Penned by resident technical adviser “Assassin”, this is the 1st of a lengthy yet comprehensive 2-part article. Part 2 [now published] looks at MIG wire, dual purpose MIG and ARC machines, TIG welding and finally – selecting a welding plant. Main photo: Marcus Cleveland
In this 2-part article, we shall be taking a look at welders. Please be aware it is being written with beginners in mind, so those more familiar with welding please be patient as it details how different machines work.
In reality, welding is something I can train a monkey to do. It is a hobby which requires a little knowledge and a lot of practice for automotive and general home welding, and anyone can learn to weld well enough to satisfy their needs in a short time if they put in the practice. There are many types of welding ranging from specialised welding methods such as submerged arc to laser welding, you can even weld plastic with the right equipment, but for our purposes we will stick to ARC, MIG, and TIG welding as these are what we will use.
Let me also state from the outset that I will refer to a company called “R Tech”, as they are a British company producing quality welders on a par with all the big names, yet at a fraction of the price. By way of example, for the price of a mid range DIY welding set, R Tech will supply an industrial set which is obviously much better value and a much higher quality welding set which will last for years, not weeks. Is value for money and supporting British companies important to you? It is to me, which is why I support British companies and make no apologies for this; oh … and you can also haggle with them to sweeten a deal, something that’s good to know in advance. [Editor’s note: I too make no apologies should this article refer to a particular company. If the business in question is competent and supplies sound products, then why shouldn’t we pass on this info and subsequent good deals on to the readers of Europe 4×4 Mag? That’s why we are here after all, to provide ‘news & information’.]
Industrial welding sets work harder and longer than DIY sets, are much heavier duty, and this is an important consideration as we will see when we get into the technicalities of duty cycles as many welder manufacturers manipulate these figures to make their welders look better than they actually are.
Any welder works on power called current, the higher the current the thicker the metal you can weld. For automotive work, the thickest material you would weld would be 4-5mm and that would be on suspension components or tow bars, most bodywork will be less than 1.5mm thick material. General household welding would mean material of up to 6mm thick material, on older type gates for example.
Traditional welders work using a transformer which quite literally transforms mains voltage down, and when you transform mains voltage down you increase current by the same proportion. In simple terms, if you have a mains supply of 240 volts at 30 amps and you transform the voltage down by exactly half to 120 volts, you double the available current to 60 amps. This is on AC or Alternating Current and the UK generates this at a frequency of 50 cycles per minute which is now called Hz or Hertz. Alternating Current gives fifty power pulses per minute and 50 negative pulses per minute, this is frequency.
Transformer sets are still very popular and relatively cheap to manufacture, they are durable but heavy and large so they make an excellent profit for manufacturers and retailers alike.
Welders take this incoming power and short circuit it through either an electrode called a welding rod, electrode or stick in the case of an ARC set; or a continually fed wire in the case of a MIG set using a small gap between the electrode to maintain the arc, the electrode or wire melts and is deposited as a filler. Both require an inert gas to cover the weld to prevent an oxidised or porous weld and they do this in two ways – the electrode in ARC welding has a flux coating which melts and generates this gas shield to exclude air/oxygen, whilst MIG uses a bottled gas which comes through a shroud with the MIG wire.
ARC welding goes back to the dawn of electricity being used to weld, it is the most flexible of welding processes as a variety of different electrodes are available. It also copes with dirtier material and you can weld in any position with it. It does take skill to weld as you have to travel in the direction of your weld and move the electrode holder nearer the workpiece in one motion as the welding electrode is consumed to maintain a steady and equal length arc. As the electrode deposits the metal into the weld, it removes the impurities from the molten metal of the weld and brings it to the surface of the weld, then deposits it on top of the finished weld in the form of a solid black slag which has to be chipped off to see the final weld. We can therefore conclude that the flux coating of an arc electrode is a flux which generates a gas shield to lift any impurities from the weld and prevent a weakened oxidised weld.
Electrodes used for arc welding have a piece of the centre metal exposed at one end and it is this which goes into the electrode holder of the welding set. Next to this bare section on the flux coating it will have a number such as 6013 and it is this number which identifies the type of electrode being used. Most popular is the 6013 and while there are many different types the 6013 means it’s a general purpose, all position electrode. In simple terms it is manufactured to weld general mild steel in all positions such as overhead, vertical up and down as well as normal down hand welding. 7018 would indicate a low hydrogen rod, and as its name suggests, it produces a lot less hydrogen gas as it welds. It is used on material liable to high shock loadings to prevent cracking of the weld, similarly, apart from the standard numbering system, many manufacturers have their own for specialised rods.
Arc welding is the quickest form of welding to set up as you plug into a power supply, connect your earth lead, set your current, put an electrode into the rod holder, switch on and you’re welding. It requires the least preparation but is the slowest form of actual welding, it’s the most versatile due to the quantity and range of electrodes available for standard and specialised applications and the preferred choice for site or maintenance applications. In reality all you need is a supply of dry undamaged electrodes and you can do most welding jobs.
Its real downside is its limitations on thin material as it generates a lot of heat which causes distortion; along with the electrode sizes of 1.6mm, 2mm, 2.5mm, 3.2mm, 4mm, and many more sizes in 1mm steps, for our purposes we will confine ourselves to the 1.6 – 3.2mm range. As the range begins at 1.6mm and most car bodywork ranges from 0.4 – 0.7mm thick we can see it will easily blow through the metal instead of welding it, for heavier sections such as chassis repairs on 4x4s it may work for a competent welder.
MIG welding is a different beast as it is the easiest form of welding to learn for a beginner and it works very differently to arc welding even though MIG is another form of arc welding. MIG works by having a transformer as a power supply providing AC power but the advancement of power electronics allowed a rectifier pack to be added after the transformer to make the power source a direct current or DC supply which is better source of power for a MIG set. This still uses the cheaper transformer as a source of supply and the addition of a rectifier or Silicone Controlled Rectifier (SCR) which is a single cheap component allowing a form of DC power to be readily available for a reasonable profit while providing a reliable welding set at a reasonable price.
MIG works by using a spool of welding wire held on a stub pipe which you can tension, this is to stop the spool spinning from the wire wound onto it having some springing capability which would unwind itself, wire is fed into a guide tube and onto a drive roller or drive rollers. Rollers come as pairs and the drive roller had a groove machined into it for a specific size of MIG wire, the other roller is the idler roller and as the rollers are closed they sandwich the MIG wire in the groove and pull it off the spool and into the Euro connector to feed the umbilical.
Wire feed rollers are driven by a variable speed motor which is controlled by a rotary knob on the front of the welder so the welder can control the wire feed speed. Two types of feed rollers are available and these are those with a “V” groove for steel and stainless steel wires and those for aluminium wires which have a “U” shaped groove, always use the correct roller for the MIG wire being used.
Shielding of the weld is done by an inert gas, generally it is a form of carbon dioxide (CO2) and Argon mix, this is denoted by its name, e.g. Argoshield 5 would be a 95% CO2 and 5% argon mix, similarly Argoshield 20 would be 80% CO2 and 20% Argon. Argon is added to intensify the arc and simply it’s a better cleaner so gives a better weld and increases the working temperature of the arc allowing power to be turned down slightly and saving money, particularly if you are in a fabrication environment running multiple higher powered MIG sets. You can run on pure CO2 if you prefer and have it readily available, on good terms with the landlord of your local licensed premises? Then he/she may sell you a pub bottle of CO2 at cost price. You will need an adaptor to allow your regulator to connect to a pub bottle as they are a different male thread to the female thread of the standard welding bottled gases, but they aren’t expensive. Large CO2 fire extinguishers are also a handy source of CO2 and if your employer still uses them they may allow you to have out of test date bottles full of CO2 for free as long as you return the empty bottle.
Your gas goes through a regulator and through a pipe into the back of your MIG set and into internal pipework to a solenoid valve which opens to allow the shielding gas to your Euro connector.
Power from your MIG set is delivered from the transformer, through the rectifier, to the power controller which is controlled by a knob on the front of your welder and for transformer MIG sets it is usually in a series of steps by a series of buttons or a multi position knob. From here the main power cable goes to? Yes you guessed it, the Euro connector on the front of your MIG welder.
The Euro connector now contains the main power feed, shielding gas, and the MIG wire but it also has a pair of wires connected to two contact points and their purpose is to switch the gas solenoid to the open position and allow gas to flow, and to power the wire feed motor to feed the MIG wire.
Next we have the umbilical which is the cable looking piece which runs from the welding base unit to the welding torch to allow you to weld and to carry power, gas, and mig wire to the welding torch, and two wires from the trigger on the welding torch to stop and start welding. One end of the umbilical contains a male version of the Euro connector to connect the umbilical to the MIG base unit, a liner to carry the MIG wire to the torch, a pipe to carry the shielding gas to the torch, and a flexible power cable to carry power to the torch.
MIG wire liners are consumables as they do wear, most standard types are a spiral would spring steel wire to allow them to bend and will accept 0.6 and 0.8mm diameter MIG wire on domestic machines, on heavier duty or industrial machines it will carry 0.6, 0.8, and 1mm MIG wire. Many specialised liners are available, some are spiral wound spring steel with friction reducing coatings, some have a plastic liner while some are made from things such as special plastics with Teflon coatings.
Steel MIG wire is quite solid and rigid but some MIG wires such as aluminium are quite soft and the friction from a normal liner would cause it to bind and cause a birds nest hence a very low friction liner to enhance the capability of the MIG set to weld aluminium. For use with stainless steel we use a standard steel MIG wire set up as stainless steel MIG wire is harder and less likely to bind than normal steel MIG wire.
Gas is carried from the Euro connector along a flexible pipe such as silicone pipe directly to the torch as silicone pipe is flexible and withstands the heat.
The power cable connects directly to the swans neck which is generally a solid brass item inside outer steel casing of the torch assembly.
If we move to the torch itself it has two wires connected from the Euro connector to the switch, one carries a small voltage to the switch and as you pull the trigger it closes a set of contacts and makes the circuit and sends power back down the other wire to the Euro connector. When you pull the trigger its these wires which feed the solenoid valve to open it and let gas through to the torch and to start the drive motor to feed the wire through.
At the working end of the torch it has a shroud and this either pulls off or unscrews depending upon the machine, if we remove this we can see inside the working end of the torch. At the very end there is something called the contact tip which unscrews, these come in different sizes to match the MIG wire we’re using, for 0.6mm wire the contact tip would have a 0.65-0.7mm hole, for 0.8mm wire it will have a 0.85-0.9mm hole, and for 1mm it will have a 1.1mm hole and they all have their size stamped on them. This is for steel and stainless steel MIG wires, for aluminium wires the hole has a larger clearance as aluminium expands more than steel or stainless steel and this extra clearance prevents the aluminium from binding in the contact tip when welding, a contact tip for aluminium will also be stamped with its size followed by the letter A.
If we look behind where the contact tip sits we will see a ceramic (usually) ring with several small holes, it is this ring which is fed by the gas feed pipe and dissipates the shielding gas into the shroud and it travels down the shroud and over the welding arc to eliminate the oxygen from the weld.
As we can already see the MIG set is more complex than an arc welder and due to having to carry around a gas bottle for the shielding gas it is more cumbersome and unlike arc where you can have long leads, you have to have the MIG base unit near the workpiece due to the length of the umbilical. Umbilical’s come in standard sizes and the Euro connector is always the same size meaning you can connect any Euro connector to any other Euro connector but umbilical’s come in different lengths of 2m, 3m. 4m. 6m. and 8m long. Remember the longer the umbilical the higher the load on the wire drive unit and drive rollers and the more chance of getting problems from friction of the MIG wire in the liner inside the umbilical. Umbilical’s are also available in differing current ratings and for our purposes these are 150 amps maximum and 250 amps maximum and as their ratings suggest this is the maximum amperage they can carry, the 150 amp rated unit contains smaller components and is thinner, lighter, and more flexible.
MIG sets are better suited to a fabrication/production environment as they lay weld much faster than arc welding and you don’t have to continually stop to change electrodes as you do with arc sets but the choice of different wires limits their capabilities to weld specialised metals. Mig is better suited to welding thinner materials than arc and can weld the thinner materials and it has less distortion on thin material, in addition the shielding gas is not created by heat as with arc and acts as a coolant on areas surrounding the arc from the MIG wire. MIG doesn’t tolerate dirty material and this means more time preparing and cleaning the item to be welded but as you can wind the power up and the wire speed up you can weld heavier items in one pass, with arc sets it may require two or more passes. As MIG uses a shielding gas it isn’t suited to welding outside in windy conditions as wind can blow away the shielding gas and leave a weld full of porosity which is a weak and ineffective weld. MIG has no slag forming so no slag to knock off after welding. MIG sets have many wearing components unlike arc sets, Contact tips, umbilical liners, wire feed rollers, and idler rollers are all consumable items requiring periodic changing and of course welding shielding gases are not cheap.
In recent years power electronics have advanced rapidly and this technology has filtered down to welding equipment and eliminated transformers altogether which brings about a massive saving in weight as transformers contain miles of copper wire windings which is the bulk of a welders weight, Modern inverters reduce this to the point where an inverter of 250 amps rating weigh less than 15Kg and a 100 amp inverter weighs less than 5Kg and can be carried on your shoulder with a shoulder strap, this weight means they are more portable than transformer sets. Not needing a transformer means the bulky transformer is not required and this makes the inverter welding set very compact and much smaller than an equally rated transformer set, an inverter set can easily be a quarter of the size of a transformer set, often smaller than this. For a little more weight you can get a dual purpose machine which gives both MIG and arc welding capabilities.
Inverters have some pretty nifty power tricks and can do some wonderful things with electricity, instead of welding with AC power they convert this to DC and they can alter the frequency, remember our incoming mains frequency is 50Hz or 50 power pulses a minute. They can clip the negative side of the frequency pulse totally and switch it to a power pulse automatically giving us double the amount of power pulses making the machine a 100Hz machine for smoother welding. They can multiply the amount of positive power pulses we get and 400Hz is fairly normal now in decent inverter machines and some are much higher giving us 8 times the power pulses and no negative pulses so a much smoother weld. This is beneficial in both arc and MIG welding as it gives a very stable welding arc and allows more specialised electrodes and welding wires to be used which would normally require the experience of a decent qualified welder to weld with, hence a beginner can engage with more specialised welding. Such advances have also improved areas of welding such as MIG’s inability to weld dirty steel and inverters with their higher frequencies have made it possible to weld rusty steels but they need any loose rust deposit removing and a good circuit by cleaning the earth connection point to clean, bright metal; also the area for the initial arc to be struck.
Many inverter sets have the ability to store electrical power, in simple terms when you switch one on it takes a few seconds for the light to go out before you can begin welding and this is due to it charging its capacitors, this is storing energy. This energy store gives functions such as “hot start” and when you strike an arc with a welding electrode it discharges this extra high frequency energy to make striking the initial arc much easier, for a beginner to arc welding striking the initial arc is the hardest part so it helps prevent the electrode sticking to the workpiece.
In MIG welding applications it allows a function called “burn back” which is where you stop welding and release the trigger while keeping the MIG torch in the welding position, this then sends a high frequency pulse of power down the MIG wire and it burns it back to the correct length to start welding again.
Many inverters have the ability to alter the frequency of the machine and many automatically alter their frequency by monitoring the electrode or wire being used, most arc and MIG sets do this automatically but altering the frequency manually is generally the preserve of TIG welding. Many inverters have an ability to switch between DC and AC welding and while this is generally the preserve of TIG welding some MIG and arc sets allow this function; for our intended uses this isn’t necessary but for many specialised fabricators it is.
Many inverters have an ability to reverse the polarity of the machine as an arc welder normally has the earth lead connected to the – or negative connection and the electrode holder to the + or positive connection and in MIG welding the umbilical is always + or positive. Due to the wide range of welding electrodes available for arc welding it is a useful feature for some specialised welding electrodes requiring reverse polarity as they work better with the electrode in the negative polarity.
Inverters allow another feature which is “DIP” and “spray” and basically these are the length of the arc gap itself on arc and MIG welders, by having capacitors the inverter allows a very short arc to be used without the arc electrode or MIG wire sticking to the workpiece as it would with transformer sets. Spray is where you can use a much longer arc gap without breaking the arc and this is beneficial when welding thicker material where you have bevelled the edges to be welded and left a root gap between two pieces of thick metal, basically it allows a long arc to jump between a gap in the material.
Inverters are crucial for TIG welding as they allow an abundance of features such as “slope up” and “slope down” which is superb for very accurate welding of thin sheet materials and works very simply. With arc or MIG you get power delivered at your setting and on thin material it burns the edge of the material away meaning you have to reduce the power while welding to prevent burning away the edge of the material.
Slope up has a timer in seconds and most are up to 5 – 10 seconds and work simply by you setting the slope up time, if you set 5 seconds and pull the trigger the power goes from 0 to whatever amps you have set over the time you have set. If you set your power to 100 amps and 5 seconds, when you pull the trigger it goes from 0 to 100 amps over 5 seconds.
Slope down is exactly the opposite, as you near the end of your weld you release your trigger and the current drops from 100 amps to 0 amps over 5 seconds.
Inverters have a nice trick up their sleeves when used as a power source, they allow a welder to become a combination welder and allow two or more types of welder to be incorporated into one machine. Most are dual purpose machines allowing arc welding and MIG welding to be carried out from one machine, multi purpose machines allow arc, MIG and TIG welding to be done by one machine, there are limitations to these machines. If we assume a MIG welding power of 250 amps then the arc welding capacity is reduced by around 20% meaning in MIG mode it would have a capacity of 250 amps and in arc mode it would have a capacity of 200 amps. In a multi function machine the TIG welding capacity is around that of the arc welding capacity.
If we remember what was stated earlier about frequency and a more stable arc it means we also weld at a lower power with an inverter than we would with a transformer set so we don’t need the extra power, we need slightly less with an inverter. I actually tested this with an R tech machine I own, this is the PRO MIG 250 and is a combination machine with MIG and arc functions, I set it to arc and plugged in the welding lead for arc welding and set the power to 190 amps and used a Lincoln electrode. When arcing up it was seriously spraying so I turned the power down to 180 amps and it was still seriously spraying so it went down to 175 amps before it settled down, according to the manufacturer these electrodes require 190 – 215 amps so we can see how much less power an inverter needs for heavy duty rods.
Transformer MIG sets have stepped power and this is the power settings go up in steps controlled by a multi position switch and at the top end of the 240V range this is usually 7-12 positions depending on the quality of the machine, basically meaning you have a choice of only 7-12 power settings. Inverter supplies are stepless and they will allow you to set any power setting you like within its working range. With transformer MIG’s you may find one power setting is too high and if you switch down one power setting it is too low a power setting. If we assume a working power range of a transformer MIG is 30 – 250 amps each step will raise the current by 31.5 amps, if we set to position 5 it will give is 30 amps + 157 amps or 187 amps, if 187 amps is too high a power setting and we go down to position 4 on the power setting it gives us 156 amps. With inverter sets being stepless and you can set any power within its working range you just wind the power up until you get 170 amps which is in the middle, this allows you to fine tune your welding power to 1 amp of your optimised setting so you can fine tune them to an exact power setting.
The Technicalities and Misleading Descriptions
This is where we get into the technical bit and understand what the figures mean and how they tell a good machine from a bad machine, and understand how manufacturers of cheaper machines use carefully chosen words and manipulated figures to sell a machine which doesn’t do what you think it does.
Many welding machine manufacturers begin with giving a machine a misleading name. They may describe it as model XYZ 190 which suggests it delivers 190 amps as its maximum power output, but when you look at its technical specifications it only delivers 175 amps; hence in my opinion – misleading. Put it this way, if you saw a welding set described as a 190, you would assume it delivered 190 amps – right? Most people would.
If we look at a Clarke 230 TEC MIG we assume this to be a 230 amp output machine. However, look at its specifications and it tells us it’s only 210 amps maximum, so already could be said it portrays itself as something it isn’t. So we will use this randomly chosen example, as it’s purporting to be a heavy duty machine.
‘Duty cycle’ is the real give away, and we really need to understand this. Don’t worry, this actually isn’t as daunting as people think as it is a standard European specification. This assumes an outside temperature of 40 degrees centigrade and works over a cycle of 10 minutes, we then look at percentages and these are simply a percentage of the 10 minute period the welder can work for continually without overheating and tripping out and the normal percentage is 60 % called the 60% duty cycle. 60% of 10 minutes is 6 minutes so we can conclude the machine can weld for 6 minutes continually without tripping out over a 10 minute period.
Next we need to know what current we can weld at on our 60% duty cycle. My R Tech Pro Mig specifications state 200 amps @ 60% duty cycle at 40 degrees centigrade in MIG mode. Clarke states only a 60% duty cycle of 102 amps, so in reality I can weld at twice the current at 60% duty cycle than the Clarke over the same period … and the Clarke is only £100 less than mine!
As the R Tech is a true industrial machine it gives a full set of specifications: Duty cycle at 250 amps 35%, or as 35% of 10 minutes is 3.5 minutes, so it can weld at full power for 3.5 minutes out of every 10 minutes at 40 degrees centigrade air temperature. That’s clear and precise, something it should be.
Mine also gives a duty cycle of 160 amps at 100% duty cycle at 40 degrees centigrade, which means I can weld at 160 amps for 10 minutes out of every 10 minutes as 100% of 10 minutes is 10 minutes which means I can continually weld with it.
If we consider the poor duty cycle of the Clarke in MIG mode and the fact it’s a transformer welder, the fact they don’t give a set of specifications at full power, the fact they don’t state the welding power at 100% duty cycle, it tells us all we need to know, then they don’t state at 40 degrees C.
This automatically tells us it doesn’t conform to the European standard for testing duty cycles, plus it automatically tells me and hopefully anyone reading this, not to touch it with a barge pole! While the Clarke was selected randomly I am not aiming anything at the Clarke welder, merely using it as an example as there are many welding plants with far worse duty cycles. In fact there is absolutely nothing illegal in this practise of manufacturers testing to their own specifications, although it does tend to muddy the waters when there is an EU standard in place … and it gets worse. Many manufacturers state their machines conform to EU or European standards and they do, only this is a little more deceit. It’s used to deceive people into thinking it is the welding performance – it isn’t! It actually applies to the construction of the machine under the EU machine directives, which are safety specifications.
One interesting case was a mate looking for a welder and he found a 250 amp MIG online at a competitive price, that was until I explained duty cycle to him. It was tested at 20 degrees C, not the EU standard 40 degrees C, and at the 60% duty cycle has a welding current of just 60 amps. This proves that machine manufacturers manipulate figures to impress those not understanding duty cycle. He went straight to R Tech and ordered a combination machine and is impressed with its performance.
In reality the UK and many parts of the world never get anywhere near 40 degrees C as they have cooler ‘cooling air’, which means the machines never get the hot air of the test standards to cool them, meaning they run cooler and their duty cycle is actually increased even in the hottest UK summers.
Moreover, even with an 8 metre umbilical you aren’t going to weld for 6 minutes continually as you will be out of umbilical well before then as most welding takes less than 1 minute and you stop. The fact is very few welders can weld for 6 minutes out of every 10 minutes, hence the EU standard. In stick mode you can only weld until the electrode is used and you have to stop welding and replace the electrode with a new one.
So lets ask a simple question, would you pay over £600 for the Clarke? A transformer based machine, a single purpose machine which is MIG only, has a paltry 102 amps output at its 60% duty cycle, and doesn’t state the temperature it was tested at, so we don’t know if it is tested at EU standards?
Would you go to R Tech, a British company with an unrivalled reputation for customer service, buy a larger true industrial machine based upon the superior inverter technology with a far superior duty cycle, and have a dual purpose machine which can also arc weld (with lead) for less than £100 more? Would you have a machine which does what it says or one which tries to portray itself as something better than it actually is, would you prefer to talk to someone at R Tech who knows what they are talking about or just buy online from abroad without the ability to talk to anyone; for me it’s a no brainer. Hope this helps – think before you buy!