Precision Machining Projects
New machine tools for tomorrow’s production

Knowing in what direction machining of parts is developing, is of importance to the project and design engineer. His or her concern is: what will be possible in the near future? And how to implement this in part designs? During the upcoming EMO Hannover Fair – the main platform for the metalworking indusries in Europe – four practical research projects will be presented. They give a clear indication what machine tools will be able to achieve in the near future in the field of precision machining of 1 µm and less on parts that cannot be regarded as falling under the micro category. A technology update.

Hosted on 15 and 16 September 2005 by the German Federal Ministry for Education and Research, jointly with the German Machine Tool Builders’ Association, the symposium “Cutting-edge machine tools for tomorrow’s production” presents different research projects. One of this event’s subject groups focuses on “Micro and precision machining”. For one to one-and-a-half years now, four projects titled HiDynMolder, MechaSpeed, SonicPrecision, and MICROSTRUCT have been researching into precision machining of 1 µm and less – on parts that cannot themselves be regarded as falling under the micro category. These projects pursue diverse approaches, all with strict practical relevance. After all, each project is accompanied by various companies that integrate their practical experience gained over many years.
The objectives of HiDynMolder and Mecha-Speed are machine tools for tool and mould construction that achieve essentially greater geometrical precisions and surface qualities than today’s machines – at greater machining speeds to boot.
SonicPrecision targets the high-precision machining of axisymmetrical components of hard brittle materials, and MICROSTRUCT has set itself the goal of machining ultrafine, replicative structures on large-area embossing rollers.

HiDynMolder:
precision and machining speed
The multidisciplinary project HiDynMolder to which the participating companies and institutes (see box) have contributed their own elements is to give rise to a five-axis machining centre for the flexible manufacture of microcomponents and -structures. This project develops not only the actual machine with maximum dynamic response and a positioning precision less than 1 µm, but also a high-frequency rotary spindle with a max. speed of 250,000 rpm and a max. radial run-out of 0.001 mm. In addition there is a laser machining module with a standard beam cross section of 2.5 µm and an optical measur-ing sensor for point-by-point scanning with axial and lateral resolutions finer than 30 nm and ±0.5 µm respectively. Industry needs such a machining centre to manufacture moulds for the mass production of microengineering products, for example microstructured mould cavities in injection micromoulds or embossing micropunches. Also the smallscale and mid-volume production of complete micro- and precision engineering products is possible on one such machine. Typical parts are micromechanical components for keyhole surgery. The machine can be used to manufacture components for complex microsystems as well (e.g. microreactors, micromixers, microdrives, bioanalytical microchips, etc.). Moreover, the HiDynMolder machining centre is suitable for rendering structures in the micrometre range – for example for the precision surface machining of functional surface elements on microcomponents such as optoelectronic coupling modules and housings for hybrid microsensors. These typical fields of application have tremendous economic relevance. Hans-Jörg Albrecht at the company coordinating the project Rolf Wissner, Gesellschaft für Präzisionstechnik mbH in Göttingen is convinced of this: “We’ve been active in high-speed and high-precision machining for a long time now. This project will help us to bring together more closely these two disciplines that are basically incompatible with each other.” The solution is based on a high-precision milling machine that combines HSC with micromilling and microgrinding tools. In detail, the responsible components are highly dynamic machine axes, a high-frequency spindle for micromachining, and a fast controller. At the conclusion of the project, the HiDynMolder machining centre is expected to achieve component precisions of ±0.5 µm on steel alloys with a max. hardness of 64 HRC. From the integrated process modules “Laser material machining” and “Optical capture of structures” the project partners expect improvements over the micromachining systems available to date with respect to the achievable minimum structural dimensions, manufacturing tolerances, and surface qualities. According to Hans-Jörg Albrecht the first prototypes will be unveiled as early as EMO Hannover 2005.

MechaSpeed:
Combined millers and grinders for better surfaces
The motivation behind the project MechaSpeed is fed by the constantly increasing demands for better delivery times and qualities in tool and mould construction, more specifically the faster and more precise 3D machining of complex surfaces. The machine this project aims to develop and the combination of HSC milling and jig grinding are to reduce the Ra values from today’s 0.2 µm possible on hardened tool steels to less than 0.1 µm and to enhance the working precision, also on larger workpieces, from 10 µm to less than 5 µm. At home in the field of HSC milling, Röders GmbH in Soltau has given itself the task of supervising this project to which in addition various parts suppliers on the machine tool sector are contributing their know-how. This project targets the optimisation of all relevant subsystems in the machine tool. This optimisation includes, for example, the development of a main spindle that is suitable for milling and grinding processes and surpasses by far the performance of spindles available at present. Also the directly driven feed axes are to facilitate considerably improved machining results through improvements to the motor design and controller hardware and the application of innovative controller strategies. Modern design methods and considerations to alternative materials are to optimise the machine design. Dr.-Ing. Joachim Findeklee, head of HSC machine development at Röders, explained: “In 2003 Röders presented an HSC milling machine that was fitted with hydrostatic guides and direct linear drives for achieving the maximum possible performance. The project MechaSpeed is a consistent continuation of this technology.” However a MechaSpeed machine tool will not yet be presented at EMO Hannover 2005.

SonicPrecision:
Ultrasonics for longer tool lives
Maximum contour and surface qualities are also targeted by the project partners for SonicPrecision, this time though in the field of hard material turning. Ceramics and specially hardened steels are to be finished to a high precision with extremely sharp monocrystalline diamonds. Before, these materials had to be ground if they were to exhibit the required tolerances, surfaces, and concentricities – an extremely time-consuming process. The approach taken by the multidisciplinary project SonicPrecision in developing a precision lathe for hard materials is divided into two parts. The first involves considerably raising the precision of a series lathe for the application by integrating hydrostatic guides, thread drives, and motor spindle. The second part consists of an ultrasonically assisted tool unit, in this case an oscillator installed beneath the tool holder and emitting ultrasonic vibrations that raise the machining diamond tool by a few micrometres along the feed direction over 40,000 times a second. This reduced contact time allows better tool cooling and there is scarcely any wearing. In addition, the affinity between the carbon contents of the workpiece and diamond tool cannot develop such a high destructive effect when steels are machined. If turned parts of hard materials are to exhibit maximum concentricity, minimum tolerances, and optimal surfaces, the lathe must be adapted. Jochen Schönfeld, managing director of Hyprostatik Schönfeld GmbH in Göppingen and head of the project SonicPrecision, is certain of the ideal solution: “Hydrostatic guides with hydrostatic thread drives are free of wearing and, when stationary, free of friction. Consequently the carriages can be positioned to within ±0.1 µm, and that after years as well. Moreover, they exhibit superior damping properties that make possible the high surface quality and concentricity. At the same time the hydrostatic oil keeps the machine temperature constant and reduces heat losses. That’s why hydrostatics has now become standard for ultra precision machines, just as for modern surface and cylindrical grinders, and in addition is featured on more and more of the better lathes and milling machines. Also the other projects described here rely on hydrostatics.” Furthermore, the project SonicPrecision uses a new hydrostatic motor spindle with a hollow shaft that promises the project’s partners the optimal concentricity under high loads and with low heating. Jochen Schönfeld explained: “Without a doubt the spindle with hydrostatic bearing effects a better concentricity on the workpiece. Our programme already includes now hydrostatic spindles for grinding machines that generate concentricities within 0.1 µm. The alternatives on ball-and-roller bearings can achieve only about 1 µm over the long term. We hope to be able to present the new main lathe spindle developed in this project as early as EMO Hannover 2005.”

MICROSTRUCT:
Microstructures on large rollers
The target of the multidisciplinary project MICROSTRUCT is a machine for the ultra precision machining of large-area rollers – up to 600 mm in diameter and 2,000 mm in length – used to manufacture embossing rollers for the low-cost, replicative, continuous mass production of surfaces with pattern sizes from 5 to 150 µm. Such films are products enjoying ever greater demand, whether aircraft construction experimenting with sharkskin structures for reduced drag and therefore fuel consumption or the building industries promising themselves cosier living conditions through light-directing films on windows. Yet such films are economical only in continuous production, which in turn needs microstructured rollers of large diameter. Ideal for their manufacture is ultra precision machining with geometrically predefined cutters. Natural diamond as the cutting material produces pattern sizes of less than a few micrometres on surfaces exhibiting roughnesses Ra less than 10 nm. The project supervisor Michael Strobel at LT Ultra-Precision Technology GmbH in Herdwangen-Schönach is all too familiar with the problems: “We manufacture optical surfaces on nonferrous metals, and the project MICROSTRUCT gives us and other specialists the opportunity to eliminate together the problems encountered on this sector. One particular challenge our task is faced with is the magnitude of the rollers we have to machine.” To date it has not been possible to machine microstructures in large-area rollers, so a new machine concept must be created. The result is a new ultra precision machine featuring three linear and one rotary axis. High rigidities and good damping properties are obtained when hydrostatic designs are applied to both the guides for the linear axes and the roller’s bearing. The carriages are driven by linear motors. An alternative option takes the form of a highly dynamic extra axis, a so-called fast tool servo system, that can be secured to the x axis in lieu of the fixed tool holder when non-axisymmetrical microstructures are to be machined. The central element for quality assurance is a surface measuring system integrated in the machine controller. Owing to the size of the workpieces and the required micrometre precision, the machine is fitted with an integral confocal 3D measuring system for characterising the machined microstructures. The expected high machining times necessitate automatic tool changes and camera-assisted tool calibrations that must satisfy the extreme precision requirements of this ultra precision technology (angular precision 0.5 sec; positional precision 1 µm). The surface measuring system initiates the automatic tool change when the surface quality no longer meets the requirements. <<