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I am very new to welding (and this site)- I am trying to understand how to do proper multi-pass MIG. I did see the post with pictures. But how do you do multi pass if you are joining steel at 90 degree angles? as opposed to two flat pieces of steel ? Do you have to tack weld then use something like a die grinder to "hollow out " the joint before welding it ? Also what about four sided tubular steel -like what is used on a boat trailer ? Is multi-pass only recommended for joining two pieces of flat steel ? Do you always have to grind and prep thicker steel when using multi-pass ?I raise all of these qustion as I contemplate the purchase of either a 115V versus a 230V Lincoln,Miller, or Hobart !
Reply:To join tee joints you use a fillet weld which is that triangular shaped section that is the bead in the corner. The larger the fillet the stronger the joint until the leg of that triangle is 2/3 the thickness of the metal on both sides. If you cannot make a large enough weld bead in one pass then you do a multi-pass weld. For butt joints it is wise to bevel the edges of the mating plates or if they are less than 1/8 thick to leave a square gap.
Reply:Multi-pass welds are only necessary where the required bead profile and penetration cannot be achived in a single pass. This is uaually due to the capability of the welding machine, and to some extent the skill of the weldor.As weldmments become thicker, multi-pass is more necessary. On thick sections it is very common to use multi-pass techniques, even with proper joint preparation.For the most part, any joint thicker than .125" should be prepared before welding. You should consider buying a welding text such as "Welding Essentials" by Galvery/Marlow and read about the process before trying to weld thicker material.As for which machine to buy, unless you plan to weld auto-body sheet metal and things like that exclusively, I'd gor for a 240V machine in at least the 180A class. A Millermatic 210 would be a good place to stert.Hank |
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发表于 2021-9-1 00:23:31