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A simple and cheap spot welder

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  • A simple and cheap spot welder

    Spot welders are used in almost all plants where it is necessary to join sheets. The advantage of welding machines is the precision of joining (with very good electrical contact), and a very low voltage between the electrodes, which makes the device safe. The presented device is of course not a professional welding machine, but an amateur device to be made in one afternoon, allowing for easy welding of metal.
    A transformer from a microwave oven with a wound secondary winding was used for the construction. The high-voltage winding was carefully removed with an angle grinder, taking care not to damage the core and the mains winding

    A simple and cheap spot welder A simple and cheap spot welder A simple and cheap spot welder

    Then, 2-3 turns of a copper wire 4AWG with a cross-section of 21mm ^ 2 were wound in the vacated place. Remember to properly protect the sharp edges of the core so that they do not damage the insulation on the wires.

    A simple and cheap spot welder A simple and cheap spot welder

    A simple wooden stand and appropriate electrodes remained to be made

    A simple and cheap spot welder A simple and cheap spot welder A simple and cheap spot welder A simple and cheap spot welder





    When using the welding machine, care should be taken due to the high temperature in the place of welding. Do not overheat the transformer and cables!

    Source: http://hackaday.com/2009/06/23/how-to-build-your-own-spot-welder

    Cool? Ranking DIY
    About Author
    megabit
    Level 18  
    Offline 
    megabit wrote 336 posts with rating 306, helped 6 times. Live in city Poznań. Been with us since 2005 year.
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  • #2 8870339
    flubber.trip
    Level 27  
    Brilliant in its simplicity. What are the electrodes made of? I would add a spring that would not allow the electrodes to be short-circuited accidentally, and a switch that turns the device on only when it is pressed. greetings
  • #3 8870462
    karol1010
    Level 21  
    I think that the switch is only for the foot because it is better if the current starts flowing only after the electrodes are firmly pressed. Interesting construction.
  • #4 8870592
    Snikers
    Level 24  
    Coolant is pumped through the electrodes in commercial equipment.
  • #5 8870713
    livetevn
    Level 11  
    Could someone write how many turns are needed on the primary?
  • #6 8870762
    Freddy
    Level 43  
    livetevn wrote:
    Could someone write how many turns are needed on the primary ??

    It all depends on how big your core is. Calculate the number of turns per volt by the formula. Patterns are easily available on the Internet.
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  • #7 8871085
    miroskop
    Level 23  
    As for the transformer, it makes more sense to ask what the minimum power must have to weld metal sheets with a thickness of, for example, 1mm.
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  • #8 8871920
    wzk
    Level 19  
    :arrow: microscope
    ? of the electrode working part = 5 mm, pressing force = 1kN, welding current = 3 kA, welding current flow time = 0.4 s.
    Successful attempts!
  • #9 8872642
    lukas1121
    Level 18  
    Very interesting and brilliant in its simplicity design. in my free time, do something similar because I have to mount a hinge to a metal cabinet :) are the electrodes maybe from some plug ??
    How much power should such a transformer be? roughly yeah ??
  • #10 8872907
    yetihehe
    Level 13  
    In this machine, the electrodes are from MIG.
  • #11 8873045
    morph13
    Level 25  
    The same solution (trafo) is used in a transformer soldering iron.
    I wonder if such a luck can be adapted for this purpose.
  • #12 8873656
    ElectroTom
    Level 25  
    In the soldering iron, the transformer has a power of approx. 100VA. The one from the microwave, I think, about 800VA. I also wonder what the smallest transformer power would be enough to make a welding machine.
    Greetings.
  • #13 8873757
    flp
    Level 12  
    What is the strength of such a connection, what loads can it withstand?
  • #14 8874444
    PawełS1717
    Level 17  
    I have a similar device, but from a Rubin transformer (yes TV from behind the eastern border) 300W. It even works well, but the welding takes about 4 seconds, which is quite a long time ... so 300W is a little bit ...


    Greetings
  • #15 8874516
    szybaro
    Level 11  
    The primary winding of this transformer is probably not connected to 230V?
  • #16 8874522
    flp
    Level 12  
    Rather, it is definitely 230V. Why should it be any different?
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  • #17 8874586
    Snikers
    Level 24  
    flp wrote:
    What is the strength of such a connection, what loads can it withstand?

    I don't want to look for scripts, but the entire production of cars is based on spot welds. Of course, we are talking about the production of the car body.
  • #18 8875397
    szybaro
    Level 11  
    flp wrote:
    Rather, it is definitely 230V. What would it be otherwise for?


    The photos of the transformer show a rather thick flat bar on the primary winding :?:
  • #19 8875443
    karol3
    Level 26  
    szybaro wrote:
    flp wrote:
    Rather, it is definitely 230V. What would it be otherwise for?


    The photos of the transformer show a rather thick flat bar on the primary winding :?:

    The visible winding is made of round wire. If you are serious about such a welder, the transformer used must have a central column cross-section above 15cm?. Below this cross-section, at most a toy will be created. A relatively useful welding machine can be made on a core with a cross section of more than 20 cm?.
  • #20 8876283
    Alya
    Level 11  
    Aa, that is, such a transformer from a welding machine will be suitable? :)
  • #21 8876357
    karol3
    Level 26  
    It all depends on which welder. While the primary winding can be used in most cases, unfortunately the secondary winding cannot.
  • #22 8876528
    Kamis47
    Level 13  
    wzk wrote:
    :arrow: microscope
    ? of the electrode working part = 5 mm, pressing force = 1kN, welding current = 3 kA, welding current flow time = 0.4 s.
    Successful attempts!


    Do the given values apply to welding two 1mm sheets with each other or materials with a total thickness of 1mm. What would the parameters for welding two 0.6mm sheets look like?
  • #23 8877998
    wzk
    Level 19  
    For 0.5mm low carbon steel sheet:
    ? working part of the electrode = 4 mm,
    pressing force = 600 N (1.5 kN),
    welding current = 2 kA (4 kA),
    current flow time = 0.2 s (0.04 s).
    In parentheses, as an example, I have given the parameters of rigid welding, which are mainly used in large-scale production.
    Source: Welding guide.

    I would recommend hobbyists to get acquainted with the method of welding with energy accumulated in capacitors. It is an ideal method for joining thin sheets, wires of various metals and alloys. Tubes were once assembled using this method.

    The welding method shown in this thread is not a pure resistance welding method. Rather, it is a game, because the current is turned on by contacting the electrodes with the material and the current is interrupted by opening the electrodes.
    It looks effective but it is not effective. :D
  • #24 8878821
    Villen
    Level 21  
    And if the elements to be welded first were placed between the electrodes, pressed and turned on, for example, with a switch under the foot?

    Would this method of welding be correct (or more correct)? ;)
  • #25 8879341
    karol3
    Level 26  
    As you wrote, first the welded sheets are pressed with electrodes, and in the final phase the voltage is applied to the primary winding of the transformer. The thickness of the sheets to be welded depends on the duration of the current flow and therefore the primary winding is switched on by a timer. Depending on the purpose and construction of the welding machine, the method of pressing itself is carried out in different ways.
  • #26 8880118
    Galareta
    Level 23  
    so, for example, it would be better to add switching on the primary winding with a foot switch and a triac? Or just a switch on the leg? And something that causes a strong pressure on 2 sheets? additionally, for example, 2 such transformers can be connected in parallel?
    Additionally, this something is able to weld a sheet to a profile? And the opposite electrode must be on the opposite side, ideally, or if it will be a little next to it or permanently attached somewhere nearby, it will work or not?

    Added after 3 [minutes]:

    In addition, pressing the electrode with a pneumatic actuator is a good idea? I mean, the higher the contact pressure, the better? I am not going to do any mass production, but the topic interested me ;)
  • #27 8888482
    audiofil
    Level 13  
    Hmm ... a welding machine, but ... well, the quality of the welds, and this is unmistakable in amateur conditions. For a simple connection of thin plates, it is okay, but hinges, i.e. plates from 0.5 mm, should be connected permanently and probably it is impossible. Here you need pressure and a strong short impulse. In my company, we use welders with powers from 70 kVA to 250 kVA. Practically, the current for point connection of two 0.7 mm sheets at a point of 5 mm is about 60 - 80 kA, heating time from 6-14 periods. Pressure with a pneumatic cylinder of several hundred kilograms (I don't remember exactly). The relationship is such a better weld is formed with a shorter impulse and higher current, and worse if it is the other way around. What is described here is such a toy with little practical usefulness.
  • #28 8889258
    Wieki
    Level 12  
    audiofil wrote:
    Hmm ... a welding machine, but ...

    It's nice that you shared the information from your plant, but I'm surprised that you want to compare professional equipment to DIY. Maybe you did not read the content carefully, but it is enough to read the title of the topic and everything is clear.
  • #29 8889775
    audiofil
    Level 13  
    It's not cool :) I don't want to compare. My main point was that miracles should not be expected. As I wrote for thin plates - some small elements, it may be suitable. The load-bearing elements are unlikely to be welded and due to current limitations, it is better to try the welding by breaking it. The rupture should tear the weld together with the material, the second sheet should have a hole - then the material is welded.
  • #30 8889920
    karol3
    Level 26  
    I suggest you type in "spot welder" in the search engine and you will get some results. For the more inquisitive, I suggest the link: http://www.google.pl/search?client=firefox-a&...udowa+zgrzewarki+punktowej&lr=&btnG=Search+w+ Google
    For those who want to build a functional device, I recommend the 376-K driver: http://www.nikomp.com.pl/opisy/ZEDJ0/ZEDK3760.htm
    Of course, you can make a simple controller by building a timer on the NE555 and apply voltage switching using a contactor in the primary circuit of the transformer. For additional regulation, the primary winding can be wound with additional taps switched with a switch.
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Topic summary

The discussion revolves around the construction and functionality of a simple, DIY spot welder using a microwave oven transformer. Participants share insights on the design, including the use of copper wire for the secondary winding, the importance of electrode materials, and the necessity of proper current and pressure for effective welding. Questions arise regarding the number of turns needed on the primary winding, the power requirements for welding different sheet thicknesses, and the potential for using pneumatic actuators for better pressure application. The conversation also touches on the limitations of DIY welders compared to professional equipment, emphasizing that while suitable for thin sheets, they may not be reliable for load-bearing applications. Suggestions for improving the design include using timers for current flow control and exploring capacitor discharge welding methods for thin materials.
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