Welding Design and Process Selection Waseem Akram
The earliest examples come from the Bronze Age. Small gold circular boxes were made by pressure welding lap joints together. It is estimated that these boxes were made more than 2000 years ago. During the Iron Age the Egyptians and people in the eastern Mediterranean area learned to weld pieces of iron together. Many tools were found which were made approximately 1000 B.C.
Why is Good Design so important? Operating conditions and application requirements are essential elements of suitable design. Both safety and service life depend upon good Welding-design for stability and functionality. Welding- design satisfactory for a certain application may not be adequate for a different one, depending on service conditions. Modern trends indicate a growing need in Welding-design team activity, to satisfy requirements covering different disciplines that cannot possibly be mastered by a single individual. At minimum, the chief designer should make sure to seek advice from expert professionals for their Welding-design review.
What is in Material Selection? Material selection is a complex procedure which has to consider, besides standard mechanical properties and manufacturing constraints, also requirements for resistance to corrosion or weathering agents, need for protection, finishing and ease of maintenance, as well as availability and economy of production. Ease of manufacturing and of welding.
Basically adhasive bonding is a nonmetalic material used to fill the space between the surface between to be joind.
Adhasive are inexpensive Weight less Comparable strength Low temperature Good load distribution Fatigue resistance Stop to crack in material Give protection against galvonic corrision
With adhasive bonding we can joined in a wide variety of sizes, shapes and thickness Delicate material such as foils can be joined to each other Heat sensitive material can be joined without damage
There is no universal adhesive Most industrial material are not stable above 180C (350F) Some adhesive shrink significantly during curing Adhesively bonded joints cannot be readily disassembled High strength adhesive are brittle
Brazing is a metal- joining process whereby a filler metal or alloy is heated to melting temperature above 450 °C (840 °F) and distributed between two or more close-fitting parts by capillary action.
The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere or flux. It then interacts with a thin layer of the base metal (known as wetting) and is then cooled rapidly to form a sealed joint.
Any substance introduced in the smelting of ores to promote fluidity and to remove objectionable impurities in the form of slag. Materials used as fluxes are limestone, silica, dolomite, lime, borax, and fluorite.
Torch brazing is by far the most common method of mechanized brazing in use. Torch brazing is performed with the help of torch torch pin is placed near the material and some filler material is used this filler material is melted and filled between plates and gives us a joint.
Furnace brazing is a semi- automatic process used widely in industrial brazing operations due to its adaptability to mass production and use of unskilled labor. There are many advantages of furnace brazing over other heating methods that make it ideal for mass production. The process also offers the benefits of a controlled heat cycle and no need for post braze cleaning
If silver alloy is used, brazing can be referred to as 'silver brazing'. These silver alloys consist of many different percentages of silver and other compounds such as copper, zinc and cadmium.
In another similar usage, brazing is the use of a bronze or brass filler rod coated with flux together with an oxyacetylene torch to join pieces of steel.The American Welding Society prefers to use the term braze welding for this process
Dip brazing is especially suited for brazing aluminum because air is excluded, thus preventing the formation of oxides. The parts to be joined are fixtured and the brazing compound applied to the mating surfaces, typically in slurry form.
Since brazing does not melt the base metal of the joint, it allows much tighter control over tolerances and produces a clean join without the need for secondary finishing. The strength of the brazed joint is likely to be less than that of the base metal(s) but greater than the filler metal. Another disadvantage is that brazed joints can be damaged under high service temperatures.
There are several techniques for joining plastic parts. Equipment cost and labor for each method vary considerably. Most techniques have limits on the sizes and types of plastic that can be joined
Mechanical fasteners (screws, rivets, pins, sheet-metal nuts) are the most common joining method. They require a plastic that can withstand the strain of fastener insertion and subsequent high stress around the fastener. Conventional machine screws are rarely used except with extremely strong plastic.
Fusion bonding: Plastic parts too complex or large to be fabricated on available molding equipment are sometimes made as subcomponents and welded together by fusion bonding. Holding fixtures ensure accurate mating and alignment of the parts to be joined.
Hot-gas welding: This is a low-speed process for fabricating large structural parts from sheet stock. A thermoplastic rod is heated with the parts to be joined until they soften and can be pushed together. The heat source is usually an inert gas. Top speed on long, straight welds is about 40 in./min. Intricate parts require more time. Operator skill is critical for both weld strength and appearance.
Vibration welding: Vibration welding produces pressure-tight joints in circular, rectangular, or irregularly shaped parts made from almost any thermoplastic material -- even in dissimilar materials having a melt-temperature spread as great as 100°F. The process is particularly suited for hollow, container-type components having the weld joint in a single plane.
Solvent bonding: Plastics are softened by coating them with a solvent, then clamped or pressed together. The plastic molecules mix together, and the parts bond when the solvent evaporates. This process is limited to thermoplastics. Fusion time is a function of the solvent's evaporation rate and may be shortened by heating.
Ultrasonic welding: Pulses are transmitted to the part by a resonant vibrating tool called a horn, causing two plastic materials to vibrate against each other. Vibration heats and fuses the parts together. Plastic products including blends or alloys of different resin families can be joined by ultrasonic welding. Such dissimilar parts should be designed carefully, and both the resin and equipment suppliers should become involved early to ensure that ultrasonic techniques can produce a suitable bond.
Ultrasonic welding is fast. Assembly rates of more than 25 parts/min are possible with a single station. There are no secondary operations, such as coating, inserting, or cleaning. The process requires fairly rigid materials. Dissimilar-material sonic welds can be made, but the melting temperatures of both materials must be quite close, otherwise only the lower-melting material will soften and a bond will not form.
flux acts as a wetting agent in the soldering process, reducing the surface tension of the molten solder and causing it to better wet out the parts to be joined
Hard soldering Soft soldering Pipe soldering Mechanical and aluminum soldering Stained glass soldering
Low power is required Low process temperature Microstructure is not affected by heat Easily automated process; Dissimilar materials may be joined Thin wall parts may be joined Moderate skill of the operator is required
Careful removal of the flux residuals is required in order to prevent corrosion; Large sections cannot be joined; Fluxes may contain toxic components; Soldering joints can not be used in high temperature applications; Low strength of joints
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