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diff --git a/_posts/2020-02-13-welding.md b/_posts/2020-02-13-welding.md new file mode 100644 index 0000000..78c3f9e --- /dev/null +++ b/_posts/2020-02-13-welding.md @@ -0,0 +1,109 @@ +--- +title: MIG welding +--- + +Recently, I took a MIG welding class at [Artisan's +Asylum](https://artisansasylum.com) in Somerville, MA. I wanted to document what +I learned so that I can refer back to it in the future, so here it is! + +## Safety + +There are four primary hazards: + +1. **Burns.** You're dealing with liquid metal, so the work piece will remain + hot even after you finish a weld. Also, small balls of molten steel will fly + away from the work area and can burn through clothing and footwear, or ignite + flammable objects nearby. Precautions: welding jacket, welding gloves, face + mask, eye protection. Scan the surrounding area for fire hazards before + welding. +2. **Electric shock.** MIG welding is an electrical process in which current is + passed between the welding wire and the ground clamp. Precautions: don't weld + in damp areas. +3. **Radiation.** Ultraviolet light emitted from the arc can damage eyesight. + Precautions: welding face shield, preferably an auto-darkening one, though a + small amount of exposure will occur due to the delay between the arc flash + and the sensor activation, mostly a concern when you spend 40 hours a week + welding. +4. **Asphyxiation.** MIG welding typically uses a gas mix called C25, a mix of + 75% argon and 25% carbon dioxide, in order to displace oxygen from the work + area which would oxidize the molten steel and prevent a solid weld from + forming. As the gas mix displaces oxygen, welding in an enclosed area could + result in hypoxia. Precautions: weld in a well-ventilated area. The welding + shop at A^2 has an exhaust system. + +## Mechanics + +There are two primary controls on the welding machine: voltage (a proxy for +temperature) and feed speed. There's a chart on the welding machine with +recommended settings for types and thicknesses of sheet metal. Some machines +have an "auto feed" setting which tends to work fairly well. + +Don't weld anything galvanized, as the zinc will vaporize and can cross the +blood-brain barrier causing neurological damage. + +There are three common gauges of welding wire: 0.023", 0.030", and 0.035". 030 +is a good general purpose wire. When you switch out a reel, be sure that the +feed rollers are fitted for the correct gauge. The number facing out on the reel +is the groove in use, regardless of whether it's actually on the same side of +the number or the opposite side. + +To reduce friction on the sleeve that holds the welding wire inside the gas +cable, try to avoid sharp loops, similar to how a garden hose can kink. + +You want to keep the nozzle about 3/8" away from the work piece. + +After a weld, slag and ash may accumulate on the surface. This can be brushed +off with a wire brush or ground down for a cleaner surface. + +The welding tip is where the current is transferred from the electrode running +down the cable into the welding wire. It's relatively easy for the tip to become +damaged and require replacement; it's a 15-cent consumable part so not a big +deal. To replace, pull off (don't unscrew) the sheath from the end of the +nozzle, unscrew the tip, and screw a new one in. The inner diameter of the +sheath may also accumulate slag buildup over time which can easily be cleaned +out using the tapered end of MIG welding pliers. + +To warn people nearby, announce "welding" before starting a weld. + +Two directions for welding: push and drag. Not much difference between them +other than what you can see: drag allows you to see the bead you're laying while +push allows you to see where you're going. + +## Tack Welds + +Useful for tacking a piece in place before laying a bead. With about 3/8" of +wire protruding from the tip, place the tip against the work surface, and +depress the trigger for about 1 second. + +## Beads + +A bead can be produced by dragging the end of the welding wire along the work +piece. The bead should be about twice as wide as the work piece is thick; e.g. +for 1/8" steel the bead should be about 1/4" wide. The width can be controlled +by regulating the speed at which you drag the nozzle across the work surface. + +A nicer bead can be laid by using a circular motion, which also produces the +aesthetically pleasing waves. + +The height of the bead should be fairly low, as the larger the angle between the +sheet metal and the bead, the less sturdy the weld will be. + +## Fillets + +This is basically just a bead laid to join two pieces at a right angle. Use the +same basic technique, but you'll be bumping then nozzle up against the side and +bottom pieces in order to be close enough to the work area right at the join. + +## "Series of tacks" + +Can be useful when welding very thin stock that welding a bead might melt right +through. This works by using the thermal capacity of the previously welded tack +to help absorb some of the heat. Place the wire right up against the previous +tack for optimal heat dissipation. + +## Fill-in + +You can fix a hole by placing a bunch of dots inside it. It won't look super +pretty, you'll almost certainly need to grind it down afterwards, and it won't +be very strong. You could use it as an aesthetic (rather than structural) fix +e.g. if it'll be painted over afterwards. |