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Ultrasonic metal welding

  • 2021-07-16
Ultrasonic metal welding is a special method that uses mechanical vibration energy of ultrasonic frequency to connect the same or dissimilar metals. When metal is ultrasonically welded, it neither delivers current to the workpiece nor applies a high-temperature heat source to the workpiece, but under static pressure, the mechanical energy is transformed into internal energy, deformation energy and limited temperature rise. Solid phase welding occurs when the two base materials reach the recrystallization temperature. Therefore, it effectively overcomes the spatter and oxidation caused by resistance welding. Ultrasonic metal welding machine can perform single-point welding, multi-point welding and short strip welding on thin wire or sheet materials of non-ferrous metals such as copper, silver, aluminum, and nickel. It can be widely used in the welding of thyristor leads, fuse pieces, electrical leads, lithium battery pole pieces, and tabs

Introduction to Ultrasonic Metal Welding

Ultrasonic metal welding uses high-frequency vibration waves to be transmitted to the metal surface to be welded. Under pressure, the two metal surfaces are rubbed against each other to form a fusion between molecular layers.

The advantages are fast speed, energy saving, high fusion strength, good electrical conductivity, no sparks, and close to cold processing; the disadvantages are that the welded metal parts cannot be too thick (generally less than or equal to 5mm), the welding point cannot be too large, and it needs to be pressurized.

Advantages of ultrasonic metal welding

1. The welding material does not melt, and the metal is not fragile.
2. After welding, the conductivity is good, and the resistivity is extremely low or almost zero.
3. Low requirements for welding metal surface, both oxidation and electroplating can be welded.
4. The soldering time is short, without any flux, gas, or solder.
5. Welding without sparks, environmental protection and safety.

Ultrasonic metal welding range

1. Ni-MH battery Ni-MH battery nickel mesh and nickel sheet mutual fusion and nickel sheet mutual fusion. .
2. Lithium battery and polymer battery copper foil and nickel sheet are mutually fused, and aluminum foil and aluminum sheet are mutually fused. .
3. The wires are fused to each other, and the wires are fused into one and multiple wires.
4. The wires are fused with famous electronic components, contacts and connectors.
5. Mutual melting of large heat sinks, heat exchange fins and honeycomb cores of famous household appliances and automotive products.
6. High-current contacts such as electromagnetic switches and non-fuse switches, and mutual fusion of dissimilar metal sheets.
7. The sealing and cutting of metal pipes can be water-tight and air-tight.

Influencing factors of ultrasonic metal welding
 
Ultrasonic metal welding amplitude
Amplitude is a key parameter for the material to be welded, which is equivalent to the temperature of ferrochrome.

If the temperature is not reached, the welding will fail, and if the temperature is too high, the raw material will be burnt or the structure will be damaged and the strength will be deteriorated. The selected ultrasonic transducer is different, the output amplitude of the transducer is different, after adapting the ultrasonic transducer with different transformation ratio

The amplitude and welding head can correct the working amplitude of the welding head to meet the requirements. Usually the output amplitude of the transducer is 10-20μm, and the working amplitude is generally about 30μm. The transformation ratio of the horn and the welding head is related to the shape of the horn and the welding head, the front-to-rear area ratio and other factors.

In terms of shapes, such as exponential amplitude, functional amplitude, and stepped amplitude, it has a great influence on the transformation ratio, and the front-to-rear area ratio is directly proportional to the total transformation ratio. Choose welding machines of different brands. The easiest way is to make them in proportion to the size of the working welding head to ensure the stability of the amplitude parameters.

Ultrasonic metal welding frequency
Any ultrasonic welding machine has a center frequency, such as 20KHz, 40 KHz, etc. The working frequency of the welding machine is mainly composed of the mechanical resonance of the ultrasonic transducer (Transducer), the ultrasonic horn (Booster), and the welding head (Horn) Determined by frequency.

The frequency of the ultrasonic generator is adjusted according to the mechanical resonance frequency to achieve consistency, so that the welding head works in a resonant state, and each part is designed as a half-wavelength resonant body. Both the ultrasonic generator and the mechanical resonance frequency have a resonance working range.
It is generally set to ±0.5 KHz, and the welding machine can basically work normally within this range. When we make each welding head, we will adjust the resonant frequency, and the error between the resonant frequency and the design frequency is required to be less than 0.1 KHZ. For the 20KHz welding head, the frequency of our welding head will be controlled at 19.90-20.10 KHZ, with a small error of 5‰.

Ultrasonic metal welding node
The nodes, welding heads, and ultrasonic horns are all designed as a half-wavelength resonator of the working frequency. In the working state, the amplitude of the two end faces is the largest and the stress is the smallest, while the node in the middle position has zero amplitude and the largest stress. .

The node position is generally designed as a fixed position, but the thickness of the usual fixed position design is greater than 3mm, or the groove is fixed, so the fixed position is not necessarily zero amplitude, which will cause some calls and a part of energy loss. The call is usually isolated from other parts by rubber rings, or shielded by sound insulation materials, and the energy loss is considered when designing the amplitude parameters.

Ultrasonic metal welding mesh
Ultrasonic metal welding is usually designed on the surface of the welding position and the surface of the base. The purpose of the mesh design is to prevent the sliding of the metal parts and transmit energy to the welding position as much as possible. The reticulation design generally has square, diamond, and strip reticulation. Metal-clad welding heads and bases such as gold hand ornaments require no lines to be designed. The size and depth of the lines are determined according to the specific welding material requirements.

Ultrasonic metal welding transducer
There is no big difference between the transducer used for metal welding device and the transducer used for plastic welding device. The special feature is that the welding metal has higher quality requirements, because the welding metal often requires a large instantaneous power. The transducer is required to have high power capacity and low impedance, and the transducer used by the plastic welding device is not used.

Ultrasonic metal welding power supply
There is no big difference between the ultrasonic power supply used in metal welding equipment and the ultrasonic power supply used in plastic welding equipment. [span] The particularity is that welding metal has higher requirements. In order to meet the needs of metal welding, it is necessary to use an intelligent ultrasonic power source-ultrasonic generator.

The ultrasonic generator has an automatic frequency tracking system. Changes in the working conditions of mechanical devices or electronic components during the welding process will cause a change in the vibration frequency. [span] The ultrasonic generator will track the frequency of the vibration system, so that the generator and the vibration system The frequency is always in resonance. The frequency automatic tracking system can compensate for the changes in the working state during the welding process, so that the system is in resonance again and the welding parameters are kept stable. The focus is on the stability of the amplitude, which is very important for metal welding. .

Ultrasonic metal welding accuracy
 
Because the ultrasonic welding head works under high-frequency vibration, it should try to maintain a symmetrical design to avoid unbalanced stress and lateral vibration caused by the asymmetry of sound wave transmission (the welding head we use for welding uses the longitudinal vibration of ultrasonic vibration). Transmission, for the entire resonant system), unbalanced vibration can cause the welding hair to heat and break. Ultrasonic welding is used in different industries for different processing accuracy requirements. For particularly thin workpieces such as the welding of lithium-ion battery pole pieces and tabs, and the coating of gold foil, the requirements for processing accuracy are very high. All of our processing equipment All use numerical control equipment (such as machining centers, etc.) to ensure that the accuracy of the machining meets the requirements.

Ultrasonic metal welding life
The service life of a welding head is critically determined by two aspects: first, material, and second, process

Material aspect: Ultrasonic welding requires metal materials to have good flexibility (small mechanical loss during sound wave transmission), so the most commonly used materials are aluminum alloy and titanium alloy, but ultrasonic metal welding requires the welding head to be wear-resistant (requires more High hardness), making the choice of materials more difficult, because hardness and toughness seem to be inherently opposed, which requires us to choose very demanding materials. The high-quality steel materials we choose can better solve this contradiction. The effective life of the welding head is increased as much as possible.

Process: Including the processing technology and subsequent processing technology. The processing technology has been described in detail above. The subsequent processing includes heat treatment and parameter trimming. Based on the materials selected by our company, we have an original heat treatment process to guarantee; After the head is made, the parameters must be measured and adjusted separately to ensure the product.

Failure Analysis of Ultrasonic Metal Welding
 
Ultrasonic metal welding heat
The welding head will have a certain heating phenomenon when it is working, which is caused by the mechanical loss of the material itself and the heat conduction of the weldment. Whether the welding head heat is normal or not is judged that when there is no load (that is, not touching the workpiece), the ultrasonic wave should be continuously emitted for more than half an hour, and the temperature should not exceed 50-70℃. If the heat is severe, it proves that the welding head is damaged or the material is unqualified. replace.

Ultrasonic metal welding whistle

When whistling occurs when the welding head is working, the following reasons should be analyzed:

① Whether the mounting screws are loose
② Whether the welding head has cracks
③ Whether the welding head is in contact with objects that should not be in contact.

Ultrasonic metal welding overload
When the generator sends out an overload alarm, it should be checked as follows:

① No-load test, if the working current is normal, it may be that the welding head is in contact with objects that should not be touched or the parameter adjustment between the welding head and the welding seat has failed.

② When the no-load test is abnormal, first observe whether the welding head has cracks and whether the installation is firm, then remove the welding head and perform no-load test to rule out whether there is a problem with the transducer + horn, and eliminate it step by step. After eliminating the possibility of failure of the transducer + horn, replace the new welding head for judgment.

③ Sometimes there may be situations where the no-load test is normal but not working properly. It may be that the internal sound energy components such as welding heads have changed, resulting in poor sound energy transmission. Here is a relatively simple judgment method: hand touch method. The amplitude of the normal working welding head or horn surface is very uniform when it is working, and the hand feels velvety and smooth. When the sound energy is not transmitted smoothly, there will be a feeling of bubbles or burrs on the hand. It is necessary to use the elimination method to eliminate the problematic parts. The same situation can occur when the generator is abnormal, because normally, the input waveform of the transducer should be detected as a smooth sine wave. This phenomenon can also occur when there are spikes or abnormal waveforms on the sine wave. At this time, another pruned acoustic energy component can be used to replace it for identification.

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