Welding of ultrasonic plastic, plastics, metals, polymeric materials, aluminum profiles. Ultrasonic welding: technology, harmful factors

Ultrasonic welding of metals is a process in which an all- in- one compound is obtained in the solid phase. The formation of juvenile sites (in which bonds are formed) and contact between them occur under the influence of a special tool. It ensures the joint action of relative alternating tangential displacements of small amplitude and compressive normal force on the workpieces. Let us further consider in more detail what the ultrasonic welding technology is.

Connection mechanism

Low-amplitude shifts occur between parts with an ultrasonic frequency. Due to them, microroughness on the surface of the parts undergoes plastic deformation. At the same time, pollution is evacuated from the connection zone. Ultrasonic mechanical vibrations are transmitted to the welding site from the tool from the outside of the workpiece. The entire process is organized in such a way as to avoid slippage of the device and support on the surfaces of the parts. During the passage of oscillations through the preforms, energy dissipates. This is provided by external friction between the surfaces at the initial stage of welding and internal friction in the material located between the support and the tool after forming the setting area. In the connection, the temperature rises, which facilitates deformation.

Specific behavior of the material

Tangential movements between parts and stresses that are caused by them and act together with compression from the welding force ensure localization of intense plastic deformation in small volumes in the near-surface layers. The whole process is accompanied by crushing and mechanical evacuation of oxide films and other contaminants. Ultrasonic welding provides a reduction in the yield point, which facilitates plastic deformation.

Process Features

Welding ultrasonic helps to form the necessary conditions for the connection. This is provided by the mechanical oscillations of the converter. Due to vibration energy, complex stresses of shearing, compression and tension are created. Plastic deformation occurs when the limits of elasticity of materials are exceeded. Getting a strong connection is provided by increasing the area of direct contact after the evacuation of surface oxides, organic and adsorbed films.

Application of US

Ultrasound is widely used in the scientific field. With its help, scientists are exploring a number of physical properties of substances and phenomena. In the industry, ultrasound is used for degreasing and cleaning products, working with hard-to-work materials. In addition, the oscillations favorably affect the crystallizing melt. Ultrasound provides them degassing and grinding grain, increasing the mechanical properties of cast materials. Vibrations contribute to the removal of residual stresses. They are also widely used to increase the speed of slow chemical reactions. Ultrasonic welding can be used for a variety of purposes. Oscillations can become a source of energy for the formation of suture and point connections. When ultrasound is applied to the welding bath during crystallization, the mechanical properties of the joint are improved by grinding the structure of the joint and the intensive removal of gases. Due to the fact that vibrations actively remove impurities, artificial and natural films, parts can be connected, with an oxidized, lacquered, etc. surface. Ultrasound contributes to reducing or eliminating the inherent stresses that occur during welding. Due to vibrations, it is possible to stabilize the structure of the compound. This, in turn, helps to prevent the possibility of spontaneous deformation of the structures afterwards. Ultrasound welding has recently become more widely used. This is due to the undoubted advantages of this method of connection in comparison with the cold and contact methods. Especially often, ultrasonic vibrations are used in microelectronics. Ultrasound welding of polymer materials is considered to be a promising direction . Some of them can not be connected by any other method. At industrial enterprises, ultrasonic welding of thin-walled aluminum profiles, foils, and wires is currently being carried out. This method is especially effective for joining products from heterogeneous raw materials. Ultrasonic welding of aluminum is used in the manufacture of household appliances. This method is effective for joining sheet materials (nickel, copper, alloys). Ultrasonic welding of plastics has found application in the manufacture of instruments of optics and fine mechanics. At present, machines for connecting various elements of microcircuits have been created and introduced into production. The devices are equipped with automatic devices, due to which the productivity significantly increases.

Power of ultrasonic

Ultrasonic welding of plastic provides an inseparable connection due to the combined effect of high-frequency mechanical vibrations and a relatively small compressive force. This method has a lot to do with the cold way. The power of the ultrasound that can be transmitted through the medium will depend on the physical properties of the latter. If the limits of strength in the compression zones are exceeded, the solid material will collapse. In similar situations, cavitation occurs in liquids, accompanied by the appearance of small bubbles and their subsequent slamming. Together with the latter process, local pressures arise. This phenomenon is used in the cleaning and processing of products.

Device nodes

Ultrasonic welding of plastic is carried out using special machines. They have the following nodes:

1. Source of power.
2. Oscillating mechanical system.
3. Control equipment.
4. Pressure drive.

The oscillating system is used to convert electric power to mechanical for its subsequent transmission to the connection site, to concentrate it and to obtain the required magnitude of the radiator speed. In this node there are:

1. Electromechanical converter with windings. It is enclosed in a metal casing and is cooled by water.
2. Transformer of elastic oscillations.
3. Welding tip.
4. Support with pressure mechanism.

The system is fixed by means of a diaphragm. Radiation of ultrasound occurs only at the time of welding. The process occurs under the influence of vibrations, pressure applied at right angles to the surface, and the thermal effect.

Features of the method

Ultrasound welding is most effective for plastic raw materials. Products made of copper, nickel, gold, silver, etc. can be combined with each other and with other low-plastic products. As the hardness is increased, the weldability by ultrasound deteriorates. The refractory products of tungsten, niobium, zirconium, tantalum, and molybdenum are effectively combined with the help of ultrasonic testing. Ultrasonic welding of polymers is considered a relatively new method. Such products can also be connected with each other as well as with other solid parts. As for the metal, it can be combined with glass, semiconductors, ceramics. You can also link the workpieces through an interlayer. For example, steel products are welded together through aluminum plastic. Due to the short stay at an elevated temperature, a high-quality compound of dissimilar products is obtained. The properties of raw materials undergo minor changes. The absence of foreign impurities is one of the advantages that ultrasonic welding has. Harmful factors for humans are also absent. When combined, favorable hygienic conditions are created. The bonds of the products differ in chemical homogeneity.

Connection Features

Welding of metal is carried out, as a rule, by lapping. This adds a different design elements. Welding can be carried out by points (one or several), a continuous seam or in a closed circle. In some cases, when the end of the workpiece is preformed from the wire, it is tied together with the plane. It is possible to carry out ultrasonic welding of several materials simultaneously (by a package).

Thickness of parts

It is limited by the upper limit. When the thickness of the metal workpiece is increased, it is necessary to use oscillations with a larger amplitude. This will compensate for the loss of energy. The increase in amplitude, in turn, is possible up to a certain limit. Restrictions are associated with the probability of fatigue cracks, large dents from the tool. In such cases, it should be assessed how suitable ultrasound welding is. In practice, the method is used for the thickness of products from 3 ... 4 μm to 05 ... 1 mm. Welding can also be used for parts with a diameter of 0.01 ... 05 mm. The thickness of the second product can be much larger than the first.

Possible problems

When using the ultrasonic welding method, it is necessary to take into account the probability of fatigue failure of existing compounds in products. During the process, the workpieces can be rotated relative to each other. As was said above, dents remain on the surface of the material from the tool. The device itself has a limited lifespan, which is due to erosion of its working plane. At individual points the material of the product is welded to the tool. This leads to wear and tear on the device. Repair of equipment is accompanied by a number of difficulties. They are related to the fact that the instrument itself acts as an element of an integral, unified design of the node, the configuration and dimensions of which are calculated exactly at the operating frequency.

Preparation of products and mode parameters

Before performing ultrasonic welding of any complex measures with the surface of the parts do not need to. If desired, it is possible to improve the stability of the connection quality. For this purpose, it is advisable only to degrease the product with a solvent. For the connection of ductile metals, the cycle with the delay of the pulse with respect to the moment of launch of the ultrasound is considered to be optimal. With a relatively high hardness of the product, it is advisable to wait for a slight heating before turning on the ultrasound.

Welding diagrams

There are several. Technological schemes of ultrasonic welding differ in the nature of the oscillation of the tool. They can be torsional, bending, longitudinal. Also, the schemes are distinguished depending on the spatial position of the device relative to the surface of the workpiece to be welded, as well as the way the compressive forces are transferred to the products and the structural features of the support element. Variations with bending and longitudinal oscillations are used for the contour, suture and point connection. The ultrasonic effect can be combined with local impulse heating of parts from a separate heat source. In this case, you can achieve a number of benefits. First of all, it is possible to reduce the amplitude of oscillations, as well as the strength and time of their transmission. The energy properties of the thermal pulse and the period of its superposition on ultrasound appear as additional parameters of the process.

Thermal effect

Ultrasonic welding is accompanied by an increase in temperature at the joint site. The occurrence of heat is caused by the appearance of friction on the surfaces of the contacting articles, as well as by plastic deformations. They, in fact, accompany the formation of a welded joint. The temperature at the contact site will depend on the strength parameters. The most important is the degree of hardness of the material. In addition, its thermophysical properties are of no small importance: heat conductivity and heat capacity. The selected welding mode influences the temperature level. As practice shows, the emerging thermal effect does not act as a determining condition. This is due to the fact that the maximum strength of joints in products is reached earlier than the temperature rises to the limit level. Reduce the duration of transmission of ultrasonic vibrations can be done by preheating the parts. This will also improve the strength of the joint.

Conclusion

Ultrasonic welding is now an indispensable method of joining parts in some industrial branches. This method is especially widespread in microelectronics. US allows you to connect a variety of plastic and solid materials. Today, scientific work is actively carried out to improve the tools and technologies for welding.