Molding cable ties is a competitive, high-volume business that, to be successful, demands fast cycles, robust processes, and nearly perfect parts.
You look at a cable tie and it looks like a relatively simple product, but it’s an exercise in contradiction in reality, because the cable tie product stretches the limits of injection molding. The molder has to get the material from the head to the tail in four-tenths of a second or it starts to freeze off and build pressure, then you blow the mold open and it goes downhill from there.
Running counter to all this high speed and pressure is the fact that molded-in stress in a cable tie is unacceptable. Each tie must meet certain tensile strength spec load requirements. Also, much of the load in a cable tie is held in the head where the end of the tie is inserted and secured. The head has molded into it a small pawl that catches the teeth of the tie and keeps it from slipping backward. If the pawl is too stiff, it exceeds the industry-recommended. Too loose, or soft, and the pawl won’t hold the strap of the tie in place. Similarly, flash is a no-no as well. Too much of it, and excessive force again is required to insert the tie into the head.
One factor critical to cable tie molding is cooling. Use multiple zone cooling channels to precisely control temperature along different cable tie sections. The result is a much faster cycle.
Hot runner systems are used on some molds, depending upon cavitation and cable tie size. Similarly, some molds are equipped with cavity pressure transducers. Otherwise, molds transfer on injection pressure.