Casting, Moulding & Powder Processing Flashcards
(64 cards)
What is Casting
Which types of Metals can be cast
Process in which a volume of material (metal) flows by a force into a mould, the metal then solidify in the desired geometry.
Ferrous and Non-Ferrous Metals (All Metals)
Describe an Open Mould
Draw and label an Example of an Open Mould
A Container in the shape of the Desired Product,
Describe a Closed Mould
Draw and label an Example of a Closed Mould
Container that Contains an Upper Cope, Lower Drag, a gating system, and a riser.
This allows for a more complex geometry to be cast.
Describe a Closed Mould with a Core
Draw and label an Example of a Closed Mould with a Core
Container that Contains an Upper Cope, Lower Drag, a gating system, and a riser.
The Mould also contains a core held up by Chaplets
This allows for a more complex geometry to be cast, with a hollow section.
What are the 3 Considerations need to be made about the Design of the Chaplets inside a Closed Mould containing a core.
Chaplets must be of the same or similar material as the metal being cast
Must Hold the Core in Place for the duration of the cast (Not too Small)
Must Melt and fuse Completely into the poured metal (Not too Big)
A Manufacturer can design a mould that doesn’t use chaplets, why is that design better?
Chaplets cause casting defects and weak spots in the casting
Explain why the Upper Chaplet in a Mould must be Stronger then the Bottom.
it has to counteract the pressure of the molten metal and any gases that may push upwards during the casting process
Why is a Riser Required in a Closed Mould
What design considerations must be made when designing the riser
Cast Metal Shrinks as it solidifies, the riser fills gaps that have formed due to metal shrinkage.
Molten metal in riser must solidify more slowly then the Metal inside the Cavity
Riser must have a larger volume-Surface Ratio
What are the Positives to casting
Creates Relatively complex geometries
Creates external and internal shapes
Can create both Net and Near-Net Shapes
Can Produce Large Parts Easily
Can be suited to Mass Production
Describe what Net and Near-Net Shapes are
Net Shapes are products which require little-to-no additional machining
Near-Net Shapes, require additional machining to reach the final product
What are the negatives to casting
Doesn’t work with High-Melting point Materials.
Poor Dimensional Accuracy and Surface Finish
Excess material needs to be used , separation and recycling processes are required.
Highly Dangerous Machines, Conditions and High Temperature Molten Metals. Mean that alot of safety precautions are required.
Explain the Positive and Negatives to Permanent Moulds and Expendable Moulds
Permanent -
Mould can be reused many times to produce many castings
Higher Production Rates
Less Complex Geometries can be cast (needs to be an open Mould)
Expendable -
More Complex Geometries can be cast.
Sacrificial Mould must be destroyed to remove casting.
Manufacture time limited by the time to create the mould.
Explain what Temperature must a furnace heat the metal until.
Heat beyond the melting point
Heat of fusion to convert from solid to liquid
Then Heat to raise molten metal to desired pouring temperature
What are factors that determine success in Casting
Pouring Temperature (needs to be above required temp)
Pouring Rate (Slow enough to not wear away the mould internal surface, fast enough so it can fill the whole cavity before solidifying)
Turbulence - (irregular variations in flow speed and direction of molten metal)
Label the cooling curve
What is the Chvorinov Rule
A casting with a Higher Volume-Surface Ratio solidifies _________________
more slowly
What does the Mould constant depend on
Mould Material
Thermal Properties
Pouring Temperature Relative to the melting point
2 Design Considerations that need to be Considered
- Riser Must Solidy after casting
- Riser volume must be 3 times the shrinkage in the casting.
Both need to be considered independently, both will produce a minimum length, the higher minimum length is then selected
Describe the Pro’s and Con’s of using Wood , Metal and Plastics as a Mould Pattern Material
Compare using Small Grains of Sand/Silica , and larger grains of sand/silica within an Expendable Mould
What are the 4 Desireable Mould Properties
Strength - Maintain Shape and Erosion Resistant
Permeability - Allow Hot air and gasses to pass through voids in sand
Collapsibility - allowing the cast to shrink without cracking (withstand thermal stresses from cast Shrinkage)
Reusability - how well is the sand recycled once used in a mould.
Explain why Hot Air and Gasses must be allowed to escape in a Cast
Prevent Porosity - so air bubbles dont form within the solidified metal
Describe the 3 Main types of Defects with Casting
