Machining weldments

[Jasonb]

Stick it in a fire then let it cool overnight in the ashes, I've recovered several chilled castings this way and as similar methods are needed with weldments thats how it can be done in the home.

I've also done similar with CRS that was going to have a lot cut off one side or out the middle to reduce the amount it will move.

Blasting for half an hour with a propane torch has also rescued chilled castings but this is really only economic on small castings as large items are hard to get hot enough and you would use a lot of gas.

J

 

[Entropy455]

Here’s the home solution:

Obtain a used (but functional) 240-v, single-phase, electric pottery kiln. They are less expensive than you might think.

Then go online and purchase a new digital oven temperature control, with a working range up to 2000 degrees F. Important note: the oven controlers quickly go up in price based on their current switching capacity ($$$). However the temperature sensing and control circuitry is the same, even for the 110-v base models. Thus purchase the inexpensive 110-v version, then purchase a 50-dollar electric contactor that’s rated for 240-v and 60 amp. This will permit the 110-v oven controller to switch current as if it were a larger and much more expensive 240 volt version.

Wire in the controller and install the thermocouple. Do not install the thermocouple directly adjacent to the heating coils, or in a position where it receives appreciable radiated heat from the coils – this will prevent unnecessary cycling of the controler relay. With the new temperature controller installed, your kiln is now a metal-working oven, capable of heating steel into its austenitic zone for hardening/annealing, capable of tempering, and also capable of proper post-weld-stress-relieving.

Important note: the aftermarket temperature controls are required, because kiln controls are approximate at best. For example, say you want heat-treat a piece of 4340 – the kiln must be able to maintain 1550 degrees F (+/- 25 degrees F). If you heat past 1650 degrees F, you’ll permanently damage the metal's grain structure.

Most pottery kiln controls are close within a few hundred degrees at best.

Consider that you use a lathe for turning, and a mill for surfacing - well, the proper tool for heat treating and stress relieving is an oven. . . .

 

[steamer]

Ah yes.... the proper tool for the job. Do you have one by the way along with a vent...ect?

Dave

 

[Dan Rowe]

Dave,
I have used my burn out kiln for stress relief. I have a programmable controller so holding a temp for a soak and slow cooling are a simple thing to do. My wife has a larger kiln for clay and I had to special order the 60 amp socket.

I could add my controls to the big kiln with a contactor large enough for the load but i have never had the need.

Dan

 

[rake60]

I have machined a lot of welded fabrications over the past 20 years.
Almost all of them were stress relived.

Some were heated up then buried in a lime pit for 12 hours to slow cool.
Some were sent out for the kiln type "annealing" style of stress relief.
Some went to a vibratory stress relief vendor.

Any of those processes help to stabilize the metal around the joint, and reduce the
risk of cracks in the parent metal.

None of them are going to soften up the fusion zone or filler area.
They are going to be harder than the patent metal no matter what you do to it.

Rick

 

[Deanofid]

Mild steel and carbon steel are the same thing.
http://simple.wikipedia.org/wiki/Carbon_steel

They are not the same thing, and the link you provide even says so.

Quoted directly from your link:

"Mild steel is the most common form of steel as its price is relatively low while it provides material properties that are acceptable for many applications. Mild steel has a low carbon content (up to 0.3%) and is therefore neither extremely brittle nor ductile. It becomes malleable when heated, and so can be forged. It is also often used where large amounts of steel need to be formed, for example as structural steel. Density of this metal is 7861.093 kg/m³ (0.284 lb/in³) and the tensile strength is a maximum of 500 MPa (72500 psi)

Carbon steels which can successfully undergo heat-treatment have a carbon content in the range of 0.30% to 1.70% by weight. Trace impurities of various other elements can have a significant effect on the quality of the resulting steel. Trace amounts of sulfur in particular make the steel red-short. Low alloy carbon steel, such as A36 grade, contains about 0.05% sulfur and melts around 1426–1538° C (2600–2800° F).[5] Manganese is often added to improve the hardenability of low carbon steels. These additions turn the material into a low alloy steel by some definitions, but AISI's definition of carbon steel allows up to 1.65% manganese by weight."

Again, Paul; Please tell us what you wish to make, and the approximate size of the item. Maybe we can give you a specific solution that does not include industrial aspects, or building your own kiln.
Honestly, it may be as simple as getting the thing hot, and giving some blows with a hammer. It could also be as simple as; Weld it up, and machine it to size. Depends on what you're making, and the machining steps involved for the piece.

 

[Paul Erland]

Thanks for all the info folks. It's the backyard/home shop solutions that will help me the most right now. I have an interest in sleeve valve engines and want to experiment around with some single cylinder variations. I am considering making the engine blocks from weldments. Castings would be nice but building a home foundry is a whole other topic.

 

[steamer]

You may want to consider temperature pencils as inexpensive temperature indicators
http://www.tempil.com/products/tempilstik-original/
Dave

 

[Entropy455]

Deanofid, perhaps your point would be better made if you could identify a type of mild steel that does not meet the classification as carbon steel also? I honestly don’t think it can be done, because they really are the same thing.

It is common in the steel industry to differentiate between heat-treatable and non-heat-treatable carbon steels, by calling the non-heat-treatable versions “mild steel” in lieu of low-carbon-steel. That was the point of the Wikipedia page that I linked. Look at it again - it’s titled “carbon steel.” And Mild Steel is clearly tabulated on that page as a “Type of Carbon Steel.”

There are even some shorter industry abbreviations for carbon steels, such as OS, HS, HTS, etc – it’s all carbon steel. . . . Some high-carbon-steels are often referred to as tool steel.

It’s really not a big deal. . . . .

 

[Tin Falcon]

Ok reality check !!!
Breath gentlemen!!
A guy asks a legitimate question for a hobby back yard project, and we end up disusing the semantics of metal classification, and quasi industrial heat treating.
While a heat treating oven is a nice thing to have IMHO a little hard to justify in the home shop. I worked in an fabrication shop USAF . we had a heat treating oven . in the 6 years I was in the shop I think the oven got used once.

It's the backyard/home shop solutions that will help me the most right now. I have an interest in sleeve valve engines and want to experiment around with some single cylinder variations. I am considering making the engine blocks from weldments.

There have been several engines build here from welding/ fabricating. IIRC markak built a hit and miss and a guy I think Tom built a repro of a 1910 benz the engine was welded and machined. So it can be done , has been done , and you have come to the right place for help.
Keep it simple get some A36 or 1018 structural steel of the sizes and shapes you need . mock it together tack weld the parts throw it in the oven at 400 then weld it up working opposite sides to keep the heat and stresses even . then throw back in the oven for an hour turn the oven off and let it cool slowly.
I have welded thousands of parts, sometimes 500 in day . our customer thought we had a robot because " No human could weld that fast and that good" I have burned through countless rolls of mig wire. Unless it is a critical needs to be x-rayed inspected certified weld pre- heats and post heats do not happen a lot in the field.
This is a hobby experiment and have fun . yes ask questions and make sure you have a steel you can machine and weld. or things could get frustrating fast. and for an engine you may want to allow for a cast iron cylinder sleeve . it will wear better than steel .Also the valve sleeves may be better in CI.
hope this helps.
a little more info here
http://www.eaglesteel.com/download/techdocs/Carbon_Steel_Grades.pdf
there are many choices. you need to balance cost weldability and machinineability and to some extent strength

Tin

 

[steamer]

What Tin Said!


For small parts....like model engine blocks.....made by welding.

It is probably enough to just allow the movement as part of the machine process.

For instance.

Weld your parts. Rough machine the parts and allow .02"-.03"...or the amount deemed required by the situation worth of stock on all critical surfaces that provide alignment to other surfaces, like the block deck/cylinder base interface.

Once all the roughing is done, the part has probably moved all it's going to. Now go back and finish machine the critical tight tolerance and or tight geometry surfaces. Geometry meaning flatness/squareness ect.

Dave

 

[steamer]

Another thing to consider, when using mild/low carbon steel....A36 or 1018...ect in our weldments

Use Hot rolled section instead of Cold Rolled.....and I bring this up so the new guys know this....not to tell you old salts how to suck eggs...

Cold Rolled is just that. it is processed...rolled if you will ,while cold. As such it contains quite a bit of residual stress...something Hot rolled doesn't have because of the difference in how the two sections are manufactured....its done hot! Keeping the stress out of the raw material in the first place can't hurt.

It's tempting to go with Cold Rolled because it is cosmetically much nicer to look at..it doesn't have the black slag that hot rolled stock has.....but it comes at a cost. In general, I find hot rolled to machine just fine so leave some padding so you can machine the ugly stuff off after.

Dave

 

[steamer]

Lastly,

Consider not welding it at all! Some parts could be advantagously silver soldered! NO I don't want to get into the semantics of solder vs braze please. Silver brazing has for ever been called silver soldering...it far predates me....and I suspect it will be that way long after I'm gone.

I bring up silver soldering, because advantageously, it is usually done at or around the stress relieving temperatures of steel, and generally speaking...with small model engine parts.....the whole part gets to the brazing/soldering temperature, while welding can have a very drastic temperature gradient between the melt zone and the rest of the part.

While not an accurate stress relieving process with demonstrable process repeatablility, brazing/soldering does knock some or dare I say most of the stress out of the part.

It's like chicken soup for residual stress....probably not going to hurt you for one part....in your shop.

Dave

 

[Tin Falcon]

good stuff Dave.
This is a hobby it should be fun. there are certainty many ways a project can go wrong and we want to avoid that and many ways things can go right. the best way is the way that works for you in your shop.
I have a cheap department store welder it is flux core wire feed. that is what I use for attaching steel to steel .
there are many other tools and methods . I have been trained in oxy-acetalene welding (yes you can weld with one of those) stick and tig as well as brazing soldering. there is also the new multi plaz unit out there.
when doing many parts in industry use the best most efficient tool for the job. At home use what you have that works. or what you can afford to buy.
Tin

 

[Tin Falcon]

Rake 60 said:

I have machined a lot of welded fabrications over the past 20 years.
Almost all of them were stress relived.

Some were heated up then buried in a lime pit for 12 hours to slow cool.

jasonb Said:

Stick it in a fire then let it cool overnight in the ashes, I've recovered several chilled castings this way and as similar methods are needed with weldments thats how it can be done in the home.

The old black smith method is get the piece red hot then put in a metal container full of lime and wood ash 50/50 by volume.
so a black smith forge would be an option for a heat source .
you can make one easy enough A used car or truck brake drum a pipe flange, nipples T, and cap drain strainer (fire pot) , a shop vac or hair drier for a blower and a bag of real charcoal from Walmart or other favorite place for fuel. . and a bag of garden lime to pack the heated part in.
And you are there.
Tin

 

[steamer]

As you point out Tin....work with what you've got

I have specified welding on prints for years...but I've never WELDED anything!....at least not on purpose! :big:

I can silver solder to beat the band though....so I tend to be SS centric on that point

Do what works for you.

Dave

 

[jonesie]

i agree with dave, and use hot roll if you need to weld it.i work in a large engine mfg. plant and do some building of weldments, but not the welding i am just the toolmaker. the boys that do that are the experts and if it is load bearing as below the hook it needs to be hot roll. if it gets welded we usually use hotroll, and no tool steel, and like said leave yourself some extra stock to remachine after welding. also if it is not bigger then our draw furnace it gets but in there to stress relieve. jonesie