Overview:

The thermal staking cell is an in-line station for heat staking plastic bosses during assembly.

Process Description:

Pallets enter the station en mass, four at a time. As the last pallet enters the work zone, the pallet stops are raised, and then the secondary pallet positioners are activated.  The pallets are then pushed slightly appart to their respective clamping positions, and clamped.

Once the pallets are clamped, the heat staking heads are lowered into the product and engage the plastic boss. The boss is heated under pressure, and slowly deformed to create the staking feature. A hydraulic speed control keeps the speed within preset limits.  After the stake is formed, the staking heads are lifted, and the pallets are released.

Technical Challenge:

Heat staking is a relatively slow process. One wants to stake at the lowest possible temperature to avoid melting the plastic boss. If allowed to melt, it will frequently adhere to the tip, creating strings of material is the tip is pulled from the boss. To avoid this problem, one should not hurry the process.  

In this case, the cycle time of the line was much shorter than the time needed to create the stake.  To extend the process time to an acceptable amount, it was decided to mount four staking heads side-by-side so that four pallets could be processed at once. However, this created a sequencing problem, as the pallets must be free on both sides while in the clamping device to avoid any loss of positional accuracy.

The solution to this problem involved a series of two-axis stops for controlling the pallets.  The pallets were allowed to enter the cell en mass, but were then aligned with their respective clamps using the in-line axis of the stop.  This provide a simple traffic handling sequence for the cell, but allowed the pallets to be isolated before clamping.