Metal Fabrication and Casting - Midterm 2026

Main hazards in manufacturing

Machinery (58% of limb-loss injuries), slips/trips/falls, overexertion, repetitive motion, molten metal and heat/burns, electrical, arc UV radiation, fumes/gases, noise, sharp edges, fire

Ensuring a safe environment

Operating procedures, training, inspections, guards/barriers, lockout/tagout, E-stops, designated work areas, warning signs, PPE, ventilation, risk assessment

Risk assessment steps

Determine hazards, identify who is at risk, weigh risks and set safety measures, document findings, review and revise

Guard priority order

1 Fixed barrier, 2 Interlocked barrier, 3 Physical barrier, 4 Presence sensing barrier

PPE

Personal Protective Equipment: gloves, hard hat, glasses/goggles/face shield/welding helmet, jackets/aprons, steel-toe boots, hearing protection, respirators

Clothing rules

Tie back long hair, close fitting clothes, remove jewelry (can be pulled in, jammed, or conduct electricity)

OSHA

Occupational Safety and Health Administration; US Dept of Labor; est. 1971; sets and enforces workplace standards

Lockout / Tagout

Lockout = physical lock keeps equipment from being energized; Tagout = warning tag, removed only by authorized person

Safety stop (E-stop)

Emergency shutoff that removes power; push-pull, paddle, or push-twist styles

Lab press brake

Small CNC press brake, 25 ton force rating

Lab welding equipment

SMAW (stick), GMAW (MIG/MAG/CO2), plasma cutting, resistance welding

Lab safety gear

Check your lab slides: typically E-stops, extinguishers, eyewash, first aid, PPE storage

Sheet metal safety

Store flat, gloves for sharp edges, safety glasses, keep scrap out of aisles, sheet conducts heat/electricity

Casting safety PPE

Safety glasses AND face shield, leather boots/leg guards, leather apron and gloves, heat resistant suit, hard hat, ear protection, respirator; cotton clothing, cuffless pants

Casting safety rule

Keep moisture away from molten metal; molten metal (except mercury) burns through clothing

Welding safety

Flame resistant jacket/cap, cuffless pants, welding gloves, closed boots, shade rated helmet, grounding, ventilation, UV radiation, fumes, fire/electric hazards

Manufacturing

Applying physical and chemical processes to alter geometry, properties, or appearance of a starting material (technological); transforming materials into items of greater value (economic)

Materials used in manufacturing

Metals, ceramics, polymers, composites

Types of manufacturing processes

Processing operations (shaping, property-enhancing, surface processing) and assembly operations (permanent joining, mechanical fastening)

Shaping process families

Casting, particulate processing, deformation, material removal

Production system

People, equipment, and procedures combining materials and processes

Parts of a production system

Production facilities and manufacturing support systems

Facility types by quantity

Job shop (low), batch (medium), mass production (high)

BCC metals

Iron (room temp), chromium, molybdenum, tungsten

FCC metals

Aluminum, copper, gold, silver, nickel (very ductile)

HCP metals

Magnesium, titanium, zinc, zirconium

Types of deformation

Elastic (temporary, returns to shape) and plastic (permanent)

Plastic deformation mechanisms

Slip (main) and twinning

Metal forming

Plastic deformation used to change shape of a metal workpiece

Sheet metal vs plate

Sheet 1/16 to 1/4 in; plate over 1/4 in

Sheet metal cutting operations

Shearing, blanking, punching, cutoff/parting, slotting, perforating, notching, trimming, shaving, fine blanking

Blanking vs punching

Blanking: cut-out piece is the part. Punching: cut-out slug is scrap

Sheet metal bending operations

V-bending, edge bending, flanging, hemming, seaming, curling

Sheet metal equipment

Presses (stamping press with punch and die), press brake, shears, punch/turret press

Bend allowance formula

Ab = 2 pi (Alpha/360)(R + Kba t); Alpha = bend angle, R = bend radius, t = thickness

Kba values

0.33 if R < 2t; 0.5 if R >= 2t

Springback

Elastic recovery after pressure removed; fix by overbending or bottoming

Metal casting

Molten metal flows by gravity or other force into a mold where it solidifies in the shape of the cavity

Types of casting

Sand casting and investment casting (main); also shell, vacuum, lost foam, ceramic mold, permanent mold, die casting

Expendable vs permanent mold

Expendable: destroyed to remove part. Permanent: reusable

Open vs closed mold

Open: no cover. Closed: has gating system

Sand mold components

Cope (top), drag (bottom), flask, parting line, pouring cup/basin, downsprue, runner, gate, riser, core

Riser

Reservoir that feeds shrinkage void; last to cool

Investment casting

Lost wax: wax pattern, refractory coating, melt wax, preheat mold, pour, break mold; high accuracy

Lost foam casting

Polystyrene pattern coated with refractory and packed in sand; metal vaporizes foam

Permanent mold / die casting

Machined reusable mold, high temp capable

Misrun

Metal solidifies before filling cavity (raise pour temp, pour faster)

Cold shut

Two streams meet but do not fuse

Shrinkage cavity

Void from solidification shrinkage (add/size a riser)

Microporosity / pinholes / sand blow

Gas related defects (vent, degas)

Hot tear

Crack from restrained contraction

Mold shift / core shift

Misalignment of cope/drag or core

Sand wash / scab / penetration

Sand and mold erosion or metal penetrating sand

Pour too slow / too fast

Slow: cold short (chills early). Fast: turbulence and mold erosion

Superheat

Temperature above melting point at pour

Avoiding shrinkage defects

Use riser, directional solidification, uniform sections, pattern shrinkage allowance

Casting design rules (key)

Uniform sections, taper toward risers for directional solidification, avoid hot spots and thin sections between heavy sections and risers, separate heavy masses need own risers

Melting point of aluminum

About 660 C (1200 F)

Melting point of steel

About 1500 C (2600 F)

Melting point of pure iron

1539 C

Melting point of copper

About 1085 C (1985 F)

Melting point of zinc / magnesium

About 420 C / about 650 C

Liquidus / solidus / mushy zone

Solidification starts at liquidus, ends at solidus, mushy zone between

Three shrinkage stages

1 Liquid contraction (about 0.5%), 2 solidification shrinkage (void/pipe at last freeze point), 3 solid contraction to room temp

Aluminum total shrinkage

About 2 percent

Where shrinkage void forms

Top of the pour

Pure metal vs alloy solidification

Pure metal at one temperature; alloy over a range

Welding

Joining by coalescence using heat and/or pressure, with or without filler

Weld joint types

Butt, corner, tee, lap, edge

Weld types

Fillet, groove (square, single bevel, V, U, J, double), plug, slot, spot, seam, flange, surfacing

Two main welding processes

Fusion welding and solid state welding

Fusion welding processes

Arc (SMAW, GMAW, FCAW, SAW, GTAW, PAW), resistance, oxyfuel gas, electron beam, laser beam

Solid state welding processes

Diffusion, friction, ultrasonic

SMAW / GMAW / FCAW

Stick / MIG-MAG-CO2 / flux-cored

SAW / GTAW / PAW

Submerged arc / TIG / plasma arc

Brazing and soldering

Do not melt the base metal

Zones of a weld joint

Fusion zone (melted, darkest), HAZ (heated not melted, metallurgical changes), base metal (unaffected)

Weld joint properties

Fusion zone has columnar grains growing toward center; HAZ properties change with peak temperature and cooling

Weld positions

Flat, horizontal, vertical, overhead (hardest/most dangerous), pipe

What affects weld quality

Welder experience, equipment quality, environment, type of equipment, condition of supplies

Good weld

Full penetration and fusion, uniform bead, no cracks/porosity/slag/undercut

Porosity

Contaminants, poor shielding gas, arc too long

Cracks

Hot cracks from heat and shrinkage; cold cracks from hydrogen or residual stress

Lack of fusion / lack of penetration

Low heat, fast travel, wrong angle / low heat, bad root opening

Undercut / overlap / underfill

Groove at toe / weld profile defects

Slag inclusion / spatter / burn-through

Embedded nonmetal / molten droplets / excessive heat melting through

Three types of weld inspection

Visual, non-destructive, destructive

Non-destructive weld tests

Ultrasonic (sound, internal), radiographic (X-ray, internal), magnetic particle (ferromagnetic surface flaws), liquid penetrant (dye, surface cracks)

Destructive weld tests

Bend, tensile, nick break, macro-etch

Weld failure case studies

Mexico City rail 2023 (26 deaths), Kielland oil rig 1980 (bad fillet weld, 123 deaths), Nova Scotia crane 2019 (lack of fusion, porosity)