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ME 330 Manufacturing Processes WELDING PROCESSES

ME 330 Manufacturing Processes WELDING PROCESSES. Overview of processes. Principle of the process Process Process modeling Defects Design For Manufacturing (DFM) Process variation. Welding.

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ME 330 Manufacturing Processes WELDING PROCESSES

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  1. ME 330Manufacturing ProcessesWELDING PROCESSES

  2. Overview of processes

  3. Principle of the process Process Process modeling Defects Design For Manufacturing (DFM) Process variation

  4. Welding • Process in which two (or more) parts are coalesced at their contacting surfaces by application of: • Heat • Pressure • Heat and pressure combination • Some welding processes add a fillermaterial to facilitate coalescence

  5. Principle of welding Assemble two parts together by creating a fusion and/or deformation in the interaction area, which is further based on the physics laws such as fusion and solid state deformation.

  6. Fusion welding (FW) Principle of welding Heat two contacting materials to melt their interface. Due to the high-temperature phase transitions in the materials, a zone is created on the interface, which contains both materials (due to the fusion process). This zone is called heat-affected zone.

  7. Solid State welding (SSW) Principle of welding On the interface between two materials there is no melting that happens but the interface of materials is reconfigured to form an interlocks structure. This principle may be called solid material fusion principle.

  8. Two Categories of Welding Processes • Fusion welding - coalescence is accomplished based on the molten material fusion principle. • Examples: arc welding, oxyfuel gas welding, resistance spot welding • Solid state welding – coalescence is accomplished based on the solid material fusion principle (materials are not in a molten state). • Examples: forge welding, diffusion welding, friction welding

  9. The general function of welding • Provides a permanent joint • One of the most economical ways to join parts in terms of material usage and fabrication costs Mechanical fastening usually requires additional hardware (e.g., screws) and geometric alterations of the assembled parts (e.g., holes) • Not restricted to a factory environment Welding can be accomplished "in the field"

  10. Limitations and Drawbacks of Welding • Most welding operations are performed manually and are expensive in terms of labor cost. • Most welding processes utilize high energy and are inherently dangerous. • Welded joints do not allow for convenient disassembly. • Welded joints can have quality defects that are difficult to detect.

  11. Welding Fusion Welding (FW) Solid State Welding (SSW) Arc Welding (AW)

  12. Principle of the process Structure and configuration Process modeling Defects Design For Manufacturing (DFM) Process variation

  13. Fusion Welding: Arc Welding (AW) A fusion welding process in which coalescence of the metals is achieved by the heat from an electric arc between an electrode and the work • Electric energy from the arc produces temperatures ~ 10,000 F (5500 C), hot enough to melt any metal. • Most AW processes add filler metal to increase volume and strength of weld joint.

  14. Fusion Welding: Arc Welding (AW) A pool of molten metal is formed near electrode tip, and as electrode is moved along joint, molten weld pool solidifies in its wake

  15. Welding Fusion Welding (FW) Solid State Welding (SSW) Arc Welding (AW) Consumable electrodes Non-consumable electrodes

  16. Two Basic Types of Arc Welding (in terms of type of electrodes) • Consumable electrodes • consumedduring welding process • added to weld joint as filler metal • in the form of rods or spools of wire • Non-consumable electrodes • not consumed during welding process but does get gradually eroded • filler metal must be added separately if it is added

  17. Arc welding (AW): Arc Shielding • At high temperatures in AW, metals are chemically reactive to oxygen, nitrogen, and hydrogen in air • Mechanical properties of joint can be degraded by these reactions • Arc must be shielded from surrounding air in AW processes to prevent these reactions • Arc shielding is accomplished by • Shielding gases, e.g., argon, helium, CO2 • Flux

  18. Arc welding (AW): Flux • A substance that prevents formation of oxides and other contaminants in welding, which comes from • granules that are created from the welded material. • a coating on the stick electrode that melts during welding to cover operation. • a core that is within tubular electrodes and is released as electrode is consumed. • Melts during welding to be liquid slag that hardens when cooled. The slag should be removed for a clean look by brushing or grinding off.

  19. Consumable Electrode AW Processes • Shielded Metal Arc Welding (or Stick Welding) • Gas Metal Arc Welding (or Metal Inert Gas (MIG) Welding) • Flux‑Cored Arc Welding • Electro-gas Welding • Submerged Arc Welding

  20. AW: Consumable: Shielded Metal Arc Welding (SMAW) • Uses a consumable electrode consisting of a filler metal rod and coating around rod. • Coating composed of chemicals that provide flux and shielding. • Low cost welding system: Power supply, connecting cables, and electrode holder available for $300 to $400.

  21. SMAW Applications • Used for steels, stainless steels, cast irons, and certain nonferrous alloys. • Not used or rarely used for aluminum and its alloys, copper alloys, and titanium. • Can be used in windy weather. • Can be used on dirty metals (i.e. painted or rusted surfaces). • Good for repair work. • Makes thick welds. They are too reactive to the oxygen, nitrogen, hydrogen in air, and the approach is not effective to them.

  22. AW: Consumable: Gas Metal Arc Welding (GMAW) or Metal Inert Gas (MIG) Welding Uses a consumable bare metal wire as electrode with shielding by flooding arc with a gas • Wire is fed continuously and automatically from a spool through the welding gun. • Shielding gases include argon and helium for aluminum welding, and CO2 for steel welding. • Bare electrode wire (no flux) plus shielding gases eliminate slag on weld bead. No need for manual grinding and cleaning of slag • Medium cost welding system: $1000 to $1200

  23. Gas Metal Arc Welding

  24. GMAW Advantages over SMAW • Continuous welding because of continuous wire electrode. Sticks must be periodically changed in SMAW. • Higher deposition rates. • Eliminates problem of slag removal. • Can be readily automated. • Has better control to make cleaner & narrower welds than SMAW.

  25. GMAW Applications • Used to weld ferrous and various non-ferrous and metals. • Good for fabrications such as frames and farm equipment. • Can weld thicker metal (not as thick as SMAW). • Metal must be clean to start weld.

  26. Non-consumable Electrode Processes • Gas Tungsten Arc Welding • Plasma Arc Welding • Carbon Arc Welding • Stud Welding

  27. AW: non-consumable: Gas Tungsten Arc Welding (GTAW) or Tungsten Inert Gas (TIG) Welding Uses a non-consumable tungsten electrode and an inert gas for arc shielding • Melting point of tungsten = 3410C (6170F). • Used with or without a filler metal. When filler metal is used, it is added to weld pool from separate rod or wire. • Applications: aluminum and stainless steel mostly. • High cost for welding system: $4000.

  28. Gas Tungsten Arc Welding Filler rod

  29. Advantages and Disadvantages of GTAW Advantages: • High quality welds for suitable applications - Welds are cleaner and narrower than MIG • No spatter because no filler metal through arc • Little or no post-weld cleaning because no flux Disadvantages: • More difficult to use than MIG welding • More costly than MIG welding

  30. GTAW Applications • Used to weld ferrous and various non-ferrous and metals. • Can weld various dissimilar metals together. • Good for fabrications such as aircraft or race car frames. • Used for welding thinner metal parts (not as thick as MIG). • Metal must be very clean to start weld.

  31. Welding Fusion Welding (FW) Solid State Welding (SSW) Arc Welding (AW) Oxyfuel gas welding

  32. Oxyfuel Gas Welding (OFW) Group of fusion welding operations by a high temperature flame that burns various fuels mixed with oxygen • Oxyfuel gas is also used in flame cutting torches to cut and separate metal plates and other parts • Most important OFW process is oxyacetylene welding (has high temperatures – up to 3480C) • Filler metal is sometimes added • Composition must be similar to base metal • Filler rod often coated with flux to clean surfaces and prevent oxidation • Low cost for welding system: $400

  33. Oxyacetylene Welding

  34. Oxyacetylene Torch • Maximum temperature reached at tip of inner cone, while outer envelope spreads out and shields work surface from atmosphere • Shown below is neutral flame of oxyacetylene torch indicating temperatures achieved

  35. Oxyacetylene Gas Welding Applications • Suitable for low quantity production and repair jobs • Used for welding thinner parts

  36. Summary Welding Fusion Welding (FW) Solid State Welding (SSW) Shielding Flux Oxyfuel welding Arc welding Consumable electrodes Non-consumable electrodes Various welding processes (AW) are developed to address the two issues: shielding and flux

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