P19603: Rod Feeding Mechanism
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Detailed Design

Table of Contents

Design Review Agenda

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Problem Definition

Metal additive manufacturing machines primarily use either wire or powder feedstock. Powdered metal is expensive and wire is hard to source for alloys that are not used in welding. The use of bar stock would be ideal, as most metals are readily available in rod form, but no standard exists for using rod stock in metal AM applications.

The goal of this project is to develop a feeding mechanism which will enable the use of various bar stock materials in metal AM applications, particularly the Vader AM machine in RIT’s Brinkman Lab. The design must provide stock material fast enough to avoid slowing the machine down, without overfilling the micro-crucible or negatively impacting part quality. The device must also be safe for both operator and machine, and be simple to use. While integration with the Vader is ideal, it is not the primary goal of this project.

Customer and Engineering Requirements

No updates since Phase 2.

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Constraints

Primary Constraints

Design Details

CAD of Final Design:

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From left to right:

Row 1: Total Assembly, Hopper, Feeder

Row 2:Agitator, Weight Bracket, Base

Row 3: Test Base

Drawings

Dimensioned Drawings Packet

Assembly Drawings:

public/Photo Gallery/Drawing - Rod Feeder Assembly.PNG

public/Photo Gallery/Drawing - Hopper Assembly.PNG

public/Photo Gallery/210-000 (Feeder v3) Drawing 1.PNG

public/Photo Gallery/300-000 (Agitator) Drawing 1.PNG

public/Photo Gallery/400-000 (Weights) Drawing 2.PNG

public/Photo Gallery/Mounting Assembly Drawing 1.PNG

Part Drawings:

public/Photo Gallery/Feeder Body v2 Drawing 1.PNG

public/Photo Gallery/Drawing - Hopper Mounting Bracket.PNG

The directory to all drawings is Here.

Drawing Package

BOM

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Live document here.

System Architecture

 System Block Diagram

System Block Diagram

Electrical Schematic

Electrical Schematic:

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Pseudocode

Pseudocode/Logic:

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Operating Procedure

Operating Procedure:

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Prototyping, Engineering Analysis, Simulation

Hopper Prototyping

To test whether the vertical hopper concept was sound and wouldn't jam, we created a prototype test plan using various 3D printed funnels. To determine optimal funnel angles we printed multiple funnels and measured their performance. The shallowest angle performed best. We built a to-scale model of the hopper system and using an appropriate motor ran the device and determined that it wouldn't jam and would easily meet the flow rate requirements.

Setup Agitator Funnels

Feeder Prototyping

We have gone through multiple 3D printed prototypes in this phase. Each iteration has fixed problems we have found with the previous version.

Vibrations Testing

The proposed design includes an agitator. AM machines require precise movement of the print head and so excessive vibration could negatively impact performance. To address this, we included vibration isolators in the design and, with the guidance of subject matter expert Dr. Ghoneim, decided on a plan to minimize vibration:
  1. Make the hopper assembly heavy with respect to the rods
  2. Measure the natural frequency of the hopper assembly in ANSYS
  3. Set the agitator motor to that frequency
  4. Dial the offset weight to produce minimum displacement

The feedback form can be found here.

Then to get a measure for allowable vibration we mounted our prototype agitator to the Vader print head and printed baseline cubes. The results below show that there was no effect from vibration.

public/Detailed Design Documents/Vader_Print_Quality.PNG

We are confident that the minimized vibration of the device, further reduced by the rubber isolators, will have no negative impacts on the Vader.

Sensor Testing

The photogate configuration was tested in lab for use in our design. A LED was powered and aimed at a phototransistor (BPX 38-4) and the output voltage was measured. The test was performed on a breadboard and ambient light was blocked by covering the setup with a box. A hole was made in the top of the box and a rod was placed through and aimed between the LED and the phototransistor to block the light, simulating operation in the design.

The voltage reading of the phototransistor under the box with the LED on was 10.9mV. With the rod blocking most of the light, the voltage dropped to 0.3mV. Because the Arduino has 10-bit ADCs, this difference of 10.6mV between readings is enough to differentiate logic high and low for operation. Increasing the distance between the LED and phototransistor to over 2 inches decreased the output voltage to 2.5mV with the LED on and unobstructed.

The phototransistor used was most sensitive to IR light and had less than 20% spectral sensitivity at the wavelength of light that we used (550-600nm). We have already ordered a photosensor that is not only more sensitive to visible light, but will amplify the output voltage make the difference between logic high and low clearer.

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Vader Integration

Communication between the Arduino and the level sensor used in the Vader was an initial concern. Researching the level sensor led to the conclusion that the sensor can output an analog or digital signal. The digital communication is through RS-422. A meeting with Dr. Barrios was held to discuss RS-422 in detail and what micro-controller would be best for this project. The Arduino Mega was selected because of the voltage requirements for RS-422 and because of the RS-422 shield that can be used for easy communication.

Along with communicating with the sensor in the Vader, another concern was whether the 1/8" rods would block this level sensor when feeding into the upper pump. The level sensor currently points directly down into the upper pump and if the rod fed in were to block the laser, level measurements would be incorrect. After discussing this with one of the Vader operators, Manoj Meda, we learned that the 1/16" wire that is presently used for operation begins to melt as soon as it enters the upper pump. With this information, feeding the 1/8" rod slow enough will allow it to melt at the top of the upper pump and will not block the level sensor laser.

MSD 1 Risk Conclusion

Risk Assessment Throughout MSD 1

Risk Assessment Throughout MSD 1

Test Plans

Full Test Matrix:

Master Test Matrix Correlates All ERs With Measurable Tests

Master Test Matrix Correlates All ERs With Measurable Tests

The live document is here.

Test Plan 1: Tests all primary requirements. Under each rod condition, run the device for 10 minutes 10 times. The counting rig shown below will create a time series, allowing us to measure both the average feed rate over a long period, and the distribution of delays between individual rods. It also confirms that the device stores sufficient rods and operates under that condition.

Test Plan 2: Confirms that device will stop and start under required conditions (RS422 signal from Vader level sensor)

Test Plan 3: Confirms that the device can be cold started in a reasonable amount of time.

Counting Device:

public/Detailed Design Documents/countingdevice.PNG

Budget and Purchasing

Budget Update:

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Purchased This Phase

Critical Part Purchasing over break: In progress

Manufacturing Plans

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Risk Assessment

Risk assessment for MSD 2:

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Opportunity: Angle Feed

We are looking into a more compatible method for the Vader system. This is both above and beyond our proposed scope for the project.

Project Schedule

Remainder of Semester:

MSD 2 Overview:

High Level Overview of MSD 2

High Level Overview of MSD 2

Start of MSD 2 Plan:

Task breakdown of first 3 weeks of MSD 2

Task breakdown of first 3 weeks of MSD 2

Lessons Learned

What we learned

Suggestions for MSD

MSD Processes

Progress Report

Progress as of 11/27/18:

Tasks Accomplished

Plan To Accomplish Before DDR

Input required from Customer


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