P17676: Vacuum Former

Preliminary Detailed Design

Table of Contents

Team Vision for Preliminary Detailed Design Phase

During this phase:

Feasibility: Prototyping, Analysis, Simulation

Surface Temperature

Surface Touch

Pain Threshold: 111 degree F Max Pain: 140 degree F Our Goal Limit: 120 F

Vacuum Tank Pressure Test

To verify that the tank can withstand the vacuum conditions needed and that the vacuum pump system can reach the desired vacuum pressure.

Vacuum Tank Test Procedure

  1. Connect the vacuum tank to the vacuum pump along with a vacuum pressure data acquisition unit.
  2. Inspect tank for any defects.
  3. Start the data acquisition and the vacuum pump.
  4. Monitor the vacuum pressure values and the tank.
  5. Once pressure values remain stagnant for a significant period of time, about 30 seconds, turn off the vacuum pump and monitor the pressure to see if there is any significant loss of pressure.
  6. Turn off the data acquisition system.
  7. Slowly release the pressure in the tank back to atmospheric conditions so that the system can be disassembled.
  8. Analyze pressure data and reproduce graphs to confirm vacuum draw rates.
  9. Repeat the test with various vacuum pump systems to compare.

Heating Temperature Test

Our previous visits to vacuum forming industries and research have told us that generally our ovens should remain at 300 degF to heat our plastic. In order to confirm this, we plan to do our own test. Using a simple box and a kitchen oven, we will heat the plastic at 300 degF to examine time to reach mold-ability, sag, and forming quality of the plastic at that temperature. We have acquired enough plastic to test PETG and HIPS at 300 degF, and at 400 degF.

Test Procedure

  1. Create simple wooden test box
  2. Pre-heat oven to 300 degF
  3. Staple plastic sheet tight across top of test box
  4. Place test box in oven, plastic sheet side up
  5. With oven light on and oven door kept shut, watch plastic
  6. When plastic sags as far as possible without ripping plastic, remove test box
  7. Record time to reach optimal sag
  8. Quickly push plastic over mold object and hold down until plastic hardens
  9. Remove plastic from box and mold from plastic to examine test mold
  10. Repeat process with oven at 400 degF

Linear Slider Load Test

Since our design designates that the plastic sheet is the only moving part of assembly for the forming process, we have created a plastic clamping fixture that is to slide vertically. The plastic clamping fixture will be a square that fits inside the frame of the whole assembly with a linear slider attached at each corner. Each slider will be created using an angle bracket with plastic slider material that fits in 8020 track. Our biggest concern with this part of the design is racking of the plastic clamping fixture as it moves up and down. Our goal is to restrict movement as much as possible to smooth vertical sliding. We have designed a test to make sure our sliders are capable of carrying the load required, and that they slide smoothly.

Slider Load Test Procedure

  1. Create the slider by drilling holes in each face of a piece of angle bracket, and screwing the plastic slider onto it.
  2. Attach the slider to a rigid rod that should sit perpendicular to the direction of motion of the slider.
  3. Slide the slider piece onto a piece of 8020 track at least 4' in length.
  4. Secure the 8020 track vertically.
  5. Apply a vertical load to the horizontal rod, and slide vertically up and down the track.
  6. Monitor the motion of the slider, and how the load affects movement.
  7. Increase the load on the horizontal rod and continue to monitor.
  8. Continue to increase the load until at least 20 pounds (slightly higher than the calculated weight of the plastic clamping fixture).

Drawings, Schematics, Flow Charts, Simulations

Vacuum Table Pic
The image above is our idea for the vacuum former. The legs are made from 1.5" 80/20 along with some support members. The oven is made from a 1" tube stock frame, sheet metal, and insulation inside of it. The vacuum tables are made from MDF sheets and birch plywood. The clamps are made from .5" tube stock. Underneath the table there is room for our tanks, pump, electronics, and hoses. In the image above you can see the cut out in the main clamp that the smaller clamps can fit into. This allows you to change sizes along with the vacuum table while still maintaining alignment. The image above is our idea of how to lock each smaller clamp on to the outside clamp with a swinging latch.
Table Base
The table base shown above that is attached to the vacuum former frame has predetermined corners in it so that you can change the vacuum tables and be sure that it is positioned correctly. It also has a hole cut in the middle that will allow the vacuum tube in each table to go through it for quick change of the tables.
Vacuum Table
The image above is our vacuum table. The top is made from an MDF sheet which will have vacuum holes of about 1/16" diameter in a 1" grid pattern and the sides and ledges are made from .5" birch plywood. The ledge on the table is to allow for the sub flush design. Inside the box is another sheet of plywood decreasing the volume of the box so we do not waste our vacuum. Each table has a tube out of the bottom in the center to allow us to connect the vacuum to. This will allow for the table to be quickly interchanged using a hose clamp and the aligning corners on the table base.

Bill of Material (BOM)


Plans for next phase

Gantt Chart

Moving Forward

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