Abstract: The coating and electroplated diamond tools were prepared by ultrasonic wave to test the hardness of the coating and the sand density of the diamond tool. The results show that when the current density is constant, the hardness of the diamond tool coating increases with the increase of ultrasonic power. In the diamond tool preparation process, the ultrasonic wave is not applicable to the whole process of sanding. As long as the diamond abrasive grains are buried in the plating layer, the ultrasonic wave can be used for the thickening process of the diamond tool to improve the preparation efficiency of the tool.
Key words: ultrasonic plating diamond hardness Electroplated diamond tools are often used for the mechanical processing of hard and brittle materials. At present, the plating is often combined with diamond abrasive grains by ordinary electroplating. The application of ultrasonic waves can significantly increase the plating speed [1]. There have been some studies on the strengthening effect of ultrasonic on the electroplating process [1~3], but there are few reports on the preparation process of electroplated diamond tools under ultrasonic conditions. This paper analyzes the influence of ultrasonic on the hardness sanding and thickening process of diamond tool coating, and strives to provide experimental basis for the preparation of ultrasonic plating diamond tool.
1 Experimental method 1.1 Plating solution and process The plating solution of this experiment is: NiSO4·7H2O, 250g/L; NiCL2·6H2O, 40g/L; H2BO3, 32g/L; C12H25SO4Na, 0.08g/L, bath temperature is 45 °C. The tool base is a Φ6mm cylindrical pin. The basic surface treatment process before plating is: mechanical treatment→water washing→deoiling→water washing→etching→washing.
1.2 Preparation of coating Ultrasonic coating The preparation process is pH=3.3～3.5, electroplating time t=1h, current density Dk=1.0A·dm-2, and ultrasonic vibration cleaning process is controlled by KQ-2500B ultrasonic cleaner. Ultrasonic working frequency is 40kHz. The input ultrasonic power is 250W, and the ultrasonic power range is 40% to 100%.
1.3 Tool preparation The pre-plating process is Dk=1.0A·dm-2, t=15min. Dk=1.0～6.0A·dm-2 in the sanding process under ultrasonic conditions, Dk=0.8A·dm-2, t=1h, diamond particle size 100/120, pH in the sanding process without ultrasonic conditions =4.4 to 4.6. Dk=1.0A·dm-2 during the thickening process, pH=4.4-4.6. First thicken for a period of time without ultrasonic conditions, and then continue to thicken for a while with ultrasound.
1.4 Test method The metallographic surface of the PGI type metallographic sample polishing machine was obtained by inlaying the cut test piece with the XQ-2 metallographic inlay machine, and the hardness was measured by a HX-I type micro hardness tester. The number of diamond particles at the same magnification line of sight was observed with an XTL-II stereo microscope.
2 Results and discussion 2.1 Effect of ultrasonic on the coating From the appearance, the brightness of the coating is significantly improved by the addition of ultrasonic waves. Ultrasonic can be used to obtain a bright coating in a common nickel plating solution. The reason is that when the cathode current density is high to a certain value, the cathode polarization increases sharply, causing the hydrogen evolution to increase, the pH value rises, and the nickel hydroxide solution appears at the cathode; and the cavitation of the ultrasonic wave refines the sol. And dispersion and stabilization to prevent sol condensation and precipitation. In this case, the finely dispersed fine sol can act as a brightener [1]. The cavitation of the ultrasonic wave improves the flatness of the surface of the coating, the ultrasonic enhancement, the thickness of the plating is reduced, but the porosity is reduced [2]. Ultrasonic plating reduces the porosity of the coating because the cavitation causes a strong emulsification. Under this strong emulsification, hydrogen bubbles are difficult to stay and grow on the electrode surface [3].
The test piece was thickened without ultrasonic conditions, and the thickness of the plating layer was measured to be 339 μm. When the test piece was thickened by ultrasonic power of 200 w, the thickness of the plating layer was measured to be 210 μm. Electroplating using high current density under ultrasonic conditions can make the coating more compact, smooth and smooth, uniform in thickness, non-porous, well bonded to the substrate, and have high strength and hardness compared with conventional electroplating [4] ]. Fig. 1 is a graph showing the relationship between the hardness of the plating layer and the ultrasonic power. It can be seen from Fig. 1 that the stronger the power of the ultrasonic wave, the higher the hardness of the plating layer.
2.2 Effect of ultrasonic on the sanding process After pre-plating, the sanding process is carried out under ultrasonic conditions. When Dk = 1 to 2 A·dm-2, no adhered diamond abrasive grains were observed on the tool substrate. When Dk = 4 to 6 A·dm-2, a small amount of adhered diamond abrasive grains can be observed on the tool substrate, and the nickel layer is blackened, and the bonding strength between the diamond and the plating layer is poor. When the current density is less than 2A·dm-2, the vibration and cavitation of the ultrasonic waves cause the diamond abrasive grains to continuously vibrate, and the stable contact state of the abrasive grains with the tool base cannot be ensured, so that there is no sand on the tool base. When the current density is greater than 2A·dm-2, a small amount of sand can be applied, but the plating adhesion is poor. Therefore, ultrasonic waves are not suitable for the sanding process of electroplated diamond tools.
2.3 Effect of Ultrasound on Thickening Process In order to analyze the influence of ultrasonic on the thickening process of diamond tools, four kinds of experimental conditions were set, and ultrasonic plating was performed under different conditions of embedded depth of abrasive grains. The specific experimental conditions are shown in Table 1.
The results are shown in Fig. 2. Under the experimental condition 1, most of the diamond abrasive grains on the diamond tool after normal sanding are shaken, but there are still abrasive grains remaining, and some pits can be observed on the surface of the tool coating. Traces of the diamond abrasive grains that were shaken; under the experimental condition 2, more diamond abrasive grains were observed on the surface of the tool coating, but there were still abrasive particles falling off; under the experimental condition 3, the surface of the tool coating was more adhesive. Diamond abrasive grains; under the experimental condition 4, it can be observed that the surface of the tool coating is adhered with diamond abrasive grains, and the surface of the plating layer has no abrasive particles falling off, and the density of the upper sand is large.
It can be seen from Fig. 2 and Table 1 that the tool after sanding is thickened without ultrasonic for 1.5 h, and then ultrasonically thickened by the same current density for 1 h. The density of the sand on the tool coating is the largest, and it can be observed that the diamond abrasive grains are almost all adhered to the plating layer. on. It can be seen that in the initial stage of thickening, as long as the time of no ultrasonic thickening is appropriate, that is, as long as the thickness of the diamond embedded in the plating layer is appropriate, the addition of ultrasonic waves will not shake off the already plated diamond, and only shake off the floating sand. Therefore, it does not affect the number of sands on the diamond tool. Ultrasonic is a thickening process that can be used for diamond tools by choosing the right conditions.
3 Conclusion The addition of ultrasonic waves increases the hardness of the coating, the coating is dense and bright, and the porosity is reduced. Ultrasonic waves should not be used in the whole process of diamond sand. As long as the time of no thickening of the ultrasonic wave is suitable at the initial stage of thickening, that is, the thickness of the diamond abrasive grains embedded in the plating layer is appropriate, and when the ultrasonic wave is thickened, the diamond abrasive grains are not shaken, and the number of sands of the diamond tool is not affected. In the process of thickening the diamond tool, the ultrasonic wave can be reasonably applied, and a larger current density can be selected to effectively improve the plating efficiency.
2.3 Effect of Ultrasound on Thickening Process In order to analyze the influence of ultrasonic on the thickening process of diamond tools, four kinds of experimental conditions were set, and ultrasonic plating was performed under different conditions of embedded depth of abrasive grains. The specific experimental conditions are shown in Table 1. 
The results are shown in Fig. 2. Under the experimental condition 1, most of the diamond abrasive grains on the diamond tool after normal sanding are shaken, but there are still abrasive grains remaining, and some pits can be observed on the surface of the tool coating. Traces of the diamond abrasive grains that were shaken; under the experimental condition 2, more diamond abrasive grains were observed on the surface of the tool coating, but there were still abrasive particles falling off; under the experimental condition 3, the surface of the tool coating was more adhesive. Diamond abrasive grains; under the experimental condition 4, it can be observed that the surface of the tool coating is adhered with diamond abrasive grains, and the surface of the plating layer has no abrasive particles falling off, and the density of the upper sand is large. 
It can be seen from Fig. 2 and Table 1 that the tool after sanding is thickened without ultrasonic for 1.5 h, and then ultrasonically thickened by the same current density for 1 h. The density of the sand on the tool coating is the largest, and it can be observed that the diamond abrasive grains are almost all adhered to the plating layer. on. It can be seen that in the initial stage of thickening, as long as the time of no ultrasonic thickening is appropriate, that is, as long as the thickness of the diamond embedded in the plating layer is appropriate, the addition of ultrasonic waves will not shake off the already plated diamond, and only shake off the floating sand. Therefore, it does not affect the number of sands on the diamond tool. Ultrasonic is a thickening process that can be used for diamond tools by choosing the right conditions. 
