The extrusion runs of Examples 1-12 were performed with a modified ABS material commercially available under the trade designation “CYCOLAC” MG94-NA1000 ABS from General Electrics Co., Pittsfield, Mass. The extrusion runs of Comparative examples A-D were performed with a standard ABS copolymer commercially available under the trade designation “AG700 ABS” from The Dow Chemical Company, Midland, Mich.
We surmised that Dow AG700 ABS may likely be the standard Stratasys ABS, and given the date of filing and material properties, the GE MG94-1000 ABS was likely the newer ABS-M30 material. I started looking into the AG700 resin first – while I was able to find something of a datasheet for the product, the fact that Dow now only sells to the automotive market (in North America, at any rate) pretty much quashes any possibility of acquiring the resin. Still, we now have a set of material properties to use for comparison, and I’m wondering which properties specifically make for an ideal Stratasys/RepRap/FDM feedstock. The “high flow” and “low gloss” aspects jump out at me in particular – obviously high flow is needed given the small orifice sizes, but I wonder if the glossiness of the extruded filament is indicative of its surface energy, and hence the amount of attraction that two layers will have for each other (thus potentially causing warp).
I had much more luck with the MG94-1000NA resin – GE sold their plastics division in 2007 to SABIC, so I dug around on their site (after needing to create an account, grrr) and pulled up the datasheet for the material. It turns out that the ‘-1000NA’ is simply the color code – they have dozens of colors available, and -1000NA is the plain old uncolored ‘NA’tural one. After a call to sales, I found that the smallest quantity I could order was 55lbs. at a whopping $30.61 per pound. Yowza. However, the price decreases drastically with quantity, and 330lbs. would only be $7.69 per pound. I don’t exactly have $2500 burning a hole in my pocket, but the quantity and pricing certainly isn’t out of reach for a few dedicated hobbyists to try. There’s a few other possibilities to research before falling back to that, however.
Recently there’s been a bit of buzz on the RepRap forums about a low-cost, very RepRap-ish 3D printer from China. What caught my eye the most was that this printer is actually using Stratasys sized 0.070″ feedstock rather than the 3mm RepRap standard. They note an ABS price of $50/kg, which comes out to $22.69/lb. Not as cheap as from NIP or other sources, but if the plastic acts just like Stratasys ABS, it would be worth it.
Speaking of NIP, I called up Donna to see what other possibilities there were for ABS. She and Jim were kind enough to provide me with the datasheet for the specific ABS they use, which is Chi Mei Polylac PA-747. They’re able to get other Chi Mei resins as well, so I took a look at their high flow offerings. The highest flow formulation, PA-756H, looks promising – the low impact strength is one of the properties that stuck out on the AG700 resin. I’ve emailed Donna to see if they can acquire this material.
So much for material musings – I have 5 pounds of HIPS that I need to wind onto spools! I’m not about to wind a half mile of filament all by hand again, so I needed to figure out a good automated system. I originally figured I’d just chuck the empty spool on the lathe and wind it that way, but then I decided to use the mill instead, as the head is variable speed on-the-fly. How to hold the empty spool, though? An expanding collet would be great, but I don’t have any as big as the 2″ bore in the Stratasys spools. A little bit of digging through scrap bins, and I found a Delrin cylinder that would work perfectly for making a pair of bullnose centers mounted on a bolt. Here’s what the assembly with spool looks like on the mill:
What to do on the unwind side was a bit trickier. Based on my winding by hand of the ABS, I knew that keeping the coil of filament in a rather static shape was very important, so I opted to make a simple spool that could be assembled around the coil itself. I used Masonite for the sides and drilled holes through each piece to allow for joining screws. Multiple sets of holes were drilled so that I could adjust the screw locations to perfectly fill out the center of the coil.
I clamped a piece of 3/4″ rod in the bench vise and slipped the spool over it (a collar on the rod kept the spool at an appropriate height). It rotated pretty freely, so I took the loose end of filament and tied it to the inside of the empty spool. I set the mill spindle to the lowest speed, and hit the power. 60 rpm is perfectly fast for winding, though I cranked the speed up to around twice that once I had a good start on the winding. I held the filament in one hand (with a rag so that I’d actually have skin left) to provide continuous tension, and the material unwound from my adjustable spool just as nicely as I had hoped, with no snarls. About a half hour later I had two spools fully refilled.
I gave the NIP HIPS a try in the Stratasys, noting that the Stratasys support material is slightly more brittle than the NIP HIPS. I ran a small test part with NIP ABS at 250° C, and the HIPS at 265° C. The HIPS performed admirably, and had good adhesion to the NIP ABS.
The Stratasys is currently running a large plate of parts, and we’ll see if I have less warping this time.