7 replies to this topic

[Minimadmatt3743]

Hi, I am new to this forum. I have owned my mini for almost 4 years, it needs alot of bodywork repairs, and I am considering doing it all myself.
My question was what exactly are all the welding types/techniques, and on what parts of the car, would you use the different techniques. I have heard of spot welds, plug welding, pulse welding, but I wouldn't know the difference, and I wouldn't know where to apply them. Any input would be much appreciated. I have checked out the pinned topic on basics of welding, but would be grateful for any advice as to what's what, what works, and what doesn't!
Many thanks

Mat

[JonnyBMX]

welcome mate,

firstly i would suggest getting urself onto the migwelding furum aswell.. there is a good guide on there for the different techniques that can be used. I have also found that the "learn to weld" guide in the Mini magazine over the past few issues is proving to be a very good guide on not only the basics of welding but it takes you right from setting up to actually making repairs this guide is still ongoing through the issues and well worth a read.

[Wakey-Dan]

As johnny bmx says above. Buy the last few back issues of the mini mag. I have no knowledge of welding either but obviously owning a mini Im gonna need to do it at some point and this has been a good guide.

[AVV IT]

I'm certainly no welding expert, in fact I only started learning myself a few weeks ago. But I have tried to explain a few of the basic welding terms as I understand them below:

Spot Welding :

The method that is generally used in the factory to weld panels together on a mini where the edges/lips of two or more panels are sandwiched together on top of one another. (obvious places on a mini include amongst others; along the top of the outer sills, between the wings and the A panels, along the rear bumper lip between the rear valance and boot floor). It involves passing a current between two points above one another on a single spot, using a specialist "Spot Welder" machine, that performs only that task and therefore cannot be performed using a mig welder.

Plug Welding:

The technique that is often used to replicate spot welds using a mig welder. Involves drilling regularly spaced holes along the edge of the upper most panel, then effectively filling/plugging the holes up with weld and thereby welding the uppermost panel to the one beneath.

Seam welding:

Long continuous welds along the edge of two panels.

Pulse welding:

Short sections of seam welding with gaps in between, often used to avoid the panel distortion caused by the heat of long continuous seam welds.

Edited by AVV IT, 04 August 2011 - 09:21 AM.

[ibrooks]

OK we'll start with the different types of welder.

Gas - you use burning gas to get the various metals hot enough to melt. The gas in the bottles is dangerous even when not in use and needs special precautions so generally not used in domestic applications. You need to spend quite a while applying heat to the area you want to weld so you can have trouble with distortion of the panels as you dump a lot of heat into them. You add metal in the form of a filler rod.

Electric - you use a high voltage spark to generate the heat to melt the metal. Heat is almost instant so less worry about distortion. Once the machine is turned off it's just a lump of metal so the only storage concern with the equipment is keeping it dry and clean. You use gas with some of the electric welders but these are inert gases and generally at lower pressures so less likely for a cylinder to turn into a projectile if it falls over and fractures the valve and no explosion/fire risk with leaks.

Now the sub-types of electric.

Arc - bit of a misnomer as they all use an arc. Also called stick welders. You have an earth clamp and an electrode holder. The earth clamp goes somewhere on the piece you are welding and you apply the electrode (held in the holder) to the area you want to weld. The electrode melts and in the process also melts the parent metals. The electrode is usually coated in fux which also melts and forms a shroud of gas around the molten weld pool to prevent it from oxidising. Generally this equipment is too heavy for car work and will just blow holes in bodywork.

Tig - Tungsten Inert Gas. A little like gas welding in that you create an arc between a tungsten electrode and the work (which has the earth clamp attached to it) and add metal from a filler rod. Very neat when you've got the hang of it and you can weld all sorts of materials which are difficult using other techniques (mainly aluminium if you have an AC machine and stainless for our purposes). It's a relatively slow process though so again not so well suited for bodywork although it will do it very well. You use an inert gas which is fed around the tungsten electrode to prevent the weld pool from oxidising. You can weld tinfoil with a good TIG set.

Mig - Metal Inert Gas. This is what's most suited to car work. You have an earth clamp as with most other electric welding but the unique part is that the electrode is a continuous reel of wire. You weld with a torch which has a couple of functions. There is a trigger on the torch to start the welding process. When the trigger is pressed the gas valve is opened and your inert gas flows around the nozzle of the torch, the motor in the machine starts feeding the filler wire and the voltage is applied to the tip of the torch. When the end of the wire touched the weld area it melts and should also melt the parent material. It can be a bit tricksy to set up as the wire speed and welding current need to be correct to get a good weld but it's the machine of choice for most car work.

Spot welders. No gas and no earth clamp. There are two electrodes that are clamped together on either side of a sandwich of bodywork. As a current flos between the electrodes the intervening metal gets hot and melts. Most cars are assembled with spot welders as they are fast and easy to control robotically. If you look under the edges of the bonnet where the wing meets the inner wing you will usually be able to see the row of dimples - these are spot welds. If you see a row of little lumps or it's perfectly smooth then the chances are that the wing has been replaced.

Plug welds and puddle welds are the same thing and are a way to replicate a spot weld with a MIG welder. The bottom panel is taken back to clean metal whilst the upper panel has a 5mm-ish hole drilled in it. The two panels are clamped together and the welder is then applied to the lower panel through the hole. As the wire from the welder melts it forms a molten puddle - you stop welding as the surface of the puddle gets around level with the upper panel. Done correctly the two panels should be fused together around the puddle and replicate a spot weld. You'll often be left with a small lump rather than the characteristic hollow of a spot weld but a few seconds with a grinder can make it disappear if it bothers you.

Pulse welding can mean several things. Generally it's used in car circles to refer to a technique whereby you continuously press and release the trigger on a MIG welder. It can help prevent blowing holes on thinner metal and with a low-ish wire speed turns it almost into a TIG weld.

Iain

[midridge2]

all mini panels from the factory were spot welded so if replacing a panel you can spot weld it in, but, you will need all the diffrent types of arms to gain access to all the areas.
you can with a mig welder do plug welds as described above or seam welding or a combination of both,

those are the ones you would use for home repairs.

[Minimadmatt3743]

Very grateful for the information guys, thanks

Mat

[Deathrow]

There is also a few examples in this thread:

http://www.theminifo...howtopic=194176