洛阳理工学院毕业设计
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WELDING PROCESS
Metal welding methods are mainly divided into above 40, fusion, bonding and brazing three categories.
In the fusion welding process workpiece is heated to interface will melt condition, not complete welding method pressure. When the heat will stay, fusion welding workpieces quickly melted at two heating, formation of molten pool. Molten pool with heat moving, cools continuous seam and will become one of two workpiece connection.
In connection with the process of atmospheric temperature, if the molten pool direct contact with the oxygen in the atmosphere will metal oxide and various alloying elements. Atmospheric nitrogen, steam into molten pool, etc in subsequent cooling process in the weld formation in the porosity, slag, weld crack defects, deterioration of quality and performance.
In order to improve the quality of welding, people developed various protection method. For example, electric welding gas protection is argon, carbon dioxide gas, such as air, in order to protect the isolation of the arc welding and welding pool, And as steel welding, add in the electrode's great affinity for oxygen and iron powder are doxycycline titanium rod can be protected in beneficial elements and silicon manganese oxide from into molten pool, cooling after welding quality.
Bonding is pressurized conditions, make two workpiece in solid between atoms, realize the combination and solid welding. The pressure welding is used, when the current through the butt weld resistance when the two parts connected by resistance, and rising temperatures, the great when heated to plastic state, in the axial pressure connection become one.
Various pressure welding method is common in welding process without pressure and filling materials. Most pressure welding methods such as
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洛阳理工学院毕业设计
diffusion welding and welding, cold welding are no melting process, thus not so good as welded alloy elements, and the harmful elements into burning weld question, thus simplifying the welding process, welding and improve the safety and hygiene conditions. At the same time as heating temperature, heating time is short of low penetration, heat affected zone. Many difficult welding materials with melting, often can use bonding welded with the base amount of quality connectors.
Brazing is the low melting point of use than workpiece materials metal brazing alloy, the workpiece and metallurgical heated to higher brazing alloy melting temperature of melting, workpiece, using the liquid filling analyzed wet parts, and with workpiece interface between atomic interdiffusions of realization, thus realize welding method.
Welding the formation of connecting the two are connected the weld seams called. When the welding seam by both in welding heat, and organization and performance variation, a region called the heat affected zone. When the welding workpiece materials for welding materials, welding current and welding in different welding and heat affected zone may cause overheating, improver, hardening or softening phenomenon, also make the welding performance deterioration, and weldability. It will need to adjust welding conditions, a former butt weld at preheating, welding and welding heat preservation can improve the welding quality of welding.
In addition, welding is a local rapid heating and cooling process, welding workpiece due to the area around the body cannot free at expansion and contraction, after cooling occurs in the welding of welding stress and deformation. Important after welding products are necessary to eliminate the welding stress, deformation correction.
Modern welding technology has a defect of internal and external welding is equal to or above, mechanical properties of welding is connected. In the space by welding welding joints, each place called the strength in double-quick weld quality, but also its geometric shapes, sizes, stress and
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洛阳理工学院毕业设计
working conditions. The basic form of joint have docking, lap, t-shaped meet (are) and Angle handover etc.
Butt weld joints of cross-sectional shape, decided to be in before welding welding and thickness of the two forms of groove. Thicker steel welded to weld fully in the place of the open mouth, so slope shape more easily into the electrode wire or. Groove is one-sided welding process of form of groove and welding process of both sides. Choose groove, except that the weld fully should also be considered welding process is convenient, the filler metal welding deformation quantity is little, small mouth and low processing cost.
The two different thickness steel butt, to avoid to cause serious change sharply section stress concentration, the thick plate cutting edge gradually, to connect the two etc. The static strength and fatigue strength than other joints. In the alternative, shock, or in low pressure vessel in the work, often give priority to the docking joints welded.
Lap joints of welding preparation work is simple, convenient, assembly welding deformation and residual stress on site installation, so smaller joints and not important structure often USES. Generally speaking, lap joints is not suitable for alternating load in corrosive medium, such as high and low temperatures under the working conditions.
Using a tee and Angle joint structure is usually due to the need. Tee on the welding seam characteristics and the Angle of lap joint Angle of weld similar. When the vertical direction with external welding become positive fillet weld seam, different surface shape can cause stress concentration, Welding the weld stress condition and joint Angle joint similar.
Angle joint bearing capacity is low, generally not used alone, only in welding, or in the internal and external has improved fillet weld when used in closed form the corner of the structure.
Welding products than riveting, castings and forgings for weight, it can reduce the transportation and energy savings. Good sealing, suitable for welding of manufacturing all kinds of containers. Joint development process,
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洛阳理工学院毕业设计
make welding and forging, casting, combining can be made into large economic and rational ZhuHan structure and forge welding structure, and the economic benefit is high. Using welding materials, effectively using junior-senior welding structure can adopt different in different parts of the properties of materials, full of various materials, high quality, achieve economic specialty. Welding has become an indispensable modern industry, but also an increasingly important processing methods.
In the modern metal processing, welding, casting forging process is relatively late, but develop very quickly. The weight of the weld structure about 45% of steel production, aluminum and aluminum alloy welding structure and increase the proportion of.
The future research on the welding technology, a new method to welding materials, welding equipment and to further improve the welding quality, safety and reliability, such as improving existing arc, plasma arc welding, laser beam, energy, Using electronic technology and control technology, improve the process performance, electric arc tracking method and reliable.
On the other hand we should improve the welding automation level of mechanization and realization process control, such as welding machine, digital control, Research from the preparation and welding quality monitor all the special welding process automation, In automatic welding line, promotion, expand the nc welding and welding robot manipulator, can improve the welding production level, improve health and safety conditions of welding.
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洛阳理工学院毕业设计
焊接工艺
金属焊接方法有40种以上，主要分为熔焊、压焊和钎焊三大类。 熔焊是在焊接过程中将工件接口加热至熔化状态，不加压力完成焊接的方法。熔焊时，热源将待焊两工件接口处迅速加热熔化，形成熔池。熔池随热源向前移动，冷却后形成连续焊缝而将两工件连接成为一体。
在熔焊过程中，如果大气与高温的熔池直接接触，大气中的氧就会氧化金属和各种合金元素。大气中的氮、水蒸汽等进入熔池，还会在随后冷却过程中在焊缝中形成气孔、夹渣、裂纹等缺陷，恶化焊缝的质量和性能。
为了提高焊接质量，人们研究出了各种保护方法。例如，气体保护电弧焊就是用氩、二氧化碳等气体隔绝大气，以保护焊接时的电弧和熔池率；又如钢材焊接时，在焊条药皮中加入对氧亲和力大的钛铁粉进行脱氧，就可以保护焊条中有益元素锰、硅等免于氧化而进入熔池，冷却后获得优质焊缝。
压焊是在加压条件下，使两工件在固态下实现原子间结合，又称固态焊接。常用的压焊工艺是电阻对焊，当电流通过两工件的连接端时，该处因电阻很大而温度上升，当加热至塑性状态时，在轴向压力作用下连接成为一体。
各种压焊方法的共同特点是在焊接过程中施加压力而不加填充材料。多数压焊方法如扩散焊、高频焊、冷压焊等都没有熔化过程，因而没有象熔焊那样的有益合金元素烧损，和有害元素侵入焊缝的问题，从而简化了焊接过程，也改善了焊接安全卫生条件。同时由于加热温度比熔焊低、加热时间短，因而热影响区小。许多难以用熔化焊焊接的材料，往往可以用压焊焊成与母材同等强度的优质接头。
钎焊是使用比工件熔点低的金属材料作钎料，将工件和钎料加热到高于钎料熔点、低于工件熔点的温度，利用液态钎料润湿工件，填充接口间隙并与工件实现原子间的相互扩散，从而实现焊接的方法。
焊接时形成的连接两个被连接体的接缝称为焊缝。焊缝的两侧在焊接时会受到焊接热作用，而发生组织和性能变化，这一区域被称为热影响区。焊接时因工件材料焊接材料、焊接电流等不同，焊后在焊缝和热影响区可
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