Extrusion parameters and tolerances
Extrusion is a compression forming process in which a material, typically metal, is forced to flow through a die with the shape of the desired cross-section. It allows the production of long profiles with constant cross-sections, offering a wide variety of geometries ranging from solid bars to complex hollow shapes. It is performed hot or cold, depending on the material and mechanical requirements.
What is extrusion?
Section titled “What is extrusion?”Extrusion is a manufacturing process where a billet is placed in a container and pushed by a ram at high pressure against a die. The material plastically deforms and exits with the shape of the die, creating a continuous profile. Unlike other processes, the material is subjected to compressive and shear stresses, allowing deformation of brittle materials without risk of fracture. A distinction is made between hot extrusion (above 50‑75% of the melting temperature) and cold extrusion (at room temperature or slightly elevated).
Applicable materials
Section titled “Applicable materials”Extrusion is versatile and accepts many metals. Aluminum alloys are the most common, followed by magnesium, copper, steel, and titanium. Each material requires specific temperature and pressure conditions. The following table presents the mechanical properties of typically extrudable aluminum alloys, and the operating parameters section details process conditions for different materials.
| Alloy | Temper | Elastic modulus | Yield strength | Tensile strength |
|---|---|---|---|---|
| 6061 | T4 | 68,9 GPa / 10,0 Msi | 110 MPa / 16,0 ksi | 207 MPa / 30,0 ksi |
| 6061 | T6 | 68,9 GPa / 10,0 Msi | 241 MPa / 35,0 ksi | 290 MPa / 42,0 ksi |
| 6063 | T5 | 68,9 GPa / 10,0 Msi | 110 MPa / 16,0 ksi | 152 MPa / 22,0 ksi |
| 6063 | T6 | 68,9 GPa / 10,0 Msi | 172 MPa / 25,0 ksi | 207 MPa / 30,0 ksi |
| 7075 | T6 | 71,7 GPa / 10,4 Msi | 483 MPa / 70,0 ksi | 538 MPa / 78,0 ksi |
| 2024 | T3 | 73,1 GPa / 10,6 Msi | 290 MPa / 42,0 ksi | 441 MPa / 64,0 ksi |
| 5052 | H32 | 70,3 GPa / 10,2 Msi | 159 MPa / 23,0 ksi | 214 MPa / 31,0 ksi |
Source: Engineering ToolBox (2024). Msi = 10⁶ psi; 1 MPa = 0,145 ksi.
Other extrudable materials:
- Steel – low-alloy and stainless steels, extruded at 1100‑1250 °C / 2012‑2282 °F with glass lubrication (Ugine‑Séjournet process).
- Magnesium – alloys AZ31, AZ61, etc., extruded at 300‑450 °C / 572‑842 °F.
- Copper and brass – allow hot extrusion at 600‑900 °C / 1112‑1652 °F.
- Titanium – alloys Ti‑6Al‑4V, extruded at 800‑1000 °C / 1472‑1832 °F, generally with glass as lubricant.
Operating parameters
Section titled “Operating parameters”The fundamental parameters in extrusion are billet temperature, applied pressure, ram speed, and extrusion ratio (ratio of the container cross-sectional area to the product area). Hot extrusion is performed between 50% and 75% of the material’s melting temperature. Pressures range from 35 MPa / 5,1 ksi to 700 MPa / 101,5 ksi depending on the material and extrusion ratio.
| Material | Extrusion temperature | Extrusion pressure | Typical extrusion ratio | Observations |
|---|---|---|---|---|
| Aluminum | 350‑500 °C / 662‑932 °F | 100‑600 MPa / 14,5‑87,0 ksi | 10:1 to 100:1 | Excellent flow; complex profiles achieved. |
| Magnesium | 300‑450 °C / 572‑842 °F | 200‑500 MPa / 29,0‑72,5 ksi | 10:1 to 80:1 | Similar to aluminum; requires inert atmosphere to prevent ignition. |
| Copper / Brass | 600‑900 °C / 1112‑1652 °F | 100‑500 MPa / 14,5‑72,5 ksi | 10:1 to 50:1 | High die wear resistance. |
| Steel | 1100‑1250 °C / 2012‑2282 °F | 400‑700 MPa / 58,0‑101,5 ksi | 5:1 to 40:1 | Lubrication with molten glass (Ugine‑Séjournet process). |
| Titanium | 800‑1000 °C / 1472‑1832 °F | 400‑700 MPa / 58,0‑101,5 ksi | 5:1 to 30:1 | Difficult extrusion; glass used as lubricant and oxidation protection. |
Values based on consolidated data from EFunda and industrial references.
Typical tolerances
Section titled “Typical tolerances”Dimensional tolerances in extruded parts depend on the material, profile size, and die design. The following table indicates the minimum geometric limits achievable according to the material.
| Parameter | Steel | Aluminum and Magnesium |
|---|---|---|
| Minimum wall thickness | 3,0 mm / 0.120 in | 1,0 mm / 0.040 in |
| Minimum corner radius | 0,8 mm / 0.030 in | 0,4 mm / 0.015 in |
| Minimum fillet radius | 4,0 mm / 0.120 in | 0,4 mm / 0.015 in |
| Minimum cross-section | 250 mm² / 0,40 in² | < 250 mm² / < 0,40 in² |
Source: EFunda (2024).
Regarding linear tolerances, in small-dimension aluminum profiles typically ±0,2 mm / ±0.008 in are achieved; for medium sections ±0,5 mm / ±0.020 in can be accepted, while for steel tolerances usually range between ±0,5 mm / ±0.020 in and ±1 mm / ±0.040 in, depending on complexity and size.
Surface finish
Section titled “Surface finish”Extrusion provides reasonably good surface finishes, although not comparable to precision machining. The average roughness (Ra) varies by material.
| Material | Surface roughness Ra |
|---|---|
| Aluminum and Magnesium | 0,8 µm / 30 µin |
| Steel | 3,0 µm / 125 µin |
Source: EFunda (2024).
The use of appropriate lubricants and temperature control improve the finish. Cold extrusion produces smoother surfaces than hot extrusion, but at the cost of higher pressures and lower deformation per pass.
Advantages and limitations
Section titled “Advantages and limitations”Advantages
Section titled “Advantages”- Capability to generate very complex cross-sections, including hollows, in a single operation.
- Suitability for brittle materials due to predominant compressive stresses.
- Good surface finish in aluminum and magnesium (Ra 0,8 µm / 30 µin).
- Possibility to improve mechanical properties by strain hardening (cold extrusion).
- Production of continuous lengths, reducing joining operations.
- High productivity for large series; minimizes subsequent machining.
Limitations
Section titled “Limitations”- Dimensional accuracy lower than machining (typical tolerances of ±0,2‑1 mm / ±0.008‑0.040 in).
- High cost of dies and equipment, especially for hard materials such as steel.
- Progressive die wear that can affect tolerances.
- Limitation to constant cross-sections; variable three-dimensional shapes cannot be generated.
- Restricted minimum wall thickness and corner radii (e.g., 3 mm / 0.120 in in steel).
- In hot extrusion, surface oxidation may require pickling or subsequent cleaning.
Selection guide
Section titled “Selection guide”Extrusion is the optimal choice when a constant cross-section profile is required, with complex shapes impossible to obtain by rolling or forging, and with medium-high production volume. It is recommended to consider:
- Product shape: long parts with constant sections (profiles, tubes, bars of special geometry).
- Material: aluminum and magnesium are the most economical; steel and titanium are justified in high-strength structural applications.
- Tolerances: if tighter tolerances than ±0,2 mm / ±0.008 in are required, subsequent machining may be necessary.
- Surface finish: the Ra obtained in aluminum (0,8 µm / 30 µin) is usually sufficient for architectural applications; mirror finishes require additional polishing.
- Cost-volume: die investment is amortized with large lots; for prototypes or short runs, other processes such as CNC machining or additive manufacturing may be more cost-effective.
Typical application cases: profiles for window and door frames, heat sinks, rails, aircraft structural components, tubes for heat exchangers.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the maximum pressure achievable in hot extrusion of steel?
Section titled “What is the maximum pressure achievable in hot extrusion of steel?”The maximum pressure in steel extrusion can reach 700 MPa / 101,5 ksi, depending on the extrusion ratio and billet temperature.
What minimum wall thickness can be achieved in an extruded aluminum profile?
Section titled “What minimum wall thickness can be achieved in an extruded aluminum profile?”The minimum achievable wall thickness in aluminum is 1 mm / 0.040 in, provided the geometry allows it and the die is properly designed.
What surface roughness (Ra) is typically obtained in aluminum extrusion?
Section titled “What surface roughness (Ra) is typically obtained in aluminum extrusion?”Aluminum and magnesium extrusion produces a surface finish of 0,8 µm Ra / 30 µin, without the need for additional operations.
At what temperature is aluminum alloy 6063 extruded?
Section titled “At what temperature is aluminum alloy 6063 extruded?”Alloy 6063 is hot extruded in a range of 350 °C to 500 °C / 662 °F to 932 °F, representing between 50% and 75% of its melting temperature.
What is the typical extrusion ratio for aluminum profiles?
Section titled “What is the typical extrusion ratio for aluminum profiles?”The extrusion ratio for aluminum typically varies between 10:1 and 100:1, allowing very significant area reductions in a single pass.
What minimum corner radius can be obtained in an extruded steel part?
Section titled “What minimum corner radius can be obtained in an extruded steel part?”The minimum corner radius for extruded steel is 0,8 mm / 0.030 in, while the minimum fillet radius is 4 mm / 0.120 in.
References
Section titled “References”- engineeringtoolbox.com: https://www.engineeringtoolbox.com/properties-aluminum-pipe-d_1340.html
- efunda.com: https://www.efunda.com/processes/metal_processing/extrusion.cfm?search_string=g%20steel
- manufacturingguide.com: https://www.manufacturingguide.com/en/ordlista/tolerances-thermal-cutting