QMT Features: October 2012
Tons of precision
 At  PMT Machines, India , precision parts for huge 60 metre diameter rotors are quality assured with a CMM from Carl Zeiss.

Rotors with a diameter of more than 60 metres anchored on multi-ton mounts – in light of the size of modern wind turbines, it is easy to forget how much precision is required to ensure that power can be reliably generated for years to come. PMT Machines Limited, the leading manufacturer of machine tools and parts for power and traffic technology in India, relies on measuring machines from Carl Zeiss.

PMT Machines is full of tradition: headquartered in Pune, the company has been manufacturing machine tools for a wide range of industries since 1963, including the automotive sector. In 2006, the company added parts for the rail industry and power generation to its portfolio. Its factories produce components for gas and steam turbines, as well as for wind turbines.

The new products brought with them increased demands on quality. After all, the parts for wind turbines must never fail despite the enormous stress they are subjected to – repairs at lofty heights would be too labour-intensive and expensive. "In the past, the precision of our machines in production was checked manually; today we can measure the quality of the products automatically and guarantee it 100%," says a proud Chetan Bhavsar.

In the past refers to the period before the acquisition of an MMZ G in 2010. The measuring machine from Carl Zeiss Industrial Metrology (IMT) measures the form, size and position of large parts with particularly high demands on precision. The times when multi-ton parts had to be measured by hand while the part was still clamped in a production machine are a thing of the past. During these measurements, the tools and machine attachments interfered with the measurements, making them complicated and leading to incorrect results. With the MMZ G, PMT Machines now relies on one of the most accurate inspection machines of this class in India.

Maximum precision to counter expensive downtimes
The rotor hub is a prime example of the enormous demands that must be overcome in quality inspection at PMT. This central part accommodates three rotor blades and the drive shaft which transfers the rotary motion to the generator. On a turbine that generates up to 1.5 megawatts of power, the rotor hub is two meters across and weighs around 7.5 tons, and rotates at a height of 75 meters. The production of such parts may seem like pure manual labour, but this would by no means meet the industry's demands on quality. The maximum error from the perfect round form of the boreholes in the rotor hub must be no more than 30 micrometers – not even 0.01 percent of the diameter of the boreholes of 95 and 34 centimetres. If the error exceeds this tolerance, the customer would immediately return the parts – the cost risk to replace components when a wind turbine fails would be too high. Although this never occurred in the past, customer satisfaction has considerably increased following the introduction of the MMZ G according to Bhavsar.

Measuring time cut in half
The speed of quality inspections has also picked up. "In the past, a complete manual measurement took up to three hours; now it doesn't take half as long," states Bhavsar. With 50 or 60 rotor hubs manufactured every month, there is enough time left over for other measurements. Parts for train engines and rail cars intended for a manufacturer in Germany are also inspected with the MMZ G. Regarding quality-consciousness, PMT Machines already focuses closely on German standards. For example, the company has been DIN EN ISO 9001:2008 certified by Technical Inspection Agency in northern Germany. Numerous customers are headquartered in Germany, not surprising considering that the company was founded by German mechanical engineer Traub.

According to Bhavsar it was clear from the beginning that PMT would acquire an MMZ G: "We have already had very good experiences with another measuring machine from Carl Zeiss IMT." The company has been using a PRISMO navigator for three years. It is ideal for particularly fast measuring jobs and unites optical and contact measurements in one system and one software.

Bhavsar summarizes the reasons for his satisfaction as follows: "Quality, reliability and precision."  Carl Zeiss was particularly advanced regarding reliability, which is a key criterion in India. Indian customers generally demand a three-year guarantee compared to the two years that are standard in Europe. For added security, Indian customers often purchase spare parts for critical components subject to heavy wear and tear when they buy the machines to ensure that their systems can work without interruptions for years to come – under particularly rough conditions. German companies often acquire several measuring machines for different jobs, a luxury many Indian companies cannot afford. They demand a robust, all-in-one system that completes all their quality inspection jobs in a single go and as close to production as possible, i.e. near the machines used to manufacture the part. At PMT Machines, for example, the MMZ G measures all parts produced for wind turbines, including the rotor hubs, gear wheels and shafts.

For the unlikely event that the measuring machine fails and PMT employees are unable to solve the problem, fast help is available on site. A service team from Carl Zeiss IMT is located nearby. In an emergency, a technician can be at PMT within one hour and finds the solution the same day.

The procurement of another machine for quality inspection is just a matter of time. The decision has been made for 2013. One thing is already certain: "We are so satisfied that we will definitely purchase another machine from Carl Zeiss," promises Chetan Bhavsar.
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