In a previous article we carried out an interview with Polymer Technology lecturer Colin Hindle, who has had over thirty years experience working in the plastics and polymer industry. At 3dprintworks we have really enjoyed collaborating with Colin to develop a range of materials.
We asked for feedback on this article and received the questions below. We hope this answers your questions!
Q. The most prominent failure mode is warping or delamination of the layers. There are so many different methods that people use try to use to tackle the problem. From “mouse ears” to brim, glue, floorwax, hairspray, enclosures, heated beds, rafts, egtc. My own solution was to print slow…10mm/sec.
So the question is, which method is the best, or what combination of methods?
A: Delamination within the part is most likely the result of too low a temperature. Warpage is the result of differential shrinkage. The higher the temperature the more the shrinkage. Optimisation is a balancing act.
Methods to improve adhesion are:
1) Make sure the bed is level and set correct
2) Make a bigger raft by printing small coins round the part such that they form part of the main parts raft
3) Increasing the extruder temperature slightly helps
4) To help with adhesion some people use hair spray, others paper glue sticks or spray glue. If you are using ABS you can make a solution of ABS and Acetone approx. 1:20, which you can paint on just before you print, all these I have found can be successful, but only experience tells you which method for any given print will work well with it.
Q. You say that warpage is a result of differential warpage. Can you expand a bit more on what causes warping?
A. This explanation is for ABS only but methods for improving bed adhesion and reduce warping are similar for both. Sometimes if the bed temperature is not uniform across its surface as can be the case, then if a part is built at the edge of the bed where it may be colder it can suffer warping. Because part of it is on a hot part of the bed and part of it is on the cooler part, the difference in temperature causes uneven contraction in the parts base which can cause it to split its adhesion with the bed and lift off and curl up (warp).
Q. I find that ABS is really particular to its extrusion rate. Too thin and it starts to peel back on overhangs. Too much and it looks terrible. Printing slower does but that more negates the larger issues and makes printing “big” objects with ABS very frustrating.
Also, what filament diameter is ideal for ABS (if any?) My 3mm clogs up much more frequently than 1.75, but only with ABS. I found the larger diameter filament may “choke out” at higher temps but that’s only a hunch.
The faster you extrude the greater the diameter of the extruded bead due to the “die-swell” an elastic recovery of the deformation.
Is the diameter of your filament constant or does it vary? A too large diameter may cause it to block extruder head; too small a diameter and drive system may not grip it. Having said that it should print at both of those sizes, so it is more likely that the quality of the filament you were using was the culprit.
Q. As all ABS filament is not the same, what properties make for a good printing resin?
Not all ABS filament is the same because not all ABS is the same. Differences in molecular weight (relative molar mass) affect melt viscosity e.g. MFR (melt flow rate) and can be assessed by measurements such as IV (inherent viscosity), but melt flow can also be deliberately modified by internal lubricants and accidentally modified by colourants. Various grades of ABS have different ratios of A (acrylonitrile) : B (butadiene) : S (styrene). More B makes it tougher, while more S makes it easier to print.