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Active Contributor

Join Date: Jan 2006
Posts: 15

Accuracy That Can be Obtained in Plastic Moulded Component

02/17/2008 11:57 PM

Dear Friends,

I am working on a project where I need to maintain an accuracy on a plastic sleeve whose ID -104,thickness - 4mm and height - 43mm.( material currently used is nylon but looking for an alternative one for transparency like Acrylic or something) used for an assembly purpose where the Id dimension tolerance needs to be maintained within 70 ~ 100 microns.

The requirements of the sleeve is to be transparent and the dimensional stability during mass production is to be within 100 microns no further machining is allowed as the transparency will get disturbed due to machining.

Can anybody guide me in this regard.

Thanks

Shesh

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Power-User

Join Date: Feb 2008
Location: Newmarket, near Toronto, Ontario, Canada
Posts: 126
Good Answers: 2
#1

Re: Accuracy That Can be Obtained in Plastic Moulded Component

02/19/2008 12:44 PM

Dear Shesh,

Please confirm that this is an extrusion. If it is I might be ableto give you some advice on a process that uses flexiable steel spring inserts, which allow fineadjustments of wall thicknesses to tolerances that you are describing.


Mirco.

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#2
In reply to #1

Re: Accuracy That Can be Obtained in Plastic Moulded Component

02/19/2008 11:30 PM

Dear Sir,

First off all thanks for your interest in this.

Now the component requirement is around 5000pcs and after some intevals 1000 pcs may be required again.

currently I am trying to go with injection moulded process where the designeres say the tolerance of 70microns ~ 100microns cannot be achieved in the bulk production.

And if that is the case I may have to go for post machining process to achieve this size control.By doing this I may lose the transparency (if post machining is done)

You are suggesting Extrusion process which i had not thought off , please give me your suggestion I will try and give you the feedback.

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#3

Re: Accuracy That Can be Obtained in Plastic Moulded Component

02/22/2008 12:17 PM

Your designers are correct. You will be experiencing a concentricity problem where your part will be more oval than circular. A 4 mm wall thickness could also give you a problem in holding this tight concentricity for the size of the diameter you want. You may want to contact a molder that is an expert in molding gears since this part will probably have to be gated as if molding one (3 gates). With all this said, this is not the way to proceed.

Microconsultant suggested having this part extruded and he is correct. Cost wise you are looking at an extrusion die a fraction of the cost of an injection molding die. You just need a cut-off station and have the cut-off area polished, if necessary per your requirements.

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Power-User

Join Date: Feb 2008
Location: Newmarket, near Toronto, Ontario, Canada
Posts: 126
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#4
In reply to #3

Re: Accuracy That Can be Obtained in Plastic Moulded Component

02/22/2008 1:49 PM

Hello again,

I am not merely suggesting an extrusion process, but a new technology utilizing spring steel inserts at the point of extrusion, which allow for oval compensation as well as final sizing and wall thickness control. Please give some more info on the assembly process, surely when the part is assembled the ambient temperature could be changed to expand or contract either of the two components. Presumably the part was designed with a 3 - 5 degree draft angle to allow for ejection from the moulding process. This would alter the size of the fit. Obvously there are some constraints that you have that we are not aware of. Please elaborate.

If you need to contact me direct please mail to mircog@canstampconsulting.com

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