Manufacturing Processes: Fundamentals of Casting and Expendable Mould Casting Methods

Comprehensive vocabulary flashcards covering fundamental casting terminology, sand casting design, gating systems, and specific expendable mould processes including vacuum moulding, freeze moulding, shell moulding, full moulding, investment casting, and the Shaw process.

what is Casting

A manufacturing process in which a material such as metal or plastic in liquid form is poured into a mould cavity and allowed to harden/solidify to produce parts or products (known as castings).

Near Net Forming

The manufacturing advantage of casting where the final part shape is produced in a single step, minimizing the requirement for subsequent finishing operations.

Casting Material Shrinkage Allowances

The expected volumetric and linear dimensional contraction that must be accounted for when creating patterns: Cast iron ($1\%$), Steel ($2\text{--}2.5\%$), Aluminum and Magnesium ($1\text{--}1.3\%$), and Brass ($1.5\%$).

Expendable Mould

A casting mould created from a pattern that is destroyed or broken down after solidification to extract the finished cast component.

Reusable Mould (Permanent Mould)

A casting mould typically machined from metal in two sections designed for precise alignment that can be repeatedly reused across multiple production cycles.

Sand Casting

The most widely used expendable mould casting process, capable of handling parts ranging from small to very large and casting alloys with high melting points such as steel, nickel, and titanium.

Sand Casting Pattern Types

The pattern configurations selected based on part quantity and complexity: solid pattern, split pattern, match-plate pattern, and cope-and-drag pattern.

Sand Casting Mould Components

The gating and tooling system comprising the cope (top flask), drag (bottom flask), pouring cup, sprue, runner, gate, riser, core, and core print along the parting line.

Riser

A reservoir of molten metal within the casting mould that supplies additional liquid material into the cavity to feed shrinkage as the casting cools and solidifies.

Core and Core Print

A core is an internal mould insert used to create hollow passages or cavities (such as engine water galleries), supported in position inside the mould by core prints.

Draft (Draft Angle)

A slight taper engineered onto the vertical surfaces of a casting pattern to allow clean withdrawal of the pattern from the sand mould without breaking the mould walls.

Pit Moulding

A specialized variation of sand casting designed for extremely large components where a foundry floor pit serves as the mould container/drag.

Foundry Sand Composition

The standard granular aggregate used in sand moulds, typically composed of $89\%$ silica, $8\%$ clay, and $3\%$ water.

Green Sand

Moulding sand that incorporates a resin or moisture-clay binder to hold sand particles together, offering higher mould strength at the expense of reusability.

Required Properties of Moulding Sand

The critical performance requirements for foundry sand: refractoriness (thermal resistance), cohesiveness (bonding ability), permeability (permitting gases to escape), collapsibility (disintegrating easily during knockout), and availability.

Chills

Rough pieces of cast iron or high-conductivity inserts placed in a mould cavity that act as local heat sinks to accelerate cooling and promote directional solidification.

Vacuum Moulding ("V-Process")

An expendable mould casting method using thin plastic sheets and a vacuum system to draw and compact unbonded, dry sand into shape, eliminating chemical binders and moisture defects.

Freeze Moulding ("Eff-Set" Process)

An expendable casting method where moulds made from sand, clay, and water are sprayed with liquid nitrogen so that formed ice acts as the binder, yielding rigid moulds and immediately reusable sand.

Shell Moulding

An expendable casting technique where a preheated metal pattern is dipped into fine sand blended with thermosetting resin to form a thin shell (approx. $3\text{ mm}$ thick) that is baked and supported by a pouring jacket.

Full Moulding (Lost Foam Casting)

An evaporative pattern casting method where an expanded polystyrene pattern coated in refractory ceramic is embedded in unbonded sand and vaporized by incoming molten metal.

Investment Casting (Lost Wax Process)

A precision casting method using wax patterns created from a master die, assembled into trees, coated with fine refractory plaster slurry, and baked to melt away the wax before pouring molten metal.

Investment Casting Process Tolerances

The operational capabilities of the lost wax process, achieving dimensional tolerances between $0.075\text{ mm}$ and $0.25\text{ mm}$ (or better) and minimum section thicknesses down to approximately $0.4\text{ mm}$.

Shaw Process

An expendable casting method using a slurry of plaster, a gelling agent, and a cracking compound poured over a pattern to form a rubbery, semi-flexible mould that can be stripped over slight undercuts prior to firing.

Micro-cracking (Shaw Process)

The network of microscopic cracks formed when a Shaw process mould is baked, which counteracts mould contraction and provides high gas permeability for venting.

Fillets and Edge Blending (Casting Design)

The practice of designing rounded internal corners and blended sharp edges to prevent stress concentrations, hot tearing, and cracking during metal shrinkage.

Machining Allowances

Extra material intentionally designed onto the surfaces of a cast part to ensure sufficient stock is available to machine critical features to tight dimensional tolerances.