Finishing or superfinishing, lapping, honing or vibratory finishing - the range of manufacturing processes that can be used for final surface treatment offers an impressive spectrum of possibilities. A proverbial "finishing touch" has an influence on the application behavior of workpieces and components, stands for uniqueness and competitive advantages. GrindingHub, the new leading trade fair for grinding technology, which will take place in Stuttgart from May 17 to 20, 2022, is setting the stage for finishing and precision machining. Much to the delight of many exhibitors: after the pandemic-related trade fair break, there is a need for communication and knowledge transfer for the consulting-intensive processes.
Uli Lars Bögelein says it took him "less than ten seconds" to decide to exhibit at GrindingHub. The Managing Director of Stähli Läpp-Technik GmbH, based near Stuttgart, is convinced that the entire industry will benefit from the trade fair. Founded over 40 years ago as a sales company for flat honing, lapping and polishing machines of the Swiss Stähli Group, the company, which is part of the group, now sees its core competence primarily in contract machining in addition to mechanical engineering and sales. This lends itself to entry into precision machining, but not only that, as Bögelein makes clear.
The Stähli Managing Director describes three groups of users, primarily from the automotive and electrical industries, medical technology, mechanical engineering and the optical industry, who contact him. For the first group, the sometimes high investment costs for both the 2- and 3-disc flat honing machines and the 1-disc lapping and polishing machines are not (yet) an issue because the required quantities are too low. But then there is also the group of those who require high, if not extremely high, quantities, but "deliberately do not want to bring the process and everything that goes with it in-house". Bögelein admits that lapping machines in particular are very special and do not fit into every production environment. It is a demanding process and still requires a lot of manual work and employees who are specially trained and appropriately motivated.
Finally, there is a third user group that is starting a series of tests at Stähli. They would first like to familiarize themselves with the process and the machine and make use of the specialist's service and expertise until the series is fully ramped up. Stähli Läpp-Technik also offers the entire range of consumables and accessories, from CBN wheels to diamond suspensions and testing equipment. Trade fairs are very important and are often used for the first contact, says Uli Bögelein. Visitors come with drawings and workpieces, as well as specific machine inquiries, and have the technology explained to them. When it comes to production tolerances in the sub-micrometer range and delicate functional surfaces, specific technological expertise is required.
Development drivers in the industrial environment
According to Thomas Harter, Product Manager at Supfina Grieshaber from Wolfach in the Black Forest, the motivation to focus more on surface quality and finishing and ultra-fine machining processes has to do with clearly identifiable "development drivers". Supfina, also an exhibitor at GrindingHub, has many years of experience in the field of superfinishing and grinding, develops machines and conducts targeted research.
Harter cites examples from the automotive industry. For example, the expected legal regulations on Euro 7 and the associated reduction in fine dust pollution are driving developments in the brake disc market. According to the expert, future brake discs will probably be designed with hard material coatings that are difficult to machine. As a development partner, Supfina takes care of the process development for grinding the coated brake discs. The expertise will be incorporated into the development of the entire process chain in order to ultimately enable cost-effective brake disc production.
E-mobility is also placing new demands on superfinishing. Future-proof solutions are needed to reduce noise in the drivetrain, steering or when adjusting seats and window regulators in the vehicle interior. Supfina has therefore developed a machine series for the economical production of low-noise bearings.
Defining specific surface characteristics
Dr. André Wagner, Head of Grinding Technology at Hermes Schleifmittel, Hamburg, explains just how much the requirements for surface quality are changing and how important the exact coordination process with customers is. While some processes, such as the high-performance machining of steel, are primarily optimized in terms of their productivity and cost-effectiveness, processes such as gear grinding must generate a high workpiece quality, says the expert. The goal often set in the past of reducing surface roughness to a minimum is increasingly being replaced by the targeted setting of specific surface characteristics. However, the selection and definition of the desired surface properties depend heavily on the respective application of the gear and the target. "This is why good and distinct communication between the customer and the grinding tool manufacturer is essential," emphasizes Wagner. Both the mechanical framework conditions and the requirements for the quality of the component to be manufactured as well as the productivity of the process must be clearly defined and agreed in advance. According to Wagner, ideal process results can only be achieved by setting precise objectives in conjunction with an application-specific design of the grinding process. Taking the gearwheel as an example, this would be maximum efficiency of the gearbox and a reduction in noise emissions, which are important for electrically powered vehicles. When selecting and designing suitable grinding tools, all process-determining parameters such as the machine environment and cooling lubricant supply must be taken into account. "It doesn't always have to be the high-performance tool. In many cases, more favorable specifications are also sufficient if the process as a whole is designed correctly," says André Wagner.
Scientific focus on process chains
Finishing and superfinishing processes can contribute to making workpieces unique. "As a trend towards the manufacture of individualized products in small batch sizes is becoming apparent, the need for adaptive manufacturing processes that can be adapted to changing product requirements is increasing," says the Institute for Machine Tools and Factory Management (IWF) at Technische Universität Berlin. Here, robot-guided machining processes are a research focus in the field of precision machining and finishing. "Robot-guided machining processes can be applied to many different components, especially in combination with flexible or freely movable tools such as brush cutting, belt grinding or vibratory grinding," explains Institute Director Prof. Eckart Uhlmann. "Even honing processes that are conventionally carried out on rigid machine tools can be realized using robot-guided honing tools in order to rework bores in different positions." Uhlmann, who is also a member of the WGP (Wissenschaftliche Gesellschaft für Produktionstechnik), sees the main advantage of using a robot as a universal processing machine in the fact that processing steps can be flexibly interlinked. Process chains can therefore be adapted to the respective component requirements with little effort.
The research interest shows that although greater use of innovative manufacturing processes for finishing and precision machining can be expected in the future, this is still problematic for many companies. The industry offers both technologically advanced machines and tools as well as extensive specialist knowledge for designing the surfaces of tribologically stressed functional surfaces. On the other hand, the special machines are too expensive for small and medium-sized companies and for rather small or medium batch sizes, the automation is complex and the knowledge of interactions is limited to specialists. Trade fairs such as GrindingHub offer the opportunity to showcase machines, tools, processes and work results transparently.
