Week 05: 3D Printing and Scanning
3D printing
3D printing is a type of additive manufacturing method, meaning objects are manufactured by adding material layers. In a few weeks we will be covering CNC machining, a subtractive method that manufactures an object by cutting into an already-existing material. 3D printing allows complex shapes to be created, as well as reducing the amount of material waste generated from the manufacturing process. There are different types of 3D printer technologies, but for the purpose of a Fab Lab (non-industrial level material quality needed, small batch production), we will be using FDM (Fusing Deposition Modeling).
A FDM 3D printer uses plastic filament from ABS, PLA, nylon and rubber. Extruding the plastic filament through a nozzle, the material arrives on the heated bed. The nozzle moves in X and Y axis. When one layer finishes printing, the nozzle continues to print the next material layer, building up the material in Z direction to create the object.
Group Assignment
Before doing the group assignment, Saverio gave us a demo on using the Ultimaker 3.0 printer we have at Fab Lab O. First, we changed the previous plastic filament. The durability of the filament varies depending on the environment of the place. In Shanghai, plastic filament usually lasts for six months, which is something to be mindful of when opening a new filament. Here is the procedure for changing the filament:
Then, we inserted the USB drive with the .gcode file we exported from Ultimaker Cura, a software used to convert a .stl model file into a layered file with printer setting for 3D printing.
From the demo, we found out the object shrinks slightly. The first layer of the design printed in its original dimension, but as the layers built up, the dimension of the design was slightly reduced. We realized there may be an issue with either the Ultimaker 3.0 printer or the plastic filament.
For our group assignment, we used a printer test file provided by Saverio. The file includes a range of tests, including tolerance, bridging, overhanging and accuracy.
To get the .stl file ready for printing, we imported it into Ultimaker Cura.
Layer height affects the print resolution, details and surface smoothness. 0.2mm will be the most commonly used setting for printing at the Fab Lab.
Printing temperature varies depending on the material. Usually filament comes with a temperature range. The plastic filament currently in the printer can be used between 205-225 degree celsius. In the demo, we used 205, which caused material shrinkage. This time, we used 215 to test whether temperature affects shrinkage.
The print speed of the Ultimaker 3.0 goes up to 150mm/s, since there are significant amount of tiny details on the test, we kept the speed at 100m/s.
Other important settings that we didn’t change, but will become useful in the future:
Wall thickness must be multiple of the size of the nozzle (for example: if the plastic filament thickness is 0.4mm, then the wall thickness must be 0.4, 0.8, 1.2 and so on), otherwise there will be an empty gap in between the print that affects the accuracy of the other layers.
Support/bridge needs to be generated when the design has an overhang above 45 degree. It is used to prevent printing in the air.
Plate adhesion can be simply done putting a layer of glue on the print bed before printing, or printing a few layers below the design. It is recommended to keep the plate adhesion on skirt, which allows some material to be extruded before printing the model
Once we got the settings ready, we clicked on Prepare to convert the design into a layered file. Then, we saved the file in .gcode format onto a USB drive and inserted it into the Ultimaker 3.0 for printing.
Before printing, we removed the print bed from the printer and clean its surface with a blade to remove the plastic filament and glue from the previous print (the printing bed can be also cleaned with a wet sponge). After putting the print bed back into the printer, we lightly put a layer of paper glue, which support the first printed material layer.
Once the file was loaded, the printer began to print.
Printing took about 1 hour and 40 minutes.
After printing, we removed the print bed from the printed and gently went through fours sides of the object from its bottom with a blade.
Then we evaluated the print quality by referring back to the original model. Here are some notes from our evaluation:
- Diameter of the small circle:
- Printed: 8/3.5; Model: 8/4
- Diameter of the big circle
- Printed: 14.1/9.8; Model: 14/10
- Width and length of the model:
- Printed: 50.6 x 50.8; Model: 50 x 50
- Overhang:
- Short: residue appeared at 45, severe at 60-75; Long: residue appeared at 60, severe at 70-80
- Bridgetest:
- Traces of shrinkages are found in the middle of each bridge
- Tip of the pyramids:
- Not pointy
- Tolerance test:
- Only 0.4, 0.45, 0.5 lines came out; the result of the test reflects the fact that the thickness of the plastic filament we used was 0.4
We concluded that the printer experienced less shrinkage than using it at 205 degree during the demo. However, at 215 degree, it experience some inaccuracy when building up structural layers (bridges are printed in slight zig zag shape) and difficulties in printing pointy tips. The printer began to experience issues with overhang at 45 degree angles, which becomes severe at 60-80 degree angles.
Individual Assignment
In my visual art practice, I have been wanting to create absurd objects that mimics a well-known functional object, such as utilitarian objects in domestic spaces. For this assignment, I want to create a cloth/tower hanger with a relief of my own head on the base of the hanger, and an arm coming out of my mouth as the hanger.
Modeling
Since I already have a 3D scanned model of my head , I created the base of a hanger in Fusion 360based on the dimension of an pre-existing hanger I found on Taobao.
Then, I imported the .stl file into Meshmixer, imported the 3d scanned model of my head and added an arm into my mouth. Then, combine all the layers and export the model in .obj format for processing it in Ultimaker Cura.
(See next section for more details on 3D scanning and Meshmixer)
Creating Slices
Since there are many details on the face and the arm, I changed the layer height to 0.1mm for a finer surface quality. I also reduced the print speed to 80mm/s. Then I prepared the model and saved it in .gcode format for printing.
Printing
I like the appearance of the final outcome.
The form of the hanger mimics a functional object. I read the arm and the face when I look into the object from close.
I do want to make the hanger more rigid. The part for hanging is the thinest part of the arm, which cannot bear much load. To redesign the hanger, I would slightly expand the arm to merge it with the chine of my face. I also want the facial features (especially around the eyes) to stand out more and reads more directly as a human face.
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3D scanning
3D scanning technologies turn atoms into bits. There are many types of scanning technologies available on computer or on smart phones. The one that is used at Fab Lab O is an infrared depth map scanner.
Scanning
There are two ways to acquire the bits of an object, either the scanner remains stationary (mount it on a tripod when scanning a person) when the object rotates, or the object remains stationary when the scanner moves. Direct sunlight needs to be avoided, since it interferes with infrared light.
The camera we use for scanning at Fab Lab O is Kinect (Microsoft Xbox). Once the device is connected to the computer, open Skanect, a free 3D scanning software (pro version comes with more high quality scan is also available).
For the assignment, I scanned my upper body. Follow the instruction in the software to begin scanning. I sat on a 360 degree rotating chair to move my body while scanning. Make sure the part of your body in the camera stays as still as possible and try to move by slowing tapping your toes against the ground.
Exporting model and prepare mesh for 3D printing
The scan quality was good. It captured my face and the wrinkles on my clothes really well. There are parts such as the chair and fragments of the room that I want to edit away. Under Reconstruct/Remove Parts, these parts can be removed automatically.
Then I saved the file in .obj format under Share, and opened it in Meshmixer, an Autodesk software I used to edit and sculpt on my model.
There are several areas in the model that were hollow, since these were the blind spots of the camera. This can be fixed under Edit/Make Solid. With Edit/Transform, the size and the position of the model. With Edit/Plane Cut, the model can be cropped from different angles. Similar to clay sculpting, a range of tools are available under Sculpt for changing the form of the model.
My favorite function is Meshmix. There are a range of models in the model library such as heads, ears, hands, letters, etc. By combining it with my model, I can create hybrids such as giving my model donkey ears or adding another hand onto my model. I used a palm from the Meshmix library and placed a part of my hand in the middle of the palm.
Before exporting the file, make sure to select all the layers and click on Edit/Combine.
Files from this week
Base of the hanger made in Fusion 360
Hanger model made in Meshmixer
Head on Palm made in Meshmixer