- Piercing (metalworking)
Piercing is a shearing process where a punch and die are used to create a hole in
sheet metalor 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.Degarmo, p. 427.] 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.
Lancing is the specialized piercing process which cuts an interior section of the sheet metal, producing a tab. Usually a die pad is used to form the tab at the same time. [Citation | last = Semiatin | first = S. L. | title = Asm Handbook: Metal Working: Sheet Forming | publisher = ASM International | page = 312 | year = 2006 | volume = 14B | url = http://books.google.com/books?id=ekEe4UwqkVUC | isbn = 0871707101] The height of the tab must be a minimum of double the thickness of the material.Fact|date=July 2008
A common example of this is the
louvers in a locker door.
The perforating process involves piercing a large number of closely spaced holes.
The notching process removes material from the edge of the workpiece.Degarmo, p. 428]
The nibbling process cuts a contour by producing a series of overlapping slits or notches. This allows for complex shapes to be formed in sheet metal up to 6 mm (0.25 in) thick using simple tools. The process is often used on parts that do not have quantities that can justify a dedicated blanking die. The edge smoothness is determined by the shape of the cutting die and the amount the cuts overlap; naturally the more the cuts overlap the cleaner the edge.
The shaving process is a finish operation where a small amount of metal is sheared away from an already blanked part. Its main purpose is to obtain better dimensional accuracy, but secondary purposes include squaring the edge and smoothing the edge. Blanked parts can be shaved to an accuracy of up to 0.025 mm (0.001 in).
The cutoff process is used to separate a stamping or other product from a strip or stock. This operation is very common with progressive die sequences. The cutoff operation often produces the periphery counter to the workpiece.
The dinking process is a modified form of piercing used on low strength materials, such as rubber, fibers, cloth, soft metals, leather, and paper. Dinking use special dies called dinking dies, or hollow cutters. They are designed differently to punch through softer materials. The edges of the dies are usually beveled about 20° and sharpened. The material is punched through into a wood or soft metal block in order to not dull the edges. [American Machinists’ Handbook and Dictionary of Shop Terms by Fred H. Colvin and Frank A Stanley 1914] The die may be pressed into the material with a hammer or a mechanical press.Fundamentals of Manufacturing By Philip D. Rufe 2001] Examples of items produced via this process include: gaskets, shoes, and cardboard boxes.
Dinking is also a term used to describe similar manufacturing processes, such as blanking and die casting in general.Fact|date=July 2008
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