Need help deciding on cnc-cutting device

[Grrrrrene]

Hi guys,

Excuse my English and my lack of cnc knowledge. For my work I need to cut composite panels (glass fibre or carbon fibre reinforced plastics like epoxy and polyester). The panels are usually around 500 x 500mm (20" x 20") and a few millimeters thick. We recently purchased an Instron tensile tester (3382 model) and our diamond saw is not accurate enough to meet the dimensional requirements in ASTM and ISO standards.

In particular compression specimens need to be machined very accurately, with dimensions of 140 +/- 0.3mm x 12 mm(5.5" x 0.5"), parallel and perpendicular within 0.03 mm. (ASTM D6641).

We are not sure yet if we should buy our own machine or outsorce the cutting work. Our first thought was that a cnc milling machine should do the job, but there is the problem with glass/carbon dust slowly destroying the guides. Most companies in the neighbourhood know us by now and won't machine our materials (which we understand), so the question is: should we get our own milling machine or is water cutting a better solution. Well, that last question is easily answered since water cutting does not produce dust and no HAZ, which is nice for composite materials. There's just the matter of the price: I have no idea what to expect. I can find little pricing on the net, just two machines between 22k and 65k, both labelled "affordable".

With the dimensions and tolerances listed above, is it realistic to look at water cutting or should we stick with milling and be very very careful about dust? We are not going to produce lots of specimens, but cutting them with the diamond saw gives very low yields and is time consuming. We could of course have other companies outsource their cutting jobs to us to reduce the pay-back time.

[SORCHEROR]

i can tell you one thing about carbon or glass composites that i had water cut,on some of the pieces the edges where seperating due to the high water pressure, i assume,we cut
them on cnc with dust collector and high speed spindle,your best bet is to purchase a router with a good water cooled spindle and buy a dust collector

[Grrrrrene]

i can tell you one thing about carbon or glass composites that i had water cut,on some of the pieces the edges where seperating due to the high water pressure, i assume,we cut
them on cnc with dust collector and high speed spindle,your best bet is to purchase a router with a good water cooled spindle and buy a dust collector

Thanks for that information, hadn't considered that. There is a Dutch composites association that wrote something about water cutting being great for composites due to the lack of dust and great surface finishes. I guess it all depends on the composition of the material.

So you recommend a router, I'll keep that in mind, but wait for a bit more feedback if it comes

[jcc3inc]

Sir,

At one time we made an X-Y machine to which a water jet system was fitted. It was to cut material that consisted of an epoxy-fiberglass core (like pc board G-10) that had stainless steel clad top and bottom surfaces (again like a PC board, clad both sides). In order to eliminate blistering, we could not pierce the material sandwich with water jet; it wopuld delaminate. Instead we had a pneumatic drill on the same cross carriage with the water jet head, first drilled a through hole, then shifted the machine to center the water jet to start at the drilled hole.

It seems that water jet application has some peculiarities!

Regards,
Jack C.

[Grrrrrene]

Sir,

At one time we made an X-Y machine to which a water jet system was fitted. It was to cut material that consisted of an epoxy-fiberglass core (like pc board G-10) that had stainless steel clad top and bottom surfaces (again like a PC board, clad both sides). In order to eliminate blistering, we could not pierce the material sandwich with water jet; it wopuld delaminate. Instead we had a pneumatic drill on the same cross carriage with the water jet head, first drilled a through hole, then shifted the machine to center the water jet to start at the drilled hole.

It seems that water jet application has some peculiarities!

Regards,
Jack C.

Thanks for the reply. I was at the JEC in Paris last week and spoke to a guy from Flow WaterJets. They were cutting carbon/epoxy composites at the exhibition floor and the surface finish looked excellent. This was abrasive cutting by the way, which seems the way to go to avoid the delaminations you spoke about.

But at a price point between 100k and 200k it's quite steep for us It's a nice technique if you mass produce small parts out of sheet composite, but for small series (cutting specimens from samples) it's too expensive for us. Maybe we'll turn to companies in the neighbourhood that own a water cutter, if the surface finish is indeed so much better than cnc milled specimens as the Flow guy said. I'll have a closer look at the cut edge this week.