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Content archived on 2024-04-30

Development of advanced tools for ecological and economic sawing of granite


The performance of the investigations have led to several improvements of the machine-construction, the tool formation and configuration just as the adaptation of the machining parameters. Contemplating the noise reduction of the machine by special protections which were applied to the transmission belt of the spindle a noise reduction of about 5-8 dB(A) can be reached. Another deliverable concerning to the machine components is the improved spindle. During the first part of the project a new spindle system has been developed. This improved spindle working with toroidal ball bearings has an increased stiffness without trouble regarding to the damages of the bearing on the account of a hyperstatic construction. Furthermore a damping system against tool vibrations and deviation has been developed, followed by a more specific guiding system that have developed, designed and build in order to stabilize the thin core during the cut. Regarding the saw blades new thin steel cores able to reduce the slot thickness enormously have been developed. Main topics are the stability of the blade, the vibration behaviour and the deviation of thin steel cores during the stone cutting process. With the help of a special thermal or mechanical treatment of the steel it is possible to influence the cutting behaviour and the working result.

Further on the elaborated results in regard of the cutting segment design are very interesting for the optimisation of stone cutting processes. Especially the knowledge about the composition of the segment in reference to the choice of the diamond specification and the bonding as far as the diamond distribution are exploitable to industrial stone cutting processes. Additionally the development and the adaptation of the strain gauge measuring system can be exploited for different kinds of online-measuring technique and for the in-process quality assurance. It is also applicable to the measuring technique for several kinds of experimental set-ups. In this regard it is possible to measure dynamic stresses in moving and rotating tools or machine components. At least cutting with a steel centre thickness of 2.6 mm and a segment width of 3.5 mm is the most important outcome of the project.
Objectives and content
Metal bonded diamond cutting tools are used in several
industrial sectors. The natural stone processing
industry, the road building industry, and the building
industry are major fields of application in which
European companies still have the world-wide leadership.
Segmented diamond tools have been introduced into the processing of natural stone such as marble and granite
about 25 years ago. Their excellent properties in
machining of natural stone have elevated this abrasive to the leading position for this utilisation. The main products of natural stone are tiles of various sizes for decoration of floors and walls. These tiles are cut out of stone blocks by machine tools and circular diamond tools especially developed for this purpose. A main disadvantage of this application is the high cutting rate (material removal) because of low tile thickness. Tile thickness has been decreased in the last years in order to clad the same area with less stone material. This leads to a decreased consumption of raw material and to an increased outcome. Despite this tendency, depending on the tile thickness, cutting rates (material removed, waste) of more than 50% are common even up to now.
Because of this quantity of waste of workpiece material, it is obviously necessary to aspire an optimisation of tool and process. To reduce the enormous amount of waste, especially the development of thinner saw blades together with machine components and adjusted machining parameters marks an opportunity (in particular when
machining granite where tool life is just about 5% of the respective one for marble). Thinner discs would also have decisive ecological advantages because a reduction of pollution by cobalt, which is a main matrix component, and reduced energy consumption could be successfully realised. Costs and quantity caused by the waste stone material could be dramatically decreased. The aim of this project is both environmental and economical: to reduce dramatically the waste generated in the stone sawing process, and at the same time to reduce the costs of the process itself. This will be reached by reducing the thickness of the cuts, especially by developing system components (tool and machine) for the sawing with extremely thin saw blades (with a width of the steel core of about Wdz 3 mm compared to Wd= 5,0 -5,5 mm of conventional blades). For the most common steel
centre (diameter D = 1 m) segments with a conical shape Land a width of ws = 6,8 mm are used to minimise side friction between tool and stone workpiece. For this tool a maximum improvement of about 59 % would be possible
with the new system. The generated waste material will be reduced by 25% when using steel cores of a width of wd = 3 mm and a conical segment of a width of ws = 4,0 mm.
To achieve these objectives the developments in the project will include a high efficiency circular diamond tool including body and segment design and new tensioning techniques for this application. Completely new guiding techniques in order to stabilise the extremely thin tool will be developed in order to maintain a stable cut over long terms of time with a high accuracy, being indispensable for a highly automatic process.
The new techniques will offer a high variety of applications. The knowledge from the development of a circular diamond tool for granite might be transferred to similar fields of application, like the cutting of marble, wood or metal. The machines for the respective fields are in many respects constructed analogously to those for granite, so the resulting knowledge must not be used exclusively for the direct project purpose.

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