Numerical simulation of surface roughness in NX

[engtipsuser100]

Greeting everyone!

I would like to simulate the surface roughness of peripheral milling in NX.
This means I have to deal with cycloids in order to get the accurate roughness values, because the cutting edges of the tool are moving on a cycloid path.
I created a few of them using the law curve command, and then created a point at one of the intersections (see on fig. 1).

My goal is that, by changing the parameters of the law curves, get the actual roughness values by reading the y coordinates of my created point. I would like to repeat this in an automated way, to get the a roughness funcion.
My first thought was to use GRIP or NX Journal, because a saw a few solved examples on the forum:
#for k 1 to 1000 do
#[law curve parameter] := 0.1*k
#read point(x,y)
#write xls [k,law curve parameter,y coordinate]
#end
I scanned through the documentation of GRIP and NX Journal, and found myself a little bit lost in those languages. Could you give me a little help, how should I create a program like this?
Thanks in advance!

 

[cowski]

I assume the goal is to find the parameter(s) that give the desired roughness value. If this is the case, I'd look at doing this entirely in Excel. Given your equations, Excel's goal seek and/or solver add-in can find the parameter given the desired roughness value.

www.nxjournaling.com

 

[markrief]

What do the blue curves represent? The contact point? Or center of the tool radius?

Mark Rief
NX CAM Customer Success
Siemens PLM Software

 

[engtipsuser100]

Hello!

(Sorry for my late answer, for some reason, I wasn't able to access this site, meanwhile other pages were still available for me.)

My goal is to compare the theoretical surface roughness of endmilling (

http://www.custompartnet.com/image/machining/end-milling-profile.png)

and peripheral milling (

http://www.nzdl.org/gsdl/collect/cdl/archives/HASH01d9/c032cb62.dir/p05a.gif).

The blue curves represent the path of the teeth of the peripheral milling tool. It is a cycloid, because it moves forward and rotates. There are forumalas to do this, but I would like to make a more accurate simulation. (You can't calculate the intersection of the cycloids, because it leads to a transcendent equation, which can't be solved with algebra. So there are only approximating formulas.)

So I would like to generate cycloid curves, which I already did. I placed a point at one of the intersections. The y coordinate of the point would give me the maximum of the surface roughness. It would be good, if I was able to repeat this some automated way, so I don't have to set manually different parameters to the curves again and again - to get a proper roughness(feed) function.

And yes, maybe NX is not the best tool for this, but it would be so elegant (and also a great skill), if I was able to do it with NX.

 

[markrief]

In NX CAM, our simulation considers the spinning tool to be a revolved solid, and we remove the material based on that, so the surface would be smooth. I am still not sure I understand the exact conditions, but I think from a practical sense, the RPM of the spindle is usually so high that the spaces between the spinning teeth would not leave any raised scallops. I think you would need a very high feed with low RPM - is this what you are simulating?

Mark Rief
NX CAM Customer Success
Siemens PLM Software

 

[Mason321]

sounds like the OP is looking to calculate surface roughness at specified locations from milling cutter centerline.
much like Radial Chip Thinning Factor formula to help CNC machinists determine proper feed rates when not milling along centerline.
i would think this RCTF formula is derived from the graphic he just posted. (cool graphic btw)
nice chart

RCTF= sq RT of 1-(1-(2 x woc/ tool dia)^2)

 

[Mason321]

i frequently use cutters that in their preferred/ efficient use, will leave a finish so Rough it will make a Mill Bastard file look smooth as glass.
LOL

trying to simulate this function seem like i could turn quite complex, especially with the need to factor tool nose radii and interpolating outside and inside arcs/ curves / splines where the feed rate at centerline does not match feed at cutter OD. which prolly explains why no CAM company has bothered to simulate it when a machinist can just cut the feed in half for the finish pass if at first the surface finish is not acceptable.