Techniques - Welding
Introduction - Types of welder and welding pros and cons
SplendiferousII: Posted up as a brief guide to different welding methods, answering a member's question - '...should I consider buying an ARC welder?'
Unless you can weld in the first instance you're going to struggle with an Arc Welder.
Allow me to tell you what I am actually doing when I weld so you get some idea of how difficult it is.
Let's start with good old gas welding. (Ahh! Very therapeutic)
First of all you need to melt the metal equally on both edges to be welded. These two small molten pools need to flow so that they join to form a single molten pool of liquid metal. You then need to push the molten pool along the seam. The edges infront might open up (pull back) so if this happens you need to add more metal (the filler rod) - this typically happens on vertical seams and we call it chasing the onion.
TIG welding is similar but uses electrical arc heat rather than combustoble gases. It is very versatile and esepcially used for high strenth alloys, fine quality work and aircraft structural welding (see Welding - Equipment)
Arc welding is the same but the filler rod is uncontrollable and spazmodic and is much more violent.
So much so that the edges will pull back very quickly in thin metal. You need to dab remove dab remove – this needs to be done very quickly before the tip cools otherwise its difficult to strike the arc again. A nightmare for the beginner. Let alone getting it to strike up at low amps and learn all about angles and how to get the molten metal to pull.
MIG – The best bit about MIG is there is no need to strike an arc. You can just about point and go.
But its not actually that easy. MIG is more about noise than anything else.
You tend to listen to it to know if its all going well down there (sizzling bacon sound).
So to sum up.
Gas is the best to learn on as you learn to actually weld metal and how to control a molten pool – No its not allowed for MOT’s these days as its easy to make look nice but with no strength – and there are very few of us left who can do it. (Ed. I'm sure it's still allowed for some situations... but not for the very latest heat-treated boron-steel body panels )
TIG is the best. But not really for the DIY’er – yet! but getting there.
ARC (stick welding) is old school.
MIG is the DIY tool.
MOT Welding Rules
kthla: Sometimes (wrongly) it depends on mood of tester.
However, I have been told that, as a rough guide, if its a complete replacement panel then it can be "weld a bit, miss a bit, weld a bit.......... ". If its a patch, however, then it needs to be welded all the way round. Think this is still the case.
The following website is by Malcolm Vardy, who has also restored several cars, including an Aston Martin V8, MGB V8 and Renault 4... it's excellent, and the other links detailing how he went about restoring these cars also contain a lot of valuable information for bodywork/chassis repair and restoration.
Emergency welding (get you home welding)
or - Emergency Welding Using Automotive Batteries
SyncroPete: When driving to the Gambia, we carried amongst the usual cable ties and clips, a set of jump leads and welding rods. Didn't have to use them, but glad to see it could have worked. So if you are thinking of a long distance trip in a remote area..
36 volts (Vs 40 often used in arc (stick) welders)- (Image courtesy of www.lcool.org Land Cruiser Owners Online)
AmazingDave: Aye, it's a good fix in an emergency....
Don't practice with your good batteries, It can warp the plates on more than tack welds.
But if it's a choice between being stuck in the back end of nowhere and getting to safety then a few sticks and some mole grips are worth carrying.
lloyd: I've used Ready Welder a few times and found it amazing. We used them with 18volt with one 6volt and one 12volt batteries. Had two 6 volts hooked up as 12volt on 4x4. www.readywelder.com/info.php