Manufacturing Process
Trimming
修边
Removing excess material around the edge of a drawn or formed part to reach the final outline and dimensional tolerance.
Process Steps
- Formed part located
- Trim die cuts edge
- Burr and outline checked
- Secondary deburr if required
What is trimming?
Direct answer: trimming cuts away the excess material left around a formed or drawn part. Blanking produces a flat shape; trimming corrects what forming did to it — the wavy or "eared" edge of a deep-drawn cup, or the flange a drawing operation could not finish to size.
When a part needs trimming
- Deep drawing leaves an uneven edge. The anisotropic flow of rolled sheet produces ears, and the drawn height is never perfectly uniform around the circumference.
- A flange has to be a final dimension. Drawing holds the flange roughly; trimming sets it exactly.
- The part was made from an oversize blank to give the forming operation material to pull from.
- The blank was pierced first and the outline is cut after forming, so the trim follows the formed shape rather than the flat one.
Trimming, shaving and blanking
| Operation | What it removes | Purpose |
|---|---|---|
| Blanking | The whole outline, in one stroke | Produce the flat part |
| Trimming | The excess material around a formed part | Bring the formed part to its final outline or height |
| Shaving | A thin layer along an existing cut edge | Improve edge quality and tolerance beyond blanking |
How it is done
- In the same tool. A trimming station in a progressive die follows the drawing or forming stations, so the part is trimmed while still located in the strip — the most accurate and the cheapest at volume.
- In a separate tool. Where the geometry or the volume does not suit a combined tool, the part is trimmed as a second operation in its own die.
- By machining. For a thick-walled extruded or drawn part, the surplus is sometimes turned or milled off rather than sheared.
What trimming holds
Because the part is trimmed after forming, the tolerance is set by the trim tool and the location of the part in it — typically ±0.05–0.15 mm on the trimmed edge and the resulting height. Where the trimmed edge is also functional, the same burr and edge requirements apply as for any other sheared edge, so a deburr step is normally part of the route.
Frequently asked
Why is my deep-drawn part's rim not flat?
Because the blank flowed unevenly as it was drawn. The ears and the height variation are normal; they are removed by trimming, and the drawing should carry the trimming allowance.
Can a drawn part be trimmed in the same die?
Often yes — a trim station after the drawing station is normal in a progressive or transfer tool. It keeps the part located without re-fixturing, which is where the accuracy comes from.
Does trimming need allowance in the drawing?
Yes. The blank or the drawn height has to include the material that will be trimmed away, so the drawing and the tool design work from the trimmed dimension rather than the formed one.
Is trimming the same as shaving?
No. Trimming removes a substantial amount of material to establish the outline; shaving removes a thin layer along an edge to improve its quality and tolerance.
Related: blanking · fine blanking · deburring · deep drawing · piercing