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Welding of different plastics

Can somebody help me on these issues,
1)If we weld two flat plastic components-Cycoloy(PC+ABS) and PC-on which component should have energy director?
At present the PC component is provided with energy director of 0.7 mm height.But after welding,
1) The welding joint is not strong enough.
2) Energy directors are not fully melting.It leaves impression on the cycoloy component.Is it because of difference in melting temperature?
Which type of welding is suggested?Pressure or delay?
What can be the welding time?
I am using 20 kHz,2000W Sonic & Material machine..
Please help


Hi Alban,

Below are some of my advise:
1. Welding Cycoloy and PC should be ok. The energy director on the PC part is the best approach
2. The weak joint that u are facing due to item 3 (energy director not fully melt). Based on my experience, the minimum weld depth required to get a good strength is 0.5mm. Using 0.7mm weld depth is the best as normally after welding based on 6 sigma, the tolerance will be around +/-0.15mm ...therefore welding 0.7mm is consider the best.

Energy director not fully melt may happen due to several factor:
1. Welding parameter:
As a rull of thumb, normally i take the welding speed is 1mm/sec...which mean if u are welding 0.7mm depth, the weld time should be around 0.7s. Anyway, this may lead to a burn mark or poor cosmetic appearance as the welding is too i would suggest the best weld time is around 0.5s. Welding to fast may result in wall the end poor wed joint.

Other parameter such as welding mode also play a big role. I do not know much on how Sonic & material welders work, as i work mostly with Herrmann, Dukane and Branson. Based on Herrmann, there are 5 type of wedling mode: Time, Energy, Power, Absolute Distance and Depth RPN. Among all this mode, the best method is Depth which the welder will weld to the exact weld depth. Some welder may call this as Collapse distance. If the welder do not have this capability...u might try to run using absolute distance mode.

The other approach try to use dual pressure mode. I would ike to suggest u to weld around 0.2mm with the weld force around 60lbf, then increase the force to around 100-120 lbf until it complete. But u need to check the welder capability first. Playing with the force also good in getting a good weld joint

2. Horn surface and levelling
Horn contact surface and nest levelling also can cause this. Anyway, if this is the main root cause... u can see the area that the energy director did not melt is consistence after u running several part... the same spot/area. Check the levelling to ensure the horn is contacting the plastic evenly especially right on top of the energy director location. u can use pressure sensitive paper to confirm this.

Best Regards