Filament Feeder for Additive Manufacturing Research System

Micah Miller12/12/16

Advisor: Ralph Stirling

AbstractAdditive manufacturing of plastics, commonly known as 3D-Printing, is the process of

extruding thin strands of melted plastic filament through a nozzle onto a workspace in order to create three dimensional structures and models. Currently Walla Walla University owns a large scale 3D-Printer intended for research purposes. This was retrofitted from a 2D Filament Printer by Kyle Bahnsen and Katie Storm in a previous project.

One of the key components of a 3D-Printer is the filament feeding device that actually pulls the plastic filament of a spool and pushes the plastic through a heated nozzle in order to be extruded onto the workspace. Previously the first iteration of the device used for this process did not perform optimally during operation. Therefore, a new design for this apparatus is necessary for future use of the printer.

A detailed outline of the design process, component list, and operation manual is included. The operations and procedures for this device must be understood before use of the device. This will allow more efficient use of this device in order to proceed with further research.

Table of Contents

FILAMENT FEEDER FOR ADDITIVE MANUFACTURING RESEARCH SYSTEM.....................1

ABSTRACT............................................................................................................................................... 2

TABLE OF FIGURES............................................................................................................................... 6

LIST OF TABLES..................................................................................................................................... 7

ACKNOWLEDGEMENTS....................................................................................................................... 8

1 INTRODUCTION AND OBJECTIVES.........................................................................................9

1.1 Introduction............................................................................................................................................... 9

1.2 Project Objectives and Requirements......................................................................................................... 9

2 RESEARCH AND DESIGN.......................................................................................................... 11

2.1 Physical Requirements............................................................................................................................. 11

2.1.1 Groove Mount.........................................................................................................................................11

2.1.2 Load Cells................................................................................................................................................12

2.1.3 Guide Path..............................................................................................................................................12

2.1.4 Drive System...........................................................................................................................................12

2.1.5 Spool Mount...........................................................................................................................................13

2.2 Original Design......................................................................................................................................... 13

2.2.1 Overview.................................................................................................................................................13

2.2.2 Issues......................................................................................................................................................14

2.3 Research.................................................................................................................................................. 17

2.3.1 Filament Material Properties..................................................................................................................17

2.3.2 Drive Mechanisms...................................................................................................................................17

2.3.3 Load Cells................................................................................................................................................18

2.3.4 Stepper Motor........................................................................................................................................18

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2.4 Initial Design Concepts............................................................................................................................. 18

2.4.1 First Concept...........................................................................................................................................18

2.4.2 Second Concept......................................................................................................................................19

2.4.3 Third Concept..........................................................................................................................................19

2.5 New Design.............................................................................................................................................. 20

2.5.1 Initial Concept.........................................................................................................................................20

2.5.2 Intermediate Design................................................................................................................................20

2.5.3 Final Design.............................................................................................................................................21

2.6 Analysis................................................................................................................................................... 22

2.6.1 Free Body................................................................................................................................................22

2.6.2 Component Comparison.........................................................................................................................22

3 MANUFACTURING AND ASSEMBLY...................................................................................... 24

3.1 Components to Manufacture................................................................................................................... 24

3.2 Manufacturing Process............................................................................................................................. 24

3.3 Fasteners and Bearings............................................................................................................................. 24

3.4 Instrumentation....................................................................................................................................... 25

3.5 Assembly................................................................................................................................................. 25

4 OPERATIONS MANUEL............................................................................................................. 26

4.1 Mounting Device...................................................................................................................................... 26

4.2 Inserting Filament.................................................................................................................................... 26

4.3 Replacing Components............................................................................................................................. 27

5 CONCLUSION............................................................................................................................... 28

5.1 Future Work............................................................................................................................................. 28

5.1.1 Complete Assembly.................................................................................................................................28

5.1.2 Spool Mount...........................................................................................................................................28

5.1.3 Extensive Testing.....................................................................................................................................28

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5.2 Final Observations and Assessments........................................................................................................ 28

REFERENCES........................................................................................................................................ 29

APPENDIX A – ABS MATERIAL DATA SHEET.............................................................................30

APPENDIX B – LOAD CELL SPECIFICATIONS..............................................................................31

APPENDIX C - STEPPER MOTOR SPECIFICATIONS.................................................................32

APPENDIX D – COMPONENT DRAWINGS AND PARTS............................................................33

D-1 – Back Housing............................................................................................................................................ 33

D-2 – Bottom Housing....................................................................................................................................... 34

D-3 – Top Housing............................................................................................................................................. 35

D-4 – Base......................................................................................................................................................... 35

D-5 – Lever........................................................................................................................................................ 36

D-6 Filament Guide........................................................................................................................................... 37

D-7 – Groove Mount Clamp............................................................................................................................... 38

D-8 – Support Rod............................................................................................................................................. 39

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Table of Figures

Figure 1. Filament Feeder Diagram, Ref. 1

Figure 2. Research Printer with Original Filament Feeder

Figure 3. Groove Mount Diagram, Ref. 2

Figure 4: Hot Shot Heating Nozzle

Figure 5. Sample Load Cell, Ref. 3

Figure 6. Wheatstone Bridge Diagram

Figure 7. Sample Stepper Motor, Ref. 4

Figure 8. Original Filament Feeder

Figure 9. Filament Guide/Groove Mount Holder

Figure 10. Load Cell Screws (Original)

Figure 11. Open Housing (Original)

Figure 12. Filament Guide/Groove Mount Holder (Original)

Figure 13: Groove Mount Holder without Nozzle (Original)

Figure 14: Groove Mount Holder with Nozzle (Original)

Figure 15. Lever Arm Mechanism

Figure 16. Initial Teeth Concept

Figure 17. Initial Spring Concept

Figure 18. Gear Rod Bearing Concept

Figure 19. Screw Bearing Concept

Figure 20. Intermediate Design

Figure 21. Intermediate Design (Exploded View)

Figure 22. Final Design

Figure 23. Mounting Rod

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List of Tables

Table 1. Component Comparison

Table 2. Manufacturing Processes

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Acknowledgements

Kyle Bahnsen and Katie Storm, for their previous work on the printer and contribution to figuring out some of the issues with the old design.

Don Riley, for his feedback in helping me refine my design.

Ralph Stirling, for providing feedback and inputs when required as well as providing all the materials and recourses required to design and create all the components in this project.

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1 Introduction and Objectives

1.1 IntroductionThe purpose of this project is to improve and redesign the device used to extrude plastic onto the workspace of Walla Walla University’s research 3D-Printrer.This project was introduced to Micah Miller in the winter if 2016 by Ralph Sterling. This project is directly related to the work that Kyle Bahnsen and Katie Storm did previously on this research printer for their senior project in 2014. However, during the process of working on their project, they discovered that the extruding mechanism, or filament feeder, did not perform very well. But redesigning this portion of the overall printer assembly was outside the scope of their project. Therefore, this task was to become this particular project. The main components of the filament feeder are the filament itself, the drive mechanism, the extruder, and the guide that directs the filament into the heated end of the extruder. Through this assembly melted filament is extruded from the end of the nozzle in order to create an object.

Figure 1. Filament Feeder Diagram, Ref. 1

1.2 Project Objectives and RequirementsThe objective of this project is to redesign the filament feeder in order to allow more

consistent extrusion from the nozzle, as well as allow for instrumentation to be implemented for

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research and testing purposes. Another requirement was for every part in the assembly to be easily accessible both during assembly and operation. The instrumentation must measure force required to extrude filament through nozzle with resolution of 0.1 N or better, with a man of 25 N. There is also a filament nominal diameter of 1.75 mm, which the device must be able to account for.

The main goals of this project consists of creating consistent performance as well as simple operation and easy access of necessary components.

Figure 2. Research Printer with Original Filament Feeder

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2 Research and Design

2.1 Physical Requirements

2.1.1 Groove Mount

The groove mount is the section of the heating nozzle that allows for the nozzle to be mounted to the filament feeder assembly, Figure 3. This mount has standardized dimensions, regardless of the model of the heating nozzle. Therefor the clamp used to hold the nozzle must have a close tolerance to this specific size. A sample heating nozzle groove mount is shown below, Figure 4.

Figure 3. Groove Mount Diagram, Ref. 2

Figure 4: Hot Shot Heating Nozzle12

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2.1.2 Load Cells

In order for a force to be measured on the filament, we need a specific type of instrumentation. In this specific application, load cells were chosen in order to perform this task. A load cell is a device that utilizes strain gauges on a long piece of metal with a specific section cut from the center of the piece, Figure 5. In order to determine the force acting on the device, deflection must occur on one end of the load cell.

Figure 5. Sample Load Cell, Ref. 3 Figure 6. Wheatstone Bridge Diagram, Ref 4

2.1.3 Guide Path

The guide path is the section between the drive mechanism and the heating nozzle that allows the filament to be forced into the heating nozzle without buckling and bending off in a random direction. This must also must take into consideration the mounting of the load cells as well.

2.1.4 Drive System

The drive system is the method by which the filament will be forced into the heating nozzle. This is typically done with some type of stepper motor of sorts that has a wheel or gear that pushes the filament along a specific path. A stepper motor is a brushless, synchronous electric motor that converts digital pulses into mechanical shaft rotations, Figure 7. Steppers motors can come in a variety of sizes and torques, making them ideal for this application.

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Figure 7. Sample Stepper Motor, Ref. 5

2.1.5 Spool Mount

The method by which the spool of filament is also important as well. This is due to the fact that if the filament is not easily accessible by the filament feeder assembly then the drive mechanism might not be able to drive the filament very well into the heating nozzle. Therefore, it is important that the spool is mounted properly inside the research printer assembly.

2.2 Original Design

2.2.1 Overview

The original design for the filament feeder, Figure 8, consisted of two stepper motors with drive wheels which were mounted to rotating arms inside a main housing. These two arms were pressed together via a screw on either side of a central load cell system in order to determine how hard the filament was being pinched between the two drive wheels. Below the two drive wheels was the guide system, Figure 9, which was mounted on a pin to the far side of the housing, this guide rested on a linear force gauge. The guide piece also had a slot to allow the groove mount to slide in from the side. The idea behind this was to have there be only one component in order to guide the filament down to the heating nozzle, as well as allow the force to be measured on the force gauge from this guide piece.

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Figure 8. Original Filament Feeder

Figure 9. Filament Guide/Groove Mount Holder

2.2.2 Issues

There were a number of issues regarding the original design of the filament feeder. Hence why a new design was recommended.

The first was that in order to pinch the filament between the two drive wheels, manual adjustments were required each time that the filament had to be changed or adjusted. The two screws that pressed against the top load cell didn’t always give consistent results. See Figure 10 and Figure 11.

Having two drive wheels seemed to add unnecessary complexity. The same function could be performed with a single motor pressed against a bearing or something similar.

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A major issue was the guide for the filament that was right underneath the drive wheels, Figure 12. The original design needed to be greatly modified due to a couple critical flaws. The first being that the groove that was initially meant to guide the filament down its hole did not have enough clearance and would grind against the drive wheels. So a section needed to be gouged out in order to create room for the drive wheels. Also the drill to create the hole wasn’t long enough, so the other side was drilled with a larger bit and piece of Teflon with a hole the same size as the smaller hole in order to have a consistent diameter all the way through the part.

The force gauge that was used to measure the force that the filament was placing on the heating nozzle was not as accurate as would be preferred.

The final issue was the fact the heating nozzle became very difficult to remove from the groove mount slot once the filament was melted inside the heating nozzle, Figure 13 and Figure 14. Because the nozzle mount need to be slide to the side, the filament needed to be sheared in order to remove the nozzle. This proved to be very difficult without any clearance between the groove mount and the groove mount holder.

Figure 10. Load Cell Screws (Original)

Figure 11. Open Housing (Original)

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Figure 12. Filament Guide/Groove Mount Holder (Original)

Figure 13: Groove Mount Holder without Nozzle (Original)

Figure 14: Groove Mount Holder with Nozzle (Original)

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2.3 Research

2.3.1 Filament Material Properties

An important aspect of this project is determining the material properties of the plastic we are using for the filament. In this application we will typically be using ABS (acrylonitrile-butadiene-styrene) or PLA (poly lactic acid) plastic. It is a low cost/ easy to machine and fabricate. The reason this is so important is because in a filament feeder, the coefficient of friction and the modulus of elasticity are required in order to determined how to optimize the drive mechanism for the filament. Refer to Appendix A for material data sheet.

2.3.2 Drive Mechanisms

There are a lot of different methods that people have found for driving their filament into a heating nozzle. The most common method however uses a single stepper motor with either a drive wheel or a gear in order to drive the filament. The motor is typically mounted rigidly to a housing while a bearing of sorts is pressed against the motor wheal via a lever arm and spring, Figure 15. With this method, the bearing will be constantly applying force to the filament until the user manually presses on the lever to counteract the spring force and release the bearing. This allows the user to replace filament with easy without having to worry about manually adjusting the bearing against the filament each time the filament needs to be changed.

Figure 15. Lever Arm Mechanism

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2.3.3 Load Cells

One of the main objectives of this project is to measure the force of the filament on the nozzle. To accomplish this, the chosen method was to use load cells which utilize a series of strain gauges in order to accurately measure force via deflection of the load beam. Dr. Stirling already possessed a large variety of strain gauges and after analyzing the specs of a few of these load cell, a cells that meets the 25 N requirement was found, Appendix B.

2.3.4 Stepper Motor

To save time and resources, the same stepper motor used in the old design will be used along with initially machined drive wheel attached to the shaft of the motor. This particular motor provides a maximum torque of 1.75 N·m.

2.4 Initial Design Concepts

2.4.1 First Concept

The initial designs involved modifying the original designs in order to allow for more consistent results. One such idea involved keeping both motors and using two linear gear rods and a circular gear in order to push both motors together at the same time, Figure 16. The other involved using springs instead to push the two motors together, Figure 17.

Figure 16. Initial Teeth Concept

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Figure 17. Initial Spring Concept

2.4.2 Second Concept

The second concept involved using a linear gear rod again. But this time the purpose was to press a bearing against a single motor to drive the filament, Figure 18.

Figure 18. Gear Rod Bearing Concept

2.4.3 Third Concept

The third concept was similar to that of the second. But instead of using a gear rod, a lead screw is used in order to push the bearing against the drive wheel in order to pinch the filament, Figure 19.

Figure 19. Screw Bearing Concept

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2.5 New Design

2.5.1 Initial Concept

After analyzing initial design concepts and researching a variety of methodologies for the main drive mechanism, the lever arm/spring mechanism was chosen, Figure 17. Part of this was influenced by the fact that many of the smaller 3D Printers used by The School of Engineering utilized this method. Therefore, it was thought best to utilize this method for this project as well. The rest of the filament feeder assembly is based around this mechanism and has been designed to work in direct correlation with the described mechanism above.

2.5.2 Intermediate Design

The intermediate stage of the design process, a design was created in Creo of the drive mechanism, Figure 20. This part of the design used a cover within the lever arm in order to keep the bearing in place. The base that the lever arm is attached to provides a space for motor to be mounted to, as well as an initial guide section for the filament and a boss for the spring that is between the base and the lever arm. This provided the force that presses the bearing against the drive wheel. At this stage of the design process, the analysis for the lever arm and forces on the filament had not yet been completed.

Figure 20. Intermediate Design

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Figure 21. Intermediate Design (Exploded View)

2.5.3 Final Design

For the final design, there were a large number of changes that needed to be made. This was due to the fact that the manufacturability of the individual parts was quite low. It is best to reduce the number of parts that require tight tolerances to a minimum. So the lever arm was redesign to utilize just a shoulder screw to keep the bearing in place. Also, after completing the analysis of both the sum of forces and moments, it was determined that the distance between the point of rotation and the bearing should be shortened as much as possible to allow more force through the bearing with less for via the spring. This was done in order to allow the lever arm to release the filament from between the bearing and drive wheel with ease. Beneath the initial guide of the base was an extra guide for the filament, which was meant not only to act as an extension of the initial filament guide, but to allow the heating nozzle to be mounted to the assembly via two clamps. The purpose of this is to allow the heating nozzle to be screwed into the assembly directly into the assembly instead of having to be slid into place and sheared off like the original design. The guide part was also designed to be mounted to two load cells which are to be mounted to the overall housing of the filament feeder. This housing was designed around the internal components and is designed to be open and easy to access all component of the assembly during operation, Figure 22. All STEP files for the assembly are located on the CD included in this report. Reference Appendix D.

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Figure 22. Final Design

2.6 Analysis

2.6.1 Free Body

All the analysis for the forces acting upon the filament and the sum of the moments for the lever arm are given in Appendix C. The sum of the forces on the filament is important because it will help determine the force that the spring needs to be in order to force the bearing against the filament to prevent slipping as the filament is being driven down into the heating nozzle. There are a number of forces acting on the filament at the point between the two wheels. This includes tension and compression as the filament is being pulled off the spool and the compressive force acting at this point from the heating nozzle. There are also frictional forces acting from the bearing and the torque applied at that point creating a net force downward toward the heating nozzle. Also, a sum of the moments was required in order to optimize the members of the lever arm to allow the most amount of force on the bearing, with the least amount of spring for to allow for easy release by the user.

2.6.2 Component Comparison

There is a total of 63 components in the old design assembly and the new design has 42 components used in its assembly. There is a larger variation of components within the new design but it only requires about 2/3 of the parts to create the final design for the filament feeder.

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Old Design New Design4 Washers 1 Washer20 Small Hex Bolts 2 Clamps8 Bearings 2 Bearings1 Double Load Cell 1 Lever Arm1 Top Housing Plate 1 Top Hosuing Plate2 Side Plates 2 Support Rods1 Bottom Plate 1 Bottom Housing Plate1 Force Gauge 2 Load Cells1 Grooved Mount 1 Base2 Axis Rods 1 M6 Pin9 Medium Hex Bots 7 M6 Button Bolt2 Motors 1 Motor2 Threaded Rod (Top) 1 Shoulder Screw1 Threaded Rod (Housing) 1 Back Housing4 Nuts (Top) 4 M4 Button Bolt2 Nuts (Housing) 10 M3 Button Bolt2 Motor Wheels 1 Motor Wheel

1 Filament Guide1 Bearing Ring1 Spring

Total 63 Total 42

Components List

Table 1. Component Comparison

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3 Manufacturing and Assembly

3.1 Components to ManufactureThere are a wide range of parts that are used in the entire assembly. Twelve of these parts must be manufactured. A complete list of all the manufactured parts and their specifications can be found in Appendix E.

3.2 Manufacturing ProcessVirtually all of the parts required to be created were manufactured via CNC (Computer Numerical Control) milling and turning machines. Two parts were created in a standard lathe due to their simplicity. Table 2 shows a list of all the manufacturing processes for each part in the assembly.

CNC Mill CNC Lathe Standard Lathe Drill Press TappingBase XLever XBack Housing X X XTop Housing X X XBottom Housing X X XSupport Rod X XBearing Ring XFilament Guide X X XClamp X X XDrive Wheel X

Table 2. Manufacturing Processes

3.3 Fasteners and BearingsThere are a wide variety of fasteners that were needed in order to assemble all the manufactured parts. A complete list of all these fasteners can be found in Appendix F. There are also two shielded bearings that were used in this assembly. One bearing being used to clamp down the filament as it is being driven downward. The other bearing is used in order to allow the lever arm to freely rotate around a pin connection to the base. These bearings can also be found in Appendix F.

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3.4 InstrumentationThere are only two types of instrumentation that are used in the construction of the filament feeder. The two load cell mentioned earlier that are referenced in Appendix B. These are used also as a support for the guide system, clamps, and heating nozzle. The other instrumentation is the stepper motor that is used to drive the filament.

3.5 AssemblyThe finally assembly of all the parts, included drilling and tapping some of the components manually. This is due to the fact that it would be too tedious to change the drills out in the CNC mill for each operation. Instead, some of the simpler parts, such as the housing components, were spot drilled in the CNC so they could either be drilled by either the end mill or a drill press. All the necessary components were then tapped by hand. After this task was completed, the entire assembly could be assembly with the necessary fasteners, bears, and instrumentation.

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4 Operations Manuel

4.1 Mounting DeviceThe filament feeder assembly is mounted to the hanging rod in the center of the research printer, as shown in Figure 23. The rod has a base section with two screws that are designed to be attached to the two open holes in the top of the filament assembly.

Figure 23. Mounting Rod

4.2 Inserting FilamentIn order to insert the filament into the feeder, the filament must be fed through the guide tub until it is directly above the feeder. With the heating nozzle detached, pull the filament down through the large open hole at the top of the feeder housing. Then press down on the lever and feed the filament through the hole in the lever and down through the hole below the bearing and the drive wheel. Continue to feed the filament through the guide hole until it can be seen at the bottom of the assembly. Put enough filament through to allow the filament to be inserted into the top opening of the heating nozzle. Make sure that the two clamps meant for holding the nozzle are placed into the groove mount. After the filament is firmly inserted into the nozzle, pull on the lever again and press the nozzle up against the bottom of the feeder guide hole until the two clamps line up with their screw holes. Insert screws into each clamp and tighten down until the two clamps are firmly in place. Make sure when releasing the lever, that the filament is pinched between the drive wheel and the bearing.

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4.3 Replacing ComponentsSince the filament feeder was designed to be open from the front and sides for easy accessibility, replacing components is a simple matter. Simply loosen all fasteners that fold a particular component to the housing and remove the desired component from the assembly. Replace the necessary component and then make sure to re attach all necessary fasteners in order to make sure the device operates properly.

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5 Conclusion

5.1 Future Work

5.1.1 Complete Assembly

There is still some work that needs to be done in the assembly process for feeder. A few more specific screws need to be obtain in order to assemble the housing properly. Due to the fact that a drill bit was broken into the guide hole of the filament drive base, a larger who was created in order to remove the pieces. This hole will need to be inserted with Teflon and a hole created to about 2 mm in diameter that lines up with both the drive wheel and the mounting component at the bottom of the assembly.

5.1.2 Spool Mount

There also need to be an updated spoon mount for the research printer that reduces the amount of force required to pull the filament off the spool. This will reduce the amount of tension is in the filament and reduce the possibility of slipping between the drive wheel and filament during operation.

5.1.3 Extensive Testing

The device needs to be thoroughly tested in order to make sure it always perform adequately during operation. This also needs to be done in order to determine if the device works for the 15 N load requirement in the objectives for this project.

5.2 Final Observations and AssessmentsDue to the fact that the assembly is not quite complete yet, it is hard to make an accurate conclusion on the device. Most of the components were created without any issues and minimal work was required in order to get most of the components to assemble together. Further assembly and testing must be done in order to future out if any future improvements need to be made or if an entirely new design is necessary. This new design seems more suited to the required task than the previous design but this still requires validation.

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References

Ref 1: 3D Printing for Beginners. 2016. Illustration 1. Available at: http://3dprintingforbeginners.com/3d-printing-technology/

Ref 2: 2016. Nozzle Holder. Available at: http://reprap.org/wiki/File:Jhn_nozzle_holder_v5.jpg

Ref 3: Al-Mtlaq, Sarah. 2016. One of many kinds of load cells. Available at: https://learn.sparkfun.com/tutorials/getting-started-with-load-cells

Ref 4: All About Circuits. 2016. Quarter-Bridge Strain Gauge. Available at: http://www.allaboutcircuits.com/textbook/direct-current/chpt-9/strain-gauges/

Ref 5: Amazon. 2016. Stepper Motor. Available at: https://www.amazon.com/Stepper-Motor-178-5oz-1-26Nm-Stepping/dp/B00PNEPF5I

Ref 6: Tridimake. (2013, April 12). Rollerstruder: a filament feeder / driver / extruder. Retrieved from http://www.tridimake.com/2013/04/rollerstruder-filament-feeder-driver.html

Ref 7: Heywood, Mark. (2013, May 30). Airtripper Extruder Filament Force Sensor - Introduction. Retrieved from http://airtripper.com/1338/airtripper-extruder-filament-force-sensor-introduction/

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Appendix A – ABS Material Data Sheet

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Appendix B – Load Cell Specifications

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Appendix C - Stepper Motor Specifications

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Appendix D – Component Drawings and Parts

D-1 – Back Housing

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D-2 – Bottom Housing

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D-3 – Top Housing

D-4 – Base

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D-5 – Lever

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D-6 Filament Guide

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D-7 – Groove Mount Clamp

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D-8 – Support Rod

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