Welding design（焊接设计）,Lesson 16,Welding design（焊接设计）,Heat input（热输入）,The main function of the heat that would be input into the welding joint is to melt the base metal and filler metal (if used).,Ar: representing the area of the filler metal melted Am :representing the area of the base metal,In arc welding: P=V I,Welding design（焊接设计）,Though the net heat as calculated above reaches the weld joint, all of it cannot be utilised for melting since part of it would be conducted away from the joint by the base metal as reflected in the heat affected zone (HAZ) .,Welding design（焊接设计）,Heat flow（热流向）,Heat transfer in a welded joint is a complex phenomenon involving the three dimensional movement of a heat source. Heat from the weld zone is transferred more to the other parts of the base metal by means of conduction（传导）. Similarly heat is also lost to surroundings by convection（对流） from the surface. Radiation（辐射） component being relatively small except near the weld pool.,Welding design（焊接设计）,Distortions（变形）,Angular distortion without restraint （拘束）,Welding design（焊接设计）,Restraining the workpieces in butt joint,Control of distortion,The most generally preferred method in the industry is using restraint.,Restrained joint,Welding design（焊接设计）,One of the important ways to control the distortions is a good design of the product with minimum number of joints.,Another method available for reducing the distortions is the preheating of the members of the weldment.,Welding design（焊接设计）,Defects in welding（焊接缺陷）,Undercut （咬边）This is generally attributed to the improper welding technique or excessive welding current. This is mainly caused by the incorrect manipulation of the electrode while depositing the bead, particularly, in horizontal and vertical welding.,Incomplete fusion （未焊透）This will be seen as a discontinuity in the weld tone. The main causes for this defect are improper penetration of the joint, wrong design of the joint or incorrect welding technique including the wrong choice of the welding parameters.,Porosity （气孔）caused by the presence of gases which get entrapped during the solidification process. The main gases that cause porosity are: hydrogen, oxygen, and nitrogen .,Welding design（焊接设计）,Slag inclusion （夹渣）it is formed by the reaction with the fluxes and is generally lighter. It will float on top of the weld pool and chipped off after solidification. The stirring action of the high intensity arc would force the slag to go into the weld pool, solidified inside in the fusion zone.,Lamellar tearing （层状撕裂） It appears as a long and continuous visual separation line between the base metal and the heat affected zone. This is caused by the presence of the elongated inclusions, such as Mn, Fe and S.,Hot cracking （热裂纹）the strain involved in solidification. It is generally occurs at high temperature and the size can be very small to be visible.,Cold cracking （冷裂纹) It is generally occurs at room temperature after the weld is completely cooled. The causes are: excessive restraint of the joint which induced very high residual stresses. Martensitic transformation making the metal very hard as a result of rapid cooling,科技论文的结构,Papers Title （ Please Center）FULL First Author1, FULL Second Author2 and Last Author3 1 Full address of first author, including country 2 Full address of second author, including country 3 List all distinct addresses in the same way,Abstract ： Keywords:,Introduction Experimental details Results and discussion Conclusion Acknowledgements References,摘要 关键词 前言 实验过程 结果与讨论 结论 致谢 参考文献,科技论文的范例,科技论文的范例,科技论文的范例,科技论文的范例,科技论文的范例,科技论文的范例,Terms,Ac welding machine Alloying elements Aluminium Annealing Arc blow Argon Atomic hydrogen welding Austenite,交流焊机 合金元素 铝 退火 弧偏吹 氩气 氢原子焊 奥氏体,Terms,Backing sand Backward hot extrusion Base metal Bead Braze welding Brass Bronze Butt joint,背砂 反向热挤压 母材 焊缝 钎焊 黄铜 青铜 对接接头,Terms,Carbon arc welding Cast iron Casting defects Clay Cold extrusion Cold working Copper Core Crater,碳弧焊 铸铁 铸造缺陷 粘土 冷挤压 冷加工 铜 型芯 弧坑,Terms,DC welding machine Defects in welding Deposition rate Die casting Diffusion welding Dry sand core Ductility,直流焊机 焊接缺陷 熔敷效率 压力铸造 扩散焊 干砂芯 延展性,Terms,Electric arc welding Electric resistance welding Electro slag welding Electron beam welding Explosive welding Facing sand Ferrite Ferrous materials Fettling Flux Friction welding,电弧焊 电阻焊 电渣焊 电子束焊 爆炸焊 面砂 铁素体 黑色金属材料 铸件清理 焊剂 摩擦焊,Terms,Gas metal arc welding Gas tungsten arc welding Gas welding Green strength Grey cast iron,熔化极气体保护焊 钨极气体保护焊 气焊 湿强度 灰铸铁,Hardenability Hardness Heat affected zone High carbon steels Horizontal position,淬硬性 硬度 热影响区 高碳钢 横焊位置,