Joining Processes Introduction, Soldering & Brazing - PDF

University of the Philippines Diliman Department of Mechanical Engineering Joining Processes  Introduction to Consolidation Processes ▪ Consolidation Processes consist of Low- High Temperature ▪ Welding ▪ Brazing Sol...

University of the Philippines Diliman Department of Mechanical Engineering Joining Processes  Introduction to Consolidation Processes ▪ Consolidation Processes consist of Low- High Temperature ▪ Welding ▪ Brazing Soldering Brazing Welding ▪ Soldering ▪ Fasteners ▪ Adhesives ▪ Shrink Fits ▪ Slots and Tabs University of the Philippines Diliman – Department of Mechanical Engineering  Soldering, Brazing and Welding University of the Philippines Diliman – Department of Mechanical Engineering  Filler metal has a melting point below 450⁰C Used for : ▪ joining thin metals Soldering ▪ connecting electronic components ▪ joining metals while avoiding exposure to elevated temperatures ▪ Filling surface flaws and defects University of the Philippines Diliman – Department of Mechanical Engineering Design an acceptable joint Selection of the correct solder for the job Six Important Selections of the proper type of flux Cleaning of the surfaces to be joined Soldering Steps Application of flux, solder and sufficient heat Removal of the flux residue University of the Philippines Diliman – Department of Mechanical Engineering Solder Joints University of the Philippines Diliman – Department of Mechanical Engineering Compatibility of Soldering University of the Philippines Diliman – Department of Mechanical Engineering Common Solder University of the Philippines Diliman – Department of Mechanical Engineering Wave Soldering Used to solder wire ends University of the Philippines Diliman – Department of Mechanical Engineering Vapor-phase Soldering Primary application is the soldering of surface mounted components to substrate materials. Also known as Vapor-phase reflow soldering Can be used to cure epoxies and stress relieve metals. University of the Philippines Diliman – Department of Mechanical Engineering Dip Soldering University of the Philippines Diliman – Department of Mechanical Engineering Brazing Permanent joining of similar or dissimilar metals or ceramics Heat + Filler metal (melting temperature above 450⁰C) University of the Philippines Diliman – Department of Mechanical Engineering Brazing Alloy ▪ Composition – significantly different from that of the base metal ▪ Strength – usually lower than that of the base metal ▪ Melting point – lower than that of the base metal ▪ Bonding – capillary action University of the Philippines Diliman – Department of Mechanical Engineering Advantages ▪ Wide range of metallic and nonmetallic materials can be brazed ▪ Process can be performed quickly and economically ▪ Reduced problems associated with HAZ, warping and distortions. University of the Philippines Diliman – Department of Mechanical Engineering Strength of Joints ▪ Depends on the following: ▪ Joint clearance – most important ▪ Temperature of the brazing process – effects of thermal expansion should be compensated when specifying the dimensions of the starting components ▪ Wettability – strong function of the surface tensions between the braze metal and the base alloy University of the Philippines Diliman – Department of Mechanical Engineering Joint Clearance in Brazing When brazing dissimilar metals, the initial joint clearance should be adjusted for the different thermal expansions (here brass expands more than steel). Proper brazing clearances should exist at the temperature where the filler metal flows. University of the Philippines Diliman – Department of Mechanical Engineering Joint Strength ▪ Typical variation of tensile strength with clearance in a butt-joint braze. (Courtesy of Handy & Harman, Rye, NY.) University of the Philippines Diliman – Department of Mechanical Engineering Common Joint Design Offers uniform thickness across the joint Offers greater bonding area and higher strength University of the Philippines Diliman – Department of Mechanical Engineering Variations of Butt and Lap Joints University of the Philippines Diliman – Department of Mechanical Engineering Common Joint Designs for Brazing University of the Philippines Diliman – Department of Mechanical Engineering Filler Metals ▪ Copper and copper alloys – most commonly used braze metal ▪ For brazing steel and other high-melting-point materials ▪ Pure silver – for brazing titanium ▪ Silver solders – used to join steels, copper, brass and nickel ▪ Aluminum-silicon alloy (with 6-12% silicon) – for brazing aluminum and other aluminum alloys ▪ Nickel-and-cobalt-base alloys – for joining assemblies that will be subjected to elevated temperature University of the Philippines Diliman – Department of Mechanical Engineering Brazing Material Families University of the Philippines Diliman – Department of Mechanical Engineering Compatibility of Brazing Materials University of the Philippines Diliman – Department of Mechanical Engineering Heating Methods used in Brazing ▪ Torch brazing ▪ Uses oxyacetylene, oxy-hydrogen or other gas flame combinations as heat source ▪ Most repair brazing utilizes this method ▪ Major drawbacks : difficulty in controlling temperature and maintaining uniformity of heating Photo: https://www.thefabricator.com/thewelder/article/as sembly/how-to-braze-in-a-six-step-process University of the Philippines Diliman – Department of Mechanical Engineering Heating Methods used in Brazing Furnace brazing ▪ Flux and filler metal are preloaded into the joints ▪ Heats the entire assembly ▪ Suited for mass production University of the Philippines Diliman – Department of Mechanical Engineering Furnace Brazing University of the Philippines Diliman – Department of Mechanical Engineering Heating Methods used in Brazing Salt-bath Brazing ▪ Parts are preheated and then dipped in a bath of molten salt maintained at a temperature slightly above the melting point of the brazing metal. ▪ Advantages: ▪ Salt bath acts as brazing flux ▪ Workpiece/ materials to be joined heats rapidly ▪ Temperature can be accurately controlled University of the Philippines Diliman – Department of Mechanical Engineering Heating Methods used in Brazing ▪ Dip brazing ▪ Assemblies are immersed in a bath of molten metal ▪ Usually employed for small products University of the Philippines Diliman – Department of Mechanical Engineering Heating Methods used in Brazing ▪ Induction brazing ▪ Utilizes high frequency induction currents as the source of heat ▪ Limited to joining electrically conductive materials University of the Philippines Diliman – Department of Mechanical Engineering Heating Methods used in Brazing ▪ Resistance Brazing ▪ Used to produce relatively simple joints in metals with high electrical conductivity ▪ Carbon or graphite electrodes provide most of the resistance University of the Philippines Diliman – Department of Mechanical Engineering Furnace Assembly Typical furnace-brazed assemblies. (Courtesy of Pacific Metals Company, a division of Reliance Steel & Aluminum, Los Angeles, CA.) University of the Philippines Diliman – Department of Mechanical Engineering Welding Consolidation of two materials by means of temperature and/or pressure to cause the materials to melt or diffuse at the joint. Can be done in a wide variety of conditions and methods and is therefore on of the most common consolidation processes. University of the Philippines Diliman – Department of Mechanical Engineering Two Forms of Welding  Solid State pressure and heat are used to cause the diffusion at the joint, causing the parts to fuse together  Fusion welding where heat is applied to create molten material at the joint, which fuses the parts upon solidification Both process can cause changes in the structure of the material, and must be considered when selecting a process University of the Philippines Diliman – Department of Mechanical Engineering Basic Joint Designs of Fusion Welds University of the Philippines Diliman – Department of Mechanical Engineering Types of Fusion Welds and Types of Joints Bead welds: Limited penetration so used on thin materials, or surface modifications Groove welds: Used on thick materials, requires joint preparation, used for single and multiple passes Fillet welds: Use for tee, lap and corner joints Plug welds: Used a permanent replacement for rivets or bolts University of the Philippines Diliman – Department of Mechanical Engineering Weld Procedures ▪ FIGURE 30-8 Various weld procedures used to produce welded joints. (Courtesy Republic Steel Corporation, Youngstown, OH). University of the Philippines Diliman – Department of Mechanical Engineering Basic Fusion Welds Preferred shape and the method of measuring the size of fillet welds. University of the Philippines Diliman – Department of Mechanical Engineering Common Weld Defects FIGURE 30-3 Some common welding defects. University of the Philippines Diliman – Department of Mechanical Engineering Zone in a Fusion Weld Heat affected zone is subjected to enough heat to cause metallurgical changes, leading to phase transformations, embrittlement, precipitation, or cracking. University of the Philippines Diliman – Department of Mechanical Engineering Microstructure of a Fusion Weld FIGURE 30-11 Grain structure and various zones in a fusion weld. University of the Philippines Diliman – Department of Mechanical Engineering  Classification of Weld Process FIGURE 30-1 Classification of common welding processes along with their AWS (American Welding Society) designations. University of the Philippines Diliman – Department of Mechanical Engineering