Machine Design


Clinching is a combination of drawing and forming that locks together layers of sheet metal. Multiple layers can be joined, though clinching is most commonly used for only two layers. The method can replace spot welding, riveting, metal screws, brazing, and staking or crimping. In clinching, a punch drives the two layers of metal into a die that produces an impression. Additional force spreads the upper layer of material into the lower layer so it cannot be pulled out.

Two basic clinching methods are used. The older one, often called a clinched or lanced lock, shears the metal, forcing the top layer through slits in the bottom layer. This method is primarily used for metals with less ductility, such as hard aluminum or stainless steel, or where there is a considerable thickness or ductility difference between the sheets being joined.

The second method, called a button or round clinch, produces no hole but simply deforms both layers so that the bottom layer locks around the top, like a circular dovetail joint. This joint is often preferred because of its neater appearance and leak resistance.

Both processes require use of ductile sheet metals, such as steel, aluminum, or brass in light gauges. Many plastics are difficult to clinch because they tend to resume their original shape after being clinched. Materials that cannot be properly clinched often can be locked between two layers of metal, however.

Factors limiting clinching are mainly joint thickness and the distance of the joint from the edge of the material. Both these limits vary with the tooling vendor chosen. Joint thickness is generally limited to a total of 0.25 to 0.30 in., but minimum joint-to-edge distances may range from 0.06 to 0.25 in.

Clinching applications include automotive and appliance assemblies, furnaces and ductwork, housings and enclosures, and metal office furniture.

TAGS: Fasteners
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