Practical MIG Welding: Machine Setup

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Machine Setup

08.04

00:00	Setting up a machine for MIG welding is a straightforward process, but getting this wrong is going to set us up for a frustrating experience when we pull the trigger for the first time.
00:08	In this module we'll cover what you need to know and the first step is confirming the polarity.
00:13	The process we use will dictate the polarity of our machine but most MIG welders will be wired in what's called positive polarity or DCEP which stands for direct current electrode positive.
00:25	We should only need to change the polarity for a specialised type of welding that calls for this.
00:30	Many flux core welding methods will require a change to DC electrode negative but for 99% of us using shielding gas, we'll be using DC electrode positive for motorsport MIG welding.
00:41	If it does need to be changed then this means we'll need to swap a cable, usually located inside the machine close to the wire drive assembly.
00:49	As discussed in our earlier module on filler wire, it's important to choose the correct wire for the material that we'll be welding.
00:56	The spool of wire will then need to be fitted into the machine and the matching roller's fitted to the drive unit.
01:02	Matching these rollers to the diameter of our wire is critical to the performance of the MIG welder.
01:07	This is going to allow for a firm grip on the wire to correctly drive it off the spool and into the handheld MIG gun.
01:14	Setting the tension on these rollers is just as important as selecting the correct rollers themselves.
01:19	First we begin with a minimal amount of tension on the adjuster knob, then remove the contact tip in the handpiece and drive the wire through the MIG gun lead until it exits the torch.
01:30	Now, we can refit the contact tip and gas nozzle, making sure that the tip matches the wire size as well.
01:35	Next, we want to pick up the torch, being careful that we're not completing the electrical circuit by handling the earth clamp at the same time.
01:43	It's rare but it's possible to receive a nasty shock from accidentally depressing the MIG gun trigger while touching the earth clamp at the same time.
01:51	After ensuring that our earth or workpiece clamp won't complete the circuit, we can depress the button on the MIG torch to drive the wire into a bench at a 45° angle.
02:01	We want just enough tension on the drive rollers to continue to drive and bend the wire as it exits the torch.
02:08	Any more than the minimal amount needed to do this may crush the wire and cause issues with current delivery from the contact tip.
02:15	This is a particular problem if we're using aluminium filler wire since the material is inherently soft and more easily deformed by the rollers.
02:24	With our wire now set up, we can close the wire feed door and connect our shielding gas.
02:29	Make sure that all the fittings are clean and free of any dirt or obstructions that could affect the gas flow and then we can tighten them up with the correct size spanner.
02:38	We want to have our bottle tightly held to the welding cart to ensure that it can't fall.
02:43	Dropping a bottle will almost certainly snap the top off it, potentially causing a substantial hazard as it becomes a powerful torpedo.
02:51	Before opening the valve on the bottle, we should make sure that our regulator is completely closed so that we can slowly increase the flow to the desired amount.
02:59	A good starting point will be around 10 litres per minute which is the equivalent of 20 cubic feet per hour depending on the units on your particular regulator.
03:07	We can run the gas by hitting the purge button on the machine or depressing the trigger on the handpiece.
03:13	Once our flow is set, we can trim off the excess wire from the contact tip to achieve around a 10mm stick out and move onto the machine settings themselves.
03:21	For more basic machines, we need to set the wire speed and voltage and this is one key area where we're likely to see some variation from one machine to the next.
03:30	Let's take wire speed for example which we know also adjusts the amperage.
03:34	If our MIG has a synergic mode or an LCD display then this may list the actual wire speed, usually in inches per minute, while non synergic machines may just have markings around the profile of 1-10 for example.
03:48	Likewise, for the voltage on machines without a synergic mode, this will likely also be listed in steps, perhaps A-J like our Lincoln PowerMig So, how do we deal with this? The first place to start is with the manufacturer's recommended settings which will usually be attached to the wire spool door or listed in the instruction manual.
04:07	Taking our Lincoln PowerMig as an example again, let's say we want to weld some 12 gauge mild steel, which is 3mm thick, using 0.8mm filler wire which equates to 30 thousandths of an inch with a shielding gas comprising 75% argon and 25 % CO2.
04:24	We would want to set our wire speed to 5.5 and our voltage to H as per the recommendations.
04:31	But what if our machine doesn't offer this information? Well all is not lost and we can use our 40 amps per millimetre rule of thumb to get us in the ballpark.
04:40	In the case of our Lincoln MIG, the specifications list the output amperage range as 30 through to 180 and we know that we have 10 settings on our wire speed dial.
04:50	If we subtract 30 from 180 we can find the amperage range of the machine which of course is 150 amps.
04:57	Now, if we divide this by the number of steps on the wire speed knob, we get 15 amps per step.
05:03	However, don't forget that our lowest output amperage is 30, so in this case 1 would give us 30 amps and each step up from here increases the amps by 15.
05:14	Coming back to our 3mm thick steel, our rule of thumb of 40 amps per millimetre means that we need around 120 amps.
05:22	Starting at 30 amps and stepping up in 15 amp increments, this would mean that setting 6 will give us 120 amps.
05:29	Not quite the 5.5 recommended but pretty close.
05:34	Setting the voltage is not quite as clear cut however and this will inevitably require some test welds to get it dialled in perfectly.
05:42	As a starting point I'd suggest matching the position of your wire speed adjustment.
05:46	For example if you're approximately in the middle of the wire speed range, then starting in the middle of the voltage range will be sufficient to get you up and running.
05:54	In the case of our Lincoln, this would have our voltage set to F.
05:58	Not quite the recommended setting of H but again it's more than enough to run some test welds on some scrap metal and then fine tune from there.
06:06	We're looking for the weld current to achieve an adequate level of penetration into the base material without burning a hole through to the other side.
06:14	Factors such as travel speed and technique will also have an influence on this but the wire speed and amperage should be the constant and these other factors modified to suit.
06:24	The voltage setting will affect the width and height of the weld bead.
06:28	Insufficient voltage will result in a tall and narrow bead while too much can result in a wide and flat or even sunken bead.
06:36	When the voltage is set correctly we should have a smooth and slightly convex weld bead.
06:42	For those using MIG welders with a more advanced synergic settings, you will simply enter your wire diameter, material type, gas type and material thickness and the machine will adjust the settings to suit.
06:52	Now, that we're ready to lay down some welds, we need to fit the earth clamp to our table or workpiece, remove any flammable items from the surroundings, fit our PPE and run some test welds to get a feel for our welder and the settings that it's now been programmed with.
07:07	Treat this module as a quick start guide to get you going.
07:10	The reality is that your technique has a lot to do with the performance of your welder so we'll be looking at mastering technique in the next module.
07:18	Let's summarise the steps that we've discussed in this module before we move on.
07:22	The very first thing we need to do is check our machine's polarity which for our purposes is most likely going to be direct current electrode positive.
07:31	Wire selection and diameter are crucial and we should always match the rollers in the drive unit to the wire's diameter and correctly set the tension.
07:38	With this correctly set, we can then connect our shielding gas and make sure that we've got a flow of around 10 litres per minute to get started.
07:45	We then trim off our excess wire to achieve a 10mm stick out and we can move on to our machine's settings.
07:52	Once we have a base set, we need to fine tune our settings by running some test welds on scrap material, aiming for adequate penetration without burn through.