Module 1 - Processes Review

1. Module 1 - Processes Review

2. Process Review • Learning Activities • Review the contents of WE602 • Look up Keywords • View Slides; • Read Notes, • Listen to lecture • Do on-line workbook • Lesson Objectives • When you finish this lesson you will understand: • The basic principles of the most common resistance welding processes Keywords Resistance Spot Weld, Resistance Projection Weld, Resistance Seam Weld, Flash Weld, Upset Butt Weld, Electric Resistance Weld, High Frequency Weld, Electro-Brazing

3. Introduction to Resistance Spot Welding Top Electrode Water Weld Nugget Distance Resistance Bottom Electrode

4. Typical Equipment of Resistance Spot Welding (a) (b) [Reference: Welding Process Slides, The Welding Institute]

5. Process Operation of Resistance Spot Welding [Reference: Welding Process Slides, The Welding Institute]

6. Advantages of Resistance Spot Welding • Adaptability for Automation in High-Rate Production of Sheet Metal Assemblies • High Speed • Economical • Dimensional Accuracy

7. Limitations of Resistance Spot Welding • Difficulty for maintenance or repair • Adds weight and material cost to the product, compared with a butt joint • Generally have higher cost than most arc welding equipment • Produces unfavorable line power demands • Low tensile and fatigue strength • The full strength of the sheet cannot prevail across a spot welded joint • Eccentric loading condition

8. Questions? • Turn to the person sitting next to you and discuss (1 min.): • The heating in resistance spot welding is related to the resistance by the equation H=I2Rt. The resistance can be both bulk and surface resistance. If we change from welding steel to welding aluminum what changes in resistance do you expect?

9. Introduction to Projection Welding (a) (b) (c) (d) [Reference: Welding Handbook, Volume 2, p.566, AWS]

10. Advantages of Projection Welding • A number of welds can be made simultaneously in one welding cycle of the machine • Less overlap and closer weld spacing are possible • 1 < Thickness ratio < 6 • Smaller in size than spot welding • Better appearance on the side without projection • Less electrode wear than spot welding • Oil, rust, scale, and coatings are less of a problem than spot welding

11. Limitations of Projection Welding • Require an additional operation to form projections • With multiple welds, require accurate control of projection height and precise alignment of the welding dies • Thickness limitation for sheet metals • Require higher capacity equipment than spot welding

12. Examples of Various Projection Designs (a) (b) (c) (d) (e) [Reference: Welding Handbook, Volume 2, p.562, AWS]

13. Examples of Various Projection Designs (CONT.) (f) (g) (h) (i) (j) [Reference: Welding Handbook, Volume 2, p.562, AWS]

14. Questions? • Turn to the person sitting next to you and discuss (1 min.): • As projections collapse, the welding electrode and head must move rapidly to keep up with the projection collapse. What things might hinder the heads rapid movement? What would you do to design a more rapid moving head?

15. Introduction to Resistance Seam Welding Roll Spot Weld Upper Electrode Wheel Knurl or Friction Drive Wheel Overlapping Seam Weld Continuous Seam Weld Workpiece Throat [Reference: Welding Handbook, Volume 2, p.553, AWS] Lower Electrode Wheel

16. Mash Seam Weld Slightly Lapped Sheets Wide, Flat Electrodes Weld Nuggets Before welding After Welding [Reference: Welding Handbook, Volume 2, p.554, AWS]

17. Introduction to Flash Welding [Reference: Welding Process Slides, The Welding Institute]

18. Basic Steps in Flash Welding Electrodes (a) (c) (b) (d) Position and Clamp the Parts Flash Upset and Terminate Current Apply Flashing Voltage and Start Platen Motion [Reference: Welding Handbook, Volume 2, p.583, AWS]

19. Equipment Example of Flash Welding [Reference: Welding Process Slides, The Welding Institute]

20. Advantages of Flash Welding • Flexible cross sectioned shapes • Flexible positioning for similar cross section parts • Impurities can be removed during upset acts • Faying surface preparation is not critical except for large parts • Can weld rings of various cross sections • Narrower heat-affected zones than those of upset welds

21. Limitations of Flash Welding • Produce unbalance on three-phase primary power lines • The ejected molten metal particles present a fire hazard • Require special equipment for removal of flash metal • Difficult alignment for workpieces with small cross sections • Require almost identical cross section parts

22. Common Types of Flash Welds Axially Aligned Weld Dies Cross Section After Welding Fixed Platen Movable Platen Transformer [Reference: Welding Handbook, Volume 2, p.589, AWS]

23. Common Types of Flash Welds (CONT.) Miter Weld Movable Platen Fixed Platen Cross Section After Welding Transformer [Reference: Welding Handbook, Volume 2, p.589, AWS]

24. Common Types of Flash Welds (CONT.) Ring Weld Movable Platen Fixed Platen Cross Section After Welding Transformer [Reference: Welding Handbook, Volume 2, p.589, AWS]

25. Questions? • Turn to the person sitting next to you and discuss (1 min.): • In flash welding of steel, the iron burns to iron oxide during flashing and removes oxygen from the flashing interface. The free energy of formation of iron oxides at 1500K are about –40 kcal/gram-atom of oxygen. The free energy of formation of titanium oxides at 1500K is about –90 kcal/gram-atom oxygen. What effect do you suppose this would have on the flash welding operation?

26. Introduction to Upset Welding To Welding Transformer Clamping Die Clamping Die Heated Zone Upsetting Force Movable Part Stationary Part Finished Upset Weld [Reference: Welding Handbook, Volume 2, p.598, AWS]

27. Typical Mill Forms and Products of Upset Welding [Reference: Welding Handbook, Volume 2, p.600, AWS]

28. Resistance Tube Welding (ERW) W. Stanley, Resistance Welding McGraw-Hill, 1950

29. High Frequency Welding Applications Induction Coil HF HF HF Tube Butt Seam Tube Butt Seam Tube Mash Seam [Reference: Welding Handbook, Volume 2, p.653, AWS]

30. High Frequency Welding Applications (CONT.) HF HF Strip Butt T-Joint HF HF Spiral Tube Fin Spiral Tube [Reference: Welding Handbook, Volume 2, p.653, AWS]

31. High Frequency Welding Applications (CONT.) HF Induction Coil Projection Seam HF HF Bar Butt Pipe Butt [Reference: Welding Handbook, Volume 2, p.653, AWS]

32. Advantages of High-Frequency Welding • Produce welds with very narrow heat-affected zones • High welding speed and low-power consumption • Able to weld very thin wall tubes • Adaptable to many metals • Minimize oxidation and discoloration as well as distortion • High efficiency

33. Limitations of High-Frequency Welding • Special care must be taken to avoid radiation interference in the plant’s vicinity • Uneconomical for products required in small quantities • Need the proper fit-up • Hazards of high-frequency current

34. Some Products of High-Frequency Welding [Reference: Welding Handbook, Volume 2, p.665, AWS]

35. Questions? • Turn to the person sitting next to you and discuss (1 min.): • If you were going to make tubing or pipe materials what might be the criteria when you would select ERW over High Frequency Welding?

36. Electro-brazing W. Stanley, Resistance Welding McGraw-Hill, 1950

37. Questions?