Stamping Die Structure

This section introduces the structure of stamping dies. While die structures vary according to different product characteristics and requirements, their basic structure remains constant, consisting of several plates, inserts, and standard components.

Dies are generally assembled from multiple plates, components (called inserts or blocks), and standard parts.

General Stamping Die Structure

The specific plates from top to bottom (including code numbers) are:

Upper die plates: Upper backing plate, upper spacer, upper die shoe (UPU), upper backing plate (UBU), upper stripper plate (PHU), stop plate (PPS), stripper plate (PSU)

Lower die plates: Lower die plate (DIE), lower backing plate (LBD), lower die shoe (LPD), lower spacer, lower backing plate

Other less commonly used plates: Upper cover plate (CVU), ejector plate, upper die plate, lower stripper plate, lower stop plate, lower clamping plate, punch holder, die holder, etc.

Die components include:

• Upper die inserts and blocks: clamping plate inserts, stripper plate inserts, punches, etc.
• Lower die inserts and blocks: lower die inserts, lower die cutting edges, etc.

Standard parts: Springs, hex screws, set screws, wire springs, spacer sleeves, guide posts, guide bushings, spacer washers, two-way pins, knockout pins, etc.

Non-standard parts: External positioning, internal positioning, pitch positioning, external limit posts, internal limit posts, etc.

Common Stamping Materials and Selection

The properties of stamping materials are closely related to stamping production. Material properties directly affect stamping process design, stamping part quality, product service life, and also impact production balance and stamping part costs.

Basic Requirements for Stamping Materials:

1. Good Forming Performance

For forming processes such as drawing, bending, embossing, and bulging, materials should have good stamping formability, including good crack resistance, die conformability, and shape retention. Otherwise, products are prone to deformation and cracking, making die adjustment difficult. For blanking processes, materials should have a certain degree of plasticity.

2. High Surface Quality

Material surfaces should be clean, flat, and free from defects. High-quality surfaces are less prone to cracking during forming, less likely to scratch dies, and produce better surface quality parts.

3. Thickness Tolerance Compliance

Material thickness tolerances should meet national standards, as specific die clearances are only suitable for materials within certain thickness ranges. Excessive thickness tolerances not only directly affect part quality but may also cause scrap. In straightening, bending, and forming processes, excessive positive thickness deviation may damage dies or presses.

Common Stamping Materials

The most commonly used materials in stamping production are metallic materials (including ferrous and non-ferrous metals), though non-metallic materials are sometimes used. Ferrous metals mainly include ordinary carbon structural steel, high-quality carbon structural steel, alloy structural steel, carbon tool steel, stainless steel, and electrical silicon steel. Non-ferrous metals mainly include pure copper, brass, bronze, and aluminum. Non-metallic materials include cardboard, laminated board, rubber board, plastic board, fiberboard, and mica.

Metal materials for stamping are generally supplied as sheet and strip of various specifications. Sheets can be used for progressive die production and also for transfer die production. Sheets are larger in size and suitable for stamping large parts, or can be cut into strips for medium and small part stamping. Strip material (also called coil material) comes in various widths with uncoiled lengths reaching tens of meters, supplied in rolls, suitable for automated feeding in continuous die mass production.

Reasonable Material Selection

Material selection should consider the usage requirements of stamped parts, stamping process requirements, and economics.

(1) Material Selection Based on Usage Requirements

Selected materials should enable stamped parts to function normally in machines or components with a certain service life. Materials should meet requirements for strength, rigidity, toughness, corrosion resistance, and heat resistance based on usage conditions.

(2) Material Selection Based on Process Requirements

For any stamped part, selected materials should stably form qualified products without cracking or wrinkling according to stamping process requirements. Selection methods include trial stamping and analytical comparison. Cold-rolled sheets have more precise dimensions, smaller deviations, fewer surface defects, brightness, dense internal structure, and superior stamping performance compared to hot-rolled sheets. (Note: t in dies generally represents thickness, such as plate thickness or material thickness.)

(3) Material Selection Based on Economic Requirements

Selected materials should be reasonably priced, readily available, and economical while meeting performance and process requirements to reduce stamping part costs.

Classification of Stamping Dies

Stamping dies can be simply classified into two types: progressive dies and transfer dies. Transfer dies can be further divided into compound dies, drawing dies, riveting dies, etc.

Transfer Die (Single-Operation Die):

Completes only one stamping operation per press stroke. After completion, products must be manually or robotically removed and placed into the next station's die until the final operation. These dies are simple to maintain but time-consuming and labor-intensive in production, with higher scrap rates.

Compound Die:

Common structures include compound blanking and compound drawing. The punch (also called male die or punch head) is designed in the lower die, with lower clamping plate (fixing the punch), lower stop plate, and lower stripper plate (outer stripping) in sequence. The upper die consists of the female die (or cutting edge), inner stripper plate, and upper backing plate. The inner stripper is suspended from the upper backing plate using spacer sleeves and supported by push rods or springs. For blanking compound dies, the inner stripper generally protrudes 0.50mm from the female die, not lower than the female die to prevent edge chipping or stripping failure. The inner stripper force must be sufficient to eject products from the female die; nitrogen springs are typically used for thicker materials.

Progressive Die (Continuous Die):

Completes two or more stamping operations simultaneously at different stations in one press stroke. These dies are more difficult to maintain and require experienced die makers, but offer high production efficiency with potential output of thousands of parts per hour at high speeds, saving labor and time costs with lower scrap rates.