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Hi, I'm new here.
I am a mechanical engineering student and my graduation project is about manufacturing deep drawing dies from plastic materials and we found that some types of epoxy resin is suitable for our application.
I am aware that casting the epoxy is way cheaper than machining.
1-will casting the epoxy resins achieve the same surface and dimensional accuracy needed for such application?
2-Is machining glass fiber reinforced epoxy is possible?
thank you for your time.
Hi,
casting is OK but nothing beats machining for dimensional accuracy.
If you try it make sure you use a casting resin, ordinary laminating resins exotherm in even small volume and you must avoid exotherm.
Cured epoxy machines OK, but like all plastics is sensitive to heat. Very wise to temp cycle epoxy before machining to ensure it is as hard
and rigid as it can be. Sharp tools, chip clearing with flood coolant preferred. Epoxy glass temps are usually 100C or lower, don't let it heat up or you will have a disater.
Machining fibre reinforced plastics is no trouble. Glass dulls tools so use carbide. If the chips clear the cutzone all well and good, if the chips remain in the cutzone then they will
be recut, heat up and fuse into a lump. Clearing chips is critical in any plastics machining be it reinforced or not.
Craig
Hi Zia - By deep drawing do you mean using a double acting press? Is this for steel or aluminium pressing? To answer your questions:
1) Even though casting maybe cheaper you still have to make the master
2) Deep drawing dies are highly polished to reduce friction (more correctly to reduce asperities height as these can be higher then the lubrication thickness which causes stick ups) and if you use a fibre reinforced epoxy the fibres will prevent you from getting the required finish. So you will have to use some sort of surface paint (more epoxy) to cover those fibres. Plus you have to use a specialty high pressure oil to ensure you don't get contact between the tool and the metal. The higher the polish the better the tool works in my experience. So we go to quite a lot of work with diamond grits to get mirror finishes
3) I expect that 3D printing using a high strength plastic will be a more direct route to a press tool
4) This all depends on what you are trying to press. If you are trying to press a car fender then steel is your best and traditional answer for the tool. The compression loads and polish required is achievable with tool steels. If its a bottle cap then maybe plastic in a steel bolster will get a few caps done
5) You ask about dimensional accuracy and finish. The epoxy (and I expect it will be a high filled metal powder epoxy maybe aluminium) will replicate the surface of the mould exactly. Your issue will be releasing the tool from the mould. Being thick and stiff they will want to stay attached to each other via the vacuum formed when cast. You will need to make a multipart mould so small bits can be removed at a time (complex hence $$$). Or you will need to make provision for a hydraulic release. This means that a fitting is placed in the mould that allows water at high pressure to be pumped into the bottom of the tool cracking the joint and pushing the part out. I also recommend a silicon liquid release to be used vs a paste wax. The liquid releases much easier in a thick part.
6) Press tools fatigue due to Hertzian stresses under the tool surface. The surface is in compression but at some depth the compression turns into tension and this transition results in fatigue. So if you want to make 1M parts you do it different to making 10 parts. Urethane is used for small production run press tooling as well. You can simulate metal forming and contact pressures these days quite well. Some 25 years ago I was involved in simulating pressing of aluminium automotive parts... aluminium due to its hexagonal grain structure does not like stretching in two directions at once hence it has not taken the place of steel in auto parts. Steel has a cubic structure and slips in three directions very easily so is a good material for pressing deep parts.
https://www.facebook.com/ScootCNC/vi...12197187552243
https://www.facebook.com/ScootCNC/vi...86821762533410
The video is machining a block of material I made. It consists of outer layers of carbon fibre and inner layers of steel fibres. The matrix is epoxy. I use diamond tools or PCB burrs to machine this sort of material. So machining composites is no big deal... But machinists will not machine this sort of material on their expensive CNCs as the fibres are abrasive and the epoxy swarf clogs the coolant systems... a few hurdles to jump I think...Peter
I think it will be very difficult to get a good outcome with epoxy if the deep draw process involves forming metal.If it involves forming ABS or similar plastics over a machined form there are several epoxy based tooling blocks that may be suitable.You might try Sika,Ren or local alternatives.Many of them are resistant to 120 deg C and I doubt that a thin sheet of material has the thermal mass to transfer a great deal of heat into a block that is a fairly effective insulator.The point of concern is that the filler in such block materials is hard on cutting tools as it is usually mineral based and consequently abrasive.
Hello! Great project you've got! To answer your questions:
Casting Epoxy Resin: Casting can be cost-effective and give you a decent finish but might not match the precision of machining without some extra work. It all depends on the mold quality and how you handle the curing process.
Machining Glass Fiber Reinforced Epoxy: Yes, you can machine this material, but it's tough on tools due to its abrasive nature. Specialized tools and careful planning will help a lot here.
For a project like yours, exploring other materials could be a good move. Maybe look into some advanced material options that could offer the precision and durability you need like here: https://www.kkrstone.com/
Hope this helps, and good luck with your graduation project!