Metal forming processes are a core consideration in part design, a top priority for manufacturers, and a critical segment of material processing. Today we break down mainstream metal forming technologies, covering casting, plastic forming, machining, welding, powder metallurgy, metal injection molding, semi-solid metal forming, and 3D printing.
Casting (liquid metal forming) refers to pouring molten metal into a mold cavity matching the target part’s geometry. The metal solidifies after cooling to produce blanks or finished components. Process flow: Molten metal → Mold filling → Solidification & shrinkage → Finished casting
Sand casting manufactures castings within sand molds, applicable to steel, iron and most non-ferrous alloy parts.
Process Flow:
Features:
Applications: Automotive engine blocks, cylinder heads, crankshafts
Investment casting creates disposable wax patterns coated with refractory layers to form shell molds. The wax is melted and drained, and the shell is fired before pouring metal.
Mold casting process flow:
Advantages:
Disadvantages:
Complex workflows, high production costs
Applications: Small high-precision complex parts difficult to machine, e.g., turbine blades
Die casting injects molten metal at high speed and pressure into precision metal dies, which solidify under pressure to form finished castings.
Process Flow:
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Applications: Automotive hardware, instrumentation, agricultural machinery, electronics, medical devices, daily hardware
Low pressure casting fills molds with liquid metal under low pressure (0.02–0.06 MPa) and solidifies components under sustained pressure.
Process flow:
Features:
Applications: Cylinder heads, wheel hubs, cylinder frames
Centrifugal casting pours molten metal into rotating molds; centrifugal force drives metal filling and solidification.
Process flow:
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Applications: Cast pipes, engine cylinder liners, bearing sleeves across metallurgy, mining, automotive, aerospace industries
Gravity die casting fills reusable metal molds with molten metal under natural gravity for solidification.
Process flow:
Advantages:
Fast cooling from high thermal conductivity metal molds, casting density ~15% stronger than sand castings
Stable dimensional accuracy and superior surface finish
Minimal sand core usage reduces dust and hazardous fumes Disadvantages:
Poor mold ventilation requires vent design to evacuate cavity gas
Low mold yield strength causes casting cracking during solidification
Long mold lead times and high upfront costs, only economical for mass production Applications: Mass-produced aluminum/magnesium alloy complex parts, steel ingots and iron castings
Vacuum die casting extracts air from die cavities during injection to eliminate internal porosity, boosting mechanical strength and surface quality.
Process flow:
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Squeeze casting solidifies liquid or semi-solid metal under high pressure to form near-net-shape blanks with simplified workflows and stable quality.
Two process variants:
Direct squeeze casting: Coat mold → Pour alloy → Close die → Apply pressure → Hold → Release pressure → Open die → Eject blank → Reset
Indirect squeeze casting: Coat mold → Close die → Feed molten metal → Fill cavity → Pressurize → Hold → Release pressure → Open die → Eject blank → Reset
Features:
Eliminates internal defects including pores, shrinkage cavities and voids
Low surface roughness and tight dimensional tolerances
Suppresses casting crack formation
Easily automated for mass production
Applications: Aluminum, zinc, copper alloys and ductile iron components
Lost foam casting bonds foam/polystyrene replicas into a cluster, coats them with refractory paint, buries patterns in dry sand, and pours molten metal under vacuum to vaporize foam and form castings.
Process flow: Pre-expansion → Foam molding → Refractory coating → Drying → Molding → Pouring → Shakeout → Finishing
Features:
High casting precision without sand cores, cutting machining time
No parting lines for flexible design freedom
Clean, low-emission manufacturing
Lower capital and production costs Applications: Complex precision castings of all sizes and alloys, e.g., gray iron engine housings, high-manganese steel pipe elbows
Continuous casting pours molten metal into water-cooled permanent molds (crystallizers); solidified cast sections are continuously pulled to produce unlimited-length profiles.
Process Flow:
Features:
Applications: Constant-cross-section long products including ingots, slabs, billets and tubes from steel, iron, copper, aluminum and magnesium alloys
Plastic forming deforms metal blanks under external mold pressure to manufacture near-net-shape or net-shape parts relying on material ductility. Core processes include forging, rolling, extrusion, drawing and stamping.
Forging applies compressive force to metal blanks via forging equipment to produce components with optimized mechanical properties, shape and dimensions. Classifications: Open die forging, closed die forging, ring rolling, specialty forging (roll forging, cross wedge rolling, radial forging, liquid forging)
Process flow: Blank heating → Preform rolling → Die forming → Trimming → Piercing → Straightening → Intermediate inspection → Forging heat treatment → Descaling → Final straightening → Quality check Features:
Higher strength, toughness and impact resistance than castings or rolled stock
Reduces raw material waste and shortens machining cycles
Fast production speeds
Open die forging offers flexible small-batch manufacturing Applications: Mill rolls, large gear blanks, turbine rotors, hydraulic press cylinders, locomotive axles, automotive crankshafts and connecting rods
(2) Rolling
Rolling reduces blank cross-section and extends length by feeding metal between counter-rotating roller gaps.
Classifications: Longitudinal rolling, transverse rolling, skew rolling
Applications: Metal sheets, plates, bars and tubes; also used for plastics and glass forming
Extrusion forces metal blanks through shaped die orifices under triaxial compressive stress to reduce cross-section and extend length. [img] Process flow: Preprocessing → Billet heating → Extrusion → Stretching & straightening → Cut-to-length → Sampling inspection → Artificial aging → Packaging
Advantages:
Disadvantages:
Applications: Long bars, deep-hole parts, thin-wall and custom profile components
Drawing pulls metal blanks through smaller die openings to form precise finished profiles.
Advantages:
Ultra-precise dimensions and smooth surface finishes
Simple tooling and equipment
Continuous high-speed production of thin long profiles
Disadvantages:
Limited single-pass deformation rate and total deformation before annealing
Restrictions on maximum finished length
Applications: Mass production of metal tubes, bars, profiles and wire
Stamping shapes sheet metal, strips, tubes and profiles via press and die force through plastic deformation or material separation.
Features:
Lightweight, high-rigidity finished parts
Low-cost mass production with consistent part quality
High material utilization and recyclable scrap Applications: 60–70% of global steel sheet undergoes stamping, including automotive bodies, chassis, fuel tanks, boiler shells, electrical silicon steel cores, household appliances, bicycle frames and consumer hardware
Machining removes excess material from raw blanks using cutting tools to achieve dimensional, geometric, positional tolerance and surface finish requirements per engineering drawings.
Common machining methods
Welding joins metals or thermoplastics via localized heating, high temperature or compressive force.
Detailed welding classifications are covered in follow-up content.
Adopt a specific heat source to locally melt the joint parts of workpieces to be connected, then cool and solidify the molten metal to form a welded joint.
Utilize physical effects such as friction, diffusion and pressurization to eliminate unevenness on the two joint surfaces and remove oxide films and other contaminants. The atoms on the two joint surfaces get close enough to reach the atomic bonding distance, so the connection can be achieved under solid-state conditions.
Use a filler metal with a melting point lower than that of the base material. Heat both the base material and the filler metal to a temperature above the melting point of the filler metal but below the melting point of the base material. The capillary action makes the liquid filler metal fill the assembly gaps, wet the base material surfaces, and form a metallurgical bond after cooling and crystallization.
Powder metallurgy produces metal parts, composites and finished goods from metal powder blends through compaction and sintering. 
Core workflow: Powder mixing → Compacting → Sintering → Post-processing
Advantages:
Disadvantages:
Applications: Self-lubricating bearings, gears, cams, guide rods and cutting tools
MIM mixes fine metal powder with polymer binders to form plasticized feedstock, injected into molds for complex near-net-shape components.
Process stages: Mixing → Injection molding → Debinding → Sintering (optional surface finishing)
Features:
One-step forming for intricate geometries
Smooth surface finish, low scrap rates and fully automated high-volume production
Lower hardness requirements for forming molds
Core technology: Polymer binders enable powder flow during injection and maintain green body integrity pre-sintering
SSM forming leverages unique flow behavior of non-dendritic semi-solid metal to eliminate typical casting defects.
Two primary variants: rheocasting and thixoforming.
Rheo casting process
Features:
Applications: Automotive master cylinders, steering components, pistons, wheel hubs, transmission and fuel system parts, aerospace and electronics hardware
3D printing (additive manufacturing) constructs physical parts layer-by-layer from powdered metal or plastic feedstock based on digital CAD models.
Comparisons of mainstream 3D printing technologies are available in extended guides.
