Stamping uses a press and dies to apply external force to sheet, strip, tube, and profile materials. This causes plastic deformation or separation to obtain the required shape and size. Stamping and forging both belong to plastic processing, together called forging and pressing. Blanks are mainly hot-rolled and cold-rolled steel sheets and strips. Sheet material, dies, and equipment are the three elements of stamping. Stamping is a metal cold deformation process, also called cold stamping or sheet metal stamping.
1. Stamping production process
1.1 Determine deformation compensation
Determine deformation compensation based on material, product structure, and other factors.
1.2 Design dies and stamp
Design dies based on compensation. Stamp finished or semi-finished parts.
1.3 Process semi-finished parts to finished parts
1.4 Tapping and thread machining
For internal threads, drill the pilot hole diameter and depth first. Pilot hole size is determined by thread specification. For external threads, turn the outer diameter to the thread major diameter first. Size is determined by thread specification.
For internal threads, use a tap of the corresponding grade. For external threads, use a thread turning tool or die.
Common defects include cracks, wrinkles, scratches, uneven thickness, incomplete forming, crossed threads, inconsistent dimensions, and failed thread gauge inspection.
Materials are selected by use requirements. Copper, aluminum, low-carbon steel, and other metals or non-metals with low deformation resistance, good plasticity, and good ductility are common.
If stamping punches, dies, discharge inserts, or tapping fixtures need replacement, we can machine them from customer drawings, in single pieces or small batches. Hansheng Automation works to drawing dimensions and assembly clearances.
2. Features of stamped parts
Material consumption is low. Parts are light and rigid. After plastic deformation, the internal structure of the sheet improves, and strength increases.
Dimensional accuracy is high. Parts from the same die are uniform and interchangeable. They meet general assembly and use requirements without further machining.
The material surface is not damaged during stamping. Surface quality is good, smooth, and neat. This helps painting, electroplating, phosphating, and other surface treatment.
3. Applications and equipment
About 50 to 60 percent of steel products are made from sheet. Most of this sheet is formed by stamping. Automotive bodies, radiator fins, boiler drums, vessel shells, motor and electrical silicon steel sheets all use stamping. Instruments, home appliances, office equipment, and storage containers also use many stamped parts.
Stamping is efficient. Compound dies and multi-station progressive dies can complete multiple stamping operations on one press and achieve automatic production. Output can reach hundreds of parts per minute, and production cost is low.
Compared with castings and forgings, stamped parts are thin, uniform, light, and strong. Stamping can form ribs, stiffeners, bends, or flanges that are hard to make by other methods, raising rigidity. With precision dies, part accuracy can reach micron level. Dimensions are consistent. Holes, recesses, and bosses can be stamped.
Thick plates are usually formed on hydraulic presses. Mechanical presses are common for other work. Modern high-speed multi-station mechanical presses can be equipped with decoiling, finished part collection, conveying, die storage, and quick die change. With computer program control, they form high-productivity automatic stamping lines.
4. Stamping production precautions
4.1 Prevent material lift and twist
In progressive dies, the outer shape of the stamped part is formed by punching the surrounding excess material. Material lift and twist are mainly caused by blanking force. During blanking, the blanking clearance causes material on the die side to be stretched and warp upward, while material near the punch side is compressed. A stripper plate presses the material and prevents upward warping on the die side. As stripper pressure increases, material near the punch side is stretched and compressive force decreases, while material on the die face is compressed and tensile force decreases. The flip of the stamped part is caused by tensile force on the die face. Pressing and holding the material during blanking is the key to preventing lift and twist.
4.2 Use reasonable die design
In progressive dies, the blanking sequence can affect forming accuracy. For small features, arrange a larger area blanking cut first, then a smaller area blanking cut. This reduces the effect of blanking force on part forming.
4.3 Hold the material
Open a material clearance in the stripper plate. When the die closes, the stripper plate contacts the die. At the material area, the clearance between stripper plate and die is material thickness t minus 0.03 to 0.05 mm. The stripper plate moves steadily and the material is held tight. For key forming areas, use an insert-type stripper plate. This makes it easier to repair wear on the pressing area after long production.
4.4 Add strong pressing
Thicken the pressing area of the stripper insert. A normal stripper insert thickness H plus 0.03 mm increases pressure on the die side material. This suppresses lift and twist during blanking.
4.5 Grind a slope or arc on the punch edge
This is an effective way to reduce blanking force. Lower blanking force reduces tensile force on the die side material and suppresses lift and twist.
4.6 Maintain punch and die edge sharpness
When the blanking edge wears, tensile stress on the material increases. The tendency for lift and twist increases.
4.7 Control blanking clearance
Improper or uneven blanking clearance also causes lift and twist. It must be controlled.
5. Common problem handling
5.1 Hole size too large or too small
In daily production, punched hole size may be too large or too small and may exceed specification. It may also differ greatly from punch size. Besides forming punch and die design dimensions, machining accuracy, and blanking clearance, check the following points.
When the blanking edge wears, tensile stress on the material increases. The tendency for lift and twist increases. When lift occurs, the punched hole size tends to become smaller.
Strong pressing of the material causes plastic deformation and makes the punched hole size tend to become larger. Reducing strong pressing makes the punched hole size tend to become smaller.
The punch edge shape also has an effect. If the edge is ground with a slope or arc, blanking force is reduced. The part is less likely to lift or twist, so the punched hole size tends to become larger. If the punch end is flat, with no slope or arc, the punched hole size tends to be smaller.
In practice, analyze the specific problem and find the method that fits it.
Our precision parts machining service is not limited to stamping production. Hansheng Automation can machine custom parts from drawings for automotive stamping support parts, hydraulic equipment parts, textile machinery parts, and medical device parts. We also cover yacht precision fittings, RC car structural parts, tobacco packaging machinery parts, and filling machinery parts. Single pieces and small batches are both available, with attention to material, tolerance, surface finish, and assembly fit.
