Integrating Project: Thermoplastic Extruder

DRAFT

CCL-BY-SA

This project is intended for use with the following courses:

This site is the common source for documentation related to this project.  All classes will share this information.

Journal

Engineering Drawings and Photos

Proposal

Scope

The documentation contained herein relates to the design and development of a single working prototype of an extrusion machine.  Scope of assigned work will extend beyond this narrower focus toward the broader scope of commercially producing a machine of the final design of the prototype.  While this documentation is “open source” and freely available on the internet, it is for educational purposes only, and is provided as-is and without warranty. See Terms of Use.

Introduction

One of the major barriers to getting students in involved with 3D printing is the cost associated with the printing material.  The goal of this project is to design, build, and operate a thermoplastic extrusion system that will supply students at the University of Memphis with an extremely low cost supply of printing material.  To leverage this goal, it is proposed that the extruder project should become the first of a series of projects that will lead to a self-perpetuating, continuously improving series of projects related to 3D printing and additive manufacturing.

3D printing (or “additive manufacturing”) is an exciting emerging technology that has become widely recognized in both technical and popular culture.  As this technology increases in popularity, the cost of owning a 3D printer has been reduced to under $1000.   In recent years an abundance of information has been widely distributed that enables home enthusiasts to construct 3D printing machines themselves.

Engineering technology students benefit greatly from exposure to this technology as it allows them to interact with their own designs in a tangible way.  Students gain increased proficiency with allied technologies such as Computer-Aided Design and Computer Programming.  In addition, it is completely feasible for students to design and build 3D printers themselves, adding exposure to machine design and manufacturing concepts in the context of a real-world design problem.

As the first step in this curriculum pathway, a series of design projects is proposed that will give student incremental exposure to 3D printing, machine design, thermoplastics processing, industrial control systems as well as manufacturing engineering functions processes associated with machine design and building.  The proposed sequence of development is as follows: 1) Design and build the TP Extruder 2) Design and build downstream extrusion equipment 3) Design and build a fused deposition modeler 4) Refine and improve designs of FDM (also called FFF) equipment 5) Design and build allied CNC equipment including routers and cutters.

Problem Statement

At the University of Memphis, the value of project-based learning is well appreciated.  The Herff College of Engineering has significant investment in industrial 3D printers, however the cost associated with producing models is too high to permit unlimited printing by students.  High resolution models such as those produced by our Objet Alaris 30 are beneficial, but come at a high cost.  Not only is the price of the modeling material high, it is considered toxic in its liquid state and therefore its use must be highly regulated and preferably minimized or eliminated.   Model material consumption is high with this machine as it does not permit hollow printing.  Furthermore these models made with this technology are highly susceptible to creep, are brittle, and have extremely limited strength at anything above room temperature.

The college also owns and utilizes a Stratasys Dimension SST fused deposition modeler.  This machine is almost ten years old and seems to be nearing the end of its useful life.  The FDM technology is preferred among faculty and students because it has good mechanical properties (the print material is true ABS), and fair resolution.  The print time with the FDM can be much faster as it permits printing hollow parts.

The primary costs associated with the operation and maintenance of both machines stem from 1) Printing material and 2) Maintenance/service contracts.  Annual maintenance contracts for each of these machines exceeds $4000 and material costs are extremely high as well.   The cost difference between commercially available extruded filament and raw ABS pellets is very high (____specifically).  Significant savings could be realized if the design and manufacturing of both the printer and the extruder were brought in-house.

Additionally, as the industrial machines age, new 3D printer design projects could be designed and built, improving continually until the point where their performance could rival the Stratasys and potentially the Objet.   At this point the maintenance service contracts could be cancelled, freeing up funds for more machine design projects potentially including routers, plasma cutters, laser cutters, and more.

One of the major goals of this project will be to provide a seemingly inexhaustible supply of filament for any student wishing to utilize 3D printers.  There are several DIY kits and open-source extruder projects online but  it seems unlikely that any of these would meet the needs of the college.  The mass flow rate of most of these machines limits their output capacity to a level that could only be useful to a single user.    The major exception is the Russ Gries version which produces approximately .33 kg/hr (footnote).  This is nearly ten times the output of the Lyman and Filabot extruders, and is an acceptable speed for our purposes.  The design for the extruder documented here builds on the Gries design. (Gries credits Lyman with his design inspiration).

In addition to having limited production capability, most of the DIY machines seem to be designed primarily as extremely low-cost, proof-of-concept machines.   Many are constructed of plywood and other materials that seem restricted to hardware store availability.  Again, the Gries model is exceptional and approaches the level of industrial quality.  The other machines studied have low power heaters, very limited length to diameter ratios and even shorter melt zones when compared to what is common for industrial laboratory and jockey extruders.

One area of similarity that the solution that is to be developed will share with almost every design of the class of extruders studied will be the use of a commercially available auger bit as the extruder screw.  The reason for this is that machining extruder screws is beyond the capacity of most small & home shops.  This kind of machining requires specialized tooling and equipment that is cost prohibitive for our purposes.  Screws and barrels were sourced for this project and did exceed our budgetary constraints.  However, auger bits with LD ratios of 30:1 are available for less than $100.  This ratio is more typical of commercial equipment and will hopefully yield good results.

Goals

The primary goal of this project is to provide students with an opportunity to learn by doing.  The benefits of designing and building both an extruder and a series of 3d printer (or allied CNC technology) are many.  First, students will benefit from *problems in context, *design experience, manufacturing experience (machining, welding, casting, extruding, tool design, project management, etc.).  Toward this goal, the following outcomes will be assigned and assessed:

  • Full 3D models of parts and assembly
  • Working drawings of all parts and assembly
  • Calculations documented
  • Working Prototype
    • Rate: .5 to 1.0 kg/hr
    • Dimension: 1.75
    • Diameter Tolerance: +/- 0.1mm
    • Time from cold to extrusion temp: 10 minutes max.
  • Related to manufacture
    • Jig and Fixture Design
    • CNC Programming
    • CMM Inspection

Budgetary and Time Constraints

The deadline for extruding plastic is the last day of class.
Budget is $300. Does not include cost of machining, welding, design, or DC Motor and control.

Literature and Suppliers

Learning Outcomes

  • Demonstrate proficiency in CAD
  • Demonstrate proficiency in CAM programming
  • Demonstrate proficiency at CNC machine operation and setup
  • Demonstrate  proficiency with CMM machine operation and programming
  • Demonstrate understanding of statics and dynamics
  • Develop a deeper understanding of project management
  • Develop a deeper understanding of time management
  • Broaden student understanding of manufacturing processes
  • Demonstrate the ability to specify suitable engineering materials
  • Develop student welding skill
  • Develop student machining skill
  • Deepen student understanding of fixture design
  • Demonstrate the ability to specify suitable mechanical fastening components
  • Deepen student understanding heat capacity & thermodynamics
  • Demonstrate an understanding of electrical circuits and components
  • Demonstrate an understanding of electrical properties including voltage, power, current and resistance.

Assumptions & Limitations

  • Material is virgin ABS
  • All machining and fabrication to be done in-house
  • End user of prototype & extrudate is internal (U of M)
  • Screw design is limited to only C.O.T.S.
  • Important: Melt heat comes from heaters only (Very different from commercial screw extruders)
  • 110v system
  • Using on-hand 90V DC Dayton gear motor.
  • Shipping is to ET Building, Memphis TN (Best Way)

Tasks (Assignments)

  • Start part numbering system & Drawing filename convention
  • Model Frame
    • Note: When modeling frame assembly, color 2 sides to keep orientation consistent in assembly.
    • Note carefully the position of the parts.
    • Typical constraint sequence: Align, Align, Touch
    • Model using linked body concept (Wave geometry linker)
  • Bill of Material with Costs and suppliers
  • Calculate roller chain capacity. Compare suppliers numbers with Wikipedia’s data.
  • Calculate mass flow rate of current extruders
  • Calculate RPM of screw for 1kg/hr
  • Create Work Breakdown Structure
  • Verify dimensions of website of Dayton Motor
  • Shear pin calculation
  • Design Nozzle Alignment Guide
  • Encoder Mounting
  • Tensile stress in barrel
  • Size a thrust bearing
  • Design HIPS Cover
  • Develop flat pattern for hopper (square, round, transition)
  • Design control panel hinge
  • Design control panel layout
  • Design thermoforming tooling for HIPS Cover
  • Model in 3D
  • Write Purchase Orders
  • Create working drawing of components
  • Shaft power transmission
  • Heat capacity calculations
  • RPM for a given mass flow
  • CNC Program for Flex Conn
  • CNC Program for Bearing Plates
  • CNC Program for Tooling
  • CMM Inspection of Bearing Plates
  • Mold Design for FC Spider
  • Mold for HIPS Cover
  • Laser program for HIPS Cover
  • Design Welding Fixture
  • Weld (tack, assemble, weld)
    • MUST have precision fixture for bearing mount crossbars
  • Machine
  • Prime and Paint
  • Thermoform
  • Cast Urethane or Silicone Flexcon Spider
  • Assemble
  • Test
  • Process Validation
  • Write Operator’s manual
  • Write Maintenance manual
  • Write Work Instruction for Operator

Future Work

Phase II – Design, Build and Test Up/Downstream Equipment

Phase III – Build FDM 3D Printer.

Future Work – CNC Router, CNC Plasma Cutters

SEE Ethical Filament Foundation

Z5X Mach3/EMC2 breakout board

Sale CNC Screw Cutting Machine

Frame Types (FDM/FFF only)

Printer Heads

Motion control

Hardware/software

 

Print Friendly, PDF & EmailPrinter Friendly

Leave a Reply

Your email address will not be published. Required fields are marked *

Scroll to Top