Steel and aluminium closed die forging – how to choose the right solution

Closed die forging is a flexible technology for high performance parts in small and medium series. It works for both steel and aluminium, but the two materials behave in different ways and fit different applications.

This article explains the basics of closed die forging and gives practical guidance on when to choose steel or aluminium forgings for your project.

Chains and lifting equipment in an industrial setting illustrate the robust applications of closed die forging, showcasing the versatility and strength of steel and aluminum for high-performance parts.

1. What is closed die forging

In closed die forging, a heated billet is placed between two shaped dies. Under high pressure, the metal fills the cavity and forms the final geometry.

Typical parameters for a modern European forge:

• Part weights from 0.05 kg to 7 kg

• Forging of steel, aluminium, copper, bronze and titanium

• Tolerances down to ±0.2 mm after forging

• Full support from tool design to machining and surface treatment
  

This provides a complete solution for customers who need ready-to-install components, not only raw forgings.

2. Steel forging – when strength and toughness lead

2.1 Process and equipment

For steel, the forging process runs at high temperatures:

• Billets are heated to 1150–1250 °C

• A CNC controlled forging hammer with 50 kJ energy performs several blows to fill the die

• Each blow is recorded in a digital system for traceability

• Typical part weight is 0.1–7 kg
  

A modern forge can process up to 800 tons of steel per year, which gives both flexibility and experience with many geometries.

2.2 Typical steel grades

Common forged steels include:

• 42CrMo4 for highly loaded shafts, levers and tools

• 27MnCrB5-2 for agricultural blades and wear parts

• C45E for structural elements and general mechanical parts

• AISI 304, 316, 420 for stainless applications

Special alloys with titanium or nickel additions are used when higher toughness or wear resistance is needed.

2.3 Best use cases for steel forgings

Steel forging is the right choice when:

• Components see extreme mechanical loads

• You need high toughness and impact resistance

• Parts work in abrasive environments (soil, rocks, tools)

• You require high temperature stability

• Safety requirements are strict (lifting components, structural joints)
  

Examples:

• Forklift and lifting system components

• Agricultural tools and blades

• Bridge and structural connectors

• Industrial mechanical joints and shafts
  

3. Aluminium forging – when weight and conductivity matter

3.1 Process and equipment

Aluminium forging uses different equipment and narrower temperature windows:

• Alloys from series 5xxx, 6xxx and 7xxx

• Part weights from 0.05 to 6 kg

• Forging on a CNC screw press rated at 1000 t

• Tight control of temperature and deformation rate to avoid overheating
  

The process is more sensitive than steel forging, but needs about three times less energy. At the same time it is three times more sensitive to temperature variations, which is why digital control is essential.

A modern forge processes roughly 200 tons of aluminium per year, which allows short lead times and stable quality.

3.2 Typical aluminium alloys

Main alloys for forged parts are:

• 6082 / 6061 (AlMgSi1)Good strength, machinability and corrosion resistance

• 7075 (AlZnMgCu1.5)High strength level, used where steel would be too heavy

• AlMg3 and AlMg4.5Mn0.7 (5xxx series)Excellent corrosion resistance, especially in marine and outdoor use
  

With proper forging, aluminium parts reach 20–30 % higher mechanical strength than cast or extruded parts. The difference in tensile strength between cast and forged aluminium can reach 80 MPa, which is critical for safety.

3.3 Best use cases for aluminium forgings

Use forged aluminium when:

• You need low weight and high strength at the same time

• Corrosion resistance is important

• The component has to conduct heat or electricity efficiently

• The product is part of e-mobility or light structures
  

Examples:

• High voltage connectors and energy components

• Electric motor parts

• Architectural brackets and mounting systems

• Light mechanical structures

• Motorsport, e-motor and e-bike parts
  

4. Steel or aluminium – a simple selection framework

When you choose between steel and aluminium closed die forging, start with four questions:

1. What are the main loads?

   • Very high static and impact loads → steel

   • Medium loads with strong weight limits → aluminium

2. What is the environment?

   • Aggressive, hot, abrasive → steel or stainless steel

   • Outdoor, marine, corrosion sensitive → aluminium 5xxx or stainless steel

3. How critical is weight?

   • High importance (e-mobility, sports, portable equipment) → aluminium

   • Low to medium importance → steel

4. What about lifecycle cost?

   • Steel tooling and forging often have lower unit cost for small series

   • Aluminium reduces transport, energy use and operating costs over time

For many projects, the best approach is to combine both materials in different parts of the same system.

5. Design and documentation tips for forged parts

To get the most out of closed die forging, prepare your project with these points in mind:

• Define load cases and safety factors early

• Mark critical surfaces and tolerances clearly

• Discuss possible weight reduction with the forge

• Check machining allowances based on ±0.2 mm forging tolerances

• Plan for heat treatment and surface protection (KTL, galvanizing, anodizing)

• Ask for traceability and measurement reports when needed

A forge that offers tool development, simulation, heat treatment, machining and surface finishing under one control will reduce coordination work and risks for you.

6. Conclusion

Closed die forging of steel and aluminium provides a flexible and powerful tool for modern engineering.

• Steel forgings serve in the most demanding mechanical and structural roles

• Aluminium forgings enable light, efficient and corrosion resistant components

• Both processes profit from CNC equipment, digital control and full traceability

For engineers and buyers, understanding these differences helps to select the right combination of material and process for long term performance and cost control.