Trials and Calibrations

One of the biggest difficulties that Spanish companies are getting into their account is exporting its products to other countries that are called technical obstacles arising incidences, among other things, the lack of recognition of certificates or certifications achieved and officially obtained in Spain.

ENAC, A Partner of Spanish Companies

ENAC accreditations are recognized in more than 70 countries around the world, thanks to the signing of the Mutual Recognition Agreements (MLA). These circumstances made available to the Spanish company a tool of great value for guarantees access to international markets.

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For Instance, If you are buying Peanuts and the shopkeeper makes you an offer with a non calibrated balance, you are going to pay more or less the uncertainty of his balance. That means that the Uncertainty of his balance makes you to pay ± of your money. This  is commonly called Legal Metrology.

This situation is embarrasing at the time to pay for a non existent service that is giving you more incidences In the real life, while going to the market to cook some dishes even cheaper than the ones  at the restaurants. ± half price. On the other hand you have to evaluate your cooking time that is not included, even shopping time is also not included, and cleaning dishes time that is also not included inside this price, but I suggest is worthly to spend some time choosing your favourite meals in order to cook what you really enjoy and like.

This analogy is also applied inside Industrial Environments where the differences of measured parts can make a big controversy between coordinate measuring machines (CMMs) in proper working condition by between shipping a good workpiece or bad part.

Then is time to think about the intercalibration periods.  And arouse some questions, like  When is necessary to reset the setup of my CMM? or

Q.: I Need to move my CMM. Can I do it by Myself?

A.: The short answer is NO, it’s not a good idea. Most stationary CMMs require an expert to relocate them, and they all require some level of disassembly and bracketing prior to moving.

A CMM is an expensive and delicate measuring instrument with many intricate parts, including glass-scales, encoders and precision airbearings, which can easily be damaged if they are not handled correctly.

Because the air supply is disconnected when a machine is moved, the air bearings are in direct contact with the guide-ways surfaces. If the CMM is not properly bracketed before moving, you risk damaging the bearings or the ways. And to be clear, I don’t suggest you to try to move a measuring instrument with the air turned on either!

Also, when you relocate a CMM – even just a few feet – it is best practice to have it levelled and recertified. Once a CMM is moved, the calibration is void and it must be recertified. So if you’re planning on moving a machine, try to synchronise the move with your regular calibration interval. Official’s Service Engineers are Experts in this matters, at CMM relocation, whether you are moving the CMM across the plant or across the country. They can make sure the job is done Right every Time.

The exception to the rule is if you have a shop-hardened CMM on a stand with wheels or a shop-floor CMM like the TIGO SF. Models such as these are designed to be relocated very easily, as long as they are moved short distances across a level floor. Any kind of CMM that has to be moved to a different level, particularly by lift, should be recertified at its final destination.

Q.: Does It matter Who Calibrates my CMM?

A.: Yes. Many third-party service companies claim they can calibrate your  CMM for almost nothing, But customer – beware! Many of these companies do not have the ability to calibrate our CMMs. They simply do a few tests and tell you how the machine is measuring without adjusting anything.

There are even some service companies that attempt to make physical adjustments, which is the worst thing they can do.

CMMs are adjusted using their proprietary software compensation map, which enhances the accuracy, that is named Computer Aided Accuracy or CAA of your Measuring Instrument Volumetric Compensation Map that is to be the best it can be. When the software compensates a CMM is properly adjusted physically, theni the integrity of the software map is compromised to the measuring accuracy, otherwise is lost, even if you relevel the CMM you can get rid of the torsions or rotations inside the 21th corrections volumetric compensation map.

Suddenly, that great deal from the third party doesn’t look so great…

Please, don’t cut corners with your CMM. After all, it is your ultimate referee for shipping good products or bad products. You would never take an expensive sports car to a cheap oil change place where the technicians have no factory training. So why not to use HighlySkilled Service Engineers Inside your Industry. They know the product Inside and Out, they have the proprietary tools, software and methods, and they will do your Calibration Right.

image004A gage that meets performance specs will ensure better measurement results.

Calibration is a process used to ensure that a measurement device meets its performance requirements. The device, a gage block, for example, is brought into an environmentally controlled room and measured against traceable standards by a trained operator using specialized equipment and a defined measuring process. All potential errors relating to the process are identified and their potential effects quantified.

Once the gage block has been measured, it is determined to be either within specification or not. A certificate is issued stating that the block is within defined limits, if that is the case, and providing the actual recorded measurements. A gage block found to be out of spec is usually replaced or downgraded to a lower grade in which it does meet the calibration specs. There is not too much that can be done to bring an out-of-spec gage block back into spec.

Most other types of gages are different from gage blocks in this respect. If the gage does not meet specification after the calibration process is performed, there are usually ways to adjust the performance of (calibrate) the gage so that it does meet the specification. This is true for handheld gages like calipers and micrometers, as well as dial indicators, bench amplifier/probe combinations, and surface-finish or form-measuring systems.

Regardless of the type of gage, all calibration processes have certain steps in common, whether you send your gages out or calibrate them in house. Let’s take a look at a typical calibration process for a Vernier, dial or digital caliper. All three of these instruments typically have the capability of measuring Outer Diameter (OD), Inner Diameter (ID) and depth with the use of an integrated depth rod. The calibration process involves comparing all these readings against known standards. In addition, ID and OD jaw parallelism also needs to be verified and certified.

Gage blocks are often used for calibration, but specifically designed masters also are available that make the process of checking calipers a little more efficient. And while not a hard and fast requirement, the inspection usually involves making measurement checks at fixed points (every 25 % of the total instrument lenght, for example at 25, 50, 75 and 100 percent of the instrument’s range. For dial calipers, it may be wise to select a couple of pairs of gage-blocks that fall within the range of one revolution of the dial to check its short-range performance.

Next, check the parallelism of the OD jaws with the precision pin. Place the pin between the jaws at the top and zero the gage, then move the pin to the center and tip of the jaw and compare the results.

Consult the manufacturer’s specifications, but there should be virtually no difference in readings. Though a little more difficult, the same test can be performed on the ID jaws using the master ring.

Now the calibration process for the caliper can begin. Close the jaws and zero the caliper. Using the gage blocks or a test piece, measure each incremental step, open and close to check repeat, and record the values. Compare the results to the manufacturer’s specifications, then repeat the process with the ID jaws. Finally, check the depth rod with a 25 mm. lenght gage block set on the surface plate by zeroing on the plate and then measuring the depth. Again, consult the manufacturer’s specifications for acceptable variation.

Hidden within all these steps are the usual sources of error that should be considered:

• Variations in the measuring force applied to the masters (too much force can distort the gage).
• Masters that have not recently been certified.
• Temperature of the masters and caliper.
• Jaws that are not parallel, are worn, have burrs or are dirty.
• Caliper beams that are bent or warped.
• Loose hand on a dial caliper and loose gibbs (some calipers have adjustments for tightening up the fit between the fixed and the sliding jaw).
• Temperature through handling.

If a caliper does not meet the manufacturer’s specs and you have addressed all these sources of error, there is little left to do to bring the caliper into spec. It may be time to invest in a replacement.

Caliper calibration is about as basic as it gets, but almost every one of the errors identified in this process can be found one way or the other when calibrating dial indicators, micrometers, gage blocks or complicated measuring systems as well. Start small, identify these basic processes and, with practice, gage calibration can become a routine for ensuring better measurement results.

Prior to starting the calibration process, gather the right tools for the job: disposable wipes and alcohol; gage blocks or a caliper test master (and the documentation that they have been recently certified); master rings; a master pin; a surface plate; and calibration stickers. Of course, all of these will be used in a room environmentally stabilized for temperature, vibration and humidity.

Once the masters and caliper have settled to ambient temperature after being cleaned with the wipes and alcohol, the inspection process can begin. First, check repeatability to zero by bringing the jaws together and zeroing the item. Next, open and close the jaws multiple times to repeat the zero reading.

Significant non-repeat is a sign of either dirt or worn guideways, which should be addressed before going any further. See more at “Centro Español de Metrología, (CEM)”

EGA is registered as 14.302 Engineer at CoitiMadrid

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