Tig Vs Mig

[cRRRRazy]

lets examine the difference between two of the more common methods of welding.

TIG requires much more practice, but it is surgical in it's accuracy.

MIG is best suited to quick fabrication where welds don't have to perfect and

speed is more important.

TIG is for when accuracy is paramount and welds need to be perfect.

TIG is also much more versatile than MIG.

They can both weld a wide array of metals, but MIG requires a filler wire spool

change for each metal, and sometimes a sheilding gas change as well.

TIG WELDING for AUTOMOTIVE FABRICATION

The TIG (Tungsten Inert Gas) welding process (also known as gas tungsten arc welding, GTAW, or HELIARC, a trade name of Linde) generates heat from an electric arc maintained between a non consumable tungsten electrode and the part being welded. This process was developed for the aircraft industry back in the early '40s. TIG may be used without the addition of a filler metal or a separate wire filler metal can be added into the puddle when additional material is required, much like the process in oxy-acetylene welding. The puddle, the tungsten electrode and the filler rod are protected from atmosphere by a shield of inert gas to prevent rapid oxidation of the weld and surrounding metal.

Argon is the most widely utilized gas.

Because the gas shield does not produce the slag that normally is created by flux, the danger of slag inclusion in the weld metal is eliminated. Also, due to the slow speed of the TIG process, gases and other impurities escape to the surface of the puddle before solidification occurs, eliminating pockets called "Porosity" common in weld processes that employ gas shielding but have greater travel speeds than the TIG process.

POROSITY Porosity is gas pores found in the solidified weld bead. these pores may vary in size and are generally distributed in a random manner. However, it is possible that porosity can only be found at the weld center. Pores can occur either under or on the weld surface. The most common causes of porosity are atmosphere contamination, excessively oxidized work piece surfaces, inadequate deoxidizing alloys in the wire and the presence of foreign matter. Atmospheric contamination can be caused by:

1) Inadequate shielding gas flow.

2) Excessive shielding gas flow. This can cause aspiration of air into the gas stream.

3) Severely clogged gas nozzle or damaged gas supply system (leaking hoses, fittings, etc.)

4) An excessive wind in the welding area. This can blow away the gas shield.

TIG also produces a welding heat is that is confined between the weld and base metal at the point of fusion and produces a narrow heat affected zone. This reduces stress, cracking and distortion in the finished weld. Spatter is not produced by this process, leaving the weld and surrounding metal clean. Because of the lack of spatter and flux smoke, the TIG process allows the operator a clear view of the weld puddle. The torch body in most cases is small enough that the operator can hold it in the same manner as he would hold a pencil allowing easier manipulation.

The power source is constant current, either AC, DC, or combination AC/DC. Type of metal determines which type is used. DC (direct current) is most normally used for TIG welding of stainless steels and mild and low alloy steels. AC (Alternating current) is used for TIG welding of aluminum. Surface oxidation is automatically removed by the action of the arc each time the electrode becomes positive, (60 times per. second). Because AC crosses over the zero volt point 120 times per second (once going positive and once going negative each cycle), the arc shuts off 120 times per second.

To keep the arc going when using AC, a high frequency "arc stabilizer" is used. The high frequency also allows the start of an arc in DC mode without having to "strike" an arc, thereby reducing the possibility of tungsten contamination. If the electrode accidentally touches the weld pool, it becomes contaminated and must be cleaned immediately to prevent weld contamination. TIG requires an extremely clean surface to weld successfully and is a fairly slow operation. On the plus side, TIG produces high quality work and does not generate slag or spatter. The welder can adjust the heat input while welding by using foot or hand amperage controls.

MIG (Metal Inert Gas)

also referred to as wire feed welding, utilizes a consumable arc. The process generates heat from an electric arc maintained between a consumable wire feed electrode and the part being welded. This process produces spatter making it difficult for the operator to see the weld and causing damage to nearby surfaces and objects from the hot particles thrown off. Flux cored "gasless" welders produce smoke from the flux, and pose a cleanup problem.

Because of the higher welding speeds of the MIG process, the chance of producing porosity is higher. A common mistake with novice welders utilizing the MIG process is the possibility of producing a good looking weld with little penetration. A MIG can produce an arc into the puddle, allowing one to create a nice looking weld while the base metal underneath is not being properly melted. This cannot be detected before failure without either destructive or non-destructive testing.

In the TIG process, the base metal is melted to produce a puddle before any filler is introduced into the weld. This allows the operator to see the penetration during the welding process. Another drawback in MIG welding in restoration of automobiles is the workability of the weld. The wire used in MIG cools harder than in TIG welding, making it harder to hammer and dolly the weld afterwards. Because MIG welding uses a constant fed wire to produce the arc, some buildup of material usually occurs that has to be ground off. This also generates heat in the panel that can cause warpage.

INCOMPLETE PENETRATION This type of defect is found in any of three ways:

1) When the weld bead does not penetrate the entire thickness of the base plate.

2) When two opposing weld beads do not interpenetrate.

3) When the weld bead does not penetrate the toe of a fillet weld but only bridges across it. Welding current has the greatest effect on penetration. Incomplete penetration is usually caused by the use of too low a welding current and can be eliminated by simply increasing the amperage. Other causes can be the use of too slow a travel speed and an incorrect torch angle. Both will allow the molten weld metal to roll in front of the arc, acting as a cushion to prevent penetration. The arc must be kept on the leading edge of the weld puddle.

LACK OF FUSION Lack of fusion, also called cold lapping or cold shuts, occurs when there is no fusion between the weld metal and the surfaces of the base plate. The most common cause of lack of fusion is a poor welding technique. Either the weld puddle is too large (travel speed too slow) and/or the weld metal has been permitted to roll in front of the arc. Again, the arc must be kept on the leading edge of the puddle. When this is done, When multipass welding thick material, a split bead technique should be used whenever possible after the root passes. When welding aluminum, the common cause of this type of defect is the presence of aluminum oxide. This oxide is a refractory with a melting point of approximately 35000F (19270C). It is also insoluble in molten aluminum. If this oxide is present on the surfaces to be welded, fusion with the weld metal will be hampered.

With TIG, filler is only added when needed, and the thickness of the filler can be changed by picking up a different size rod. This reduces post weld finishing.

While TIG welding requires greater skill, the results are far better than other welding methods. Welders of both types are available from many sources, such as Eastwood, Daytona Mig, and Professional sources such as Miller Electric. A source that I have found to be particularly helpful and has excellent prices is RRAM Sales. If you are looking for a welder, I recommend staying away from Flux cored units. They are messy and many do not have the power required to do most welding you will get into. Small 110 volt welders are available that will do a good job with practice, but go with gas for MIG (MIG by definition is metal INERT GAS, not flux) Flux cored units are advertised as "wire feed", Don't assume that they are MIG welders. If you are looking for a TIG, there are also several nice small units available, but consider it only if it has "high frequency" and AC if you don't want to mess with striking an arc and there is a remote possibility that you may want to weld Aluminum someday.

Most local race car builders tell me that Chromoly cannot be Mig welded. I realize that sanctioning bodies such as NHRA mandate TIG, but for SCORE I see no such mandate. After e-mailing their tech. director, he suggested I refer to AWS. I understand cold starts affect the overall integrity of the weld, and with the choice ($) I would use TIG over MIG, but with the cost difference being 3 to 4 times that of MIG, I'de like to get your take on this. (Also, with a few exceptions, most buggy chassis builders sell 4130 Mig welded chassis and only offer TIG as an option)

open to additions/discussion.....................................

[gdizzle]

soooo, what's your point? Tig generally provides a deeper burn in the metal with greater penetration.

[cRRRRazy]

for those who have inquired and for those who want to know..........................

they both "weld" however the differences in finish, strength and quality are noteworthy

also indicates some of the reasons for cost differences

[prasamin]

TIG is better. we knew that right?

[Guest 300+_T5R_855]

TIG is better. we knew that right?

mmmm TIG

[ms007]

Tig & octane,, WOW imagine that!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! :lol:

[viperman135]

TIG weld on 3003 aluminum. Anyone thinking about starting welding its not as easy as it looks. There are about 15 things that you have to think of at once. Just to name a few heat, speed, penetration of the weld and about a dozen other things. To get really really good at TIG welding it takes years and years of practice.

Thats not my welding. I could only wish I could do that good. I have practiced a screwed around but can not do anywhere as good as that one.

[tknutson]

So how about old style OXY Fuel welding, somebody still says this is the best way to weld aluminium.

Also many exhaust shops use it

???????

Thor

[Adam Franke]

Only welding i've ever done is with an acetylene torch on an aircraft frame....that was fun .

[cRRRRazy]

this topic doesn't belong in off topic deleted correct? shouldn't it be either in here or in cosmetic detailing right??? just curious as to why it was moved and am not questioning authority.

http://volvospeed.com/vs_forum/index.php?showtopic=46206&hl=

[bloc]

possibly because it's not a "performance modification".

that or it's pretty much irrelevant for the vast majority of people on this site.

good info, imo. but many people wont get much from it.

[cRRRRazy]

decisions based on this information can be helpful to the performance and overall well being of the vehicle............

[Boomin850]

Tread wisely and choose words carefully...

[EricF]

Could just as easily ask a moderator. We're not too happy with having to move the same thread over and over lately

Welding does not directly affect performance... Yes, it's something you use when working on cars but it's just a tool. Like what jack you use, or what brand of sockets you prefer.

I'm going to move it to OT again, because it is off-topic. Don't think of that forum as deleted posts, because the posts that *really* get deleted go to the Moderator's lounge

Sorry if you feel offended, it's just not relevant.

[Guest 300+_T5R_855]

Tig & octane,, WOW imagine that!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I'm actually having a hard time believing you can imagine two things at once.