Modern welding technology has been able to weld welds with mechanical properties equal to or even higher than those of the connected body, and there are no internal and external defects. The mutual position of welded bodies in space is called welded joint, and the strength of the joint is not only affected by the quality of weld, but also related to its geometry, size, stress and working conditions. The basic forms of joints are butt joint, lap joint, T-joint (positive joint) and angle joint.
The cross-sectional shape of butt weld depends on the thickness of the welded body before welding and the groove form of the two edges. When welding thick steel plates, grooves of various shapes are made at the joints for penetration, so that covered electrode or welding wire can be easily fed. Groove forms include single-sided welding groove and double-sided welding groove. When choosing the groove form, in addition to ensuring the penetration depth, factors such as convenient welding, less metal filling, small welding deformation and low groove processing cost should also be considered.
When two steel plates with different thicknesses are butted, in order to avoid serious stress concentration caused by the sharp change of cross section, the thicker plate edges are often gradually thinned to reach the same thickness at the two butted edges. The static strength and fatigue strength of butt joint are higher than those of other joints. Butt welding is usually the first choice for connections working under alternating and impact loads or in low temperature and high pressure vessels.
Lap joint is easy to prepare before welding, easy to assemble, with small welding deformation and residual stress, and is often used for on-site installation of joints and unimportant structures. Generally speaking, lap joints are not suitable for working under alternating load, corrosive medium, high temperature or low temperature.
T-joints and corner joints are usually used for structural needs. The working characteristics of incomplete fillet weld on T-joint are similar to those of lap joint. When the weld is perpendicular to the direction of external force, it becomes a frontal fillet weld, and the surface shape of the weld will cause stress concentration to varying degrees. The stress of penetration fillet weld is similar to that of butt joint.
The bearing capacity of fillet joint is low, so it is generally not used alone. It can only be improved by full welding, or when there are fillet welds inside and outside, and it is mostly used at the corner of closed structure. Welded products are lighter than riveted parts and cast forgings, which can reduce their own weight and save energy for transportation tools. The welding has good sealing performance and is suitable for manufacturing various containers. With the development of combined machining technology, welding, forging and casting can be combined to manufacture large-scale, economical and reasonable cast-welded structures and forged-welded structures, which has high economic benefits. The welding process can effectively use materials, and the welding structure can use materials with different properties in different parts, giving full play to the advantages of various materials and achieving economic and high quality. Welding has become an indispensable and increasingly important processing method in modern industry.
In modern metal processing, welding develops later than casting and forging, but it develops rapidly. The weight of welded structure accounts for about 45% of steel output, and the proportion of aluminum and aluminum alloy welded structure is also increasing.
In the future welding process, on the one hand, we should develop new welding methods, welding equipment and welding materials to further improve welding quality and safety and reliability, such as improving existing welding energy sources such as arc, plasma arc, electron beam and laser; Using electronic technology and control technology, the technological performance of arc is improved and a reliable and portable arc tracking method is developed.
On the other hand, it is necessary to improve the level of welding mechanization and automation, such as program control and digital control of welding machine; Develop a special welding machine to realize the whole process automation from preparation, welding to quality control; In the automatic welding production line, the promotion and expansion of numerical control welding manipulator and welding robot can improve the welding production level and improve the welding hygiene and safety conditions.
As an industrial technology, the appearance of welding caters to the demand of new technology and new means for the development of metal art. On the other hand, the unique and wonderful changes of metal under the action of welding heat also meet the demand of metal art for new artistic expression language. In today's metal art creation, welding can and is being shown as a unique artistic expression language. Artistic creation and technical methods are always inseparable.
Metal welding art can be branched from traditional metal art and become a relatively independent art form, because:
Firstly, welding is artistic.
Welding can produce rich artistic expression language. Welding is usually carried out at high temperature, and metal will produce many wonderful and rich changes at high temperature: the color of metal parent material will change and thermally deform (that is, welding heat affected zone); The welding wire will form some beautiful textures after melting; Welding defects are often used in welding art, and welding defects refer to defects that do not meet the design or process requirements in the welding process. Its main manifestations are welding cracks, blowholes, undercut, incomplete penetration, incomplete fusion, slag inclusion, flash, collapse, pits, burn-through, inclusions and so on. This is a very interesting phenomenon: the artistry of welding is usually reflected in some failed operations of industrial welding or hidden in some welding defects that industrial welding tries to avoid.
Secondly, the language of welding art is unique.
The manifestations of the above welding defects and welding heat affected zone are formed by welding operation under certain specifications, and these artistic languages can only be produced through welding. The surface effect of welding art works is impossible or difficult to achieve by other metal processing technologies, so welding art has unique artistry.
By choosing different metal materials and using different welding techniques, the artistry of welding can be brought into full play in different metal art forms: in welding sculpture, welds and cuts do not exist passively as traces of technical processing, but are embodied in a wonderful and indispensable expression language. In a welding sculpture, the thick weld is exposed on the surface of the sculpture, and all kinds of irregular cutting marks have become the artist's beautiful artistic language ... In many cases, due to the rough and simple style pursued by the welding sculpture, according to the needs of the work, most of the metal corrosion and defects are retained. Therefore, we can often feel a kind of uncut primitive beauty in welding sculptures.
The welding seam of the steel plate splicing at the lower part of the sculpture is very thick. Judging from the firmness of the welding process, this is obviously not only due to the consideration of the firmness of the sculpture. In this sculpture, the lower twisted welds, as an important factor of the overall aesthetics of the sculpture, have become an indispensable part. On the whole, there are distorted weld marks everywhere, whether it is the text modeling in the upper part or the texture processing in the lower part, and the whole work has achieved the unity of the overall visual language. If a mural is regarded as a painting, the treatment of points, lines, surfaces, black, white, gray and even colors in the picture can be realized by welding. Metal wires of various models and materials will appear on the screen in different forms with different welding processes. Different metals have different colors, such as bright silver in stainless steel, silver in aluminum, jet black in carbon steel, titanium steel, bronze, copper and brass ... and as far as steel products are concerned, different steel products will have different color changes when heated at high temperature, that is, the welding heat affected zone is different. In addition, cutting is also one of the creative methods of welding art wall decoration, which can be used in combination with welding or alone, depending entirely on the creator's creative intention and mastery of technology and effect. Taken together, these methods mentioned above can be imagined to be varied.
Manual plasma cutting method, using the heat of current when cutting, makes the cutting edge produce heat affected zone, thus "dyeing" bright white stainless steel into a slightly gradual color. At the same time, by adjusting the welding specifications, the strong air jet from the cutting gun will "blow" a circle of randomly formed textures on the cutting edge at the moment when the cutting steel plate melts. After cutting, the metal cools and solidifies into beautiful cuts, which is in contrast with the stainless steel plate with smooth and bright middle. The formation process of this random effect is accidental, but it is an inevitable phenomenon under certain welding specifications.
In terms of size, semi-automatic CO2 gas shielded welding can be used to weld larger artistic wall decorations, and manual TIG welding can be used to weld smaller ones.