Manufacturing Process
Cold Extrusion
冷挤压
Forming metal by forcing it through a die under high pressure at room temperature, improving strength and surface finish.
Process Steps
- Blank prepared and lubricated
- Extrusion press forms part
- Dimensions and surface checked
- Heat treat if specified
What is cold extrusion?
Direct answer: cold extrusion pushes a metal slug through or into a die at room temperature and makes the material flow into shape. The part is formed, not cut — almost no material is turned into chips, and the grain structure is reoriented along the part rather than across it.
There are two common forms. In forward extrusion the material is pushed out through a die to make a smaller section. In backward (impact) extrusion the punch drives into the slug and the metal flows back up around it, which is how a cup-shaped part is made.
Cold extrusion compared with the alternatives
| Process | Material use | Best shape | Typical volume |
|---|---|---|---|
| Cold extrusion | Very high — near net shape | Solid or cup-shaped parts with thick walls | High |
| Deep drawing | High | Thin-walled cups, housings, sleeves | High |
| CNC turning | Low — much becomes chips | Any turned profile, any volume | Low to high |
| Hot forging | High | Heavy, high-strength parts | Medium |
Why it is chosen
- Material cost. A turned part can lose half its bar stock as chips; an extruded part is near net shape, and that saving scales with the price of the material.
- Strength. Cold working raises yield strength and the grain flow follows the part's shape, which is better for fatigue than a cut part.
- Surface finish and tolerance. Extruded surfaces come off the die with a good finish and repeatable dimensions, often removing a finishing operation.
- Speed. Once the tool exists, parts come out at press speed.
What it needs
- Ductile material. Low-carbon steel, aluminium, copper and brass extrude well; high-carbon or highly alloyed steels do not.
- Surface preparation. Steel is normally phosphated and soaped so the lubricant film survives the pressure — without it, the part galls to the die.
- Tooling that takes the load. Pressures are high; die inserts are made from tool steel or carbide and supported in a shrink ring.
- A part geometry that flows. Wall transitions, corner radii and punch geometry all decide whether the metal flows or tears.
Frequently asked
What is the difference between cold extrusion and deep drawing?
Both form metal without cutting it. Deep drawing pulls a flat blank into a cup with a thinning wall; cold extrusion pushes a solid slug into shape under much higher pressure. Deep drawing suits thin-walled shells, extrusion suits thick-walled or solid parts.
Does cold extrusion make the part stronger?
Yes — the material work-hardens and the grain flow follows the part. Whether that matters depends on the application; where it does not, an anneal can be added to the route.
Which materials can be cold extruded?
Low-carbon and low-alloy steels, aluminium, copper, brass and some stainless grades. The deciding factor is ductility at room temperature and the cost of preparing the surface for lubrication.
When does extrusion beat machining?
When the part is roughly axisymmetric and the volume is high enough to pay for the tooling. The material saved and the eliminated chip handling usually decide it before the labour rate does.
Related: deep drawing · CNC turning · fine blanking · deep draw stamping · heat treatment