Practical MIG Welding: Diagnosing Welding Issues

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Diagnosing Welding Issues

10.29

00:00	We've already touched on some of the problems that can creep into our welds that can affect its quality, appearance and strength, but in this module we're going to dive deeper and highlight each of the common issues so that we know what these look like and then how to prevent them.
00:13	Let's start with what a quality weld should look like, which of course you'll become familiar with as you gain experience and you'll always be self assessing your welds as you work through a project, both during and after each weld.
00:26	A quality weld is going to have a consistent bead profile in both the width and the height of the weld bead.
00:32	We're also looking for a smooth transition at the toes of the weld which is the point where the edge of the weld meets the base material.
00:40	Our weld should not show any signs of cracking, holes or porosity as these will understandably affect the weld's strength and reliability.
00:47	While some spatter is to be expected with the MIG process, this shouldn't be excessive.
00:52	A good weld should also have sufficient penetration into the parent material which is critical to the strength of the finished weld.
00:59	We covered penetration in detail in the last module as well as how we can test for this so we won't go over it again here.
01:05	Now, that we've seen what a good weld looks like, we can start to cover the common problems that almost everyone is going to experience as you're getting started.
01:13	The first of these, and in no particular order, is porosity.
01:17	This can look different depending on how extreme the problem is and of course there are different issues that can cause it.
01:24	Essentially porosity will look like a tiny group of air bubbles on the surface of the weld.
01:28	These may be localised or we may see these throughout the weld depending on the cause.
01:33	The most extreme level of porosity is easy to recreate by simply forgetting to open our gas bottle before welding.
01:40	This is going to present as severe porosity due to the reaction with atmospheric air but at the same time, the weld will also have a burnt or dirty brown look to it.
01:49	Assuming that we haven't forgotten to turn the gas bottle on, we can still end up with porosity in a weld but it's likely to present as a much milder version with minor to moderate levels of air bubbles visible, often limited to just one small area.
02:03	Regardless of how extensive the porosity is, this still indicates an underlying issue though.
02:08	This porosity can be caused by a lack of proper part preparation that's left the workpiece dirty or oily.
02:15	Moisture on the workpiece or filler wire, excessive stick out length or poor or insufficient gas coverage due to low gas flow, wind or air movement or a clogged gas nozzle can also cause porosity.
02:28	To rectify a porosity like this, we'll need to ensure that we have our gas bottle open, the gas flow is correctly set to around our 10 litres per minute target and we want to make sure that the gas nozzle is clear of debris.
02:39	If there's any wind or air movement then it's best to mechanically block this to prevent it affecting the weld.
02:45	However, if this isn't possible, then increasing our gas flow in 2 to 3 litre per minute increments can help.
02:52	Next, up we have an undercut weld which looks like a groove or trench running along its edge.
02:57	This is caused by the arc melting the base material but with insufficient filler wire to fill it back in, resulting in the base metal being thinner in the undercut area and therefore being weaker which can of course become a potential failure point.
03:11	This can be caused by excessive heat as a result of too much voltage, insufficient wire speed, or a combination of both.
03:19	It's also possible to create an undercut weld by travelling too fast with the mid gun, moving the weld pool along before enough filler wire has been deposited.
03:28	The solutions to an undercut weld include reducing voltage, increasing wire speed, or slowing down the speed of travel until the weld is properly filled in.
03:36	If we're using a weaving technique then it can be beneficial to pause briefly at each edge of the weave to ensure proper tie into the base metal.
03:44	Our next problem to diagnose is referred to as lack of fusion which is where the weld bead appears to be just sitting on top of the base metal instead of fusing properly with it.
03:54	This results in a very weak weld that's very likely to become a failure point in the future.
03:58	Generally, this is created by insufficient heat being applied to the weld pool, meaning that the base metal isn't getting sufficient heat to melt and fuse with our weld pool.
04:08	This is typically a result of insufficient voltage however we can create the same result by travelling too fast with the mid gun.
04:15	Contaminated surfaces can also be responsible however this would normally also show some sign of porosity as well.
04:21	The first place to start with this sort of issue is to increase the voltage and run some test welds to dial it in.
04:27	Slowing down our travel speed can also help.
04:29	Now, we can move on to excessive spatter which results in tiny balls of molten metal sticking to the workpiece in the vicinity of the weld.
04:37	As we've mentioned already, some amount of spatter is a natural byproduct of MIG welding and is hence unavoidable.
04:43	However, excessive spatter is indicative of potential problems.
04:47	The cause of this spatter is due to an arc that's either unstable, too hot or a combination of both.
04:53	In addition, insufficient shielding gas or contamination of the base metal can also cause this so there are a few elements to work through here.
05:01	Assuming that we're confident in our gas flow settings and material preparation, the first place to start would be to reduce the voltage and wire feed slightly and run some test welds to get these correctly dialled in for our application.
05:13	Next, up we have cracking of the weld which is a little more rare than the problems we've discussed so far, however it's still worth understanding.
05:21	This will present as visible cracks or fractures across or along the weld which may not be visible until the weld has cooled down.
05:28	It probably doesn't take much imagination to understand that these are bad news if weld reliability and strength is important as any stress introduced to the part is liable to result in the crack propagating until a complete failure occurs.
05:41	The most likely culprits here include cooling the finished weld too quickly, such as immersion in water, use of an incorrect or incompatible filler wire, contaminants in the joint or in some situations, this can result from the base material not being preheated prior to welding.
05:56	The solutions should be pretty apparent but we always want to allow our parts to air cool and if you need a better understanding of what filler wire is required, you can check the material specific modules for a guide.
06:08	As we continue to learn, parts prep and cleanliness is crucial to avoiding issues like this.
06:14	We haven't covered preheating so far in this course as it's not something that we'll typically need to do, however it can have its place particularly when welding thicker sections or specific materials such as high carbon steels like 4130 chromoly and cast iron.
06:30	Preheating is the process of using a heat source such as a propane torch to bring the material in and around the weld area up to around 1 to 200°C prior to welding which can be measured with a simple infrared thermometer.
06:43	This has the effect of slowing the cooling time, reducing thermal shock and it can also help with fusion and penetration, particularly if we're at the limit of our MIG's material thickness capability.
06:54	Ultimately, this can help eliminate the chance of hydrogen induced cracking.
06:58	Our next issue is burn through which is something all welders will come across at some point, particularly when you're welding thinner material.
07:06	This presents as either a hole through the material or a weld that's sunken and thin.
07:11	This is a result of applying too much heat to the workpiece, effectively melting a hole right through it.
07:16	The causes are generally excessive voltage or amperage for the material thickness but this can also be caused by travelling too slowly with the MIG gun.
07:25	Poor fit up on thinner material will also make burn through much more likely.
07:29	The solution to this particular problem can include reducing the voltage and or our current and wire speed and increasing the travel speed.
07:37	With thin sheet metal, we're likely to find the heat builds up in the base metal faster than it can dissipate and settings that worked well at the start of our weld can result in burn through as the weld progresses and the heat builds up.
07:49	Using shorter stitch welds and then allowing the material to cool before proceeding can be beneficial in these circumstances.
07:56	Next, on our list is inconsistent weld appearance where one weld looks perfect but the next weld with no setting changes is very different.
08:03	This can include variation in bead width, height and penetration, perhaps combining with some of the issues that we've already covered.
08:11	As usual there's a variety of potential causes here including welding technique, a jerky or inconsistent travel motion can cause what we're seeing as can poor body position that makes it difficult to be smooth and consistent with the gun.
08:24	Varying the stick out length as we weld will also affect the weld appearance as will problems with our wire feed system.
08:31	This may include using the wrong or a worn contact tip or incorrect tension on the wire feed.
08:36	The solution to this is to ensure our wire feed is set up and operating correctly in the first instance as we've already learned.
08:42	Beyond this we should ensure that our technique is correct and maintain a consistent stick out length, gun angle and travel speed.
08:49	We can't complete a module on diagnosing weld issues without discussing the sound the welder makes as this can tell us a lot about our settings.
08:57	You'll recall that for the short circuit method we want to be hearing that nice consistent sizzle or crackle that sounds like bacon frying.
09:06	If we're not hearing this, then it can give us some clues.
09:09	For example if we're hearing an intermittent popping sound then this is often indicative of excessive wire speed or a voltage that's too low.
09:17	Excessive wire speed can also cause the gun to be physically pushed back off the workpiece since the filler wire isn't being melted fast enough so the solid wire is contacting the workpiece and forcing the gun away.
09:28	If we're hearing almost nothing and the welder's progressing in near silence or with a light hissing sound, this can indicate an issue with the gas flow.
09:36	This of course will also result in porosity which we've already covered.
09:40	A low frequency buzzing sound or sputtering can indicate that we have insufficient wire speed or incorrect voltage.
09:47	This will most likely be accompanied by an intermittent arc that cuts in and out, as well as inconsistent or insufficient penetration.
09:54	Lastly if you're hearing a buzz or hum but there's no arc initiated, then this can indicate a poor ground connection.
10:01	In this case, confirming that the ground clamp is attached to a clean unpainted part of the workpiece should fix the issue.
10:07	This has been a fairly exhaustive list of the most common problems you're likely to come across with your own welds and I'm not going to repeat them all in here in summary.
10:16	Instead, I'd suggest making sure you're familiar with each of the problems we've covered, and then coming back to this module if you're struggling with the quality of your welds and you just can't seem to fix them.