CHAPTER 3 Metal Works, Casting & Heat

Treatment

Content

Metal Works

Casting

Heat Treatment

Metal works is a forming process by plastic deformation

process in which the volume and mass of metal are

conserved and the metal is displaced from one location to

another.

Metal Works

Types of Metal Works

Cold Work : Mechanical

working/forming of metals below its recrystallisation

temperature.

Hot Work : Mechanical

working/forming of metals above its recrystallisation

temperature.

1. Better dimensional control than hot working is possible because the reduction in size is not much.

2. Surface finish of the component is better because no oxidation takes place during the process.

3. Strength and hardness of the metal are increased.

4. It is an ideal method for increasing hardness of those metals which do not respond to the heat treatment.

Advantages of Cold Work:

1. Only ductile metals can be shaped through cold working.

2. Over-working of metal results in brittleness and it has to be annealed to remove the stress because the grain structure.

3. Subsequent heat treatment is mostly needed to remove the residual stresses set up during cold working.

4. Need high power/force in forming process.

Disadvantages of Cold Work:

Rolling

Wire and tube drawing

Blanking

Swaging

Embossing

Example of cold work :

Cold rolling is generally employed for providing a smooth and bright surface finish to the previously hot rolled steel. It is also used to finish the hot rolled components to close tolerances and improve their toughness and hardness.

Reduce the thickness of metals.

Cold Rolling

Typically it's a process in which the metal sheet or strip stock is placed between rollers and then compressed and squeezed. The amount of strain generated determines the hardness of the finished product. There can be numerous types of cold rolling mill, which can produce different types of rolled product, with thicknesses as low as 0.05mm.

Cold Rolling

Cold rolling produces sheet, plate and foil.

Foil- The Thickness is less than 0.2 mm

Sheet- .Thickness ranges from 0.2 mm and 6mm

Plate-It is the rolled product, which is over 6mm in thickness.

Cold Rolling

Cold Rolling

Wire drawing is a process used to reduce the diameter of a wire by pulling the wire through a single, or series of, drawing die(s).

Drawing is different from extrusion, because in drawing the wire is pulled, rather than pushed, through the die.

Wire drawing

Wire drawing process is quite simple in concept. The wire is prepared by shrinking the beginning of it, by hammering, filing, rolling or swaging, so that it will fit through the die; the wire is then pulled through the die.

As the wire is pulled through the die, its volume remains the same, so as the diameter decreases, the length increases.

Wire drawing

Tube drawing is a metalworking process to size tube by shrinking a large diameter tube into a smaller one, by drawing the tube through a die. This process produces high quality tubing with precise dimensions, good surface finish, and the added strength of cold working.

Tube drawing

Tube drawing is a reduction process in which one end of a tube is grasped and pulled through a die that is smaller than the tube diameter. To obtain the desired size, a series of successive reductions, or passes, may be necessary. Because of its versatility, tube drawing is suited for both small and large production runs.

Process Characteristics

Stock is pulled through a die, reducing its diameter, increases length as diameter decreases.

Typically requires several passes. Results in improved material properties through cold working and is suitable for small production runs of long workpieces.

Tube drawing

Tube drawing

Wire and tube drawing

1. Larger deformation can be accomplished and more rapidly by hot working since the metal is in plastic state.

2. Porosity of the metal is considerably minimized.

3. Concentrated impurities, if any in the metal are disintegrated and distributed throughout the metal.

4. Grain structure of the metal is refined and physical properties improved.

Advantages of Hot Work

1. Due to high temperature a rapid oxidation or scale formation takes place on the metal surface, leading to poor surface finish and loss of metal.

2. On account of the lost of carbon from the surface of the steel piece being worked the surface layer loses its strength, which is a disadvantage when the part is put to service – fatigue failure.

3. Close tolerances cannot be maintained.

4. It involves excessive expenditure on account of high

cost of tooling. This, however, is compensated by the

high production rate and better quality of products.

Disadvantages of Hot Work:

Forge and Smith forge

Hot Rolling

Extrusion

Example of hot work:

Forging is the shaping of metal using localized

compressive forces.

Forge & Smith Forge

Smith Forge also known as open-die forging.

In open-die forging, a hammer strikes and deforms the workpiece, which is placed on a stationary anvil.

Therefore the operator needs to orient and position the workpiece to get the desired shape.

Forge & Smith Forge

Impression-die forging is also called closed-die forging.

Metal is placed in a die resembling a mold, which is attached to the anvil. Usually the hammer die is shaped as well.

The hammer is then dropped on the workpiece, causing the metal to flow and fill the die cavities.

Forge & Smith Forge

Excess metal is squeezed out of the die cavities, forming what is referred to as flash. This also forces the metal to completely fill the die cavity. After forging the flash is removed

Forge & Smith Forge

Hot rolling is a metalworking process that occurs above the recrystallisation temperature of the material.

After the grains deform during processing, they recrystallize, which maintains an equiaxed microstructure and prevents the metal from work hardening.

The starting material is usually large pieces of metal, like semi-finished casting products, such as slabs, blooms, and billets.

Hot Rolling

Extrusion is a process where the materials is pushed or drawn through a die of the desired cross-section.

The two main advantages of this process over other manufacturing processes are its ability to create very complex cross-sections . It also forms finished parts with an excellent surface finish.

Extrusion

Extrusion

Direct extrusion is also called forward extrusion and it is the most general extrusion process. Its work operation includes the placement of the billet in a container, which is heavily walled. Ram or screw is used to push the billet through the die. In between the billet and ram, there is a dummy block, which is reusable and is used for keeping them separated.

Direct Extrusion

Direct Extrusion

Indirect extrusion is also called backwards extrusion and in this process, the die is constant whereas the billet & container move together.

As the billet movement is along with the container, all the frictional forces are easily eliminated.

Indirect Extrusion

Indirect Extrusion

What is casting? Casting is a manufacturing process by which liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify.

Casting

Sand casting (Tuangan pasir) Lost-wax casting (Tuangan lilin hilang) Die casting (Tuangan acuan tekanan)

Types of casting

Sand Casting Process

Sand Casting

A Sand Mold

Place a pattern in sand to create a mold.

Incorporate the pattern and sand in a gating system.

Remove the pattern.

Fill the mold cavity with molten metal.

Allow the metal to cool.

Break away the sand mold and remove the casting.

Sand Casting

Sand Casting

Lost-wax Casting

The process is capable of making parts from prototypes to high volume.

Cast tolerance is better (+/- .005 per inch).

Cast surface finish is smooth.

Excellent cast details with regards to cast letter i.e. logo, names, part number, etc.

Benefit s of Lost-wax Casting

Reduced machining due to castings designed to near net shape. Investment castings can have undercuts, blind holes, thru holes with almost any geometric shape or size.

All of the above advantages reduce your casting costs.

Benefit of Lost-wax Casting

What is die casting?

Die casting is the process of forcing liquid metal under pressure into cavities known as dies.

The die casting method is especially suited for applications where a large volume of small to medium sized parts are needed with good detail, a fine surface quality and dimensional consistency.

Die Casting

The mould is sprayed with lubricant and closed. The lubricant has two purposes, firstly to help control the temperature of the die and secondly, to assist in the removal of the casting from the mould.

Molten metal is then shot into the die under high pressure. Once the die is filled the pressure is maintained until the casting has cooled and hardened.

The die is then opened and the shot is ejected.

Die Casting Process

Finally, excess material which includes the gate, runners, sprues and flash, must be separated.

Often a secondary operation is performed to produce features not readily castable, such as tapping a hole, polishing, plating, buffing, or painting.

Die Casting Process

Die Casting

What is heat treatment?

Heat treatment is the controlled heating and cooling of metals to alter their physical and mechanical properties without changing the product shape.

Heat treatment is sometimes done inadvertently due to manufacturing processes that either heat or cool the metal such as welding or forming.

Heat treatment

What is the purpose of doing heat treatment to the steels?

The purpose of heat treating carbon steel is to change the mechanical properties of steel, usually ductility, hardness, yield strength, or impact resistance and sometimes is to alter certain manufacturability objectives such as improve machining, improve formability, restore ductility after a cold working operation.

Heat Treatment

Heat Treatment Cycle:-

Heat treatment is an operation involving heating, soaking and cooling of metal obtain desirable structure and mechanical properties. Heat treatment cycle consist of the following steps.

Heat the metal and alloys to a definite temperature.

Soaking/holding at the temperature for a sufficient time to allow uniform temperature of core (centre) and surface.

Cooling at a rate necessary to obtain desire structure and mechanical properties.

Heat Treatment - cycle

Heat Treatment

It involves, heating the steel up to 950 to 1000º C (.i.e. austeniting temperature).

Then soaking or holding the steel at that temperature for a definite time so that the steel (Job) become completely austenite (.i.e. core and outer surface become austenite).

Then cooling it to room temperature in a furnace (i.e. very slow cooling) this whole process is called "Annealing Process".

It improves the structure of steel specially ductility and toughness.

Heat Treatment - Annealing

Full annealing is the process of slowly raising the temperature about 50 ºC (90 ºF) above the Austenitic temperature line A3 or line ACM in the case of Hypoeutectoid steels (steels with < 0.77% Carbon) and 50 ºC (90 ºF) into the Austenite-Cementite region in the case of Hypereutectoid steels (steels with > 0.77% Carbon).

It is held at this temperature for sufficient time for all the material to transform into Austenite or Austenite-Cementite as the case may be. It is then slowly cooled at the rate of about 20 ºC/hr in a furnace to about 50 ºC into the Ferrite-Cementite range. At this point, it can be cooled in room temperature air with natural convection.

Full annealing

Full annealing is the process of slowly raising the temperature about 50 ºC (90 ºF) above the Austenitic temperature line A3 or line ACM in the case of Hypoeutectoid steels (steels with < 0.77% Carbon) and 50 ºC (90 ºF) into the Austenite-Cementite region in the case of Hypereutectoid steels (steels with > 0.77% Carbon). It is held at this temperature for sufficient time for all the material to transform into Austenite or Austenite-Cementite as the case may be. It is then slowly cooled at the rate of about 20 ºC/hr (36 ºF/hr) in a furnace to about 50 ºC (90 ºF) into the Ferrite-Cementite range. At this point, it can be cooled in room temperature air with natural convection.

The grain structure has coarse Pearlite with ferrite or Cementite (depending on whether hypo or hyper eutectoid). The steel becomes soft and ductile.

Full annealing

Full annealing is the process of slowly raising the temperature about 50 ºC (90 ºF) above the Austenitic temperature line A3 or line ACM in the case of Hypoeutectoid steels (steels with < 0.77% Carbon) and 50 ºC (90 ºF) into the Austenite-Cementite region in the case of Hypereutectoid steels (steels with > 0.77% Carbon). It is held at this temperature for sufficient time for all the material to transform into Austenite or Austenite-Cementite as the case may be. It is then slowly cooled at the rate of about 20 ºC/hr (36 ºF/hr) in a furnace to about 50 ºC (90 ºF) into the Ferrite-Cementite range. At this point, it can be cooled in room temperature air with natural convection.

Stress Relief Anneal is used to reduce residual stresses in large castings, welded parts and cold-formed parts. Such parts tend to have stresses due to thermal cycling or work hardening. Parts are heated to temperatures of up to 600 - 650 ºC (1112 - 1202 ºF), and held for an extended time (about 1 hour or more) and then slowly cooled in still air.

Stress Relief Annealing

Spheroidization is an annealing process used for high carbon steels (Carbon > 0.6%) that will be machined or cold formed subsequently. This is done by one of the following ways:

1.Heat the part to a temperature just below the Ferrite-Austenite line, line A1 or below the Austenite-Cementite line, essentially below the 727 ºC (1340 ºF) line. Hold the temperature for a prolonged time and follow by fairly slow cooling. Or

2.Cycle multiple times between temperatures slightly above and slightly below the 727 ºC (1340 ºF) line, say for example between 700 and 750 ºC (1292 - 1382 ºF), and slow cool. Or

3.For tool and alloy steels heat to 750 to 800 ºC (1382-1472 ºF) and hold for several hours followed by slow cooling.

Spheroidizing

All these methods result in a structure in which all the Cementite is in the form of small globules (spheroids) dispersed throughout the ferrite matrix. This structure allows for improved machining in continuous cutting operations such as lathes and screw machines. Spheroidization also improves resistance to abrasion.

Spheroidizing

It involves, heating the steel 40 to 50 ºC above the annealing temperature for a short time and then cooling in air up to room temperature (cooling rate is slightly faster then annealing).

It improves the structure and mechanical properties of steel. It is slightly harder than annealed steel.

Also used to soften and relieve internal stresses after cold work and to refine the grain size and metallurgical structure.

Normalizing

Quenching is a heat treatment process in which steel is heated (up to 1000-1050 ºC like normalizing). Then steel is hold at that temperature for uniforming the temperature then cooling in quenching media e.g, water, brine, oil etc.

After rapid cooling steel will become hard and brittle and its structure will be martensite. Steel is hardened to increase the wear-resistance.

Heat Treatment - Quenching

Quenching media used to prevent quench fracture:

1. Air

2. Brine (salt water)

3. Oil

4. Water

5. Polymer quench

Heat Treatment - Quenching

Please be prepared for your test..