Heat affecting accuracy

[rickcact]

We have a Mikron HSM 400U LP that was installed in early September of 2011. Everything went fine as far as accuracy goes, up until now. Come the erratic temperature changes of spring, I am having a tough time holding the tolerances (.0002). We get a temperature change of up to 15 degrees during the day so far. This is only the begining of whats to come as far as heat goes too!! We have 80's era air conditioners, which couldn't keep up with the cooling demands of the building.

I have tried to explain this to the owners before it was a problem. They are supposedly "looking into it". In the mean time, I still need to make good parts.

Has anyone else run into a problem with accuracy and heat? How have you overcome this problem?

 

 

Sorry about the first post, but I have not had internet at work in a few years( dont get me started on that on)

 

 

Thanks,

Rick

[GoetzInd]

What type of feature? Bore, positioning, contouring? What kind of material? .0002 is a tall order and I would say temperature control is a must.

 

 

Mike

[Guest]

I would say temperature control is a must.

 

 

^^^^^ +1

 

Material matters as well, Aluminum is more more susceptible to ambient temperature changes than many other metals.

 

You may need temp controlled room & a coolant chiller

 

Not quite enough info to be exact but thse are things you can run into.

 

I have seen guys keep gage blocks in a buck of water to keep them fairly stable for gage setting.

[rickcact]

regular old 420ss. Its a core for a suringe. Medical part. Injection mold part

 

It is contouring. Position is also critical obviously. The begining of the day is easy to hold that tolerance, but once the temperature is above 75 deg. its almost impossible to. Its a very detailed part, which takes 3hrs per part. I am pulling out my remainder of my hair on this job.

 

I would just do all the roughing in the afternoon, and finish the shutoffs in the morning, but the part is too irregular to do this, so the roughing and finishing need to happen in one setup.

[rickcact]

^^^^^ +1

 

Material matters as well, Aluminum is more more susceptible to ambient temperature changes than many other metals.

 

You may need temp controlled room & a coolant chiller

 

Not quite enough info to be exact but thse are things you can run into.

 

I have seen guys keep gage blocks in a buck of water to keep them fairly stable for gage setting.

 

 

Its a similar part that you helped me program during inhouse 5 axis training. Ivanhoe

 

 

Rick

[Guest]

Have you tried warming the machine up before running parts?

 

On my Mori's back when, when running tight jobs I ran them through a half hour motion and spindle cycle, the head would grow several .0001's once it was up to running temp it would stay all day

[rickcact]

Have you tried warming the machine up before running parts?

 

On my Mori's back when, when running tight jobs I ran them through a half hour motion and spindle cycle, the head would grow several .0001's once it was up to running temp it would stay all day

 

 

This problem is AFTER its warmed up. I run the preheatup cycle, and laser check the tool lenght before cutting too. 2nd shift has an easier time with them. I contribute that to the temperature.

[Guest]

This problem is AFTER its warmed up. I run the preheatup cycle, and laser check the tool lenght before cutting too. 2nd shift has an easier time with them. I contribute that to the temperature.

 

Yup, it sounds like the machine is not staying stable.

 

Is it possible it needs a longer warmup cycle and that what you're running it through isn't enough?

 

If it's continuing to warm after you've gone thru it, it wasn't warmed up completely.

 

It does sound like getting it into a temp control environment is going to have to happen.

 

On a side note, have you taken a good look at the process itself? Are you certain you're not seeing some variation based on the cutting conditions as well?

 

ON tight tolerance stuff, these things can start to compound

[rickcact]

My process is most likely part of it also. I am close to finishing the job, so I will have to work on that on the next one.

I am being pressured to get the job out the door (or at least out of the machine), so I am struggling through it.

 

here's the problem. It is leaving stock when it is hot in here, but when its cool I can hold size very well. Almost like the tool is too warme up and cools off during the cut. That tool is 2 hrs into the program, so it is difficult to adjust for it.

[#Rekd™]

Hard to even measure accurately if your shop is not climate controlled. Coolant temperature is also a factor if you are using coolant.

 

The high end machines have thermal compensation built into them to account for temperature changes.

[YoDoug®]

If the machine has a probe and there is enough room for a reference artifact in the machine you can use that to help do real time checks for part growth and comp.

[Joe788]

I'd try coolant temperature control first. Obviously air conditioning the whole shop is the best choice, but depending on your shop, that might be $30-$100K. Cooljet makes a coolant temp control unit that's about 10K-15K if I remember correctly. (Even that is pretty overpriced for what you're really getting). This can be a pretty big deal. The Mori salesman told me about one of their customers running an NH4000 with aluminum tombstones, in an un-airconditioned, un-insulated, metal shop. Keep in mind, the valley goes from 65º at 6am to 105º at 4pm. They were seeing .008-.010 growth in the Y axis, from the aluminum tombstone expanding and getting taller throughout the course of the day. They added a coolant temperature controller, and completely solved the problem.

[GoetzInd]

If the machine has a probe and there is enough room for a reference artifact in the machine you can use that to help do real time checks for part growth and comp.

 

+1. Although that would be on the edge of even our MP700.

 

Mike

[Newbeeee™]

As the guys have already said, I'd look at the coolant. Get a cheap thermometer and put it in the tank and monitor it against your shop ambient temperature every 1/2 hr.

If it is the problem, your gunna need a chiller unit.

 

Also I might have miss-read, but are you using just the one tool for the 3hr of cutting? If so, tool wear and heat going into the part becuase of it?

[Joe788]

+1. Although that would be on the edge of even our MP700.

 

Mike

 

Yep. Trying to measure the thermal expansion of a thermal expansion controlled cast iron and steel machine through a 15 degree temp swing, with a 6 inch long, thin walled piece of aluminum is always

[Guest CNC Apps Guy 1]

I'd reccommend coolant temperature stabilization first. Eliminating that variable in the equasion could solve it. Maybe not, but there's a solid chance it will and it's relatively cheap considering the cost of updating/upgrading A/C in a machine shop.

 

Holding .0002" is a challenge in the best of circumstances, add ambient air temperature fluxuation into the mix and you'll be yanking hair out by the handfuls.

 

JM2C

[mcpgmr]

Can you dynamically adjust lead compensation and static offsets in the machine? I programmed some 80's era Sundstrand Omni Mills back in the early 2000's. We had no AC and the temperature and humidity would change drastically throughout the day. I would have to monitor following error and adjust the machine several times a day just to keep the machine from trapping out. Have you called the machine tool builder? There are tons of shops out there without AC that manage to make good parts. Might be worth a try. Good Luck.

[Guest CNC Apps Guy 1]

There are tons of shops out there without AC that manage to make good parts. Might be worth a try. Good Luck.

Tons of shops holding .0002 contouring (not on diameter) all day long??? Really?

[Bruce Caulley]

Why not look at putting AC just inside this particular machine? Cheaper than doing the whole workshop.

 

Bruce

[rickcact]

First I want to thank you all for your resopnses. But most posts were on Sunday? I am also going to appologize for my spelling and my proper (or inproper) use of grammer. I am a toolmaker, not an english major.

 

Anyhow, to answer some of your questions. I dont know how to do the multi question quote like I have seen before so I have to go by memory...

 

 

There are multiple tools cutting this part. The finish cutter (that has to hold the .0002) is the 3rd of 7 cutters. The unfortunate part is that the part has been roughed to within only .01-.015/side. I am roughing then semi-finishing. Like I said before, it would be ideal to rough all the parts and then finish all of them, but in this case I am unable to.

 

I am not using the coolant. Just a mix of air and oil.

 

The machine does have thermal comp, but I dont know enough about it to give an educated answer.

 

The machine is in the same room with older( early 90's era) machines, also mixed into the bunch is a mori seiki millturn, that has a chip blaster unit attatched. That unit could heat the whole room in the winter by itself. With the chiller on the 5 axis, along with the millturn, it made it almost 75 this last winter.

 

 

The machine does have a probe, along with the probing inspection program installed. Unfortunately, up to this point, I have not had time to learn the 5 axis probing with it. I have a gage that I install over the part to measure "drop". That determines my size. I check it in the machine against gage blocks.

 

This job should be out of the machine late this week, so I think I will have some breathing room to get some more advanced training on the machine

 

I have, along with a few other workers, complained that it is not realistic to even come close to those tolerances consistantly without some sort of a/c upgrade.

 

 

Thanks,

Rick

[bob flat]

get the hand book and look up thermal expansion. a 16 inch piece of steel will change .001 inch with 10 degrees of temp change. i can hardly detect 10 degrees of change with my hand.

[Kevangel]

Oh My Gosh..they want you to hold .0002 without air conditioning??? I build gages with my shop kept at 68F...You need to look up linear coeffcients of expansions per degree growth above 68F and per inch...then talk to your Boss.....I have 2 Moore jig grinders and Moore has heaters in upper head which keep them at 85 F even in a 68 degree shop. Sort of preheating to the highest tempreature they will raise to.. If time and Money are short I might look at framing machine in and air conditing that room with wal-mart window units....even wood and visqueen or drywall and just tape joints..nuthin fancy....

 

Heating the coolant to the highest machine temp might be the way also...some small electric heaters blowing on machine at night with thermometers on machine table..MSC sells them and I keep one on my surface plate in the lab at all times..cause I am sort of a hillbilly Gage shop now....was building Molds,Parts, etc..all gages at the moment. Putting some thermometers around on machine will help figure out what is happening..$100

[Kevangel]

get the hand book and look up thermal expansion. a 16 inch piece of steel will change .001 inch with 10 degrees of temp change. i can hardly detect 10 degrees of change with my hand.

Gagemakers use their Lips..most sensitive part of the Body...looks weird..

[Kevangel]

If you machine your part and its NOT 68F degrees and its inspected at 68F in Lab it will have changed..... .0002 is not much...I had 2 customers that claimed to build high production Molds like Gages and .0001 callouts on their prints...I did some Jig Grinding for them, and some EDMing etc and they were out over .001 at times. If your out 10 millionths on gages they might get rejected..

 

on the lip comment..you touch your lips to a 1-2-3 block thats 68 F and then your workpiece to compare....no comment on Germs..

[rickcact]

***update****

 

There has been 2 commercial A/C contractors in the shop in the last week. I just hope they get one installed before the hot weather hits.

 

Thank you all for the help.