Practical MIG Welding: Welding Technique

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Welding Technique

10.08

00:00	Once we have the settings optimised on our welder, the actual welding technique is the next part that we need to understand and perfect in order to produce high quality, consistent and strong welds.
00:10	In this module we're going to cover what you need to understand and master.
00:13	First let's talk about the stick out length which you may hear referred to as electrode extension.
00:18	This is the distance between the contact tip and the end of the filler wire before it enters the weld pool and we should aim to keep this in the vicinity of 10mm in length.
00:26	This distance is important as it has a significant effect on the weld and the welding process.
00:32	Increasing the stick out length will increase the resistance in the wire, resulting in more heat being generated in the filler wire itself.
00:38	It'll also reduce the arc voltage which reduces the penetration of the weld.
00:43	As the stick out length increases we can also end up with less arc stability, increased weld spatter and a decrease in our weld quality.
00:50	The arc itself will also become less forceful which can lead to poor fusion.
00:54	Lastly the filler wire may melt prior to reaching the weld pool, resulting in less deposition efficiency which refers to the amount of filler wire deposited into the weld as a percentage of the total amount of filler wire consumed.
01:07	Conversely as we reduce stick out length, we get the opposite effect, notably the arc stability and control is improved and since less heating occurs in the filler wire, more power is directed into the weld, producing more penetration.
01:20	We'll also see less weld spatter and improved weld quality.
01:24	At this point it probably sounds like less is more when it comes to stick out, however that's not necessarily the case.
01:31	As the stick out length is reduced, we run the risk of the gas nozzle and the contact tip becoming damaged by the excessive heat from close proximity to the weld pool.
01:40	A very small stick out length will also result in the gas nozzle potentially obscuring our view, making it difficult to see what we're doing.
01:47	With all of this in mind, keeping a constant stick out length of around 10mm will result in a reliable weld that's clearly visible and well shielded with gas.
01:57	Adjusting the stick out length within reason however can be used to our advantage.
02:01	For example it's common to increase stick out length slightly to increase the resistance in the filler wire and reduce the heat input if the workpiece gets too hot.
02:09	This can be really useful when encountering a thinner section of material that would otherwise be susceptible to burn through if we were to maintain a 10mm stick out length.
02:18	This is simply done by moving the gun further away from our workpiece.
02:22	This brings me to the actual noise of MIG welding and this is a good time to mention the four types of weld transfer methods that are used.
02:29	The first of these is short circuit transfer and this refers to the filler wire touching the base material and shorting out.
02:35	This can be heard as an intermittent crackling sound that is most often compared to the sound of bacon frying in a pan and of all of the transfer methods, this produces the least heat in our workpiece.
02:49	The reason for this is that the arc is only active for short bursts, meaning heat is applied intermittently.
02:55	It also operates at a lower voltage and amperage which again results in less heat input to the workpiece.
03:01	Short circuit transfer however does result in more weld spatter.
03:04	This transfer method is best suited to thin materials like sheet metal, out of position welds and low heat applications to prevent burn through.
03:12	It's also the method most prevalent in the motorsport industry but for the sake of completeness, we'll cover the other three here.
03:18	The second transfer method is known as globular transfer and is similar to the short circuit method but more heat is applied, causing the filler wire to melt into large irregular molten droplets that fall into the weld pool due to gravity.
03:31	This process is erratic and less controlled.
03:33	Since we're relying on gravity with this method, we're limited to flat and horizontal fillet welds too.
03:39	This transfer method sounds like a long drawn out slow pop and crackle sound.
03:48	While this method gives us moderate to deep penetration, it also results in an increase in weld spatter, inconsistent arc stability and poor weld appearance which is not well suited to our needs.
03:59	Next, up we have the spray arc transfer method which uses high heat which results in the filler wire being transferred to the workpiece in a fine mist or spray of tiny droplets, creating a smooth controlled arc with minimal spatter.
04:12	Unlike the other welding methods, this one is almost silent.
04:18	This method results in deep penetration making it suitable for thicker materials, however the high heat makes it unsuitable for thinner sheet metal that we regularly come across in a motorsport application.
04:29	Spray arc transfer is also only suitable for horizontal welding.
04:32	The last method is referred to as pulsed spray transfer which uses a pulsed power source that momentarily increases current to detach a single molten droplet at a time.
04:42	This results in a stable arc without the continuous high heat of regular spray transfer.
04:47	While this method produces less heat than the spray transfer method, it's still higher than the short circuit transfer method, limiting its usefulness on thin sheet metal.
04:55	It results in moderate to deep penetration with very low weld spatter.
04:59	Pulsed spray transfer is suitable for all welding positions due to its lower heat input, however it does require a MIG machine that offers this more advanced pulsed method and also requires shielding gas with greater than 80% argon.
05:12	For the majority of metals that we MIG weld in motorsports, the short circuit transfer method with its fast paced, crackling bacon sound will be the method of choice.
05:20	Now, let's move onto discussing the actual welding technique or how we move the MIG torch.
05:26	As we move along our weld seam, we do so in a direction that's known as either pushing or pulling.
05:31	It's recommended that the torch is pushed along the workpiece so therefore it'll need to be rocked back around 15° towards the direction of travel to assist the shielding gas to flow over the molten weld pool.
05:43	Pulling the torch would see it go the opposite way and this can be useful if utilising flux core arc welding to reduce the inclusion of slag in the weld.
05:51	A common saying within the industry is, if there's slag, then drag, referring to the pulling motion of torch travel.
05:58	This however is largely irrelevant to our use in motorsport.
06:01	The direction of travel is pretty fiercely debated in MIG welding circles.
06:05	While we recommend the push direction in most instances, the reality is that dragging or pulling can still provide reliable results and in some situations we may need to use the pull technique, so it is worth practising.
06:17	If you're right handed, then you'll hold the gun with your right hand and in this instance, it's going to be most comfortable to travel from right to left.
06:24	If you're left handed, then the opposite holds true.
06:27	It's also beneficial to use your free hand to help support the torch as you move along the weld.
06:32	When we're welding, we need to make sure that even amounts of heat are input into each side of the workpiece.
06:38	To do this, we need to angle our MIG torch into the root of the weld seam at the intersection of the two parts.
06:44	This will keep the penetration and inclusion into both sides of the workpiece even and ensure a consistent and reliable weld.
06:51	For a flat weld between two parts, this requires the gun to be held at 90° or perpendicular to the workpiece.
06:57	On the other hand, for a 90° fillet weld, we want to angle the torch at approximately 45° so that it's angled equally towards both sides of the workpiece.
07:06	Moving the torch in a stop start motion allows us to build up the size of the weld pool before moving along and continuing this will produce a stacked dime look in our MIG weld.
07:15	A straight pass weld like this, with or without the stop start motion, is also referred to as a stringer bead.
07:22	It's also common to use a weaving motion of the torch when welding different material thicknesses together because it allows us to focus more heat on the thicker portion of the workpiece.
07:32	This weaving motion can also be helpful when bridging gaps that have resulted from poor fit up as well as for some out of position welds.
07:39	There's a variety of techniques to this weaving including a literal side to side weave as we travel down the weld seam.
07:46	Other techniques include more of an oscillating movement where the tip of the torch moves in small overlapping circles as the weld progresses or more of a triangular or V style movement where the tip of the torch traces out the shape of the letter V as we move from side to side.
08:01	There isn't necessarily a right and wrong weaving technique and it comes down to what we're comfortable with and personal preference.
08:08	I'd recommend practising to find out what you like best.
08:12	We should be mindful that weaving the torch during a fillet weld can starve the root of the joint from adequate fusion and penetration.
08:19	So, if we need a larger weld bead, then it's preferable to make an adjustment to the voltage and wire speed instead of trying to do this by varying our technique.
08:28	As we near the end of the weld, we also need to be mindful of our post flow gas coverage.
08:32	By terminating the arc and hovering the torch over the heated area, we shield the heated zone from the atmosphere and protect the metal while it's cooling.
08:40	If the metal is still glowing and our gas shuts off too early, it can create some discolouring of the weld area, or worse still, a crater in the weld pool from an atmospheric reaction.
08:50	These craters can develop into a crack within the weld joint and will be a certain point of failure if the part is highly stressed.
08:57	In our industry, we're often forced to weld under cars and in tight places which makes MIG welding more difficult, making machine setup more critical.
09:05	This type of welding is known as out of position and refers to any large object that needs to be welded without having the ability to be rotated or shifted to improve access for welding.
09:16	Due to the unique requirements that out of position welding creates, we'll cover this in detail in its own separate module shortly.
09:22	As we get further into this course, you'll begin to get a really good understanding of welding technique and the resulting changes that the torch position has on your finished weld.
09:31	A good weld is the result of a combination of all of the practical skills in this section.
09:35	Before we move into tack welding, let's quickly run over the main points covered in this module.
09:40	Maintaining a consistent stick out length of approximately 10mm results in a reliable and well shielded weld.
09:47	The short circuit transfer method is most common in our industry and when set up correctly, the weld will sound like frying bacon.
09:54	Proper torch movement is also essential.
09:56	Pushing the torch along the workpiece with a slight tilt around about 15° to the direction of travel helps the shielding gas flow over the molten pool.