How to MIG Weld - Tutorial

How to MIG Weld - Tutorial

Search Home - Tutorial - Welders - Practical - Forum - Gallery DIY MIG Welding > Tutorial

MIG Welding Tutorial The MIG welding tutorial (the pages below) covers the steps you'll need to take to learn how to MIG weld. It's the sort of thing you'd find in a welding for dummies or welding secrets book, but this one is free and includes videos. It's not a complete alternative to one to one tuition - see the college course page to find a course.

Welding Safety Find out some of the ways welding can damage your health or kill you, and how you can protect yourself.

Installing the wire Wire feed is the most common cause of MIG welding problems. A few tips on how to install the wire and tension the wire feed.

Power and wire speed calculator A tool to help you estimate initial power settings for your welder. Further pages in the tutorial will help fine tune the settings for that perfect weld.

http://www.mig-welding.co.uk/tutorial.htm (1 of 5)28-03-2008 7:58:39 PM

How to MIG Weld - Tutorial

Torch position and laying welds Prepping for welding, positioning the torch, and making some practice welds.

Setting the wire speed MIG welders are sensitive to wire speed. There is a very narrow wire speed range where the welder welds nicely between burn back and stuttering. This page should help you fine tune the wire speed for your welder.

Finding the right power setting The choice of power setting will vary from welder to welder, and can be influenced by technique. The best way to find the appropriate power setting for your welder is to experiment on scrap metal then examine the welds

Butt welding It's best to develop neatness and technique before attempting to join two pieces of metal together. It's a tricky first weld, so easier overlap welds are touched upon too.

MIG Welding Techniques

http://www.mig-welding.co.uk/tutorial.htm (2 of 5)28-03-2008 7:58:39 PM

How to MIG Weld - Tutorial

Thin Metal Blowing holes in thin metal? But don't want to buy a TIG? Here's a technique that should be good for 0.6mm sheet.

Gasless MIG Welding You can use it in the wind. A page with pros, cons and techniques.

Plug weld Plug welding is a DIY alternative to spot welding. It's a useful technique in automotive repairs where the panels were originally spot welded.

Finishing Welds There's only one way to end up with the invisible welded repair and it doesn't involve your ordinary angle grinding disc. This one is a real welding secret.

http://www.mig-welding.co.uk/tutorial.htm (3 of 5)28-03-2008 7:58:39 PM

How to MIG Weld - Tutorial

Welding thick metal Manufacturers claims of welder capability often seem exaggerated. The Clarke 90EN claims to be capable of welding 4mm steel sheet, but the calculator says 2mm. The page looks into the techniques required to achieve the claimed thickness.

Tips and tricks A few random thoughts and techniques that haven't found a home elsewhere in the tutorial.

Welding other metals with a MIG welder

Setting Up for Alu Welding Aluminium welding can be frustrating until you de-bug your welder. The wire is much less stiff than steel wire so is prone to crumple after the roller. An oversized tip and plastic wire liner are required together with other tweaks to your welder.

Aluminium Welding How to weld aluminium (turns out it's not so bad). Aluminium very quickly forms an oxide layer which needs to be removed before welding. From there the welding process is tricky because of the rather narrow window between melting the aluminium and blowing holes.

http://www.mig-welding.co.uk/tutorial.htm (4 of 5)28-03-2008 7:58:39 PM

How to MIG Weld - Tutorial

MIG Brazing MIG brazing is a relatively new technique that tends to be used by automotive manufacturers on modern steels that can't really be welded using conventional techniques. The material is intended to be used with specially developed MIG welders, though it can be carried out with a standard MIG with some loss of benefit. The page suggests a technique and includes a strength test.

Cast Iron MIG Welding A very useful application of MIG brazing wire is in the repair of cast iron. Braze is much softer than steel filler wire so reduces problems with cracking of the cast iron. This page describes a traditional studding technique as well as the use of braze to join a cast iron gear casing, and discusses alternative methods that could have been used to join the casting.

Postscript

We Learn… 10%…of What We 20%…of What We 30%…of What We 50%…of What We 70%…of What We 80%…of What We 95%…of What We –William Glasser

Read Hear See See and Hear Discuss With Others Experience Personally Teach Others

Feedback - for any information you would like to add or for reporting incorrect information. © Copyright: MIG welding - the DIY guide. Please notice the disclaimer

http://www.mig-welding.co.uk/tutorial.htm (5 of 5)28-03-2008 7:58:39 PM

The quote to the left relates to learning in general, but it seems especially appropriate for MIG welding. A college course or one to tuition is the easiest way to learn mig welding, but a little interaction on the welding forum can be helpful. I've learned a lot from trying to answer other people's questions and realising I didn't really know the answer myself.

MIG Welding Safety

directly at a welding arc even for a split second causes arc eye when the bright flash

http://www.mig-welding.co.uk/welding-safety.htm28-03-2008 8:00:02 PM

Installing MIG Wire and Setting Wire Feed Tension

Search Home - Tutorial - Welders - Practical - Forum - Gallery DIY MIG Welding > Tutorial > Installing and tensioning wire

Installing the wire Hobby MIG welders tend to be plagued by wire feed troubles. The wire feed arrangements on the cheaper MIGs don't tend to be up to the job, although their effectiveness can be improved by a good set up procedure. MIG welders are very sensitive to wire feeder settings and liner condition. The wire liner is a service item and should be replaced regularly especially if rusty wire has been run through it. See replacing a wire liner for details.

Preparing the wire The wire reel mounting normally includes a spring tensioner. This tensioner should be initially tightened to the point where the reel of wire doesn't unravel under it's own spring tension. The first 3 inches of wire should be as straight as possible to reduce the chance of damage to the liner or snagging as the wire is fed through. Sharp wire cutters can be used for trimming. Letting go of the end of the wire would cause it to unravel and tangle. (In the photo the hand normally used to hold the wire when cutting is being used to operate the camera.)

http://www.mig-welding.co.uk/wire-feed.htm (1 of 5)28-03-2008 8:01:16 PM

Installing MIG Wire and Setting Wire Feed Tension

Feeding the wire to the torch The wire is inserted through the guide tube and over the roller. On the torch side of the welder the small hole of the end of the wire liner should be visible. The end of the wire can be aligned with that hole using a small screwdriver or the piece of wire that was removed at the start. The wire can then be pushed into the liner manually for a few inches, and should feed easily and without any force. If force is required it is likely that the wire has missed the liner.

The wire feed roller itself will normally have two grooves, and is secured either by a grub screw in the side of the roller, or a knurled plastic cap as in the photo. The groves on UK welders are normally matched to 0.6mm and 0.8mm wire and the roller can be reversed to line up the appropriate groove for the wire size being used. Rust or grease on the wire can reduce the effectiveness of the rollers, and they need to be cleaned with a dry cloth before inserting the wire. With the wire pushed a couple of inches into the liner replace the tensioner clamp, switch on the welder and use the wire feed mechanism to push the wire through the liner. The torch should be a straight as possible especially near the torch to reduce the chance of the end of the wire wire catching inside the liner.

http://www.mig-welding.co.uk/wire-feed.htm (2 of 5)28-03-2008 8:01:16 PM

Installing MIG Wire and Setting Wire Feed Tension

On some welders it can help to remove the contact tip from the end of the torch before feeding the wire through. The gas shroud is secured by a spring and can be removed by pulling and twisting in a clockwise direction, and the tip has a standard screw thread that unscrews in an anti-clockwise direction (viewed as in the photo). Never unscrew the tip when it is still hot or it may break or strip the thread inside the torch. If the wire snags in the torch it may be possible to withdraw a little wire onto the reel, and use a rotating motion with the torch to get the wire past the snagging point.

Setting the roller tensioner The wire is driven by friction between the wire feed drive roller and the wire. This method of drive commonly causes problems on hobby welders where the tensioner is not robust. Care in tensioning the wire feed can prolong the life of the tensioner mechanism. Tightening the tensioner fully can cause the tensioners or tensioner mountings to bend and could also shear the motor gearing if the wire were to stick in the tip during welding. The minimum tension that will ensure good wire feed is recommended.

http://www.mig-welding.co.uk/wire-feed.htm (3 of 5)28-03-2008 8:01:16 PM

Installing MIG Wire and Setting Wire Feed Tension

One way to judge the wire feed tension is to grip the wire very lightly between your fingers and pull the trigger. Care is needed with this approach as if the wire were to touch the earth clamp it would arc, resulting in burned fingers and possibly arc eye. Starting with very little tension on the wire feed mechanism, Increase the tension until the wire feed stops slipping, but do not grip the wire so tightly that the wire feed motor slows. The wire should ideally start to slip inside the rollers before the motor stalls.

Setting the reel tensioner Finally check the tension on the wire reel. The tensioner on the reel is there to stop the wire becoming loose and tangled, but the tension should be as light as possible to make life easy for the wire feed mechanism. Set your wire speed to the maximum you are likely to use, and press the trigger on the torch. The wire reel should stop without unraveling when you lift off the trigger.

http://www.mig-welding.co.uk/wire-feed.htm (4 of 5)28-03-2008 8:01:16 PM

Installing MIG Wire and Setting Wire Feed Tension

Avoiding wire feed problems Wire feed problems are commonly caused by rusty welding wire. The rust acts as a lubricant on the feed rollers causing slip, and as an abrasive on the wire liner which increases resistance. Wire can quickly go rusty when left unused inside a welder. Ideally the wire should be removed and stored indoors when the welder is not in use. This wire in the photo was reusable after the top couple of layers of wire had been removed. Liners damaged by rusty wire can be replaced fairly cheaply.

Other wire feed info ●

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Wire liners do wear and are considered to be a service item. Professional welders might replace the liner after every 100kg of wire. On most welders the liner can be unscrewed at each end and pulled out of the cord. Replacement liners only cost a few pounds. See replacing a wire liner for details. The grove in the roller varies between metal type. A V shaped groove is used for standard mild steel wire. For flux cored wire the groove often has a knurled finish. Aluminium wire is much softer than steel and tends to be used with a U shaped groove. The common sizes of wire reel are 1kg, 5kg and 15kg. The 5kg and 15kg reels have similar mountings, but the reels are different in width and diameter, and the 1kg reel has a smaller mounting. Welders won't necessarily be supplied with the fittings to suit all types, and hobby welders might not be big enough to take 15kg reels. Wire liners come in steel, plastic and teflon. The steel liners are the most robust and are excellent for mild steel wire, offering the lowest resistance to the wire. Teflon liners are intended for use with aluminium wire, though plastic liners can also be used for aluminium welding.

Next: DIY MIG Welding > Tutorial > MIG settings calculator

Feedback - for any information you would like to add or for reporting incorrect information. © Copyright: MIG welding - the DIY guide. Please notice the disclaimer

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Learning MIG Welding

Search Home - Tutorial - Welders - Practical - Forum - Gallery DIY MIG Welding > Tutorial > Torch positioning and laying welds

Learning MIG Welding It pays to practice on scrap sheet until you have a good technique before trying any project welding. Welding fabricators are often happy to sell off-cuts from their scrap bins for cash. Select a few different thicknesses. A good thickness for a first practice session is 1.5mm. That's thick enough to stop blowing holes being a big issue, and is a handy thickness for experimenting with power settings.

Preparing the metal Metal needs to be completely clean and free from rust or paint before welding. Not just because it is difficult to arc against a dirty surface, but because any contaminants will tend to find their way into the weld and reduce it's strength. An area should be cleaned for the earth clamp mounting too. Light use of an angle grinder or flap wheel will quickly remove surface rust and paint, and for more inaccessible areas an air grinder or dremmel can be effective.

Holding the torch MIG can be used one handed, but it's much easier when you can use both hands to steady the torch. Throw away the hand held mask that came with the welder and buy a full face mask. Welding control will be further improved if you can rest an arm against something solid. In the photo the left arm is resting on the chassis and supporting the neck of the torch. The back of the fingers are too close to the weld will get hot quickly, but this position should be fine for a short period of welding. The head is angled to one side to make the weld pool visible (the gas shroud gets in the way).

http://www.mig-welding.co.uk/learning-mig.htm (1 of 3)28-03-2008 8:05:30 PM

Learning MIG Welding

Positioning the tip I tend to angle the torch at maybe 20 degrees from vertical with the shroud angled forward. The contact tip should be about 6mm to 10mm from the metal to be welded, so cutting the wire about 10mm long and holding the torch so the wire touches the sheet is a good way to position a MIG welder.

Welder movement There are a variety of torch movements used in MIG welding. Generally some form of zig-zag or weaving motion is used to ensure the arc acts against both sheets to be welded. For thinner metal I prefer a curved zig-zag as illustrated in the photo.

Video

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It's much easier to lay weld onto a sheet of steel than to do a join, so it's best to practice technique that way. After a couple of seconds welding a liquid weld pool should develop. If the weld pool becomes too large (welding too slowly or too high power settings) it might create a hole in the metal. Weld too quickly and the weld will not penetrate through the metal.

Welding direction http://www.mig-welding.co.uk/learning-mig.htm (2 of 3)28-03-2008 8:05:30 PM

Learning MIG Welding

This page describes welding in the "push" direction. Pushing the torch rather than pulling is a good habit to get into as it improves coverage of shielding gas. For thin mild steel welded horizontally the direction of welding doesn't make a great deal of difference to the weld, so if visibility is better with the pull technique then that can be used.

Practice laying welds until the welds start looking neat. It should only take a couple of hours practice to get a feel for MIG welding. The welds in the photo were mostly made by a first time MIG welder using initial settings for wire speed and power setting from the calculator. Spend a little time laying welds on sheet to get a feel for welding on different power settings before trying to join two pieces of metal. And keep working through the tutorial for more tips.

What mistakes are you going to make? I've taught a few people to weld and the same mistakes happen every time. Here are some trouble-shooting tips for when the same thing happens to you: ●

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You'll hold the torch too far from the metal. If you don't bang the shroud against the metal you are welding every now and again you'll probably be holding the torch too far away. Some DIY welders suggest touching the shroud against the metal to help hold position, but that's just a little a too close and you'll overheat the contact tip which makes the wire stick. I bang the shroud against the metal often even after 15 years of DIY welding. You'll move the torch too fast. You'll end up with a tall thin weld doing it that way, and you'll have real trouble joining two bits of metal together later on in this tutorial. Use some sort of regular side to side movement as you go along. That'll make the weld wider and less tall, and will help control your speed of travel. If you blow holes then turn down the power and wire speed. If you still blow holes then practice on something a bit thicker until you get the hang of it.

Next: DIY MIG Welding > Tutorial > Fine tuning wire speed

Feedback - for any information you would like to add or for reporting incorrect information. © Copyright: MIG welding - the DIY guide. Please notice the disclaimer

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Setting Wire Feed Speed

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Setting wire feed speed Wire speed is probably the most important setting on a MIG welder. This page is intended to help you fine tune your wire speed and includes a video to demonstrate what the different speeds sound like. Many wire speed adjustment problems are due to wire feed set up issues, so it's worth checking that page if this one doesn't help.

Technique It's possible to weld neatly at the wrong power setting - penetration might be too little or too much, but the welds can still be neat. Get the wire speed wrong and it can become very difficult to weld at all. The trick to finding the right wire speed is to experiment. Adjusting wire speed on the fly while welding a scrap piece of steel is a quick way to test. Set the welder to approximately the right power setting for the thickness of metal, start welding, and while welding alter the wire speed knob until you get somewhere near.

http://www.mig-welding.co.uk/wire-speed.htm (1 of 4)28-03-2008 8:06:56 PM

Setting Wire Feed Speed

Video

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In the video to the left the wire speed has been gradually increased from very slow to very fast. The captions at the top show where I think the wire speed is too slow, good, and too fast. Be sure to turn your sound on - the sound of the weld reveals what is happening more than the images. There's a control at the bottom of the video you can move to listen again to each segment.

Guide to video

off

The wire feed starts at zero. It takes a little turning to get it going at all.

Far too slow

The wire is making occasional contact with the metal, but as soon as contact is made the wire burns back (forms a ball and melts back to the contact tip).

Too slow

The wire is still burning back after contacting the metal, but the process is repeating more quickly.

Good

http://www.mig-welding.co.uk/wire-speed.htm (2 of 4)28-03-2008 8:06:56 PM

The wire is going fast enough to give a constant arc to the metal, and there is a nice consistent sizzle sound to the weld. (said to sound like bacon frying, though I fail to replicate the sound with my cooking. Maybe a more expert hand holding the frying pan might get closer.)

Setting Wire Feed Speed

The weld is still consistent but but the crackle is starting to sound fierce and the penetration is increased. Cheaper welders might start making a machine gun like noise at this point. Too fast

Far too fast

Wire speed actually controls welding current (the power knob on the welder only sets the voltage). Increasing the wire speed past the point where you achieve a nice consistent weld will only increase the current and can cause blow through on thinner steel.

Here the wire is moving so quickly that it bends as it hits the metal. The torch feels like it is being pushed away from the metal, and there is a lot of spatter.

Wire speed tips and tricks ●

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Generally for thinner metal the wire speed is set at the lowest speed that welding can take place smoothly. This is because the current actually reduces as the wire speed is reduced so thin metal can be welded more slowly and controllably. It's possible to reduce wire speed further by reducing the distance between the contact tip and the work piece. This can cause the tip to overheat, grip and stop the wire, and ruin the tip, but it can be a useful technique for delicate welding such as end on to an edge especially if an oversized tip is used or when welding for short periods. For welding into a corner increase the wire speed. This reduces the length of the arc and makes it easier to weld directly into the corner rather than arcing against the sides. Wire speed will need to be increased slightly when welding on a vertical surface vertically or to the underneath of a horizontal surface. Wire speed control and different welders

Wire speed will need to be increased as the welder power setting is increased. For DIY MIG welders the wire feed is usually independent from the power setting. On these welders the wire speed will have to be manually increased as the power is increased. For my Clarke welder running 0.8mm wire a speed setting of 2.3 was good for the lowest power setting, and 5 worked well on the highest setting. More expensive welders normally have automatic adjustment of wire speed - the speed is changed by the welder when the power setting is altered. On my Portamig 181 a setting of 5.5 is good for both low and higher power settings, and the wire speed knob is only there to allow tweaking. Next: DIY MIG Welding > Tutorial > Fine tuning power settings http://www.mig-welding.co.uk/wire-speed.htm (3 of 4)28-03-2008 8:06:56 PM

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Setting Wire Feed Speed

Feedback - for any information you would like to add or for reporting incorrect information. © Copyright: MIG welding - the DIY guide. Please notice the disclaimer

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MIG Settings Calculator

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Hobby MIG Welding Calculator This calculator is intended as a guide to initial power and wire feed settings for people new to welding. It's not completely accurate, but further pages in the tutorial will help you fine tune these settings.

How to use the calculator

Enter information about your welder

These figures can be found from manufacturer or retailers' specs.

Minimum output current:

amps

For example a Sip Migmate 130 has a minimum output current of 25 amps, maximum of 130 amps, and has 6 power settings.

Maximum output current:

amps

Use the links below to fill in the form with data for the following welders: Clarke 90EN

Number of power settings:

SIP Migmate 130 Choose Units:

metric

Clarke 160TE

imperial

Portamig 181

Submit

The estimates will appear in a table (above) after you have filled in the form.

Wire speed Reference The 0.6mm wire size figures have been tested to 2mm and the figures are extrapolated. The 0.8mm figures http://www.mig-welding.co.uk/calculator.htm (1 of 3)28-03-2008 8:08:14 PM

MIG Settings Calculator

have been extrapolated from the 0.6mm results so will be less reliable, but they are at least a starting point. Where the figures are against a grey background the wire size isn't really suitable for the material thickness. The markings on welder wire feed controls do not represent speed in metres per minute. Measure the speed using a stopwatch and tape measure. It might be useful to mark positions around the wire feed knob for future use.

Steel Thickness (mm)

Wire Speed (metres per minute)

0.6mm wire

0.8mm wire

0.8

2.5

1.6

1.0

3

1.9

1.2

3.6

2.2

1.5

4.3

2.6

2.0

5.6

3.5

3.0

7.9

4.9

4.0

9.8

6.1

5.0

12.5

7.7

How it was done The estimates are based on experimental results from a Clarke 90EN, a Clarke 155T, and a Portamig 181, and gaps have been filled in by extrapolation. The method is un-scientific, but the results seem quite accurate for http://www.mig-welding.co.uk/calculator.htm (2 of 3)28-03-2008 8:08:14 PM

MIG Settings Calculator

my own welding technique and at the very least should be good for a starting point. The settings are only intended as a starting point. The wire speed and power settings pages should help fine tune the settings for your welder and welding technique. Feedback Do post on the forum with any feedback or problems you may have with the calculator or my suggested settings. Next: DIY MIG Welding > Tutorial > Torch positioning

Feedback - for any information you would like to add or for reporting incorrect information. © Copyright: MIG welding - the DIY guide. Please notice the disclaimer

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MIG Power Settings

Search Home - Tutorial - Welders - Practical - Forum - Gallery DIY MIG Welding > Tutorial > Fine tuning power settings

Adjusting Power Settings

Power controls, amps and voltage The power controls on a MIG welder adjust the voltage rather than the amps, though to some extent that's academic as increasing the voltage will also increase the amps. It's worth knowing that the wire speed also controls the amps.

Comparing the different settings The calculator provides a rough starting point for power settings. The easiest way to fine tune the setting is to practice on scrap steel of the same thickness as the steel you want to weld. Here a series of welds have been laid on 1.2mm sheet using increasing power settings from left to right. Welds made on the lower settings are quite narrow and tall, and welds on the higher settings are wide and flat.

http://www.mig-welding.co.uk/power-settings.htm (1 of 3)28-03-2008 8:08:28 PM

MIG Power Settings

Weld penetration Looking at the reverse side of the weld is more informative. The two welds on the left side haven't penetrated all the way through the sheet, but the three welds on the right have penetrated a little too far. The aim when welding two pieces together edge-to-edge is to end up with the edges of the metal melted into the weld on both sides of the joint, but not to have excessive penetration.

Sectioned welds The sectioned sheet shows the effect of the increasing power settings more clearly. In the first two welds the weld builds up above the sheet, but doesn't penetrate through. The third weld has build up on the top and bottom of the sheet. It is the best weld in the photo. The welds to the right have more penetration below the sheet than above which shows the power setting is too high.

Fine tuning using technique ●

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The speed of welding will affect the weld appearance and penetration. Decreasing the speed of torch travel will increase penetration. The weave pattern of the torch also influences weld penetration. Preparing the joint in to a "V" shape or leaving a root gap can dramatically reduce the power required for a given metal thickness. These techniques are touched upon in the 90amp 4mm challenge.

Next: DIY MIG Welding > Tutorial > Butt welding

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MIG Power Settings

Feedback - for any information you would like to add or for reporting incorrect information. © Copyright: MIG welding - the DIY guide. Please notice the disclaimer

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MIG Weld a Butt Joint

Search Home - Tutorial - Welders - Practical - Forum - Gallery DIY MIG Welding > Tutorial > Butt Welding

MIG welding - the butt weld This page starts off describing the technique for making an edge to edge butt weld, though the technique is similar for most types of joint. The torch positioning is covered on the learning mig page.

Torch Movement Various torch movements are used in MIG welding. The one I tend to use most on metal thinner than 2mm is a curved zigzag motion illustrated by the photo. It lays a little weld on the edge of each sheet, then gets out of there before the sheet has a chance to blow through. Next time the arc gets to the sheet it is a little thicker and less prone to blowing through. This tends to result in a reasonably flat, neat looking weld. Other torch movements include a ziz-zag with no curves (useful for thicker metal), and welding in a straight line without going from side to side at all (actually that one is useful for all thicknesses of metal but takes a whole lot of practice to ensure the heat is evenly distributed into both sheets of metal).

http://www.mig-welding.co.uk/butt-weld.htm (1 of 5)28-03-2008 8:10:34 PM

MIG Weld a Butt Joint

Tack welding The heat in welding will distort metal. If you started welding with two pieces of metal perfectly aligned, then after an inch of welding one of the sheets would have moved and you'd end up trying to weld across a gap. Tack welds (shown in the photo) stitch the two sheets together to prevent movement. For car bodywork the tack welds would be spaced at an inch apart. When welding a seam don't start the weld on a tack as it will break. Start between the tacks, keep welding over the tacks, and finish the weld between tacks if possible.

Video

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The video shows a butt weld in progress. The metal is fairly thin (1.2mm) so the curved motion is being used to quickly extend the weld pool on either side of the join before dipping back into the pool.

Butt Welding Here's a butt weld I made earlier. Looks neat enough but embarrassingly it's http://www.mig-welding.co.uk/butt-weld.htm (2 of 5)28-03-2008 8:10:34 PM

MIG Weld a Butt Joint

under power (see the photo below). I used the wrong power setting for this one. It is good practice to note down which power settings and wire feed speeds are good for each steel thickness. I've printed out a table from the calculator for reference in the garage where I can add my own scribbles where I find power settings I prefer.

Penetration is always poor when the weld starts, and in this case the weld started just before a tack weld. The tack increased the thickness of the metal and reduced penetration. The weld between the tacks has good penetration (see the power settings page for more thoughts on penetration) Had I used an angle grinder to remove the excess metal on the tacks I would have had perfect penetration all the way. Although if this were car bodywork I wouldn't bother. After this photo was taken I welded some sheet of the same thickness in the real world. I used the next power setting up and welded a bit faster. No problems with poor penetration near tack welds - the penetration looks very even. Hmm, maybe different photo to come, but while the old one is here you can learn from my mistakes.

http://www.mig-welding.co.uk/butt-weld.htm (3 of 5)28-03-2008 8:10:34 PM

MIG Weld a Butt Joint

Weld penetration With sufficient penetration it should be impossible to see the original edges of the metal. For the weld on the left there isn't enough penetration and the joint will be weak and prone to fatigue. The middle one is about right, and the one to the right has too much penetration. Click on the picture to the left for a larger version that will help you see what I'm talking about. The balance is between no sharp edges left by poor penetration, and too much penetration which would leave a sharp change of section between the weld and the surrounding metal.

Overlap Weld Overlap welds are far easier to do than butt welds and are a good first step in practicing joining metal with MIG. In a butt joint you have two sheets of metal of equal thickness. With overlap welding there will be a double thickness on one side of the weld which makes it a lot easier not to blow holes in the joint. Overlap welds are much like butt welds apart from the torch is angled towards the double thickness (see photo) to direct the heat towards the thicker metal. Unlike the photo, the two sheets should be clamped tightly together, otherwise it will be easy to blow holes in the top sheet.

When to leave a gap A root gap between two sheets will reduce the power needed to penetrate fully through the joint. This is the http://www.mig-welding.co.uk/butt-weld.htm (4 of 5)28-03-2008 8:10:34 PM

MIG Weld a Butt Joint

last thing you'd want with thin metal as the power setting on MIG welders doesn't go down all that far. Any steel up to 1.5mm is best welded without a gap, though a small gap or perhaps between 1/2 the thickness of the steel can be useful on steel thickness 2mm or above. Joint preparation for thicker metal In addition to the root gap, preparing the edges of the joint in a 'V' shape will aid penetration in metal above 3mm and will allow welding of metal approximately 50% thicker than would be possible without the joint prep. The effect of a V joint this can be seen on the Clarke 90 page.

Next: DIY MIG Welding > Tutorial > Welding Thin Metal

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Mig Welding Technique for Thin Metal

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How to weld thin metal The thin metal technique is a non-continuous process that is used for thin metal such as car body panels. The aim with this technique is to melt a bit of metal and then let it cool slightly before melting the next, and it's a handy way to avoid blowing holes.

Welding thin steel The butt weld page showed how to do a seam weld using a continuous torch movement. Try applying that technique to steel less than 1mm in thickness and you are likely to blow a hole in the metal. The photo is 1mm steel welded at a power setting normally reserved for 2mm steel.

Blow through You can see what's happened from the photograph. The puddle of molten metal http://www.mig-welding.co.uk/thin-metal.htm (1 of 5)28-03-2008 8:14:42 PM

Mig Welding Technique for Thin Metal

has become so big and heavy it's dropped off the steel. Often this can be prevented by reducing the amp setting of the welder and the wire speed. Using thinner wire (0.6mm instead of 0.8mm) will also help reduce amps.

Technique for thin metal

1.4Mb Flash video preloads before playing and includes sound

The way around this is to weld in short pulses, allowing a second or more between pulses for the steel to cool down. In the video I've left about a second between pulses. Turn your sound on for best effect. The movie is about 1.4MB so will take a little time to load.

http://www.mig-welding.co.uk/thin-metal.htm (2 of 5)28-03-2008 8:14:42 PM

Mig Welding Technique for Thin Metal

The completed weld The steel is 0.8mm thick and the welder power was set to minimum. The effect is quite neat, though this is a cold method of MIG welding. The danger with this technique is the individual beads of weld might not melt into each other fully resulting in a weak joint. For thin metal this isn't a problem, but a continuous weld seam weld would be much more appropriate for steel over 1mm.

Reverse Side The penetration is higher than might have been hoped, but the weld is perfectly strong enough.

http://www.mig-welding.co.uk/thin-metal.htm (3 of 5)28-03-2008 8:14:42 PM

Mig Welding Technique for Thin Metal

The stitch welding technique can be very powerful. Here's a shot of 0.3 mm stainless cut from a 5L thinners can that was welded in this way. I was hoping to manage a butt weld too, but the metal was far too thin for MIG and I just blew holes. TIG welding is the way forward for metal under 0.6mm, and a MIG welder with decent power and wire control is needed for anything less than 0.8mm.

Welding Car Panels If you are welding a large panel then the expansion of the metal during welding is likely to cause the panel to distort. The problem is that the panel expands with heat, so while it is the correct shape during welding (when the panel is hot), the panel changes shape on cooling. Distortion can be minimised by first tacking the metal together at intervals of maybe 20mm, and only welding very short sections (20mm length) at a time, allowing the metal to cool between each section of weld. If you have a long seam then the first section might be at one end of the seam and the second at the other etc. The technique is discussed a little more in welding floor panels. Another welder suggested cooling the panel (not the weld) with a wet cloth between sections (which sounds like a good idea though I've never tried this technique), and a brass block placed behind the weld can be effective for soaking away the heat. Reduced Duty Cycle The transformer has to work hard to start the arc. This technique relies on the arc starting and stopping regularly, so bear in mind the duty cycle will be much shorter than for normal continuous welding on the same setting, so the welder will need longer breaks from welding to allow it to cool down. Next: DIY MIG Welding > Tutorial > Gasless MIG Welding

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Mig Welding Technique for Thin Metal

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Plug Welds and MIG Spot Welding

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Plug Welding Plug welding is an alternative to spot welding used by vehicle manufacturers where there is insufficient access for a spot welder. For DIY car restoration it's generally used instead of spot welding on panels flanges that would have originally been spot welded.

Plug welding Start off by drilling 7.5mm holes in the front sheet of metal at a spacing of normally 25mm to 40mm (or whatever the original spot weld spacing was). Then clamp this sheet onto the back sheet. 7.5mm is a reasonably good hole size for 0.8 or 1.0mm sheet. Thicker sheet might require a slightly larger hole size. Try a little test piece out like this one before welding a whole sill onto a car and check the weld has penetrated through both sheets.

http://www.mig-welding.co.uk/plug-weld.htm (1 of 4)28-03-2008 8:17:04 PM

Plug Welds and MIG Spot Welding

Welding through the hole Position the welding torch with the wire in the center of the hole contacting the back sheet of metal. It is important to arc against this back sheet rather than on the edge of the hole, otherwise the weld might not penetrate into the back sheet. The torch should ideally be pointing directly into the hole rather than at the angle in the photograph. Start welding in this position and don't move the welder until the hole is almost full of weld. Then move the welder outwards in ever increasing circles until the weld is completed.

The completed welds If the sheets are the same thickness then the power setting used for plug welding would be the same as you would use for 1.5 times the thickness of one of the sheets. Plug welding can be seen in action on the Aston Martin sills page.

http://www.mig-welding.co.uk/plug-weld.htm (2 of 4)28-03-2008 8:17:04 PM

Plug Welds and MIG Spot Welding

Weld penetration This is the sort of penetration you would expect from a plug weld. The molten pool is just breaking out of the reverse of the back sheet. The heat marks indicate the weld has arced against the back sheet rather than at the side of the hole. If you don't get these marks then consider a little seam welding just to be sure.

Plug welding clamp There is a special clamp designed for plug welding that makes life really easy. The parts you see in the photograph are attached to a normal mole grip. This clamp came in a set of three random welding clamps all of which are extremely useful. The clamp holds together the flanges and there is space in the middle for the torch to weld the plug weld. The rear face of the clamp is offset so it can fit over flanges.

MIG Spot Welding One alternative to plug welding is "MIG spot welding". It is similar to plug welding, although a hole is not drilled in the front sheet of metal. Instead the power of the MIG is relied upon to fully melt the top sheet and penetrate into the back sheet. This technique would require less preparation work than plug welding, but the two sheets need to be in tight contact and high amps used to complete the weld or else the weld could be very weak. Plug welding is a much more suitable technique for all but the most experienced welders. Next: DIY MIG Welding > Tutorial > Tips and tricks

http://www.mig-welding.co.uk/plug-weld.htm (3 of 4)28-03-2008 8:17:04 PM

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Plug Welds and MIG Spot Welding

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Weld Finishing With Flap Discs

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Finishing a weld Ever thought the weld finishes on TV hotrod programs were unachievable or that those guys must be able to weld awfully well? They can weld well, but if you can line everything up nicely at the start and get some decent penetration in your welds the finish isn't too difficult at all. Throw out that plastic body filler and finish welds the easy way.

The repair in the photo is a repair to the top of a wing (fender) mounting panel. It's made from 1.0mm mild steel and I've made the repair section from 1.2mm sheet. The real trick in a nicely finished weld is prep work. This is a butt weld (edge to edge) and I took some time making sure the top edges were level while tacking up.

http://www.mig-welding.co.uk/finishing-welds.htm (1 of 4)28-03-2008 8:18:10 PM

Weld Finishing With Flap Discs

I've always used angle grinding discs to finish welds, but the ordinary grinding discs are very coarse and difficult to control, so I tended to grind almost back to the parent metal then use a little body filler. This is a (slightly worn - they come with straight edges) 40 grit flap disc. These are the way forward for finishing welds. If you don't have one then go out and get one.

Flap discs are flexible, and will tend to follow the contours of whatever you are grinding. Not much use if you want to get rid of those contours. Trick is angling the disc (maybe 20 degrees for this job) and using light pressure. Even with light pressure they are still quicker than a grinding disc. The flexibility makes them directionally sensitive too. On a curve they seem to cut more from before the weld (as the disc spins). Here I've ground the weld just about level with the thicker repair section.

http://www.mig-welding.co.uk/finishing-welds.htm (2 of 4)28-03-2008 8:18:10 PM

Weld Finishing With Flap Discs

Next step was to grind the weld into a curve until I met the next panel. Close comparison of this photo and the ones above show the weld has been finished, but the metal on either side has hardly been touched. There are still the couple of scribing marks to the right of the weld which are more visible if you enlarge the photos by double clicking them. The advantage of the flap disc over the grinding disc is amazing.

A tiny bit more finishing and the weld is invisible, yet the panel thickness hasn't been compromised. I'll be able to paint that without using any body filler. Got to be careful though - if everything isn't level to start with one sheet will be thinned getting it to this finish. In that case it would be better to go so far then finish with body filler.

Those flap discs seem to have been a secret known only by the TV hot rod builders. Now I know and I'm really bad at keeping secrets. Just a shame I don't sell things as this would be a great opportunity, but you should be able to pick up these flap discs for less than £20 for a pack of 10. 40 grit is good for the weld finishing in the photos, and a little finer for final shaping and preparing for paint might be handy, though I'll probably use a load of filler primer. Go get a flap disc and try it out. You'll love the things. Or if you are now really enthusiastic about fender mountings there's a whole page about the repairs with some real craftsmanship on it. http://www.mig-welding.co.uk/finishing-welds.htm (3 of 4)28-03-2008 8:18:10 PM

Weld Finishing With Flap Discs

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Welding thick metal

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Clarke 90EN - Can it really weld 4mm steel? I've always wondered whether the "hobby" mig welders were any good. The challenge for the Clarke 90EN review was to see whether it would weld at all, and then to test out the manufacturer's claims and see if it could really weld up to 4mm thick steel.

The Clarke 90EN MIG Welder That's just 90 amps. But it's a natty little welder that can do both gas and gasless welding. The knobs at the bottom marked "+" and "-" are for attaching the earth wire and power feed to the gun. The wires can be changed over to go from gasless to gas shielding welding. (The photo shows the set up for gasless with a positive earth). Machine Mart claims "Power settings from 24 - 90amps. Welds mild steel up to 4mm thickness." Which seems quite a lot for such a little welder so I thought I'd put it to the test. I set it up with 0.8mm steel wire and Argon/ CO2 mix shielding gas.

http://www.mig-welding.co.uk/clarke-90.htm (1 of 6)28-03-2008 8:19:33 PM

Welding thick metal

The welder works very well on thin metal. Here are some welds on 1.5mm sheet at different power settings (which are marked below the welds). I'd assumed the order of increasing power would be 1min, 1max, 2min, 2max. But I admit I haven't read the manual. The order of increasing power appears to be 1min, 2min, 1max, 2max. The results are just as good as more expensive welders for 1.5mm steel, although the welder did seem a little more sensitive to wire speed settings than my normal 155 amp welder. The duty cycle is worse for this one as well, but I normally spend 10 minutes preparing for every 1 minute welding so for car welding so that wouldn't be a problem for me.

Let's try some 2mm sheet Back to the point of the exercise. With the power cranked up to maximum I had a go at 2mm sheet steel. I welded very slowly to try and get as much heat as possible into the weld. It ended up looking quite neat.

http://www.mig-welding.co.uk/clarke-90.htm (2 of 6)28-03-2008 8:19:33 PM

Welding thick metal

The penetration was reasonable. It took a little time for the metal to heat up, so the first 15mm is a bit marginal, but once I'd got going the penetration was perfectly acceptable. Had I been using a more powerful welder I'd have rejected the weld, turned the power up another notch and welded a bit faster which would have improved the penetration at the start. But since we were already at max I'll be kind and accept the little welder's attempt at 2mm steel.

3mm sheet So with me already wanting more power I decided to try some 3mm steel. With the the power still set at maximum I tried butting two sheets of 3mm steel together. Maybe welding even more slowly would be enough to get some penetration.

http://www.mig-welding.co.uk/clarke-90.htm (3 of 6)28-03-2008 8:19:33 PM

Welding thick metal

Nope - no sign of any penetration on the reverse.

I tried a bend test in the vice. It took a bit of hammering to break the weld, but when it did break the weld broke in two which means it was less strong than the steel it was trying to join together. Penetration turned out to be very poor, with the weld barely penetrating a quarter of the way through the sheet. So we can't weld 3mm sheet never mind 4mm.

http://www.mig-welding.co.uk/clarke-90.htm (4 of 6)28-03-2008 8:19:33 PM

Welding thick metal

Let's try adding a V and a root gap to the 3mm sheet. Thick sheets are hard to weld, so it's probably not unreasonable for the manufacturers to expect us to do a little preparation. Here I've tapered the edges of the 3mm sheet to create a 90 degree V. Also I've spaced the two sheets apart by 1mm (root gap). That's about all I can do to help the poor welder. The weld looks neat, how's the penetration?

Once again the penetration was quite good once the welder got going. But for the first 15mm the welder couldn't get the metal hot enough and penetration was poor. Again, even with the V and the root gap I find myself reaching for another power setting.

http://www.mig-welding.co.uk/clarke-90.htm (5 of 6)28-03-2008 8:19:33 PM

Welding thick metal

I tried another bend test. This time the parent metal broke rather than the weld, which is a good sign that the weld was OK (apart from that first 15mm where there just wasn't enough heat - there the weld broke before the metal). It seems unfair to even ask the welder to try anything more than 3mm, never mind claim that it can manage it.

Conclusions I've never been able to understand manufacturer's claims for MIG welders. At best they are misleading. It's the same with my 155 amp welder. I can butt two sheets of 3mm together and make a reasonable weld. With a V and a root gap I can maybe do 5mm. But the 6mm the manufacturer claims? No chance. The calculator provides estimates for the thickness MIG welders can achieve at each power setting. It guesses about 2mm max for the Clarke 90 which seems about right. Next: Back to DIY MIG Welding > Tutorial

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MIG Welding - Random Tips

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Welding tips and ideas This page contains a few tips and ideas that didn't fit anywhere else on the website.

Earth Clamps A poor contact between the earth clamp and your vehicle can make it very difficult to weld consistently. My old clamp was well past it's best (it didn't want to clamp any more), so I purchased a nice new one from Axminster. It's wonderful - the clamping force is much higher than the old clamp and it's corrosion resistant. Best of all it looks really cool. The only downside is there is no thermal insulation on the handles. It's an old trick - the experienced welder asks the apprentice to remove the earth clamp after really heavy welding. Trust me - the clamp can get very hot. I'm thinking I'll buy four more and make up a really nice set of jump leads.

http://www.mig-welding.co.uk/welding-tips.htm (1 of 2)28-03-2008 8:20:10 PM

MIG Welding - Random Tips

Welding an edge I had to weld an edge today, and it had to be neat so I practiced on some scrap metal to develop a technique. The problem with welding edges is that there is nowhere for the excess heat to go, so it's easy to melt the edge away making the end result very blobby. I found that turning the wire speed down very low was the answer. Problem is the wire vaporised as it left the torch. My technique was to hold the torch very close to the steel, so close that the outer shield touched the metal. This resulted in a neat weld, but overheated the welding tip so I could only do short sections at a time.

Welding thick metal to thin metal It's tricky welding a 1mm thick sheet of steel onto 4mm plate. The problem is that you'll need to use a high amp setting to get the weld to penetrate into the 4mm sheet, but this setting would vaporize the 1mm sheet. My approach is to use the high amp setting. Strike an arc against the thicker sheet and get a weld pool going, then dip across into the thinner sheet and immediately back to the thicker sheet. The center of the weld will be on the thick sheet side of the join with the thin sheet just at the edge of the weld. Good contact between the sheets makes the job much easier. Next: Back to DIY MIG Welding > Tutorial

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MIG Brazing

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MIG Brazing MIG brazing is a new technology. It's major application is in the repair of modern boron steel automotive panels. Boron steels are high strength steels, and much of that strength is gained through heat treatment. The heat treatment is lost when the metal is heated through welding. But running MIG brazing wire through an ordinary MIG would also generate too much heat and lose the heat treatment. Body repair shops need to invest in expensive synergic MIG welders with special brazing programs. This page does not cover these welders or modern bodyshop techniques. Hobby MIG Brazing I have an application in mind for MIG brazing - I reckon it could be a good way to repair an iron casting. This page covers some initial experimentation with MIG braze on mild steel sheet just to find out how to use it. Pure argon gas is required for shielding.

A MIG Brazed joint Silicon-bronze brazing wire feels a lot like mild steel wire to use, though because braze melts at a lower temperature than mild steel it can be applied at much lower power settings. For brazing a butt joint (as in the photograph) the two sheets of steel should be spaced apart by about the same thickness as the steel. For an overlap joint the two sheets should be spaced apart by at least 1mm. The steel sheets aren't melted during brazing, so there has to be a gap for the filler material.

http://www.mig-welding.co.uk/brazing.htm (1 of 4)28-03-2008 8:22:20 PM

MIG Brazing

The MIG Brazing Technique The technique for mig brazing is to weld in a straight line, moving the torch forward. The forward angle of the torch pre-heats the metal about to be brazed. During brazing there is a bright blue shimmering light traveling on the surface of the metal ahead of the weld. This is an effect of the arc which apparently does the same job as the flux in gas brazing. I'm brazing 1.2mm steel, so my welder is set at the minimum power setting (less than for normal mild steel welding), but the wire speed is roughly double that which I'd use when welding.

Braze Penetration I found I needed to space two sheets of 1.2mm steel apart by somewhere between 0.5mm and 1mm for the braze to flow all the way between the two sheets of metal. The gap is important. While ordinary welding will penetrate to the back of the weld through melting through the two sheets of steel, brazing doesn't melt the parent metal, so it needs a gap to get to the rear of the joint.

http://www.mig-welding.co.uk/brazing.htm (2 of 4)28-03-2008 8:22:20 PM

MIG Brazing

So How Strong is MIG Brazing? It certainly took a lot of effort to bend it backwards and forwards in the vice. After bending it backwards and forwards a few times I thought I'd film the fatigue test. It took a further 22 cycles to break the brazed joint, and even then it was the steel that broke not the joint. I was very impressed. Here's the video of the fatigue test for those with a high boredom threshold.

Results of the Fatigue Test When the joint finally broke it was the steel rather than the braze that had failed. Suggests the brazed joint is at least as strong as the parent metal. That really impressed me, as I've read that brazed joints aren't as strong as welded joints. Kind of gets irrelevant when the brazed joint is stronger then the metal you are welding.

http://www.mig-welding.co.uk/brazing.htm (3 of 4)28-03-2008 8:22:20 PM

MIG Brazing

Distortion with Brazing It is still possible to distort panels when brazing as the photograph shows. Distortion can be minimised by brazing in short runs, and allowing the metal to cool between runs.

Advantages of brazing might include welding of dissimilar metals. Because the two sheets of metal aren't melted together it doesn't really matter if they are the same type of metal so long as the melting point is above about 950C. Most metals will melt at a higher temperature than bronze. It's even possible to braze galvanised steel without removing the galvanising (although this still needs to be done outdoors or with an extractor). Brazing is not a technique I would use in place of an ordinary weld (without the appropriate equipment and training), though it has hobby uses for joining other materials. Next: DIY MIG Welding > Tutorial > Cast iron welding/ brazing

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