Plastic cam with spring as follower
Plastic cam with spring as follower
(OP)
Hello. I am a first time poster, and, as such, I am hoping this is the correct forum to post this in. If not, would someone please kindly show me to one that is more appropriate?
I am working on eliminating metal springs from a design for a linear peristaltic pump for medical purposes. The current design involves two plastic cams, each with two followers attached to them. Springs are placed over the followers to press against a metal covering that goes over the cams, so that there is enough force to operate the pump correctly. What I'd like to do to remove the springs is to make the cam followers themselves the spring. Currently, the cam and followers are one injection molded piece. This aspect needs to remain the same, just with the followers as plastic springs instead of straight rods. Is this something that can be injection molded? Has anyone ever seen something like this done before, and if so are there any pictures I could look at to help with my design? Also, what kind of material would be best for something like this?
I am a recent graduate and am new to my company, so I am trying to do all that I can to impress my superiors. Any help at all would be greatly appreciated! Thank you.
I am working on eliminating metal springs from a design for a linear peristaltic pump for medical purposes. The current design involves two plastic cams, each with two followers attached to them. Springs are placed over the followers to press against a metal covering that goes over the cams, so that there is enough force to operate the pump correctly. What I'd like to do to remove the springs is to make the cam followers themselves the spring. Currently, the cam and followers are one injection molded piece. This aspect needs to remain the same, just with the followers as plastic springs instead of straight rods. Is this something that can be injection molded? Has anyone ever seen something like this done before, and if so are there any pictures I could look at to help with my design? Also, what kind of material would be best for something like this?
I am a recent graduate and am new to my company, so I am trying to do all that I can to impress my superiors. Any help at all would be greatly appreciated! Thank you.






RE: Plastic cam with spring as follower
Acetal (polyoxymethylene) is about the best for creep in it's unfilled state. Still nowhere near metals though...
H
www.tynevalleyplastics.co.uk
It's ok to soar like an eagle, but weasels don't get sucked into jet engines.
RE: Plastic cam with spring as follower
You got trouble enough just getting a linear peri pump to work. Steel springs are cheap and dependable. By all means, check the design of the ones you have, and improve that if you can, but you don't want to be explaining to the FDA why you decided to use plastic springs in a medical device.
Here's a hint: If you cite that you did anything, ahem, 'creative', in order to save money, that's the end of the discussion with FDA; all that remains to decide is who gets to write the recall letter.
Mike Halloran
Pembroke Pines, FL, USA
RE: Plastic cam with spring as follower
RE: Plastic cam with spring as follower
As for that vendor, I have been buying Lee springs for a very long time. I trust their metal springs to behave pretty much as described, and their stock metal springs to be damn close to optimal for any properly designed application.
However that product is new to me, and I suspect to Lee also.
I might order a few hundred just to mess around with (did I mention that Ultem is expensive? ), but I'd be very hesitant to put it in a medical product until it's got fifty years of history behind it.
Is there some compelling factor that would cause you to prefer plastic coil springs over metal?
Mike Halloran
Pembroke Pines, FL, USA
RE: Plastic cam with spring as follower
I was tasked to develop a few ways to "poka-yoke" the design so that the springs (which are essential to the proper function of the pump) cannot be left out or forgotten. This was my best idea, apart from simple process controls like checklists and kitting the springs, which don't guarantee the springs actually made it into the part. However, with the high cost it looks like it will take to produce such a part from a plastic, the X-ray is starting to look like less of an issue. Here's to hoping my boss sees it the same way!
Thank you for all of your help.
RE: Plastic cam with spring as follower
As in:
It might take an analytical balance to get the resolution to detect a single missing spring, but try weighing the subassembly.
Add inspection ports so you can see the springs in the assembly.
Arrange it so that some portion of every part reaches the outer perimeter of the assembly, as in buying coil springs with a tangential 'tail' at one end, like a torsion spring's tang, that projects through a hole. Similarly for molded leaf springs; you can even use contrasting colors.
Use an automated spring dispenser at the assembly station; set it up to count the springs per assembly as they are dispensed.
Use an automated dispenser to fill a 'pallet', visually inspect that the pallet is full, and use the pallet to drop in all the springs at once.
Use an automated spring dispenser to feed a robot that places the springs; robots don't get tired or forget a step in their jobs.
You can surely think of more...
Mike Halloran
Pembroke Pines, FL, USA
RE: Plastic cam with spring as follower
Just my 2 cents.
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Plastic cam with spring as follower
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Plastic cam with spring as follower
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