17 SQ: Primary Shaping

What is the main task for primary shaping processes?

• Creating cohesions from shapeless materials

How can primary shaping be categorized?

• According to nature of shapeless material (DIN 8580)

• Nature:

  • Liquid

  • Plastic

  • Pulpy

  • Granular/Powdered

  • Splintered/Fibrous

  • Gaseous/Vaporous

  • Ionized

  • Primary Shaping by Welding

  • Primary Shaping by AM

Name advantages of casting processes

• Complex geometries realizable

• Near net-shape production (less post-processing and machining afterwards)

• Wide range of materials

• Wide range of parts (mass)

• Economic

• Circular economy

Name disadvantages of casting processes

• Sometimes expensive systems

• Sometimes bad surface qualities

• Tradeoff between mass production and surface quality/precission/complexity of geometry

How can casting processes be categorized?

• In permanent form and lost form

• Lost form:

  • Sand Casting

  • Investment Casting

  • Lost Foam Casting

• Permanent Form:

  • Die Casting

  • Mold Casting

Sketch the sand casting process

1. Covering of one half of the mold with casting sand

2. Filling the box with coarse casting sand

3. Repeat for the other half

4. Join the two halves and add feeders and degassing pipes

5. Open boxes and take out the mold

6. Pour molten material and wait to solidifaction

7. Take part out, remove feeders, bur and degassing pipes

Why is sand casting or lost foam casting more suited for iron-based materials than mold casting or die casting?

• Because mold and die casting require the material to be melted to a fully liquid phase, which is more energy expensive for ferrous alloys

Why are cooling rates for sand casting typically slower than for mold or die casting?

• Due the higher heat capacity of sand when compared to metal

Give a process description of investment casting

1. Wax mold is created (and mounted together if the case)

2. Coating and sanding

3. Shellform completed with the sound around the wax positive mold

4. Wax is molten out

5. Casting

6. Deforming

What are the main advantages for investment casting?

• High surface quality and precission

• Small components realizable

• Near net-shape production

Whar is the main difference between common sand casting and lost foam casting?

• Sand casting leaves the mold used to do the form in sand untouched, while in lost foam casting the mold is burnt be the melts

What casting processes are suited for what types of materials?

• All metals: sand casting, lost foam casting, investment casting

• Low melting temp. alloys: die casting and mold casting

Name typical casting deffects

• Undersize

• Cavities

• Warpage

• Cold shut

• Stress cracks

• Inclusions

• Gas porosity

Name the process steps for injection molding

• Closing

• Injection

• Topping up

• Consolidation

• Opening

What are the main differences between injection molding and extrusion?

• Injection Molding: with a mold and higher pressures

• Extrusion: without mold for linear components

• Both of them use the same screw + temp principle

True or false? Extrusion is suited for manufacturing parts with complex geometries in all three spatial directions. Why?

• False. Extrusion can only create complex geometries in 2 dimensions, since the third dimension is the extrusion direction an is therefore basically linear

What are the advantages and drawbacks for Additive Manufacturing?

• Advantages:

  • Lightweight design

  • Funtional Integration

  • Mass customization and personalization

  • High complexity in geometry

• Disadvantages:

  • Small series

  • Not yet standarized

  • Pre- and post-processing needed

  • Expensive systems

When does it make sense to used addtivie manufacturing as porduction process?

• For small series with high mass customization and personalization needed

• For lightweight design

• For functional integration as extremely complex geometries

Name additive manufacturing processes used for aerospace industry

• Selective Laser Melting

• Electronic Beam Melting

• (Fused Depositon Modelling and Stereolithography)

What are the main differences between EBM and SLM? How does this affect the production process?

• SLM (Selective Laser Melting): layered melting of powdered material with laser and with no vacuum

• EBM (Electronic Beam Melting): layered melting of powdered material with electron beam and with vacuum → more complex and expensive process due to vacuum but with better results