Newbie- Getting rid of tooling marks

[chet]

Hello all,

My company has purchased a Mulitcam CNC router to use in making small aluminum dies. We use the dies for making rubber mats in a compression press. I have a problem with tooling marks left in the Aluminum (6061-T6) and I need to know how to get rid of them. We have used a dial indicator to ensure the router head is perpendicular to the machining plane. We have tried finishing passes, using ball nose bits with extremely high overlap (98%) and we still get marks which are visible in the rubber on the finished product. I am using consumables such as small steel brushes, sanding disks, ets now but this is tedious, and comes in a high cost in both the consumable and labor. Any help would be greatly appreciated.

Chet

[BYTHEBOOKBOB]

Dear Chet,

If very low rms surface finish is not of high concern, you might try blasting the surfaces with very fine glass beads. This will help to even out the surface for you.

Good luck,

Bythebookbob

[Delw]

run a .002 or less step over 3/16ball endmill and your finish will be good when you run plastic in it.
if I need a really good finish I run .0005- .0002 step over I found that running smaller than a .025 -.030 finish depth of cut gives me the best finish on alumin. with small step overs.

of coarse thats with a decent sized endmill.

Plastic compounds are funny as what you are mainly seeing is basically and optical illusion cause from the light and shadows ir reflection.
you can mill a circle pocket and your finish is 8 or better and when you mold plastic into it it looks like its 150-250 finish by looks. the darker the color the worse it looks.

[mc_n_g]

I too make rubber compression moulds but for antique car parts. We make moulds out of 7075 and 2024 AL. We are luck that most of the final parts do not need to have the marks removed. We clean the mould up just to get rid of the big marks. One thing about rubber is it is like silicone and it picks up every blemish. There are too many questions to ask?
Have you tried radiused endmills rather than regular square endmills to minimize the toolmarks? How bad are the tool marks? Are you sure the machine and spindle are stable enough for aluminium cutting? Is your spindle moving too fast and galling the chips to the surface? Are you using coolant or cutting fluids?

When we do need to clean up the marks we use light bead blast with taped off areas or a Foredom flex shaft grinder with different heads. Use anything from rolled conical sandpaper replacable tips to rubber abrasive replacable tips to felt bobs with grinding compunds. If you can afford it a reciprocating die profiler is nice but expensive, time consuming and an art form.

mc_n_g

[MikeyL]

In my experience dies for rubber molding need to be ground in order to get a clean finish on the rubber.
Cheers
Mike

[Allen123]

Can you post a picture of some of the tool marks ?

[herbet]

You can use polishing stones or fine grit sand paper with a cutting fluid to polish the surface to a mirror finish. Takes some practice and time to get it right.

[MrMold]

Surface finish has many variables. Some you can control. others maybe not.
First start with the set-up of the part. Bolting the part to the table is most secure, however, if you have your part up on parallels you might find that it negetively effects surface finish. Also, if using a knee type mill make sure you have your knee up as high as you can and locked, letting your spindle "hang out like a sore dick" is a sure way to finish problems. I'd next look at your tooling and holders, Again you want to keep everything as short as possile. Try milling with a 3" long End Mill the with a 1" long one and you see my point.
Replacing collets of the tool holder might help, use solid tool holders when possible.
Carbide end mills will give you the best finishes.
Machining strategy will help, making rough cuts then light semi or finish passes. Employing some high speed machining strategies provided your machine has the spindle speed and travel speeds required will help also.
When having surface problems Start with set-up and tooling issues then your machining strategies for optimum performance.

[titan99]

Tool marks can't be totally avoided in moulding. Expect that and face it with further polishing. If you use high speed machining, tool marks can be virtually polished within 10 microns. It takes times and experience to get this. Always try to use bull nose cutter and ball nose cutters, this way the cutter marks will be minimal with better surface finish.

http://www.titanengg.com.sg

[jetski]

The problem you are trying to get away from "tool marks" in the injection molding we have to polish them out. You may be getting excessive ones because the head of the router is not sturdy enough for aluminum and is getting torqued and then cutting with one half of the diameter leaving a spiral mark in the aluminum. In most cases when we produce an aluminum tool we use carbide in a steel cutting machine. In a few min with a good polisher he can remove all tool marks in several square inches. He can also take air hardened H-13 to a mirror finish in a short amount of time. Let me know if I can be of any more help gsilberberg@progressive-plastics.net