Cutting technologies

In shear cutting, the service life of the active components is crucial for economical production. To optimize this, a holistic approach to the entire system is necessary. This includes considering material selection, the manufacturing processes used for producing active components, coatings, and ultimately the process parameters during shear cutting. At Fraunhofer IWU, cutting tests can be performed on various presses. For service life studies, a Bruderer stamping automat is available.

Another focus is on the quality of the cut surface. Depending on the material, the design of the active components, and the process parameters (cutting clearance), the cut surface will have varying proportions of smooth cut and fracture surfaces. If higher cut surface qualities are required than can be achieved with shear cutting, other processes such as shear cutting with superimposed stress or high-speed shear cutting are available.

Through years of experience in shear cutting, we have expertise in the following areas:

• Tool design
• Consultation on material selection, heat treatment, and coating of active components
• Conducting experiments and long-term tests
• Processing sheet metal thicknesses ranging from 0.1 mm to 10 mm
• Materials: aluminum, titanium, steel (high-strength)
• Integration of measurement technology (speed, force, structure-borne sound, acceleration)

Advantages of the process

• Quantification of service life
• Inline condition monitoring of active components
• Capturing and storing process data
• Improvement of service life
• Enhancement of cut surface quality

An innovative and patented cutting process developed by Fraunhofer IWU is shear cutting with fluid counter-support. In this method, the die is completely filled with oil. After the hold-down is applied, a preliminary pressure is generated in the oil using a hydraulic unit. During shear cutting, the oil is slightly compressed. After the trimming process, the oil decompresses and pushes the slug back into the strip. The slug is then removed through the strip and ejected in the next stage.

The advantages of this process include the oil providing an overlaying counter-pressure in the cutting zone during the cutting process. Additionally, the oil penetrates the shear zone area as soon as initial cracks form. As part of the research project "Shear Cutting Strategies for High-Strength and Ultra-High-Strength Steels (UHSS); Sub-project: Innovative Approaches for Shear Cutting of Ultra-High-Strength Steels," excellent cut surface qualities and minimal wear of the active components were achieved for high-strength steels (C75, 1400 MPa, 2 mm sheet thickness). The testing of the process for thicker sheets and additional materials will be part of future research activities.

Advantages of the process

• High cut surface quality
• High dimensional accuracy and minimal component deformation
• Reduction of active component wear, even when trimming ultra-high-strength materials

Another process involving stress superposition is precision cutting. Similar to fine blanking, a counter-support is used to apply a counterforce to the slug. However, no ring burr is used. The counterforce can be applied, for example, by a gas pressure spring in the cutting tool. Unlike shear cutting, small cutting clearances are used, and the cutting edges are slightly rounded, resulting in an increased smooth cut proportion.

Stress superposition processes can be used to reduce wear (adhesion, abrasion, surface disruption) during the trimming of materials such as ultra-high-strength steels, aluminum, or titanium, and to improve cut surface quality compared to shear cutting.

Advantages of the process

• High cut surface quality
• High dimensional accuracy and minimal component deformation
• Reduction of active component wear, even when trimming ultra-high-strength materials

High-speed impact cutting (HSIC) differs significantly from conventional cutting in terms of process phases. The punch impacts the sheet at high velocity, and after elastic deformation, the sheet material in the area between the cutting edges of the die and punch is rapidly plastified. In HSIC, complete sliding of the punch through the punch grid is typically not required, so the component can be ejected due to kinetic energy even if the punch is stopped at approximately 1/3 of the sheet thickness. Depending on the material and process parameters, local strain rates increase due to the localization of plastic deformation. This localization is favored by high strain rates, low strain rate sensitivity, and low thermal conductivity. The high plastic deformation and the resulting conversion of deformation energy into heat, along with friction, combined with short process times and low heat conduction, can generate high temperatures in the localization zone. This can lead to plastic instabilities, such as the formation of an (adiabatic) shear band.

The ratio of cutting forces in HSIC compared to conventional shear cutting depends on the material. The appearance of the cut surfaces is also strongly influenced by the increased process speeds. Only minimal edge draw-in occurs, with virtually no smooth cut and very little burr. The separation surface in HSIC is almost entirely characterized by the fracture surface. In contrast to conventional cutting, the fracture surface exhibits a fracture angle close to 90° and low roughness. In addition to high straightness in HSIC, the generation of adiabatic shear bands offers the possibility of specifically influencing local microstructures to achieve exceptional (surface) property combinations. This can enable the use of surfaces produced by HSIC as functional surfaces.

HSIC is suitable for a wide range of materials. For very ductile materials, edge draw-in is significantly reduced compared to conventional shear cutting. For very strong or hardened materials, HSIC allows for general trimming with excellent cut surface properties due to high local heat and associated local thermal softening. Sheet thicknesses ranging from 0.2 to 10 mm can be cut at Fraunhofer IWU.

Advantages of the process

• Very high quality of the cut surfaces produced
• Trimming of very strong (hardened) and ductile materials is possible, with significantly improved cut surface quality and minimal heat-affected zone
• Formation of adiabatic shear bands at the cutting edge, which possess additional positive properties