Stamping dies are the primary process equipment for stamping operations. Stamped parts are formed through the relative motion of upper and lower dies. During processing, the upper and lower dies continuously open and close. If an operator’s fingers enter or remain within the die closing zone, it poses a serious threat to personal safety.

(I) Main Die Components, Functions and Safety Requirements

1. Working Components

Punches and dies are working components that directly shape the blank, making them critical die parts. Punches and dies are precise and complex, and shall meet the following requirements: (1) They shall have sufficient strength and must not fracture or fail during stamping; (2) Appropriate requirements shall be specified for material selection and heat treatment to prevent brittle cracking caused by excessive hardness.

2. Locating Components

Locating components define the mounting position of blanks, including locating pins (plates), stock stops (plates), pilot pins, stock guide plates, side cutters for pitch control, side pressure plates, etc. When designing locating components, easy operation shall be considered. Over-positioning should be avoided, and positions shall allow easy observation. Forward feeding positioning, outer profile positioning, pilot pin positioning and other methods may be adopted.

3. Material Clamping, Stripping and Ejecting Components

Material clamping components include blank holders and pressure plates. The blank holder applies blank holder force to deep drawing blanks to prevent wrinkling caused by blank bulging under tangential pressure. The pressure plate prevents blank shifting and spring-back. Ejectors and stripper plates facilitate part removal and scrap cleaning. Supported by springs, rubber and air cushion push rods on the equipment, they can move up and down. Ejectors shall deliver sufficient ejection force and be equipped with travel limits in design. Stripper plates shall minimize the closing zone or have finger clearance slots milled at operating positions. Guard plates shall be installed around exposed stripper plates to prevent finger insertion or foreign object entry. Sharp edges on exposed surfaces shall be chamfered.

4. Guide Components

Guide pins and guide bushes are widely used guiding components. They ensure precise fitting clearance between punches and dies during stamping. Therefore, the clearance between guide pins and guide bushes shall be smaller than the blanking clearance. Where guide pins are mounted on the lower die set, the top end face of the guide pin shall be at least 5 to 10 mm above the top surface of the upper die plate at the bottom dead center of the stroke. Guide pins shall be placed away from die blocks and pressure plates so that operators do not need to reach over guide pins to load and unload workpieces.

5. Supporting and Clamping Components

They include upper and lower die plates, shanks, punch/die fixing plates, backing plates, limiters, etc. Upper and lower die plates are the base components of stamping dies, onto which all other components are mounted and secured. The planar dimensions of die plates, especially in the front-rear direction, shall match the workpiece. Excessively large or small dimensions hinder operation. For certain dies (blanking and piercing dies), backing plates are fitted under the die set to ease part ejection. The backing plates are fastened to the die plate with screws. The two backing plates shall be of equal thickness. The spacing between backing plates shall be just enough for part ejection and shall not be overly large to avoid die plate fracture.

6. Fastening Components

These include screws, nuts, springs, dowel pins, washers and so on, mostly standard parts. Stamping dies use a large quantity of standard parts. During design and selection, requirements for fastening and elastic ejection shall be satisfied. Fasteners shall not be exposed at operating surfaces to prevent hand injuries and operation interference.

(II) Key Safety Points in Die Design

The structure shall facilitate material feeding, positioning, part ejection and scrap cleaning as much as possible. When processing small parts, operators are strictly prohibited from putting fingers, wrists or other body parts into the die zone. When processing large parts where hand entry into the die is mandatory, the entry area shall be minimized and the residence time of body parts inside the die shall be shortened. The hazardous zone of the die shall be clearly defined with necessary protective measures and devices equipped.

All die components shall possess sufficient strength and stiffness to prevent damage and deformation during service. Fasteners shall be fitted with anti-loosening measures to avoid accidental injury to operators. Scrap or workpiece flying during processing is not permitted, as it distracts operators and may cause impact injuries. In addition, burrs on blanked parts that cut operators’ hands shall be avoided. Stamping operations shall not require large movements or unstable postures; overly complex or strenuous motions during work shall be minimized. Intense noise and vibration during stamping should be avoided as far as possible. The die weight shall be marked on the general assembly drawing for safe installation. Lifting and handling equipment shall be provided for components over 20 kg to reduce labor intensity. Die components shall be easy and safe to assemble and disassemble, eliminating risks of pinching or cutting hands. The die shall be easy to disassemble and store.

In summary, even minor defects in dies can compromise safety. Safety precautions for dies can only be formulated by analyzing specific risks in each operation.