Welding Procedures

http://www.millerwelds.com/resources/bookspamphlets.html

chuck, if you haven't checked it out, Miller has an 84-page instruction book on TIG welding as a free download. It was a good read. Miller has a pretty good set of resources in general and an active forum as well.

I have had some thoughts about the Diversion 165 welder, but I am lusting hard for a Dynasty 200 DX. I used a 300DX and some big Lincoln's (can't remember model) in a TIG class at our local comm. college---drool.

I've got a MIG and a TIG. I've been welding at a hobby level for about 10 years.

Chuck is right the MIG is much faster to do production work and it has the advantage of 1 handed operation. Another big advantage is that it can be used with magnetic clamps. The first time I used my TIG I nearly burned a hole in my hand because of a magnetic clamp.

But for all that if I could only keep 1 welder it would be the TIG. The reason is flexibility. I only need one tank of gas, just argon and the appropriate filler rod (or scrap of similar material) and I can weld pretty much anything. With the MIG every time I change metals I have to swap the gas tank and load a new roll of wire. For aluminum I have to insert a teflon liner in the gun cable. Changing to 0.023 or 0.035 from the standard 0.030 means changing the roller, the wire and the tip. Trying to just get by with the wrong thickness and adjusting the feed rate can lead to more frequent birdsnesting or problems with burn through or inadequate penetration.

If I have a lot of similar welding to do I'll still set up the MIG. I might do that two or three times a year. But most every week I find a use for the TIG. Sometimes I'll do several different things with it in one day. Lots of jobs are completed in far less time than it would take just to swap all the stuff on the MIG.

Anyway if you expect to be doing small unpredictable jobs, frequently working with differing metals of differing thicknesses, etc. a gas torch or a tig will make you happy.

I have two spool guns for my Miller machine. I used one spool gun for aluminum, the other for stainless. Most of my welding is mild steel so I just use the large bulk rolls for steel. The spool guns make changing to different materials a lot easier and I consider a spool gun mandatory for aluminum. Not that its absolutely necessary but it saves me a lot of hassle.

So, after reading all this, I'm not quite sure now why I am able to weld .035" CrMo tubing with my 120V Miller MIG. The penetration looks good and I blow through if I get careless. I'm running the controls at about 4/10 voltage and 45/100 feed speed. It's loaded with .025" ER70-S6 and the usual C-25 shielding gas.

FWIW, this is my first MIG and I'm self-taught. Yes... I decided to splurge and get a unit with variable voltage. Without knowing how the switched units work out, I think this was the best decision I made as I have learned how to fine tune the controls instead of being forced to vary my travel speed. And, FYI, nearly 15 years ago, I was taught how to braze using propane and OA, but the I'm a little hazy now on the OA operation now. IMO, this is so much easier than brazing that I wonder why people who don't make lugged frames even bother with it.

ensen.

The reason that lugged bike frames are brazed has to do with fatigue. Brazing has been shown to have less long-term hassles than welding on thin wall chrome moly tube as it tolerates the application of long-term varying stress very well. A brazed, lug-built frame will allow a great deal of repeated flex before developing cracks and generally the tubes tend to fail before the brazed lugs.

I've done a lot of stuff in 4130 chrome moly (aircraft structure) and it can be TIG/MIG welded without post-weld heat treatment fine as long as the wall thickness is greater than about 35 thou and as long as the tube diameter is fairly small (say less than an inch). Once you get into bigger diameter thin wall tube, then welded joints tend to develop cracks in the heat-affected zone after prolonged varying stress exposure (this can also happen with smaller diameter tubes, but the effect tends to be worse the bigger the diameter). This can be minimised by stress relieving the whole structure after welding (essentially sticking it in a big oven and heat treating it), but this isn't often an option for hobby stuff.

It's possible to crudely heat treat welded joints if you have a big torch handy, but it's a slow process to do absolutely correctly as the joint has to be held for some time at the temperature where the structure of the metal in the heat-affected zone can return back to normal. You can get a reasonable approximation of the normalised condition by heating the joint area to dull red with a torch (after welding) and then letting it cool slowly, the slower the better.

A welded and heat treated chrome moly frame is probably close to being as good as a brazed lug frame in terms of fatigue resistance, but ends up being more hassle to make because of this need to stress relieve it after welding.

Jeremy

Thanks Jeremy for those chromoly tips. I built a very large cargo trailer using 1" and 3/4" 0.035 4130 tubing. It was a partially trussed and triangulate frame. I only trussed the areas I thought would bear the most load, that is near the wheels & hitch. And those areas have been perfect. But with repeated heavy loading cracks developed at a couple other points near joints of sections that were boxed without triangulation and thus able to flex.

I've welded up the cracks and have reduced loading until I can add more triangulating members. Because I don't have a good easy way to do the angle miter cuts I had been considering the option of going with bigger diameter tubing to get more stiffness with a minimum of mitering in future builds. However, from your post that appears to be a poor choice.

So I need to find a better way to miter tubing. I currently have two methods. My first is to use a joint jigger with a hole saw. This gives good results but is tedious because I first have to plug the tubing with wooden dowel that I have to sand down by the wall thickness of the tubing to make it slide in snugly. Without the wooden plug the coarse 6 tpi? teeth of the saw tend to snag and shear off. My second method is to do it by hand with an angle grinder. However if I do it fast the result is poor. If I do it slow and careful with many repeated fittings the result is mediocre. What would be the best tool for this job? Are there high tooth count hole saws? Would some sort of mill or lathe be good for this?

I've done this mitreing job in the lathe, using an end mill of the same diameter as the tube in the chuck. I have some wooden blocks that clamp different diameter tubes to the lathe toolpost, centred on the chuck centreline. It's then just a matter of setting the tube angle up by adjusting the toolpost angle and moving the tube on to the cutter using the cross slide.

This works well, I've found, as it's possible to take small cuts with really thin wall tube. The only slight problem is that the fit you get can be too good - I tend to add a chamfer afterwards in order to get a good weld.

Jeremy

Thanks Jeremy! Do you think the small benchtop lathes or the convertible mill/lathe machines would be up to this job of mitering 1" OD 0.035" wall chromoly? And would the tubing have to be as short as the bed of the machine or can it hang way out with additional support?

The biggest tubes I've done this way were 3/4", using a tiny Chinese mini lathe. The cutter was a second hand 3/4" multi flute end mill, so not that sharp (these things are expensive - I was lucky enough to get some cast-offs from a local machine shop).

The only problem with the mini lathe was holding the tube. A long length of tube was enough to tip it over! In terms of power, then there was no problem at all, it just ate through the tube very quickly. It's worth going slowly, though, to avoid the risk of the cutter grabbing the tube edge.

I've done a similar mitering job on some big (1 1/2" diameter) alloy tube (1/8" wall), using the milling machine and a fly cutter. Not for the faint hearted, as it makes a hell of a row and fly cutters are, in my opinion, the spawn of the Devil, but it did the job. I just took very gentle passes, plunging the mill head, moving the tube in a small amount each time. It wasn't too fast, but did do a surprising neat job.

Jeremy

Thanks Jeremy, I've been sitting on the fence a long time thinking about getting one of those machine tools and now I'm going to start digging into it in earnest to learn what will work best for me.

I do not wish any ill will towards anyone here, I don't want to hurt anyones feelings, but,

Off the top of my head, and do correct me if I am wrong.

Brazing has brass in the rod. The brass molecular size molten is small enough to slip into the microscopic pores of the stronger steels, such as 4130.
When the when the combination of 4130 and brass cools, the 4130 shrinks more than the brass. What happens next. The brass acts like a wedge in the structure of the 4130, creating stress cracks. Which cause joint failure. A properly brazed joint on 4130 with out lugs will fail.

Jeremy, I guess you are saying the aircraft brazing you are doing is with lugs? Standard joints will fail using brass rod on 4130, perhaps lugs don't fail on aircraft.

Lugs for bikes. Who here is going to build something with lugs? I am not talking about using lugs. But, I have 2 older Raliegh bikes, a road bike and a mountain bike made from 4130, both are lugged. They both weigh in at about 20 lbs.

How are the tubes made. The tubes in these bikes are double and triple butted. In other words, the tubes have thicker walls near the lugs. I cannot do this at home. Vary the thickness of the tube. for a bicycle, to save weight, the manufacturer can do this.

4130 What is it? It is a structural steel too. So what is aircraft grade 4130?. It will cost more. Generally, the engineers at the manufacturer will order a specific ladle analysis and a specific heat treatment from a steel mill. The engineer of the manufacturer will specify inner and outer wall diameters and a range of tolerance. The more restrictive the tolerances, the more the steel will cost. Aircraft grade tube will come from the mill with a tag stating that it meets the manufacturers specifications. The tag will have a ladle analysis on it. The ladle analysis will list the exact chemical qauntities in the steel in the molten state. This steel will be more uniform as to wall thickness. The tag will define the grain structure size and the type of grain structure. The tag will define the state of the steel. Normalized is a state of the steel. The tag will state the actual tensile strength of steel and the specific heat treatment applied to that steel.

Not all 4130 is welded. I only know of two companies that bronze welded chromoly. Norton motorcylces, who found that bronze welding failed, and Schwinn bicycles, who bronze welded a lot of bike frames, with success. I do not know of any companies that braze 4130 steel nor have I heard of a company that braze welds 4130.

4130 is a water quenchable steel. This is important. It is an ultra high strength steel. You can buy 4130 in an annealed state, excellent for welding, then bring it to a heat treating facility and have it strenghened and tempered to a very exacting standard. If you want 4130 heat treated to a tensile strength of 200,000 psi it can easily be done. This is not so easily done to other alloyed steels.

At the local metal yard, 4130 comes in a normalized state. What is that. Let me get my books out to find the actual tensile strength of normalized 4130.

Back in a bit.

chuck

Well, let me qoute from the American Society of Metal Handbook, volume 1, Properties and selection of Metals, copyright 1961, Publisher, American Society for Metals. (page 87)

"the steels discussed in the article are characterized by higher yield strength than plain carbon structural steels. There are two categories,(a) proprietary pearlitic structuaral steels with 40,000 to 50,000 psi minimum yield point, known commercially as either high strength or high strength low alloy, the latter fulfilling ASTM A242 or SAE 950 specifications, and (b) high strength heat treated constructional alloy steels having a somewhat highter content of carbon or alloy or both and minimum yield strength of 70,000 to 100,000 psi. In each of the two categories the actual composition, thickness of section, and heat treatment (if applicable) markedly affect the mechanical properties, fabrication procedures and applications.

High strength seels were developed primarily to obtain improved strength to weight ratios by permitting an increase in nominal unit stresses, thus decreasing section moduli.

The original demand for this class of steel arose from the need for reducing the dead weight of transportation equipment, and this has been the largest single field of application of the high strenth low alloy grades. More recently the need for structural steels of still higher strength to weight ratio , but with no major loss of weldability or fabrication properties, has led to the development of the heat treat grades in this class of steels."

Lets go to page 92

"High strength low alloy steels are readily weldable by any of the arc welding processes used for plain carbon structural steels and are not subject to the hardening of the weld in the heat affected zone as are the plain carbon steels of sufficient carbon content to obtain the same mechanical properties."

What does that say,, readily weldable,,,, and are not subject to the hardening of the weld in the heat affected zone.

4130 is a unique steel as it is a water quenchable steel.

Carbon content, .27 to .33 percent
Maganese content, .30 to .70 percent
Silicon content, .20 to .35 percent
Chromium content, .75 to 1.2 percent
Molybendum content, .15 to .25 percent
Normalizing temp 1650 F
Austenitizing temp 1600 F

Do you see the wide range of alloying contents, vary these amounts, and with virtually any quench medium available, makes this steel suitable for a wide range of applications.

Carbon is the most easy to understand when discussing 4130. Thin sections have less carbon, thick sections have more. The less carbon, the more weldable.
The other alloying elements, while affecting the mechanical properties, combined, prevent the formation of martensite when welding and quenching this steel. For most applications, when welding 4130 in the normalized state, absolutely no post tempering or heat treating of the welded joint is required. If, this steel is to be quenched, then the carbon content is more important. Thicker sections do not cool as quickly, requiring more carbon to achieve the same mechanical properties as a thinner section.

Next, 4130 normalized

These are three steels, found at most metal suppliers, in the standard sizes

4130 steel, normalized, cold drawn
Tensile strength, 85,000 to 110,000 psi
Yield strength, 70,000 to 85,000 psi
Modulas of Elasticity, 30 million psi

A 513,1020-26 steel, cold drawn DOM, (drawn over mandrel)
Tensile strength , 87,000 psi
Yield strength, 72,000 psi
Modulas of Elasticity, 30 million psi

1020, hot rolled, seam welded
Tensile strength, 68,500
Yield strength, 55,700
Modulas of elasticity, 30 million psi


I like A 513 steels because of their weldability, but mostly for their formability. I can bend them myself and get a high degree of uniformity when bending

The hot rolled steels bend easily, but do not give much uniformity after the bend. using the same setup the spring back is different for each piece, requiring more effort for uniformity. The surface appearance after painting is generally on the poorer side so much more paint prep is required.

I have already discussed 4130 formability, tighter bends require mandrels, not generally a do it yourself proposition

chuck

chuck said:

Brazing has brass in the rod. The brass molecular size molten is small enough to slip into the microscopic pores of the stronger steels, such as 4130.
When the when the combination of 4130 and brass cools, the 4130 shrinks more than the brass. What happens next. The brass acts like a wedge in the structure of the 4130, creating stress cracks.

Click to expand...

Brass is an alloy consisting of copper and zinc. Most 'fillet brazing' rods used in bike fabrication contain an exacting mixture of several elements - copper, tin, iron, lead, zinc, nickel, maganese, aluminum and silicon, to name a few. Most Professional frame builders typically use LFB (low fuming bronze) such as Gasflux C-04, Aufhauser C680 or similar which meets AWS A5.8 Class RBCuZn-B. However, even budget, off-the-shelf LFB and quality paste flux from your local welding supplier can produce satisfactory, crack-free results on 4130.

chuck said:

A properly brazed joint on 4130 with out lugs will fail.

Click to expand...

News to me!...

As a pro frame builder, I haven't had a 'fillet brazed', chromoly joint failure in 30 years, nor do I experience the 'cracks' you speak of - And I'd hazard to guess, that the following Professional builders haven't either;

http://www.bohemianbicycles.com/fillet.html




http://www.donwalkercycles.com



http://www.oswaldcycleworks.com/gallery2.php

chuck said:

Jeremy, I guess you are saying the aircraft brazing you are doing is with lugs?

Click to expand...

I can't speak Jeremy, but I can add that the FAA has not, and won't permit 'fillet brazing' on ANY structural members in airframes. Nearly all vintage 4130 airframes were oxy-acetylene 'welded', a jointing practice which is still widely used, even today.

Papa,

Now, lets see here, is that a bronze welded joint or a braze welded joint?

I am pretty sure that the AWS would call those bronze welded joints.

I also know that the AWS has made a clear distinction between braze welding and bronze welding. I have several resources in my welding collection that mention this difference. All of these sources say the same thing. Do not braze weld alloyed steels and discuss the cracking process. If what you are doing is bronze welding, then it should be discussed here as bronze welding. I know the distinction between the processes, others here probably do not.

I do not have any personal experiance worth mentioning on applying the two distinct processes. I did take my mandatory year of metallurgy, and I do remember looking at the brass inclusions and microfractures in alloyed steels caused by braze welding through the microscope. I don't remember exactly, but I don't think it was much more than a 5x or 10x scope and I don't think it requires dyes to see these cracks.
It should be enough for those here to know that the two processes are different.

chuck

In the American Societies of Metals Handbook on corrosion, bronze welding problems in industry are discussed, with many industry specific examples given. One problem with bronze welding involves removing the flux from the weldments. Discusses in great technical detail the problems these residual fluxes can cause. The operating enviroment and its affect on bronze welded steel is also discussed, more specifically, how electrosis can affect these types of weldments.

Papa,
The only reason I wrote this is to provide the total amatuer, good information.
I believe that good information would include calling braze welding unacceptable on alloyed steels.
I also believe that you can share good information with us on bronze welding process, how to apply it, what materials to use, and its application to frame building.

Brazing

IMO, Brazing should be referred to more correctly as Capillary Brazing. Successful joints depend on the ability of filler metal to penetrate small gaps between metal surfaces by capillary attraction. Under the correct conditions the brazing alloy (usually copper based) wets and bonds by surface diffusion alloying to form a strong joint.

Bronze Welding

The term "bronze welding" is misleading since it implies fusion of the parent metal and the use of a bronze filler metal. This is clearly not the case. Bronze welding, until the development of the low temperature capillary brazing process, was a classic process in which a bronze alloy was used as a filler metal to form a surface bond between unfused parent metals. Unlike capillary brazing, the strength of the bronze welded joint is derived from the tensile strength of the filler metal deposited in the joint. The process of bronze welding did have a poor reputation for joint strength as early filler materials were a basic 60/40 commercial brass with relatively poor tensile strength. Bronze welding alloys have developed significantly in the last fifty years and the addition of elements such as nickel or silicon have significantly improved the mechanical properties of the filler.

Bottom line; While you may wish to differentiate between the two processes, in the cycling arena, they are typically lumped together and simply referred to as Brazing or Fillet Brazing.