AWS RWPH:2011 pdf download.The Resistance Welding Processes
Spot Welding
In this most widely used resistance welding process, two opposing electrodes apply force and current to metals that overlap (lap joint).Figure 2 shows examples of the various types of spot welds. Additional information may be found in Chapter 1 of the AWS Welding :Handbook, 9th Edition, Vol. 3, or Chapter 2 of the RWMA Resistance Welding Manual.
Seam Welding
Similar to spot welding, except the circular elec-trodes (seam welding wheels) are rotating when the weld is being made. If the time between the welds is increased such that the welds do not overlap to form a continuous seam weld, the result is known as a roll spot weld. Additional information may be found in Chapter 1 of the AWS Welding Handbook, 9th Edition, Vol. 3, or Chapter 4 of the RWMA Resistance Welding Manual.
Projection Welding
In this variation of the resistance welding process, the metals to be welded meet at a local-ized point, which exists to concentrate the force and current. In some parts, such as cross-wire welding, the localized point of contact results from the natural part geometry. Most of the time, the projection must be formed or machined in one of the parts. Figure 3 shows some examples of projections before welding.
Additional information may be found in Chapter 2 of the AWS Welding Handbook, 9th Edition, Vol. 3, or Chapter 3 of the RWMA Resistance Welding Manual.
Flash Welding
During the initial sequence, the parts are held lightly together while current is applied. Then as material is flashed away and the proper temper-ature is reached the parts are forced together to complete the weld.
Additional information on these processes may be found in Chapter 3 of the AWS Welding Handbook, 9th Edition, Vol. 3, or Chapter 5 of the RWMA Resistance Welding Manual.
Importance of Water Tubes One of the most common errors in cooling welding electrodes is to overlook the impor-tance of the water tubes and their effect on water passage in the electrodes. Figure 7 shows the conventional water circuit for cooling a stan-dard welding electrode. Although the location of each part may be different with various types of holders, the principle is the same.
Keep in mind that sparks and metal expulsion in resistance welding are a sign of incorrect balance between current and pressure. Among the items to check when frequent sparking or expulsion of metal from the joint is encountered are the squeeze time, excessive current, or weld time. Material condition is also a factor. Proper pressure between the electrodes is essential to minimize expul-sion. On some jobs, expulsion is difficult to prevent; in such cases make sure that the slides and other vulnerable parts of your machine are protected. Above all PROTECT YOURSELF, espe-cially your eyes.AWS RWPH pdf download.