Optical quality injection moulded components

[Stella]

I am currently developing optical quality parts in polycarbonate for a bespoke application.<br>
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The part in question is a dome - used to house a camera. The 1st off tooling samples in optical grade polycarbonate exhibited macroscopic optical distortion as have the samples following some tooling rework and high level polishing. The tool material is Nak80 and the surface finish specification is SME1. <br>
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I am keen to find out what are the main points to be aware of when producing optical grade plastic parts - you know the general dos and donts.<br>
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Also, how much bearing the machining process and the process control of the tooling manufacture have to bear - how important for example is the tool cutting machine resolution in relation to the cutter path - similarly the programme. Is it necessary to ensure exact compensation for tool wear during the tool machining process to a level beyond that which is utilised for other parts. Is this an extremely specialised field? Any help, pointers, or names of experts in the field would be useful. <br>
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Any help appreciated.<br>
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Stella

 

[BrianDennis]

I also need to make an optical dome to house a camera.
I have not found a standard part, we need a 6&quot; diameter hemisphere for a gimbaled videocamera. I have already tried thermoforming PC sheets, which is 99% good enough, but we require extremely high clarity. (the surface seems adequate but there seem to be some slight internal variations which barely affect the optical clarity at maximum zoom).

Injection tooling is too expensive for us, and so I am looking into casting methods and prototype tooling.

Have you found any economical methods yet?

I suggest looking up

http://www.mxl-industries.com/

if you have not already.

Would like to know what you have learned so far...

thanks,

 

[troppo]

Hi stella
i was just curious as to why your making the camera domes out of polycarb wouldn't perspex give a better clarity then polycarb?you can also polish perspex.
in regards to the above maybe its somthing to do with uneven cooling of the product after molding only a thought.

for the second poster
a company called benthos(benthos.com) makes glass spheres for the marine industry i don,t know about there optical clarity and weather they have a cast mark in the centre maybe worth a look . they should be able to point you in the right direction if they don,t have what you want.
Ps this is marine gear so Big dollars.

 

[JGPOLYBENDS]

Stella,
Try GE Plastics website as they can help you in all aspects from designing to implementing.Best wishes
Chandrashekhar
chandra_jgp@satyam.net.in

 

[jason777]

I am an Optical Mechanic, if you still want some advice leave a message for me and I will write all I know. ps look into coatings (Multi-coatings)

 

[patprimmer]

Acrylic (perspex, Plexiglass, Oroglass etc) is somewhat more transparent than polycarbonate, and generally easier to mould and more scratch resistant, but also a bit brittle.

There is extensive knowledge on producing lenses and windows from it. (It was developed during WW2 for aircraft windows and canopies)

Suppliers such as Atofina or Sumitomo should be able to give technical advice on tooling and moulding.

There could be any number of tooling or moulding problems with your camera housing. Most common are:-
Change in shape when polishing
Poor surface finish after maching
(Your toolmaker might just go round and round machining to get shape, polishing to get finish, machining to correct shape etc)
Uneven cooling of tool
Poor location of gate
Moulded in stress
Damp moulding granules
Mould deposite buildup on mould
To much melt decompress
Splashing at the gate at start of injection stroke
Wrong grade of PC (mould release grades are not as clear)