| As one of the most important parts of Proton Exchange MembraneFuel Cell, metal bi-polar plate supports fuel cell stacks and provides flowchannel for fuel and cooling water. One piece of metal bi-polar plateconsists of two connected single metal bi-polar plates which are made of0.1mm thick stainless steel by stamping and have complex channelstructure. The connection method and technical parameters have greatinfluence on the shape error and joint property of metal bi-polar plate.Therefore, how to ensure the quality of connectivity of metal bi-polarplate is one of the key issues in manufacturing process of ProtonExchange Membrane Fuel Cell.With high beam quality and fast weld speed, fiber laser welding is seenas the main connection method for metal bi-polar plate. However, as thesingle metal bi-polar plate is made of0.1mm thick stainless steel, in thewelding process, with high heat input, stainless steel plates in weld regionare prone to warp and generate clearance, which lead to weak jointingand burn-through problem. Meanwhile, in the welding process, under thecoupled effect of factors such as heat input, forming precision andcomplex channel structure of single metal bi-polar plate, there is obviousand complex weld deformation which cause unevenly distribution ofassembling pressure and decrease the performance of the cell.To the problem of weld joint property and weld deformation, this paperintroduced laser weld bonding into the connection process for metalbi-polar for the first time. The complete process, established in this paperand including laser weld bonding system, parameters of adhesive processand parameters of laser welding process, can meet the weld joint property,minimize weld deformation. With the system, influence of parameters (laser power, weld speed and flow rate of shield gas)on jointperformance(surface appearance, cross-section dimensions,microstructure and Corrosion resistance) was studied and suitable laserweld bonding parameters window for metal bi-polar plate weredetermined. On that basis, influence of heat input and clamping force onangular deformation of weld bead were studied. Meanwhile, anassessment method of weld deformation of metal bi-polar plate wasestablished. It combined digital holographic interferometry and surfacereconstruction program. With this method, influence of heat input andclamping force on angular deformation of metal bi-polar plate werestudied.The main contents are as follows:a) The establishment of laser weld bonding process and developmentof process parametersLaser weld bonding process which combined adhesive process andlaser welding process was established.3M instant dry structuraladhesive was used as adhesive in laser weld bonding process. WithHydraulic control system, under the condition of0.5T hydraulic forceand210s pressing time, the thickness of adhesive was controlled at10μm±2μm. The fiber laser weld system was established. Laserwelding parameters such as laser power(100W-220W), weldspeed(30mm/s-50mm/s) and shield gas(Ar,0L/mim-20Lmin) werecontrolled precisely.b) Experimental research on performance of weld bead of laser weldbonding for metal bi-polar plateBased on laser weld bonding system, the influence of parameterson performance of weld bead and relations of interaction betweenlaser heat input and adhesive were investigated. Suitable laser weldbonding parameters window for metal bi-polar plate were determined.The research result shows that: in laser welding process, there isair-gap layer between two metal plates in overlap join and the shapeof fusion zone is T-shaped in cross section of weld bead. In laser weldbonding process, adhesive take the place of air-gap layer, promotetransfer of heat from top plate to bottom plate. The shape of fusion zone is wedge-shaped in cross section of weld bead. Compared withlaser welding process, in laser weld bonding process, the penetrationof weld bead increases by100%, the weld width increases by26%and the surface smoothness decreases but can still meet the weld jointproperty. In laser weld bonding process, when laser power is from130W to160W, weld speed is40mm/s and shield gas flow rate is10L/min, weld bead meet the weld joint property for metal bi-polarplate can be received.c) Assessment and control method of weld deformation of metalbi-polar plateInfluence of heat input and clamping force on angular deformationof weld bead were studied. An assessment method of welddeformation of metal bi-polar plate was established. It combineddigital holographic interferometry and surface reconstruction program.With this method, influence of heat input and clamping force onangular deformation of metal bi-polar plate were studied. Theoptimum laser weld bonding processing parameters was determined.The research result shows that: compared with laser welding process,in laser weld bonding process, adhesive take the place of air-gap layer,promote transfer of heat from top plate to bottom plate, decreasedeformation caused by lateral heat spreading. Two single metalbi-polar plates were connected by adhesive, so clamping forcedecrease and weld deformation decrease. The research result showsthat: compared with laser welding process, in laser weld bondingprocess, angular deformation of weld bead decrease by60%. With theoptimum laser weld bonding processing parameters(laser power130W, weld speed40mm/s, shield gas flow rate10L/min, Clampingforce1.1Mpa.), arch level of metal bi-polar plate weld deformationdecrease by33%, dispersion level of metal bi-polar plate welddeformation(a, b) increase by53%and102%. |
