Re: 3D printing (Was: New early P&R steel.....)
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It's great to hear from a subject matter expert that actually works in this industry . Thank you for your excellent explanation.
For reference, here is a quote from both Projet 3600 and Projet 5500 specs:
Accuracy (typical) ±0.001-0.002 inch per inch (0.025-0.05 mm per 25.4 mm) of part dimension. Accuracy may vary depending on build parameters, part geometry and size, part orientation, and post-processing.
That means accuracy should be within approximately 0.1% to 0.2%
For reference, Shapeways specification for Fine Detail Plastic is way looser: ±0.3- 0.7 mm for every 100 mm
Would you please answer these questions?
1. Is part orientation a factor in process control?
2. I've had multiple copies of the same 205mm long model made in Smoothest Fine Detail Plastic vary in length -0.5mm to about -1.0mm, even from the same order. Yet, about 60% of the same part are the correct length. I've been stonewalled by Shapeways' Quality Control person , saying that the lengths are within specification. So the question to you is "Are these dimensional inconsistencies a limitation of the machine, or could Shapeways do something better?"
3. If I interpret the specs correctly, my 205mm long part should be within ±0.2mm to ±0.4mm of 205mm, or between 204.6mm and 205.4mm. A difference of 0.8mm would mean the parts might not fit another printed part or a part from another source. 0.8mm is almost 3 inches in HO scale. My question then is "How can such 3D parts be used to create masters or molds?" "How can 3D printed parts be used for low volume parts instead of injection molded parts?"
4. Finally, as you probably know, Formlabs is coming out with the Form 3L late next year. I didn't see any specification on accuracy for the Form3 on their web site. In your opinion, would a Low Force Stereolithography (LFS) machine like the Form3 give more accuracy?
Thank you for taking the time to answer these questions. My hope was to be able to create low volume kits for items I need and share these with others. However, I can't do that with large parts due to the accuracy limitations with large parts, such as a passenger car or bridge girder.
From: main@RealSTMFC.groups.io [mailto:main@RealSTMFC.groups.io] On Behalf Of Ryan Mendell
Sent: Saturday, December 21, 2019 12:26 PM
Subject: Re: [RealSTMFC] 3D printing (Was: New early P&R steel.....)
I would like to offer to shed some light on the Jet printing Process, as it seams there is a genuine interest by this group to further understand the process. At work I manage and run both a 3D Systems Projet 3600 and Projet 5500 printers. These are what are know as ‘Polyjet' or ‘Multijet' 3d printers and is what Shapeways uses for their Fine Detail processes. The 3600 has a build area of about 8" x 12” inches and the 5500 16” x 20”.
The print head on these printers has two rows of jets, one for the model or body material as Tom called it and another for the wax or support material. The print head on the Projet 5500 has 2400 jets across a width of 8”. This works out to 300DPI. To achieve higher resolution the print head shifts sideways by a pixel width and makes two passes for each layer to achieve 600DPI. For 750DPI it makes three passes for each layer and shifts both left and right of the first pass by 0.66 of a pixel width. I may have the math wrong for 750 DPI but I hope you get the idea.
After each layer is deposited at what ever DPI selected, the head has a spinning roller that pushes or forces the deposited resin down into the previous layer. Behind the roller is a knife blade that slices the resin layer to the choose layer thickness. The final step is the head has a UV light that turns on and cures the layer. The 5500 head is only half the width of the build plate and must make a shift half the build plate width to print the entire 16” width. The 3600 print head is the full width of the build plate.
Part print orientation is critical to get better printed parts. The head moves in the x axis. Thus if you want to orient your part along or across the print direction you need to pick which side of your part aligns with the X axis in your CAD file. I always design models as flat kits with the show side facing up on the build plate so no wax is used to support the critical faces of the part.
To answer an earlier question as to the rigidity of these machines. They are built like machine tools. They have heavy frames, use servo motors(not stepper motors) and linear guide way bearings just like the CNC mills we have at work also. The Projet 5500 weighs in at 3000lbs.
As far as process control. There really isn’t any. You load the part into the software, Orient it the way you want and press the print button. The only human involvement is the support removal. The wax is melted off in an oven, and then the last of it is removed in an ultrasonic cleaner. The big issue is warpage caused when the part is in the oven. I no longer remove wax for model parts in the oven. I remove it with a hobby knife and a dissolve the last of it with alcohol. Thus avoiding warpage. Unfortunately Shapways doesn’t offer manual removal of support material. If your part is not symmetrical, or has thin sections and thick sections there is a good chance it will warp in the support removal oven. You end up with bent parts or dimensional issues.
I hope this explains things a bit.
On Dec 21, 2019, at 1:25 AM, Tom Madden via Groups.Io <pullmanboss@...> wrote:
If these don't sound like very high resolution printers, remember that there are two jet nozzels per pixel - you can place either wax or body material at each location.