Speaking of Force…
Imagine not applying a controlled force through the re-solidification phase of a plastic welding process…any plastic welding or forming process. Not a sound approach. Experienced processors realize the benefit of force – especially a programmable force value that may differ from the force applied through the welding phase, as the material re-solidifies. The best ultrasonic and vibration welding machines offer this control…but most hot-plate welders do not – bogus!
As a matter of fact, when you analyze what is really happening through the hold or seal phase of traditional hot-plate welding when using tool ‘stops’, true hold force values actually drop off – right off the map, when the stops are contacted. Oh, the platens continue to push and force is generated – but against the hard stops, not the components welded!?
Take a look at the graph that shows the force application through the weld cycle phases. As you can see, when tooling stops are contacted during the seal phase of the weld cycle there is a significant drop in force, how much is really not known…
We can almost hear our competition arguing that “…without hard stops you can push right past the melt front and cause a ‘cold weld’ and…blah, blah, blah”. Yes, when you try to eliminate stops with pneumatic or hydraulic controlled welders you can generate all sorts of cold, bad, or otherwise nasty welds.
Exactly. They are stuck in a very old paradigm of acceptable practices and standards in hot-plate welding.
Get rid of the stops and start controlling the weld process by distance and force – with velocity control, and watch weld strength increase while overall cycle times decrease…in some applications, dramatic cycle time reductions can be realized.