Welding_resistancespot and seam machines:SOLUTIONS with Effective, Powerful AdviceWelding_resistance, equipment, resistance welders, spot welders, seam welders, projection welders, resistance welding, spot welding, seam welding, projection welding, equipment selection, spotwelding tips, seamwelding wheels, welders controls, welding monitors, welding links, welding tips, joining questions needing answers: these are some of the items developed in this Site for the benefit of interested readers. What is in here for me? Whenever looking for a specific piece of Welding_resistance equipment one should make sure it will perform the job at the required quality level at the lowest cost per piece (all included, not only the machine). In our opinion the Welding_resistance machines manufacturers should be asked to compete at the best they know, to present a welding plan for the items required, (parts per hour, in process maintenance, accessories, self adjusting controls etc.) and prove what they say. Important Announcement
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Fully controllable Welding_resistance machines are worth their higher price if they help provide quality welds, repeatedly, at the required production rate, without breakdowns. Get help from suppliers, let them know exactly what you are looking for and let them prove to you that their solution will be the best for you. In a previous page on WELDING EQUIPMENT, (click for seeing), a short review was offered of the main concerns that should be addressed when procuring new hardware as needed to perform any given welding process. Here we are going to enter into some more details on Welding_resistance equipment. For more information on the Resistance Welding Process, including data on electrode materials, you may click on the underlined subject title.
Spot welders... SPOT welders are a sub-class of Welding_resistance equipment that provide the capacity to process the materials as follows. Two or more sheet metal or wire parts are overlapped and then welded in separate spots by causing a fused weld nugget to form in correspondence to the place where the elements are been held in place. Force is exerted between two short copper bars called electrodes or tips, and heat is developed at the point of contact as a consequence of resistance to the passage of an electric current. The electric current needed is generally of low voltage and high amperage, obtained directly from the plant grid through a one or a three phase transformer. For consistent results the amount of current drawn at each cycle is exactly metered by electronic controls. As already pointed out elsewhere in this Site, drawing such a high current imposes a heavy charge on the grid, even if of short duration, so that other nearby instruments might suffer if no precautions are taken. Quite different types and sizes of Welding_resistance machines are available, fixed and portable, depending on the materials and on the maximum thickness to be welded, and, if not simply for manual working, to the degree of complexity needed for automatic operation. The three main elements always present in a Welding_resistance machine are the transformer and the electric circuit, initiation and control devices for precise operation not only of the current intensity and duration but also of the timing of the successive phases, and the frame with the mechanical force application devices. Voltage regulators should be considered if the voltage of the electric grid tends to fluctuate, because of the negative effect on quality of the nuggets and on uniformity of results. An Article on Automatic Resistance Welding was published in our Practical Welding Letter No. 12, issue of August 2004. To read the Article click on PWL#012. An Article on "How to select your Resistance Welder" was published in Practical Welding Letter issue No. 22 for June 2005. To see the article click on PWL#022. An Article on Extending Life of Copper RSW Electrodes was published in Practical Welding Letter issue No. 41 for January 2007. To see the article click on PWL#041. An Article on MFDC Power Supplies for Resistance Spot Welders was published in Issue 42 of Practical Welding Letter for February 2007. Click on PWL#042 to read it. To receive at no cost all the issues of PWL as they are published, please subscribe. Specifications...
For general specification requirements on Welding_resistance equipment and Spot Welding Machines one can visit the site of the Resistance Welders' Manufacturers Association at RWMA. Single phase spot welders are simpler and less expensive than three phase ones but their influence on the balance of the electric grid is more drastic and should be addressed as an objective concern, because of the penalty that the Electric Company might decide to impose. Three phase Welding_resistance machines draw a more equilibrated load from the power grid. In most cases they deliver high current to the secondary windings of alternate current transformers. Single-phase direct current, three-phase direct current, three-phase frequency converter, and medium frequency direct current power systems are also used. For Welding_resistance machines developed to weld aluminum, one should remember that current requirements are higher than for other materials, and controls must be capable of exact timing to ensure consistent high quality. The mechanical force for clamping is usually produced by pneumatic devices when compressed air supplies are available. Mechanical force application was used in older Welding_resistance machines. Best quality with best controls... Controls are specialized instruments of Welding_resistance machines designed to permit the passage of precise amounts of current by establishing the exact position of firing on the curve (from zero to maximum and back to zero) describing the voltage as a function of time (or of phase). See also Welding Control. They initiate and terminate the exact timing of current flow to the transformer, while controlling the current magnitude measured in amperes, and they also establish the timing and sequence of mechanical motions and force application in Welding_resistance equipment. The selection of spot welding equipment should be based on the characteristics of the work at hand, with reasonable projections for future work: in particular, materials used, minimum and maximum thickness and maximum throat length. The production rate required should also be taken in consideration, and the degree of automation required, if any, the electrical load on the power grid and the floorspace. For simple applications the use of portable grip welders of pliers type may suffice. All Welding_resistance machines are driven by unskilled workforce, which contributes to the economy of operation, after the proper welding schedules have been developed and set up by competent technicians for each job. Now for seam... SEAM welding is performed on Welding_resistance equipment similar to the preceding one except that the electrodes are here rotating copper wheels which grip the overlapping sheets and move progressively the workpiece while producing a sequence of overlapping spot weld nuggets. The wheel axis can be parallel or perpendicular to the throat of the machine to provide for circular or longitudinal welding: normally there are provisions to change from one configuration to the other as needed. The design of the machine should be carefully studied because it limits the dimensions (diameter and length) of the workpiece that can be welded. The shape of the electrode wheels can be adapted to accommodate protrusions which interrupt the regular continuous thickness of the joint. One of the axes of the wheels can be angled in order to accept wheels shaped to avoid interference with a wall when a narrow flange is welded. Electrode wheels of Welding_resistance equipment must be effectively cooled in order to control the geometry of the spots and prevent damage to the wheels: this can be done by having cooling water circulate within the wheels or externally by flooding, or by a combination.
As for projection... PROJECTION Welding_resistance machines of the press type tend to be custom made or at least must be capable of accommodating the design of the workpieces. As such they are useful for planned mass production. Projections are small protrusions obtained in sheet metal by forming the material with a die under a press. Welding occurs at the same time at once on all the projections pressed by the platen, against a plain sheet, also held by a different platen. These machines essentially include all of the main elements of other Welding_resistance machines reviewed above except for some differences as follows. The movement of the platens relative to one another must be parallel (that is no rocker arm) in order not to move the elements. The upper electrode must follow immediately the collapse of the projections, otherwise the necessary force is relieved too soon with dangerous consequences on the quality of welds. This requirement demands special provisions like low inertia welding head. The establishment of the correct force needed and its adequate control is essential to the production of consistent high quality welds. The weld time is determined only after the proper electrode force and the required current have been determined, and its duration should be sufficient to produce nuggets of suitable size.
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