曹彪焊接joining processes and equipment2.ppt

28 Solid-State Welding Processes,welding,Fusion,Brazing and soldering,Solid state,Chemical,Electrical,Mechanical,Electrical,Chemical,Cold Welding,Ultrasonic Welding,Friction Welding(FRW)InertiaLinearStir(FSW),Resistance WeldingSpot(RSW)Seam(RSEM)Projection(RPW)Et al,Explosion welding,Diffusion Bonding,Solid-State Welding Processes(固态焊接）（压力焊）Processes in which joining takes place without fusion(melting)of the workpieces.Unlike in the fusion-welding processes described in chapter 27,no liquid(molten)phase is present in the joint.？If two clean surfaces are brought into atomic contact with each other under sufficient pressure,they form bonds(结合)and produce a strong joint.Apply external heat improves the bond by diffusion(扩散).Heat may be generated by friction,electric-resistance heating or chemical reaction.,28.2 Cold Welding（CW）冷(压)焊In cold welding(CW),pressure is applied to the workpieces,through either dies or rolls(冲模或滚轮).If the rolls are used,the process is called roll bonding（滚压焊）.Because of the plastic deformation involved,it is necessary that at least one,but preferably both,of the mating parts（配合件，焊接件）be ductile（易延展的）.Prior to welding,the interface is degreased,wire-brushed,and wiped to remove oxide smudge（擦除氧化物污染）.Cold welding can be used to join small parts made of soft,ductile metals.,Figure 28.1 Schematic illustration of the roll bonding,or cladding process,28.3 Ultrasonic Welding(USW)超声波焊接In ultrasonic welding,the faying surfaces（结合面）of the two components are subjected to a static normal force and oscillating shearing(tangential 切线的)stresses.The shearing stresses are applied by the tip of a transducer（换能器，变换器）.The frequency of oscillation is generally in the range of 10kHz to 75kHz.The shearing stresses cause plastic deformation at the interface of the two components,breaking up oxide films and contaminants and thus allowing good contact and producing a strong solid-state bond.The temperature generated in the weld zone is usually in the range from one-third to one-half of the melting point of the metals joined;consequently neither melting nor fusion takes place.But different for welding plastic(low melting point).,Anvil 砧台，平台；coupling system 偶合系统；transducer 变换器，换能器；polarization 极化,Figure 28.2(a)Components of an ultrasonic welding machine for lap welds.The lateral vibrations of the tool tip cause plastic deformation and bonding at the interface of the workpieces.(b)Ultrasonic seam welding using a roller.(c)An ultrasonically welded part.,Process capabilities:The ultrasonic welding process is versatile and reliable.It can be used with a wide variety of metallic(ductile)and nonmetallic materials,including dissimilar metals.battery assembly solar energy converter It is used extensively for the joining of plastics,in packaging with foils（箔）and for the lap welding of sheet,foil,and thin wire.,28.4 Friction Welding(FRW)摩擦焊 In friction welding,the heat required for welding is generated through friction at the interface of the two components being joined.In friction welding,one of the components remains stationary(固定的）while the other is placed in a chuck（卡盘）or collet（夹头）and rotated at a high constant speed.The two members to be joined are then brought into contact under an axial force.,Figure 28.3(a)Sequence of operations in the friction welding process:(1)Left-hand component is rotated at high speed.(2)Right-hand component is brought into contact under an axial force.(3)Axial force is increased;flash begins to form.(4)Left-hand component stops rotating;weld is completed.The flash can subsequently be removed by machining or grinding.(b)Shape of fusion zone in friction welding,as a function of the force applied and the rotational speed.,After sufficient contact is established,the rotating member is brought to a quick stop(so that the weld is not destroyed by shearing),while the axial force is increased.Oxides and other contaminants at the interface are removed by the radially outward movement（径向排除）of the hot metal at the interface.The pressure at the interface and the resulting friction produce sufficient heat for a strong joint to form.The shape of the welded joint depends on the rotational speed and on the axial pressure applied.These factors must be controlled to obtain a uniformly strong joint.,Process Capabilities:FRW can be used to join a wide variety of materials,provided that one of the components has some rotational symmetry.（轴对称）Solid or tubular parts（实心或管状零件）can be joined by this method,with good joint strength.(Solid steel bars up to 100mm in diameter and pipes up to 250mm in outside diameter)The surface speed of the rotating member may be as high as 900m/min,the productivity is very high(one to several ten seconds a joint).Welding flash,can easily be removed（容易清除）by machining or grinding.FRW machines are fully automated,and the operator skill required is minimal.,Other Friction Welding ProcessesInertia Friction Welding 惯性摩擦焊 The kinetic energy of a flywheel.Linear Friction Welding 线性摩擦焊 Linear reciprocating motion（线性往复运动）Tropism(Phase Controlled)Friction Welding 相位摩擦焊 For some square geometric or other shapes.Friction Stir Welding 摩擦搅拌焊（搅拌摩擦焊）,28.4.4 Friction Stir Welding(FSW)(搅拌摩擦焊)Whereas in conventional friction welding,heating of interfaces is achieved through friction by rubbing two contacting surfaces,in the FSW process,a third body is rubbed against the two surfaces to be joined in the form of a small rotating nonconsumable tool that is plunged into the joint.The contact pressures cause frictional heating,raising the temperature to the range of 230 to 260.The probe at the tip of the rotating tool forces heating and mixing or stirring of the material in the joint.,Figure 28.4 The principle of the friction stir welding process.Aluminum-alloy plates up to 75 mm(3 in.)thick have been welded by this process.Source:TWI,Cambridge,U.K.,FSW of Steal Pipes,FSW process,Processes Capabilities The welding equipment can be a conventional,vertical spindle milling machine（立式铣床）and the process is relatively easy to implement.The thickness of the welded material can be as little as 1 mm and as much as 30mm or so.FSW welds are of high quality,with minimal pores and with uniform material structure.The welds are produced with low heat input and,therefore,low distortion and little micro-structural changes.There are no fumes or spatter produced and the process is suitable for automation.,28.5 Resistance Welding(RW)（电阻焊）The category resistance welding covers a number of processes in which the heat required for welding is produced by means of electrical resistance across the two components to be joined.H=I2RtConsider the heat lose,the effective heat becomes He=I2RtK,The resistances include electrode resistance,workpiece resistance,and contact(electrode-workpiece,workpiece-workpiece)resistances which are not constant in welding.,The factor K is less than 1,depending on the material to be welded.,The actual temperature rise at the joint depends on the specific heat（比热）and on the thermal conductivity of the metals to be joined.Similar or dissimilar metals can be joined by RW.These processes have major advantages,such as not requiring consumable electrodes,shielding gases,or flux.RW processes require specialized machinery,much of it is now operated by programmable computer control.,28.5.1 Resistance Spot Welding(RSW)（电阻点焊）In RSW,the tips of two opposing solid cylindrical electrodes(电极）touch a lap joint（搭接接头）of two sheet metals,and resistance heating produces a spot weld.In order to obtain a strong bond in the weld nugget(熔核，焊核），pressure is applied until the current is turned off.Accurate control and timing of the electric current and of the pressure are essential in RSW.,The welding process,Figure 28.5(a)Sequence in resistance spot welding.(b)Cross-section of a spot weld,showing the weld nugget and the indentation of the electrode on the sheet surfaces.This is one of the most commonly used process in sheet-metal fabrication and in automotive-body assembly.,The strength of the bond depends on surface roughness and on the cleanness of the mating surfaces（接合面）.Oil,paint,and thick oxide layers should therefore,be removed before welding.The weld nugget is generally 6 to10 mm in diameter.The surface of the weld spot has a slightly discolored indentation（压坑，压痕）.Currents range from 3000A to 40000A,depending on the materials being welded and on their thicknesses.The shape and surface condition of the electrode tip and the accessibility（可达性）of the site are important factors in resistance spot welding.,Welding Machine Design,Figure 28.6(a)Schematic illustration of an air-operated rocker-arm spot-welding machine.Source:American Welding Society.(b)and(c)Electrode designs for easy access into components to be welded.,Examples of Spot Welding,(c),Figure 28.7(a)and(b)Spot-welded cookware and muffler.(c)An automated spot-welding machine with a programmable robot;the welding tip can move in three principal directions.Sheets as large as 2.2 m X 0.55 m(88 in.X 22 in.)can be accommodated in this machine.Source:Courtesy of Taylor-Winfield Corporation.,Spot Welding Example,Figure 28.8 Robots equipped with spot-welding guns and operated by computer controls,in a mass-production line for automotive bodies.Source:Courtesy of Cincinnati Milacron,Inc.,Process Capabilities Welding may be performed by means of single or multiple pairs of electrodes（相应多点焊采用多对电极）(a variety of electrode shapes are used),and the required pressure is supplied through mechanical or pneumatic(气动的）means;Spot welding is widely used for fabricating sheet metal parts.Automobile bodies(车身)can have as many as 10000 spot welds;Modern spot-welding equipment is computer controlled for optimum timing of current and pressure;its spot-welding guns are manipulated（操作）by programmable robots.,28.5.2 Resistance Seam Welding(RSEW)电阻缝焊 Resistance seam welding is a modification of spot welding wherein the electrodes are replaced by rotating wheels or rollers（滚轮或辊子）.Using a continuous AC(others:DC or Pulsed Current)power supply,the electrically conducting rollers produce a spot weld whenever the current reaches a sufficiently high level in the AC cycle.These spot welds actually overlap into a continuous seam and produce a joint that is liquid-tight and gas-tight（密封的）.,Figure 28.9(a)Seam-welding process in which rotating rolls act as electrodes.(b)Overlapping spots in a seam weld.(c)Roll spot welds.(d)Resistance-welded gasoline tank.,Process capabilities:The RSEW process is used to make the longitudinal side seam（纵缝）of cans for household products（家用产品）,mufflers（消声器）,gasoline tanks（油箱）,and other containers（容器）;It is used for welding sheet plate(1.5mm)of ferrous and nonferrous metals;The typical welding speed is 1.5 m/min for thin sheet.Shunt Heat Accumulation-Programmed current Rotation,electric conduction,28.5.3 High-Frequency Resistance Welding(HFRW)High-frequency resistance welding（高频电阻焊）is similar to seam welding,except that high-frequency current(up to 450 kHz)is employed.Squeeze roll(挤压辊），apex(接合点、顶点），high-frequency coil(高频感应圈）,Figure 28.10 Two methods of high-frequency butt welding of tubes.,28.5.4 Resistance Projection welding(RPW）电阻凸焊 In RPW,high electrical resistance at the joint is developed by embossing one or more projections（冲凸点）on one of the surfaces to be welded.The projections may have different shapes for design or strength purposes.High localized temperatures are generated at the projections,which are in contact with the flat mating part.The electrodes,are of copper-based alloys,and water-cooled to keep their temperature low,are large and flat.Weld nuggets similar to those in spot welding are formed as the electrodes exert pressure to compress the projections.What is different comparing RPW to RSW?,Electrode,Mechanical(electrode movement),Current（step up）,Figure 28.11(a)Schematic illustration of resistance projection welding.(b)A welded bracket.(c)and(d)Projection welding of nuts or threaded bosses and studs.(e)Resistance-projection-welded grills.,Process Capabilities Spot welding equipment can be used for RPW by modifying the electrodes;The process produces a number of welds in one pass,extends electrode life,and is capable of welding metals of different thicknesses;Nuts and bolts can be welded to sheet and plate by this process;joining of a network of wires can also be done by this process.metal basket（金属篮）,grills（烤架）,oven rack（炉架）,shopping cart（购物车）,28.5.5 Flash Welding(FW)(闪光焊)In FW,also called flash butt welding(闪光对焊)，heat is generated from the arc as the ends of the two members begin to make contact and develop an electrical resistance at the joint.After the proper temperature is reached and the interface begins to soften,an axial force is applied at a controlled rate,and a weld is formed by plastic deformation of the joint.Some metal(flash)is expelled from the joint as a shower of sparks during the process.Contact and back(arc)duration of high current(a shower of sparks)heating until interface soften axial force(plastic deformation,molten metal expelled from joint),The features of the Process:Impurities and contaminants（杂质与污染物）are squeezed out（挤出）during this operation,so the quality of the weld is good.A significant amount of material may,however be burned off（烧掉）during the welding process.(material loss)The joint may later be machined to improve its appearance（外观）.(remove burr 毛刺)The machines for FW are usually automated and large,with a variety of power supplies ranging from 10kVA to 1500kVA.,Process Capabilities The flash-welding process is suitable for end-to-end or edge-to-edge joining of sheets of similar or dissimilar metals 0.2 mm-25 mm thick and for end joining of bars 1 mm-75 mm in diameter.The process can be automated for reproducible welding operations.Typical applications are the joining of pipe and of tubular shapes for metal furniture and windows.The required operator skill is minimal.,Note the design of uniform cross-section at the joint.（the same cross-section),28.5.6 Stud Welding(SW螺柱焊)Stud welding,also called stud arc welding,is similar to flash welding（but structure different).The stud,which may be a small part or a threaded rod（螺杆）or hanger（挂钩）,serves as one of the electrodes while being joined to another component,which is usually a flat plate.In order to concentrate the heat generated,prevent oxidation,and retain the molten metal in the weld zone,disposable ceramic ring（一次性的陶瓷环）is placed around the joint.The equipment for SW can be automated,with various controls for arcing and for applying pressure.Structure different from FW,Figure 28.13 The sequence of operations in stud welding,which is used for welding bars,threaded rods,and various fasteners onto metal plates.,28.5.7 Percussion Welding(PEW)冲击焊，电容储能焊Energy is stored in capacitorand then is discharged within 1-10 ms during weldingFor high conductive materials(Cu，Al and so on),常见点焊电流波形,Precise Resistance Welding,28.6 Explosion Welding(EXW)爆炸焊 In EXW pressure is applied by detonating（引爆）a layer o