Study On Nickel-phosphorus Composite Electroless Plating Process And Its Machinability In Ultra-precision Machining

The pins of mold steel with specific shapes and optical surfaces are critical for the precision injection molding process.However,due to the chemical reaction with diamond,the diamond cutter can be worn quickly during ultra-precision machining.Although this issue can be resolved by depositing a layer of Ni-P alloy on the surface of the mold steel,the following problems still exist in Ni-P deposited layer: The thickness of the deposited layer is generally around 200 ?m and the pinhole range is within 20 ?m or even larger.The deposited layer has certain pore defects on the surface after cutting.There is no further study on the damage of the cutter after long-distance cutting of diamond tools and the surface quality of the Ni-P deposited layer.The main research contents and achievements of this work are as follows:1.A combination method of depositing a high-phosphorus Ni-P alloy on the substrate of S136 mold steel is determined based on the characteristics of Ni-P alloy and mold steel and combined with the actual application requirements.We explore the effects of various process parameters on the growth of the coating and develop an effective and complete nickel electroless plating process for mold steel substrate based on high temperature and acid bath.2.A 10 L stainless steel plating tank system is built for the investigation combined with cathode rocker,regulated power supply,PH controller and other auxiliary equipment.Under the condition of a long time(>30 h)plating,automatic tuning of temperature and p H and the circulating filtration of the plating solution in the electroless plating system can be achieved.It can successfully maintain the concentration of the main salt,the reducing agent and the stability of process parameters in the plating.The effect of double activity of plating solution and workpiece on rapid plating is studied,which can improve plating efficiency to 145%in the short-term(2h)plating.Under the cathode rocker vibration and stabilization process,a high-phosphorus Ni-P coating with a thickness of 300 ?m and a pinhole range below 10 ?m is finally deposited on the substrate mold steel of S136.3.It is determined that nickel slag is the cause of the pore defects after turning by detecting and analyzing the surface and subsurface of the deposited layer before and after turning.And this problem is solved by increasing the anode protection voltage and filtration.The surface of the optical mold having a roughness of less than 1.1 nm(Ra)is achieved by single-point diamond turning.4.Turning experiments show that single crystal diamond tools still wear when cutting high phosphorus Ni-P alloys over long distances.The rake face begins to wear after turning 6.68 km,and the rake face is seriously worn and the edge is cracked after12.57 km.The subsequent processing shows an increase in the surface roughness to4?5 nm(Ra),and the rainbow phenomenon.