Qunitax (5) Axis Router / MasterCAM 9.0

[sfdesign]

We received our Quintax Router a number of weeks ago and have yet to trim a "good" part. We had to address some machine issues, (painful) fixture issues, and post processer issues. With all those issues behind us, we are now focusing on the CAM software.

 

Our MasterCAM rep's have offered great support in the editing of our post. But we are still having some issues. By late this week we should be successfully trimming parts, fully programmed by MasterCAM. The post we have obtained is from CNC Software with some minor revisions to suit our application.

 

For the group trimming plastic, how do you compensate your cutter path for changes in part size (different shrink)? Those minor adjustments are very difficult.

[Guest CNC Apps Guy 1]

Does your router support 3D Tool Compensation?

[Christian Raebild]

I do not think 3D compensation is his problem. I think his problem is that plastic parts change shape due to stresses and heat to a much higter degree than metal parts. Do you have a solution for that problem, James?

[cadcam]

I sugesst better form tools and a better vacum on them to.

but you still get problems.

[sfdesign]

Our machine does support 3D tool compensation.

~~~~~~~~~~~

We are adjusting our forming process to ensure we have repeatable parts. In our start-up we had parts that varied by .06" - .125" in over all size. (we are trimming wheel liners)

 

It appears that our fixture has the difficult task of holding the parts that are slightly different. With the overall complex geometry involved, it is diffucult to hold the varying parts. Which in turn affects trimming and the problem is appearant when placing on the check fixture. The trim fixtures are holding our parts with about 20-23 inHg, and the perimeter is held well. So I am confident we are not facing issues there.

[Guest CNC Apps Guy 1]

At our company, we do Vacuum Forming and trimming with 5 Axis Routers. First and formost, a stable REPEATABLE process is foremost on the list. If your parts are varying up to .125, that seems a bit high. .030 or less is better. What profile tolerance are you trying to hold? Is there any way to get more Vacuum without collapsing your trimming fixture? Perhaps you nd to be holding more on the inside rather than around the periphery(sp?).

[sfdesign]

Our parts are HMWPE (apprx. 28" x 58" formed LH & RH), .030" is like impossible. When we open our "bay" door our parts change by .030". haha

We do "rough" trim the parts, seperating LH & RH for trimming.

 

What material and size are you thermoforming to hold a tolerance of .030" or less?

~~~~~~~~

Our vacuum seal is near the perimeter of the part to resist any cutter "chatter". The seal is just a few millimeters from the trim line, which allows the entire "interior" surface to be held by vacuum. When trimming is completed, the flashing falls off.

~~~~~~~~~

We are forming new parts, and more closely measuring our repeatability. I am not sure what tolernaces we will acheive, but it should be better than the proto's ran that were .06 - .125 different.

~~~~~~~~~

Today we made better progress, but ran into a wall. The Quintax Router will not rotate past -10 degress in the C axis. Before we adjust the post to compensate for this axsis limit. We need to find a solution from Quintax on how to correct this limit. (if possible)

[Guest CNC Apps Guy 1]

quote:

---

What material and size are you thermoforming to hold a tolerance of .030" or less?

---

I believe it's the tool (Aluminum) and the temperature/process stability that give us the repeatablilty. I'm not sure of the material(s). They're dark grey, and off white for the most part. I don't really spend too much time over on that side.

 

I know that while I was working for the Mastercam Dealer here, gstephens and I moved the hard limits on a couple of routers. Now they are +- 15 Deg. on the C-Axis which helps a TON.

 

You mention chatter, are you running straight flute E/M's? I'd stay away from those if at all possible. Nice sharp HSS seems ti work best though tool like is not great but carbide seems to heat hop the material more. I get you about the seal, that is the better way for your application.

[ERIC14779]

let me chime in on this issue

 

We have been forming plastic for 35+ years exclusively and I have been using cnc equipment to trim for 12 years.

 

as you know HMWPE has a shrink rate of .015 to .030 inch per inch average. I would never try to hold more than plus/minus .060" on a Polyethelene part.

 

Do you have a temp. controled mold (ie. water cooled) ?

 

Also Quintax should have told you that C can not go negitive (the post should not alow this either) in the literature shows C 0 to +360 and B -120 to +120.

 

I do not know of any way to compensate for shrink variance other than using the scaling funtion in the xxxxor Control.. MAYBE

 

my thinking is that if you calculated a zero pont in the geometric center of the part/fixture then posted a program and added the scaling funtion to the program to ajust from a nominal start point... that might work..

 

You have to control the temp of the part when it comes off the mold... a hotter part will shrink MORE and a cooler part will shrink LESS (after the part is off the mold)

 

I suggest that the part temp be 140 degrees F to 155 degrees F when it comes off the mold and that this temp be consistant all across the sheet. If you have a hot spot it will warp and shrink diff.

 

again maybe the scaling thing will work I do not know for sure.. if you have to control tollerances that tight you have to control the mold temp and enviroment temp / drafts ect. to be able to come anywhere close.

[Guest CNC Apps Guy 1]

quote:

---

you have to control the mold temp and enviroment temp / drafts ect.

---

This is probably the least thought of and least understood part of ANY manufacturing process "How will temperature affect ...".

 

I worked in a shop one time where my machine was right next to a roll up door where the sun would shine on half of the machine in the afternoon. I'll just asay that it was a real pain repeating to +/- .005 on a decent CNC with a Meehanite(sp?) Base. and in the summer time where temps woould approach 115 in the shop, it's a wonder we spent 25% of the time chasing offsets.

 

In our facility, where they do the Vacuum Forming, it's away from doors in the back where the temperaure varies maybe +/- 10 Deg. the whole day (it's ALWAYS hot back there) so that part of the process is stable, they have temperature monitoring on the mold as well. I'm not sure of the temps they hold but they manage to keep things stable and repeatable.

[ERIC14779]

thats right James

 

We consider Plastic forming an ART. You are right about the sun changing heat times. and we also tell our forming machine operators that (for the most part) when it is uncomfotable for the person that is when it is best for the forming machine. It is all because of drafts that are much more problematic when the ambient temp is lower.

 

sfdesign needs to realy check out what I said above.

[sfdesign]

I appreciate all the feed back. Our molds are water cooled and monitored for control. I am not sure exactly what our temperatures are. But will request that information be provied to me for review. Typically our process is much more repeatable in production mode. The parts provided here were from our prototype run. (less than a two hour run). So it was difficult to run consistant.

 

I do feel that we will be repeatable +/- .060 when we run again for production. (our machines are in the rear of the shop, away from any drafts)

~~~~~~~~~~~~~

In regards to the negative "C" axis. We stumbled onto that problem. And our post has since been adjusted to accomodate that value. That is part of our headache, the lack of a "proven" out post for the Quintax machine. We are certainly learning as we try to move ahead with programming. Fortunatly our MasterCAM dealer has been by our side assiting with all these issues. Or would be lost in the dark.

~~~~~~~~~~

I think the scale feature is something I may want to look into. I see a few potential uses for that type of function.

~~~~~~~~~~~~~

We are hoping to see some parts that fit our check fixture this week. Then we are moving onto another part number for programming. I am sure there will be issues there.

[ERIC14779]

Richard Taft at CNC has been working on a Quintax post for some time now and I/he think that it is working. I have a copy that I could e-mail to you if you would like.

 

e-mail me and I will reply with an attachment.