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What are the main joint design considerations for clinch joining?


To get the best out of a joining process, the parts to be assembled need to designed with that process in mind.

Clinching requires open flanges with good access to both sides for punch and die tooling. The flange width must be sufficient to accommodate the interlocking button produced during the joining operation. The clearance between the centre of the joint and the flange outer edge should be 1.5 times the punch diameter. Also, the clearance between the joint and the flange inner edge must be enough to allow tooling access to make the joint.

Clinch joints should be spaced to avoid previously formed joints as well as the immediate area around them which may have been work-hardened. Clinching in or near prior joints may result in unsatisfactory joint appearance, excessive thinning of the bottom sheet and accelerated tool wear. Also, joints should not be placed so close together that the material distorts. However, there must be enough joints to ensure that the assembled component meets its strength requirements. A minimum joint spacing of 2 to 3 times the button diameter is recommended.

Accurate fit-up and alignment aid the formation of good joints by ensuring that the sheets are drawn together between punch and die in the correct manner. Joints should be fully closed after the clamping stage: the purpose of the punching force (next stage) is not to close large gaps between sheets! Poor fit-up and alignment are major contributors to inconsistent clinch quality.

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