05-25-2014, 07:01 PM
I finished up a project at work that I've been working on lately and thought I would share the results.
We have an injection molded plastic part with 96 wells that requires a coating applied to the sides, but not the bottom. It's in a production environment, so they also need to be coated quickly, as in a few seconds per part. The fixture I came up with is based on a plate with 96 little (.31" x .44") sponges mounted on pins. The plate is kept immersed in the coating solution and then raised so the sponges enter the wells, coating the sides and then retract. It sounds simple enough, but the solution is quite volatile and insanely expensive, so the mechanism needs to be in a sealed chamber with a door that opens when needed and then closes automatically to seal the chamber.
The mechanism for moving the sponge plate was stolen from another of my fixtures. It's a shuttle moved by an air cylinder with bearings that ride in angled slots to raise and lower a platen, constrained so it can only move vertically. The sponge plate is attached to this platen.
Creating the football shaped sponges turned out to be quite a challenge. The low durometer 1/2" thick open cell foam they are made of is too soft to saw or even cut with a razor blade. I ended up having them cut with a water jet which worked quite well.
The fixture has a plate with a cutout to hold the plate and a trip lever to start the sequence. When the part is pressed into the pocket, it trips the switch which actuates a time delay relay which in turn applies air to the pneumatic cylinder that opens the door. When the door is fully open, it trips a switch which actuates another time delay relay to apply air to the double acting cylinder that raises the sponges and then retracts them. Once the sponge plate retracts, power is cut to the system and the spring loaded door is allowed to slide shut. The entire cycle takes about three seconds.
This stuff is great fun to design and build AND it keeps me out of trouble.
Tom
We have an injection molded plastic part with 96 wells that requires a coating applied to the sides, but not the bottom. It's in a production environment, so they also need to be coated quickly, as in a few seconds per part. The fixture I came up with is based on a plate with 96 little (.31" x .44") sponges mounted on pins. The plate is kept immersed in the coating solution and then raised so the sponges enter the wells, coating the sides and then retract. It sounds simple enough, but the solution is quite volatile and insanely expensive, so the mechanism needs to be in a sealed chamber with a door that opens when needed and then closes automatically to seal the chamber.
The mechanism for moving the sponge plate was stolen from another of my fixtures. It's a shuttle moved by an air cylinder with bearings that ride in angled slots to raise and lower a platen, constrained so it can only move vertically. The sponge plate is attached to this platen.
Creating the football shaped sponges turned out to be quite a challenge. The low durometer 1/2" thick open cell foam they are made of is too soft to saw or even cut with a razor blade. I ended up having them cut with a water jet which worked quite well.
The fixture has a plate with a cutout to hold the plate and a trip lever to start the sequence. When the part is pressed into the pocket, it trips the switch which actuates a time delay relay which in turn applies air to the pneumatic cylinder that opens the door. When the door is fully open, it trips a switch which actuates another time delay relay to apply air to the double acting cylinder that raises the sponges and then retracts them. Once the sponge plate retracts, power is cut to the system and the spring loaded door is allowed to slide shut. The entire cycle takes about three seconds.
This stuff is great fun to design and build AND it keeps me out of trouble.
Tom
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