A car door outer or a fender is not formed in a single press stroke. The sheet passes through a line of dies, and each die does one part of the job. Knowing what each die does helps buyers read a die plan, compare quotations and understand where quality problems come from. Hailong Group designs and builds cold stamping dies for automobile body panels and sheet metal parts. This article walks through a typical die line.
Why a panel needs several dies
One die cannot stretch the sheet into shape, cut off the excess, punch the holes and bend the edges at the same time. These operations need different forces, cutting directions and tooling. The work is therefore split into a sequence of dies, run on a tandem press line or a large automatic line. How many dies a panel needs depends on its shape: a simple part needs fewer operations, a complex outer panel more.
1. Blanking
Coil or sheet is cut into a blank close to the shape the draw die needs. The blank shape affects material cost and how the metal flows in the next step, so it is developed together with the draw die.
2. Drawing: forming the shape
The draw die is the most critical die in the line. A binder, or blank holder, clamps the edge of the sheet while the punch stretches it into the die cavity. Draw beads on the binder control how fast metal flows in. Too much restraint and the panel splits. Too little and it wrinkles. Most surface quality issues on outer panels start here, which is why draw dies take the most tryout time.
3. Trimming
Trim dies cut away the binder area and excess material along the panel edge. The cutting steels must be sharp and precisely aligned to give clean edges without burrs. Where the trim line is not in one plane, cam-driven cutters trim from the side. During development or for low volumes, laser trimming is a common alternative to a trim die.
4. Piercing
Holes for mounting, drainage and assembly are punched, either in the trim die or in a separate piercing die. Hole positions decide whether the panel fits in the body shop, so they are among the first features checked on every part.
5. Flanging and restrike
Flanging dies bend the edges to form hems and joining flanges. Restrike dies sharpen feature lines and radii and correct the shape. Sheet metal springs back partly after forming, and this springback is compensated in the die surfaces and in these final operations.
What each die has to control
| Operation | What it does | Typical problems it must control |
|---|---|---|
| Blanking | Cuts the starting blank | Material use, blank position |
| Drawing | Forms the panel shape | Splits, wrinkles, surface lows |
| Trimming | Cuts the panel edge | Burrs, trim line position |
| Piercing | Punches holes | Hole position, slugs |
| Flanging and restrike | Bends edges and sets features | Springback, flange angle, radii |
How the dies are proven before delivery
Every die is tried out on a press, the panels are measured, and the die is adjusted until parts meet the drawing. Hailong’s mold unit uses large CNC processing equipment, mechanical and hydraulic presses, a large mould tryout press, a large laser three-coordinate measuring machine and a five-axis laser cutting machine. Checking fixtures then confirm each panel’s shape and hole positions. Read how automotive stamping dies are made and why stamped parts need checking fixtures.
From die line to production
The same group runs stamping production, including an 8,250-ton closed automatic stamping line, a 3,400-ton automatic line and further press lines from 400 to 2,400 tons. Die makers and stamping engineers therefore work with the same presses the dies are built for. Our dies have served automobile manufacturers including BAIC, FAW, SAIC, Great Wall, Beijing Benz, Chery and GAC.
What to send for a die line quotation
- 3D part data, material grade and sheet thickness
- Annual volume
- Details of the press line where the dies will run: tonnage, bed size, shut height and automation
- Whether you also need checking fixtures or stamped parts
See our automotive stamping dies and the RFQ guide for the full checklist.
Talk to our engineers
Send your part drawings or 3D data using our RFQ guide or the contact page. You can also email nora@qdhailong.com or call +86-532-66090318.