Welding "thick" metal

[rosco454]

Hi everyone,

Im new to mig welding and as im just about to restore my mini,i have been practicing on 1mm sheet.After spending a bit of time on it i think i have got the hang of it reasonably well.After getting the hang of it on the thinner stuff ive moved onto 4mm mild steel box section as im making a jig for the car to sit on.

I am using an SIP migmate 105 - not the best i know but i bought it years ago and never got round to using it.Im using new 0.6mm wire and tips.The welder has had a steel liner fitted and i am still using the disposable argon/co2 mixture bottles. (Going to boc to get a proper set up during the week i hope).

On the 4mm stuff ive got the welder set at maximum power and about 2/3rds for wire speed.Its not as neat as on the thinner sheet but the bead is going down reasonably well for a learner bar a bit too much spatter but i cant seem to get it to penetrate properly.Turning the wire speed up makes the bead sit higher.Tried turning the speed down and passing really slowly and it is only slightly better.The weld is only just showing through on the reverse side of the material.I tried a joint with an old bit of scrap and the weld has penetrated slighly better.When i say showing on the reverse,its kind of the outline of the weld and the heat marks surrounding it.

Any advice on what the problem could be in my techinque?Would changing to 0.8mm wire make the difference?Or is it just that my machine isnt quite powerful enough for the job?

Some pics to help.Ive cleaned then up a bit so you can see them a bit better as they had a bit of brown residue from the gas around them.

 

[malcolm]

Prepping the joint with a V and a root gap will help. Well worth using 0.8mm wire too. Some the effects of V prep with a similar power welder here: http://www.mig-welding.co.uk/clarke-90.htm

You'll find the thicker the steel gets the less distance the weld penetrates - heat gets sucked away before the weld has a chance to melt the parent material. Pre-heating can help.

For a jig it might not matter too much. I used a Clarke 155 to make my chassis jig from 8mm girder. Struggled a lot on penetration, but was rigid and didn't fall apart.

Forgot to mention - if you can change the polarity and use gasless wire you should get more penetration. Apparantly that's what the manufacturers do when they guess maximum thickness.

 

[rosco454]

Hi Malcolm,

Thanks for the advice, as the box section has a slightly rounded shoulder i might just angle the piece i am butting onto it to form a v.I will get some 0.8mm wire and tips when i get my proper gas setup and see how that goes as well.

I could just take my bits to the fitting shop at work and borrow a more powerful welder as they weld on machines and wagons.I thought it would be a good learning exercise to have a go with myself though.

Cheers Ross.

 

[Hitch]

I think your major problem is lack of power Ross.

When you do a T-joint in the box, you will have a ready prepared joint, with a bit of a gap, put a root run in there, then fill the rest in level or slightly higher.

Spatter wise, could well be the angle of your torch, try pointing it upright a bit more.

If you have the oppertunity to use the machine at work, do so, i assume theres someone there that can help you set it up. Good chance to see the difference with a higher power machine.

 

[rosco454]

I had a feeling that the welder didnt really have enough power,the lads at work will be able to set the gear up for me.

My only fear is that once ive seen a decent welder in action then the SIP is going to seem even worse

 

[ttoks]

a simple way of getting a little more peno with a low power welder is run thinner wire with less wire then you normally would, same heat with a little less wire means more heat in the weld pool of a similar size.

you can try using a backstep or circular mation when welding as well, 4mm shouldn't need more then 150 amps/18-20 volts with most welders

 

[rosco454]

Thanks for the advice,ive had a bit more play about and think its mostly down to the low power of the welder (its an sip 105).

Im making a trolley for it at the moment and forming a v on the joint and leaving the 1mm or so gap that Malcom suggested is working pretty well.

Ive sorted the wire feed mechanism with a brace as well as the liner change and my welds are getting neater with less spatter even on the thicker stuff.The feed was very stop/start before but now its about as smooth as an sip is going to get