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Blanking and piercing are shearing processes in which a punch and die are used to produce parts from coil or sheet stock. Blanking produces the outside features of the component, while piercing produces internal holes or shapes. The web is created after multiple components have been produced and is considered scrap material. The "slugs" produced by piercing internal features are also considered scrap. The terms "piercing" and "punching" can be used interchangeably.
The punch/die clearance is a crucial parameter, which determines the load at the cutting edge of the tool, commonly known as point pressure. Excessive point pressure can accelerate tool wear. The surface quality of the trimmed piece is affected by the clearance, too.
Material specific design guidelines are developed by companies in order to define the minimum acceptable values of hole diameters, bridge sizes, slot dimensions. Similarly, the strip lay-out must be determined (strip width and pitch). The bridge width between the parts and the edge allowance between the part and the edge of the strip also have to be selected.
A simple operation may only need a pancake die. While many dies perform complex procedures simultaneously, a pancake die may only perform one simple procedure with the finished product being removed by hand.
The cut made in lancing is not a closed cut, like in perforation even though a similar machine is used, but a side is left connected to be bent sharply or in more of a rounded manner.
Lancing can be used to make partial contours and free up material for other operations further down the production line. Along with these reasons, lancing is also used to make tabs (where the material is bent at a 90-degree angle to the material), vents (where the bend is around 45 degrees), and louvers (where the piece is rounded or cupped). Lancing also helps to cut or slight shear of sheet on cylindrical shape.
Normally lancing is done on a mechanical press, lancing requires the use of punches and dies to be used. The different punches and dies determine the shape and angle (or curvature) of the newly made section of the material. The dies and punches are needed to be made of tool steel to withstand the repetitious nature of the procedure.
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. For added accuracy and smoothness, most shapes created by nibbling undergo filing or grinding processes after completion.
Materials that can be fine blanked include aluminium, brass, copper, and carbon steel, alloy steel, and .
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 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 . Currently parts as thick as can be cut using fine blanking. Tolerances between ± are possible, depending on the base material thickness and 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.Bralla, pp. 3.47–3.48. Some combinations may require progressive fine blanking operations, in which multiple operations are performed at the same pressing station. Due to the higher lifetime, blanking punches are usually covered by PVD protective coatings.
The advantages of fine blanking are:
One of the main advantages of fine blanking is that slots or holes can be placed very near to the edges of the part, or near to each other. Also, fineblanking can produce holes that are much smaller (as compared to material thickness) than can be produced by conventional stamping.
The disadvantages are:
Shaving
The shaving process is a finishing 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).
Shaving of metals is done in order to remove excess or scrap metal. A straight, smooth edge is provided and therefore shaving is frequently performed on instrument parts, watch and clock parts, and the like. Shaving is accomplished in shaving dies especially designed for the purpose.
Trimming
The trimming operation is the last operation performed, because it cuts away excess or unwanted irregular features from the walls of drawn sheets.
Fine blanking
Fine blanking is a specialized form of blanking where there is no fracture zone when shearing. This is achieved by compressing the whole part and then an upper and lower punch extract the blank.Degarmo, p. 425. This allows the process to hold very tight tolerances, and perhaps eliminate secondary operations.
Bibliography
James G. Bralla (1999). 007007139X, McGraw-Hill. 007007139X
(2025). 9780471656531, Wiley. ISBN 9780471656531
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