Stamping is a metalworking process by which sheet metal strips are punched using a press tool which is loaded on a machine press or stamping press to form the sheet into a desired shape. This could be a single stage operation where every stroke of the press produce the desired form on the sheet metal part, or could occur through a series of stages. The process can also be used on other suitable materials, such as polystyrene plastic.
The most common stamping operations are:
- Piercing
- Fine blanking
- Bending
- Forming
- Coining
- progressive stamping
- Deep Drawing
- Embossing
- Extrusion
Piercing is a shearing process where a punch and die are used to create a hole in sheet metal or a plate. The process and machinery are usually the same as that used in blanking, except that the piece being punched out is scrap in the piercing process.[1] There are many specialized types of piercing: lancing, perforating, notching, nibbling, shaving, cutoff, and dinking.
The amount of clearance between a punch and die for piercing is governed by the thickness and strength of the work-piece material being pierced. The punch-die clearance determines the load or pressure experienced at the cutting edge of the tool, commonly known as point pressure. Excessive point pressure can lead to accelerated wear and ultimately failure.
Burr height is typically used as an index to measure tool wear, because it is easy to measure during production.
Fine blanking presses are similar to other metal stamping presses, but they have a few critical 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[1]. 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 .5-13mm[2]. Currently parts as thick as 19mm can be cut using fine blanking[3]. Tolerances between ±.0003"-.002" are possible based on material thickness & tensile strength, and part layout[4].
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[5]. Some combinations may require progressive fine blanking operations, in which multiple operations are performed at the same pressing station however.
