Manufacturing Engineering and Metal Casting Flashcards

Flashcards on Manufacturing Engineering and Metal Casting

Metal Casting

Manufacturing process where molten metal is poured into a mould, allowed to solidify, and then removed to create a final part.

affect of cooling rate on metal

Cooling rate influences the microstructure, mechanical properties, and overall functionality of metal casting.

effect of solidification

Cooling to ambient temperature influences grain size, shape, uniformity, chemical composition, and overall part properties in metal casting.

Solidification of Pure Metals

Pure metals have a defined melting temperature and solidify at a constant temperature, forming a solidified skin at mould walls and columnar grains.

Solidification of Alloys

Alloys solidify over a temperature range between the liquidus (TL) and solidus (Ts), existing in a mushy state with dendrites, impacting material strength.

Effects of Cooling Rate on Dendrites

Slow cooling leads to coarse dendrites, while high cooling rates result in finer structures; grain size impacts strength and ductility.

Sprue

Tapered vertical channel for molten metal flow in the mould; length affects solidification time.

Runners

Channels carrying molten metal from the sprue to the mould cavity, preventing premature solidification.

Gate

Section of the runner through which molten metal enters the mould cavity.

Risers

Reservoirs of molten metal compensating for shrinkage and preventing porosity; must solidify slower than the casting.

factors affecting fluidity

influenced by viscosity, surface tension, inclusions, and solidification pattern.

Degree of Superheat, effect on fluidity

Higher temperature above the melting point improves fluidity in metal casting.

Shrinkage

Dimensional changes in castings that may lead to warping or cracking due to thermal contraction at different stages: liquid, solidification, and solid.

Blow (Mold Defect)

A large cavity formed due to trapped gases displacing molten metal during solidification.

Scar (Mold Defect)

A shallow blow defect on flat surfaces caused by poor permeability or insufficient venting.

Hot Tears

Cracks that occur when a casting cannot shrink freely during solidification due to constraints in material.

Porosity

Occurs due to trapped or dissolved gases or shrinkage which can be reduced by ensuring use of adequate liquid metal.

mould and pattern type for sand, investment and die casting

Expendable Mould & Permanent Pattern, Expendable Mould & Expendable Pattern, Permanent Mould

Sand Casting pros/cons

Can cast almost any metal with no limit to part size, cheap

Coarse surface finish, wide tolerances

Investment Casting pros/cons

Intricate part shapes and excellent surface finish, can cast almost any metal

part size is limited, expensive patterns, molds, labour

Die Casting pros/cons

Excellent dimensional accuracy and surface finish with a high production rate

high die cost, limited part size, long lead time, limited to non ferrous metals

Types of Sand Moulds

Green sand - mix of sand, clay and water

cold-box mould - various binders blended into sand to chemically bond grains for greater strength

no-bake moulds - synthetic resin mixed with sand, mixture hardens at room temp

Cores

Inserts, usually made from sand, used to form hollow regions or define specific surfaces in the casting.

Patterns

Used to mould the sand mixture into the shape of the casting and may be made of wood, plastic or metal; can be designed with a variety of features to fit specific application and economic requirements

Permanent Mould Casting

Uses moulds made from materials with high resistance to erosion and thermal fatigue, surface is coated with refractory slurry, and clamps are generally used.

High Pressure Die Casting

Molten metal is forced into the die cavity at high pressures and there are two types of die casting machines: hot chamber and cold chamber machines

Investment Casting

Uses expendable moulds and patterns where wax patterns are coated with a slurry, placed in an autoclave, then filled with metal.

Parting Line

The boundary between the cope and the drag, which should be along a flat lines ends and shouldn’t follow the geometry of the part

Welding

The process of joining two metal pieces by rendering them plastic or liquid using heat, pressure, or both. A filler metal with a melting temperature similar to the base material may or may not be used.

Gas Flame Welding

Uses a gas flame to generate heat

Electric Arc Welding

Heat is produced by electric current flow

Laser welding

Uses a laser beam for precise energy input

Friction Welding

Generates heat through friction and pressure

Shielded Metal Arc Welding (SMAW)

Manual process, handheld consumable stick electrode, flux coats electrode, high skill low productivity, all positions possible

Flux-Cored Arc Welding (FCAW)

Semi-automatic or automatic, flux embedded in core of filler, mid skill mid productivity, all positions possible

Submerged Arc Welding (SAW)

Mechanized process, flux granules fill welding groove, use multiple heads (scalable), 1g position only, low skill high productivity

Fluxless welding processes

Protect the weld pool using an inert gas (e.g., argon) instead of flux

Gas Tungsten Arc Welding (GTAW)

manual process, producing high-quality welds but with a low deposition rate, filler introduced seperately

pros/cons

operator has independent control over heat source + addition of filler wire, no flux, high quality welds

low productivity, high skill required

Gas metal arc welding (GMAW)

Semi-automatic or automatic process, all positions possible, mid skill mid productivity

pros/cons

has self correcting arc length, less skill required than gtaw, produces good quality welds with good deposition rates

prone to spatter, range of filler metals limited

Short Circuit Transfer

minimises heat transferred to work piece, to weld out of position, suitable for thin materials, surface tension pulls droplets across work piece

Globular Transfer

least desirable, high heat input, poor weld appearance, spatter

Spray Transfer

large heat input to work piece, suitable for thicker materials,

The peak current

Promotes droplet detachment, due to the high pinch force

The background current

Maintains the arc between detachment events

Keyhole Mode Welding

Keyhole formation occurs when power density is high enough to vaporize the material

Solidification Behavior during fusion welding

During fusion welding, epitaxial growth occurs, where existing grains at the interface extend into the weld pool

Hydrogen cracks

Normally initiate in the HAZ, but they may extend into the fusion zone