Best Way to Remove Knife Edge from Molded Parts

[CPosner]

Hey Gurus,

I'm doing a production run of some glass-filled PP parts. I'm getting a knife edge at the parting line that needs to be polished down to a small chamfer/fillet. Due to the geometry,schedule, and cost, we cannot change the mold.

Is there any special abrasives that will not leave any residue on the parts, machinery, or tools that will quickly and consistently polish the knife edge? Costs need to be low and quantity is less than 10k pieces.

Currently, the most effective way is with a sanding block and person doing each part by hand. There are inconsistencies and time involved. I was thinking about maybe a special heated tool that will melt the edge of the parts that will quickly melt down the knife edge.

Any ideas are appreciated.

Thanks In Advance.

 

[patprimmer]

I presume you are trying to describe flash at the parting line.

The typical method is with a simple knife or sometimes a special shaped blade.

Sometimes moulding technique and material grade selection can eliminate or reduce it.

A machine with clamp capacity to spare and good injection stroke control helps a lot.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[CPosner]

Thanks, but it's more than just flash. The actual flash is very minimal and can actually be removed with a finger nail. The molding facility wanted to avoid knives if possible. The part itself has a sharp edge around it's perimeter which coincides with the parting line. It's the part geometry.

 

[Pud]

Try "flaming" it - a brief pass over with a small butane/propane blowtorch. Works with unfilled PP - glass may be a problem.

H

www.tynevalleyplastics.co.uk

Got nothing to say? - say it on Facebook®

 

[patprimmer]

http://safetyknife.net/safetytrim500.htm

This is just one of the designs that virtually makes it impossible for a worker to accidentally cut themselves if that's the issue.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[ornerynorsk]

You say the part itself has a sharp edge that is part of the geometry, yet you want to remove it? Do you need to de-flash and maintain a degree of sharpness, or is the sharpness due to excessive parting line erosion?

If you are material safe on the tool and have the tolerance on the part, the parting line faces can be re-ground to help eliminate flash.

A picture or drawing would help greatly.

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.

 

[CPosner]

It's easier to show with a shot from the 3D model. I've highlighted the edge that needs to have the edge rounded over slightly. There is minimal, if any, flash on the parts coming from the mold.

I understand that we could have put a radii on the part and then shift the parting line up. Likely, down the road we will make this change.(When time/money permits)

We're going to try the safety knife and will report back, but still open to trying other things.

Thanks.

 

[ornerynorsk]

Are the parts consistent enough to hold them in a cavity fixture with vacuum and route the edge? The fixture could be as simple as an mdf vacuum chuck with multiple pockets cut into it.

My other thought is tumbling, but that will likely cause a very disagreeable surface finish on glass PP. Years ago the factory that I made a number of transfer molds for did de-flashing by freezing their elastomeric and rubber parts and tumbling them.

Just a couple of thoughts.

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.

 

[patprimmer]

It kinda looks like a surf board fin.

To mould the dad on the leading edge you need to cut a cavity in the other half as well. I agree that substantially increases the cost of tooling.

The safety knife is the way to go if the rad or chamfer can be small and precision is not required.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[CPosner]

We actually discussed routing the parts, but that would be too costly at this stage. Will keep that in mind.

Pat, yes, it kinda is!

We will try adding the fillet to the flat side on our next parts. Like .010" rad.

For now, looking forward to results of the safety knife.

Thanks

 

[Demon3]

I want to make sure you didn't miss Pat's suggestion to apply a flame briefly. It appears that was overlooked and I think it's definitely worth trying.

Chris DeArmitt - PhD FRSC CChem
Plastic & Additives Webinars
Instant Downloads & Inexpensive

http://www.plastictraining.com

 

[HDS]

Use a deburing tool. They even make them with special blades for plastic parts.

http://www.mcmaster.com/#bur-tools/=irv8dq

 

[CPosner]

Flaming the parts is still an option to try. Is there a fixture/setup/guidelines/temperatures on how to do it properly?


I tried some deburring tools and they did not yield consistent results. Sometimes the blade will really dig into the edge and gouge it., but a B-70 style looks promising.

 

[patprimmer]

Flaming is really a mater of trial and error to set the conditions. It usually involves a gas torch and some operator skill re adjustment of flame, distance of flame from job and speed of traverse.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[HDS]

I've had that problem with the deburing tools also.

Scotchbrite is also an option. You will have to find the right grade through trial and error.