The main process parameters of ultrasonic metal welding are power P, frequency f, amplitude A, static pressure F and welding time t.
①The power P (W) required for welding depends on the thickness δ (mm) and hardness H (HV) of the workpiece, and can be determined as follows:
P=kH3/2δ3/2
where k is the coefficient
②Ultrasonic vibration frequency f: The resonant frequency is generally between 16 and 80 kHz. The frequency selection should consider the physical properties and thickness of the material to be welded, and select a relatively high resonant frequency when welding thin parts. The optimum operating frequency varies with the applicator tip, workpiece and pressing force.
③ Amplitude A: It determines the size of the friction work, which is related to the removal conditions of the oxide film on the surface of the welding zone, the frictional heat generation of the joint surface, the size of the plastic deformation range, and the plastic flow of the material. The selected amplitude is generally between 5 and 25 μm. The relationship between ultrasonic welding machine power P and amplitude A is:
P=4μSFAf
F is the static pressure, MPa; S is the solder joint area, mm2; μ is the friction coefficient; f is the vibration frequency, Hz.
There is a close relationship between the joint strength and the amplitude, and there is an optimal amplitude range for a specific material.
④ Static pressure F: Static pressure is used to transmit ultrasonic vibration energy to the workpiece, which is an important factor that directly affects the power output and the deformation conditions of the workpiece. Its selection depends on the material hardness and thickness, the type of joint, and the ultrasonic power used.
When the static pressure is too low, a lot of vibration energy will be lost on the surface friction between the upper applicator and the workpiece, and it will also make the pole slip and affect the welding quality. When the static pressure is too large, in addition to increasing the required power, it will also reduce the strength of the solder joint due to the crushing of the workpiece.
⑤Welding time t: Welding time refers to the time when ultrasonic power is input to the workpiece. It will determine the amount of energy input to the workpiece. Ultrasonic welding is characterized by a particularly short welding time. However, if the welding time is too short, the welding strength will be too low, and the joint will not even be formed. Therefore, choosing high-power and short-time welding conditions is much better than using low-power and long-time welding conditions. Because, too long welding time will only cause bad appearance of solder joints and fatigue damage of joints and workpieces that may be caused.