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  1. JacobP12345

    Robot Welder Issues

    Thank you in advance to any tips and advice. My company is currently working on getting production up and running with a Capital Robotics Fusion Arc 180. Our current objective is to perform a consistent outside weld on a piece of stitch cut 14 ga sheet metal folded into a piece of angle. These...
  2. JacobP12345

    Welding 4140 Bar to 4140 Tubing

    I am looking to weld to 4140 HT components together. I know that welding HT 4140 is generally a bad idea, but in the current situation it is unavoidable. the bar is a round bar at .5'' diameter, and the tubing is .049'' thick at 5/8'' diameter. I was planning on preheating both to roughly 400...
  3. JacobP12345

    Welding 4140 HT

    All these things are fantastic to know. After extensive testing and calculation the 4140 is needed because the torsion bar is subjected to a required 90 degree twist and needs to provide enough torque to open a 32 inch long 150 lb lid. This ends up subjecting it to roughly 140ksi of stress. The...
  4. JacobP12345

    Welding 4140 HT

    We are working with a heat treated torsion bar of .5'' diameter and 36'' long (HRC 43). We have been welding it to standard A36 we had plasma cut on both ends. One for a tab, and one for a mounting point. So far even with 140 ksi of subjected stress the weld has held with no heat treatment...
  5. JacobP12345

    Pre-stressing a torsion bar

    I am looking to extend the fatigue life on a torsion bar I am designing. Currently it is tempered to the highest rating possible and is made of 4140, and has a diameter of .5''. I don't have much knowledge on the theory behind pre-stressing or pre-torquing a torsion bar and considering the price...
  6. JacobP12345

    High angular displacement torsion bar failure analysis

    Thanks for the help, that is one of our concerns but currently we are remedying this via coating the material. So far it has proven effective. We are currently concerned mainly about mechanical fatigue of the material over time.
  7. JacobP12345

    High angular displacement torsion bar failure analysis

    I'm testing two different diameter (1/2'' and 9/16'') torsion bars made of tempered 4140 (tensile strength of 200-220 ksi, tempered at roughly 725 degrees Fahrenheit) for the purpose of acting as a lid assist for heavy vertical opening concrete lids on a subterranean enclosure. The expected...
  8. JacobP12345

    Lift Assist Torsion Bar

    It was, we're trying a tempered and quenched bar next as per your suggestion. The bar we had was rated at 100ksi. Will report in with the results of the tempered bar.
  9. JacobP12345

    Lift Assist Torsion Bar

    Considering the relationship of UTS to yield strength provided earlier, the new UTS should be in the ballpark of 1375 MPa and the yield strength should be roughly equivalent to that from my plot of the relationship. Thank you for the help
  10. JacobP12345

    Lift Assist Torsion Bar

    Would there be deformation considering a much stronger heat treated 4140 bar?
  11. JacobP12345

    Lift Assist Torsion Bar

    I fully trust your analytical calculations and have always wanted to learn FEA methods better. Our issue is that after testing a 1/2 inch bar of low carbon steel with a yield of 54 ksi and a hardened bar of 4140 with a yield of 110 ksi we still experienced plastic deformation and rapid fatigue...
  12. JacobP12345

    Lift Assist Torsion Bar

    Thank you. This should be my last question for a little while till after I do some testing. What is the relationship between UTS and yield strength? Is their a relatively consistent means of estimating maximum shear/yield strength from the UTS? I am considering testing a larger diameter rod just...
  13. JacobP12345

    Lift Assist Torsion Bar

    Thank you for your help, we have tried 4140 round from McMaster which claimed to be hardened, but the yield strength was around 100 ksi. Their hardened 4340 is around 122 ksi. We really were looking at a buy-and-try kind of idea to test out, but if you're suggesting simply hardening 4140 instead...
  14. JacobP12345

    Lift Assist Torsion Bar

    Thank you both for all your help by the way. I have narrowed down my search to hardened 4340 and 6150. Both seem to have yield strengths (all be it very close) to our calculated 120 ksi. I imagine if I had them heat treated it could increase their fatigue resistance and strength modestly. 300m...
  15. JacobP12345

    Lift Assist Torsion Bar

    From my math, not doubting just wanting to make sure, I used .25'' for r as my diameter is .5'' so my distance to stressed surface (r) should be half that, or .25''. I used 11*10^6 psi for G, 1.57 for alpha, and 36'' for L. This yielded t= 1.57*11*10^6*.25/36 which gives me approx 120 ksi.
  16. JacobP12345

    Lift Assist Torsion Bar

    We have one to test but it's welded in place to the frame of the door we are improving on. It has rust on the surface from end to end so I'm pretty sure its steel. That's why I've been pounding my head against a wall for a solid few weeks trying to figure out what they're using. I assume its...
  17. JacobP12345

    Lift Assist Torsion Bar

    Thanks for the input, the issue we're having is on a few we've seen in the field they operate off a 1/2'' hex torsion bar and are simply mounted by hex sleeves on both sides, overall length of 36'', and rotate the full 90 degrees and act as a lift assist for the lid. It's a simple straight bar...
  18. JacobP12345

    Lift Assist Torsion Bar

    So I came to realize I made a pretty substantial error in my calculations, and used the diameter in place of the radius. Considering a = deflection in radians, and our deflection to be 90 degrees, that gives us 1.57 radians. Applying this to the equation, 1.57 = length (36 inches) * (shear) /...
  19. JacobP12345

    Lift Assist Torsion Bar

    I will give that approach a try. Given that yield strength is roughly accurate, is there any material you know of or could recommend that could either be heat treated to have that effect yield strength on the surface or otherwise? My trouble so far isn't in the kinematics but the material...
  20. JacobP12345

    Lift Assist Torsion Bar

    What would be an ideal material for a torsion bar assisting lifting a 200 pound lid with the rod being subjected to a displacement of 90 degrees? Hardened 4140 has been attempted but it yielded and is not ideal. Looking elsewhere has suggested higher carbon steels such as 1074, but before trying...

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