by Harold Hilborn
The Anvil's Horn, Issue 142, January 2010
(a publication of The Arizona Artist Blacksmith Association)
Lately, I have been asked a lot of questions regarding welding issues of all types. Someone even suggested I write some articles to help with some of these problems you might be having. I also know for some of you purists, WELD is a four letter word unless preceded by the word forge, but it is a necessary evil in a modern shop today.
Before I begin, maybe I should start by giving you some of my background, so those who do not know me, will feel comfortable with the advice I suggest to you. I have been working as a welder/fabricator for 32 years. During this time I have had two years in a vocational school and another two years at a university studying welding technology. I have worked as a master welder and fitter and have certifications in all major welding process on ferrous and non ferrous materials. I also have ASNT certifications as a welding inspector and have also been a welding instructor. All this being said, I still can not weld the crack of dawn or fix the crack in a broken heart. So some of you might have been lucky enough to have received a sweet, new 110 volt MIG welders from the fat man in the big red suit for Christmas. You might have an older one, or if you're lucky, a larger machine. Hopefully this article will help all of you who have not had formal welding training unlock some of the mysteries of your machine.
Let's begin with some basics and the term MIG, it is an acronym for metal inert gas or the correct definition GMAW, gas metal arc welding by the American Welding Society. This is a welding process using a continuously fed wire with an inert gas for shielding.
Lincoln Power MIG 140C
Models that come from home improvement centers usually come set up for self shielded wire (which we will cover later in this article). So if you want to run shielding gas you will have to go to your local welding supplier anyway.
We also need to explain duty cycle. This is the time a machine can run at maximum amperage in a 10 minute period. Most 110 machines are 20% duty cycle, which means they will weld 2 minutes in a 10 minute period. Machines that run on 220 amps are usually rated at 60% duty cycle. It is very hard to exceed a 60% duty cycle.
Now, let's decide what kind of shielding gas you should run. The two most popular ones are 100% carbon dioxide or 75/25 which is 75% carbon dioxide and 25% argon. I run CO2 in my shop, it is far less expensive. It gives better penetration and handles rusty material better. The disadvantages are that there can be more spatter and it is harder to run on thin gage material (16 gauge or thinner). Both of these disadvantages can be overcome if your machine has a variable voltage control. 75/25 is a more refined gas. It produces better bead definition and less spatter and works better on sheet metal. The draw backs are, less penetration and higher cost. Oh yes, don't be shy about negotiating with your supplier. Everyone does not pay the same price.
When I get requests for help from people or go into someone's shop, the first thing I notice is that most machines are not set up correctly. If the machines do run satisfactorily, they are afraid to touch the settings and they weld everything on one setting.
Let's begin with drive roller tension. You should be able to pinch the wire with your thumb and index finger at the end of the contact tip and almost be able to stop the feed when the trigger is pulled. (Be careful not to feed into a grounded table or part.) The wire speed and voltage parameters that are given on your machine are a good place to start. Keep in mind that these are laboratory settings and are for welding usually in the flat position. Do a test weld on the same material you're going to weld before welding the actual piece.
Next lets talk about the term stickout. This is the unmelted wire distance from the end of the contact tip to the weld puddle. This should be ¼ to 3⁄8 of a inch. Practice holding it up to a piece of material of the same thickness to get a good visual picture. It is very important to maintain this distance when welding because, along with your wire feed speed, it controls the welding amperage. If you go closer, the amperage goes up. If you pull back, your amperage will go down. Your voltage controls the heat and the arc length.
There are 3 types of metal transfer. This is the way the metal melts off the end of your wire. They are, short circuit transfer (sometimes referred to as short arc), globular transfer and spray transfer. It is important to know all these and that they are controlled by wire diameter, voltage settings, and shielding gas. To keep it simple, for now, we will concentrate on the short arc because that is what is happening for us.
Polarity is the direction the current flows when we weld. We weld with DC current, in this case, reverse polarity. Which means the current travelsfrom the welder, through the ground, into the part and across the arc gap, into the wire. A droplet of wire melts off and is deposited into the puddle. This happens between 20 to 200 times a second depending on settings. Your welding gun should be on the + lug on your machine and your ground on the - lug. Herein lies the most common problem I see with beginning welders. The machines that come from home centers are set up to run self-shielded wire (instead of shielding gas), which means they are set up to run straight polarity. Often when people need help, it is when they are switching over to hard wire and don't know to change the polarity of their machine.
Since we are talking about self shielded wire let's look a pros and cons. The pros are portability and being able to weld in a windy environment. The cons are more spatter, more skill is required to weld out of position, and larger diameter wire is required to get the same size weld. For example, if you are running .023 hard wire you would need to run .035 flux cored wire to get the same deposition rate.
So, now you are up and running, I hope. When welding you must be able to see. Keep your lenses clean and get cheater lenses (magnifiers) if you need them. You can't make a good weld if you can't see what you are doing. "Let the force be with you" does not apply here.
Let's discuss welding technique and what we should weld with our 110 MIG welders and what we should not. Unless you are a seasoned welder, you should not weld anything over ¼ thick and nothing that someone's life depends on, such as, trailer hitches and automotive suspensions. Even if you are a seasoned welder, there are almost always better choices.
Weld vertical up when strength counts. Remember, when you weld vertical down it might look pretty, but the penetration and strength in the throat of the weld are not there. Concentrate your wire on the leading edge of the puddle. Wire concentration in the middle or in the back of the puddle will lead to lack of penetration or cold lap as it is commonly called. When welding thicker than 16 gauge manipulate or oscillate your welding gun like a small cursive e, or in and out; back and forth. I am sorry I don't have the ability to draw in this article. It probably would make more sense. Above all, practice, practice, practice.
Hopefully, this will help you in your welding needs. If you need help or have questions please feel free to contact me. Remember a "Beautiful Weld" is a good thing. It does not always have to be ground off, blended, or hidden just because it is an electric weld.
Gee Mom, look what else I've found!
- The Anvil's Horn, Issue 142, January 2010
(a publication of The Arizona Artist Blacksmith Association)
|Wisdom of my father: "It takes more of a man to walk away from a fight than to stay and fight."||