QMT Features: September 2015
Measurement - Just how wrong can it be?
Ahead of the GTMA’s Make Measurement Matter 2015 event, Chairman for the event and Head of Metrology for Coventry University, Trevor Toman, speaks to QMT

He explains that “Business needs to get away from the notion that all measurement is correct, because there is a probability that our measurements are incorrect. Therefore, we should understand the probability density function of our data and then quantify the probability and bias.”  This information on how our measurement process is behaving is critical to the understanding of the process under study. 

Generally speaking the real purpose of metrology is fairness in society and trust in our transactions; if you buy a litre of fuel at the forecourt how close to a litre are you actually getting? How accurately do you think it can be measured? On a full tank for the car, any variation might not add up to much. However, when you consider a shipping tanker filled with fuel the variation can accumulate to a significant cost or profit.

Measurement really does matter.

Within a manufacturing company the role of metrology, first and foremost, has to be seen as a business tool and not as an unwelcome cost. As Trevor Toman states: “Used correctly, metrology actually adds value and reduces costs, that will ultimately improve the relationship with customers. In order to achieve this we need metrologists that can really understand our measurement systems and management that understands the implications of good quality metrology.

“While measurement systems put a stamp of quality on a product, a process or even a service, metrology puts the stamp of quality on the measurements made by those systems. Metrology gives us the confidence to make the right business judgements and decisions. It enables us to understand and quantify the behaviours of processes.”

As the complexity of manufacturing increases so does the need to achieve production that is right first time, because repairs are not process-controlled and cost significantly more than an investment in good in-process metrology. Repair processes and costs are also rarely factored into the business structure. A good metrologist understands this and can reduce the need for repair and rework very significantly.

Coventry University is using an approach to developing competencies for metrologists with coloured belts that emulate the lean manufacturing designations. “My approach with the green and black belts I mentor,” Trevor Toman explains, “is to challenge the assumption that my data is good. My role as a metrologist is to assume that the measurement data is always wrong. What I need to understand is how wrong. Once I know that, I can determine a value for it and make evidence-based decisions knowing the level of confidence I can place on my measurement systems. This is ‘measurement uncertainty’ and it is very important to every business. A measurement is simply not valid without an understanding of its uncertainty.

“I also have to compare the measurement uncertainty that I can achieve with the tolerance required for the part, product or process. If my measurement uncertainty exceeds the required tolerance, I am using the wrong approach to my measurement, and possibly the wrong equipment. A good metrologist will also understand why the stated tolerance has the value assigned to it – and should be able to challenge it.
“Medical disciplines tend to have a different culture from manufacturing industry; they start from the understanding that treatments are imperfect and then work towards understanding how imperfect – how uncertain. Once they achieve that they can decide whether a treatment is good enough or not. If not, the studies needed to achieve the understanding will have provided opportunities to improve the treatment and the measurements needed to assess it.”

Metrology applies a level of honesty by quantifying the confidence in any measurements made, a concept that people in calibration laboratories fully understand. Now, many major businesses are applying the best practices that exist under the controlled environment in the laboratory onto the shopfloor. Why? Because they need to meet the tighter tolerances required to make things to a better standard. It does not have to be more expensive, if you have a good system and it is capable then quantifying the capability of the measurement systems allows the level of control to be increased – this is laboratory mentality.

“Understand it as a metrologist would; a good metrologist will always apply the right measurement system for the job in hand. There is no point using a co-ordinate measuring machine when Vernier calipers will adequately perform the task. We need to promote understanding measurement from first principals rather than just throw everything on a CMM,” Trevor Toman says.

Good metrology that is applied with understanding embeds reality and confidence in measurement results that allows management to make decisions with the greatest degree of confidence. It will also tell you how well you are performing, acting as a key tool to help a business to outperform global competition.
Trevor Toman says: “Any new product launch on the shopfloor will have detailed processes that are created by an engineering team that understands how the product will be made, but often there is not enough thought put into the measurement. If as much care was applied to metrology we could avoid both the cost of rejecting good parts, and the cost of supplying substandard parts to the customer.”

He concludes: “Better to understand what you can achieve than base decisions on shifting measurement results. Variation is both the enemy of production and the biggest enemy of any measurement system. If we can reduce the variation in the measurement system then we can truly understand the real variation that exists in our production process.”

Good measurement systems equate to fairness, honesty and the understanding and control of production processes and Make Measurement Matter 2015, held on 15th October at the Kettering Conference centre, will provide the ideal opportunity for visitors to find out about how metrology can influence and improve their businesses.
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