Burr removal from Ticona Fortron molded part

[Jaymant]

Hello,

I have a molded part which is made of Ticona Fortron (40% glass). This part has a thru hole which is 0.018" in diameter and 0.0625" long with burrs (flash) on one end. I am considering using liquid honing on the part. This system would be used in a completely automated system. If anyone could suggest a supplier or alternative method to remove this flash, I would appreciate it. We have already tried a hard tool without success. Thanks.

Jason

 

[patprimmer]

Have you tried fixing the mould or moulding conditions so that it doesn't flas in the first place

Regards
pat

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[Jaymant]

The mold is not our own and can not be changed due to the complexity of the tooling. The flash is roughly 0.0005 in size.

 

[unclesyd]

Damn, Why can you have a larger flash?

What shape is the flash a feather, nub, raised edge. We did tumble and vibratory finish some parts. These were not very complex and the flash was fairly large.

Are you molding the part or you having contracted out.
I know we worked with a vendor on similar problems on Ryton parts with flash, a little larger. All I know is they worked on the process, pressure, temperature, filler % and got rid of most of the problems.

The engineer that worked to resolve the problem is long gone and I can't get to his reports.

 

[patprimmer]

Can it be removed with a quick pass of a flame, or does this leave a blob in the wrong place.

Can you push an 0.017" rod through the hole. Does the flash break clean.

When you say hard tool, do you mean that you tried to machine it. if so, why did it not work.

Regards
pat

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[unclesyd]

patprimer,
We talked to Surftan and they didn't want to try any thing like PPS, we used Ryton.

 

[GregLocock]

Can you describe where the flash is occurring more accurately, ie is it across the end of the hole, or is it a continuation of the 'hole' proud of the pierced surface?



Cheers

Greg Locock

 

[patprimmer]

unclesyd

I guess Surftan is a company involved in flame treatment

I don't know which PPS is isotactic and which is atactic, but it afects there properties slightly. As I understand it Fortron and Ryton are different types of PPS.

At ,0005" the flash probably contains no glass fibre.

I presumed the flash was accross the end of a pin that was not blanked off correctly, but it might be down the side as Greg suggests.

I still wonder why vibration, rumbling or countersinking the hole slightly won't work.

Can't the pin be lengthened 0.001". This is really a very minor modification.

Regards
pat

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[patprimmer]

Would nylon 4.6 do for your part.

It has a better HDT than PPS and is easier to mould, and is especially easy to mould re elimination of flash

Regards
pat

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[Jaymant]

To clarify and answer some questions:

The part has two inner diameters. The large diameter is 0.098", 0.777" deep. The small diameter is 0.018", 0.045" long.

This part is used in most anti-lock braking systems.

The flash is a feather, 0.002" long, occuring at the entrance to the small hole, generally pointed towards the center of the hole, sometimes pointed away from the small hole, towards the large hole.

The part is molded by our customer. We have developed a FULLY AUTOMATED system to process the part.

The material can not be changed.

A flame can not be used and the inside of the hole can not be touched.

The part can not be tumbled as there are too many "Class A" surfaces on the outside.

We are currently machining the flash. This is sometimes chattering and at times creates a chamfer which is too large for the customer.

 

[patprimmer]

You have me scratching for ideas, as you just ruled out every method I know.

I can only suggest to continue with the machining. With good attention to detail on the cutting tool sharpening angles. you might improve reliability.

You keep saying that you can't do anything to fix the problem, but you want the problem fixed.

As this is a brake system part, failure to function correctly might lead to some very expensive litigation.

I am guessing that the pins come into the hole from each end, and blank off against each other.

I am now guessing that the flash is in an area where a large and a small pin but up to each other. The pins will build up heat, depending on the section thickness of the plastic part where the part touches the pin, and on the aspect ratio of the pin. This heat build up in the pins will be more than the rest of the mould, causing the pin to expand more than the mould. This extra expansion means the pin cannot reliably blank off all the time.

If this is the case, an isopipe down the pin might control it's temperature, and therefore it's expansion, giving a more reliable blank off.

Another possibility would be to use a stepped pin from one side only, but maybe this has problems extracting the pin from the moulding, and would only serve to move the flash to where the pin blanks of on the wall of the cavity.

Is the flash were I am presuming, or is it at the surface of the moulding.

As I said earlier, pins are cheap and easy to modify, if the flash is at the point where the two pins butt, why not put a hole in the biggest pin, to accomodate a longer smaller pin as a spigott.

It is difficult to analyse problems when the description is limited. Looking at parts, or at least photo's and drawings greatly assists.

Regards
pat

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[Jaymant]

Pat, you do seem to understand the part and the mold quite well. When I say that we "can not" do something, this is because the process is customer driven and also driven by their customer. If you would like to give me your e-mail, I can send you an image of the part. I don't think you can post images in the forum can you? Thanks for your help.

Jason

 

[patprimmer]

You can post images. I have seen it done, but I don't know how.

My new e-mail is pjprimmer@optusnet.com.au

Regards
pat

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[CoryPad]

Scroll down near the bottom of the page to the [blue]Your Reply[/blue] section. Under [red]Step 2 Options[/red], there is a link named [blue]Process TGML[/blue]. Click it and it will show you how to post images. One comment - you must host the image on another server (not at Eng-Tips).


Regards,

Cory

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[HDS]

Jaymant
look at the customers drawing for the part. What is thier tolerance for the hole. If it is out of spec find a way to have your quality department respectfully bring it to the atention of thier quality department.
Your other option is to give them a cost reduction. If you can eliminate the machining step you can save them money. If the only way to eliminate the machineing is for them to mold a better part they might go for it.

good luck, the nontechnical problems are allways the hardest to solve.