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Technical Articles :: Die and Mould

Suresh Bhat : ' Metacut Finsh' for manufacturing 'High Accuracy & Fine Finish Moulds in Lesser Time'


M/s.Northwood Desings Inc.,USA
Metacut Products for 'Feed Optimisation during Finish Passes ' and ' Toolpath Verifications '
Suresh Bhat - Sri Ganesh Machine Tools & Automation ,Bangalore,India
‘’ ACCURACY ,FINE FINISH AND SPEED’’ , IN CNC MACHINING ( Better parts in lesser time )
( Prepared by Suresh Bhat – CEO , Sri Ganesh Machine Tools & Automation ,Bangalore, Dealers in India for M/s. Metacut i.e. Northwood Desings,Inc.,USA ,)
Source : Mr.Bill Elliott – President, Northwood Designs, Inc. )

MetaCut eliminates most of the limits which keep you from getting better finishes in less time on your CNC machine tools.

The key thought to remember throughout this discussion is "Accuracy is everything and the only thing ", Everything you do when making a ‘ Mold or Die ‘ is centered around Accuracy. The challenge has always been for a better way to become more accurate during the machining process.

Why do we really need to be so accurate, and how accurate is "good enough"?

The main reason you should be concerned about accuracy is that there is NO OTHER WAY to get a good finish on your part. This cannot be over emphasized. Poor finishes are the result of poor accuracy somewhere in the process.

There are two places that the accuracy must be controlled. The first place is the data (the tool path) and the second is the CNC machine.

OVERCOMING THE PROBLEMS OF CNC MACHINING BY USING METACUT :

MetaCut ‘Machine Optimization Software ‘ will help you get the full potential from all of your machine tools, both old and new.

MetaCut accurately fits arcs to the point to point data produced by your CAM system. One arc often replaces more than nine out of ten lines with a single arc, even at extremely small tolerances. This means that the physical length of each block is longer. With longer blocks the BPT ( Block Processing Time ) of the control can be much slower without inducing the stuttering or shaking problems caused when the BMT (Block Machining Time ) is shorter than the BPT.

How much slower can the control be? Well in the case where MetaCut replaces nine out of ten blocks of code with a single block, the control can be 90% slower at similar tolerances. Or a better way to look at this is that you can make a much more accurate part before the BPT of your control becomes the limit.

If all you wanted to do was to go faster, it would be enough to make your tolerances larger in your
CAM system. This would make longer and longer lines and help to alleviate the BPT problems. Anything which reduces the number of blocks reduces the chance that you will have BPT problems. Unfortunately this method also makes a very bad finish, and you want more than this, you want a better part. and as you know, better finishes require accuracy.

MetaCut virtually eliminates the BPT problem even from an older control, you can produce data more accurately than ever before without BPT problems. You should also remember that the correct accuracy for the data is something slightly better or equal to the physical capabilities of the machine tool. Without MetaCut this was not possible because there was simply too much data and your control couldn’t handle it, with MetaCut as part of your process, small tolerances will be welcome on your control. The second major factor which controls the accuracy of your part is the machine. When the strain is taken from the control, suddenly the mechanics of the CNC machine become the limit to how fast and accurately you can cut your part. With MetaCut you can actually machine your ‘Molds and Dies ‘ TOO FAST.

You probably wonder how you could possibly machine too fast. Isn’t that good? No. ‘Too fast’ results in over travel, and over-travel means inaccuracy and inaccuracy means a bad finish. Machining fast without controlling the error only makes a bad part faster! Many machinists don’t realize that small gouges that they give to the polishing department to clean up are often not caused by bad data, but rather by over-travel. This is particularly true in areas of sudden direction change like the area of a cavity where the tool travels from the floor of the cavity to the wall. The trick to all of this is to always maintain feed rates which don’t allow the machine to leave the programmed data in the first place. When you maintain an accurate federate relative to the curvature and the physical ability of the machine, you will never put your machine into an
over-travel condition. An added benefit is that when you prevent over travel conditions, you reduce the wear and tear on your CNC machine, and you will actually get better parts while extending the useful life of your machine tool. MetaCut will provide this machine specific accuracy control.

MetaCut has the ability to be customized to individual machine tools and to produce feed rates which will prevent over-travel and maintain accuracy. In fact every arc produced by MetaCut will get a unique feed rate which is specific to your machine tool and it’s physical capabilities. MetaCut will also look for any sharp corners in the tool path and insert the appropriate G-code to prevent the thumping and bumping so common in these areas. What this means to you is a more accurate part with substantially better finishes in a fraction of the time. With MetaCut you need to think a little differently about how you program your tool paths. First, you can finally make more accurate tool paths without the hassles. You can also program higher feed rates. Since MetaCut controls the maximum feed rate at any particular curvature and because the BPT problems are virtually eliminated, for the first time, you can analyze your part and program your feeds and speeds based upon the best case scenario on your Mold or Die. Your decisions for feeds and speeds are currently centered on the worst case scenario. Now, you must decide where your biggest problem area is (like the sharp transition from the cavity floor to the wall) and then program a feedrate which only gouges a little in this area. The unfortunate part is that this means that you are machining slower than needed everywhere else on the mold. MetaCut will allow you to program for the best case scenario, and then MetaCut slows down only as much as is needed in all other areas to maintain an accurate cut.

This difference in feed control alone can cut your machining time in half while producing a better finish. Imagine machining your entire part at the fastest possible accurate feedrate, instead of the feedrate that only gouges ‘a little’. Although machining faster and making better parts on your current equipment sounds to good to be true, it isn’t. MetaCut simply tackled the same problems.

Do you want to know how to get the absolute best results? Combine MetaCut with your CNC Control. This is the ultimate in finish, quality and speed.

The data from MetaCut comes much closer to providing both a higher accuracy and faster machining than any other method. MetaCut is able to do this by providing data to the control and machine that lends itself to machining faster while simultaneously holding a high accuracy.

It does this in a number of ways :,

1.It provides large areas of constant curvature which have no sudden direction changes requiring decelerations.

2.It reduces the total number of endpoints and consequently, transition points.

3. The remaining transition points have a much lower angular change.

The results of this are that the machine will typically reach higher feed rates along a cut, and maintain them longer because it doesn’t need to decelerate as frequently. This has been confirmed by independent testing at a major control manufacturer and is in large part why the control manufacturers are currently pushing NURBS machining. Never the less, it really is very difficult to say how much time this will save on any given part. It will vary with the shape of the part, the size of the part and the maximum programmed feedrate. If the feedrate is programmed very slowly, you will see less time difference with and without MetaCut. The faster the programmed feedrate and the smaller the error allowed by the control, the larger the time difference. Finish quality is also improved because you can easily machine data that is more accurate than the machine without any problems, furthermore this data is represented with large areas of constant curvature with smoother transitions at the block endpoints.

In a nutshell, you get the best finish, at the highest tolerance, in the least amount of time, by using MetaCut.

Conclusion

MetaCut will help all machine tools to make better parts faster. If you are currently using a machine that does not allow you to cut high precision data and does not control the error (over-travel) while cutting, MetaCut can often double (or more) the throughput of the machine on finish passes. It can do this while providing the very best finish that your particular machine is physically capable of, which is much higher than you can imagine if you don’t have MetaCut.

Here is a brief list of the major benefits of ‘ MetaCut Finish ‘ to your CNC machining.

1) Better quality parts at higher accuracy

2) Reduced machining time (on some machines 3-4 times faster)

3) Reduced polishing times (for many shops, it has eliminated polishing)

4) Reduced machine maintenance and longer machine life

5) Reduced file transfer times to older controls (typically transfer in ¼ the time)

6) Reduced storage problems (files usually fill only about ¼ of original the disk space)

As you can see, MetaCut works by simply doing a very good job of making your tool path data perfect for reaching the physical potential of your machine tool and control. MetaCut doesn’t use any magic, just an understanding of the process and the various limits, along with the ability to overcome them.

Metacut also offers MCU ( Metacut Utilities ) and following are the Features and Benefits :

1.Graphical G -Code Editing

2. Verification of Tool paths and Tool Path Problem Solver

3. A Shop floor Set up Sheet

4. A quick G –Code Viewer

5.A Technical Support Aid

Closing Notes :

We started the entire discussion by talking about accuracy. Good finishes require accuracy. The truly difficult thing to do is to produce accuracy AND in the shortest possible machining times. This is the entire purpose of MetaCut and Metacut Utilities.

Today Metacut Products are used all over the world with concentrations in the major industrial markets. YOU CAN DOWNLOAD A ‘FREE TRIAL VERSION’ FROM THE WEB SITE www.nwdesigns.com .

Please contact us for further details , at + 91 – 94483 76319 , + 91- 80 -65364695 or write to sales@sriganesh.org , ceo.sriganesh@gmail.com or nwd@nwdesigns.com

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