Soldering Brazing

Objectives To understand Soldering, Brazing Laser Welding

PRINCIPLE

Capillary action

Introduction Brazing and soldering are joining processes that use a combination of heat, filler metal, and typically a flux to join many similar and dissimilar materials. The essential difference between brazing and soldering is the melting temperature of the filler metal. Brazing filler metals melt above 840o F / 450 o C while solder filler metals melt below that temperature. In all cases filler metal melting temperatures are below the melting temperatures of the work pieces being joined.

MATERIALS USED IN BRAZING The most common filler metals used in brazing include: • Aluminum-silicon • Copper • Copper-phosphorus • Magnesium • Silver • Nickel alloys

Soldering process The joint area is cleaned and fluxed. A heat source is used to raise the temperature of base metal above the filler metal (>840 0F) The filler metal should melt due to the heat of the metal, not due to the heat source. The filler metal flows to the joints and adheres to the surface. The heat source is removed then the filler metal solidifies, bonding the surfaces together.

Soldering and Brazing Methods Grouped according to method of applying heat: Torch (TB) Furnace Induction Dip

Brazing Methods • Torch brazing - uses a oxyfuel gas on previously fluxed joints. Usually a manual operation, but can be automated. • Furnace brazing - a high production method where fixtured parts preloaded with filler metals and, when needed, flux are put in a furnace. The furnace may be either a single batch model or a conveyor model for continuous brazing. • Dip brazing - assembled parts are typically dipped in a heated chemical bath which serve as both fluxing agent and heat source to melt pre-applied filler material. • Induction brazing – a process that uses inductor coils to induce an alternating current into and around a pre-assembled part. The electrical resistance of the part generates the heat to melt the filler metal.

Brazing advantages • The joining of dissimilar metals, and materials • Very thin material can be brazed which would otherwise be damaged by welding • Inaccessible joints can more easily be brazed • Brazing is easily and more economically automated than many welding processes

Soldering/Brazing Applications Steps in Sweat Soldering 1) Copper pipe is cleaned 2) Flux is applied 3) Heat is applied 4) Solder is added 5) Solder is drawn into fitting via heat (capillary Action) 6) Pipe is wiped cleaned 7) Brazing steps are the same except for Brazing filler metal s added instead of solder.

Braze Welding Steps in Braze Welding 1) Base material is cleaned 2) Flux is applied 3) Heat is applied 4) Braze is added 5) Braze material is added into a joint. Capillary Action is not used. 6) Post Braze weld is cleaned

Advantages of Soldering and Brazing Some advantages of soldering and brazing: Low temperature Permanently or temporarily joined Dissimilar materials can be joined Speed of joining Less chance of damaging parts Slow rate of heating and cooling Parts of varying thicknesses can be joined Easy realignment Disadvantage Service Temp!!!!!!!!!!!!!!!!!

Mechanical Properties

Tensile and Shear Strength Tensile strength of a joint is its ability to withstand being pulled apart Brazed joints have a tensile strength 4-5 times higher than the filler metal itself As joint spacing decreases, surface tension increases the tensile strength Shear strength is ability of a joint to withstand a force parallel to the joint For a solder or braze joint, the shear strength depends upon the amount of overlapping area The greater the area overlapped, the greater the strength

Ductility Ductility is the ability of a metal to plastically deform without breaking or fracturing, with the cohesion between the molecules remaining sufficient to hold them together to bend without failing. Most soldering and brazing alloys are ductile metals

Fatigue Resistance Fatigue resistance is the ability to be bent repeatedly without exceeding the elastic limit Elastic Limit Plastic Limit For most soldering or brazing joints, fatigue resistance is low Fatigue failures may occur as a result of vibration and/or cycles of load.

Fluxes Fluxes used in soldering and brazing have three major functions: Remove oxides that result from heating parts Promote wetting Aid in capillary action (if soldering or brazing) Flux must be thin, when heated to its reacting temperature Fluxes are available in many forms Paste Liquid Powder

Furnace Soldering and Brazing Advantages of using a furnace: Furnace brazing is a semi-automatic process Temperature control Controlled atmosphere (Common atmospheres used include: inert, reducing or vacuum atmospheres all of which protect the part from oxidation) Uniform heating Mass production Disadvantages of using a furnace: Size Heat damage

Figure 31-20 Furnace brazing permits the rapid joining of parts on a production basis.

SOLDERING ALLOYS- Tin-lead Most popular solder Least expensive Most commonly used on electrical connections Never used for water piping

Laser welding Laser beam welding (LBW) is a welding technique used to join multiple pieces of metal through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume applications using automation, such as in the automotive industry. It is based on keyhole or penetration mode welding.