The present i nventi on rel ates to a method of machi ni ng a hi gh hardness carri er sheet, and more particularly to a method of forming cavities on one si de of a carri er sheet of high hardness i n a predetermi ned pattern for mounting electronic units therein.

Claddi ng and decorative elements made of natural and artificial materials such as stone, machined wood, natural wood, composite materials, plastic or a combi nation thereof are preferred i n the construct! on i ndustry . V ar i ous opaque ti I es are thi nned i n cert ai n areas to such an extent that they can function as a di splay surface, for example, they are suitable for displaying pictograms and animations. Sufficient thinning of high-strength carrier sheets in relatively small size ranges, such as a few centimeters in diameter, is a major technological challenge with currently known mechanical machining techniques.

The patent document ES1 129455 discloses a robot cell for cutting, mi lling, grinding and polishing large sheets of natural material . The multi -axis robot can also be equipped with a water jet head for individual machining of boards.

The patent document CN 109968543 describes machining of a product made of natural stone. The stone products have at least one light-transmitting surface and at least one light source i 11 umi nati ng the I i ght-transmi tti ng surface. I f the I i ght source bui 11 i nto the stone product is not active, only the natural pattern of the rock is visible on the surface of the stone product. The wall thickness of the transl ucent surface is between 0.5 mm and 3.5 mm by sawing, sanding and polishing.

The disadvantage of the above solutions is that when thinning carrier sheets of high- hardness, the light transmitted through the surface suffers a significant attenuation due to the relatively high roughness of the machi ned inner surfaces, which necessitates the installation of relatively high and therefore large electronic light emitting units. Large-scale electronics requi re the cutting of wide cavities, which on the one hand, weakens the mechanical strength of the carrier sheet as a whole, and on the other hand, significantly reduces the resolution of the i mage that can be di spl a ed.

I n addi ti on, pri or art machi ni ng processes can cause breakage and hai rl i ne cracks i n the carrier sheet’s material , resulting in quality problems or loss of production.

It is an object of the present invention to improve the prior art methods of processing carri er sheets of hi gh hardness to enabl e such carri er sheets to di spl ay hi gher resol uti on i mages without significantly reducing the maximum available light intensity.

The above obj ect i s achi eved by the method accordi ng to cl ai m 1 . Preferred embodi ments of the method accordi ng to the i nventi on are def i ned i n the dependent cl ai ms.

The process accordi ng to the i nventi on wi 11 now be descri bed i n more detai I wi th reference to the drawi ngs. I n the drawi ngs:

- Figure 1 is a flow diagram illustrating the main steps of the shaping method according to the invention;

- Figures 2a and 2b are schematic sectional views of the shaped carrier sheet before and after shaping.

As used herein, a "carrier sheet of high hardness" is asheet of rigid, natural or man-made material that is opaque to a commercially available thickness, but which, when sufficiently thinned, can be illuminated with light sources of relatively low power. Such materials incl ude gres, stoneware, natural marble, artificial marble, concrete, and the like. The carrier sheet can be a wall tile, a floor tile, a home furniture tile, an office furniture tile, a multi -function table top, a stand-alone di splay panel , a worktop, etc., depending on the purpose of use.

The mai n steps of the method accordi ng to the i nventi on are descri bed wi th reference to the flow dia ram shown in Fig. 1. The shaping process is performed on a carrier sheet 1 shown in Fig. 2a in asectional view.

The carrier sheet 1 is an initially solid sheet having afront surface 10, which is generally the surface of the carrier sheet 1 visible to the user. On the si de opposite the front surface 10, the carri er sheet 1 has a back surface 11 , i n whi ch the el ectroni c uni ts necessary f or i 11 umi nati ng the carrier sheet 1 are mounted. In order to beableto illumi natethe carri er sheet 1 , it isthinned from the di recti on of the back surface 1 1. The back surface 11 of the carri er sheet 1 isgenerally not vi si bl e to the user duri ng use, after the carri er sheet 1 has been i nstal I ed.

The typical size of the carri er sheet 1 shaped by the method is at I east 100 mm x 100 mm, typically 1200 mm x 1200 mm, but not more than 6000 mm x 2000 mm. The thickness of the carrier sheet 1 before shaping is typically at least 6 mm.

Prior to the start of the shaping process, the carrier sheet 1 is preferably cleaned, for exampl e by al cohol or other cl eani ng agents, so as to compl etel y remove the organi c and i nor- gani c contami nants, such as f ats or any auxi I i ar i es whi ch may have come i nto contact wi th the carrier sheet 1 , from its front surface 10 and back surface 11 .

I n the first step S100 of the method according to the invention, the front surface 10 of the carri er sheet 1 is covered with a protective layer 20. The protective I ay er 20 is preferably a high-tensile plastic film. By using the protective layer 20, the mi cro-vi brations of the carrier sheet 1 caused by the mechanical processing means can be significantly reduced during the shaping steps. The elimination of mi cro-vi brations is necessary because the ai m of the high- preci si on surf ace treatment i s to achi eve a surf ace roughness smal I er than the ampl i tude of such micro-vibrations. I n the present i nvention, the protective layer 20 may be, for example, the protectivefilm ‘Protect’ of the company 3M having a thickness of 50 to 500 gm. The protective layer 20, in particular the plastic protective film, is electrostatically fixed to the front surface

10 of the carrier sheet 1 , so that the protective layer 20 can be removed from the carrier sheet 1 at the end of the shaping process or at a later time thereafter. Since the protective layer 20 remains on the carrier sheet 1 throughout the process, it also protects the front surface 10 from mechanical impacts, such as chips, dirt, scratches and low-power shocks.

I n a further step S1 10 of the method, a glass sheet 30 with a thickness of at least 4 mm is placed on the surface of the protective layer 20 opposite the carrier sheet 1 , which is glued to the carrier sheet 1 (more precisely to its protective layer 20). Since the glass sheet 30 is mechanically consistent with the material of the carrier sheet 1 , it further increases the rigidity of the carrier sheet 1 and further reduces the mi cro-vi brations resulting from machining and di st r i butes wel I the I ocal I y generated mechani cal stresses on the carri er sheet 1 due to mechan- ical loads. Therefore its use prevents the formation of undesired hairline cracks in the carrier sheet 1 during machi ning.

The glass sheet 30 and the protective layer 20 together form a transparent layer on the front surface of the carrier sheet 1 , thus any material structural defects in the front surface 10 of the carri er sheet 1 can be detected already during the shaping process.

On the one hand, the glass sheet 30 provides mechanical , static rigidity to the carrier sheet 1 up to the final stage of machining, and si nee it forms an integral part of the carri er sheet 1 , it also protects the front surface 10 of the carri er sheet 1 from external infl uences. The carri er sheet 1 provided with the protective layer 20 and the glass sheet 30 can be arranged in a fas- teni ng frame for moving and machining, which hoi ds the sandwich- 1 ike layers together during both machining and subsequent i nstal lation.

After the appl ication of the protective layer 20 and the glass sheet 30, the cavities 50, into which the light emitting electronic units can be inserted, are formed on the back surface

11 of the carrier sheet 1. The shaping is started in step S120 by milling. The mil ling is pref er- abl y carri ed out u si ng a CN C machi ne, f or exampl e the mi 11 i ng center ‘ Prof i I e 6033 CN C’ f rom CMS. Based on a predetermi ned pattern of the cavities 50 to be formed, the machining plan is prepared and then the tool paths are generated using the software of the CNC machine. The cavities 50 to beformed are typically formed with afloor area between 100 mm x 100 mm and 1900 mm x 1100 mm, depending on the function of the electronic units to be installed. The CNC milling in step S120 creates the cavities 50 in the carrier sheet 1 with atypical accuracy of tenths of a mi llimeter, but optionally up to a hundredth or a thousandth of a mil limeter. For example, for acarrier sheet 1 having thickness of 6 mm, each cavity 50 isformed by removing a thickness of approx. 2.1 mm, i .e. the thickness of the thinned parts of the carrier sheet 1 will be approx 3.9 mm, which in the case of gres sheets, for example, results in a sufficiently reduced thickness to al low its transillumination by a laser light source having a power of 0.1 -30 W (e.g. laser matrix or laser projector).

Some factors that greatly influence the choice of technological parameters of the mil ling operation in step S120 include the fol I owing:

• the composition of the material of the given carrier sheet 1 because gres, stoneware or marbl e i s not a compl etel y consi stent materi al ;

• the humidity and the temperature in the vicinity of the carrier sheet 1 because if too many parameters of the material change duri ng the mil ling of the carrier sheet 1 , it can lead to breakage;

• the thickness of the carrier sheet 1 because the materi al loses its strength during thinning, thus cracks may appear on the front surface 10 or the back surface 11 of the carrier sheet 1.

• the position of the cavity 50 to be machined on the carrier sheet 1 , i .e. if , for example, a cavity 50 is located at the edge of the carrier sheet 1 , the cutting speed must be increased, for example by i ncreasing the tool speed, which amplifies the micro-vibrations in the materi al ;

• the thickness of the thinned parts of the carrier sheet 1 because the cutting speed must also be increased when machini ng the bottom of the cavity 50, which also amplifies the micro- vi brat i ons formed i n the materi al on the thi nned parts.

In order to reduce or eliminate the adverse effects described above, the carrier sheet 1 provided with the protective layer 20 and the glass sheet 30 is preferably placed on a vacuum work tabl e, where the ent i re area of the carri er sheet 1 i s f i xed to the work tabl e wi th a substan- tially uniform force distribution. However, in order to avoid an i ncrease i n the i nternal stress in the material as a result of the machining, the vacuum fixation al lows the carrier sheet 1 to resonate to a small extent.

In order to avoid high resonance, in step S120, a real-time resonance test is performed on the carrier sheet 1 duri ng milling, as a result of which the machining parameters such as CNC machine speed, milli ng head feed, coolant flow rate, etc. are continuously controlled so that the vi brat i on properti es of the carri er sheet 1 do not exceed predetermi ned threshol d val ues.

During the resonance test, various physical properties of the carrier sheet 1 , such as the vibration amplitude, the vibration frequency, the lateral propagation of the vibrations, etc. can be measured. The resonance test can be performed i n several ways, such as:

• physical vibration measurement in the four corners of the carrier sheet 1 , preferably by means of sensors;

• optical vibration measurement at a mini mum of four poi nts i n the range of 80 mm to 200 mm from the surface to be machined, preferably by a laser measurement system; and

• vibration measurement along theentiresurfaceof thecarrier sheet 1 , preferably by means of a camera system.

During the mil ling in step S120, the sound effects can also be examined in order to deduce any defects in the material . If, for example, an imbalance occurs during drilli ng at the beginning of the mil ling, the sound effect of the machining changes, thus it may be learned even before the formation of cracks that some technological parameter is not appropriate. The sound effects that have changed as compared to pre-stored sound samples can indicate, for example, the following problems: drill bit wear, support movement, change of the rotational speed, change of the cool ant volume, and so on.

When milling materials of high hardness, such as gres, diamond-coated mi lling heads with a diameter of between 1.5 mm and 4 mm are preferably used. During milling, the rotational speed of the CNC machine is preferably regulated in the range of 7,500 to 12,000 rpm.

Si nee the thinned areas in the cavities 50 may be macroscopically wavy due to the small vibrations of thecarrier sheet 1 during mil ling, the thickness of the carrier sheet 1 after cutting is uneven and the machining tools leave grooves and tracks on the surface of the cavities 50. These surface irregularities are optically i maged with a fi rst image resolution in step S130 of the method. The image is preferably captured by optical scanning, so-cal led scanning, where the scanning is performed with an image resol ution of 10-500 |im. The purpose of 3D scanning of the surfaces is to allow the surface of the cavities 50, in particular the inner surface of the thinned portions, to be further refined for transparency in the next shaping step, or i n other appl i cat i ons to achi eve sensory detecti on or f I ui d exci tat i on.

After the f i r st scanni ng step, the i rregul ar i ti es created by the mi 11 i ng on the i nner surfaces of the cavities 50 i n step S140 of the method are further reduced by shot blasting. As a result of the surface scanni ng in step S130, a 3D image is obtained of the grooves and troughs formed on the surface of the cavities 50. Based on thi s 3D image, the edges of the troughs created by the milling head of the CNC machine are blown, but only to the extent for obtaining a sufficiently smooth surface for an additional surface smoothing step.

I n the method of the present invention, in step S140, the inner surfaces of the cavities 50 are preferably sandblasted. For this purpose, a sandblasting system is preferably used, with which a surface roughness of approx. 10 pm can be achieved. The sandblasting system is preferably operated with the operational parameters determined on the basis of analyzing the 3D image obtained during the scanni ng i n step S130. Preferably, the flow rate of the parti cl es can be control led. Several types of sand can be used duri ng sandblasting, the grain size of the applied sand may be between 1 1 jim and 800 pm. The sandblasting head is continuously moved by a robot arm so that the sandblast! ng head never returns to the same surface poi nt and always follows a different path on the carrier sheet 1 . Convex surfaces can also be machined with a sandblasting head having a robotic arm tilting mechanism. The sandblasting system may be, for example, the sandblasting system ‘M istral Zephir’ of the company Fratelli Pezza, but other systems may also be used for other production parameters.

During the shaping in step S140, not only sandblasting but also other types of blasting media, such as steel or corundum grains, may even be used.

After shot blasting, another step of 3D scanni ng with an i mage resolution higher than that was used in the first scanning step is performed in step S150 of the method. During the scanning in step S150, 3D images with a resolution of preferably 1 to 10 |im are taken of the inner surface of the cavities 50.

Following the shot blasting, in step S160 of the method, an extremely precise fi nish! ng is performed on the inner surfaces of the cavities 50 using a mill ing head of the excimer laser beam type to create substantially polished surfaces. By applying the laser beam mil ling, no further significant amount of material is removed, only the surfaces of the cavities 50 are made to be completely uniform, as aresult of which the thickness of the carrier sheet 1 in the thinned areas will be entirely the same (at least the change in thickness falls within a submicron tol erance range).

During the laser beam machining, it is preferred to conti nuously measure the resonance of the carri er sheet 1 agai n by means of the i ntegrated sensors and to control the operati ng parameters of the laser beam milling machine on the basis of the measurement data

During the laser milling in step S150, a standard industrial excimer laser beam mi lling machine is preferably used, wherei n the laser beam emitting head is moved into the surface region to be machi ned by means of a driver unit on a machining station. The surfaces obtained as a result of the laser mil ling are already smooth enough for the light of the light sources placed in the cavities 50 to pass through the material of the carrier sheet 1 with a minimum of loss (reflection, scattering).

The carrier sheet 1 produced by the method according to the invention is illustrated in Figure 2b in a sectional view.

The advantage of the method according to the invention is that, as a result of the multi- step shaping, extremely thin surface areas can be economically formed on one side of a carri er sheet of hi gh hardness accordi ng to a predef i ned pattern so that the i nner surface of the cavi ti es behi nd the thinned areas is very fine and machined to be extremely uniform in thickness.

Although the method of shaping a carri er sheet has been described herein in connection with the mount of electronic light emitting units therein, it will be apparent to those ski I led in the art that the cavi ties in the groove may be used to mount other functional electronic units as wel l . For example, a fluid exciter for sound generation or other electronic units performing sensor detection or heating/cooling may also be mounted into the carrier sheet behind the thinned surface areas.