In this Q&A session, Dalibor Dordic, sales director, for Europe North & East at Swiss cylindrical grinding experts Fritz Studer discusses with Ed Hill the advantages of the grinding process for aerospace components.
Part of the United Grinding Group, Studer has been making grinding machines since 1912. Over the years the company, which specialises in cylindrical grinding machines, has developed technology and processes that are widely used in the aerospace industry due to their high accuracy, component surface finish and reliability.
Q) Can you explain why the grinding process is so advantageous when it comes to producing aerospace components?
Let me quote Dr Konrad Wegener from the Swiss Federal Institute of Technology in Zürich: “In the combination of cost effectiveness, efficiency and machining quality, grinding is superior to all other manufacturing processes.” It’s important that the machining process is consistent, and when it comes to high surface qualities and tight tolerances then grinding is the only process that guarantees this.
Q) What kinds of aerospace components are your machines most suitable for?
We’ve developed many different processes on different machines for different parts and applications. For example, match grinding of components for hydraulic valves such as spools and sleeves and other hydraulic aerospace components is another critical and challenging cylindrical grinding operation. With match grinding, the OD of a hydraulic component, for example a spool, is matched ground to the ID of the appropriate sleeve. What makes match grinding so challenging is that the match grinding tolerances on the parts are typically within 1µm, and the same holds true for the form tolerances, such as roundness and straightness.
Another aerospace application that tests the abilities of a cylindrical grinder is the profile of curvic couplings. These special teeth profiles are ground axially onto the matching surfaces of the components such as the interchangeable discs in a compressor rotor assembly for an aircraft jet engine.
To generate these shapes, cylindrical grinders use cup-type wheels and must be able to grind above and below the centreline in the Z-axis as well as accurately index in the C-axis. The machine grinds the convex and concave form of a tooth, one below, one above the centreline and then indexes the part with the C-Axis for the next pair until all teeth around the face of the component have been ground. The grinder must produce perfect tooth forms and pitch tolerances as well as hold the current pitch over the whole part diameter.
Grinding is also used when special coated surfaces have to be ground. One example of this is with high-velocity oxygen fuel (HVOF) thermal coated landing gear components. HVOF-coated cylinders and other landing gear components are typically ground with diamond wheels that require special dressing applications. For these parts, aerospace manufacturers will pre-grind surfaces that are then coated with the HVOF or other types of coating. After coating, the parts will be ground to their final size to ensure that there is a consistent, even thickness of the coating.
Q) How widely are Studer (and United Grinding Group partner machines) used in the aerospace industry?
Studer and machines from our United Grinding Group sister companies are widely used in the aerospace industry. Mägerle and Blohm provide sophisticated solutions for aerospace manufacturers worldwide when it comes to engine components, such as blades, vanes and shrouds. Manufacturers require extremely reliable and highly productive grinding machines with stable and consistent processes day-after-day and year-after-year. Studer is often the first choice for cylindrical part production.
Q) Aside from price, quality and performance, what other demands are placed on you by customers?
We’re often involved in turnkey solutions for our aerospace customers and almost 40% of all Studer machines delivered in 2019 have been delivered this way. Other demands are the availability of service engineers and a fast reaction time; up-time is essential for all our customers. We have more service engineers in the field than any other grinding machine manufacturer and we believe that an excellent service network is as important as an excellent grinding machine. To cover the fields of mechanical, safety, electrical, assembly, grinding, etc., Studer has developed more than 80 different training courses for our service engineers.
Q) How important is the relationship between your machines and the consumables of the grinding wheel?
We sometimes face the issue that a customer buys our machines but then tries to save money by using inadequate consumables; fortunately, this doesn’t happen often. It’s like buying a new Ferrari and trying to save money by putting the cheapest tyres on it. The machine is only one important link in the chain, which is why we work in very close cooperation with all our suppliers, not only the grinding wheel manufacturers.
When we developed our ‘WireDress’ dressing technology, we had very close cooperation with the wheel manufacturers. The result is, we are the only grinding machine manufacturer, that can offer dressing of metal-bonded diamond wheels within the machine and fully-integrated in our CNC control and grinding cycles. The close cooperation we had with the grinding wheel suppliers saw the development of a technology that really pushes the limits.
Q) How are you addressing the demand for more automation, Industry 4.0 or end users who may lack specific grinding expertise and skills?
All Studer machines come with StuderTechnology software. It’s a big benefit to those companies who are expanding their business and entering into grinding, or typical job shoppers with huge variety of parts in small batches. With StuderTechnology, you can enter your workpiece material, hardness, required quality and it recommends the correct grinding wheel and calculates the feed rates and switchover points for rough, semi finish and finish grinding.
Industry 4.0 is a wide term. Most of the demands concern how to incorporate our machines in an already existing digital environment or how third-party machines can be added to our digital systems. This is why we offer United Grinding Digital Solutions products, which consists of Remote Service, Service Monitor and Production Monitor.
Smart Factory is another term we take very seriously. At present, we have an internal project where a part of our in-house grinding shopfloor will be rearranged in a way that will mean we have a grinding cell for grinding our main spindles without human intervention.
Q) What is your approach to R&D and what will be the major developments in grinding technology in the coming years?
Digitisation of our products and services will play a more important role. Today, the machine tool industry is at the beginning of a major transformation. Machines and surrounding systems will be increasingly connected with value chains - horizontally as well as vertically. We will gain more process and data transparency for faster decision making and production efficiency, in all aspects.
The way we interact with machine tools will change. Process and machining technology intelligence will be incorporated in the machine tool system itself to a higher degree, machine operators are converging more towards managers of productivity. Therefore, intuitive and supporting machine tool user interfaces, software and services will become more important in the development of all United Grinding Products.