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Resistance-welding-tipsuseful Hints and References.SOLUTIONS with Effective, Practical Advice
Resistance-welding-tips may have two meanings. One is the electrode end, that in this case, in resistance welding, transmits compressive force and electric current to the item submitted to welding. The other one, to which we are devoting this page, refers to suggestions that may be helpful to anyone engaging in this type of process. We dealt with this process in two previous pages, Resistance Welding Processes and Resistance Welding Equipment. Now we want to present additional details and Resistance-welding-tips not addressed adequately till now, that influence setup and conduct of welding. Classic application of resistance spot welding refers to overlapping joints of the same material and of the same thickness. In such case the electrode tips are identical in material, shape and dimensions resulting in heat balanced distribution and in a central spot welded nugget located symmetrically at the interface. If the thickness of the elements and/or the thermal conductivity of the materials are different, the distribution of the current and of heat build up may be non symmetric, causing the nugget to be lop-sided and possibly unacceptable. One or more of the following Resistance-welding-tips can be applied to redress the situation. An electrode tip with a smaller face area can be used from the side of the higher conductivity alloy or of the thinner sheet. Otherwise an electrode of higher electrical resistance (e.g. tungsten) may face the higher conductivity material. Such provisions will shift the current density and the heat distribution. When using sets of different electrodes, proper controls must be established by design to avoid their erroneous location. Electrode tip faces are progressively deteriorating with use. To assure continuing high quality production it is imperative to follow Resistance-welding-tips that require to check periodically and to dress again their surface after the prescribed number of spot welds has been performed. In automated systems rigid schedules of electrode maintenance should be established. Depending on the configuration of the parts to be welded, electrode Resistance-welding-tips of various shape and dimensions are available, mostly available as shelf items from suppliers of equipment and accessories as advertised in their catalogues. Special bent tips may be needed to reach difficult spots but should never be used when the work can be done with standard cylindrical electrodes. Of the various Resistance-welding-tips one should remember that cooling water direction should be checked to make sure that the central cool water jet impinges on the internal back side of the electrode tip closest to the weld face to ensure maximum effective cooling. Portable spot welding machines may be required to perform spot welding on large and cumbersome objects that cannot be readily brought to a standing welding machine. They are usually held by a structure that bears the weight and eases manual manipulation. While the machine carries the electrodes and the force application mechanisms to deploy the necessary compressive force, the required power source can be either separate or integral with the unit. In the first case electrical cables are connected to fixed transformers. Because of large power losses due to the cables, a higher secondary voltage is needed than in a stationary machine of the same current output. In the second case as recommended by Resistance-welding-tips the transformer is integral with the portable unit which is called a "transgun", with the advantage that there is no voltage drop on the secondary cable. Although this configuration is used in manual units it can be easily mounted on robotic arms, especially after the adoption of Inverter technology since such transformers became much smaller and lighter. This application of Medium Frequency Direct Current (MFDC) Power Sources was briefly reviewed in an article published (2) in Issue 42 of Practical Welding Letter for February 2007. (see PWL#042.) The introduction of Insulated Gate Bipolar Transistors (IGBT) for MFDC, and the increased use of Silicon Controlled Rectifiers (SCR) permit fine adjustment of the amount of energy flowing to the transformer. Resistance-welding-tips suggest that modern control devices based on feedback should be employed to permit supply of constant direct current to each weld, even in cases of primary alternating current (AC) line voltage fluctuations. The other necessary functions are easily regulated with standard equipment. Force gauges are currently used for monitoring and controlling the applied force. Time control functions are now based on microprocessor digital technology. Obtaining consistently high quality welds is nowadays a much easier task than it was only a few decades ago. Resources Overview of Resistance Welding (10 pages) http://www.livco.com/UMchapter1.pdf Handbook for Resistance Spot Welding (20 pages) Resistance Welding - Trouble Shooting Guide Understanding Control Modes in Resistance Welding Testing Resistance Welding Transformers
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