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ME 330 Manufacturing Processes WELDING PROCESSES (cont.)

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Presentation on theme: "ME 330 Manufacturing Processes WELDING PROCESSES (cont.)"— Presentation transcript:

1 ME 330 Manufacturing Processes WELDING PROCESSES (cont.)

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

3 Weld Joints: Five Types (a) Butt joint, (b) corner joint, (c) lap joint, (d) tee joint, and (e) edge joint

4 (a) Inside single fillet corner joint; (b) outside single fillet corner joint; (c) double fillet lap joint; (d) double fillet tee joint Weld Types: Fillet Welds Filler metal is used

5 ©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e (a)square groove weld; (b)single bevel groove weld; (c)single V ‑ groove weld; (d)single U ‑ groove weld; (e)single J ‑ groove weld; (f)double V ‑ groove weld (for thicker sections) Weld Types: Groove Welds Filler metal is used

6 Weld Types: Plug Weld and Slot Weld (a) Plug weld and (b) slot weld Filler metal is used

7 Fused section between surfaces of two sheets or plates: (a) spot weld and (b) seam weld  Used for lap joints  Used commonly with resistance welding  No filler metal Weld Types: Spot Weld and Seam Weld

8 Weld Types: Flange Weld and Surfacing Weld (a)Flange weld; (b)Surfacing weld used not to join parts but to deposit filler metal onto surface of a base part

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

10 Cross section of a typical fusion welded joint: (a) principal zones in the joint, and (b) typical grain structure Typical Fusion Welded Joint

11 Weld Quality Motivation: Obtaining a weld joint that is strong and absent of defects Topics: 1.Residual stresses and distortion 2.Welding defects 3.Inspection and testing methods

12 Residual Stresses and Distortion Principle: Rapid heating and cooling in localized regions during fusion welding result in thermal expansion and contraction that cause residual stresses, and stresses cause distortion and warpage Butt welding Shrinkage Residual stress warping of weldment

13 Techniques to Minimize Warpage  Welding fixtures to physically restrain parts  Heat sinks to rapidly remove heat  Tack welding at multiple points along joint to create a rigid structure prior to seam welding  Selection of welding conditions (speed, amount of filler metal used, etc.) to reduce warpage  Preheating base parts  Stress relief heat treatment of welded assembly  Proper design of weldment

14  Welding cracks: On weld or near weld  Very serious because strength is reduced significantly  Caused by low of weld and/or base metal combined with high stresses during contraction Weld Defects: Welding Cracks

15 Welding Defects: Cavities Two defect types: 1.Porosity - small voids in weld metal formed by gases entrapped during solidification, caused by inclusion of atmospheric gases, sulfur in weld metal, or surface contaminants 2.Shrinkage voids - cavities formed by shrinkage during solidification

16 Welding Defects: Solid Inclusions Nonmetallic material entrapped in weld metal: 1.Most common form is generated during arc welding processes that use flux. Instead of floating to top of weld pool, globules of slag become encased during solidification 2.Other forms: formation of metallic oxides, such as Al 2 O 3 when welding aluminum

17 A weld bead in which fusion has not occurred throughout entire cross section of joint. Forms of incomplete fusion are shown below: Welding Defects: Incomplete Fusion

18 (a)Desired profile for single V-groove weld joint, (b)undercut - portion of base metal melted away, (c)underfill - depression in weld below adjacent base metal surface, and (d)overlap - weld metal spills beyond joint onto part surface, but no fusion occurs Weld Profile in Arc Welds

19 Inspection and Testing Methods: Visual Inspection  Most widely used welding inspection method is manual examination for: 1.Conformance to dimensions, warpage 2.Surface defects, such as cracks, cavities, incomplete fusion  Limitations: Only surface defects are detectable

20 Inspection and Testing Methods: Nondestructive Evaluation (NDE) Tests 1.Ultrasonic testing - high frequency sound waves through specimen to detect cracks and inclusions 2.Radiographic testing - x ‑ rays or gamma radiation provide photographs of internal flaws 3.Dye ‑ penetrant and fluorescent ‑ penetrant tests - to detect small cracks and cavities at part surface 4.Magnetic particle testing – iron filings sprinkled on surface reveal subsurface defects that distort the magnetic field

21 Inspection and Testing Methods: Destructive Testing -- Mechanical Tests (a) Tension-shear test, (b) fillet break test, (c) tension-shear of spot weld, and (d) peel test for spot weld

22 Inspection and Testing Methods: Destructive Testing -- Metallurgical Tests  Metallurgical tests – to examine metallic structure, defects, extent and condition of heat affected zone, presence of other elements, etc. of the weldment  Microscopy is an example of this

23 Weldability  Capacity of a metal or combination of metals to be welded into a suitable structure, and  For the resulting weld joint(s) to possess the required metallurgical properties to perform satisfactorily in intended service  Good weldability characterized by 1.Ease with which welding is accomplished 2.Absence of weld defects 3.Strength, ductility, and toughness in welded joint

24 Weldability Factors: Welding Process Some metals or metal combinations can be readily welded by one process but are difficult to weld by others Example: stainless steel readily welded by most arc welding and resistance welding processes, but difficult to weld by oxyfuel welding

25 Weldability Factors: Base Metal 1.Some metals melt too easily; e.g., aluminum 2.Metals with high thermal conductivity transfer heat away from weld, which causes problems; e.g., copper 3.High thermal expansion and contraction in metal causes distortion problems 4.Dissimilar metals pose problems in welding when their physical and/or mechanical properties are substantially different

26 Other Factors Affecting Weldability  Filler metal. Must be compatible with base metal(s)  Surface conditions (how clean) 1.Moisture can result in porosity in fusion zone 2.Oxides and other films on metal surfaces can prevent adequate contact and fusion

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

28 Design Considerations in Welding  Minimum parts ‑ welded assemblies should consist of fewest number of parts possible Example: usually more cost efficient to perform simple bending operations on a part than to weld an assembly from flat plates and sheets  Design assembly to allow for welding gun access  Assembly should allow for welding from above

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