PEM fasteners and self-clinching nuts

Self-clinching fasteners, often called inserts, are small metal fasteners such as self-clinching nuts, self-clinching studs and self-clinching threaded studs. These self-clinching fasteners can be pressed into sheet metal with a self-clinching machine. Pressing in, also called clinching, takes place in a hole that was punched or laser-cut into the sheet metal beforehand.

The self-clinching fasteners have a collar. During pressing, this collar bites into the inner contour of the hole in the sheet.

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PEMSERTER

The PEM fasteners can be pressed into sheet metal with a PEMSERT machine. We also call this machine a PEMSERTER. At Contour, we call the pressing-in process PEMSERTING.

The PEMSERTER is typically used before or after bending. At Contour, the PEMSERTER is therefore set up in the department next to the press brakes. The best moment to carry out the PEMSERT operation depends on the batch size, the geometry of the sheet, the geometry of the self-clinching machine and the geometry of the press brake.

The PEMSERT operation must be taken into account when designing the sheet metal part. In flat or bent condition, the part must fit in the PEMSERT machine so that the hole in the sheet where the self-clinching fastener goes lies within the reach of the press head and anvil of the self-clinching machine.

When the bent product does not fit in the PEMSERT machine because of its geometry, for example because the anvil and press head cannot reach the location of the PEM after bending, the PEM can be installed in the flat sheet. Installing the PEM in the flat sheet can also have advantages for high-volume production, because the flat sheet is easy to stack and easier to move logistically.

If the product still has to be bent after the self-clinching nuts have been installed, the design must carefully take into account that the nuts may collide with the press brake or the bending tool.

PEMSERT self-clinching machine

Contour uses Haeger PEMSERTER self-clinching machines. The machines are equipped with automatic feeding of the self-clinching fasteners up to the press head. The required self-clinching fasteners can be loaded into a vibratory bowl feeder, which supplies a new self-clinching fastener to the head each time the previous insert has been pressed into the sheet metal.

The PEMSERT machine is CNC-controlled and has a control system with a touchscreen. A CNC program is created and saved for reuse for each part. The machine thus indicates exactly how many and which inserts have to be installed in the part. The program can be extended with photos so that the required instructions appear visually on the touchscreen. This reduces the chance of errors and makes the work easier for our CNC operators.

Production process

These are the process steps for pressing a PEMSERT self-clinching fastener into sheet metal.

• The operator selects the correct CAM program. They can call it up from the network via the touchscreen. If the program does not exist yet, the operator creates it and saves it in the machine.
• The operator checks the CAM program against the bill of materials of the assembly in the production order. This bill of materials specifies the part numbers of the self-clinching nuts to be pressed in. The operator then places the correct self-clinching nuts in the vibratory bowl feeder(s).
• The program is started and the machine feeds the correct self-clinching nut to the press head.
• The operator positions the sheet metal part so that the hole where the self-clinching fastener has to go is exactly on the anvil under the press head. Depending on the type of self-clinching fastener, positioning can be made easier by placing the hole over a pin protruding from the lower tooling or onto the insert in the anvil.
• When a foot pedal is pressed, the press head closes, which clinches the self-clinching fastener into the sheet.
• The press head opens after the press force set in the CAM program has been applied and the set dwell time has elapsed. The cycle repeats until all self-clinching fasteners in the part have been pressed in.