Fine Blanking Manufacturing Review
Fine blanking is a specialized form of shearing which produces parts with tighter toleranceand a clean sheared edge. This smooth edge is the result of special tooling configuration that holds the materials during the shearing operation. While compressing the material an upper and lower punch extracts the blank. This allows the process to hold tight tolerances, and often will eliminate secondary manufacturing operations, such as deburring.
Most ferrous and no-ferrous materials that can be fine blanked, such as: aluminum, brass, copper, and carbon, alloy and stainless steels.
Fine blanking machines are similar to other metal stamping machines, but they have a few additional parts. A typical compound fine blanking press includes a hardened die punch (male), the hardened blanking die (female), and a guide plate of similar shape/size to the blanking die. The guide plate is the first applied to the material, impinging the material with a sharp protrusion or stinger around the perimeter of the die opening. Next a counter pressure is applied opposite the punch, and finally the die punch forces the material through the die opening. Since the guide plate holds the material so tightly, and since the counter pressure is applied, the material is cut in a manner more like extrusion than typical punching. Mechanical properties of the cut benefit similarly with a hardened layer at the cut edge from the cold working of the part. Because the material is so tightly held and controlled in this setup, part flatness remains very true, distortion is nearly eliminated, and edge burr is minimal.
Clearances between the die and punch are generally around 1% of the cut material thickness, which typically varies between 0.5–13 mm (0.020–0.51 in). Currently parts as thick as 19 mm (0.75 in) can be cut using fine blanking. Tolerances between ±0.0003–0.002 in (0.0076–0.051 mm) are possible based on material thickness & tensile strength, and part layout.
With standard compound fine blanking processes, multiple parts can often be completed in a single operation. Parts can be pierced, partially pierced, offset (up to 75°), embossed, or coined, often in a single operation. Some combinations may require progressive fine blanking operations, in which multiple operations are performed at the same pressing station.
The advantages of fine blanking are:
- excellent dimensional control, accuracy, and repeatability through a production run.
- excellent part flatness is retained.
- straight, superior finished edges to other metal stamping processes.
- smaller holes possible relative to thickness of material.
- little need to machine details.
- multiple features can be added simultaneously in 1 operation.
- more economical for large production runs than traditional operations when additional machining cost and time are factored in (1000–20000 parts minimum, depending on secondary machining operations)
The disadvantages are:
- slightly higher tooling cost when compared to traditional punching operations.
- slightly slower than traditional punching operations.