Aluminum molds for thermoforming

[drcrash]

The only time it would be of benefit to use water cooling is in very large tooling, thick material forming that transfers a lot of heat and in-line forming where cycle time is critical. The complications of water lines and cooling towers might not be worth the maintenance hassles in most job shop environments. Even less for home shops.

I sorta guessed as much. I'm toying with some related ideas, though, that might likewise not be worth the trouble.

I'm wondering if it would be worth embedding some thin aluminum rod in an aluminum-filled epoxy mold, rather than tubing, just to provide long paths of solid aluminum for heat to travel through, or maybe putting strips of windowscreen in the layup.

Two applications of that are for a small rotomolder, and for a vacuum forming mold (& a plug-assist plug) for rigid sheet foams like Depron (an extruded polystyrene). Vacuum forming that stuff seems to be pretty tricky, and to depend on very even heating in a narrow range of temperatures. Molds and plugs that even out the heat well might be useful.

(Then again, maybe aluminum-filled epoxy is already plenty conductive enough that if you preheat the mold properly, the problem is solved.)

[skippy]

Fernando, I think you'll need to answer Igor's questions about what material and what thickness and what draw depth are you molding before you can get a decent answer that relates to your case. There's been some fantastic and very knowledgeable advice given above but you must admit that vac forming 5 million .020 PETG chocolate trays on a high speed vac former requires a totally mould to vac forming 200 signs (or face masks or whatever) using 5mm acrylic or polycarbonate. No one wants to know what the actual product is as that is your business.

[One of Many]

I sorta guessed as much. I'm toying with some related ideas, though, that might likewise not be worth the trouble.

I'm wondering if it would be worth embedding some thin aluminum rod in an aluminum-filled epoxy mold, rather than tubing, just to provide long paths of solid aluminum for heat to travel through, or maybe putting strips of windowscreen in the layup.

Two applications of that are for a small rotomolder, and for a vacuum forming mold (& a plug-assist plug) for rigid sheet foams like Depron (an extruded polystyrene). Vacuum forming that stuff seems to be pretty tricky, and to depend on very even heating in a narrow range of temperatures. Molds and plugs that even out the heat well might be useful.

(Then again, maybe aluminum-filled epoxy is already plenty conductive enough that if you preheat the mold properly, the problem is solved.)

I cannot comment on rotomolding. I've seen it, but that is all.

For what it is worth, styrene has the lowest forming temp and the most rapid chill off as I recall. I would expect the heat time verses the form time to transfer the least amount of heat into the die. Unless automated to the point the short heat cycle time does not allow the tool any time to disipate heat with a simple fan array. Forming a couple scrap blanks PE was what we used to pre-heat the tool, because it held heat the longest and at a higher temp.

Having a screen tray between the heat source and the plastic sheet will allow shadow screening of either top and/or bottom ovens. This is simply a way to add in screen mesh of different densities to vignette heat off areas for better control about the sheet. You might not want the whole sheet to be all at the same temp.

You are in control of how much material thickness you hope to manipulate to your advantage. Be that with plug assist, snap back, bubble pre-stretch, placing the die off-center of the blank or pedestal mounted to retain thickness at the trim edge are tricks often not easily learned without going through tons of plastic over years of trial and error.

The best path to take is with your specific equipment and ways that you learn to make it work for you.

DC

[fer_mayrl]

Sorry, with all this info, i just forgot to answer that,
Im molding 12 and 15 mills PET for some food product trays. And I hope a lot of trays will be made, since its my brother who is starting his food business.

[One of Many]

In that case, a rough basis for vacuum hole diameters would be around 1 material thickness up to around .040 and a .06 hole size limit there after. Much more than that risks pulling the material into the holes or they could show up as dimples in the part.

As with all of the cycle events that make up your sequence to produce a good part. Having reliable cycle timers that either turn on a bulb indicator that informs the operator the heat cycle has completed or tiggers a chain reaction to say heat for xx seconds, open door, slide out material, activate upper and lower plattens, turn on and off vacuum, fans or compressed air for ejection. The fancy features need automation for consistancy.

You might look into getting PET in rolls and do some looking around for an in line former that either includes or can append a trimming die punch. This is how coffee cup lids, plastic cups and plates are made efficiently, but those are primarily styrene. I cannot imagine anyone trying high production food service items on manual forming machines.

I'd at least get a part price quote from those already in the business to see how much an initial investment would be if YOU produced the tooling to fit their equipment. If the parts costs run in the 5-35 cents by the 1000. You will have a hard time competing with that as a lone single product former. I'd question if quantities at 10,000/month would make it a worth while side line business.

DC

[fer_mayrl]

Thanks for your insight,
We dont own a thermoforming machine, we are having the trays made, we just provide the tooling.
Thanks Again
Fernando

[coonhunter]

Okay, I'am going to tell ya how I do it at my work place. We use cnc's to cut pine or mdf patterns with shrinkage included. We sample parts then send pattern out to be cast.We used to Drill 1/64 holes with high speed drills using wax, 1/16 holes if apperance does'nt matter. But know we use a vac. button,looks like a .500 inch button with small hole in it, we just place them in strategic ares and eliminate all the hours of drilling the small holes. Now some people are going to ? this saying that there is a formula for how many hole per inch with draw of vac ect... We build around 200 vac. molds a year and they are working great with no forming problems We use cooling line to cool or heat mold, do not use copper,get some high pressure water line(300psi).
p.s. if apperance is a factor then do not use buttons drill the 1/64 hole

[rickharris]

Unless your vac form is going to be high volume or very complicated why not do as we do at school and use MDF as a pattern?

It CNC routes well and gives a reasonably long lasting pattern. In general we don't need to put draw down holes in the pattern unless very deep or a complicated shape.

Give it a try MDF is cheap at least it will serv as a test for your Drawing.

[darrell]

There is a pourus aluminum product called Metapor that can be machined easlily with no coolant. It is air permeable so no vacuum holes need to be drilled. CMT materials sells it. METAPOR® Air Permeable Thermoforming Products by CMT Materials Inc.

[Deltic_Engine]

I've been designing Pressure and Vacuum-forming molds for 11 years.

PORUS aluminum. But it is extremely expensive - Use only for porus 'Plugs'. Here is the trick:

1. CNC your mold in conventional 6061-T6 or 7075-T6 if your budget allows.
DO NOT remove the mold from the milling machine just yet.

2. Mill some 1/4" diameter pockets into the mold where you want the venting most.
Then use a smaller drill bit to drill almost to the bottom of the mold (not into your vise

3. Fabricate some 1/4" diamater PLUGS in PORUS Aluminun (McMaster.com or elsewhere).

4. Press/glue the Plugs into the pockets you milled.

5. Re-run your CNC program (or create localized programs) to re-machine the plugs
so that they perfectly conform to the mold's surfaces.

6. counter-bore the back side of the mold or just make some shallow
cross-cuts to break-thru and connect the vent holes.

Alternately if you design the mold from the outset to include the counterbores
for the plugs you could even put the plugs in before the initial machining.
Hence you are only adding the labor of doing the counterbores and plugs
vs breaking bits trying to drill tiny holes afterwards.

Jeff Krause
EVA CASES, EVA CASE DESIGN, Custom Protective Cases by Designer Jeff Krause