Study On The Hi-frequency Induction Brazing Of PDC Cutting Tools

The polycrystalline diamond compact (PDC)'s brazing is a key procedure of making polycrystalline diamond cutting tools. Nowadays, the high-frequency induction brazing is the main technique used in the PDC's brazing around the world, due to its notable advantages such as less pollution to environment and higher production efficiency. However, because the PDC has poor brazing processability, and the research and application of the PDC in China still stays at a lower level currently. Compared to other countries, the PDC cutting tools sometimes can break off when it is used in practice for the low brazing intensity between the PDC and base materials. Therefore, it is necessary to investigate the influence factors on the hi-frequency induction brazing technique of PDC in detail as soon as possible, in order to upgrade the performance of PDC cutting tools.The PDC's brazing experiments were carried out in air atmosphere with two base materials (45# steel and YG8 cemented carbide), using high-frequency induction brazing machine GP15-CW6. The effect of pre-treatment before brazing, the arrangement of braze alloys and soldering flux, brazing parameters and coolant method after brazing on PDC tools' brazing quality were studied systematically by means of self-made shearing equipment, as well as scanning electron microscopy (SEM) and electronic probe microscopy (EPM).Firstly, the effects of base materials' surface pre-treatment on the shearing strength of brazing joints were investigated. It was indicated that high-strength brazing joints would be obtained when the surfaces of the PDC and base metal were both filed, and the brazing joint would reach the greatest effect especially when the filing strips on the compacts were aligned with that on base metals surface.Secondly, through comparison experiment with two cooling medium (air coolant and plaster powder coolant), the influence of the cooling on PDC tools' using performance was analyzed. The results showed that the plaster powder cooling could restrain brazing joints of PDC cutting tools from oxidation and microcracks, so the effect of the plaster powder cooling was much better than that of the air coolant.Subsequently, the effect of braze alloy and soldering flux matching in pairs on brazing performance was investigated, using two different braze alloys (1#,2#) and two different soldering fluxes (QJ102 and F500A). It was founded that the best brazing joint of the PDC and YG8 cemented carbide could be acquired in arrangements of braze alloy 1# and soldering flux QJ102, and the worst one was the compounding of braze alloy 2# and soldering flux QJ102. On the other hand, for the brazing of PDC and 45# steel, braze alloy 2# and soldering flux F500A was the best arrangement, while the braze alloy 1# with soldering flux F500A was the worst.By means of single factor experiments, the high-frequency induction brazing parameters of PDC tools such as brazing temperature and brazing pressure were analyzed quantitatively later. The results indicated that with the increase of brazing temperature, the shearing strength increased gradually, but the joint width diminished otherwise. To get a better integrated property of brazing joints, it was proposed that the brazing temperature of the PDC compact/ YG8 cemented carbide should be controlled at about 690℃, and the PDC compact/45# steel at 670℃. The results also showed that, with the increase of brazing pressure, the shearing strength increased first, decreased afterward, and became steady after reaching a certain value while the joint width just decreased all along with the increase of brazing pressure and reached a steady value at last.Finally, special technical measures such as the again-brazing technology and applying brazing pressure with ceramic bar were discussed in case of stationary braze alloy and brazing parameters, and they were considered as functional methods with an apparent enhancement of shearing strength of the PCD tools.