. Don't leave the metal for too long before you commence welding as oxides form very quickly upon aluminium. SET-UP THE WORK-PIECES In this exercise we will be working upon a welding bench. A stainless steel "backing plate" has been attached to the bench and all welding operations will take place upon this plate. Follow this procedure:

o Wipe the stainless steel backing plate to remove all traces of dirt, grease or other "contaminants".

o Lay your aluminium plates upon the stainless steel. Allow at least 3 plate "thicknesses" of overlap for this joint.

o Clamp the sections using a suitable clamping device. NOTE: Take care, if "appearance" is important, that you do not mar or damage the metal surfaces with the clamp. Remember that aluminium is very soft.

o Make sure that the plates are fiat upon each other and that no "air gaps" exist in the weld zone.

o Use Run-on and Run-off tabs if your TIG machine does not have tapering current. WELDING PROCEDURE Note that, if the work has been securely clamped, tack-welding should not be necessary.

o Set your TIG equipment to the "optimum settings" as given in Table 6. o Strike the arc slightly inside the right hand edge and then draw the arc to the edge. o Bring the filler wire into the gas shield.


o As soon as the weld-pool forms begin moving the torch to the left. o Add filler material continuously in a "dipping motion" as the torch moves. o Hold the torch at the correct angle and maintain a consistent arc length (3 mm). o Note that this action must be used for tack welds as well. o Remember that the upper plate will tend to "draw the heat" more than the lower

plate. For this reason the arc should be drawn slightly to the lower plate. Add filler into the front of the weld-pool.

o Continue along the weld seam until completed. o Depending on the specification you may need to turn the work over and weld the

reverse side as well. o Inspect the weld. The bead should be straight with even ripples. There must be no

porosity evident and the bead must not overlap the top edge.

VIEW THE VIDEO SECTION 5.3 FOR THE LAP-JOINT AND THEN PERFORM THE PRACTICAL EXERCISE.



EXERCISE 5.2 - ALUMINIUM LAP JOINT OBJECTIVE OF THIS EXERCISE The main objective is that you obtain experience in performing a satisfactory weld on aluminium, using standard TIG equipment. MATERIALS REQUIRED

o 2 pieces of 3 mm aluminium plate approximately 200 x 50 mm. o 2 mm Filler wire for aluminium. o 2.4 mm zirconium (white) tungsten-electrode. o Rotary cleaning disc (rated for stainless steel). o Cleaning fluid (acetone) and clean cloth or rag.

INSTRUCTIONS

1. Prepare and set up your work-pieces for a Lap-Joint as described in the video section.

2. Use your TIG equipment to weld the joint, as explained and demonstrated in the video.

3. Check the completed work against the checklist on the following page.


CRITERION CHECK LIST 5.2 (FOR ALUMINIUM-LAP JOINT)

INSTRUCTIONS When you have completed the running of fusion beads and stringer beads on your practice plates, check your work against the checklist below.

CRITERIA YES NO

5. The weld is free of contamination and craters.

6. The weld-bead is evenly distributed between the plates.

METHOD

4. Weld zone has been thoroughly cleaned?

5. Correct electrode selected.

6. Current setting to AC. HF

7. Filler wire has been cleaned.

HAVE YOUR FACILITATOR CHECK YOUR WORK. THIS EXERCISE COMPLETES THE "BASIC TRAINING MODULE" ON THE TOPIC OF TIG WELDING.

tungsten inert gas welding - techav

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