Practical MIG Welding: Voltage, Amperage and Wire Spread

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Voltage, Amperage and Wire Spread

06.05

00:00	The most important aspect of MIG welding is being able to produce a strong and consistent weld and this requires the ability to fine tune the machine's parameters to suit the material that we're welding.
00:10	At a high level, MIG welding relies on the voltage, amperage and wire speed controls which can be adjusted to suit the material being welded.
00:17	You can think of the voltage as the amount of electrical energy that's available to force the current to flow through the contact tip to create the arc and result in the molten weld pool.
00:26	For example, let's start by discussing voltage which in basic entry level machines will likely be adjusted in fixed steps between the minimum and maximum values specified.
00:35	With more advanced modern machines, the voltage will be adjustable infinitely between the minimum and maximum which provides a little more control over the weld.
00:44	So, what does changing the voltage actually do? It will affect the weld arc stability, penetration and overall weld quality.
00:53	As the voltage is increased, the arc length will be increased and the weld bead will become wider with increased penetration.
01:00	As you can expect, reducing the voltage has the exact opposite effect.
01:04	The voltage also affects the amount of heat that will be input into the material.
01:08	Thinner materials will require less heat and hence less voltage in order to prevent burn through.
01:13	Thicker material on the other hand will benefit from increased voltage to provide proper penetration of the weld bead.
01:19	Next, we can move onto amperage and this is one of the key specifications you'll need to understand when selecting a suitable machine for your requirements.
01:27	The specifications of a MIG welder will list the range of amperage the machine is capable of outputting, from a base amperage of around 20 amps all the way up to its peak amperage output.
01:37	The peak amperage doesn't really mean much until we understand how this relates to material thickness.
01:44	In the industry there's a basic rule of thumb that says that we'll require approximately 40 amps per millimetre of material thickness.
01:51	If you prefer an imperial measurement, then this aligns to 1 amp per thousandth of an inch material thickness.
01:57	Using this as a guide, a 200 amp machine has the capability of welding extremely thin materials from about half a millimetre all the way up to plate that's around 5 millimetres thick.
02:07	However, this is only a rule of thumb and the reality is that with proper preparation of the workpiece such as bevelling the edges, as well as a slower approach to the welding process, it's normally accepted that a 200 amp machine can handle up to quarter inch plate which is approximately 6.5 millimetres thick.
02:24	This is why we've already mentioned that a 200 amp machine is usually adequate for the majority of motorsport fabrication tasks and it's only usually industrial applications where more powerful machines are necessary.
02:36	It's worth noting that this rule of thumb is just that and there's definitely some room to move the amperage up or down to suit the application as well as personal preference.
02:45	Particularly in industrial welding applications where time is money, higher amperage than what we'd calculate for a given material thickness may be used to allow the weld to progress more quickly.
02:56	Wire speed goes hand in hand with amperage and what I mean by this is that a higher amperage will require a faster wire speed and vice versa, hence both of these parameters are typically adjusted simultaneously by a single rotary knob on modern machines.
03:10	Many modern machines now also include an LCD screen that allows access to and adjustment of many of the different parameters and controls, often including what's referred to as a synergic function.
03:21	This term comes from the word synergy which means different elements working together to create a better result.
03:27	The intention with this feature is to simplify the setup process by letting the machine adjust the voltage, amps and wire speed to suit our specific welding application.
03:36	The synergic function takes into account the type of material that we're working on, the thickness of it, the diameter of our filler wire and the type of gas that we're running.
03:44	It then adjusts its internal settings to supply us with a pre programmed set of parameters that the manufacturer has deemed should be perfect for our situation.
03:53	This can take all of the guesswork out of MIG welding, but it won't cover every situation we're faced with.
03:59	It's still possible however to switch back to manual mode and adjust these parameters as we deem necessary.
04:04	It's important to also consider duty cycle when it comes to peak amperage.
04:09	This is measured in percentage and essentially lets us know the amount of time that the MIG machine can continuously output this amperage for.
04:16	It's common for many machines to have a duty cycle percentage of around 25% at their advertised peak amperage level, which means that in a 10 minute period, the welder will only be able to output this peak amperage for around 2.5 minutes non stop and then will require resting for the following 7.5 minutes.
04:34	Although the duty cycle is worth understanding, it's pretty unlikely to have an impact on our MIG welding ability in motorsport purely because it's extremely rare to run a welder at its peak output for extended periods of time.
04:46	It can however dictate our ability to tackle larger items like a trailer for example, where long 200 amp plus welds are quite possible.
04:55	If you're learning to weld or tackling a material you haven't used before, then it's a good idea to buy a little extra material or clean up some off cuts to perform a series of test welds on.
05:04	This will allow you to get the amperage dialled in so that you can weld at a speed that's comfortable for you.
05:10	If you're interested in seeing the penetration in the material or performing some destructive testing, we've detailed this in its own module in the practical skills section of this course.
05:19	This is a really good way to gain confidence with amperage and voltage control and understand its effects on your chosen material.
05:25	Let's cover the key takeaways before finishing up this module.
05:29	MIG welding machines come in a variety of maximum amperage capabilities and you'll need to select this based on the material thickness you intend to weld.
05:36	A good rule of thumb is that you'll require around 40 amps per millimetre of material.
05:41	Modern MIG machines often feature technology like the synergic function which automatically adjusts settings based on material, wire and gas type.
05:50	Duty cycle, indicating continuous operation time at peak amperage is relevant for longer welds though it's unlikely you'll ever come up against these limitations due to the nature of motorsport welding work.