TECHNIQUES FOR JOINING DISSIMILAR MATERIALS METALS AND

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Techniques for joining dissimilar materials metals and polymers 153. Fig 1 Joining methods for dissimilar materials adapted from 10. the formation of complex shapes in the molding pro topic summarizing the advantages and disadvan. cess 8 tages of the approaches and techniques discussed. In structural applications it is therefore impor, tant to maximize effectively the joint contribution of 2 JOINING METHODS FOR. each material in order to ensure optimal mechani DISSIMILAR MATERIALS. cal performance while still maintaining a weight and. a cost effective solution 8 However joining of dis Several joining techniques exist for hybrid joints. similar materials is often difficult to achieve and the between metal and polymer workpieces These. behavior of such joints is rarely fully understood methods are divided into groups as shown in Fig 1. particularly when using bonding and heating tech adhesive bonding mechanical fastening and weld. niques The most frequently used joining methods ing 10 The processes can be utilized individually. for dissimilar materials are mechanical fastening and or combined in a single technique to ensure a suc. adhesive bonding 9 However these joining pro cessful and durable joint between the metal and. cesses present several limitations such as stress polymer in the hybrid structure It should however. concentration the demand for extensive surface be noted that these joining techniques have their. preparation extra weight material metallurgical dif advantages and disadvantages and the most ap. ferences and harmful environmental emissions propriate method will depend on application and. Promising welding techniques and approaches service requirements. for joining dissimilar materials have been developed. as a way to address problems related to traditional 2 1 Adhesive bonding. joining techniques Examples of such new emerg Adhesive bonding is a solid state joining technique. ing techniques are laser welding ultrasonic weld that relies on the formation of intermolecular forces. ing friction spot welding and friction stir welding between the workpieces and the polymeric adhe. The effective application of these processes neces sive itself for joint formation 11 Adhesive bonding. sitates an understanding of the processes and the involves the use of a polymeric adhesive which un. behavior of metals and polymers in the processes dergoes a chemical or physical reaction for even. as well as knowledge of the capability and limita tual joint formation. tions of the joining processes when joining dissimi In recent years the use of adhesive metal join. lar materials ing has grown substantially due to the development. This paper presents a comprehensive overview of high strength and tough adhesives that can with. of joining techniques for dissimilar materials found stand both static and alternating loads 12 The. in metal to metal polymer to polymer and metal to drive towards considerable weight reduction in aero. polymer joints The paper comprises four sections nautics aerospace and automotive applications has. First general concepts and the need to join dis contributed to the rapid development of this joining. similar materials are explained Second the vari method which offers unique weight reduction along. ous methods of joining dissimilar materials are pre with homogeneous stress distribution during load. sented The third part of the paper focuses on weld ing 12 However adhesive bond joints can prove to. ing of dissimilar materials Welding receives par be problematic as the bonded joints cannot be dis. ticular attention since it is an emerging technology assembled without damage Moreover the joints are. with promising future prospects in the joining of dis prone to environmental degradation from factors. similar materials The welding of metal to polymer such as moisture humidity and temperature 13. is given greater emphasis in this section than metal The most important factor limiting the use of adhe. to metal and polymer to polymer welding since sive bonding is however uncertainty in forecasting. metal to polymer is a novel technique and there are the long term durability of this kind of joint and diffi. fewer publications in this area The final section of culties in carrying out reliable non destructive test. the paper presents concluding remarks about the,154 P Kah R Suoranta J Martikainen C Magnus. ployed in the joining of plastics polymer to poly,mer and also metal to plastic 18 However it. comes with limitations such as increased compo,nent weight and evolution of stresses around fas. tener holes which induce strength degradation and,eventually create corrosion related problems 19.
Different types of mechanical joining techniques exist. for metal to plastic joints but the emphasis is cur. rently on riveting as it establishes a reliable joint. Joint configuration often depends solely on ser,Fig 2 Schematic presentation of metal to polymer. vice conditions an example is whether leak tight,riveted joint adapted from 22. ness is required In some cases the joint may be, designed to tolerate mismatch in the coefficient of. thermal expansion during assembly Joints can also, ing A further limitation is the fact that bonded joints. be made to allow complete freedom of movement in, often fail instantaneously instead of progressively.
the plane perpendicular to the clamping member,when applied in engineering structures 12. Settineri et al 21 investigated self piercing rivet. The workpiece surface properties in an adhesive, ing for metal to polymer joints Fig 2 shows a typi. bond play a vital role in the bonding process and,cal self piercing riveting procedure Experimental. bond strength and joint durability can be significantly. results showed that in rivet joining between a me,improved by surface treating the workpieces prior. tallic and polymeric material the process depends,to the bonding During surface pretreatment the.
on the geometric parameters of the rivet such as, surface energy of the workpieces increases but the. sheet thickness and tool design and the riveting,contact angle of water decreases and the surface. tension increases Typical surface pretreatment,Due to the fact that the bottom material sheet. techniques include solvent cleaning alteration of,undergoes the highest deformation it is important. surface chemistry and abrasion and other topo, to place the metallic sheet as the bottom sheet and.
graphical changes Environmental factors have a,the polymeric material as the upper sheet 23. strong influence on the durability and ultimate me. Metal to polymer hybrid joints present unique prop. chanical performance of an adhesive bond joint The. erties and efficiency in terms of design and manu,most important environmental factors are climatic. facturing flexibilities along with overall weight re. factors such as temperature and humidity,However both mechanical fastening and adhe. 2 2 Mechanical fastening sive bonding necessitate an overlapping joint con. Mechanical fastening incorporates the use of addi figuration to achieve the required joint strength which. tional clamping components without fusing the joint however increases the weight thickness and stress. surfaces It relies on the use of clamping or mem concentration of the structure 24 25 This limita. bers such as screws and rivets for eventual joint tion in joint design restricts the use of these joining. formation Features of mechanical fastening include techniques It is therefore important to develop a. 14 joining technique for dissimilar materials that has. ka heating cycle during which the rivets utilized for greater design flexibility and fabrication rates than. clamping are heated prior to the fastening so that adhesive joining and mechanical fastening 26. upon cooling the rivets shrink enabling the com, ponent to be clamped tightly 15 However the 2 3 Welding. heating is used only for some type of riveting,Conventional welding processes such as shielded.
kspecial mechanical operations required by the,metal arc welding gas tungsten arc welding gas. method such as drilling of holes making screw,metal arc welding and submerged arc welding have. threads etc prior to the joining process 16 17, been used to weld dissimilar materials in metal to. Different kinds of mechanical fastening still re,metal joints Nevertheless the high energy inputs. main the most used method in joining components, of these fusion welding processes result in material.
due to the simplicity of the process 18 Originally. metallurgical mismatch 6 thus hinder their use in,mechanical fastening was used to join metallic. dissimilar metal to metal joints as well as polymer. materials metal to metal but it can now be em,to polymer and metal to polymer joints. Techniques for joining dissimilar materials metals and polymers 155. Fig 3 Classification of polymeric materials adapted from 10. Welding of dissimilar materials with new emerg lar materials such as metal to metal polymer to. ing techniques such as laser welding ultrasonic polymer and metal to polymer. welding friction spot welding and friction stir weld. ing is somewhat more feasible because polymeric 3 1 Ultrasonic welding. materials such as elastomers thermoplastics and, thermosets 9 11 as shown in Fig 3 comprise Ultrasonic welding is a solid state joining technique. structural macromolecules that are held together that initiates coalescence via the simultaneous ap. by the Van der Waals force whereas metals con plication of localized high frequency vibration energy. sist of densely packed crystal structures with high with a moderate clamping force 29 This welding. cohesive energy 10 27 28 The melting tempera technique is characterized by low energy input and. ture of metallic materials is extremely high com requires the clamping and positioning of the. pared to the polymer melting temperature Hence workpieces between the welding tool sonotrode. polymers tend to degrade before metals melt 9 and an anvil by static force The workpieces in ul. However although thermoset and thermoplastic trasonic spot joining can be two thin sheets and. polymeric materials can be both adhesively bonded thick thin sheets combinations in a simple lap joint. and mechanically fastened welding can only be 30 or a butt joint depending on the direction of. employed on thermoplastics 9 10 This limitation supply of the energy of elastic oscillations to the. exists because the processing of thermosets and welding zone 31 Ultrasonic vibration can be ap. chemically cross linked elastomers is characterized plied to welding both metals and plastics but the. by an irreversible crosslinking reaction which results welding process differs and the actual weld achieved. in degradation hence they cannot be reshaped by depends on how the ultrasonic energy vibration is. means of heating 9 11 On the other hand ther delivered to the weld 30. moplastics and thermoplastic elastomers can be In ultrasonic metal welding the direction of ul. melted and softened by heat due to the weakening trasonic oscillation is parallel to the weld area When. of the secondary Van der Waals and hydrogen bond ultrasonic metal welding is realized the frictional. ing forces among interlocking polymer chains 9 action of the workpiece surfaces initiates a solid. This makes it possible for thermoplastics and ther. moplastic elastomers to be remolded upon applica,tion of heat and they can consequently be fusion. 3 EMERGING TECHNIQUES FOR,JOINING DISSIMILAR MATERIALS.
Efficient and effective ways of joining dissimilar. materials by welding techniques such as ultrasonic. welding laser welding and friction spot welding have. increased productivity in industries such as the au. tomobile industry and have also helped to solve prob. lems related to traditional joining techniques This. section elaborates on the principles and prospects Fig 4 Schematic comparison between ultrasonic. of such emergent techniques in welding of dissimi plastic and metal welding adapted from 30. 156 P Kah R Suoranta J Martikainen C Magnus, Fig 5 Typical specimen geometry for CFRP Al joint adapted from 30. state bond without any melting action of the the fabrication and processing of joints which previ. workpieces the reverse is the case in plastic weld ously had been difficult or impossible to achieve by. ing For ultrasonic plastic welding the direction of other welding methods 32 Recent investigations. ultrasonic oscillation is perpendicular to the weld in laser welding of dissimilar metals include laser. area as shown in Fig 4 30 Ultrasonic plastic weld welding of Ti6Al4V and lead metal and laser weld. ing brings about melting and fusion of the workpiece ing of TiNi shape memory alloy and stainless steel. material at much lower temperatures than arc or using cobalt Co filler metal In the laser welding of. laser welding processes Ti6Al4V and lead metal it was observed that the. Balle et al 30 investigated the ultrasonic metal strength of the joint obtained between the two dis. welding of aluminum sheets to carbon fiber rein similar metals was at least equal to or higher than. forced thermoplastic composites Their experiment the strength of the lead base metal 33 In laser. studied the weldability of aluminum alloy 5754 and welding of TiNi shape memory alloy and stainless. carbon fiber reinforced polymer CFRP with thick steel using Co filler metal it was noticed that the

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