A stamped part is a flat component that a tool cuts from web material in a single stroke. At GOBA, stamped parts are made from electrical insulating materials: polyester films, aramid papers, technical laminates, pressboard, glass fabric and mica products. Material thickness ranges from 0.023 to 3.0 mm, maximum dimensions reach 1,000 x 2,000 mm. This page covers the tooling options and their cost logic, achievable tolerances, the typical defects that occur when stamping soft materials, and the route from sample to series.
Stamped insulating parts follow different rules than sheet metal parts
Most searches for stamped parts lead to sheet metal, steel and bulk forming. That is a different craft. Sheet metal deforms plastically, it flows under the punch and keeps the new shape. Insulating materials do not. A polyester film springs back, an aramid paper tears along the fibre, a laminate splits at the edge. Cutting clearance, blade geometry and cutting speed have to match the material, not a sheet thickness.
For purchasing this has a practical consequence: a supplier of metal stampings is rarely the right partner for insulating parts, and the other way round. We work exclusively with insulating materials. Anyone needing slot insulation, phase separators, cover discs or cell insulation will find our stamped and bent parts from insulating material.
Stamping separates material along the tool contour
The tool presses a closed cutting contour through the material resting on a counter surface. Stamping runs either from the roll or from pre-cut sheets. Working from the roll is faster and produces less waste, but requires material that unwinds cleanly. Stiff materials such as thick pressboard run better as sheets.
Besides cutting all the way through, two variants matter in insulating part production. In kiss cutting, the tool cuts only the upper layer of a self-adhesive build-up and leaves the liner intact, so the part can be peeled off at the customer. In partial punching, the part stays attached to the sheet by narrow tabs and is released during assembly.
Tooling determines tolerance, volume and tool cost
The tooling decision comes before the first enquiry and drives the price per part more than the material does. Three designs cover the full range.
| Tool type | Construction | Strength | Limit |
|---|---|---|---|
| Steel rule die | Plywood board with laser-cut slots holding steel blades | Low tool cost, short lead time, good for samples and medium runs | Limited tool life and dimensional stability, blades settle over time |
| Solid steel die | Cutting contour machined from solid steel | Tightest dimensional accuracy, long tool life, first choice for high volumes | Higher tool cost and longer lead time to first delivery |
| Rotary die | Cylindrical tool stamping continuously from the roll | High output, clean kiss cut, no cycle stops | Contour length tied to cylinder circumference |
Our recommendation for a new part is almost always the steel rule die. The tool is quickly available, the contour can still be changed after the first sample, and for most insulating parts the achievable accuracy is sufficient. We switch to a solid steel die once the series runs and either the volume carries the tool cost or the drawing demands tolerances the steel rule die cannot hold across its life. We use rotary die cutting for high volumes of simple contours, above all for self-adhesive build-ups.
Insulating materials we process into stamped parts
The material determines the dielectric strength, temperature class and mechanical stability of the finished part. These material groups run regularly on our stamping machines:
- Polyester films such as Hostaphan and Mylar, thin, tough and dimensionally stable
- Aramid papers for high temperature classes in motors and generators
- Technical laminates such as DMD and NMN, bonding paper and film into one composite
- Pressboard in the heavier gauges, stiff and easy to crease
- Glass fabric and mica products for temperatures above the polymer limit
- Self-adhesive build-ups on a liner for automated assembly
The right thickness depends on the required dielectric strength and the available space. Selection in detail is covered in the article on material thickness, the material range on our insulating materials page.
Tolerances on stamped parts follow DIN ISO 2768
Where a drawing carries no individual tolerance for a dimension, the general tolerance from the title block applies. In insulating part production the note DIN ISO 2768-m is the normal case, 2768-c for uncritical contours. Tighter tolerances drive tool and inspection cost without making the part work better. Permissible limit deviations for a specific nominal size come from the calculator in the article on DIN ISO 2768.
Two dimensions justify an individual tolerance on a stamped part: the fitting dimension that engages the slot or the lamination stack, and the hole spacing where a screw or rivet has to pass through. Everything else carries the general tolerance. On bent parts the minimum bending radius is an additional parameter, otherwise the material cracks at the edge.
Typical defects on stamped insulating materials
Most complaints about stamped insulating parts trace back to five causes. Knowing them lets you judge from the sample whether tool and material match.
- Delamination at the cut edge when a laminate is cut with a blunt blade
- Fibre tear-out on aramid and cellulose papers, usually a question of cutting speed
- Burr and edge lift on films when the cutting clearance does not suit the thickness
- Spring-back at crease lines, shifting the finished dimension after folding
- Distortion after hot forming when the part cools too quickly
Delamination and fibre tear-out are tooling issues, spring-back and distortion are process issues. Both are settled on the sample, not in the drawing.
What the drawing for a stamped part should contain
Most queries from our work preparation arise because the drawing omits details that are taken for granted in sheet metal work but govern production with insulating materials. Four details noticeably speed up a quotation.
- Material with trade name and thickness, because two films of equal thickness cut differently
- Temperature class of the application, which determines the permissible material group
- Grain direction where the material is anisotropic, as with papers and laminates
- Call-off quantity per lot and per year, which drives the tooling decision
A drawing without a material specification cannot be costed, a sample without a quantity cannot be assigned to the right tool class. If individual details are missing, send the drawing anyway. We will propose the material once you tell us the electrical and thermal requirement.
From sample to series
An enquiry for stamped parts runs through four steps. The sequence is deliberately short, because the decisive questions have to be answered early.
- Submit drawing or sample, stating material, thickness, quantity per call-off and the temperature class of the application
- We check the contour for stampability and propose the tool type, adjusting tab widths or radii where needed
- Sample parts from the steel rule die, checked for fitting dimension and edge quality, for release in the actual lamination stack
- Series production with a fixed inspection sequence, on request stacked, packaged or with marker lines for sensor detection in your assembly
Release in the actual component is the step that resolves most problems. An insulating part that measures correctly on the bench can still compress inside the lamination stack. That is why we fit insulating parts into your lamination stack before the series starts.
Does a dedicated stamping tool pay off at low volumes?
This is the most common objection from purchasing, and a fair one. A tool is a one-off investment that has to amortise across the parts. With a steel rule die, tool cost is low enough that the calculation turns after a few hundred parts, as soon as the alternative is manual cutting or laser cutting. Stamped edges are also reproducible, while laser cutting thermally loads plastic films and changes the edge.
Two cases argue against a dedicated tool: a geometry that is still going to change, and a genuine one-off requirement without repetition. In the first case, wait for design release. In the second, cutting from sheet is the cheaper route. Talk to us, we will tell you openly when a tool does not pay off for your requirement. For recurring geometries with varying call-off quantities we offer customer-specific production with stockholding.
Where stamped insulating parts are used
The largest application block is electric motor manufacturing: slot insulation, phase separators, cover slides and cover discs separate live parts from each other and from the lamination stack. In electromobility, cell and module insulation is added, thin parts with high dielectric strength and a tight fit. In household appliances stamped insulating parts serve as covers and separating layers, in telecommunications as insulating washers in assemblies.
For stamped parts with bends, creases or embossing, this topic continues with bent parts and formed parts.
