Lesson 5 WeldingLesson 5 Welding

Chapter 2

The definition of “welding”The definition of “welding”

•fusion•heat& metals• plastics & heatless welding•pressure welding•sound or light from laser•So we have the definition of welding today:___________________________________

The definition of “welding”The definition of “welding”

•Definition 3: Welding is a fabrication that joins materials, usually metals or thermoplastics, by causing coalescence( 接合） . This is often done by melting the workpieces and adding a filler material to form a pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld. This is in contrast with soldering and brazing, which involve melting a lower-melting-point material between the workpieces to form a bond between them, without melting the workpieces.

Naming welding processesNaming welding processes

What’s the main idea of this paragraph?

There is no uniform method of naming welding processes.

Why?

Many processes are named according to the heat source or shielding method, but certain specialized processes are named after the type of joint produced. An overall classification can not take account of this because the same type of joint may be produced by a variety of processes

solderingsoldering

What is soldering?

Soldering is the process of joining two metals by a third metal to be applied in the molten state. 熔化第三种金属来连接其他两种金属。

What does “these method” refer to ?

brazing （硬钎焊）， riveting （铆接） or welding( 熔焊）

Solder Solder 焊料焊料Solder is a fusible metal alloy with a melting point or melting range of 90 to 450 degree Celsius, used in a process called soldering where it is melted to join metallic surfaces. It is especially useful in electronics and plumbing（铅管业） . Alloys that melt between 180 and 190 °C are the most commonly used. By definition, using alloys with melting point above 450 °C (840 °F) is called brazing. The word solder comes from the Middle English word soudur, via Old French solduree and soulder, from the Latin solidare, meaning "to make solid".

Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a relatively low melting point. Soldering is characterized by the melting point of the filler metal, which is below 400 °C (752 °F). The filler metal used in the process is called solder or soft solder.

Soldering differs from welding in that soldering does not involve melting the work pieces. In brazing, the filler metal melts at a higher temperature, but the workpiece metal does not melt.

Soldering is distinguished from brazing by use of a lower melting-temperature filler metal; it is distinguished from welding by the base metals not being melted during the joining process. In a soldering process, heat is applied to the parts to be joined, causing the solder to melt and be drawn into the joint by capillary action ( 渗透） and to bond to the materials to be joined by wetting action（润湿 ). After the metal cools, the resulting joints are not as strong as the base metal, but have adequate strength, electrical conductivity, and water-tightness for many uses. Soldering is an ancient technique mentioned in the Bible and there is evidence that it was employed up to 5000 years ago in. Mesopotamia.

Pressure weldingPressure welding

A weld occurs when pieces of metal are joined by causing the interface to melt and blend prior to solidifying as a uniform metal joint.   This process may be caused by heat, pressure or a combination of both.   When heat alone is used the process is called fusion welding.Pressure welding usually involves heating the surfaces to a plastic state and then forcing the metal together.  

Pressure weldingPressure welding

Several steps should be followed for pressure welding:Step 1:_________________________________________Step 2:____________________________________Step 3:_____________________________________Step 4:_____________________________________

Clean the surfaces thoroughly first.Heat the ends of metal to a white heat.Press or hammer the ends together.Smooth off the joints.

Flux ( 焊剂 )In high-temperature metal joining processes (welding, brazing and soldering), the primary purpose of flux is to prevent oxidation of the base and filler materials. Flux is a substance which is nearly inert at room temperature, but which becomes strongly reducing ( 分解） at elevated temperatures, preventing the formation of metal oxides. Additionally, flux allows solder to flow easily on the working piece rather than forming beads as it would otherwise.

acetylene  ['setili:n] n.   ['setili:n] n. 乙炔乙炔 ,, 电石气电石气

acetylene gas 乙炔气

acetylene generator

乙炔发生器

acetylene welding

乙炔焊

liquid acetylene

液态乙炔

acetylene cutting

乙炔切割

Oxy-Oxy- 氧基氧基

oxyhydrogen  氢氧的

oxydant  氧化剂

oxygenation  氧化

oxyacetylene  氧乙决的

Oxyacetylene WeldingOxyacetylene Welding

• Flame formed by burning a mix of acetylene (C2H2) and oxygen

• Fusion of metal is achieved by passing the inner cone of the flame over the metal

Inner Cone: 5000-6300 deg F Combustion Envelope 3800 deg F

2300 deg FTORCH TIP

Fusion weldingFusion welding

In this important series of welding processes the electric arc supplies the heat for fusion while a flux is responsible for the shielding and cleaning functions and often also for the metallurgical control.

在这一系列重要的焊接过程中，电弧为熔化金属供热，而焊剂起保护和清理的作用，而且也是常常起着熔炼控制作用。

Fusion weldingFusion welding

The most widely used form of flux-shielded arc welding is a manual process known as metal-arc welding.

最常用的助焊剂保护电弧焊是被称为是金属弧焊的手工操作过程。

Fusion weldingFusion welding

In this method, an electric current is passed across two electrodes, and the metal surfaces are placed between them. The work itself constitutes one of them and the other is insulated filler rod( 焊条） . An arc struck between the two, and the heat which is generated melts the metal at the weld. 在这一方法中，电流经两个电极流过，而金属表面则被置于两电极之间，工件本身构成它们中的一级而另一极是一具有绝缘填充剂的焊条。两极之间电弧放电，由此产生的热量熔化在焊缝处的金属。

Fusion WeldingFusion Welding

BASE METAL

WELD

SOLIDIFIED SLAG

ARC POOL

WELDING ATMOSPHERE

CORE WIRE

ELECTRODE COATING

ARC STREAM

PENETRATION DEPTH

Fusion Welding PrinciplesFusion Welding Principles

• Base metal is melted

• Filler metal may be added

• Heat is supplied by various means• Oxyacetylene gas• Electric Arc• Plasma Arc• Laser