USAGE OF LASER TECHNOLOGIES FOR SURFACE ENGINEERING OF METAL MATERIALS POUŽITÍ LASEROVÝCH TECHNOLOGIÍ PRO ZPRACOVÁNÍ POVRCHU KOVOVÝCH MATERIÁLŮ

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1 USAGE OF LASER TECHNOLOGIES FOR SURFACE ENGINEERING OF METAL MATERIALS POUŽITÍ LASEROVÝCH TECHNOLOGIÍ PRO ZPRACOVÁNÍ POVRCHU KOVOVÝCH MATERIÁLŮ Roman ŠVÁBEK a, Radka BIČIŠŤOVÁ a, Jiří DUNOVSKÝ b a CTU in Prague, Faculty of Mechanical Engineering, Research Center of Manufacturing Technology, Horská 3, Prague 2, Czech Republic, r.svabek@rcmt.cvut.cz b ČVUT v Praze, Faculty of Mechanical Engineering, Department of Manufacturing Technology, Technická 4, Prague 6, Czech Republic, jiri.dunovsky@fs.cvut.cz Abstract This work is focused on the usage of laser technologies in the production of tools and moulds. Development and production of new formers and injection moulds poses claims on the added value of these tools. One of the possibilities, how to increase the durability, hardness, toughness and other mechanical properties, is the usage of laser technologies. With the laser beam it is possible to obtain results, which would be very difficult to obtain with conventional technologies. The new and progressive method of hardfacing layers rating is laser cladding. This could be also used repeatedly by the renewal of the specific part. Very good properties of the final laser weld deposit predestine this method for usage in very ambitious applications, for example formers, dies or injection moulds. The laser beam can be used for immediate heating of a specific part of a tool, too. With this case of modification it is possible to obtain a local heat treatment of a tool. The heat treatment with laser is suitable to use for edges of shear and bending tools, moulds or cutting tools. The result is a database of optimal working conditions for laser tool heat treatment (various hardening temperatures in dependence on various feed speeds). Significant modification of functional properties of tools for cold forming is possible to achieve by laser beam texturing and polishing. Keywords: Laser, Heat Treatment, Cladding, Texturing 1. LASER CLADDING The research work deals with possibilities of creation of protective hardfacing layers by laser cladding. A solid solid state laser JK 701H with output peak power 550 W is used. In this work different nickel based hardfacing alloys are used. The purpose is to raise wear resistance, hardness for formers and repairing damaged mold and dies. Laser cladding is a deposition welding process in which a layer of powder is deposited on the substrate material, and the two materials are fused by metallurgical bonding through the action of a laser beam. The characteristical features of this process are: highly precise, automated deposition of a layer of material with a thickness varying between 0,1 mm and several cm metallurgical bonding of the cladding material with the base material absence of undercutting low heat input into the substrate a wide selection of homologous and non-homologous powder materials the ability to process virtually any type of metal alloy

2 By varying the process parameters and selecting different powder materials, a component s surface can be either alloyed or cladded with a carbide or similar coating. Typical deposition rates lie in the region of several cm 2 per minute for layers with a thickness of around 1 mm. In this work special laser cladding head is used for experiments. It has been developed at Reseach Centre of Manufacturing Technology. 1 Input powder 2 Input gas (protection lens) 3 Cooling system 4 Input gas Fig. 1. Laser Cladding Head Coating powders were chosen HA5 and HA8 (producer UTP). Basic materials were (11 373) and (11 523) steels. Optimalization of cladding proces parameters has been determined optimal parameters for the best quality of coating. Many of the process parameters must be manually set, such as laser power, laser focus, substrate velocity, powder injection rate, etc. Fig. 2. Tested specimen Fig. 3. Laser cladding metallographical analysis The main fields of application are to be found in machine-tool and plant engineering, and engine manufacturing for the aircraft and automotive industries. Laser cladding can be used for a wide variety of purposes, including the application of wear-resistant or anticor rosion coatings, the repair of worn or poorly machined workpieces, deposition welding of shaped parts, and the complete manufacture of 3-D components. The results were used for extend laser cladding technology instead of other technologies with better quality and high productivity of laser process.

3 2. LASER HEAT TREATMENT In this part are presented the results of experiments which have been performed on the and Vanadis 6 tool steels with a 550 W Nd:YAG laser. To obtain the optimal laser parameters during the process was an infrared camera used. The microhardness in the depth, the wear resistance and the changes in the microstructure have been analyzed. The target of our research was to extend the database of the hardening parameters of tool steels by measuring with a thermal camera. With the thermal camera the temperatures of heat treatment process have been measured. These temperatures were compared with table values. With reference to this fact were the process parameters subsequently modified. The results were verified through the usage of the hardness measurements, metallographical tests and wear resistance tests. Fig. 4. Laser hardened surface steel Fig. 5. Laser hardened surface Vanadis 6 steel The experimental materials were represented by a high-alloy tool steel and by a Vanadis 6 ledeburitic type tool steel steel. During the experiments the temperature via a FLIR ThermaCam PM675 thermal camera was measured. The mechanical properties of the materials were evaluated through hardness tests on a Shimadzu HMV-2 hardness tester, tensile tests, fatigue tests and wear resistance tests on linear tribometer. The microstructure of the heat affected zone was studied on a ZEISS NEOPHOT 32 light microscope. On each steel specimen two laser tracks were made. For each specimen were different process parameters used. The specimens were before the tests not heat affected. During the tests also the thermal camera was used. For the next analysis the samples with different temperatures were chosen. The reason was a comparison with table values. The measured temperatures varied between 620 and 1280 C. The table value of the hardening temperature of the steel is C. By the measuring of the hardness was the hardened depth determined ca. 0,8 mm in the axis of the laser track. On each Vanadis 6 steel specimen one laser track was made. For each specimen were different process parameters used. The specimens were before the tests not heat affected. During the tests also the thermal camera was used. In the following table and on the following pictures (first two specimens) are the measured temperatures introduced. For the next analysis the samples with different temperatures were chosen. The reason was a comparison with table values. The measured temperatures varied between 412 and 1458 C. The table value of the hardening temperature of the steel is C. By the measuring of the hardness was the hardened depth determined ca. 1 mm in the axis of the laser track. The best measured hardness value is about 800 HV 0,3. The following picture shows the heat affected zone on the specimen 4. In top of the picture we can see the zone of partial melting. In the melting zone is a structure which matches the structure of the primary crystallization. Under this zone we can find the martensite, but its part in this area is less than

4 10%. Deeper under the surface is a wide track which equals the partial austenitization. In the picture bottom is an area of over tempering. The hardness in this area is lower than in the basic material. Fig. 1. Microstructure near surface On the materials was also the wear resistance tested. The achieved results were fully comparable with conventional hardened materials. Wide experimental program made possible to set optimal parameters for heat treatment of two tool materials ( and Vanadis 6 steels). By the right choice of laser parameters it is possible to obtain very good results. Very important is also the reproducibility of the results. It must be checked by sufficient counts of experiments. 3. LASER SURFACE TREATMENT The aim of research was finding of effect of laser treatment surface on tribological properties of surface for improvement of forming tools function properties. There were created 9 experimental laser treated surfaces (material of specimens tool steel ). For surface treatment was used Nd:YAG laser with output power 50 W and laser technologies laser polishing (surfaces tex1, tex2, tex3) laser soft texturing (surfaces tex4, tex5, tex6), combination of laser polishing and laser soft texturing (surface tex7) and holes creating (surfaces tex8, tex9). Tribological properties of laser treated surfaces (friction coefficient, friction moment, size of wearing, testing time until wearing generation) were tested and compared with tribological properties of untreated surface. Tests of tribological properties of laser treated surfaces were performed on tribometer THT-S-CE-0000 and on tribometer Amser. During tests on tribometer THT-S-CE-0000 hardened steel ball was rolled back onto laser treated surface of specimen, which carried out rotational movement and the ball created circular trajectory on planar surface of specimen. Tests were performed with setting of loads 1 N, 5 N and 10 N. During tests on tribometer Amsler were investigated tribological properties at touch face to face (outside cylindrical surface untreated, part of inside cylindrical surface laser treated) with setting of load 600 N. Further chemical analysis GDOES was performed on surfaces tex1, tex2 and tex3. Test of corrosion resistance was performed on all laser treated surfaces. In the following tables are measured values of friction

5 coefficient from tests on tribometer THT-S-CE In the following graphs are illustrated dependencies of friction coefficient on distance for laser treated and untreated surfaces. On tribometer Amsler better results of tribological properties were measured out on laser treated surface tex4 friction moment was from 50 to 70 cm.kg and testing time until wearing generation was 400 s. Lower fiction moment was measured out on laser treated surface tex2, tex3 and tex5, but testing time until wearing generation was shorter than values of untreated surface. During chemical analysis of surfaces tex1, tex2 and tex3 were measured out differences of concentration of elements - carbon and chrome. As a result of laser treatment of surface was detected disappearance of these elements in surface layer. High value concentration of carbon on surface of specimens was due to adhesive deposit molecules of atmosphere (e.g. CO2) and another hydrocarbon substrate which was in contact with surface. In the following graph are illustrated dependencies of concentration of elements on depth for laser treated and untreated surfaces.

6 From corrosion resistance tests was not established negative effect of laser surface treatment on corrosion resistance. It was no difference between laser treated surfaces and untreated surface. 4. REFERENCES [1] ABBOUD, J., BENYOUNIS, K.,OLABI, A. G.: Laser Surface Treatment of Iron- Based Substrates for Automotive Application. Journal of Materials Processing Technology, 2007, Vol.182, Issues 1-3, pp [2] SHIN,H.J., YOO, Y.T., AHN, D.G.: Laser Surface Hardening of S45C Medium Carbon Steel Using Nd:YAG Laser. Journal of Materials Processing Technology, 2007, Vol , Issues12, pp [3] JURČI, P., CEJP, J, BRAJER, J.: Metallurgical Aspects of Laser Surface Processing of PM Cr-V Ledeburitic Steel. Advances in Materials Science and Engineering, 2011, Article ID , 8 pages. [4] STRUTT, P. R.; NOWOTNY, H. TULI, M., KEAR, B.H.: Laser surface melting of high speed tool steels. Materials Science and Engineering, vol. 36, no. 2, 1978, pp