Joining Processes R. Jerz

Transcription

1 Joining Processes R. Jerz 1 4/16/2006

2 Chapter Outline R. Jerz 2 4/16/2006

3 Welding Processes Gas, electricity, or other heat source? Is electrode consumed? Is a filler material used? Is flux used? Anything else? Video Introduction to welding R. Jerz 3 4/16/2006

4 Welded Joints R. Jerz 4 4/16/2006

5 Fusion Welding Processes Video Fusion welding processes R. Jerz 5 4/16/2006

6 Oxyacetylene Welding Acetylene gas most common (6,000 F) Welding Cutting Straightening Can be with or without filler R. Jerz 6 4/16/2006

7 Oxyacetylene Torch Figure 30.2 (a) General view of and (b) cross-section of a torch used in oxyacetylene welding. The acetylene valve is opened first; the gas is lit with a spark lighter or a pilot light; then the oxygen valve is opened and the flame adjusted. (c) Basic equipment used in oxyfuel-gas welding. To ensure correct connections, all threads on acetylene fittings are left-handed, whereas those for oxygen are right-handed. Oxygen regulators are usually painted green, and acetylene regulators red. R. Jerz 7 4/16/2006

8 Weld Joint Structure Figure Characteristics of a typical fusion-weld zone in oxyfuelgas and arc welding. Figure Grain structure in (a) deep weld and (b) shallow weld. Note that the grains in the solidified weld metal are perpendicular to their interface with the base metal (see also Fig. 10.3). (c) Weld bead on a cold-rolled nickel strip produced by a laser beam. (d) Microhardness (HV) profile across a weld bead. R. Jerz 8 4/16/2006

9 Arc Welding Processes Nonconsumable electrode Gas tungsten-arc (TIG) Plasma arc (PAW) Consumable electrode Shielded metal arc (SMAW) Gas metal arc (GMAW or MIG) Flux-cored arc welding (FCAW) Submerged arc welding (SAW) R. Jerz 9 4/16/2006

10 Gas-Tungsten Arc Welding Video TIG welding Figure 30.4 (a) The gas tungsten-arc welding process, formerly known as TIG (for tungsten inert gas) welding. (b) Equipment for gas tungsten-arc welding operations. R. Jerz 10 4/16/2006

11 Plasma-Arc Welding Process Video plasma arc welding 60,000 degrees F R. Jerz 11 4/16/2006

12 Shielded-Metal Arc Welding Video shielded metal arc welding Figure 30.7 Schematic illustration of the shielded metal-arc welding process. About 50% of all large-scale industrial welding operations use this process. R. Jerz 12 4/16/2006

13 Shielded-Metal Arc Welding Figure 30.8 A deep weld showing the buildup sequence of eight individual weld beads. R. Jerz 13 4/16/2006

14 Gas Metal-Arc Welding Videos gas metal arc welding R. Jerz 14 4/16/2006

15 Fluxed-Cored Arc-Welding Video flux core welding Figure Schematic illustration of the flux-cored arc welding process. This operation is similar to gas metal-arc welding, shown in Fig R. Jerz 15 4/16/2006

16 Submerged-Arc Welding Video submerged-are welding Figure 30.9 Schematic illustration of the submerged arc welding process and equipment. The unfused flux is recovered and reused. R. Jerz 16 4/16/2006

17 Other Welding Processes Electron beam - video Laser beam - video R. Jerz 17 4/16/2006

18 Weld Design Figure Some design guidelines for welds. Source: After J.G. Bralla. R. Jerz 18 4/16/2006

19 Welded Joints Metallurgy concerns Solidification process Heat-affected zone - weakest part of joint R. Jerz 19 4/16/2006

20 Defects in Fusion Welds Figure Examples of various discontinuities in fusion welds. Figure Examples of various defects in fusion welds. R. Jerz 20 4/16/2006

21 Cracks in Welded Joints Figure Types of cracks developed in welded joints. The cracks are caused by thermal stresses, similar to the development of hot tears in castings (see also Fig ). R. Jerz 21 4/16/2006

22 Distortion of Parts After Welding Figure Distortion of parts after welding. (a) Butt joints and (b) fillet welds. Distortion is caused by differential thermal expansion and contraction of different regions of the welded assembly. R. Jerz 22 4/16/2006

23 Weld Testing Figure (a) Specimen for longitudinal tension-shear testing; (b) specimen for transfer tension-shear testing; (c) wraparound bend test method; (d) three-point bending of welded specimens (see also Fig. 2.11). R. Jerz 23 4/16/2006

24 Solid-state Processes Mechanical methods Ultrasonic Friction Electrical Resistance R. Jerz 24 4/16/2006

25 Ultrasonic Welding Video - ultrasonic Figure 31.2 (a) Components of an ultrasonic welding machine for making lap welds. The lateral vibrations of the tool tip cause plastic deformation and bonding at the interface of the workpieces. (b) Ultrasonic seam welding using a roller as the sonotrode. R. Jerz 25 4/16/2006

26 Ultrasonic Welding Vibrating tool at high frequency Lap joints of thin materials R. Jerz 26 4/16/2006

27 Friction welding Rub two parts together Video R. Jerz 27 4/16/2006

28 Resistance (Spot) Welding (RW) Figure 31.6 (a) Sequence of events in resistance spot welding. (b) Cross-section of a spot weld, showing the weld nugget and the indentation of the electrode on the sheet surfaces. This is one of the most commonly used processes in sheet-metal fabrication and in automotivebody assembly. R. Jerz 28 4/16/2006

29 Resistance Welding Video Spot, projection, and seam Heating H=I 2 RT, where I=current R=electrical resistance T=time R. Jerz 29 4/16/2006

30 Spot Welding Equipment Figure 31.7 (a) Schematic illustration of an air-operated, rocker-arm, spot welding machine. (b) and (c) Two electrode designs for easy access into components to be welded. R. Jerz 30 4/16/2006

31 Resistance Projection Welding Figure (a) Schematic illustration of resistance projection welding. (b) A welded bracket. (c) and (d) Projection welding of nuts or threaded bosses and studs. (e) Resistance-projection-welded grills. R. Jerz 31 4/16/2006

32 Spot Weld Testing Figure Test methods for spot welds: (a) tension-shear test, (b) cross-tension test, (c) twist test, (d) peel test. (see also Fig. 32.9). R. Jerz 32 4/16/2006

33 Brazing & Soldering Video Filler material Temperature below melting point of metals Differences from welding brazing alloy strength of brazing alloy capillary action Soldering - lower temperature than brazing R. Jerz 33 4/16/2006

34 Joint Designs used in Brazing Figure 32.3 Joint designs commonly used in brazing operations. The clearance between the two parts being brazed in an important factor in joint strength. If the clearance is too small, the molten braze metal will not penetrate the interface fully. If it is too large, there will be insufficient capillary action for the molten metal to fill the interface. R. Jerz 34 4/16/2006

35 Joints Should be clean Should have close tolerance R. Jerz 35 4/16/2006

36 Advantages of Brazing Join a variety of metals Quick Low temperature Automation is possible R. Jerz 36 4/16/2006

37 Adhesives R. Jerz 37 4/16/2006

38 Adhesives Epoxies - most are 2 components Cyanoacrylates - super glues Anaerobics one component, cure when oxygen is removed Acrylics catalyst primer and adhesive Urethanes low temperatures Silicones - flexible joints Hot melts R. Jerz 38 4/16/2006

39 Advantages & Disadvantages Combination of materials Low temperature Joining of thin materials Joining of heat sensitive materials Inexpensive Less assembly time Unstable at higher temperature Destructive testing required Surface preparation Cure time R. Jerz 39 4/16/2006

40 Design for Assembly (DFM) Many ideas Function Cost Time DFM Video R. Jerz 40 4/16/2006

41 DFM - Concepts Reduce the number of parts Reduce number of fasteners Use modular designs Reduce need to handle several components at the same time Limit number of directions Use high quality components Design fasteners that can be easily automatically feed R. Jerz 41 4/16/2006

42 DFM Examples R. Jerz 42 4/16/2006