Welding/Brazing/Soldering
29 flashcards · Other · by Liam Kehoe
Advantages and disadvantages of soldering
Adv. Lower energy Good electrical conductivity Easily repairable Dis. Lower strength Limited series temp
Brazing design guides
Common filler materials for brazed joints
Melting temp compatible with base metal Low surface tension High fluidity No chemical and physical interactions with base metal
Disadvantage of brazing
Strength compared to welding Low service temp Color mismatch
Capillary action (joining mechanism brazing and soldering)
Pulling of liquid through small gap due to surface tension Area of contact determined by the joint gap and should be wide enough capillary action Insufficient clearance will result in poor flow and weak joint strengths If the joint gap is too large then the strength of the joint will be reduced to that of the filler metal
Alloying and spreading (joining mechanism brazing and soldering)
The strength of the joint determined by the extent of metallurgical bonding between the solder/braze and base metal NO MELTING of the base metal occurs but a reaction layer is established and responsible for holding the bonding surfaces together.
Wetting (joining mechanism brazing and soldering)
Takes place when one or more elements of the filler metal or flux react with the base metal being joined Surface oxides inhibit surface wetting and therefore, mechanical cleaning of surfaces is essential before applying a "fluxing agent"
Why brazing and soldering instead of welding?
Join non-electrical materials Join dissimilar materials Metals with poor weldability No heat damage Less warpage Not permanent
Advantages of brazing
Any metals can be joined Very thin can be joined No HAZ (heat affected zone) Inaccessible area by welding
Weld Design Considerations
Factors that affect weldability
The capacity of a metal to be welded into a suitable design and the resulting weld joint to perform satisfactorily in the intended service Welding process, base metal, filler and surface condition
Metal treatments for welding
Annealing (residual stress) Shot peening (compressive stress on the surface) Preheating (low warpage and energy input)
Weld Defects
Geometric defects Misalignment Warpage Lack of weld penetration Notches -> stress concentration Intrinsic Defects Inclusions: slags, rusts, grease on weld zone Porosity: gas entrapment due to surface or moisture on electrodes Metallurgical Defects HAZ (heat affected zone) Surface slags (oxides, fluxes)
Types of solid state welding
Forge welding (heat metals by hammering them together) Diffusion welding (Movement of atoms across the interface) Friction welding (Heat generated by friction out the interface) Ultrasonic welding (Oscillating shearing stresses to generate heat)
Oxyfuel Gas Welding
Mixture of acetylene and oxygen Acetylene: odourless but commercial acetylene has a garlic order Filler metals Versatility Control over heat input Cost-effectgive, potable, small scale project Repair works
Resistance Welding
Heat and pressure to accomplish coalescence by the electrical resistance RSW 10,000 spot welds per automobile Need to apply pressure
Laser Welding
High powered laser beam as the source of heat to produce a fusion weld without a filler material Due to the high density of energy on a small focused area, narrow and deep penetration capability Adv. No vacuum is needed Easier to automation X-rays Better quality
Electron beam welding (EBW)
High velocity, narrow-beam electron converting into heat to produce a fusion weld in a vacuum Adv. No shielding gas, flux or filler metal Deeper penetration Low HAZ and distortion No oxidation Dis. Very small comp General X-ray Expensive equipment
Types of fusion welding
Arc welding with consumable electrodes Shielded material arc welding Gas metal arc welding AW with non-consumable electrodes Gas tungsten arc welding Electron beam welding Laser welding Resistance welding Oxyfuel welding
Arc welding
Fusion welding where heat generated from electrical arc Metal must be electrically conductive Technical issues Electrodes - consumable vs. non con Arc Shielding - Surrounding by gas Power sources - Thin parts, better quality, higher temp Flux - Shielding, clean oxides
Examples of joints and welds
Different types of welding
Pros and cons of welding
Pros Fast, cheap, portable, strong, permanent No waste Using strong filler materials gives strong property than parent material Cons Skilled workers Surface prep. Dangerous (electrical, thermal hazard, radiation, fumes) Dislocation Warpage
What is welding?
A joining process of two metals that coalesced at their contact surface by application of heat/pressure (sometimes, a filler material is used to facilitate coalescence)
Joining factors for joints
Composition (mechanical, chemical and physical properties of materials being joined) Permanent/temporary joints Whether heat can be applied Strength required Size and shape of the components Degree of seal required Cost Corrosion resistance
Adhesive design guidelines
Adhesive Types
Natural Adhesives Gums, starch, dextrin, soy flour, collagen Low-stress applications, cardboard, furniture, bookbinding, plywood Inorganic Sodium silicate or magnesium oxychloride Low cost, low strength Synthetic Adhesives Various thermoplastics and thermosetting Curing mechanisms (crosslinking) Mixing catalyst or reactive ingredient with polymer prior to applying Heating, radiation, evaporation
Advantages and disadvantages adhesive bonding
Usually a polymer requiring curing sometime with heat Strength depends on the bonding Surface preparation (needs clean and rough surfaces) Adv. Variety of materials, different sizes, bonding over an entire surface, flexible adhesive, low temp curing, sealing, simple joint design Dis. Weaker bonding strength, limited service temp, curing time, no inspection method
Fluxes in brazing and soldering
Low melting temp Low viscosity Dissolve surface oxide Promote wetting Must hot react with base metals Easily remove after joining