Positining error in new hmc

We purchased new hmc[ Doosan hm 1250 W] machine 6 months ago
Machine is fitted with heidenen linear scale.

We are machining injection moulding platens in which postining accuracy by boring is required within 20 micron (0.001") from centre hole.

when we machined 2 holes at 500 mm centre distance then in inspection on trimos height master we get centre distance about 499.940

All centre distances are 50-60 micron minus in both X and Y axis in all jobs over 500mm

i just checked geometey on 1 meter granite and all readings are fall within 30 micron so i do not know the reason behind this error.

Someone tell me to do laser calibration for improvment of positining accuracy.

So in this closed looped system with heidenen linear scale machine gets all readings from scale so pitch error in ballscrew effects positining accuracy of machine in closed loop system??

In india temperature variation is very high so all data for pitch error compensation vary from company calibratin(i think so..!!)

please give me some suggestion.

thanks in advance

9106872762 said:

We purchased new hmc[ Doosan hm 1250 W] machine 6 months ago
Machine is fitted with heidenen linear scale.

We are machining injection moulding platens in which postining accuracy by boring is required within 20 micron (0.001") from centre hole.

when we machined 2 holes at 500 mm centre distance then in inspection on trimos height master we get centre distance about 499.940

All centre distances are 50-60 micron minus in both X and Y axis in all jobs over 500mm

i just checked geometey on 1 meter granite and all readings are fall within 30 micron so i do not know the reason behind this error.

Someone tell me to do laser calibration for improvment of positining accuracy.

So in this closed looped system with heidenen linear scale machine gets all readings from scale so pitch error in ballscrew effects positining accuracy of machine in closed loop system??

In india temperature variation is very high so all data for pitch error compensation vary from company calibratin(i think so..!!)

please give me some suggestion.

thanks in advance��

Click to expand...

This particular question seems to come up / come back on a periodic basis.

There are a few threads that deal with pretty much the same core issues.

I can dig around later to find you suitable links.

Setting aside shaft wind up issues on really long ball screws,

1. Your scales expand and contract at a different rate than the machine.


Unless you have serious thermal compensation for the scales themselves i.e. temperature sensors in the scales and temperature sensors in the frame of the machine and the means to compute and compensate these differences on the control then stuff is really going to drift.

2. Your scales can get you in the right ball park but is no substitute for climate controlled metrology of your inspection department.

IF you have major changes in shop environment and different machine conditions , coolant , heat build up etc. you may have to have thermal data loggers in your shop.

Between inspection / CMM and thermal mapping of your shop and machine it is possible to close the gap on all that. But you may have to tweak your programs and CAM files and intermediate part geometry to compensate for various distortions i.e. program inverse distortions to the normal part geometry so the parts "Come out" mostly corrected.

There are in process "artifacts" / physical gauge bars (of different materails and geometry) that could also be probed for on the table gauging. I'm not sure what kinds of programs you would have to run to scale accordingly for thermal distortions ? Non linear distortions from clamping and materials can be mapped out but more time consuming "Project"

Can you build a partially thermally controlled sub space in your larger machine shop / warehouse ?

Sometimes a cheaper option if all else fails ?

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Temporary place holder

What does the foundation look like ? Did you follow the Manuf's guidelines, and no skimping ?

Have you checked the levelling lately ?

9106872762 said:

We purchased new hmc[ Doosan hm 1250 W] machine 6 months ago
Machine is fitted with heidenen linear scale.

We are machining injection moulding platens in which postining accuracy by boring is required within 20 micron (0.001") from centre hole.

when we machined 2 holes at 500 mm centre distance then in inspection on trimos height master we get centre distance about 499.940

All centre distances are 50-60 micron minus in both X and Y axis in all jobs over 500mm

i just checked geometey on 1 meter granite and all readings are fall within 30 micron so i do not know the reason behind this error.

Someone tell me to do laser calibration for improvment of positining accuracy.

So in this closed looped system with heidenen linear scale machine gets all readings from scale so pitch error in ballscrew effects positining accuracy of machine in closed loop system??

In india temperature variation is very high so all data for pitch error compensation vary from company calibratin(i think so..!!)

please give me some suggestion.

thanks in advance��

Click to expand...

1.
Linear scales as such do not assure positioning accuracy. It is mandatory to perform pitch error compensation activity with laser interferometer. During this process air temperature and machine temperature are scanned and taken into consideration while generating the correction parameters values. This process is supposed to reference the machine axes accuracy in temperature of 20 degrees Celsius.

2.The temperature fluctuations have severe impact on produced parts accuracy. In vast majority of cases the linear scales expand and shrink along with the machine body, quite rarely scales with low or zero temperature expand coefficient are used. The machined material itself (I believe in this particular case steel, expansion coefficient of 9 micro per meter per Celsius degree) is subject to these changes too. One must be aware about difference between part temperature while being machined and while being measured in quality control room.

3. In general, one should not expect high parts accuracy when machining process is performed in environment not temperature controlled. Air conditioning in such cases is mandatory.

i dont think so we can build thermally controlled subspace

but can you tell me
ball screw pitch error compensation effect positining accuracy in closed loop system with linear scale or not?

we get 50-60 micron error in centre distace of 500 mm 2 bore from starting(after installation of machine) and i am prerry sure that CMM results are accurate.

i think i am expecting to much accuracy from brand like doosan beacuse it is not a mazak,makino..!!!

yes foundation is as per guidelines and there is no change in level.

i checked all geometey readings 3 days ago

table flatness is within 30 micron
xy, yz,xz squareness are also within 30 micron on 1 meter granite

i do not think it is a geometry issue...!!

9106872762 said:

i dont think so we can build thermally controlled subspace��


i think i am expecting to much accuracy from brand like doosan beacuse it is not a mazak,makino..!!!

Click to expand...

I would say the first part is your problem and not the second. I don't see how you can expect anything to repeat with large temp swings.

PROBE said:

1.
Linear scales as such do not assure positioning accuracy. It is mandatory to perform pitch error compensation activity with laser interferometer. During this process air temperature and machine temperature are scanned and taken into consideration while generating the correction parameters values. This process is supposed to reference the machine axes accuracy in temperature of 20 degrees Celsius.

2.The temperature fluctuations have severe impact on produced parts accuracy. In vast majority of cases the linear scales expand and shrink along with the machine body, quite rarely scales with low or zero temperature expand coefficient are used. The machined material itself (I believe in this particular case steel, expansion coefficient of 9 micro per meter per Celsius degree) is subject to these changes too. One must be aware about difference between part temperature while being machined and while being measured in quality control room.

3. In general, one should not expect high parts accuracy when machining process is performed in environment not temperature controlled. Air conditioning in such cases is mandatory.

Click to expand...

thanks for your information

yes you are right...!!!
i can not expect high accuracy in open environment

and air conditioning for this type of 33 ton big machine is not economical particularly country like india

so my last option is laser calibration of the machine and see what it will effect on positioning accuracy...!!!

How about leave a couple thou then probe the 2 holes then make adjustments to the part finish the bore to spec
Don


Sent from my iPhone using Tapatalk Pro

9106872762 said:

yes foundation is as per guidelines and there is no change in level.

i checked all geometey readings 3 days ago

table flatness is within 30 micron
xy, yz,xz squareness are also within 30 micron on 1 meter granite

i do not think it is a geometry issue...!!

Click to expand...

You can test the what looks to be the consensus.

Just take the Trimos out to the machine and measure the part on there. With a suitable temp normalization period of course. Some of the newer Trimoses are aluminum though FYI.

Man, I wince every time I see GENERALDISARRAY.

Always think it's Generic Default....

BIG difference, though.

PROBE said:

2.The temperature fluctuations have severe impact on produced parts accuracy. In vast majority of cases the linear scales expand and shrink along with the machine body, quite rarely scales with low or zero temperature expand coefficient are used. The machined material itself (I believe in this particular case steel, expansion coefficient of 9 micro per meter per Celsius degree) is subject to these changes too. One must be aware about difference between part temperature while being machined and while being measured in quality control room.

Click to expand...

In many cases the actual linear scales on machine tools are a grating "printed" onto a low CTE glass sheet, which is then mounted within a protective enclosure in a way to minimize stress and displacement on the scale due to temperature excursions.

If this is the case with the IN machine, then ideally at least two compensating laser measurements should be made at different temperatures (with the machine having a chance to equilibrize at those temps). Near the max and min temps would be best, and better still additional readings to "fill in the gaps" so that a proper correction table could be made.

I join everyone else in saying that a proper controlled environment is best, but understand the finances and logistics may not (don't) work. Gotta do what ya' gotta do...

It may appear like Cato the Elder's preaches, but once more the comparative measurement will assure best results.
Have a master piece, made from material similar to the machined, installed just next to your piece. Have 2 holes machined in the master, distance 500 mm. Cool down the master in quality control room. Have this distance measured , notice the result (499.069 for example, deviation -0.031).
1. Cut the first bore.
2. Get probe, set the WCS in the center of it.
3. Using the probe, measure the distance between 2 holes on master piece (due to material expansion in working environment temperature, 500.02 for example).
3. Command the machine to move just measured distance with addition of master deviation(in our case 500.02 + 0.031). This is the coordinate of the center of second bore.

This method assures continues in tolerance results of the distance between the bores, regardless of temperature changes.

PROBE said:

It may appear like Cato the Elder's preaches, but once more the comparative measurement will assure best results.
Have a master piece, made from material similar to the machined, installed just next to your piece. Have 2 holes machined in the master, distance 500 mm. Cool down the master in quality control room. Have this distance measured , notice the result (499.069 for example, deviation -0.031).
1. Cut the first bore.
2. Get probe, set the WCS in the center of it.
3. Using the probe, measure the distance between 2 holes on master piece (due to material expansion in working environment temperature, 500.02 for example).
3. Command the machine to move just measured distance with addition of master deviation(in our case 500.02 + 0.031). This is the coordinate of the center of second bore.

This method assures continues in tolerance results of the distance between the bores, regardless of temperature changes.

Click to expand...

thanks for your advice!!!

I don't know if I would trust a trimos. Can you check it against gage blocks or a ring gage or some other known standard to verify accuracy?

That's where I would start.

PROBE said:

It may appear like Cato the Elder's preaches, but once more the comparative measurement will assure best results.
Have a master piece, made from material similar to the machined, installed just next to your piece. Have 2 holes machined in the master, distance 500 mm. Cool down the master in quality control room. Have this distance measured , notice the result (499.069 for example, deviation -0.031).
1. Cut the first bore.
2. Get probe, set the WCS in the center of it.
3. Using the probe, measure the distance between 2 holes on master piece (due to material expansion in working environment temperature, 500.02 for example).
3. Command the machine to move just measured distance with addition of master deviation(in our case 500.02 + 0.031). This is the coordinate of the center of second bore.

This method assures continues in tolerance results of the distance between the bores, regardless of temperature changes.

Click to expand...

I agree,

This is about all you can do in a situation where thermal stability is unavailable.
500mm centre distance is large to hold 20 microns, unless everything is just right.

Milland said:

...with the machine having a chance to equilibrize at those temps.

Click to expand...

Did you just invent a word?

Booze Daily said:

Did you just invent a word?

Click to expand...

Nope. I actually have the bestest words, and knows how to useses them!

equilibrize - Google Search

cameraman said:

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Temporary place holder

Click to expand...

Seems I can't edit the original post to add, (D' oh),

@9106872762

Doosan HP 4000 M19 Issue

(from the forum);
^^^ That seems to be going in a positive direction in spite of difficulties.

And

Who makes or can make this type of machine

Who makes this type of machine discussion ? (also from the forum), Kinda scales versus temperature problems vs. on shop floor metrology versus full metrology department + corrections and various machines.

I'm sure there are many other good links that are relevant too.

@OP Machines with various types of scales (modern ones, not all , but some ) have temperature sensors in the scales/ scale assemblies and variously about the machine, but the compensations at best with a ten degree Celsius change* have a hard time keeping things under 8 micron shift over several hours with active automated thermal compensation on a machine from the control, at the best of times. larger machine, bigger distances, and much greater temperature differentials 30 micron could be your worst case "ball park" scenario, un gauged and un corrected. Two tenths over a thou ? 0.0012" / 30 micron ?

Some machines use a design approach where the scales expand at the same rate as the machine and if you are machining ferrous alloys then things can hang together more easily. For ferrous based scale, cast iron frame and bed and mostly ferrous based alloy parts to be machined.

Nickel alloy part, granite epoxy castings and glass scales ? Aluminum part , invar based scale, Concrete / aggregate base ? Quartz nano positioning scale … ceramic... Blah blah blah, The point is DOOSAN should be able to make or engineer a machine that thermally compensates fairly well ? They don't build rubbish ? , something seems wrong with "New Machine" maybe install / control settings etc. ? (I understand your environment is very challenging .). So does that mean you have thermal changes as high as 30 degrees Celsius I guess in the machine, as other wise if that was in the shop I think most people would die wouldn't they ? I know for example there have been terrible heat waves in Rajisthan but strangely the daily maximum and daily minimum (for example in Jaipur) rarely exceed 10 or 12 degrees Celsius, biggest difference being in the winter ? Not sure how that compares to California maxima and minima , or South Korea where the machines are built ?

The way you are cutting the parts are you putting a ton of heat into your parts ?


@9106872762 what is your biggest temperature swing ? Through a day or particular day of the year ?

Or is it literally your inspection department is at 21 degrees Celsius and your shop floor is at 40 degrees Celsius ? And your parts heat up by ten degrees through cutting ?

So comes back to the repeatability of the machine and the inspection department essentially indirectly calibrating your machine ?

I haven't done the research on shop floor based CMMs yet, but allegedly they are designed to take into account shop floor thermal conditions ? Up to a point ?



@9106872762 On one of threads cited above there was reasonably heavy finger pointing towards shaft wind-up on very long ball screws ? Stored motion and torsional springiness on a new machine versus a machine really well run-in and warmed up over a week at a time for a more normal run ?

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* It's kinda Odd as John Harrison sort of solved this core problem nearly 300 years ago with a "grid iron" bi-metallic pendulum that uses dissimilar metals with different rates of thermal expansion to create a pendulum of constant length regardless of what the temperature is , so time keeping was accurate to within seconds a year ~ Eventually leading him to the development of marine chronometers and solving the problem of "Longitude" and accurate navigation at sea.

Gridiron pendulum - Wikipedia

John Harrison - Wikipedia

https://demonstrations.wolfram.com/GridironPendulum/

Here's one ^^^ with knobs on you can twiddle (imbedded app in web page) ^^^ (it's an interactive Harrison grid iron pendulum of constant length … ).