ME 330 Manufacturing Processes WELDING PROCESSES

Overview of processes

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

Welding Process in which two (or more) parts are coalesced at their contacting surfaces by application of: Heat and pressure Some welding processes use a filler material added to facilitate coalescence

Principle of welding Assembly 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. Add pic of assembly by no fasteners Or give example

Principle of welding Fusion welding (FW) Heat materials to melt the materials of compositions and melting points. Due to the high-temperature phase transitions inherent to these processes, a heat-affected zone is created in the material Add pic of assembly by no fasteners Or give example

Solid State welding (SSW) Principle of welding Solid State welding (SSW) On the interface between two materials there is no melting that happens but the interface of materials is reconfigured to form many structure. Add pic of assembly by no fasteners Or give example

Two Categories of Welding Processes Fusion welding - coalescence is accomplished by melting the two parts to be joined, in some cases adding filler metal to the joint Examples: arc welding, oxyfuel gas welding, resistance spot welding Solid state welding - heat and/or pressure are used to achieve coalescence, but no melting of base metals occurs and no filler metal is added Examples: forge welding, diffusion welding, friction welding

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"

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.

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

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

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. - Uses an electric arc to generate heat - Electric arc melts the metal parts that you are welding & it also melts the filler metal to increase the strength of the weld joint

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

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

Two Basic Types of Arc Welding (Based on Electrodes) Consumable electrodes consumed during 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

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 reaction Arc shielding is accomplished by Shielding gases, e.g., argon, helium, CO2 Flux

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.

Consumable Electrode AW Processes Shielded Metal Arc Welding (or Stick Welding) Gas Metal Arc Welding (or Metal Inert Gas Welding) Flux‑Cored Arc Welding Electro-gas Welding Submerged Arc Welding 2 main processes are:

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.

SMAW Applications Used for steels, stainless steels, cast irons, and certain nonferrous alloys. Not used or rarely used for 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. good for all purpose welding

AR: 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

Gas Metal Arc Welding

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.

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.

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

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 used, it is added to weld pool from separate rod or wire. Applications: aluminum and stainless steel mostly. High cost for welding system: $4000.

Gas Tungsten Arc Welding Filler rod Filler rod is fed separate

Advantages and Disadvantages of GTAW 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

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.

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

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

Oxyacetylene Welding

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

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

Solid State Welding (SSW) Summary 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