Partial stamping refers to the chipless cutting or punching of contours out of sheet metals, films, laminates or insulating materials using a punch and die. In simple terms, partial stamping creates the required shapes directly from the roll or sheet, quickly, economically and reproducibly. In the electrical insulation industry, as well as for gaskets, labels and technical blanks, partial stamping is the standard process because it enables high quantities with constant quality.
Technical Fundamentals and Operating Principle
The fundamental elements are the punch, the die, the tool holder and the counter-holder. As the punch enters the die, shear occurs in the material. Decisive factors are the cutting clearance, tool geometry and stress progression. Typical results include the cleanness of the cut edge, the formation of burr and rolldown, as well as possible voids or fibre tearing in fibrous carriers.
Key process variants are:
- Through-cut (full cut): the component is cut completely.
- Kiss-cut (half cut): only the top layer and adhesive are separated, the liner remains intact.
- Perforation and scoring: conditional separation or predetermined breaking points.
- Rotary die cutting and flatbed die cutting: continuous versus cyclical processes.
In the machine setup, matrix stripping and web guiding additionally affect process stability.
Tool and Machine Design
Tools consist of properly matched punch and die pairs. Materials and surface treatments influence tool life and cutting quality:
- Material: high-speed steel (HSS) for medium loading; carbide for abrasive films or large batch sizes.
- Coatings: DLC, hard chrome or TiN reduce wear and adhesion.
- Flexible die plates on magnetic cylinders allow fast setup changes in rotary processes.
- Stripper elements and guide bushings prevent deformation and support part ejection.
Design rules: moderate draft angle, appropriate radii on the punch, defined cutting clearance and careful deburring concepts.
Material Influence and Special Features of Insulating Materials
Material type and layer structure strongly determine cutting behaviour. Ductile metals cut cleanly with little burr. Fibrous insulating materials such as aramid paper behave differently: they can fray and produce dust and fibre breakage. Nomex, for example, offers high temperature and dielectric strength but requires special tool concepts and extraction.
For laminate structures (for example PET/adhesive/liner), matching the cutting clearance and the die backing is decisive to avoid delamination or adhesive smearing. For self-adhesive systems, the liner hardness and adhesive temperature must also be considered.
Key Process Parameters
- Cutting clearance: typical range 5 to 15 percent of the material thickness, set according to the material.
- Punch radius: larger radii reduce notch effects, tighter radii enable fine contours.
- Pressure and stripping force: prevent sticking to the punch and damage to the liner.
- Cutting speed: affects burr formation and heat; reduce for heat-sensitive adhesives.
- Web guiding and registration: critical precondition for dimensional accuracy and repeatability.
- Draft angle and matrix stripping: for clean waste removal and stable part retention.
Dimensional requirements should be coordinated in the design with general tolerances, for example according to DIN ISO 2768.
Quality, Testing and Typical Defect Patterns
Quality characteristics are dimensional consistency, freedom from burrs, flush edges and an undamaged liner. Relevant tests include visual inspection, edge roughness, peel force tests on adhesive parts and sample dimensional checks. Typical defects and countermeasures:
- Burr formation: sharpen the tool, check the cutting clearance.
- Tear-out on fibrous substrates: increase the punch radius, reduce the cutting clearance, use a slower feed rate.
- Liner damage: reduce pressure, change the liner material (PET liner instead of paper).
- Adhesive smearing: adjust laser parameters or cutting speed; check suitable material pairing.
- Tool wear: sharpening schedule and coatings, tool life monitoring.
Process capability indices and inline image processing help to detect deviations early.
Economics and Process Selection
For high batch sizes, investment in solid carbide cylinders and rotary die cutting pays off. Flexible die plates are economical where variant diversity is high and setup times are short. Laser die cutting offers advantages for prototypes and fine geometries, but introduces heat and can affect adhesives. Contract slitting is often cost-effective for small batch sizes or when additional processing steps (lamination, printing) are needed.
Safety and Environment
Dust extraction, filters for fibrous waste, machine guarding and sound insulation are mandatory. For laser processes, extraction and heat management are particularly important. Ensure the disposal of stamping waste and lubricants according to regulations.
GOBA Takeaway
Partial stamping is a highly specialised but widely used manufacturing process. The decisive success factors are well-thought-out tool design, material-appropriate process parameters and close coordination between design and production. For insulating materials such as aramid paper, the cutting concept must take into account dust, fraying and thermal sensitivity. A clear specification of tolerances, a targeted tool strategy and inline inspection make partial stamping a reliable building block in the series production of insulating parts, labels and gaskets.