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solid state welding
Solid State Welding Processes Ir Tri Prakosa, M Eng Proses Manufaktur II, Januari 2010 INTRODUCTION Institut Teknologi Bandung Introduction This lecture describes processes in which joining takes place without fusion (melting) of the workpieces Unlike the processes described in previous lecture, no liquid (molten) phase is present in the joint The principle of solid-state welding is best demonstrated with the following example Institut Teknologi Bandung Introduction If two clean surfaces are brought into atomic contact with each other under sufficient pressure and in the absence of oxide films and other contaminants they form bonds and produce a strong joint Heat and some movement of the mating surfaces by plastic deformation may be employed to improve the strength of the joint Institut Teknologi Bandung Introduction Applying external heat improves the bond by diffusion Small interfacial movements on the faying surfaces (contacting surfaces of the two pieces to be joined) disturb the surfaces, breaking up oxide films and generating new and clean surfaces, thus improving the strength of the bond Heat may also be generated by friction, which is utilized in friction welding Institut Teknologi Bandung Introduction Electric-resistance heating is utilized extensively in resistance welding processes with numerous applications In explosion welding, very high contact pressures are developed, causing welding of the interface Institut Teknologi Bandung Introduction This lecture concludes coverage of welding processes The topics of the metallurgy of welding, welding design, weld quality, and welding process selection are described next week Other joining processes such as brazing, soldering, adhesive bonding and mechanical fastening methods are covered in the next two weeks Institut Teknologi Bandung COLD WELDING (CW) Institut Teknologi Bandung Cold Welding (CW) In cold welding (CW), pressure is applied to the workpieces, either through dies or rolls Because of the plastic deformation involved, it is necessary that at least one, but preferably both, of the mating parts be ductile The interface is usually cleaned by wire brushing prior to welding Institut Teknologi Bandung Cold Welding (CW) However, in joining two dissimilar metals that are mutually soluble, brittle intermetallic compounds may form, resulting in a weak and brittle joint An example is the bonding of aluminum and steel, where a brittle intermetallic compound is formed at the interface The best bond strength and ductility is obtained with two similar materials 10 Institut Teknologi Bandung DIFFUSION BONDING (WELDING) 89 Institut Teknologi Bandung Diffusion bonding/Welding (DFW) Diffusion bonding, or diffusion welding (DFW), is a solid-state joining process in which the strength of the joint results primarily from diffusion (movement of atoms across the interface) and, to a lesser extent, small plastic deformation of the faying surfaces This process requires temperatures of about 0.5Tm (where Tm, is the melting point of the metal on the absolute scale) in order to have a sufficiently high diffusion rate between the parts being joined 90 Institut Teknologi Bandung Diffusion bonding/Welding (DFW) The bonded interface in DFW has essentially the same physical and mechanical properties as the base metal 91 Institut Teknologi Bandung Diffusion bonding/Welding (DFW) The bonded interface in DFW has essentially the same physical and mechanical properties as the base metal Its strength depends on pressure, temperature, time of contact, and the cleanliness of the faying surfaces These requirements can be lowered by using filler metal at the interfaces 92 Institut Teknologi Bandung Diffusion bonding/Welding (DFW) Although developed in the 1970s as a modern welding technology, the principal of diffusion bonding actually dates back centuries, when goldsmiths bonded gold over copper Called filled gold, a thin layer of gold foil is obtained by hammering; the gold is then placed over copper, and a weight is placed on top of it The assembly is then placed in a furnace and left until a good bond is obtained 93 Institut Teknologi Bandung Diffusion bonding/Welding (DFW) In diffusion bonding, pressure may be applied by dead weights or a press, as well as by using differential gas pressure or utilizing relative thermal expansion of the parts to be joined The parts are usually heated in a furnace or by electrical resistance High pressure autoclaves are also used for bonding complex parts 94 Institut Teknologi Bandung Diffusion bonding/Welding (DFW) Process capabilities { Diffusion bonding is generally most suitable for dissimilar metal pairs { However, it is also used for reactive metals, such as titanium, beryllium, zirconium, and refractory metal alloys, and for composite materials { Because diffusion involves migration of the atoms across the joint, this process is slower than other welding processes 95 Institut Teknologi Bandung Diffusion bonding/Welding (DFW) Process capabilities, con’t { Although DFW is used for fabricating complex parts in low quantity for the aerospace, nuclear, and electronics industries, it has been automated to make it suitable and economical for moderate-volume production { Equipment cost is related approximately to the diffusion bonded area and ranges between $3/mm2 and $6/mm2 ($2000/in.2 and $4000/in.2) { Unless the process is highly automated, considerable operator training and skill is required 96 Institut Teknologi Bandung Diffusion bonding/Welding (DFW) Application example { Diffusion bonding is especially suitable for metals such as titanium and superalloys used in military aircraft { Design possibilities allow the conservation of expensive strategic materials and reduce manufacturing costs { The military aircraft illustrated below has more than 100 diffusion-bonded parts, some of which are shown in the following Figure 97 Institut Teknologi Bandung Diffusion Bonding Applications More than 100 difussion-bonded parts 98 Institut Teknologi Bandung Diffusion bonding/superplastic forming An important development is the ability to fabricate sheet-metal structures by combining diffusion bonding with superplastic forming Typical structures in which flat sheets are diffusion bonded and formed are shown in the next Figure 99 Institut Teknologi Bandung Diffusion bonding/superplastic forming Urutan operasi pada pabrikasi berbagai struktur dengan diffusion bonding dan superplastic forming dari (aslinya) pelat lembaran Sumber: (a) After D Stephen and S.J Swadling (b) dan (c) Rockwell International Corp 100 Institut Teknologi Bandung Diffusion bonding/superplastic forming After diffusion bonding of selected locations of the sheets, the un-bonded regions are expanded into a mold by air pressure These structures are thin and have high stiffness-to-weight ratios Hence they are particularly important in aircraft and aerospace applications 101 Institut Teknologi Bandung Diffusion bonding/superplastic forming This process improves productivity by eliminating mechanical fasteners and produces parts with good dimensional accuracy and low residual stresses The technology is now well advanced for titanium structures (typically Ti-6AI-4V alloy) for aerospace applications Structures made of 7475-T6 aluminum alloy and other alloys are also being developed using this technique 102 Institut Teknologi Bandung 103 ... developed, causing welding of the interface Institut Teknologi Bandung Introduction This lecture concludes coverage of welding processes The topics of the metallurgy of welding, welding design,... Teknologi Bandung RESISTANCE WELDING 38 Institut Teknologi Bandung Resistance welding (RW) Resistance welding (RW) covers a number of processes in which the heat required for welding is produced by... Institut Teknologi Bandung Resistance Spot Welding Process capabilities { Spot welding is the simplest and most commonly used resistance welding process { Welding may be performed by means of single