Preliminary Detailed Design
Table of Contents
Team Vision for Preliminary Detailed Design Phase
For this phase in our design process, the team decided to split up and tackle the different subsystems that compose our product in the following manner:
Adam: Lead screw and nozzle design
Tim: Heating element and effects of heating.
Dylan: Working with the cooling element, and form rollers system
Maria: Motion control programming for the different subsystems
The hand sketch represents the schematic introduced in "Fluid Mechanics for Chemical Engineers" by Wilkes. The variables described in the schematic that are crucial for lead screw design include:
The Navier-Stokes equation for flow is simplified to detail 1-D flow in the flight axis of the lead screw. When integrated once, it gives way to the velocity profile below.
Integrating the velocity profile again produces the flow rate equation. The pressure difference is needed in this calculation and can be extracted from the pressure differential across the die design.
After researching to topic, several important
characteristics were found to implement into the die
design. The first was a streamlined area that will neck
the melted plastic down to the correct filament size.
Reducing the amount of stagnation area and having a die
that promotes constant compression will give a high
quality and consistent extrudate.
Special thanks to Dr. Ghosh for providing valuable guidance on this topic.
After research upon the heating element and the temperature maximum given by our customer of 400 C, the data shows that this likely won't be a problem as was a concern. The heat can be mostly contained with only 4 inches of insulation, the graph of which can be shown below.
As for the issue of the barrel and lead screw fit, the barrel will only expand .003" with an ID of .625". Tests in the coming week will determine how much the lead screw will expand but given the results from the barrel test, it most likely won't be a problem.
Special thanks to Professor Landschoot for providing feedback on this topic.
The chosen motion control system for operation of the lead screw is an Anaheim Stepper Motor. This bipolar 4 wire stepper motor has specifications 1 Amp, 2.7 Ohms, 2.7volts, 1.4Kg-cm and 200 steps/rev. This stepper motor will be programmed using an Arduino Microcontroller Board and an additional driver board. Preliminary research showed that a Pololu Stepper Motor Driver Carrier will be appropriate to run the Stepper Motor.
The motion control system to be used for the rollers is yet to be defined. Potentially, a stepper motor similar to the one used for the lead screw could be implemented. However, a DC Motor could be used. The decision will be based on price, availability and functionality. There will be more research to be done in order to take this decision.
Feasibility: PrototypingTesting was completed on a rig made of 3D printed rollers and a plywood base. The test ran successfully, and it was proven that the rollers can shape the final filament. Other lessons learned include things like drive requirements for the rollers and spacing requirements relative the nozzle.
Drawings, Schematics, Flow Charts, Simulations
The initial sketch for the base of the roller prototype was simple and used mostly to dimension cutouts for motors and record overall size constraints.
The prototype wheels as initially modeled, included a plug-and-play base and an upright orientation to better suit the horizontal nature of the Filabot used for testing. The base would fail to print leading to the plywood base actually used. The upright orientation was scrapped due to the testing layout.
Some updates have already been made to the model. A system for opening and tensioning the rollers has been added to ensure better contact between the rollers and to aid in feeding. Eventually, another prototype closer to this model will be used in testing roller efficiency relative distance from the model. The final design will be able to vary this distance to allow for testing and multiple plastics.
Arduino Code: In order to power the wheels, a small stepper motor was incorporated into the design of the system. A code to operate the wheels was written using the Arduino IDE system software and an Arduino Board.
Bill of Material (BOM)
At this point in the design, the team is not yet prepared to issue a bill of materials. As we progress in our testing and development we will gather enough information to produce a preliminary document. As the design process continues, this document will be updated and refined accordingly.
In the coming weeks we will be testing the heating element. Aside from getting familiar with the heater itself, the following tests will be conducted.
- Heating of the stock barrel to test the math of thermal expansion.
- Heating of the lead screw to see what the expansion of it is.
- Surrounding the heater in insulation to test heat escape.
Further in the design process, several other tests will be required in order to arrive to define different aspects of the design. One such test will be to determine the optimal distance between the nozzle and the roller wheels in order to achieve the desired diameter of filament.
- Updated assessment from Subsystems Design.
- Our Risk Analysis Matrix was updated to consider several risks that were identified through our findings so far.
Design Review MaterialsSpecific Design Review Materials can be found following these links:
- Notes from review
- Action Items
Plans for next phase
The team has set out to work in four main components of the project before the semester is over.
- Testing involving the heating components, as well as
- CAD Modelling
- A complete CAD model shall be complete by the end of the semester
- Technical Requirements Research
- More research regarding technical aspects of the heating elements and their interactions with the lead screw and barrel is required
- The team will start investigating what items we want to start acquiring in order to move forward in the project. Key items to consider are the stepper motors and their relevant drivers.
- Each one of the members on the team took the time to outline what individual actions they would take to further move the project forward.