Finishing and superfinishing, lapping, honing, and vibratory grinding:
a range of manufacturing processes can be used to create a final surface finish. The
proverbial “finishing touch” influences the functional behavior of
workpieces and components, yielding unique characteristics, and competitive
advantages. GrindingHub,
the trade fair for grinding technology, will be held in Stuttgart from 17 to 20
May 2022 and provide a platform for finishing and superfinishing. After the
pandemic-related hiatus in trade shows, many of the exhibitors registering a
strong desire for face-to-face communication and knowledge transfer regarding
the more complex processes.
Companies looking for specialists to help
them move into superfinishing
It took Uli Lars Bögelein “less than ten
seconds” to make up his mind to exhibit at GrindingHub. The entire industry is
certain to benefit from the trade show, says the managing director of Stähli
Läpp- Technik GmbH, based near Stuttgart. Founded over 40 years ago as a sales
company for flat honing, lapping and polishing machines produced by the Swiss
Stähli Group, Stähli Läpp-Technik GmbH is now part of the group. Its core
competences include engineering, sales, and contract processing. The latter
represents an ideal way into superfinishing and to much more besides, as
Bögelein makes clear.
The Stähli Managing Director describes the three main groups
of users who contact him. These come primarily from the automotive and
electrical industries, medical technology, mechanical engineering, and the optical
industry. The first group of users is not (yet) concerned about the investment
costs for both the 2- and 3-wheel flat honing machines and the 1-wheel lapping
and polishing machines because their production quantities are too low. Then
comes the second group which needs high, if not extremely high, quantities, but
which “specifically wants to avoid taking care of these processes, and all
they involve, within their own company”. Lapping machines bring their own
challenges and do not fit into every production operation, Bögelein admits. It
is a demanding process which still requires a lot of manual work – and
specially trained and highly motivated employees.
Finally, there is a third group of users. These run test
series at Stähli. Until the series is working smoothly, they would first like
to familiarize themselves with the process and the machine and take advantage
of the service and know-how offered by Stähli Läpp-Technik. The company also
offers the entire range of consumables and accessories for this, including
everything from CBN wheels and diamond suspensions through to testing
equipment. Uli Bögelein notes that trade fairs are very important and are often
used for making the first contact. Visitors come with drawings and workpieces,
but also specific machine inquiries, and to have the technology explained to
them. Specific technological know-how is required in cases involving
manufacturing tolerances in the submicrometer range and filigree functional
surfaces.
Drivers of industry development
According to Thomas Harter, Product Manager at Supfina
Grieshaber, based in Wolfach in the Black Forest, companies’ increased
motivation to concern themselves with surface quality and finishing and
superfinishing processes stems from clearly identifiable “development
drivers”. Supfina has many years of experience in the field of superfinishing
and grinding. It develops machines and conducts related research – and will
also be exhibiting at GrindingHub.
Harter cites examples from the automotive technology field.
For example, the expected legal regulations for Euro 7 and the associated
reduction in particulate matter are driving the development of the brake disc
market. Future brake discs, he says, will probably feature hard coatings that
are difficult to machine. As a development partner, Supfina takes care of
developing the process for grinding the coated brake discs. The know-how is
used in the development of the entire process chain, ultimately enabling
cost-effective production of the brake disc.
e-mobility is also placing new demands on superfinishing.
Future-proof solutions are needed to reduce noise in the powertrain, the
steering or when adjusting seats and windows inside the vehicle. For example,
Supfina has developed a machine series for the economical production of
low-noise roller bearings.
Defining specific surface parameters
Dr. André Wagner, Head of Grinding Technology at Hermes
Schleifmittel, Hamburg, makes clear just how much the demands on surface
quality are changing and how important precise coordination with customers is
becoming as a result. While some processes, such as high-performance steel
cutting, are optimized primarily for productivity and cost-effectiveness,
processes such as gear grinding must yield high workpiece quality, says Wagner.
The goal of reducing surface roughness to a minimum, which was common in the
past, is increasingly being replaced by that of achieving specific surface
characteristics. However, the selection and definition of the desired surface
properties depends to a great extent on the gear application and the specific
goal. “Effective communication between the customers and the grinding tool
manufacturer is therefore essential,” Wagner emphasizes. The general
machine conditions, the quality requirements for the component being produced
and the productivity of the process must be clearly defined and coordinated in
advance. According to Wagner, ideal process results can only be obtained by
setting precise objectives and designing the grinding process on an
application-specific basis. In the case of gears, for example, this would
ensure maximum efficiency of the transmission and reduce noise emissions, which
are crucial for electrically driven vehicles. All process-defining parameters
such as machine environment and cooling lubricant supply must be considered
when selecting and designing suitable grinding tools. “High-performance
tools aren’t always necessary. In many cases, less exacting specifications may
also suffice if the process designed correctly,” says André Wagner.
Scientists focusing on process chains
Finishing and superfinishing processes can play a role in
creating unique workpieces. The Institute for Machine Tools and Factory
Management (IWF) at the Technical University of Berlin believes that
“…there is a noticeable trend toward manufacturing
individualized products in small batches. This is giving rise to an increasing
need for manufacturing processes that can be adapted to changing product
requirements.” Research is being conducted into robot-guided machining
processes for finishing and superfinishing by the Institute. “Robot-guided
machining processes can be used on many different components, especially in
combination with flexible or freely movable tools, as in abrasive brushing,
belt grinding or vibratory grinding,” explains Institute Director Prof.
Eckart Uhlmann. “Honing processes that are conventionally performed on
rigid machine tools can also be taken care of using robot-guided honing tools
to rework bores in different positions.” Uhlmann, who is also a member of
the WGP (German Academic Association for Production Technology), believes that
the main advantage of using a robot as a universal processing machine is that
it allows the different processing steps to be linked flexibly. Process chains
can then be adapted to the respective component requirements with little
effort.
Interest in the research proves that greater use is expected
to be made of innovative finishing and superfinishing processes in the future.
However, they are still fraught with problems for many companies. It is true
that the industry offers both technologically advanced machines and tools as
well as extensive specialized knowledge for creating surfaces of tribologically
stressed functional surfaces. Yet the special machines are too expensive for
small and medium-sized companies and for relatively small or medium batch
sizes, the automation is complex and knowledge about cause-effect relationships
is limited to specialists. Trade shows such as GrindingHub offer an opportunity
to showcase machines, tools, processes, and work results.
