- Slides: 20
Projection Welding Lesson Objectives When you finish this lesson you will understand: • The advantages and limitation of projection welding • Projection design for various thickness materials • Typical Applications of the process Learning Activities 1. View Slides; 2. Read Notes, 3. Listen to lecture 4. Do on-line workbook Keywords Projection Welding, Projection Design, Thin Material Projections, Thick Material Projections
Introduction to Projection Welding (a) (b) (c) [Reference: Welding Handbook, Volume 2, p. 566, AWS] (d)
Examples of Various Projection Designs (a) (b) (c) (d) (e) [Reference: Welding Handbook, Volume 2, p. 562, AWS]
Examples of Various Projection Designs (CONT. ) (f) (g) (i) (h) (j) [Reference: Welding Handbook, Volume 2, p. 562, AWS]
Considerations for Various Materials • Mild and HSLA Steels: – – – • Both are considered readily projection weldable. Both can adequately retain projection welding shape until adequate heating has occurred and are weldable using either embossed or solid projections. The HSLA steels may, depending on the particular composition, suffer an array of metallurgical problems. Galvanized Steels: – – – Projection welding can offer some major advantages in resistance welding galvanized steel. The relatively low contact resistance is a major concern. The use of a projection can put contact resistance back into the welding circuit directly at the faying surface. This, in turn, results in lower welding currents and possibly better electrode-life characteristics as compared to resistance spot welding.
Considerations for Various Materials (CONT. ) • Aluminum and Aluminum Alloys: – – – • They are considered not projection weldable. Most aluminum alloys are of too low a strength to allow the projection to survive under the necessary welding forces. The oxide formed appears to prevent the solid-state bond necessary to form the type of joint. High Alloy Steels: – – Projection welding is also quite readily applicable to the higher alloy steels. The major concern here is material hardenability. Adequate precautions must be taken to prevent the development of brittle microstructures.
Considerations for Various Materials (CONT. ) • Copper Alloys: – – – Projection welding has definite implied advantages for resistance welding copper and its alloys. Just as for the galvanized steels, the weld circuit resistance can be localized at the faying surface. Effective projection welding is largely a function of the specific copper alloy used. With respect to embossed projection welding, the suitability for welding appears to vary with the material strength level. Higher-strength copper alloys are relatively projection weldable. However, lower-strength alloys appear to have difficulty retaining projection shape under the applied welding force. Most copper alloys appear to be weldable with one or more forms of solid projection welding
Advantages of Projection Welding • • • Ease of obtaining satisfactory heat balance for welding difficult combinations More uniform results in many applications Increased output per machine because several welds are being made simultaneously
Advantages of Projection Welding (CONT. ) • • Welds may be placed more closely together Parts are more easily welded in an assembly fixture Finish, or surface appearance, is often improved Parts may be projection welded that could not be otherwise resistance welded
Limitations of Projection Welding l l Requires an additional operation to form projections Requires accurate control of projection height and precise alignment of the welding dies with multiple welds Requires thickness limitation for sheet metals Requires higher capacity equipment than spot welding
Requirements for A Projection in Sheet Material • • Rigid enough to support the initial weld force before current is applied. Sufficient mass to raise a spot or weld nugget in the plane surface to welding temperature. If it is too small it will collapse before the other surface is heated. Collapse without extruding between the parts. Surfaces should be in intimate contact after welding. Not be partially sheared. Such projections are weak, tear out easily and are of low shear strength. Easy to form, so that the punch and die require little maintenance. Cause minimal distortion of the part during forming.
Basic Projection Design in Steel Sheet Punch Spherical Radius Die A D T H Projection D Wall Thickness Should Be at Least 70% of Sheet Thickness 15° B Projection Should Blend into Stock Surface without Shouldering Point Radius “R” [Reference: Welding Handbook, Volume 2, p. 563, AWS] 45°
Bubble - Button Type Projections (a) (c) (b) (d) <T [Reference: Resistance Welding Manual, p. 3 -3, RWMA]
Projections for 0. 500 -in & 0. 250 in Stock 120° 60° 0. 15” 0. 52” 45° 0. 094” 0. 50” 90° 0. 45” 0. 25” When the thickness is greater than 0. 125 -in, the projection will not be completely forged back [Reference: Resistance Welding Manual, p. 3 -4, RWMA]
Embossed Annular Projection [Reference: Resistance Welding Manual, p. 3 -5, RWMA]
Punch & Die Dimensions for Spherical Dome Projections [Reference: Welding Handbook, Volume 2, p. 563, AWS]
Projection Types for Sheet and Solid Applications Spherical Projections Elongated Projections [Reference: Metals Handbook, Volume 6 (Welding, Brazing and Soldering), p. 503 -524, ASM]
Projection Types for Sheet and Solid Applications (CONT. ) Annular Projections Pyramidal Projections Annular Projection on Pin-and-Tenon Joint Cross-Wire Weld [Reference: Metals Handbook, Volume 6 (Welding, Brazing and Soldering), p. 503 -524, ASM]
Projection Welded Front Axle and Radiator Support for Tractors [Reference: Resistance Welding Manual, p. 3 -4, RWMA]