Self clinching hardware minimizes handling and saves money during box and luggage assembly

Self clinch hardware can provide many benefits for the box, case or luggage manufacturer and is recommended when case volumes exceed 50,000 units per year although lower volumes can sometimes be justified. A significant reduction in overall assembly cost, compared with standard riveting techniques in the attachment of handles, latches and hinges to consumer or industrial products is possible. Also, clinch type hardware can be substituted for rivet-on hardware in many current applications with no loss of product strength.

Clinch type hardware has been available for many years, and is characterized by projections commonly called "prongs" or "legs" that extend from the hardware piece itself. During the attachment operation, the legs are pushed through the case material and are curled over on the reverse side, holding the unit firmly in place.

For example, the following hardware items utilize identical components except for the back or attaching plate: the #9315 latch has holes for four rivets while the #9311W latch has four self clinching prongs (refer to large illustration above - click on it to view in clear detail). Conservatively, you can expect to acheive a 50% labor savings when attaching two pronged latches to a standard sized case instead of two rivet-on latches.

The application of pronged hardware to the typical case is quite simple and is outlined below.

  • The hardware component is inserted into a nest
  • The box or case is located over an anvil
  • The two-hand anti-tie down controls are activated and the pneumatic system cycles once
  • As the system cycles, the prongs on the hardware are pushed through the case material and clinched over on the back side
  • The completed case is removed from the anvil and the cycle is ready to begin again.

    Another advantage of the clinching operation is that both the top and bottom halves of a latch can be installed at the same time, during the same machine cycle, with all parts lined up as required and no hand fitting. By ganging machine heads on an adjustable base, any number of latches could be installed at one time.

    On the other hand, the typical rivet application might require a set of prepunched or drilled holes with the rivets then being inserted one or two at a time. In those applications not requiring prepunched holes, the top or bottom half of a latch would typically be applied first. Then, the mating half of the latch would be fitted to the part already installed and finally riveted in place. This procedure requires a relatively high level of operator skill, can result in misalignment and is obviously time consuming.

    A number of fastener users have found it advantageous to use pronged hardware in some applications requiring prepunched slots because they still save the costs of at least four rivets per latch application. Typical applications include:

  • Injection molded plastics (0.125")
  • Vacuum formed plastics (0.220")
  • Cardboard (0.200")
  • Pressedboard (0.125")
  • Wood (Plywood and pine up to 0.375")
  • Sandwiches (vinyl + plywood, vinyl + cardboard, vinyl + foam + pressedboard, 0.010" steel + cardboard)

    Use of self clinch hardware is a path to increased productivity in many assembly operations. It is certainly not the cure-all for all production problems, but it does offer the advantages of fewer parts to handle, better part fitup, no rivet costs and the simplicity of the attaching machinery.

    Atco can supply clinching tools to fit existing machines or complete attaching systems. The double-headed clinching machine shown here can attach two lock sets to one end of both half-shells of your case in one cycle. After changing tools, the same machine can then attach two hinges to the other end of both half-shells in a second cycle.

    By: Martin Gornstein, President, Atco Products, Inc. originally appearing in Assembly Engineering

  • Click to enlargeAssembly MachinesThis three headed assembly machine allows our customers to apply three complete pieces of hardware to both sides of a case shell at the same time.

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