need a fast hardening filler for nesting uneven forgings in a fixture

INCONELDAVE · Mar 28, 2015

I am nesting aluminum forgings in a aluminum fixture .

Presently I am spraying parts and fixture with a oil based penetrate to prevent the JB weld wood filler from sticking to the the part and fixture.

JB wood filler comes in two separate tubes a hardener and a resin this works but its really hard to appy where I need
it because it doesnt stick

I have seen the two part epoxys in the syringe type tubes maybe something like this?

in case your wondering why?
I am trying to fill voids and or uneven areas so after the filler is set my clamping will not distort the part.

I know one of you out there has an easy solution.
Thanks

L Vanice · Mar 28, 2015

Can you suspend the forging, held in a wire fixture to keep the position constant for each part, in a cake pan (or similar), and pour melted bismuth alloy in around it? The alloy is fairly hard, but melts at 158 degrees F. I do not think it will bond to aluminum, so your parts will stay clean and you do not need to get oil on everything. I have seen the alloy on eBay for less than retail. Cerrobend is one of the trade names for bismuth alloy.

After machining, you can wash off the chips and put the pan in a 175 degree oven to melt the alloy. If you don't overheat it or contaminate it, the alloy will last forever.

Larry

gwilson · Mar 28, 2015

Fixturing metal is fairly hard,and very low temp. melting. We have been using it to make concave oval dies for pressing 1/8" brass sheet into,to make 18th. C. brass doorknobs. It lasts for several knobs,then is easily re melted to re make the die.

Not the cheapest stuff to buy,but pretty effective at standing up to pressing the thick brass into with a 50 ton press cold.

INCONELDAVE · Mar 28, 2015

Thanks for the replies ,but I dont think your seeing what I am trying to accomplish.

Think, liquid shim that will harden to fill the areas not making contact between the forging and the fixture.

Tomorrow or monday I will post a picture of my current issue .

alonzo83 · Mar 28, 2015

I was reading a thread a couple months back that you can use plaster of paris for this application.

I do know hot water makes it set up faster.

Never had the need to try it myself.

Nmbmxer · Mar 28, 2015

I agree with the suggestion to use fixturing alloy to bed your parts and not some sort of glue that will be hard to remove.

upthebikes · Mar 28, 2015

If you aren't reheating or welding, soft modeling clay worked well for me. I had a one off tubular, welded structure that had curved "arms" of different lengths coming off the top, and the bottom had several mounts that needed faced relative to each other. I welded up a simple rectangular tray, like the lid of a shoebox, and filled it with modeling clay. I clamped the tray to the mill table, sunk the part in the clay upside down, then clamped the part to the sides of the tray. It was both to avoid bending/distorting the curved arms, and because i didn't have a horizontal mill at the time and couldn't for the life of me figure out how to clamp this thing directly to the table and the shape did not allow a vise. Light facing cuts worked great, part did not move or distort. I suspect play-doh might have worked too, the filler didn't have to be too "hard" just had to take up the space. Depending on what operation you are doing to the forgings in the fixture, maybe something along these lines will work for you.

gvidas · Mar 28, 2015

alonzo83 said:
I was reading a thread a couple months back that you can use plaster of paris for this application.

I do know hot water makes it set up faster.

Never had the need to try it myself.

Heat, small amounts of salt, and vigorous mixing will accelerate the curing of plaster. You can get it to set pretty rapidly if you want.

Tonytn36 · Mar 28, 2015

We use a two part machinable plastic called DynaCast. Disadvantage is that it takes a few hours to fully set. Just 12-15 minutes to get stiff, but about 12 - 24 to be fully cured. It is pretty stout as we sometimes use it as an ID driver for parts on a lathe.

extropic · Mar 28, 2015

Link is to a similar thread (regarding castings) almost two years old. There may be something that will spark for you.

http://www.practicalmachinist.com/vb/cnc-machining/casting-fixturing-ideas-large-quanity-job-269538/

gbent · Mar 28, 2015

INCONELDAVE said:
... I dont think your seeing what I am trying to accomplish.

Think, liquid shim that will harden to fill the areas not making contact between the forging and the fixture.

I don't think you understood Larry described exactly that. Cerrobend is a metal with a liquidus temperature of 158 degrees. It hardens almost instantly. Depending on the amount of shrinkage or expansion you want or will accept, there are several metal alloys that will melt in hot water.

metlmunchr · Mar 28, 2015

Nearby shop, now owned by GE Aerospace, makes a lot of thin ring parts for jet engines. They make an aluminum nest with some locating points and then put some chisel marks in the clear areas of the fixture to allow it to grip the bismuth alloy mechanically. The heated alloy is simply poured in the space between the part and the fixture.

When the work is done, the operator puts the assembly in a pan of hot water and loads the next one which has been fixtured while the other one was running. The bismuth evidently doesn't bond to the surface of the aluminum or the part itself, which is typically a titanium or inco alloy. I've watched them do it, and they don't have to use any sort of release agent and the fixture and part is clean when they melt out the fixturing alloy.

DMF_TomB · Mar 29, 2015

INCONELDAVE said:
I am nesting aluminum forgings in a aluminum fixture .

Presently I am spraying parts and fixture with a oil based penetrate to prevent the JB weld wood filler from sticking to the the part and fixture.

JB wood filler comes in two separate tubes a hardener and a resin this works but its really hard to appy where I need
it because it doesnt stick

I have seen the two part epoxys in the syringe type tubes maybe something like this?

in case your wondering why?
I am trying to fill voids and or uneven areas so after the filler is set my clamping will not distort the part.

I know one of you out there has an easy solution.
Thanks

.
bondo auto body filler ?
.
smelly but works for a lot of stuff and easy to get a can of it

crossthread · Mar 29, 2015

I have used Marine Tex for just what you are doing and it worked very well.

challenger · Mar 29, 2015

If any thread topic needed pictures this is one IMO.
I'll be interested to see the set up.

Auto body supply houses have guns that hold two tube and mix an epoxy as the parts A and B get dispensed through through the tube. There are a few varieties. They are viscous but maybe you need faster cure rate?

What exact requirements does the ideal substance have to have? In what order of importance?
Cheap
Cure rate
Strength
Removability
Clean up
Viscosity
And more attributes?

I like the bonds and plaster idea. If you need stronger there is also a gun that dispenses a thick polyester resin with shredded fiberglass and hardener.

adama · Mar 29, 2015

You would have to be quick applyig it, but hot glue is anouther option, if wood filler has enough compressive strength that also would.

Anouther thought, rather than solid, what about hard rubber blocks - the hardening rubber compound? Would have enough give to conform to the shape, but flexible enough to conform to the clamp pressure maybe give you the alignment and holding you need? Would also be reusable once molded to hold the part for more of the same part if that makes sense? Some of the harder rubber compounds would be more than solid enough to not vibrate when machining, but soft enough to support the part.

DMF_TomB · Mar 29, 2015

INCONELDAVE said:
I am nesting aluminum forgings in a aluminum fixture .

Presently I am spraying parts and fixture with a oil based penetrate to prevent the JB weld wood filler from sticking to the the part and fixture.

JB wood filler comes in two separate tubes a hardener and a resin this works but its really hard to appy where I need
it because it doesnt stick

I have seen the two part epoxys in the syringe type tubes maybe something like this?

in case your wondering why?
I am trying to fill voids and or uneven areas so after the filler is set my clamping will not distort the part.

I know one of you out there has an easy solution.
Thanks

.
marine or boat supply store usually sell epoxy in different hardening times. it is thin and you add materials that they also sell if you want it thicker, ketchup, mayonnaise or peanut butter thickness
.
beware faster curing it gets hot if you mix any container with more than a 1" as in fill a coffee can 1/2 way and it can be boiling giving off toxic fumes.
.
beware some items like petroleum jelly can affect epoxy cure and can even prevent surface from ever curing. they sell release agents so epoxy does not stick made for epoxy. i have also use a alcohol soak rag and wipe a block of wax and then wipe part

Scottl · Mar 29, 2015

I wonder if shellac would work. If you mix it from flakes you can get any viscosity you want and alcohol will remove it.

Another suggestion would be wax. Apply hot and press parts in place.

5 minute epoxy sets quickly and can be popped with moderate heat.

If using a resin mix PVA or similar mold release would work much better than oil. I think Brownells sells aerosol cans of mold release. Polyester resin/hardener is quick setting and with proper mold release a thin shim layer could be flexed to release any part with draft.

PeteM · Mar 29, 2015

Another option might be to consider a different fixturing strategy.

Trying to get a complex cast shape to nest in an equally complex fixture requires the sort of filler (and patience) you're presently dealing with. I suspect you could use Bondo (or the plaster suggestion above) for a quicker setting bedding compound if the price of low temp alloy is an issue. As also suggested, even something like modeling clay might be enough to allow secure clamping. You might even try a few dabs of a weak hot melt glue if there isn't heat, excessive machining force, etc.

But, another possible strategy -- if the exterior design isn't critical -- is to design the casting with fixture points (the minimum needed to fixture it in place). Then design a fixture that bears and clamps only on those points. This takes away the steps of applying a release compound, adding filler, then cleaning everything off.

Limy Sami · Mar 29, 2015

Place a sheet of waxed paper in a shallow baking tray, pour in ''enough'' plaster of paris, spray with mould release and place parts and leave to set, by the time you've done a few trays the first will be ready for breaking out and machining.

Any p of p left after machining will come of in a quick acid dip.

Cheap, quick and easy.

Job Done!

need a fast hardening filler for nesting uneven forgings in a fixture

Aluminum

Diamond

Diamond

Aluminum

Stainless

Stainless

Cast Iron

Aluminum

Diamond

Stainless

Diamond

Diamond

Diamond

Titanium

Stainless

Diamond

Diamond

Diamond

Diamond

Diamond

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