Detailed Design Review & Component SelectionP15551 High Temperature Pellet Based 3D Printer Head

Alyssa Palmieri, James Allen, Kylan Ames, Ray AliNovember 13, 2014

High Temperature Pellet Based 3D Printer Head

Most current 3D printers use plastic filament as feedstock. The goal of our project is to create a 3D printer head that uses ordinary plastic injection molding pellets as feed stock. It should be able to withstand temperatures up to 380°C, which is 100°C higher than max operating temperatures of current printers, and should also be able to print for 10 hours continuously.

Engineering RequirementsTop 8 Engineering Requirements (Importance of 7+)

System FunctionsPRIMARY

Storing: HopperHeating: Cartridge HeaterCooling: Cooling FanDriving: Auger Screw

Stepper Motor

Feedback: Thermal Feedback

Pressure Feedback

ALTERNATIVE

Storing: HopperHeating: Cartridge HeaterCooling: Cooling FanDriving: Metering Gear Pump

Stepper Motor

Feedback: Thermal Feedback

Pressure Feedback

Justification for Alternative+ History of screw solution difficulties+ Simplicity of Gear Pump+ Innovative Design+ Similar size/weight to current printers+ Contingency plan for solution failure

- Unknown solution feasibility- Difficult to design/fabricate?

Subject Matter ExpertsName Expert in Feedback

Dr. Steven Day/Dr. Michael Schertzer Fluids ● A pump is feasible

● Calculations for non-newtonian and newtonian fluids are similar

Dr. Michael Schrlau Heat Transfer ● Decouple functions - heat then drive

Harbec Inc. Injection Molding ● Time while molten increases plastic degradation● Stock auger screw is cost-effective solution

Professor Bonzo Machining Capabilities

● Machining of a variable flight depth screw is possible ● Test stock auger screw for POC before fabricating one

Rachel Screw driving plastic pellets ● Found out what didn’t work with screw driving

Subject Matter Experts Cont.Name Expert in Feedback

ITT Goulds Pumps Centrifugal pumps

● Positive displacement pump (Gear Pump) is a strong option● PD pumps handle high viscosity well● Limit thermal conduction paths between components

Liberty Pumps Pumps

● Gears meshing might add unwanted shear energy to molten plastic ● Elastomer seal within the pump may not be able to withstand high temp.● “Mag-drive” pump could eliminate need for a seal● Progressive cavity pumps are used for very viscous fluids and have “fairly

accurate flow rates”● Wet end of heated pump should be metallic

Component: Hopper

Functions● Hold plastic pellets

Comments/Concerns● Unsure of cost associated with fabrication● Concerned with added weight to the print

head

Component: Heater Cartridge Functions

● Provide necessary heat to the system to melt thermoplastics

Comments/Concerns● Maximum operating temperatures of 540°C to 760°C depending on sheath

material● To achieve a temperature of 350°C, the heater will need to be roughly 300 Watts

Costs and Information● Omega ¼” diameter heating cartridge, 2” length, 250 Watts. PN: CIR-1024/120V,

cost $66.00● Omega ⅜” diameter heating cartridge, 2” length, 300 Watts. PN: CIR-

20204/120V, cost $50.00

Component: Heater Cartridge (cont.)

Component: Auger Screw FunctionsTransport bulk material through barrell to nozzle. Produces shear heat in screw.

Comments/Concerns● Initial proof of concept with the filabot works with ULTEM pellets● Produced non-uniform cross section of filament with air bubbles● Cylindricity of auger

Costs● $27.02

Auger Screw Proof of ConceptLearn how to use the Filabot Wee

Testing Process:1. Locate Filabot2. Ask Brinkman Lab employees for help with testing

for the first time3. Plug in the Filabot4. Turn up the temperature to 240°C5. Once temperature is at 240°C, add pellets & start

running the screw6. Test for about 2 minutes to watch the process7. After testing look at how hot the Filabot can get

Auger Screw Proof of ConceptLearn how to use the Filabot Wee

What we’re looking for:● Observe how the Filabot works to transport the pellets throughout the

system● Also see if the Filabot can get up to 350 degrees C to test our

ULTEM pellets.

Results:The extruder worked and printed filament strands.

Auger Screw Proof of ConceptTake off insulation and see what is heating

Testing Process: 1. Cut zip ties off the insulation and take off insulation2. Look to see what is heating the aluminum to heat the plastic pellets3. Look to see how big the aluminum cylinder is compared to the screw driving the pellets

Auger Screw Proof of ConceptTake off insulation and see what is heating

What we’re looking for:● What was heating the pellets● How big the aluminum cylinder is

compared to screw driving the pellets

Results:We found that there is a small heating cartridge melting the pellets held by a set screw. The aluminum block is also much larger than we thought.

Auger Screw Proof of ConceptTest Filabot with ULTEM 1000 Plastic Pellets

Testing Process: 1. Turn on the Filabot

2. Get temperature up to 240°C to purge out any of the old material

3. Once at temperature, turn on the screw to purge

4. Once material is purged, turn the temperature up to 350°C

5. Once at temp, add ULTEM pellets and turn on driving motor

6. Run for 2 minutes and observe

Auger Screw Proof of Concept

Test Filabot with ULTEM 1000 Plastic Pellets

What we’re looking for:● If Filabot can extrude ULTEM 1000 pellets

Results:The Filabot worked with the ULTEM pellets.

● Some residual material was still in Filabot and coated the ULTEM filament initially● Then turned down temperature to 320°C to see if the pellets would still melt and noticed that

the strand of plastic coming out of the Filabot was chunky and inconsistent● 350°C found to be ideal temperature (Sufficient melting, without burning)● Screw moved material too fast through the nozzle for it to melt consistently● Moisture in pellets cause air bubbles when being printed. Need to dry first.

Auger Screw Proof of ConceptTest Filabot with ULTEM 1000 Plastic Pellets VerticalTesting Process1. Turn on the Filabot

2. Get temperature to 350°C

3. Add plastic ULTEM pellets

4. Cover hopper to prevent pellets from falling out while vertical

5. Run screw

6. Tip the Filabot vertical when the material starts to come out of the nozzle

7. Run for 2 minutes

8. Stop and let Filabot sit for 10 minutes to allow pellets more time to warm up

9. Run the screw for 2 minutes

Auger Screw Proof of ConceptTest Filabot with ULTEM 1000 Plastic Pellets VerticalWhat we’re looking for:

● If Filabot can be tipped vertical (like a 3D printer) and still properly function

Results:The Filabot works with it being turned vertical.

● Noticed air bubbles ○ Pellets having moisture in them○ Material moved too quickly through the system, didn’t melt enough

● Possibly require additional heating prior to driving● The speed of the screw needs to be slower for our application

Auger Screw Proof of ConceptTest Filabot with ULTEM 1000 Plastic Pellets Vertical

❖ Material Starts off smooth during initial printing

❖ Material is chunky after running for about a minute

Auger Screw Proof of Concept

❖ Allowed the Filabot to sit for about 10 minutes with the pellets in the hopper to try to dry the pellets and create a more consistent flow, which it started off chunky and then became more consistent

❖ Material is very consistent after the heat took part in helping to dry the pellets

Component: Gear Pump (Alternative) Costs

● Spur gears: ~25 each● Housing: ~20● Seal/ gasket: ~5

Functions● Precisely outputs a volumetric flow rate● Heating cartridge maintains appropriate temperature

Comments/Concerns (pressure)● Gear meshing leading to unwanted shear energy, could negatively affect pump performance● Mechanical seal (elastomers) do not perform at these high temperature

Component: Stepper MotorCosts

● $10-20 (free from customer)

Functions ● Produces a torque to drive the auger screw.

Comments/Concerns● Compatible with 3D printers● Reliable● Easily adjust RPM● Can adjust torque output with speed belt/ gear ● Must be properly separated from heated components

Size ● Torque must be able to produce a 35lb linear force

Additional Misc. ComponentsInsulation

● Required to maintain safe printing environment for consumer● Also considered to lower heater wattage required● Fiberglass or mineral wool can insulate high temperatures

Arduino Microcontroller● Provided by customer● Used to control stepper motors, axis controls, temperature monitors, power supply, etc.

Nozzle● 0.4mm diameter exit, can be purchased relatively cheaply from various sources. ● Alternatively it can be machined without significant difficulty.

Aluminum Block● Our 3D printer has 1.75” diameter aluminum bar for an extrusion head, which will be used as a

starting point for the barrel outer diameter

Extrusion Screw● Extrusion screws are used to melt plastic and create filament● Typically they are multiple feet in length, we are constrained to inches● The flight width for this design is only 0.04”, so there are concerns with bending or breaking

○ Might be able to deviate from accepted designs to increase this width● Screw to barrel clearance is also small, 0.0004”. Tolerance will be difficult to hold● This design will be considered if the small scale auger screw design fails or is insufficient● Cost is likely to be high

Screw Design Calculations

Screw Design Calculations (cont.)

Test Plan: Heater CartridgeWhat ● Temperature● Wattage

How● Simulate operating conditions.

○ Temperature:■ Use thermocouples to measure temperature of heater after

steady state conditions○ Wattage:

■ Power heat cartridge until the output is at the proper level, then measure the voltage and current to calculate wattage

Test Plan: Stepper Motor/Auger Screw

What ● RPM● Mass/Volumetric Flow rate

How ● RPM

○ Visually identify the number of rotations in a given minute.● Flow rate:

○ Extrude filament for a certain amount of time onto a scale to measure the weight of material coming out.

Test Plan: Thermal Feedback❖ Thermocouples should be calibrated before use. ❖ A common way to calibrate thermocouples is to place

them in a heated bath at 30°C and measure the voltage. ❖ Voltages are measured at 5 degree increments up to

60°C, and then again at room temperature. ❖ A voltage-temperature plot can be created and

compared to known values. ❖ There should be programmable methods of cutting

power once the desired temperature is attained.

Test Plan: PrintheadWhat:● Print time● Flow consistency

How:● Print Time

○ Load printer and set run time for 10 hours, check for any failures and add additional material as necessary.

● Flow consistency○ Setup printhead and visually inspect material leaving the nozzle for air bubbles,

surface texture, color, uniformity, etc., to ensure consistent flow.○ Measure mass flow rate coming out of nozzle

Bill of Materials

Bill of Materials

Risk Assessment

Risk Assessment

Risk Assessment

Risk Assessment

Risk Assessment

Risk Assessment

Risk Assessment

Next Steps! Week 13-15➔ Focus on narrowing down components ➔ Start to order some components with long lead times➔ Focus on understanding Non-newtonian fluids

◆ see SME◆ look up more textbooks

➔ Update test plans◆ focus on low-risk subsystems

➔ Focus on calculations for the gear pump◆ see SME

➔ Continue 3D modeling and creating drawings➔ Continue adding more to BOM ➔ Visit machine shop to see if pump casing is machineable inhouse ➔ Lower scores/takeaway risks on the risk assessment➔ Test auger screw with BFB stepper motor

Questions?