Plastic welding only needs to know two things

To solve the welding quality problem, it is not only necessary to use the DOE test method to optimize the parameters, but more importantly, to grasp the two key factors affecting welding - heat and pressure.

In order to facilitate everyone's understanding, I take hot plate welding as an example here. The hot plate welding process is simply that the two parts are in contact with the heating plate and the surface of the part is heated and melted. Remove the heating plate and push the two parts together until they stick to each other. Let's take a look at how to control the heat and pressure in hot plate welding.

The remaining welding processes, such as ultrasonic welding, vibration friction welding, laser welding, infrared welding, and hot gas welding, are essentially similar. The same analysis method can be used when encountering problems.

1.Heat

You need precise control of the heat transfer to the soldered surfaces of the plastic parts, causing them to become semi-molten. Too little heat, the weld surface will not melt, no strength and no sealing. Too much heat burns degraded materials, weakening their mechanical properties and airtightness. In the hot plate welding process, you can use three main parameters to control heat.

Hot plate temperature >>> refers to the temperature of the hot plate in contact with the plastic part. Thermodynamics tells us that the greater the temperature difference between the heating plate and the plastic part, the faster the heat transfer. Therefore, the hot plate temperature affects the speed of the heated part.

Melting time >>> is the contact time between the plastic part and the heating plate. The longer the part is in contact with the heater plate, the more time it takes for heat to penetrate the soldered surface of the part.

2. Pressure

Now that the soldered surface has enough heat, you need to apply the proper pressure to the soldered area. If the applied pressure is too small, the molten surfaces will not mix with each other and will form fewer molecular bonds on the weld surface. If you push too hard, you will squeeze out most of the semi-molten material, leaving little bond at the weld. We call it "cold weld". There are two ways to control the welding pressure.

Depth Control >>> is suitable for all kinds of welding processes. The theory is simple: the greater the weld depth, the greater the pressure the component is subjected to. This is because the temperature of the material in the welded joint gradually cools with depth, so the deeper the part, the harder the pressure is.

Force Control>>> Force control has been realized since the recent rise of servo-driven hot plate welding. The amount of force required to properly weld depends on the total area of the welded joint. Larger parts require more force. The smaller the part, the smaller the force.

Looking at it is easy, just focus on heat and stress. Of course, like everything, the theory is simple, but the reality is very complicated and it makes people feel bad. But keep in mind that all other factors affecting soldering are due to the direct or indirect effects of these two factors, resulting in changes in solder quality.