Welding of Active Diamond Elements on Cutting Disks Using CO2 Laser

Transcription

1 2ND on Innovations, Recent Trends and Challenges Welding of Active Diamond Elements on Cutting Disks Using CO2 Laser Georgios Charalampides 1, Octavian Dontu 2, Gheorghe I. Gheorghe 3, Daniel Besnea 2, Iulian Avarvarei 2, Robert Ciobanu 2, P.Beca 3 1 President TEI Univ. West Macedonia Kozani-Greece 2 - University Politehnica of Bucharest, Dept. of Mechatronics, 313, Spl. Independentei, 77206, Bucharest, Romania (corresponding author to provide phone: (4021) ; fax: (4021) ; 3 National Institute for Research & in Precision Mechanics, Bucharest. ABSTRACT In this paper there are presented the results of welding experiments using a CO2 laser of active diamond elements on the body of cutting tools used to cut hard materials in construction field (marble, concrete, granite). Key words: laser welding, diamond segment INTRODUCTION Starting from the necessity of cutting of hard materials used in construction industry (granite, marble, different types of concrete, reinforced concrete) as well from the new EU regulations regarding user protection (whom in most cases are persons with modest training), new requirements were set to manufacture diamond disks. [1,5,6]. These disks used in intense working regimes (peripheral speeds up to 30-50m/s, variable cutting depths and sometimes mechanical shocks) requirements for these tools were set, especially concerning the strength of diamond elements joint. The solution that we turn to was CO2 laser welding, continuous wave at λ = 10.6 µm, which offers the following advantages: - achieve high quality welding in areas difficult to reach - allows welding metallic materials with different fusion spots: stainless steel, titan, nitinol, platinum, - high speed of welding [mm/s]; - high strength welding for all the welded elements with good repeatability; The tools used with synthetic diamond granules fixed in a metallic matrix of composite materials with a complex composition. Positioning active elements on the tools body for welding must assure the complex geometry of the cutting tool and at the same time to have a high mechanical strength for different working regimes [5,6]. In what concerns the construction, cutting disks have a support- the steel disk, profiled with teeth with a specified geometry well specified on witch diamond elements [2,3,7], fig. 1. must be welded with standardized elements from table

2 2ND on Innovations, Recent Trends and Challenges Fig. 1 Tool support configuration Table 1. Standard dimension for disks D/L L X X 1 T T 1 R ±0,30 ±0,25 ±0,05 ±0,25 ±0,10 ±0, ±0,30 ±0,25 ±0,05 ±0,25 ±0,10 ±0,5 Table 2. materials used in manufacturing support disks Steel typel Improvement Treatments Annealing Hardening Tempering Hardness T( 0 C) Hardness T( 0 C) T( 0 C) HRC W HB Oil cooling Air cooling W HB Oil cooling Air cooling Active elements of the tool are segments, fig. 2, with a composite structure made of [4,5] : - a matrix of metallic alloy, Co (65%), W 2 C (18%), Si (7,5%), B(1,5%); - synthetic diamond granules reinforcement; Fig 2. Segment configuration\ 307

3 2ND on Innovations, Recent Trends and Challenges Table 3. Dimensions of the diamond segments Disk Number of R L T T 1 x x 1 Diameter (D) segments (n) D/2 40 1,7/2,0...5,5/6,5 1,2-4,5 x x On order ,5/7,5...14, x x x Welding these elements at the outskirt of the disk was performed using a CO2 laser installation [8,9,10] continuous wave (CW), with protection gas argon. The most important characteristics of the laser installation are: - peak power [W] - power density [ Wcm -2 ] - wave length 10,6 [µm ] - traveling speed: 0,7-1,0 [m/s] - focalized spot size; φ [mm] In figure 3, there is a detail of the disk s tooth. Fig. 3. Disk detail welding area tooth The metallographic analysis of the welding area between the diamond segment and the support disk was performed on probes, fig. 4. \ Fig. 4, Stereo micro structural aspect of the investigated probe (10X) It is visible that the resulted welding area has a good quality; the small number of small pores doesn t affect the assembling quality. The metallographic structure of the welding, fig.5, cross section shows the heat affected area close to the weld is minimum, as well as some discontinuities and pores µm that don t affect the joint quality. In the microscopic analysis (fig.5) after a short chemical attack it is evidenced the base mass of inhomogeneous components of superior banita, troositc and residual austenite, and in the 308

4 2ND on Innovations, Recent Trends and Challenges weld it can be observed insular areas, with needle shape, formed out of inter metallic compounds. The areas are of considerable dimensions µm, uniform displayed in the tooth matrix. a. microstructural aspect of the base material b. Micro structural aspect of the weld and base material c. micro structural aspect of a compound from the addition material with evidence of the polygonal particle detail Fig. 5. Microstructure aspect of the interface between the weld and the base material after chemical attack with natal 2% for short time in the presence of the additional material (x-50). In the welding area, after a chemical attack for a longer period of time, an heterogeneous solid solution, with dendrites segregation, is observed, fact evidenced by the detail image from figure 6.b, and also, in the weld area it is shown a macro pore type discontinuity (fig. 6.c).a (X-50) b (X-250) c (X-500) Fig. 6. Micro structural aspect of the weld chemical attacked with 2% natal 309

5 2ND on Innovations, Recent Trends and Challenges CONCLUSIONS The study, metallographic analysis and tests to which the welding were submitted on the batches of analyzed disks it allows to appreciate that these assemblies performed on laser welding correspond in all the aspects, being the only technological process which allows manufacturing diamante coated tools for cutting, highly used in geology and geodesy. By comparison to another methods of welding assembly of the diamond coated segments on the tool body, for example brazing, the proposed process has a better quality, it is not pollutant, it may be considered a clean process in accordance to all the environmental standards. REFERENCES [1] Gh. I. Gheorghe, P. Beca, s.a., Dezvoltarea unui sistem tehnologic de realizare prin sudare laser a discurilor diamantate de taiere, INDUSTRIAL APPLICATIONS OF LASERS - INDLAS BRAN, Romania, mai [2] V. Drăgănescu, V.G.Velculescu- Prelucrări termice cu laseri, Ed. Didactică, Bucureşti, 1986 [3] W.M.Stern Laser material Processing, Spinger Verlog, New York,1991 [4] A.R. Rosental Pre-stressing Disc-Shaped Tools by Laser, Industrial Diamond Review, Nr.5/1992. [5] S.T.Palauchik - Sawing reinfoced concrete with diamond blades General Electric, Specialty Materials Department Wortbington Ohio (SMD ) [6] Elio Morelli New laser welding machine for diamond tool manufacture, Industrial Diamond Review,Nr.582/1999. [7] O.Dontu, Sudarea cu laser a unor oteluri inoxidabile utilizate la instalatii de proces din industria chimica, Revista de Chimie, vol.56, nr.3/2005. [8] G.Adziev, T.Adyiev, A.Sedmak Mechanical Engineering Faculty, Belgrad, Serbia & Montenegro - Influence of the weldstrength mis- match on HAZ cracked specimens fracture - Buletinul Institutului National de Cercetare- Dezvoltare in Sudura si Incercari de Materiale Timisoara /nr.1/2007. [9] Sz. Bella, A.Bernath, J. Dobransky Budapest University of Technology and Economics- TIG, laser beam and resistance projection microwelding - Buletinul Institutului National de Cercetare- Dezvoltare in Sudura si Incercari de Materiale Timisoara nr [10] Dezvoltarea unei facilitati nationale de cercetare si aplicatii tehnologice de prelucrare termica cu fascicul laser, Contract CEEX 1/