1. Solid Projections (Solid State Welds)
The object of this section is to describe the design concept for projection welding processes with solid projections.
Solid projection welding has not been nearly as heavily researched as embossed projection welding. However, solid projection welding has become a very common and well-accepted manufacturing process. Solid projection welding differs from embossed projection welding in one fundamental way: solid projection welds are solid state welds. In this section, some of the mechanisms of bonding during solid projection welding will be reviewed, along with potential application and some examples of structures of solid projection welds.

2. Solid Projections Learning Activities View Slides; Lesson Objectives
Read Notes,
Listen to lecture
Do on-line workbook
Lesson Objectives
When you finish this lesson you will understand:
Solid State Weld as applied to projections and studs
Applications of Solid Projection Welds
Keywords
Solid Projection Weld, Solid State Weld, Swelling

3. Typical solid projection details are given here
Typical solid projection details are given here. Two standard types are represented, I.e. the full width projection and the restricted width projection.
Resistance welder Manufacturers Association Bulletin # 35

4. The typical weld fixture device for making these welds is illustrated here.
Resistance welder Manufacturers Association Bulletin # 35

5. Current Flow Heats Pipe
Heat Flows
Into Cold Plate
Thicker Plate = More Heat Loss
Current Flow Heats Pipe
The two parts of the joint forming an annular projection weld have different physical structures which inherently cause a heat balance problem The welding current flowing through the pipe wall in back of the interface heats the pipe wall sufficiently to nullify any heat loss to this area from the weld interface while welding. The opposite effect occurs in the sheet. Heat starts to flow away from the weld area into the surrounding cold plate. This part of the heat is lost for welding at the interface.
Resistance welder Manufacturers Association Bulletin # 35

6. Current Density Less in Thicker Sheet
Current Flow in the Solid Projection
The current flow pattern is illustrated here. The level of current density near the interface keeps decreasing as the sheet thickness increases. The heating effect, or lack of it, is more exaggerated than the current density pattern because the heating varies as the square of the current density.
Current Density Less in Thicker Sheet
Resistance welder Manufacturers Association Bulletin # 35

7. Progression of Projection Collapse for a Simple Angled Projection
As mentioned above, solid projection welding is a solid-state welding process and resembles resistance butt welding more than spot or embossed projection welding. Joining is accomplished by applying the current and forging the parts together under the generated heat. Bonding is accomplished by a combination of metal forging and diffusion bonding. Generally, no melting occurs during solid projection welding. Melting would be extremely detrimental since, usually no provision is made to constrain any molten material. Melting would be synonymous with expulsion.
A schematic representation of the progression of a solid-state projection weld is presented in the above slide. Initially, parts are brought into contact under some applied force. Then, the current is initiated and the projection begins to collapse. The projection cannot collapse back into the parent material (as is the case with projection welding). Metal, both from the projection and from the substrate, is extruded to the weld periphery. As projection collapse is complete, there is typically visible extruded material around the base of the joint (flash). Due to the forging of the substrate, the effective bond surface typically is displaced into the substrate material.

8. Proper Weld Conditions Proper Restricted Width Weld
Short Weld Time
Low Weld Force
Proper Weld Conditions
Note Swelling of OD
Slight Swelling of ID
Excessive Weld Time
Excessive Weld Force
Illustrated above are diagrams of the various types of weld appearances. With short weld times or low weld forces incomplete forging of the weld occurs. The weld region is limited with the bond being only a fraction of the wall thickness. Low weld strength results. With proper conditions, the weld seats and forges as shown in the second diagram. Note that some outside diameter wall swelling occurs as the heated and plastic metal flows (A) and the inside wall may also show some swelling (C), although usually not as significant as the OD. Some notches may be present, but in general, the weld thickness is nearly equal to the wall thickness of the pipe. With excessive weld time or force, excessive swelling on both faces of the pipe wall occur. In cases where wall swelling is not allowed, the restricted width projection design can be used. With this design, it is often common to not have a full cross section weld, and the weld has notches on both walls, but this may be acceptable to reduce the wall swelling (A).
Proper Restricted Width Weld
No Swelling of OD
Resistance welder Manufacturers Association Bulletin # 35

9. Photomicrographs Of Full Width Solid Projection Welds
Micrographs of the various full width solid projection welds described above are presented here.
Resistance welder Manufacturers Association Bulletin # 35

10. Photomicrographs Of Restricted Width Solid Projection Welds
A micrograph of the Restricted Width Solid Projection weld is presented here.
Resistance welder Manufacturers Association Bulletin # 35

11. Parameters
The Welding Parameters appear to be more dependent on Sheet Thickness than on Pipe Thickness
From past experience, there seems to be a relationship between the pound/linear inch of projection and the required amperes/linear inch but the relationship seems to be related more to the thickness of the sheet than to the pipe thickness. These curves give the starting parameter relationships established.
Resistance welder Manufacturers Association Bulletin # 35

12. Excessive Swelling Acceptable Swelling
Weld Force
Acceptable Swelling
When setting weld parameters, a secondary effect is to be concerned about excessive pipe swelling. The figure above illustrates ranges of parameters over which welds can be made without experience excessive swelling of the pipe for two weld forces. With the higher weld force, more restrictive current and time values apply.
There is a parameter limit which exceeded results in excessive pipe swelling
Resistance welder Manufacturers Association Bulletin # 35

13. Progression of Projection Collapse for a Beveled Annular Projection
Projection welding of annular sections to flats is a common application of projection welding. The development of a solid projection weld in this application is shown schematically in the above slide. In this example, a beveled projection has been machined onto the contacting edge of the tube. Actual formation of the joint is quite similar to the simple solid projection described above. However, the location of the tip of the projection dictates how the projection will forge. In this case, since the projection is beveled towards the center of the tube, the projection will tend to "roll" to the center of the tube, leaving little or no flash exposed on the outer surface.

14. Typical Screw & Stud Parts for Projection Welding
The recommended designs for solid projections are highly dependent on the specific application. For round sections of relatively small diameter (studs, screws), radiused projections are used. Some examples of these are presented in the above slide. The projection covers the full cross section of the part and, during welding, will create a full face solid state joint.
Multiple projections are also commonly used for attaching larger parts. Common applications include welded bolts, welded pins, and welded nuts. Typically rounded projections are used in these applications. However, pyramidal projections are also commonly used.
The simplest application of screws and bolts suitable for welding is shown in the above slide. Any rod, stud, or screw with a radiused head constitutes the projection. A round or oval head screw without the slot constitutes an ideal application. In this case, it is not necessary to clamp the screw, but merely to provide a socket in the lower die. Electrical contact is made on the under side of the head.
If the screw or rod has no head, it is necessary to clamp it in a hand toggle or air operated fixture which also contains the lower electrode. If the threads are sharp, as in the lower left one in the above slide, the clamp fixture should be provided with a backup to take the thrust of the welding force. Otherwise, the clamp pressure required to hold the part against slipping may not only damage the threads, but also cause rapid die wear and misalignment of parts.
[Reference: Resistance Welding Manual, p.3-6, RWMA]

15. Correct & Incorrect Location of Annular Projection
With larger-section circular parts, annular projections are commonly used. Annular projections are typically formed onto the end of the part to be attached. Both angular and radiused types of annular projections are commonly used. When using annular projections, care must be taken in the projection design to insure that adequate forging of both the projection and the opposing surface occurs. Examples of both correct and incorrect designs for angular annular projections are presented in the above slide. The correct projection is a balanced design which, during welding, will forge relatively equally to the inside and the outside of the part. This type of forging action will also upset the most material from the opposing surface, promoting the formation of an effective joint. The design shown in the above slide labeled “incorrect projection,” on the other hand, would show very poor collapse and forge characteristics. In this case, when the current is applied, the projection will collapse to the outside of the part, folding over without particularly disturbing the opposing interface. When this occurs, the possibility of forming an effective joint is substantially reduced. The above slide illustrates a screw machine product. The ring, if located on the very edge will squeeze out, leaving a poor weld. Annular projections may have either rounded tops or sharp 90° edges (45° each way). The latter is frequently used on screw machine parts which are applied to sheet stock. The rounded top gives a better heat balance when applied to heavier parts. The annular projection is used in sheet parts to be joined around a hole. The annular projections in screw machine parts, or forgings where the stock thickness is sufficient to warrant it, should have annular cavities on either side of the projection. This is particularly desirable in applications similar to that shown in the above slide, as it will prevent flash from fouling the threads.
Correct Projection Incorrect Projection
[Reference: Resistance Welding Manual, p.3-5, RWMA]

16. Application for Welding Studs or Bushing into Metal Opening
Start of Welding Finish of Welding
Electrode
Electrode
Weld
The above slide shows a special application for welding studs, bushings, etc., into metal opening. The sheet metal stock must have a minimum thickness of in for this type of weld to be practical. The hole in the sheet must be punched cleanly, and the pilot of the stud should be just a few thousandths (0.005-in in) smaller than the hole. The shoulder angle is approximately 45°. As the weld is made, the edge of the sheet fuses into the angular shoulder, thus making a strong air and water-tight joint. Such welds are frequently made in hot water tanks and similar applications.
Electrode
Electrode
[Reference: Resistance Welding Manual, p.3-5, RWMA]

17. Application of Annular Projections
Weld
(a) (b)
(c) (d)
Threaded Boss
Shoulder Stud
Weld
Annular projections are frequently used on forged parts to carry heavy loads and for applications that require a pressure-tight joint around a hole between two parts. Such preparation also produces a high-strength weld when a large stud or boss is welded to thin sheet metal. The above slide shows two applications of annular projections. The summit of the circular ridge should be rounded, particularly with heavy sections, to improve heat balance. Relief, as shown in Figure (c), should be provided at the base of the projection, for the upset metal to fill as the projection collapse. This will assure a tight joint without a gap, as shown in Figure (d).
Tight Joint
Relief for
Upset Metal
to Fill in
[Reference: Welding Handbook, Volume 2, p.564, AWS]

18. Typical Projection Weld Fasteners
Weld Bolts
Weld Pins
Weld Nuts and Pads
Various designs of weld fasteners are available commercially for projection welding applications. Typical examples are shown in the above slide. Projection designs and their number depend upon the application.
To weld a countersunk screw head into sheet material, four flutes or bosses are formed on the contacting surface of the head as shown in the top row of the above slide. The sheet is punched to form a countersunk contacting surface.
The preferred application for all weld nuts and bolts is that the design be such that the welds are in compression rather than tension. The two screws, A and B, do not meet this requirement, while C, D and E do. In the center row, F does not, H does, and the center G may or may not, depending on which side the screw is on.
All of these parts can readily be hopper fed.
Location of the parts on the sheet can be accomplished by means of a pilot pin, in cases where a hole is used, or by stops and locators, where there is no hole.
[Reference: Resistance Welding Manual, p.3-6, RWMA]

19. Illustrating Use of Insulated Locating Pin for Welding Nut
Insulated Steel Pin with
Shoulder
Electrode
Electrode
Weld
Electrode
Electrode
The above slide presents an insulated pilot in the lower electrode, over which the sheet and weld nut are located. If the nut is hopper fed, it is more practical to be loaded into the upper electrode.
[Reference: Resistance Welding Manual, p.3-7, RWMA]

20. Recessed Electrode for Locating Nut for Welding
The above slide shows an application where the weld nut has its own pilot over which the sheet is located. If this nut is hopper fed, it should be loaded into the lower electrode.
Weld
Nut
[Reference: Welding Handbook, Volume 2, p.567, AWS]

21. Two Methods to Provide Accurate Location for Projection Welding Bolts to Sheet
Insulation
Bolt Retainer
Projection
Weld Bolt
Projection
Weld Bolt
Flat Spring
Figure (a) shows a weld bolt loaded into the upper electrode and held in place by a spring detent. The sheet, having no hole, must be positioned by outside stops or gages.
In Figure (b), the bolt is first inserted in the hole in the sheet. The bolt shank is then inserted in the recess in the lower electrode.
Sheet Metal
Insulation
Drill Hole in Electrode
to Clear Threads
[Reference: Resistance Welding Manual, p.3-8, RWMA]

22. The two basic types of electrode-die designs are shown here. 1
The two basic types of electrode-die designs are shown here. 1. Large flat electrodes often made from bar stock, 2. A series of contact surfaces, made by relieving a bar between projections or by brazing inserts of hard copper alloy to the bar.
Solich, T “Improving Projection Welding Results” Practical Welding Today, Nov-Dec 1997

23. Flat electrodes should be made from RWMA Class 2, 3, or 4 alloys
Flat electrodes should be made from RWMA Class 2, 3, or 4 alloys. Class 3 or 4 electrode material is recommended for high-production applications or applications involving larger parts with projections spread over a large area.
Solich, T “Improving Projection Welding Results” Practical Welding Today, Nov-Dec 1997

24. Ideal Microstructure for a Solid Projection Weld
As described above, solid projection welds are solid state welds. As such, the microstructures of solid projection welds are dominated by metal flow characteristics rather than the position or size of a zone of resolidified material. Concern in the microstructures of projection welds includes the integrity of the bond line, the presence of any detrimental phases, the incidence of any cracking, and the overall geometry of the final joint.
An example of an ideal microstructure for a projection weld is presented in the above slide. This is a section of an annular projection weld made on 1045 steel. In this weld there has been complete collapse of the projection, providing a wide effective bond area. The bond line indicates forging of the opposing face of the joint as well as the projection itself.

25. Effect of too Little Upset on Solid Projection Weld
A weld made with too little upset is presented in the above slide. In this case, there has been too little current and time to fully collapse the projection. The result is a weld of limited bond area and potentially reduced strength. Note the dark etching artifact on the bond line. Such artifacts are often mistaken for bond line cracks, but usually are the result of preferential etching. No evidence exists relating the incidence of these etching artifacts to any reduction in weld performance.

26. Effect of Excessive Upset on a Solid Projection Weld
The above slide shows a weld with excessive upset. In this case, the attached assembly has collapsed to the point that the residual projection has folded over against the body of the attachment, creating an internal notch. Since such notches can act as fatigue initiation sites, they are a concern.

27. Excessive Weld Related Cracking
An example of an excessive weld related cracking is shown in the above slide. In this case an implied notch, similar to the one described previously, resulted in a cooling crack which propagated almost completely through the structure.

28. Crack Propagation in a Solid Projection Weld
A crack in a solid projection weld propagating from a high stress concentration point with the displaced flash of the projection is shown in the above slide.

29. Effects of Weld Time and Projection Shape
Tube
Pronounced
Bulge
Slight Bulge
Notch
Notch
Sheet
Geometry effects of these structures are summarized in the above slide. In Figure (a), too little upset results in a narrow effective weld. The correct upset, Figure (b), produces the necessary bond area without excessively forming a notch during projection collapse. Finally, excessive upset is shown in Figure (c) in the next slide. In this case, the projection has folded over against the substrate, forming an excessive notch.
Before Welding After Welding Before Welding After Welding
(a) Short Weld Time
Full-Width Projection
(b) Correct Weld Time
Full-Width Projection
[Reference: Metals Handbook Volume IV - Welding, Brazing and
Soldering, ASM, p ]

30. Effects of Weld Time and Projection Shape (CONT.)
Extensive Bulge
Notch
Notch
These two slides also show the effect of using reduced-width projections in annular projection welding. Reduced-width projections are those which the base of the projection is narrower than the thickness of the part being joined. On full projection collapse, the volume of the projection of simply forges to, but generally not beyond, the limiting surfaces of the part. This both reduces any notch effects and improves the appearance of the joint, thus giving reduced-width projection a major advantage.
Before Welding After Welding Before Welding After Welding
(c) Excessive Weld Time
Full-Width Projection
(d) Correct Weld Time
Reduced-Width Projection
[Reference: Metals Handbook Volume IV - Welding, Brazing and
Soldering, ASM, p ]

31. Troubleshooting Guide
Flashing of projections or “spitting of molten metal
Increase Pressure
Shorten Weld time
Increase squeeze time
Reduce heat
Check for dirty or scaly material
Check insulation in locating fixture
Burning, discoloration
Increase pressure
Shorten weld time
Add hold time
Reduce heat
Poor, weak or missing welds
Increase welder force
Increase welder KVA capacity
Increase weld time
Increase heat
Reduce electrode pressure
These are troubleshooting recommendations by Solich.
Solich, T “Improving Projection Welding Results” Practical Welding Today, Nov-Dec 1997