Classification of Stamping Processes

Stamping processes can be broadly categorized into two major types: blanking operations and forming operations (which further include bending, deep drawing, and shaping). Blanking operations involve separating the stamped part from the workpiece along a defined contour during the stamping process, while ensuring that the resulting part meets specific quality standards for the separation edge. Forming operations, on the other hand, aim to induce plastic deformation in the workpiece without causing fracture, ultimately transforming it into the desired final shape—while also meeting stringent requirements such as dimensional tolerances.

There are two methods of stamping: cold stamping and hot stamping, depending on the temperature conditions during the process. This choice is influenced by factors such as the material’s strength, ductility, thickness, degree of deformation, and equipment capabilities—and it should also take into account the material’s original heat treatment state as well as its final application conditions.

1. Cold stamping is a metalworking process conducted at room temperature, typically suitable for workpieces with thicknesses less than 4 mm. Its advantages include no need for heating, absence of oxide scale, excellent surface quality, ease of operation, and lower costs. However, a drawback is the occurrence of work hardening, which, if severe, can cause the metal to lose its ability to undergo further deformation. Cold stamping requires the workpiece to have uniform thickness with minimal variation, as well as a smooth, flawless surface free from spots or scratches.

2. Hot stamping is a metal forming process that heats the material to a specific temperature range. Its advantages include eliminating internal stresses, preventing work hardening, enhancing the material's ductility, reducing deformation resistance, and minimizing energy consumption in equipment. (Source: China Machinery Network)

1. Punch and Die Structure: A punch and die is a tool used to cause separation or deformation in sheet metal. A typical punch and die structure is shown in Figure 3-17, consisting of two main parts: the upper die and the lower die. The handle of the upper die is securely attached to the slide of the press, moving up and down along with it, while the lower die is fixed firmly to the press’s worktable.

The punch and die are the working components of a stamping die that deform or separate the blank, and they are securely fixed to the upper and lower templates using pressure plates. The upper and lower templates are equipped with guide bushings and guide posts, respectively, to ensure precise alignment of the punch and die. Meanwhile, the stripper plate and positioning pins are used to control the feeding direction and feed length of the blank. Finally, the unloading plate plays a crucial role by ejecting the finished part or blank from the punch after stamping is complete.

2. Classification of Punch Dies

Punch dies are essential tools in stamping production. Punch dies can be broadly classified into three types: simple dies, progressive dies, and compound dies.

(1) Simple Die A simple die is a type of stamping die that completes only one operation during a single stroke of the press. Figure 3–17 shows a simple die used for blanking or punching, while the assembly drawing of the simple die is illustrated in Figure 3–18. During operation, the strip material advances between the two guide plates 9 on the cavity die until it comes into contact with the positioning pin 10. As the punch moves downward to perform the stamping action, the punched part (or scrap material) falls into the cavity hole, while the strip material remains clamped around the punch and returns upward along with it. When the strip touches the stripper plate 8—fixed to the cavity die—it is pushed off, allowing the strip to continue advancing between the guide plates. This process repeats, producing the second stamped part.

(2) A continuous progressive die is a type of die used in a press, where multiple stamping operations are simultaneously completed at different stations within a single stroke of the press. As shown in Figure 3–19, during operation, positioning pin 2 aligns with the pre-punched locating holes. As the upper die moves downward, punch 1 performs blanking, while punch 4 carries out punching. When the upper die returns to its original position, the stripper plate 6 pushes the scrap material off the punches. At this point, the workpiece 7 is fed forward again, initiating the second cutting operation. This process repeats continuously, with each feed increment precisely controlled by the stop pin.

(3) A compound die is a type of die that simultaneously completes multiple stamping operations at the same station within a single stroke, as illustrated in Figure 3–20. The most distinctive feature of a compound die is the presence of a combined punch and die assembly—designated as component 1. The outer circumference of this assembly serves as the blanking punch edge, while its inner hole forms the drawing die cavity. When the slide moves downward carrying the combined punch and die assembly, the strip material is first blanked between the combined punch and die assembly (component 1) and the blanking die cavity (component 4). The blanked part is then held firmly against the drawing punch (component 2) located within the lower die. As the slide continues its downward motion, the die assembly follows suit, initiating the deep-drawing process. Finally, during the return stroke of the slide, the stripper (component 5) and the unloader (component 3) push the drawn part (component 9) out of the die. Compound dies are particularly well-suited for producing high-precision stamped parts in large volumes.