Fraunhofer Institute for Machine Tools and Forming Technology
Fraunhofer Institute for Machine Tools and Forming Technology

Cold and warm bulk forming

Our core business area is automotive engineering. We focus on the "Car of the Future," characterized by efficient resource use and minimal environmental impact through low fuel consumption and reduced pollutant emissions during operation. Key development trends include electromobility and more efficient, high-performance, and environmentally friendly internal combustion engines. For these, we develop solutions ranging from transmission and drivetrain components to engine, chassis, and steering components. Our core competency lies in developing processes for manufacturing solid and hollow shafts, gears, and structural and chassis parts. The technologies realized at the Fraunhofer IWU include forging, axial forming, profile and gear rolling, extrusion, hole expanding, and radial forging.

Trends

  • Resource-efficient, forming-based process chains
  • Functionally and mass-optimized components (drivetrain)
  • Shortened process times
  • Avoidance of material loss and increased material utilization
  • Improved component properties through the introduction of forming effects

Forming technologies

Axial forming

Axial forming is a cold bulk forming process used to introduce longitudinally oriented internal and external profiles with net-shape quality into rotationally symmetrical components. The recursive feed motion of the tools significantly reduces the forming force compared to continuous processes. This allows thin-walled lightweight structures to be provided with profiles generated by forming technology without failing under the influence of the forming force.

Process Advantages

  • Use of new, high-strength materials
  • Gear production without post-processing
  • Production of complex component geometries
Radial forging — a process for lightweight construction and achieving a wide variety of shapes

Radial forging is a stepwise compressive forming process for reducing the cross-section of primarily rotationally symmetrical components. In principle, radial forging is performed in two process variants:

In feed radial forging, relatively long reduced cross-sections with a shallow transition angle are produced, whereas in plunge radial forging, localized cross-section reductions with steep transition angles are created. The workpiece is fully or partially enclosed by two or more tool segments. With each downward stroke, a portion of the workpiece is formed according to the tool geometry and stroke. This allows for variation of outer and inner diameters, as well as simultaneous production of internal profiles.

Process Advantages

  • Improvement of mechanical component properties
  • Material efficiency through expanded shaping possibilities
  • Forming of alternative materials with high strengthening potential
Spin extrusion process / Burnishing

The spin extrusion processg is an incremental, rotary compressive forming process developed jointly by the Fraunhofer IWU and the Technical University of Chemnitz for producing hollow parts from solid cylinders. This bulk forming process combines the principles of backward cup extrusion and ironing. Depending on the manufacturing task and material, forming can be performed cold, warm, or semi-warm.

Process Advantages

  • Optimal material utilization
  • Suitable for processing cost-intensive materials
  • Alternative to extrusion for thick-walled hollow parts or hollow parts with steps
  • No chemical surface pre-treatment required
  • Eliminates the need for complex dies due to kinematic forming
Profile and gear rolling
Profilwalzen

Profile cross-rolling with round tools is a partial forming process involving rolling kinematics between the tool geometry and the resulting workpiece profile. The initial rotationally symmetrical shape is clamped axially between centers. The rolling kinematic formation of the gear profile is achieved through a diameter-related penetration process of the tool teeth in the radial direction. The rolling process is divided into the initial rolling, penetration, and calibration rolling phases.

Improved final component properties, such as load-bearing capacity, root strength, surface quality, and minimal distortion, result from work-hardened surface strength and a contour-adapted fiber flow. Process advantages include very short cycle times and the elimination of chip disposal.

Process Advantages

  • Shortened process times compared to machining
  • Avoidance of material loss through forming
  • Elimination of chip generation and disposal
  • Increased strength of the tooth contour through work hardening
  • Mirror-like surface finishes
  • Contour-adapted fiber flow
  • Reduced notch sensitivity and increased fatigue strength
Extrusion

Extrusion is a cold bulk forming process used to produce near-net-shape preforms or components from blanks, bar sections, tubes, and similar materials. For manufacturing complex components, extrusion is also performed in semi-hot or warm forming ranges.

In a shaping tool, the workpiece material is displaced and flows through an opening in the die, changing its cross-section. The requested component geometries can be very complex. To achieve a wide variety of shapes, several variants of the extrusion process are available. These can be combined both sequentially and in parallel.

Process Advantages

  • Material efficiency through expanded shaping possibilities
  • Use of new materials
  • Reduction in the number of work steps
Die forging

Die forging, a high-pressure forming process, can be used to produce highly stressed components with or without flash. It is a highly productive manufacturing process, primarily for large quantities. Research in die forging is closely linked to forming units, tooling systems, and the materials being formed. In technology development, adjacent processes, such as preforming (cross-rolling), are included in studies of the overall process chain. This allows for individual adaptation to specific operational conditions and requirements.

Process Advantages

  • Resource-efficient forming process for producing complex components with optimal use of input material
  • Die forging is suitable for almost all materials (e.g., classic steel materials, aluminum and magnesium wrought alloys, nickel-based and titanium alloys)
  • Highly productive manufacturing process with short cycle times and a high degree of automation in the forming process chain, including heat treatment of forged blanks
  • Semi-hot forming as an energy-efficient process in large-scale production, specifically for improving microstructure and reducing the tolerance spectrum of forged blanks
  • Precision forging as a special process in hot bulk forming for workpieces with the highest demands on component properties (dimensional and mass properties, fine-grained structure)
Radial forging — a process for lightweight construction and achieving a wide variety of shapes

Radial forging is a stepwise compressive forming process for reducing the cross-section of primarily rotationally symmetrical components. In principle, radial forging is performed in two process variants:

In feed radial forging, relatively long reduced cross-sections with a shallow transition angle are produced, whereas in plunge radial forging, localized cross-section reductions with steep transition angles are created. The workpiece is fully or partially enclosed by two or more tool segments. With each downward stroke, a portion of the workpiece is formed according to the tool geometry and stroke. This allows for variation of outer and inner diameters, as well as simultaneous production of internal profiles.

Process Advantages

  • Improvement of mechanical component properties
  • Material efficiency through expanded shaping possibilities
  • Forming of alternative materials with high strengthening potential

Reference projects

Warm rolling of large gears

In the GearForm research project, a large gear module (m = 9.5 mm) was successfully produced using a warm rolling process for the first time worldwide. For this purpose, a novel rolling system with an integrated inductive heating unit was designed, developed, and implemented at the Fraunhofer IWU.

Precision windings for electric motors

To achieve resource-efficient production and higher efficiency for electrical machines, the greatest potential lies in, among other things, the targeted use of high-quality materials, thinner stator laminations, and their innovative arrangement. The goal of various projects pursued at IWU is to leverage the advantages of forming process chains in the production of electric motor components.

Gear production on a lightweight shaft for a modular electric powertrain concept

Using the cold forming process of axial forming, a gear was produced that can be used without post-processing or heat treatment. In addition to improved mechanical component properties, the process time was reduced compared to machining technology.