The active development of high-tech methods for the thermal welding of metals overshadows alternative processing methods. At the same time, there are quite worthy techniques of the most ancient cold deformation of plastic products. Such methods include dry welding. For metal, in particular, directional deformation with increasing internal stress is applied. In this process, a variety of active tools, tools and consumables can.
Technology Overview
Dry welding is one of the types of cold welding in the solid phase, during which significant deformation processes occur with an insignificant degree of localization of the working structure. An important difference of this technique is the high pressure applied to conduct deforming processes. Compared with the basic methods of thermal hot welding, this technology makes it possible to perform operations at normal or even negative temperatures. The above photo of dry welding for metal under pressure shows the result of such work under conditions of temperature conditions below the degree of recrystallization. The main focus of this technology is the mechanical impact on the material, as a result of which a connection is formed between two or more workpieces.
Step-by-step welding process
Standard dry welding technology is performed according to the following instructions:
- Plastic extrusion of the metal is carried out, affecting the deep structure. In this operation, special units are used that provide a deformation process.
- After the end of the deforming action, a contact of the deep layers of the metal is formed.
- A single crystalline structure is formed. The time to perform dry welding for metal at this point can be calculated in fractions of seconds, which leads to the absence of volume interaction between the workpieces.
- A special external surface treatment is carried out with protective and reinforcing compositions - including those with anti-corrosion effect and the effect of relieving internal stress.
Key process characteristics
The parameters of the operation on the one hand reflect the magnitude of the physical impact on the workpiece, and on the other, the quality of the connection. The paramount characteristics of both spectra include the following:
- Depth of indentation. Usually, a punch is used for deformation - a pressing tool, due to which the shape of the part changes. Also, this characteristic of dry welding for metal can be assigned as the degree of ductility, which, depending on the material, can allow a coefficient of entry into the structure from 10-15% (indium) to 85-90% (copper, nickel).
- Compression action. It is expressed by indicators of compressive force and shear, which is calculated by the tangential force. This is not a direct indicator of structural changes, but a characteristic that determines the potential displacement of the joined surfaces.
- Ability to weld. Depends on the complex resistance of the metal structure to the mechanical effects of dry welding. The most accessible products for such operations are copper, aluminum, silver, cadmium, etc. With increasing hardness, the ability to weld decreases.
Types of dry welding
Basically, the methods are distinguished by the type of compound formed, as with thermal exposure. It can be butt, spot and seam welding. Less commonly used are shear and high pressure joint techniques. When performing spot welding, cylindrical punches are used as a tool, and with seam technique, roller elements. Both of these methods are characterized by high productivity, but as a result they give quite rough and outwardly unattractive seams. Butt dry welding for metal involves the use of special pressures, as well as making notches to prevent slipping of the workpiece. The advantages of the method include the ability to work with solid-state parts and, in principle, the use of high pressure, which increases the power of the deformation force. On the other hand, due to the need for notches, the appearance of the product may deteriorate even in places outside the work area.
Preparation of the workpiece for work
The main problem of preparing materials for dry welding is due to the need for careful removal of adsorbed and organic films. It can be oil and grease traces, as well as acid and paraffin coatings, which are often applied to preserve and support other technological processes in the factory. To remove such layers, alcohol-containing and gasoline products, solvents and special chemicals for metal processing are used. In addition, the dry welding instruction for metal involves the following preparatory operations:
- Cleaning surfaces with steel abrasive brushes.
- In the case of aluminum billets, calcination is used at temperature conditions from 300 to 400 ° C.
- Coating the product with a thin layer of chromium or galvanic nickel.
- If we are talking about conductors with insulation, then all the outer protective layers are removed with a small capture of the inoperative zone.
Welding mode parameters
Among the main parameters of this type of welding can be called the departure of the part from the clamp, specific pressure, punch thickness, etc. For example, the pressure indicator is selected based on the physicomechanical characteristics of the target workpiece. So, aluminum is welded at 800 MN / m 2 , and copper parts at 2500 MN / m 2 . As for the departure of the workpiece from the clamping mechanism, then in this case everything is individual. For example, for aluminum rods of length d, the offset will be 1.2d, and for copper 1.5d. Coefficients may vary depending on the shape of the part. Particular attention in evaluating suitable parameters is given to the dimensions of the punches, which directly realize dry welding. For metals like the same copper and aluminum, the characteristics of the pressing mechanism are calculated based on the fact that the load should be from 600 MPa to 2000 MPa. Dimensional parameters are adjusted to the mass of the structure, and the shape and design - to the parameters of the product.
Dry welding
Using special pressing equipment, the operation is performed in the following order:
- Clips are fixed corresponding to the size of the welded workpieces.
- Compressed air is supplied to the machine to provide the required pressure through the compressor.
- A functional unit is brought into an active state, the deformation of which is performed by its force.
- Immediately before the production of dry welding for metal, the instruction on the use of technology indicates the need for processing parts with acetone or alcohol.
- Welding of the workpiece rods and trimming of the flare is performed (excess metal at the joints, delighted when extruding).
- Welded elements are released from the clamps.
- The movable mechanism returns to its original position, the latches loosen.
Throughout the entire working process, the operator interacts with the functionality of the machine through the handles, control levers and devices for feeding blanks. In modern models of equipment for dry welding, electronic means of controlling operations are also provided, with the help of which an in-line mode of processing parts is organized.
The advantages of dry welding
Eliminating the need for high-temperature heating of workpieces is the main advantage of this technology in comparison with electrochemical types of welding. This eliminates the use of powerful energy sources, removing a significant cost item. In the same group of advantages, one can note a decrease in the probability of electrochemical blockages, from which, with thermal methods, it is necessary to protect the workpieces with gaseous media and flux. Also, depending on the complexity of the task and working conditions, there are other advantages of dry welding for metal:
- High performance with little time.
- The minimum set of auxiliary and expendable materials.
- The ability to automate the process.
- The operator does not have to be highly qualified as a welder.
- Requirements for post-processing parts are minimal.
The disadvantages of dry welding
With all the advantages, this technology is not so widespread in comparison with hot welding, which is explained by severe limitations in terms of the admissibility of the method to metals and alloys with low ductility. Mostly, non-ferrous and pure metals can be processed. But in this case, it is not always possible to count on a high quality result. Moreover, the main technological disadvantages of dry welding for metals of high ductility are associated with the deformation of the internal structure, which may adversely affect the future operation of the product. In general, we can say that the technology is convenient and low-cost, but not universal and rather highly specialized.
Conclusion
Cold welding methods have fundamental differences with the thermal technology for joining metal workpieces. They are associated with the nature of the impact on the structure of the material and the conditions of the technical organization of the process. As reviews of dry welding for metal show, this method manifests itself well in working with electrical consumables, small workpieces of the electrical industry, etc. Mostly, we are talking about conductors and small stamped elements. If it comes to metal structures, large-sized pipes and stainless steel sheets, then the work process must be trusted in high-temperature welding. Changing the structure due to deformation in such cases will be ineffective.