Now we get to the interesting stuff I built this setup to test!.. I ran some Polymaker PA612 Carbon Fibre today, and it did not disappoint, being about 50% stronger than the best PLA… Here are the results… BTW, I am using a layer height of 0.25mm for the CF-Nylons, as a 60% minimum of nozzle diameter (I’m using 0.4mm) is recommend for carbon fibre…
The tensile strength in the horizontal (X) direction exceeded 13,000 psi… The vertical (Z) test coupon got to 5300 psi before breaking… All samples broke cleanly, with no noticeable stretch, as you would expect with carbon fibre… The pieces were very stiff… The X-direction peaked in strength at 270C, while the layer adhesion was pretty flat from 260-290C… Within those temperatures, the lowest yield occurred at 270C, but at 5080 psi, within 5% of the 5313 max, which on data from single coupons is probably within the region of being statistically equal…
Bed adhesion was a bit tricky… I used Garolite (FR4) which is basically printed circuit board, laminated glass fibre and epoxy… In fact, I got a piece of copper clad one-side (and used the back), I figured the copper back couldn’t hurt the heat distribution on the bed… I used 70C, with the first layer at 80C with a nozzle temperature of 270C, and had no problems once I found that combination… I didn’t try my PEI bed, but I probably should have… I had trouble with the retraction settings, the ones that gave the greatest strength were very stringy, and when I increased the retraction distance to clean up the prints, the outer surface was no longer smooth and the strength dropped in both axes… Strings are not that hard to remove, so for an engineering material where strength is everything, I’ll put up with them until I find a solution that doesn’t lose strength…
More CF filaments to come, it will be interesting to see if price corresponds to strength!..
Bob