Technical requirements for welding

【Summary Description】 Welding technology What is welding technology? Welding, also known as welding, is a manufacturing process and technique for joining metals or other thermoplastic materials such as plastics by heat, high temperature or high pressure. What is welding technology? Welding applications are very wide, can be used for metal, can also be used for non-metal. The welding process is mainly determined according to the material, brand and chemical composition of the welded workpiece, the type of weldment structure and the welding performance requirements. First of all, it is necessary to determine the welding method, such as manual arc welding, submerged arc welding, tungsten argon arc welding, gas shielded welding, etc. There are many types of welding methods and can only be selected according to the specific situation. After determining the welding method, the welding process parameters are formulated. The types of welding process parameters are different. For example, manual arc welding mainly includes: electrode type (or brand), diameter, current, voltage, type of welding power supply, polarity connection, number of welding layers, number of passes, inspection method, etc. Technical requirements for welding Technical requirements: 1. The welding seam shall be smooth during welding, and there shall be no welding defects such as pores and slag inclusion, and the defects shall be repaired in time. The weld height is generally close to the steel plate. When intermittent welding is used, the weld length and interval shall be uniform. 2. When the manufactured parts are required to be sealed and welded continuously, there shall be no blowhole trachoma at the weld. 3. When welding, the height of the weld seam shall not be less than the thickness of the base metal (weldment). When base metal (weldment) of different thickness is welded, the weld height shall not be less than the thickness of the thinnest base metal (weldment). Welding achieves the purpose of joining through the following three ways: 1. Fusion welding-heating the workpiece to be joined to make it partially melt to form a molten pool, which will be joined after cooling and solidification. If necessary, molten filler can be added to assist. It is a Welding processing suitable for various metals and alloys without pressure. 2, pressure welding-the welding process must apply pressure to the welding parts, which belongs to the processing of various metal materials and some metal materials. 3. Brazing-metal materials with lower melting point than the base metal are used as brazing materials, liquid brazing materials are used to wet the base metal, fill the joint gap, and diffuse with the base metal to realize the link welding parts. It is suitable for Welding processing of various materials, and also suitable for Welding processing of different metals or heterogeneous materials. Welding principle: Preheating can reduce the cooling rate after welding, which is conducive to reducing the maximum hardness of the heat affected zone of medium carbon steel and preventing cold cracks, which is the main process measures for welding medium carbon steel. Preheating can also improve the plasticity of the joint and reduce the residual stress after welding. Typically, 35 and 45 steels are preheated at ~ °C. If the carbon content is high or the crack tendency is large due to the large thickness and rigidity, the preheating temperature can be increased to ~ ℃. If the weldment is too large and the overall preheating is difficult, local preheating can be carried out, and the heating range of local preheating is on both sides of the weld ~. 2 Welding rod conditions: acid welding rod is preferred when permitted. 3 groove form: the weldment as far as possible to open into U-shaped groove type for welding. If it is a casting defect, the shape of the groove excavated by the shovel should be smooth, the purpose of which is to reduce the proportion of the base metal melted into the weld metal, so as to reduce the carbon content in the weld and prevent cracks. 4 process parameters: since the proportion of the base metal melted into the first layer of weld metal is up to about 30%, when welding the first layer of weld, small current and slow welding speed should be adopted as far as possible to reduce the penetration depth of the base metal, which is what we usually call burns (the base metal is burned when the current is too large). 5 Heat treatment: After welding, it should be kept at-℃ for 2-6 hours to further slow down the cooling rate, increase plasticity and toughness, and reduce the hardening tendency to eliminate the diffused hydrogen in the joint. Therefore, welding can not be carried out in a cold environment or rain. It is best to perform stress relief heat treatment on weldments immediately after welding, especially for weldments with large thickness, high rigidity structures and weldments working under severe conditions (dynamic load or impact load). The tempering temperature for stress relief after welding is ~ ℃, heat preservation for 1-2h, and then cooling with the furnace.

Previous Page

What tools do you need to weld things?

Next Page

What is brazing welding?