1. ME 330 Manufacturing Processes WELDING PROCESSES

2. Overview of processes

3. Principle of the process
Structure and configuration
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 and pressure
Some welding processes use a filler material added to facilitate coalescence

5. 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.
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6. 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
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7. 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.
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8. 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

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. Solid State Welding (SSW)
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.
- 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

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

16. 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

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 reaction
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 Welding)
Flux‑Cored Arc Welding
Electro-gas Welding
Submerged Arc Welding
2 main processes are:

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 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

22. 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

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 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
Filler rod is fed separate

29. 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

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. Solid State Welding (SSW)
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. 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