Quality assurance control highly depend on CMMs. Over the last 20 years, they have almost replaced other inspection techniques such as fixtures and gauges. Since CMMs are very flexible, they reduce investment costs and increase inspection throughput.
Nationally and internationally recognised performance standards provide the means for CMM users to rate the calibration services of different providers. These standards are necessary when comparing competing suppliers, to help determine how well they will perform and to check whether they know how to work properly and safely.
At Status Metrology we meet both ISO 10360-2 & UKAS Standards, and below we will take a deeper look at them.
ISO 10360-2 Standards
ISO is an international organisation that develops standards for different industries. The aim of the ISO 10360-2 standards is to define the probe and the performance verification of a CMM. The reliance on certification standards reproduces known values and the objects used by the standard include a precision sphere, gauge blocks, and step gauges.
ISO 10360-2 specifies the key uncertainties - volumetric probing uncertainty or MPEP, volumetric length measuring uncertainty MPEE, and volumetric scanning error or MPETHP.
In order to verify MPEE, a set of special gauge blocks is necessary. The procedure is complex but the main idea is to take measurements in seven locations, in different positions and directions within the measuring module of a CMM for the test. Then, for each location, the length of the gauge blocks is measured several times. A total of 105 measurements are taken and each of them must be within the tolerance specified by a certain CMM machine.
The tests should be very precise in execution and definition. It's really important to remember that the uncertainty of a CMM under real conditions can be larger than stated in the specifications since there are many factors that influence the measurements; for example, slender probes, probe extensions, rotary tables, temperature changes, articulating probe heads, and airborne contaminants.
Environmental conditions also influence the uncertainty of a CMM. Therefore, CMM manufacturers specify the temperature variation per day and per hour, the temperature range, and the temperature variation per metre within a certain CMM.
UKAS or the United Kingdom Accreditation Service is the national accreditation body in the UK. UKAS is officially recognised in the country and they assess organisations that provide, test, certify, and inspect calibration services against agreed standards. When a company is accredited by UKAS, it means competence, performance capability, and impartiality.
In order to make sure a company complies with the latest UKAS standards, the accredited companies are assessed every year. The standards are harmonised with a range of ISO standards, including ISO 9000 and ISO 17025.
In order to comply with the standards, a company must go through an independent assessment of all its components, including equipment and staff. Companies willingly choose to undergo the assessment and follow UKAS standards.
In the UK, accreditation is recognised as an important tool across different industries for higher public confidence, better regulation, and fair markets. ISO and UKAS standards have been used by the UK government and companies of all sizes as an effective marketing tool.
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