RICERCA ITALIANA     

Technologies to machine and to control the surfaces in natural stone

Università degli Studi di Cassino

Abstract

In the last forty years the stone material has been used in a continuous way and it has seen only short periods whereas its employment has decreased. This means that stone employment has faced an increase of demand to which an increase of the offer has corresponded. This offer increase has been due to new countries whereas stone has started to be extracted, to the intensification of the extraction by the just operating quarries and to the discovery of new quarries. From 1999 the increase of granite and marble use has ever stopped, despite it has faced the competition of alternative materials; it has been very bigger than the expansion of the whole international economy. The rate of production increase has been of about 6.8% and the exchange rate has achieved 8.3%. The achievement of this results has been possible thank to the development of technology, to the increase in speed of the transport and to the re-discovery of marble and stone by the designer and builder.
Stone field and its surrounding has seen an increase in extraction and use of about sixty times in the ninth century, while the world population has increase of fifth times. The world stone production has overcome 100 millions of cubic metres with a turnover higher than 20 milliards of euro.
To strengthen and increase the Italian position in stone field it is necessary to create a net of technological and scientific competencies that support the innovation of the manufacturing processes and systems >>>

Principal Investigator

Luigi CARRINO Università degli Studi di CASSINO

Research Objectives

The general purpose of the project is to exploit the competences of national network constituted during the previous financed project COFIN 01 (entitled Stone Manufacturing technologies) by Universities and firms operating in stone manufacturing field. In this previous project studies on cutting of natural stone by traditional technology using diamond mill, disk or bead and by abrasive waterjet technology have been faced. Particularly, the aim of the present project, that goes on with the activities started in COFIN 01, looks at surface machining of natural stones through traditional and innovative technologies.
Moreover this project aims to develop procedures for natural stones products management from a quality viewpoint, satisfying the new norms related to building products.
The surface machining is constituted by the set of processes on surfaces of a natural stone to give them aesthetic properties. Surface machining is fundamental to exploit stone product's expressive properties, such colour, texture, roughness, patterns and all the possible aesthetic attributes of a natural rock can be valorized, modified or minimized using the proper processes. Moreover, stone machining may improve its technical properties, like weather- or absorption-resistance. However, choosing a surface finishing depends on a set of variables, the most important of which are the final colour and, obviously, its related machining cost. In the range of superficial processing have a >>>

First Results

To have the set of tools and stones needed to develop the activities of the project, the test procedures and the values of the process parameters to model all the processes involved in the following stages.Expected results stage 2.1: Experimental equipment and model of the polishing forces for the two considered stones that will be function of both the process parameters and the used wheels.

Expected results stage 2.2: a tool life model and a methodology of validation by means of experimental tests.

Expected results stage 2.3: a semi-empirical relationship between the tool wear and the cutting forces.Expected results stage 3.1: Determination of the energetic material removal model in function of the process parameters for AWJ surface machining.

Expected results stage 3.2: Determination of the energetic material removal model in function of the process parameters for AWJ incision. An equipment to mark by AWJ small areas on rough surface of a product in natural stone.

Expected results stage 3.3: an equipment to mark by laser small areas on the rough surface of a product in natural stone.

Expected results stage 3.4: Selection and set-up of testing methods for the micro and macro mechanical properties of specimens provided by the project partners for the main processes considered in this project. Evaluation of the applicability of tests in the laboratory and possible extension to production, to acceptance >>>

Timescale

24 months

National and international background

Surface finishing is fundamental to exploit a stone product's expressive potential: colour, texture, roughness, patterns and all the possible esthetic attributes of a natural rock can be valorized, modified or minimized using the right treatments. Stone machining may improve its technical properties, like weather- or absorption-resistance. However, choosing a surface finishing always depends on a series of variables, the most important of which are the final colour and, obviously, its related cost.
Traditional manufacturing of natural stones uses diamond tools. The process occurs through chip removal due to the interaction between diamond grits and stone. Interaction between tool and stone generates process forces that depend by the properties of stone, of the tool and by the process parameters. Force and energy of cutting are very important parameters in studying and optimisation of cutting process. They have a direct influence on tool wear, on process temperature and on surface quality.
Very few researches exist in the literature about stone cutting. Jerro shows a mathematical approach to define and derive theoretical chipping geometries [1]. He empirically investigated the relationship between tangential cutting force and chip thickness. Brach et al. studied the problem to convert dynamometer reading of specific cutting energy into consumed power [2]. Asche et al. showed empirical studies on the influence of process parameters on tool wear [3]. Konstanty >>>