Ultrasonic welding: setting parameters
First of all, it is important to only change one parameter at a time. If you change the welding time and pressure after the initial weld, you may not be able to determine which change is a positive step. Usually, the pressure and welding time are inversely related. If you increase the pressure, you need to reduce the welding time to get the same result. Certain materials, such as polypropylene, will require more corrosive soldering. High-pressure welding in a short period of time may be more effective than a longer welding time at low pressure. Understanding plastic properties and good relationships with welding suppliers can go a long way toward solving setup challenges. Most welders have features such as welding by energy and force triggering, which are useful if used properly.
Here are some of the different parameters to consider:
The amplitude, ie the amount of movement of the horn on the surface of the horn, is affected by changes in the boost ratio or generator/power settings. It can be established according to the "amplitude requirement map". Most equipment manufacturers. This value is used to calculate the boost ratio that needs to take into account the transducer output and the horn gain factor. Generally, semi-crystalline plastics require more amplitude than amorphous resins.
The low speed of the welder head should also be recorded as a setting parameter. Its effects are most pronounced in inserts, riveting and polycarbonate welding. This value should vary from the initial setting of 2-4 inches/second. Produce the expected results. Hydraulic speed control usually provides excellent control.
The alignment/levelness of the horn, fixtures and parts is also an important factor. In addition to aligning the horn and the ferrule, there must be a way to make the horn and part contact level in the tool/welding system. As mentioned earlier, the fixture, the leveling screw on the corner of the board may be a simple and effective method, although others warn against the use of leveling screws or "jack screws." It is recommended to use a solid gasket as a better choice. If a jack screw is used, it is important that only two of the four are used during the leveling process. In any case, leveling ensures uniform welding throughout the welded joint area.
The carbon paper placed between the horn and the part or fixture can be used to indicate the initial contact area, and the welded part can be broken to check the degree of soldering. The level can then be used to raise (or apply more force) to areas that lack welding. Sometimes the weld head must not be flush with the clamp to ensure optimum welding results. Use the known "good" part of the last run to align the horn with the nest is a real-time protection program.
Welding/retention is the amount of force that the stamping system exerts on the horn and the part during the welding and holding process. The initial approximation of the good values used is based on the total joint length (in linear inches) and is shown in the figures. The process is fine-tuned according to these general guidelines. Usually, larger parts require more force. Some modern computer controlled welders allow the force to be changed during the welding cycle to allow for more complete control of the heating rate of the joint material and the collapse of the material.
The trigger force is the preload applied to the part before the ultrasonic wave is turned on. Most applications require this preload to "install" in place to put the parts together before welding. The value is based on the total length of the joint. A bent or deformed part will weld better at higher forces or ultrasonic waves at a certain distance. Applications such as insertion, riveting, and forging may require pre-triggering of the activation of the ultrasonic waves before the horn contacts the workpiece, which allows machining to begin with little or no initial force.