Waste-free die design
Waste-free die design is a highly efficient forming technology that optimizes nesting patterns to achieve virtually zero material waste during the blanking process (material utilization >95%). It is suitable for the mass production of narrow, elongated parts (such as blades and saw blades) and washers, using materials ranging from 0.1-2mm thick cold-rolled steel and copper strip. Its core principle is to utilize staggered or overlapping nesting patterns, leveraging the contours of adjacent parts and eliminating the overlap margin (typically 2-5mm) associated with traditional nesting. Combined with continuous coil feeding, this technology can achieve annual material cost savings of 10%-30%. During design, material utilization must be simulated using CAD nesting software to ensure that the width of the connecting portion (bridge) between parts is greater than or equal to the material thickness (≥0.5mm for 0.5mm thick material) to prevent breakage during feeding.
The die structure adopts a progressive layout, with blanking and separation stations. Key components include the zero-waste punch, die, precision feed mechanism, and tension control system. The zero-waste punch is designed according to the part contour and utilizes a monolithic structure (Cr12MoV steel, HRC58-62). The cutting edges are machined synchronously to ensure consistent dimensions, with a spacing error of less than 0.01mm between adjacent punches. The die is machined using wire-cut electro-discharge machining to ensure a uniform clearance with the punch (±0.005mm). The die is made of cemented carbide (YG15) for improved wear resistance (a lifespan of over 1 million cycles). A beveled punch with a 5°-8° cutting edge is used for the bridge blanking process to reduce peak blanking forces and prevent material tearing.
Feeding and tension control are the core technologies of the waste-free die process. A servo-motor-driven roller feeder delivers a feeding accuracy of ±0.005mm, with a step width equal to the part width (no overlap). A linear scale provides real-time position feedback, ensuring accurate alignment of the bridge with the die edge. The tension control system, comprised of an unwinder, a tension sensor, and a magnetic powder brake, maintains a stable material tension of 5-20N (adjusted based on material thickness) to prevent feed deviation caused by loose coils. For parts wider than 100mm, two or three sets of feed rollers are required to evenly distribute tension and prevent lateral deflection (less than 0.5mm/m).
Punching process parameters must be precisely matched, with the punching speed controlled between 100 and 200 strokes per minute. Excessively high speeds can easily lead to bridge fracture. For high-strength materials (such as 65Mn), the speed should be reduced to 50 to 100 strokes per minute. Extreme-pressure emulsion lubrication (5% to 8% concentration) should be used to reduce edge wear. The bridge punching sequence is “shallow punching first, then separation.” The first station punches half the bridge depth, and the second station completely separates. This reduces the single punching force and protects the die edge. The punching force of a zero-waste die is 10% to 15% greater than that of a traditional die. Therefore, a press with sufficient tonnage (rated tonnage ≥ 1.2 times the calculated punching force) should be selected.
Stringent commissioning and quality control requirements apply. During die trials, 100 pieces must be stamped continuously, and part dimensions (deviation must be <0.1mm) and bridge residual weight (<0.05mm) must be measured. The servo system must be recalibrated if the feed step deviation exceeds 0.01mm. After every 5,000 pieces, the die cutting edge is inspected for wear (re-grinding is required if the radius exceeds 0.03mm). Any scratches on the punch surface are polished with diamond paste (grit size W5). Maintenance requires daily removal of scrap from the bridge to prevent accumulation and die jamming. The tension sensor is calibrated weekly to ensure a tension error of <5%.
