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Sheet-Metal Shearing

 

Process description

Various shearing processes used to cut cold rolled sheet metal with hardened punch and die sets. The most common shearing processes are: cutting, piercing, blanking and fine blanking.

Materials

  • All ductile metals available in cold rolled sheet form, supplied flat or coiled.
  • Most commonly used metals are: carbon steels, low alloy steels, stainless steels, aluminum alloys and copper alloys. Also, nickel, titanium, zinc and magnesium alloys are processed to a lesser degree.
Sheet-Metal Shearing

Process variations

  • Mechanical drives: faster action and more positive displacement control.
  • Hydraulic drives: greater forces and more flexibility.
  • Cutting: large sheets of metal are clamped and cut along a straight line.
  • Piercing: removal of material from a blank, for example, a hole.
  • Blanking: parts are blanked to obtain the final outside shape.
  • Fine blanking: uses special clamping tooling to produce a smooth and square-edged contoured blank or hole.
  • Smooth wall hole piercing: special punch profiles are used to produce crack-free holes.
  • Other operations include: nibbling, notching, trimming and shaving.
  • Computer Numerical Control (CNC) common on piercing and blanking machines.

Economic considerations

  • Production rates high, 10 000+/h for small components.
  • High degree of automation possible.
  • Cycle time usually determined by loading and unloading times for stock material.
  • Progressive dies can incorporate shearing and forming processes.
  • Lead times can be several weeks depending on complexity and degree of automation, but more typically, several days.
  • Material utilization moderate to high, however, substantial amounts of scrap can be produced in piercing and blanking.
  • Production quantities should be high for dedicated tooling, 10 000+. Economical quantities can range from 1 for blanking and piercing to 2000 for fine blanking.
  • Tooling cost moderate to high, depending on process and degree of automation.
  • Equipment costs vary greatly. Low for simple guillotines to high for high speed, precision CNC presses.
  • Labor costs low to moderate depending on degree of automation.
  • Finishing costs low to moderate. Deburring and cleaning usually required.

Typical applications

  • Blanks for forming work
  • Cabinet panels
  • Domestic appliance components
  • Machine parts
  • Gears and levers
  • Washers

Design aspects

  • Complex patterns of contours and holes possible in two dimensions.
  • Material used dictates press forces and die clearances.
  • Blanked parts should be designed to make the most use of the stock material.
  • Pierced holes with their diameter greater than the material thickness should be drilled.
  • Fine blanked holes with diameters 60 per cent of the material thickness possible.
  • Holes should be spaced at least 1.5 times the thickness of the material away from each other.
  • Maximum sheet thickness =13 mm.
  • Minimum sheet thickness =0.1 mm.
  • Maximum sheet dimension for cutting is 3m; 1m for fine blanking.

Quality issues

  • Conventional hole piercing, blanking and cutting do not result in a perfectly smooth and parallel cut.
  • Acceptable hole wall and blank edge quality may be achieved with fine blanking and piercing processes.
  • Holes placed too close to a bend line can be distorted subsequently in forming operations.
  • Inspection and maintenance of die wear and breakage is important.
  • Variations in stock material thickness and flatness should be controlled.
  • Surface detail is good.
  • Surface roughness values ranging 0.1–12.5 µm Ra.
  • Process capability charts showing the achievable dimensional tolerances for several sheet-metal shearing processes are provided.

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