need help creating molds

[mechman01]

Hello all,

 

I need some help creating molds. I have been using mastercam (V9) for just about a year and a half. All I have needed to do up until this point was program our thermwood routers to trim thermoformed plastic parts on a vacuum fixture. For about 2 months I have been tasked to start creating our own molds for thermoforming. I have created a few that turned out ok but I need more help.

 

Our molds vary in complexity. Most of the ones that I have created to this point have been fairly flat parts with 7 degree drafts on them. The part surfaces would come out smooth but the drafts would be rough and/or pitted. The drafts did't matter too much so they were used. Now I have to create more molds but they have a rolled edge that is about 5 degrees at its sharpest angle. And the current method I use will and has left the surfaces rough again.

 

We use thermwood 5-axis routers (unfortunately) to cut these molds. To me, they are too shaky but I guess they have to do.

 

My method for mold creation is as follows:

1.Surface Rough Pocket

2.Surface Finish Parallel

 

I have just recently tried the following method:

1.Surface Rough Pocket

2.Surface Finish parallel(top flat surfaces only)

3.Surface Steep Parallel(steep sides only)

 

I thought this would be good but it turns out when I ran number 2 then 3 the cuts didn't match and the tool dug too deep in at the abutting edge.

 

The following is what I use:

Mastercam V9 level 3

Thermwood 5-Axis router

Our own post for that router

Material: Renshape 450 from Vantico

 

So my questions, after this long novel I wrote, would be:

 

How do I cut on a steep level without the roughness and/or pitting?

 

If I must use multiple toolpaths, how do I blend them?

 

Will filtering the toolpath eliminate some of the shakyness in the router?

 

Could Ren cause the pitting?

 

I'm sure I will have more questions later.

 

Andy

[Guest CNC Apps Guy 1]

There is probably some porosity in the ren. Have you tried Surface Finish Scallop, or surface finish project???

[Eeyore-nonhuman forum member]

I make molds all the way (pure mold production and I stick to this ->

Surface -pocket

Surface ->contour

Surface ->shallow

Filtering will reduse a program size and speed it`s machining but will add aditional devation to geometry tolerance .

I use filtering all the way on all toolpathes settings (0.005 mm or less total tolerance ratio 2:1.

I do not have a router but my old retrofit (second machine ) SUX bweause of backlashes and other problems and I would never get smoothness and accuracy of my first machine ) .

I made molds on old big strong machines and on old slow and week ones , anythig that can hold geometry accuraccy +-0.01+- 0.015 mm total are good for plastic molds ,for alluminium and bronze it can be +- 0.02-+- 0.025 mm)

 

HTH

ETHH

[Dan_AKA_ROY]

Renwood will pit when machining flat surfs using flat endmills IF your feeds and speeds are too high. Slow them down to prevent "pitting".

 

Try Finish/Project/Blend [3D Along - thorough] or try quick if no steep vertical walls are present. If possible you can try flowline toolpath along your fillets. Or pencil toolpaths. Your geo shape, number of surfs, etc. determine the effectiveness of toolpaths such as finish flowline and pencil toolpaths.

 

Finish parallel toolpaths won't give you the results you want along the parts exterior edges or fillets. Surf rough pocket works well, but you may want to try a rough restmill also. And, add more finish toolpaths such as the ones I've mentioned.

 

Do you have Mold Plus? If not, look into it. Its well worth it!

 

quote:

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Could Ren cause the pitting?

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yes, its the reason as I've already mentioned. Its the renwood - thats why you see the pits. Like I said earlier, slow down your feeds and speeds. Do a test cut, observe how the pitting decreases at slower cut speeds. Eventually, when you got the right F&S, no more pitting will happen.

 

quote:

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How do I cut on a steep level without the roughness and/or pitting?

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Project Blend [Thorough], or Flowline and cut it SLOWER.

[cadcam]

mechman01, if you can throw one of these bad boys on the FTP and over the weekend, I will take a look and throw a few paths on it.

So you have some typ of refrence on some paths.

 

While I am programming two other Form Molds for a Customer.

 

Mold back round Plastic,Wax Investment,Die Cast,Roto molds,thermo molds,Tooling for foarming sheet metal..

 

Let me know.

[MACHINEMASTERG]

we use butter board for our thermoforming and we too get some pitting or porosity but we found a 2 part mix that is butterboard for pouring into a mould and we mix this up and fill in any voids then sand smooth maybe they have some thing simular for renboard????

[Travis_Buchanan]

You might also want to look at your tangency setting to reduce some of the shaking during machining. My post spits out a default G09 F8. I found that G09 F3 seems to work fair with our model 67 when surfacing with a 1/2" ball end mill on steep surfaces.

[mechman01]

Thanks everybody for the quick replies. I am trying a few out in MC to see what I like.

 

I have been roughing the ren leaving 0.080 inches left and then finishing it, taking the remaining 0.080 inches off. Is that too much in one shot?

 

I have put a file on the FTP server, it is:

 

MC9_files/MECHMAN01_MC9.zip

 

Once again, thank you all for the replies and I'll let you know how it goes.

[steve f]

mechman01,

 

you have the right idea using surface rough pocket for roughing out your moulds, that toolpath works for 95% of roughing applications. You may be allowing too much stock for finishing, try leaving .03" with smaller stepdowns so the cusps don't show up as much during finishing cuts. For finishing, there are some basic rules of thumb I follow for complex parts:

 

steep walls = contour

fillets = flowline

flat sloped surfaces = parallel

convoluted surfaces = scallop

flat floors = 2D pocket

 

cavities = cut inside to outside

cores = cut outside to inside

 

One trick I've used occasionally for complex surfaces that aren't particularily steep is to create a 2D pocket spiral toolpath from a chain defining the perimeter of the surfaces and then useing "surface finish project" to create a path similar to scallop except without the little stepover to keep constant load on the cutter...works pretty slick (similar to Delcam's "constant spiral offset" finishing toolpath if you know anything about the competition).

 

HTH,

 

steve

[mechman01]

I usually use a 1/4 inch ball endmill for my finish passes where applicable. Is this tool good for a finish pass?

[Keithm]

We cut a lot of ren shape. On steep slopes I use Parallel with it as a one way going down the slope. To keep the chipping down use a shape endmill instead of a ball nose. It takes a littl getting use to but they work well. The ren shape 5008 is the worst. The 440 and 450 machine good. To get any 5 axis cutting to lineup perfect you may have to abjust your work offsets a little if your machine is not in tram.

[mechman01]

quote:

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To keep the chipping down use a shape endmill instead of a ball nose.

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What exactly is a shape endmill?