SteveCox3D 87
@geert_2 Thanks for contributing to the discussion. Indeed, DfAM is influenced by many factors, and what your intended use for the 3D printed part is. So this is quite a large subject and my original post is there to encourage debate and other people's perspectives and techniques for DfAM.
Many of the things that you mention I also do in my 3D printing work. One technique I use often is to split a print and make it in several parts which can be glued together rather than have to use support material. I do tend to be a little obsessed by quality and on a single extruder machine I would rather find ways of printing without support to get the best surface finish without extensive post-processing.
You also make a good point that the quality of the layer "weld lines" is very dependent on the printer settings and have a big influence on how the layers fuse together
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JohnInOttawa 104
This is a great read, thank you for putting it together.
Eliminating or bypassing the load paths that can track along a 'weld' joint feels to me like the holy grail of FDM printing. Technologies like MarkForged have made significant improvements, but only in one direction, AFAIK there is nothing yet that can provide this advantage in more than one plane short of a sintering/annealing process of some kind.
All that said, the print core concept seems to me to allow for the use of just about any technology in a print core bay. Right now we are using only FDM heads. Maybe one day we will see a laser reheat/sinter ability or continuous fibre cutting process incorporated into a 'print core'. That, to me, holds some of the greatest promise as design for additive manufacturing starts to point the way toward execution options.
Cheers
John
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geert_2 560
@SteveCox3D: thanks for the write-up. Yes indeed, it would be great if we could get a good list of design considerations for 3D-printing. This will be a great help for new designers. But also after a couple of years of experience, it is good to see things from different viewpoints. We always learn from the experiences of others.
Also, a lot depends on the purpose of the models: in my case I don't need ultimate strength. The functionality of the design and ease of printing are more important. So, for me design considerations usually go along this line:
- the model has to be functional, thus function determines the shape of the model (contrary to artwork),
- orientate it on the build plate so that it requires the least amount of post-processing,
- have a good flat underside for good adhesion to the build plate, thus the biggest flattest side is the bottom (no inverted prisms),
- the least amount of overhangs requiring support, because supports create ugly undersides and require post processing (I have two UM2 printers, single nozzle),
- in case of doubt about strength, oversize the model: I prefer crude "flintstone-like" models above models that fail. Thus some "flintstonisation" is not uncommon,
- in case of doubt about fit: provide enough tolerances in the model to ensure a good fit,
- avoid big roundings or chamfers at the bottom, since they tend to worsen the tendency for edges of 3D-prints to curl up (thus again: no inverted prisms),
- visual quality has to be good, but not perfect: I don't need the smoothness of injection moulded models, I can live with layer lines,
- the least possible amount of hollow areas where liquid can seep in (thus I print at 100% filled),
- if assembling and glueing is required in post-processing, design alignment features into the model so that fitting parts together is easy,
- no threads in the model: if screws are required for assembling, or for clamping parts, then the thread should be provided by a nut; and the nut should be sunken into the model in a hex opening, with some retention, so it does not fall out,
- if a models requires supports, design custom supports into the model, and take good care that they can easily be removed afterwards,
- edit: if the model needs to be injection moulded for mass production later on, or CNC-machines, incorporate all guidelines for these methods too in the design,
I guess these are the most important considerations for me, usually.
But the requirements may be very different for other people. People producing art or jewelry will require a much better surface finish than me. For them "no visible layer lines" will have a way higher priority. That is part of the beauty of 3D-printing, that it is so versatile.
@sander: I always print in 0.1mm layer height, except for occasional tryouts. The reason is that my typical models have slopes which look ugly when printed in 0.2mm. So I don't have much experience with 0.2mm.
When parts in PLA, PET and NGEN break, in my experience the fracture always starts at an inside corner, or an indent between layers, due to stress concentrations, like SteveCox showed in his pictures above. But after that, the fracture goes diagonally straight through everything. It does not follow layer-lines or sausage-lines at all. It breaks more or less like a solid injection moulded model would do. This is for PLA printed with 100% cooling fans, and PET and NGEN printed without cooling fans. I have no experience with other more difficult to print materials like ABS (which appears to separate along layer lines, in the photos on the forum).
added consideration about injection moulding
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Brulti 177
That was a very interesting read, thank you @SteveCox3D.
I would like to point out that more and more 3D software have add-ons or plug-ins that allow you to check your model before you export it in CURA or any other slicer. I'm learning to use Blender, and it has an official add-on for 3D printing that can check for overhangs and any default in the model, as well as ensure that it is manifold. While it is not perfect, especially when it tries to fix a model, it's still a great help and catches most of the very bad design faults that would make printing impossible.
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SteveCox3D 87
@Brulti That's a really good point and something I think we will see more of in the future. For instance in Fusion 360 there is a dedicated CAM environment where you can carry out your machining set-up, and in the longer term I expect to see a similar environment for 3D printing being added, maybe based upon Autodesk's Netfabb software.
It's important, as you say, to catch the manufacturing problems at the design stage when it's easiest to do something about them.
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