Brazing & Soldering. Training Objective

Transcription

1 Training Objective After watching the program and reviewing this printed material, the viewer will become aware of the basic principles of brazing and soldering, the differences between the two processes, and their specific applications. Both brazing and soldering processes are explained in detail Fluxes and filler metals specific to each process are shown Both manual and automated methods are demonstrated Brazing & Soldering Fundamentals 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 840 o 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 workpieces being joined. Joining is accomplished by the flow of filler metal between closely fitted joints ranging from to of an inch, or to 0.13 of a millimeter in brazing, to to of an inch, or 0.08 to 0.15 of a millimeter in soldering. The result is a joining of the parts by capillary action as the liquid filler metal exhibits a stronger attraction to the base materials than itself. A common term for capillary action is wetting. To facilitate this wetting action a fluxing agent is commonly employed. The flux lowers the molten filler metal surface tension and inhibits the formation of oxides between the joint surfaces and the filler metal. However, flux residue is corrosive, requiring a separate post-joining cleaning operation. Soaking in hot water and/or wire brushing are tow common methods. Along with joint clearances, proper joint designs are critically important to successful brazing and soldering. The primary joint types employed are: The lap joint The flanged lap joint The butt joint The flanged butt joint For proper brazing and soldering joint cleaning is especially important. Grease, paint, rust, and any other impurities must be removed. This may be accomplished by a variety of either chemical or mechanical methods. Brazing As a joining process brazing has certain advantages over mechanical fastening and welding. These advantages include: 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 Fundamental Manufacturing Processes Study Guide, DV03PUB

2 Most ferrous, non-ferrous, and many carbides and cermets can be joined by brazing. Fluxes used in brazing consist of fluorides, chlorides, borax, borates, fluoroborates, alkalis, wetting agents and water. The fluxes may be in the form of pastes, powders, liquids, and preforms and are applied by a variety of methods. Fluxes, especially when heated, can be toxic, so adequate ventilation and safeguards are required. The most common filler metals used in brazing include: Aluminum-silicon Copper Copper-phosphorus Magnesium Silver Nickel alloys Each of these flow at specific temperatures and are available as wire, foil, paste, powders, and preforms. Filler metals typically have significantly different compositions from the materials being joined, for this reason their selection is critical to successful brazing. 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. Soldering Soldering is one of the oldest methods of joining metals. Because filler metals melt at low temperatures there is minimum part distortion and heat damage to sensitive parts. Many combinations of metal to metal, ceramic to metal, and glass to metal may be joined. Soldering is used extensively in the electronics industry where it s limited mechanical strength is not a major factor. Fluxes for soldering fall into three categories, the inorganic acid fluxes, organic fluxes, and the rosin-based fluxes. These are available as liquids, powders, pastes, solid and in flux-cored wires. Soldering fluxes may also be toxic and corrosive and require post-cleaning operations. Filler materials include combinations of tin-lead, tin-silver-lead, tin-zinc, silver-copper-zinc and zinc-aluminum alloys. Again, as with brazing filler metals, solders are supplied as wires, foil, sheets, pastes, preforms, or as bars and ingots. Fundamental Manufacturing Processes Study Guide, DV03PUB

3 Soldering Methods Iron soldering is the oldest and simplest soldering method and is still widely used today. Soldering irons have copper tips which easily stores and transfers heat to the joint. Wave soldering is a specific method used in the fabrication of electronic components and printed circuit boards (PCB). In this method, continually circulating fountains or waves of solder are lifted into contact with the joints. As only limited sections of the PCB are immersed in the solder, excess heat and distortion is controlled. Due to the high speed of the process, flux and vapor entrapment is reduced. Wave solder machines are highly automated being able to flux, preheat, solder, and remove flux residue on one continuous conveyor. Fundamental Manufacturing Processes Study Guide, DV03PUB

4 Review Questions 1. An advantage of both brazing and soldering is: a. Lower production costs b. Less operator skill needed c. Many similar and dissimilar materials can be joined d. Joints have excellent mechanical strength 2. The essential difference between brazing and soldering is the: a. Types of filler materials b. Means of automation c. Melting temperature of the filler metals d. Melting temperature of the fluxes 3. Joint clearances for both brazing and soldering commonly range from: a of an inch / of a millimeter b of an inch / of a millimeter c of an inch / of a millimeter d of an inch / of a millimeter 4. Another term for capillary action is: a. Flow b. Bonding c. Spreading d. Wetting 5. A brazing process that does not use torches, brazing furnaces or electric coils is: a. Braze welding b. Silver brazing c. Dip brazing d. Electrical bonding 6. A limitation of the soldering process is: a. Joint brittleness b. Joints are corrosion prone c. Joints retain excessive flux residue d. Lack of mechanical strength 7. Soldering is not used to join: a. Thermoplastics b. Metal to ceramics c. Metal to glass d. Ferrous to non-ferrous metals 8. In wave soldering excess heat and distortion of the PCB s is avoided by: a. The amount of flux applied before soldering b. Exposing only a small area of the board to the solder at any one time c. Using special low melting point solder d. Employing cooling fans as the boards travel through the machine Fundamental Manufacturing Processes Study Guide, DV03PUB

5 Answer Key 1. c 2. c 3. a 4. d 5. c 6. d 7. a 8. b Fundamental Manufacturing Processes Study Guide, DV03PUB