What To Look For When Buying A MIG Welder
Buying a MIG/MAG welder can be a daunting task as there are so many to choose from. So let's look at the things I would look for when choosing the best welder for welding on vehicles. I'm looking at this from a bodyshop, home/workshop angle for the repair of vehicles.
This is the big question? You would be surprised but you can get some really good MIG/MAG welders for surprisingly small amounts of money today. You can also blow your wallet on the highest specification, with most of its functions you probably won't use.
Set a budget that is reasonable and includes most of the points we will go through here.
Transformer Welders have been around for many years, the Old ARO 2022 is what I started with when I first became an engineer and its still my favourite MIG even though it was built 35 years ago. Many of its features that made it a success in the bodyshop, are still required today and are what you should be aiming for when looking to buy,
It was a step switch transformer MIG MAG with Synergic wire feed settings. making it a simple machine to weld with and it was loved by bodyshop technicians. It also had the unusual thing of a handheld spot welder on top. This was the part that broke down the most due to heat and overuse. Slowly a lot of shops removed these as new spot welders came on the market but there are still a lot of the MIGS in constant use today.
SINGLE PHASE OR THREE PHASE?
Obviously, in your home workshop or garage, you will have no choice but to choose the single-phase but to get the best from a transformer MIG MAG welder you really need three-phase.
The rectifier cuts off the negative part of the AC wave to create DC inside the welder, a single-phase has gaps in the wave three-phase welder doesn't. This you will feel in smoother welding.
To compensate for the gaps in a single-phase welder we use capacitors (the red in the single-phase drawing). The better the capacitors the smoother weld is. Cheaper hobby type welders may not have capacitors in them making the arc quite course especially down low.
So if you cant have three-phase then choose a MIG with good capacitors for a smooth arc. ( or pick an inverter, more about that later)
The old AROs main plus point was its transformer. It had a very low open-circuit voltage 15V which was great for welding thin car body panels, it also had many settings.
The more settings a voltage switch has the smaller the jump in voltage between settings. There is nothing worse than not quite having in enough current then switching to the next setting to find we now have way too much. So the more settings a welder has the smaller the jumps in voltage between the settings.
This is where thyristor control welders came in. they have a lot finer adjustment of the voltage as its electronic and so can help you achieve the perfect setting easier.
So if you cant choose a thyristor controlled welder, pick a welder with a low open-circuit voltage on setting 1 and many switch settings.
This really isn't important when welding vehicle body panels as you wouldn't normally get to the overheating scenario even on the cheapest welder. Welding a quarter panel on a vehicle will typically be done between 60 to 80 amps you would need to do a lot of continuous welding to cause the welder to overheat. See my post on What does duty cycle mean on a welder?
The choke is a very important part of MIG welding, remember we are essentially blowing a fuse and this is quite an aggressive explosion. This might be great and just what we need for fabrication but for vehicle welding, this explosion could end up blowing a hole in our panel. We, therefore, need to slow down the aggressiveness of this explosion and we do this with the aid of choke.
The better the choke the smoother the welding.
The main trouble with a choke in a transformer MIG though is that it is set by the designers for the optimum current of the machine. This could mean it's not quite there when welding down low, it's perfect in the middle and not enough at the top.
The wire feeds on smaller MIGs are essentially car washer bottle motors and are a bit rough. The drive rollers are a little spindly and thin all surrounded by bendy cheap plastic.
What does the wire feeder do? It needs to pinch 0.6 or 0.8mm of wire and push it 3 metres through a torch, a hot welding tip and into a weld pool. How good and how smoothly it does it is important, the better the wire feeder the smoother your welding is. Two roll feeders are sufficient for hard wires such as steel but you really need 4 roll feeds for soft wires.
Choose the best wire feed system for your budget. Try it, see how smoothly it feeds and feel the quality.
As we have just stated before for wire feed units, the torch is the main feed for the wire and it transfers the welding current so you can weld.
The length of the torch and size just depends on what wires you are using.
If you are welding with 0.6mm steel wire, the maximum length of the torch you can use is 3 metre. If you're using 0.8mm steel wire then you could go to 4 metres but again you could get wire feed faults unless you keep the torch straight during use.
Soft wires like MIG braze and Aluminium I would only recommend 3-metre torches.
For normal bodyshop use, BZL 150 type torches are all that's needed the 250 nozzle is just too large to get into places on a vehicle and is anyhow designed for gates and railings.
TYPES OF TORCH
There are three types of MIG torch, direct fitted, euro adapted and manufacturer specific.
Directly fitted torches usually are lower quality and tend to have plastic or Teflon liners fitted inside. The steel wire cuts into the plastic liners, so sooner or later you will get wire feed faults. Once you start to get faults its a bit of a pain to change the liners.
Euro Adapter Torches are a standard torch that is fitted to many manufactures machines. Euro adapted torches can be exchanged from machine to machine and the consumables tend to be standard Binzel (BZL) fitment. It is also easier to repair, change liners. and source spares. The torches also tend to be of a more professional standard.
These types of torches tend to have their own manufacturers liners and consumables on them, this invariably means they are more expensive to replace, I tend to steer clear of these types of torches for this reason unless it actually makes the machine perform better.
I always look for euro adapter torch fitments when choosing a welding machine.
- Check the quality of the case and if it has quality wheels. Pneumatic is ok but the rubber can spread and get soft from oil ingress. Also, Remember this has to support a heavy gas bottle.
- Support, ensure you have good technical support and that the person that is selling it so you can repair or fix any problems.
- Warranty, this speaks for itself but it isn't any good if the above point is not applicable. This is why I wouldn't buy from eBay or Amazon.
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