Materials - Part C - Metal Processing techniques Processing Routes

In metal manufacturing, what is the main method behind liquid processing?

Casting

What are the 4 mains steps in casting?

• Melt metal

• Introduction into mould cavity

• Solidification

• Finishing process (post processing)

What are the 2 mains ways to optimise a casted practice?

• Porosity is kept to a minimum

• Defects and inclusions are reduced in number and size

What are the 3 types of casting techniques?

• Sand casting

• Investment Casting

• Permanent mould

How do the techniques compare to each other in terms of applicability, finish and tolerance?

How do they vary economically?

• Sand casting is the cheapest but offers the lowest production rate.

• Investment casting has medium mould and equipment costs with medium production rate of around 100 units per hour.

• Permanent mould casting is medium on all 3 categories but offers highest production rate.

When would use each technique?

• Sand casting would be used for 1 off prototype components when part quality or dimensions are not critical.

• Investment casting would be used for one off or small batch production for bespoke parts where quality is more of a concern.

• Permanent mould casting is used when producing large quantities if high quality parts.

What are the different types of solid state processing techniques?

• Primary

  • Rolling

  • Extrusion

  • Forging

• Secondary

  • Wire drawing

  • Machining

When rolling metal what factors increase rolling force?

• Increasing flow stress

• Increasing rolling reduction

• Increasing roll radius

• Increasing width

What are the main steps in extrusion?

• Round billet is placed in chamber

• Billet is forced through die by ram

• The die shape dictates the final cross section

What are the two main types of extrusion?

• Direct extrusion - Billet slides relative to the container wall.

• Indirect extrusion - Die moves towards the billet.

What key parameter can be adjusted to change the force required for a given extrusion ratio (ratio of the billet cross section over the die cross section)?

Changing the die angle changes the force required and there exists an optimal die angle for a given configuration.

What are defects that can occur in the previous 2 solid state processing techniques?

• Rolling - Surface cracking

  • Temp is too high

  • Temp is too low

  • Rolling speed is too high.

• Extrusion - Piping: when impurities move to the centre like a funnel

  • changing flow pattern

  • Machining billet prior to extrusion.

What it the main process behind forging?

Deformation of metal components at elevated temperature to achieve desired shape.

What is meant by a materials forgeability?

It is the materials ability to withstand deformation at low temperatures without cracking.

What is the main parameter to calculate when forging a part?

The upsetting force calculated using this equation.

What is the specialised form of forging?

Isothermal forging: Involves heating dies to the same temperature as the workpiece.

What advantages does this technique pose?

• Cooling / flow stress of the material is eliminated

• Forging can be carried out over a very narrow temperature range

• Much greater control of the microstructural and therefore mechanical properties

• Very good dimensional accuracy

What is the main type of defect that can occur with forging?

Surface cracking.

What is a problem that can occur in parts produced by all three solid state processing techniques?

Anisotropy - Non consistent material properties throughout the materials.