Fabrication of High Strength Bonded Abrasive Wheel with Ultrasonic Composite Plating

Transcription

1 Materials ransactions, Vol. 46, No. 9 (05) pp. 47 to 51 #05 he Japan Institute of Metals Fabrication of High Strength Bonded Abrasive Wheel with Ultrasonic omposite Plating Masahiro Okumiya 1, Yoshiki sunekawa 1, Akira Ueno 1, Yasuo Imada 1, Ryouichi Ichino 2, Satoshi amura 1 and akuma Saida 1; * 1 oyota echnological Institute, Nagoya , Japan 2 Nagoya University, Nagoya , Japan he life of an abrasive wheel, in which cbn and Ni P are co-deposited on a steel surface by electroless plating, is dependent on the grit adhesion and projection height. In electroless plating, it is difficult for Ni to deposit on ceramic grains. herefore, surface shape at the grain periphery is not flat but sunken. In this study, with the aim of achieving higher grain support for the abrasive wheel, the surface shape at the grain periphery is improved with the application of ultrasonic vibration. he grain periphery of the specimen obtained with ultrasonic vibration (amplitude 11 mm) revealed an interface with about a 10 mm embossment at the periphery. In addition, the deposition rate with ultrasonic vibration is 1.6 times faster than that without it. his paper also demonstrated that the ideal interface between the cbn grits and Ni P matrix is expected to have a heaped-up morphology, based on the results of a horizontal pushing-away test by a micro Vickers hardness tester for measuring the adhesive strength of grits. At the same time, the stress distribution around the grits in applying the lateral force to grit was simulated using the finite element method (FEM). he interfacial morphologies were observed between the cbn grits and Ni P matrix which were prepared with and without ultrasound. It assumed a flat or slightly sunken shape without ultrasound, whereas it exhibited a heaped-up morphology with ultrasound. he heaped-up height and width depended upon the amplitude, and reached their the maximum at an amplitude of 11 mm. With the best interfacial morphology, the adhesive strength becomes 22% greater than that without ultrasound in the horizontal pushing-away tests. If the grit is pushed to 0.03 N, the maximum interface tensile stress without a heaped-up interface is about 160 MPa in stress analysis by FEM, whereas with such an interface (height: 11 mm; width: 7 mm), it is about 210 MPa, for an increase of about %. (Received February 8, 05; Accepted June 6, 05; Published September 15, 05) Keywords: adhesion analysis, simulation, abrasive wheel, electroless composite plating, ultrasonic vibration 1. Introduction ubic boron nitride (cbn) is the second hardest of all materials after diamond, with a value of about 5000HV, 1) and a thermal conductivity superior to that of silicon carbide or alumina. Its crystal structure is stable up to 1600 K. 2) Electroless plated cbn abrasive wheels have been used to grind ferrous materials. 3) Nickel phosphorus (Ni P) electroless-plating is mainly used for co-deposition with cbn. he adhesive strength of electroless-plated cbn grits exceeds that of organic or inorganic binders. 4,5) It is also excellent for recycling. 6) It is possible to make electroless-plated cbn abrasive wheels in various shapes and to grind parts with complex shapes such as gears. he wheel life is dependent on the grit adhesion and projection height at the periphery, of the grits, since cbn grits are worn down under grinding. However, if the projection height of cbn grits is increased in order to increase wheel life, their adhesive strength is reduced and they readily become loose and are easily pulled out. However, if the projection height is reduced to improve adhesive strength, wheel life is shortened. Development of practical electroless-plated abrasive wheels at high-revolution speeds has been reported. 7,8) he cbn grits in such wheels are plated as a monolayer. herefore, if the cbn grits become worn down, the wheel life is diminished. hus, the development of a process in which the adhesive strength improves with an increase in the projection height of the grits is highly desirable. 9) he ideal interface between cbn grits and the Ni P matrix is expected to show a heaped-up *Graduate Student, oyota echnological Institute Present address: Noritake Bonded Abrasive o., Ltd., Nagoya , Japan morphology in the matrix side. Melt stirring with ultrasonic vibration has been carried out to incorporate alumina particles into molten aluminum-magnesium alloy. 10) he beneficial effects of ultrasonic vibration correspond to a reduction in the apparent contact angle between the alumina particles and the molten alloy system. Gas defects disappear in solidified metal matrix composite samples of composite slurries stirred with ultrasonic vibration, in which the particle distribution is also improved. his paper reports the effects of ultrasonic vibration on the interface shape between the cbn grits and matrix and the plating rate, and also demonstrates that the ideal interface between cbn grits and a Ni P matrix is expected to exhibit a heaped-up morphology, using the horizontal pushing-away test by a micro Vickers hardness tester for measuring the adhesive strength of grits. At the same time, the stress distribution around the grits was simulated using the finite element method (FEM) to apply lateral force. 2. Experimental Procedure Electroless plating was carried out in a conventional nickel sulfate (NiSO 4 ) bath to which sodium hypophosphorous (NaH 2 P 2 ) was added. A schematic diagram of the plating system with an ultrasonic vibration generator is shown in Fig. 1. he vibration direction of the substrate is perpendicular. he resonant frequency is 15.5 khz in the present vibration system. For the substrate we used plate (25 mm 25 mm, thickness: 3 mm) of JIS-S45 (0.46 mass%), a material generally used as a substrate for abrasive wheels. he ph was adjusted to 4.5. A cbn particle with an average diameter of 150 mm was

2 48 M. Okumiya et al. Heater Plating solution Agitator PZ oscillator Substrate Jig Horn Universal counter Function generator Storage scope High frequency amplifier Deposition rate, Dp / mm -1 ks Fig. 2 he effect of ultrasonic vibration amplitude on deposition rate. Fig. 1 Schematic diagram of the plating system with an ultrasonic vibration. used for abrasive grit in composite plating. At first, the cbn was co-plated on a substrate without ultrasound for over 3.6 ks. In the investigation of the effect of ultrasonic vibration amplitude on the deposition rate, the plating temperature used was 363 K and the plating time was 15 ks. he deposition rate was estimated by measuring each deposited thickness. Using a potentiostat, the effect of amplitude on the exchange current density was investigated. A silver chloride electrode was used as the reference electrode, and a platinum plate with a surface area larger than that of the working electrode was used for the counter electrode. A nickel-plated JIS-S45 substrate was used for the working electrode. he gross surface area of the specimen was 1: m 2. Once the polarization curve of the cathode reaction was obtained, we used the prescribed content of nickel sulfate aqueous solution whose ph value was corrected to 4.5 by the sodium hydroxide (this ph value is equal to ph which electroless Ni P is plated). After the polarization curve of the anode reaction was obtained, we used the prescribed content of sodium hypophosphorous aqueous solution whose ph was corrected to 4.5 by sulfuric acid. he relationship between the current and electrode potential was plotted on a afel plot in order to obtain the exchange current. Scratch marks were inscribed on the thin aluminum films set above the substrate by the cavitations caused by ultrasonic vibrations, and were then counted to compare the cavitation quantities. he thickness of the aluminum film was 12 mm, the distance between the film and substrate was 5 mm, and the measuring time was 10 s. After the electroless plating with ultrasound, the interfacial morphology of the cross section between the cbn grits and Ni P matrix was observed using SEM, while the adhesive strength was measured by a horizontal pushing-away test using a micro Vickers hardness tester. At the same time, by applying lateral force to the grits, the stress distribution around the grits was simulated using FEM. urrent, I / A Amplitude: 11 µm, 0µm Potential, Ep / V vs Ag/Agl Fig. 3 Anode reaction 3. Result and Discussion athode reaction he effect of amplitude on anode and cathode reactions. 3.1 Effect of ultrasonic vibration amplitude on deposition rate he effect of ultrasonic vibration amplitude (A U ) on the deposition rate was observed, the effects of ultrasonic amplitude on electroless plating rate are shown in Fig. 2. Although the deposition rate increases with an increase in A U up to 11 mm, it declines beyond A U of 12 mm. he maximum deposition rate at A U of 11 mm is 1.6 times higher than that without ultrasound. In electroless plating, it is necessary to remove the hydrogen generated during the plating reaction from the substrate surface, since it inhibits that reaction (it is easily removed by applying ultrasonic waves); however a few hydrogen bubbles remained on the substrate at A U of 10 mm. he thickness of the diffusion layer is reduced by strong agitation, thus enhancing the supply of ions. 11,12) he polarization curves of the sodium hypophosphate and nickel sulfate solutions with and without ultrasonic vibration are shown in Fig. 3. he current of hypophosphorous acid, a

3 Fabrication of High Strength Bonded Abrasive Wheel with Ultrasonic omposite Plating (a) (b) Exchange current, Ie / ma Surface area: 1.18 x 10-4 m 2 H W grit grit plating plating substrate 50 µm substrate 50 µm Fig. 6 he cross-section SEM photographs without ultrasound and with ultrasound (A U ¼ 12 mm). Fig. 4 he effect of amplitude on exchange currents. races on Al foil by cavitations, n / s/dm Length, L / µm Fig. 7 8 Width 10µm Height Relations between amplitude and heaped-up height or width. Fig. 5 Influence of ultrasonic amplitude on cavitation traces on Al foil. reducing agent, increases, when ultrasonic vibration is used. he exchange currents for the various ultrasonic vibration amplitudes were measured. he effect of A U on exchange current shown in Fig. 4 bears some resemblance to the effect of A U on deposition rate. We examined the reasons why the deposition rate decreases beyond A U of 12 mm with the following results. avitations are generated with the ultrasonic vibration, and their number was measured by traces on the Al foil placed 5 mm from the substrate. he cavitation traces on the Al foil are shown in Fig. 5. he number of traces rapidly increases at amplitudes exceeding 8 mm. herefore, as shown in Fig. 2, the plating rate decreases with increases in amplitude beyond 11 mm, since the plating inhibitory effect is strengthened by the generation of cavitations. As a consequence, the exchange current rises with a rise in amplitude, thus increasing the deposition of Ni. However, since the peeling of a plated film during cavity generation by ultrasonic vibration occurs concomitantly, the deposition rate drops below A U of 12 mm. 3.2 Interfacial morphology of cross section between cbn grits and Ni P matrix with and without ultrasonic vibration he interfacial morphologies between the cbn grits and Ni P matrix prepared with and without ultrasound were observed. he surface and cross-section SEM photographs with and without ultrasound (A U ¼ 12 mm) are shown in Fig. 6. Without ultrasonic vibration, the interface is a flat or slightly sunken. In contrast, it exhibits a heaped-up morphology on the matrix side with ultrasound. he heaped-up height and width were measured from SEM photographs, and their relation to A U are shown in Fig. 7. Both dimensions depend upon A U, reaching a maximum at A U of 11 mm, and declining beyond 11 mm. Since the thermal conductivity of cbn is greater than that of Ni, the heat generated at the interface between cbn and the substrate by ultrasonic vibrations is easily conducted to cbn. In electroless plating, Ni deposits only on the metal, and will not deposit on the material without catalysis. herefore, it deposits easily on the interface of cbn and Ni P. As a consequence, the deposition rate of the Ni increases with an increase in the amplitude, thus increasing the heaped-up height and width around the grits. However, due to the simultaneous peeling of a plated film

4 50 M. Okumiya et al. :ompression :ension Substrate Load Grid Matrix Fig. 8 Stress distribution analysis by FEM of grit and matrix plated without ultrasound under the load of 0.03 N. Drop away load, Sa / N Simulation value during cavernous generation by ultrasonic vibration, both dimensions around the grits decline below A U of 12 mm.his tendency is similar to the increase and decrease in the deposition rate of Ni. 3.3 Effect of ultrasonic amplitude on grit adhesive strength he stress distribution of the grits and matrix without ultrasound was estimated by FEM under a 0.03 N horizontal load, with the result shown in Fig. 8, whereas the distribution with ultrasound were estimated by FEM under several horizontal loads. he tensile stress is generated in the grit and matrix at the point where the peel force is loaded, while the compressive stress originates on the opposite side. In FEM analysis, the tensile stress of the interface between the grit and matrix rises as the applied load increases, and when it becomes equal to the adhesive strength between the cbn grits and Ni P matrix, the grits drop away. 0.2 Experimental value Fig. 9 Effect of amplitude on grit drop away load of experimental and simulation. he effects of A U on the grit drop-away load as estimated by FEM are shown in Fig. 9. Both experimental results are also plotted in Fig. 9, showing that both reached a maximum value at A U of 11 mm. With the best interfacial morphology at A U of 11 mm, the grit drop-away load becomes % higher than that without applying ultrasound in the horizontal pushing-away tests. Hence, the electroless plating process with ultrasonic vibration is proven effective for the fabrication of highly adhesive grits of abrasive wheels, since the interface between the cbn grits and Ni P matrix exhibits a heaped-up morphology. When the tensile stress of that interface exceeds the adhesive strength between the grits and matrix, peeling occurred on the interface. he FEM analysis results show higher values than the experimental results. he following results are considered. In the simulation, the grit is assumed to be a quadrangular pyramid to the side of which the force is loaded horizontally. Since the grits have various shapes, they can be moved more easily. Using FEM to measure the peeling strength simulated from the sample plated without ultrasound, it was estimated that the value was 0.4 MPa probably an overestimate. In this simulation, only the elastic deformation of the Ni P matrix is considered. However, both experiments and simulations the drop-away load of grits shown maximum values at the identical amplitude as 11 mm. omparing to Figs. 7 and 9, the drop-away load of grits depend on the heaped-up height and width. 4. onclusion he fabrication of highly adhesive grits for abrasive wheels by electroless-composite plating with ultrasonic vibration was studied. he following results were obtained: (1) he deposition rate increases with the ultrasonic vibration amplitude, reaching a maximum deposition rate 1.6 times higher than that without ultrasound. Ultrasound promotes the dispersion of hydrogen bubbles generated during the plating reaction. (2) he exchange current and deposition rate are dependent on the ultrasonic vibration amplitude. In the amplitude range from 6 to 11 mm, the exchange current increases, as the amplitude rises. Below an amplitude of 12 mm, the deposition rate calculated from the exchange current is identical to the actually measured deposition rate. (3) he interface of the grit and matrix is either flat or sunken in shape in the absence of ultrasonic vibration, whereas ultrasound creates a heaped-up morphology. he heaped-up height and width depend upon the amplitude. (4) With the best interfacial morphology at an amplitude of 11 mm, the grit drop-away load becomes % higher than that without ultrasound in the horizontal pushingaway tests. (5) In FEM analysis, the maximum grit drop-away load is obtained at an amplitude of 11 mm. Both in experiments and simulations, that loads show identical maximum values at the same amplitude, such as 11 mm. he dropaway load of grits depend on the heaped-up height and width.

5 Fabrication of High Strength Bonded Abrasive Wheel with Ultrasonic omposite Plating 51 REFERENES 1) S. Itoh: J. Surf. Finish. Soc. Japan 50 (1999) ) M. Estman: utting ool Eng. 42 (1998) 26. 3) M. Abe and K. omita: J. Surf. Finish. Soc. Japan 53 (02) ) M. Oota: utting ool Eng. 44 (00) 14. 5) H. Kobayashi: utting ool Eng. 42 (1998) 47. 6). Imai, R. Mukai and Y. Mizutani: J. Japan Soc. Abrasive echnol. 41 (1997) ). Imai, R. Mukai,. Yoshimi and M. Yoshikawa: J. Japan Soc. Abrasive echnol. 41 (1997) ) K. akeuchi and N. Kawabata: utting ool Eng. 40 (1996) 47. 9). Ishikawa: J. Japan Soc. Abrasive echnol. 37 (1993) 7. 10) Y. Genma, Y. sunekawa, M. Okumiya and N. Mohri: Mater. rans. JIM 38 (1997) ). Watanabe: J. Surf. Sci. Jpn. 11 (1990) ) H. akeuchi, Y. sunekawa and M. Okumiya: Mater. rans. JIM 38 (1997) 43.