Make It or Break It: Testing Plastics and Fill Patterns for the 3D Printer

Make It or Break It: Testing Plastics

and Fill Patterns for the 3D Printer

Henry Mason
Grade 8
Science Project

Abstract

In the last years, a lot of attention has been paid to the technology of the 3D printer since its availability for home and office use. The 3D printer allows for the making of objects by laying down plastic filament layer by layer. This project explores how different filaments and fill patterns affect the strength of a 3D printed object. For the experiments, I used objects made from the Solidoodle 2 Pro 3D printer. The two types of plastic filaments were ABS (acrylonitrile butadiene styrene), PLA organic filament (polylactic acid).

The following forces were tested to measure the strength of each plastic material:

  • shear – a test where the breaking point of the plastic is tested after applying a force across it

  • torque/torsion – a test that determines how the plastic behaves when it is twisted

  • tension – a test where the plastic is pulled in opposite directions

  • flexure – a test that measures the flexibility of an object

  • compression – a test that determines the behavior of an object under increasing weight

Wooden instruments were made to perform the different tests. Rectangular prisms made of the different plastics and fill patterns were printed for the experiments. The fill patterns are linear, rectilinear and honeycomb.

Introduction

Because the 3D printer is a new device for home users, it is becoming very popular. Most of the home printers are used for making prototypes and scale models. A lot can be found online about 3D printers, filaments and the things users make with them. There is a blog from Solidoodle, a maker of 3D printers that invites users to a World Makers Faire from their website. The Faire is an opportunity for users to show off the idfferent designs and products they can make with the Solidoodle 2 Pro printer (http://www.solidoodle.com/blog/) 2013.

People can make many different objects including tools and medical supplies. Engineers and architects use it for prototyping their ideas. It is a versatile technology according to Matt Petronzio (2013) who wrote the article “How 3D Printing Actually Works”. It will probably be a technology that people will want to use for a long time in the future because things can be made easily and inexpensively.

The 3D printer works by laying down layers of plastic filament and making patterns to create shapes. the form and design are made in computer programs with 3D design software. Then they are prepared and printed with prep and control programs like Repetier Host and Slic3r. This is called “additive manufacturing”. (Brewster 2013). The software takes the design and breaks it down to segments and pushes or extrudes heated filament through the printhead. The print takes shape on a surface called a print bed that is usually glass. Conductive metal like copper can be added with adhesive for leveling and conducting heat to the print bed.

The printer used in this project is a Solidoodle 2 Pro. It is a small printer that uses three types of plastic filaments. The filaments are ABS, PLA. ABS is acrylonitrile butadiene styrene. It is commonly used for making toys such as Legos and for making containers. It is often worked at higher temperatures than some other plastics (Brewster 2013). PLA is made from corn or sugar cane. It is popular because it is made of organic materials. PLA cannot be mixed with other plastics and it takes a long time to biodegrade even though it is organic (West 2013). It is still the choice of the environmental minded 3D printer users.

I created wooden materials testers to gain information about the strengths and the different behaviors of the plastics as created items. A summary of the durability of ABS and PLA can be found on a site called Protoparadigm whic is a blog about 3D printing and related topics. Here is an excerpt of the summary:

ABS

Extrudes at 195–205 degrees centigrade
Printbed must be heated
Prone to cracking
Flexible for the most part
Bonds well
Oil-based
Has a strong smell when heated

PLA

Extrudes at 180–190 degrees centigrade
Can use a heated printbed
Should cool while printing
Adheres to most surfaces
Brittle
Plant-based (more “green”)
(English, 2013)

I performed my tests on identically shaped prisms made from each of the plastics with the following fill patterns: honeycomb, linear, and rectilinear. I found I had to print nine at a time so that there were 300 objects altogether to be tested. This translates to almost 250 hours of print time, counting just successful prints and leaving out printer prep, cleaning, and troubleshooting. The testing instruments will test shear, torque, and tension. From these tests I am able to determine which type of plastic filament and which type of fill pattern is best for different uses

One part of my research involved investigating the different types of testing instruments and the physics involved in durability testing. From this information I was able to design my own instruments for the project. I thought at first I would need to use springs to be able to measure the force applied. After talking to William, a salesman at Orchard Supply Hardware, I got the idea to make a testing set out of wood with levers. The problem of gauge was solved by using a fish scale (like the one for weighing fish) to measure tension. It turned out to be easier than measuring the length of a spring to calculate force like I had thought originally. For compression I decided to take my plastic prisms to a local gym! The first compression instrument I designed was made of wood, but it required more strength than I was able to exert on the test objects. In my second attempt at compression I tried to test the plastic items at a health club by applying gym weights one at a time, but after reaching 168 kg, and there was still no break in the plastic. At first I abandoned this manner of testing, then I revisited the idea with shorter prisms using less plastic.

Hypothesis:

Objects printed with honeycomb fill pattern and PLA filament will resist greater forces than objects of different materials or fill patterns.

Independent variables: The filament and fill patterns.

Dependent variables: The force required to break the object.

Controlled variables: The shape of the object (rectangular prism)

Manipulated variable: The material structure and the force applied.

The results are measured in kilograms.

Materials:

  • 1 5′ x 18” sheet of particle board

  • 12 nails

  • 5 nuts, 0.25”

  • 5 bolts, ¼” x 3”

  • ABS filament, 1.75mm diameter

  • PLA filament, 1.75mm diameter

  • Taulman nylon 618 filament, 1.75mm diameter

  • 5 eye screws, ¼”

  • 145 test objects (18 of each plastic-fill pattern combination)

  • 2 clamps

  • 4 3¾” long by ¾” (extending from corner) corner brackets

  • goggles or safety glasses

  • Solidoodle 2 Pro 3D printer

  • 1 roll of transparent adhesive tape

  • 1 fish scale

  • 1 exercise machine for squats

Method:

Over 300 rectangular prisms were printed of the two types of plastic (ABS and PLA). The fill patterns used were linear, rectilinear, and honeycomb. Wooden test instruments were made to perform the four different force tests. The force applied to test objects was measured in kilograms usin a fish scale. The tests were run three times for each type of object.

Detailed Procedure:

  • Print three sets of test objects with three different fill patterns: rectilinear, honeycomb, and linear, all with fairly thin outer shells from two different materials: ABS, PLA. All prins have layer heights of 3mm, fill densities of 20%, and in-fill on every two layers. ABS objects are printed at 205ºC on the first layer and at 198ºC on the rest of the layers, and with an initial bed temperature of 95ºC. PLA objects are printed at 195ºC on the first layer at 190ºC on the rest of the layers. The bed temperature is the same as with ABS. The nylon objects are printed at 210ºC on the first layer and 205ºC for the rest of the layers.

  • All test objects are rectangular prisms measuring 2cm x 2cm x 10cm except for the objects to be used in the Tension trials, which will have a flair of 15º starting 2cm from each end. Objects will be printed in sets of 3 of each material with each fill pattern and in two directions, resulting in six pieces of each material-fill combination for each trial.

Test Procedures:

Fl exure

  1. Mount wood stops and lever board on test platform.

  2. Clamp test platform securely to sturdy and stable bench.

  3. Insert first test object into wood stops. With a pencil, trace a line along the long edge of the test object opposite the lever board. Remove test object.

  4. Using a protractor, determine and mark an 18º angle, with the guide line traced in step #3 as 0º, and the point where the guide line touches the wood stops as the vertex of the angle.

  5. Replace first test object in wood stops and gently position one end of lever board against side of test object.

  6. Attach fish scales to end of lever board, opposite test object, using eye screw.

  7. Pull slowly and consistently on fish scales along path perpendicular to test object, away from test object, so that the opposite end of the lever board is pressed against the side of the test object, until the test object either breaks or bends as far as the 18º mark.

  8. Record the reading on the fish scales.

  9. Repeat steps #5 through #8 for each of the test objects (3 for each material with each fill pattern) for this set of trials.

T ension

  1. Mount wood stops, guides for directed compression block, and lever board on test platform.

  2. Clamp test platform securely to sturdy and stable bench.

  3. Insert first test object into wood stops. With a pencil, trace a line along the short edge of the test object opposite the wood stops. Remove test object.

  4. Using a ruler, determine and mark points 10% beyond of the distance from the base of the wood stops from the line traced at the end of the test object, and draw a guide line across those points, extending an few centimeters beyond each edge of where the test object was lying, so that the line will be visible when the test object is in position with its end cap.

  5. Replace first test object in wood stops and fit the end cap/holder over its flaired end.

  6. Attach fish scales to end end cap using eye screw.

  7. Pull slowly and consistently on fish scales along path in line with test object, away from the wood stops, so that a stretching force is applied to the test object, until the test object either breaks or is stretched to the 10% mark.

  8. Record the reading on the fish scales.

  9. Repeat steps #5 through #8 for each of the test objects for this set of trials.

I simplified and strengthened this test by using two screw-down steel clamps.

S hear

  1. Mount wood stops and guides for directed compression block and lever board on test platform.

  2. Place carriage and rail on guides.

  3. Clamp test platform securely to sturdy and stable bench.

  4. Insert first test objects into wood stops and carriage. Measure a couple of points at 10% of the width of the test object from the sides of the wood stops, and draw a line through the points, parallel to the wood stops.

  5. Replace first object in wood stops.

  6. Attach fish scales to end of lever board, opposite test object, using eye screw.

  7. Pull slowly and consistently on fish scale along path perpendicular to test object, away from test object, so that the opposite end of the lever board is pressed against the side of the railed carriage, until the test object either shears or compresses enough for carriage to hit the 10% line marked in step #4.

  8. Record the reading on the fish scales.

  9. Repeat steps #5 through #8 for each of the test objects for this set of trials.

The wooden test platform can’t handle the stresses of this test. I had to redo it with steel brackets and screws instead of wood blocks and nails.

T orsion

  1. Mount bases on test platform.

  2. With a protractor, mark a line where lever board would be rotated by 18º counter clockwise with the center of the hole for the test object as the center of the rotation.

  3. Insert first test object into base, and slide lever board onto test object.

  4. Attach fish scales to lever board using eye screw.

  5. Pull slowly and consistently on the fish scales, causing the test object to be twisted clockwise, until the test object either breaks or twists by 18º.

  6. Repeat steps #3 through #5 for each of the test object

Compression

      1. Place test object on weight.

      2. Slowly, lower weights one at a time onto test object until the object breaks.

      1. Repeat steps #1 through #2 for each of the test objects.

Observations

I recorded my observations of the stresses applied to each type of object in the tables below. All the values in the charts are in kilograms.

The mean values for each test show that objects printed with the honeycomb fill pattern are stronger for all of the tests performed. The linear fill pattern is almost as good in the tests that included it, and the rectilinear fill pattern is much weaker.

Results

The results below show the comparative strengths of the two plastics PLA and ABS and the three fill patterns. PLA was consistently stronger than ABS in all of my tests, and the honeycomb structure tended to be stronger, except in compression tests where the linear structure was stronger.

I had expected PLA to be stronger, because it is used in prosthetic bones, and it seems less brittle than ABS. I also expected the honeycomb structure to be stronger, because that pattern seems to provide a more regular, interlocked structure of support.

I believe that PLA was stronger, because each layer takes longer to harden as it cools, so the next layer bonds better to the previous one.

I had hoped that PLA would turn out to be the stronger, because of the fact that it biodegrades, even if it does it slowly, and so is more environmentally friendly.

PLA: Comparison of Strengths in Fill Patterns

v
alues are in kilograms

ABS: Comparison of Strengths in Fill Patterns

v
alues are in kilograms



Results of all tests per material,
in kilograms

Conclusion

This project examined the behavior of two different 3D printer plastics and three different fill patterns when subjected to force tests. The results show that for both plastics, the honeycomb pattern was able to withstand greater forces than the linear and rectilinear, except in compression, in which linear was stronger than honeycomb. The experiment also found that PLA filament consistently withstood greater forces than ABS. The prints made with PLA filament with the honeycomb fill pattern were stronger than prints made with other fill patterns, except for ABS with linear structure being slightly stronger in my flexure tests. This research also proved that durability of 3D printed objects is dependent on the strength of the fill pattern. My hypothesis was correct. The PLA filament printed with the honeycomb fill pattern was the strongest.

Future Work

My project could be basically useful to 3D printer users, but I think that a more comprehensive and fine-tuned study would provide valuable information. I hope to continue this study to include other filaments like Taulman nylon, which is another commonly used filament, and trimmer nylon (as in weed whackers). I would like to include the study of the behavior of filaments under other stresses like impact and fatigue. I would like to have access to materials testing equipment like that which is found in a testing facility. With access to professional testing instruments, I could test objects on a greater scale.

Bibliography

Brewster, Signe. (2013). “How Does a 3D Printer Work? The Science and Engineering Behind this Emerging Tecnology”. Retrieved, Sept. 19, 2013 from http://gigaom.com/2013/08/26/how-does-a-3d-printer-work-the-science-and-engineering-behind-this-emerging-technology.html

English, Alex. (2013). “What to do with a 3D printer”. Retrieved, Sept. 14, 2013, from http://www.photoparadigm.com

Johnson, Todd (2013). “What is a polymer: Discovering the basics of polymers”. Retrieved, Sept. 19, 2013, from http://composite.about.com/od/whats-a-composite/whats-a-polymer.htm

Meet us at the World Maker Faire (this weekend) blog from Solidoodle. Retrieved, Sept. 19, 2013, from http://www.solidoodle.com/blog

Petronzio, Matt. (2012). “How 3D Printing Actually Works”. Retrieved, Sept. 19, 2013, from http://masable.com/2013/3/28/3d-printing-explained

Royte, Elizabeth (2006). “Corn Plastic to the Rescue”. Smithsonian Magazine pp 1-4. Retrieved, Sept. 7, 2013, from http://www.smithsonianmag.com/science_nature/plastic.html

Soliform 3D Printing Community Forum. Retrieved, Sept.5, 2013, from http://solidoodle.com/

Testing Different Materials. World of Tests. Website. Retrieved Sept. 14, 2013, from http://www.worldoftest.com/

The Difference between ABS and PLA for 3d Printing. Retrieved Sept. 14, 2013, from http://www.protoparadigm.com/blog/2013/01/the-difference-between-abs-and-pla-for-3d-printing

The Physics of Plasticity. Website. Retrieved Sept. 18, 2013, from http://ceberkeley.edu/coby/plas/CH2.pdf

West, Larry (2013). “Pros and Cons of the Corn-based Plastic PLA” from about.com’s Environmental Issues. Retrieved Sept. 14, 2013, http://environment.about.com/od/greenlivingdesign/a/pla.htm

Acknowledgements

Thanks to

Dr. Dan Fernandez, professor of Physics and Environmental Science at California State University of the Monterey Bay, for the initial idea of studying 3d printed objects, materials, and fill patterns.

My Dad for the use of the Solidoodle 2 Pro, printing the test prisms and for helping build the testing instruments and for his assistance in conducting the experiments.

Dr. Li Liu for the use of the acupuncture needles for repairing the 3D printers.

Mr. William at Orchard Supply Hardware for his help in problem-solving.

Mr. Richard Herbert for the idea of using a fish scale to gauge the force applied during testing.