A stamping die is a special type of equipment used in cold stamping to process materials (metal or non-metal) into parts (or semi-finished products). It uses a die installed on a press to apply pressure to the material, causing it to separate or undergo plastic deformation, thereby obtaining the desired parts through a pressure processing method.

According to the process properties, stamping dies can be classified into: (1) Drawing dies. These are dies that form sheet metal blanks into open hollow parts, or further change the shape and size of hollow parts. (2) Trimming dies. These are dies that cause material separation along closed or open contours, such as trimming dies, punching dies, cutting dies, slotting dies, and blanking dies. (3) Forming dies. These are dies that directly replicate the shape of a blank or semi-finished workpiece according to the shape of the convex and concave dies, with only local plastic deformation occurring in the material itself, such as bulging dies, necking dies, flaring dies, embossing dies, and shaping dies. (4) Flanging dies. These are dies that cause the sheet metal blank or other blanks to bend along a straight line (flanging line), thereby obtaining workpieces with a certain angle and shape.

I. Trimming Die Structure and Principle

A trimming die is used to cut off the supplementary parts of the drawn parts process and the excess parts of the pressing surface. According to the movement direction of the trimming insert, it can be divided into three categories: vertical trimming die, oblique wedge trimming die, and vertical oblique wedge trimming die. Under the premise of ensuring uniform release of the shear stress of the workpiece, the die design fully considers the shear stress, lateral force, and impact force on the die. The working process is as follows: the upper die is locked on the machine slide, the lower die is fastened to the machine bed, the drawn part is placed on the lower die of the die, and reasonable die stamping parameters and stamping times are set. The upper die mechanism moves downward. As the slide moves downward, the core first presses the workpiece, and the lower slide continues to move downward until the upper and lower die edges, punch, and concave die sleeve interact to separate the workpiece. The separated waste material and slugs slide down to the bottom of the worktable along the set chute (slug plate). At the same time, the machine slide returns to the top dead center, and the punching process completes one complete cycle. Since impact force is unavoidable in punching, polyurethane buffer blocks are added to the four corners of the lower die to reduce impact force and extend the service life of the die. The strength of the die itself is also important, so there are corresponding design requirements for each wall and reinforcing rib.

II. Process Design of Trimming Dies

The rationality of the process design of trimming dies directly affects the quality of the stamped parts and the service life of the dies. Good process design saves debugging time and improves the direct pass rate of parts, greatly improving the efficiency of automated production.

1. Design of Limiting Operations for Trimming and Punching

The shapes of stamped parts vary. The surface at the trimming line (punching) often forms a certain angle with the bottom surface of the die. When the angle exceeds a certain value, an oblique wedge mechanism is required for trimming (punching) to ensure the service life of the die and the quality of the parts. Design basis: Usually an obtuse angle, acute angle ≤20°. However, in the process, if it exceeds 20°, the shearing surface is made into a plane, and subsequent re-trimming operations are required.

2. Design of Trimming and Punching Clearance

Punching clearance is the basic guarantee for high-quality parts. Different materials and thicknesses have different punching clearances. As the hardness and thickness of the material increase, the punching clearance needs to be increased accordingly. In addition, reasonable punching frequency and regular maintenance of the die are also essential factors for high-quality stamped parts. Experience has shown that a cutting section of l, 3 cuts, and 2/3 breaks is the best punching clearance. In this case, burrs can be avoided, and the service life of the cutting edge can be ensured, reducing the maintenance cycle.

3. Separation and Cutting Process

This process separates the waste material first and then cuts it. It is mainly used for large outer panels such as front and rear outer panels, top outer panels, and hood outer panels. The advantages of this process are: reducing the generation of waste material in the trimming process and preventing the waste material from scratching the parts in subsequent processes. Generally, the waste material knife is 3-5 mm lower than the separation trimming line, and the inside is close to the trimming surface. Or a height difference of about 3 mm is made at the splicing of the trimming knife block. The separation process should comprehensively consider the die structure and size, and pay attention to referring to the machine tool process parameters.