Intro: Vacuum Forming a Large Part
I made it at TechShop! www.techshop.ws
Here is a large bowl-shaped part I'm making. It is a prototype for a ram-air type of air cleaner for older cars, you can see a rendering of the finished product at www.fastlaneinnovations.com/ramduct.html
(Fixed the address, sorry about that)
Step 1: Turn on the Main Power
Turn on the main power switch.
Step 2: Turn on the Heater
Use the touch screen on this machine (Formech model 686) to turn on the heater. It takes 15-20 minutes to warm up.
Step 3: Change Aperture Plates
The small aperture plates are normally installed, which are ok for parts up to about 10". This part is about 19", so I fabricated my own plates that work with a 24" square of plastic. Just remove 2 bolts on the lower and upper plate, swap them out, and replace the bolts.
Step 4: Set Up Program
Use the touch screen to set up and save the settings like heater power, auto-vacuum, etc. After you press the button in the last picture, press "Start" on the Touch screen, and then load current settings when it prompts you.
Step 5: Clamp Material Into Place
After pushing the last button on the previous step, press "Start" and then "Load Current Settings" to bring up the workflow. Put your mold on the platen, and press and hold "Table Down" until it lowers all the easy down. Place material onto the gasket and clamp it. You may need to adjust the clamps to get a good amount of force.
Step 6: Run the Workflow
This machine has a workflow layout on the screen. Pull the heater over the material to start the timer. Watch the material, waiting for a good uniform sag a couple of inches deep for this size aperture. Use an infrared thermometer if possible to check plastic temperature (slide the heater back a bit first). When ready to form, slide the heater all the way back, and for large and deep parts, use the button next to the heater that looks like a yellow dome to puff up the plastic which stretches it. Then push and hold both "Table Up" buttons to bring the mold up all the way into the material. If the vacuum doesn't start automatically, press the vacuum on button on the top right of the screen. The cooling timer will now start. Once the part has cooled, you can press the air pulse button to help separate the mold. This probably won't get it done, so you may need to unclamp the plastic and separate the part yourself. Wear gloves, the plastic and mold will be hot! Then just put the mold back on the platen, press table down until it is all the way down, and repeat the workflow for your next part. When done, turn off the main power and swap the aperture plates back (using gloves as they'll be hot) for the next person.
The finished part is shown. Almost finished anyway, the excess material needs to be cut away. You could use a jigsaw or coping saw, I'll use the Shopbot CNC router. Smaller parts could also be cut out on a laser cutter but it won't take 24x24" parts (24x18" max)