Innovations have dampened vibrations in long cutting tools
What we today know as modern anti-vibration tooling originated in a nail-making factory in Trondheim, Norway. The factory started manufacturing during the nineteenth century, and after many years of making nails and associated products, in 1967, the seeds of a dramatic change of direction occurred at the company - Teeness as it came to be called. A young engineer presented a prototype of a damped boring bar which was the result of his diploma-work at university. The idea tickled the imagination of engineers at Teeness who, well aware of the problems of vibrations, particularily in internal turning, set about trying to put the idea into a practice. A chain of innovations followed, in collaboration with Sandvik Coromant, to establish the unique Silent Tools programme.
Going back fifty years in time, tool-chatter lead to compromised machining performance, component-quality issues, excessive noise-levels, poor tool-life and even scrapped components. In many cases operations were impossible to perform and therefore presenting a potential for improvement – a new means waiting to be recognized and developed.
In the sixties, Teeness then started what was to become decades of research into the causes, nature and solutions related to vibrations originating from the cutting edge. It was established that a vibration could be seen as a variable deflection of the cutting tool, where no defection means no vibration. Vibrations in tools are triggered and maintained by the dynamic cutting forces, where even in a seemingly continuous cut, forces will have small, rapid changes. The main ways to eliminate vibrations in machining are to increase static-stiffness of the set-up, reduce cutting forces acting on the tool and to increase dynamic stiffness. It was the latter that the original idea presented to Teeness tackled by using a passive dymanic vibration-absorber.
The idea was based on that of a mass suspended by springs in a fluid inside the shank of the tool – in this case a boring bar. The extra mass was devised to vibrate at a different frequency to that generated in the cutting process, causing a neutralizing effect : dampen vibrations. Thus, vibrations in machining cannot be entirely eliminated but they can be minimized through dampening the tool to within acceptable limits. The original concept was based on this principle and it was up to the Teeness engineers to make a boring bar that worked – which they did. But it was the development into a marketable tool, application and distribution that became the real challenge.
After several years of development into a product, Teeness contacted the leading cutting tool manufacturer of the time, in the neighbouring country of Sweden, to enquire about a possible collaboration. Sandvik Coromant, being well into the development of indexable-insert tools for most types of metal-cutting, at once recognized the potential of the Teeness (TNS) concept and drew up a direction for dampened boring bars to be developed and introduced in the Coromant-tool programme in 1973. Anti-vibration tooling was to take off on a route that, in time, would lead to most machine shops in the world.
The first Sandvik Coromant TNS dampened boring bar was made available in three diameters : 32, 40 and 50 mm in lengths of 450, 550 and 700 mm - designed for problem-free machining at overhangs up to ten times the diameter. These bars had exchangeable cutting heads which were radially adjustable and allowed different holder-types and indexable inserts to be used. The new design included a slug of heavy moderating-mass, spring-suspended in a special type of oil. The oil took up the energy from vibrations being generated during machining and turned it into heat absorbed by the oil. The inertness of the slug, and thus the frequency of vibration could be set with an adjustment screw on the bar, altering the tension of the spring suspension, until optimum dampening was obtained. The bars also had a built-in system for coolant flow to help evacuate chips.
The improvement in internal turning, even with this first product, was dramatic : material removal capacity was doubled. The surface finish, at a bar-overhang of eight times the diameter, with the higher cutting data, was reduced to Ra 1.3 microns with the tuned bar - down from Ra 8.8 microns with a conventional solid boring bar.
By 1980, a Sandvik Coromant TNS short boring-bar – for use up to overhangs of seven times the diameter – had been introduced. This bar had the advantage of not needing any tuning to optimize dampening. This was a further development in that the possible frequencies within the overhang area of the bar had been completely covered by the design of the dampening arrangement. A further innovation that made theapplication and use of dampened tools easier and saved set-up time.
The next step was to make use of the tool- and design-material that Sandvik Coromant was the leader in : cemented carbide. It was not only to be used as cutting edges but also as sleeves round the boring bar to increase the static stiffness of the tool (2.5 times that of steel). The overhang of dampened boring bars could be increased to twelve times the diameter. It also meant that there was scope for tools to be used as rotating tools. Impossible operations became possible – even using cutting data used for cemented carbide. Dampened tools were widely accepted as crucial problem solvers.
As from the 1980s, components within several manufacturing industries evolved to include deep and sometimes complicated bores that needed machining. The aerospace, energy and die and mould industries were examples of some with very demanding holes or compartments. But also many manufacturers in general engineering, automotive and machine-making could apply dampened tools to solve problems. The unique anti-vibration concept had been available in standard tools for more than a decade as well as lending itself well to engineered tools, designed to suit specific machines, components and operations. Examples included cylindrical, tapered, bent and elliptical boring-bar sections. The aim was to maximize rigidity, dampening vibrations when deep accessibility was needed. By then, experience and know-how in designing and applying dampened tools had been built up by jointly by Teeness and Sandvik Coromant.
During the nineties, the growth of the oil and gas industry needed a number of deep-bore components to be efficiently machined. Flat-bed lathes experienced a rebirth partly as oil-country lathes. These are more rigid and better equippped to machine the long bores needed in the oil-exploration parts. A range of dedicated dampened boring-bars (type 580) were developed in a diameter range of 80 to 300 mm, ideal for roughing and finishing when bars capable of ten times the diameter were needed – and specials that could do fifteen times the diameter. These could be manually tuned, through a radial tuning screw and had exchangeable cutting-heads. Carbide re-inforced bars were also available with the largest dimaters weighing almost three tons. These bars provided a solution to many demanding operations and saved delivery times of parts needed at very short notice in oil fileds.
For slant-bed CNC-lathes, a standard programme of pre-tuned dampened bars (type 570) was developed for a diameter range of 16 to 100 mm. These were equipped with small, light cutting units that were easy to change, very securely mounted through a serration-type coupling. A short and long version of boring bars was available for up to seven and ten times the diameter, respectively. These formed an efficient, easy-to-apply solution to many varied internal-turning operations and were used extensively for many different applications in different industries. These were the forerunners to the Silent Tools programme of today`s dampened tools, with cylindrical clamping, Coromant Capto, CoroTurn SL and QC for internal turning, grooving and threading. Quick changing of tools in turning machines have been increasingly seen as an important route to better machining economy and dampened boring bars have been a vital part of the tool assortment.
Vibration dampening is also an issue in milling and boring as a rotating tool. Today`s Silent Tools, developed by Sandvik Teeness, have solutions for these machining areas when long tool-overhangs are needed. A range of adaptors in various lengths, with exchangeable cutters, have been especially developed for the specific demands of these methods, that are quite different from single-point turning. Tool assemblies that incorporate a Silent Tool adaptor are part of solutions where milling cutters or boring tools can perform to higher cutting data, provide better results and provide longer, more secure tool-life. The dampening system has also been developed so as to be built into the shanks of certain milling tools, such as endmills that need long reach in industries like die and mould making.
Dampened tools, of different sizes and reaches, are also becoming an increasingly important part of tooling in multi-task and mill-turn machines. Development of dampened tooling, as standard tooling or advanced engineered bars, for solving complicated applications in various industries have been ongoing since the start in the seventies and have also included solutions with machine tool builders. Seperately today, dampening units have been developed to be incorporated in Serration Locking blades, engineered particularily for the aerospace and energy industry to make deep and complex grooves, often in demanding materials.
Today, the Silent Tools programme includes standard tools with diameters up to 250 mm. The largest boring bar delivered has a 450 mm diameter for a ten times the diameter overhang, weighing seven tons. Dampened tools are on the increase for rotating-tool applications within the CoroBore range in machining centres. Quick-change of Silent Tools is being applied increasingly on turning centres. Especially in larger machines, such as when Coromant Capto C10 couplings are used, the quick-change facility is an advantage when boring bars stick out so far that it is hard for other operations to be carried out with the bar in the turret. Instead of rigging the large boring bar every time, which take an average of forty minutes, the quick-change takes five minutes. Also automatic tool change has been installed, such as when a robot (which also changes components) changes a 100 mm Silent Tool boring bar with an overhang of fourteen times the diameter.
A recent example of a state-of-the-art solution for large dampened boring bars was together with the maker of large mill-turn machines. The application in question was the internal turning of long titanium components. The bar was engineered and made to have a reach of thirteen times the diameter – 176 mm diameter with an unsupported reach of 2300 mm. The bar also had to have automatic tool change at the front of the bar. To provide easily-evacuated chips for operational security, the bar was equipped with an ultra-high-pressure coolant supply (350 bars) for a jet at the cutting edge to form chips.
Silent Tools is today the leading, global brand in vibration dampened tooling. Sandvik Teeness in Norway has made a long journey in the development of the original viration-dampening idea for machining to today`s position, since 2008. Today, it is the global competence centre for anti-vibration machining within Sandvik Coromant, with research, concept-development, design of engineered and standard tools and application support.
Today`s innovative, patented systems of dampened tooling is seen globally as state-of-the-art technology. Although very distant compared to the original concept at the outset, tool-dampening can still be said to be based on the principle of a heavy mass, supported by specially designed rubber springs in a special fluid. It is the result of R&D into the nature of dynamic vibrations, and decades of experience from solving tool-reach applications. It has resulted in that Sandvik Coromant Silent Tools have moved dampened tooling on from problem solving to means of productivity boosting.
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Sandvik Coromant
Sandvik Coromant is a world-leading supplier of cutting tools and tooling systems for the metalworking industry and is represented in 130 countries. 27 state-of-the art Productivity Centers located around the world provide customers and staff with continuous training in tooling solutions and methods to increase productivity. Sandvik Coromant is part of the Tooling business area of the Sandvik Group.
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Contact: Lianne Mills
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Email: Catherine.li@sandvik.com
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