1 the introduction

With the high-speed development of modern science and technology, composed of polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN), and other varieties of superhard material tool more and more rich, its performance has also been developing and improving.The particle size of blade abrasive varies from tens of microns, several microns to nanometer scale.The contents of diamond and cubic boron nitride are low, medium and high.The binder has both metal and non-metal mixed materials.PCD layer thickness from millimeter to micron;The combination of PCD layer and hard alloy substrate includes plane and corrugated surface.PCD layer has high wear resistance, high toughness, high heat resistance and other characteristics.Application scope of the PCD, PCBN cutting tools to the automotive, aerospace, precision machinery, household appliances, such as wood, electrical and electronic industry, used to produce turning tool, boring tool, milling cutter, and drill, reamer, economic razor knife, saw, ornamental engraving knife, etc.

Despite the rapid development of PCD and PCBN tools, the difficulty of tool edge grinding due to its high hardness has been plaguing most users, and the regrinding of blades is mainly completed by the original tool manufacturer.Not only the tool price is high, the delivery period is long, but also occupies the working capital of the enterprise.Therefore, it is necessary to study the grinding characteristics of PCD tool and the cutting technology of PCD tool.

2. Manufacturing process of PCD tool

The production process of PCD cutting tool generally includes polishing, cutting, bonding, edge grinding, quality inspection, etc.PCD blank diameter of superhard materials usually have 1/2, 1, 2, 3, 4 inches, its surface is generally rough (in Ra2 ~ 10 microns), cannot be directly used to produce cutting tools, need to the grinding and polishing the surface mirror (Ra 0.01 microns or less), and then through the laser cutting or wedm processing into a certain geometric shape and size requirements of the blade, further on solid surfaces of blades and matrix for mechanical and chemical processing, then USES the silver base brazing blades fixed on the substrate, finally the diamond grinding wheel grinding.

One of the key technologies of PCD cutting tool manufacturing is the quality of cutting edge grinding.The lack of ideal cutting edge grinding technology and technology for high-quality cutting materials will result in waste of resources. The adoption of good cutting edge grinding technology will improve the quality of cutting tools and reduce the cost of tool use.

3. Grinding characteristics of PCD materials

PCD is made of specially treated diamond and a small amount of binder sintered at high temperature and high pressure.Disordered diamond grain makes PCD have uniform, high hardness and wear resistance.PCD can be used for cutting tools, grinding wheel dressing, geological drilling, measuring head, drawing tool, sandblasting tool, etc.However, the high hardness and wear resistance of PCD also bring great difficulties to its processing.

Scholars at home and abroad for PCD material processing problems brought by the high hardness and high wear resistance for a lot of research and test, including electrical discharge machining, ultrasonic machining, electrochemical machining, laser processing, etc., and achieved some results.However, the comprehensive analysis shows that these processing techniques are more suitable for rough machining of PCD materials.In order to obtain good PCD cutting edge quality, the most ideal processing method is still to use diamond grinding wheel grinding or grinding.

The grinding process of PCD is mainly the result of the combination of mechanical and thermal chemistry.The mechanical action is the microfracture, wear, peeling or cleavage of diamond formed by the continuous impact of diamond grinding wheel on PCD materials.The thermochemical action is that the high temperature formed by diamond grinding wheel grinding PCD causes the oxidation or graphitization of diamond.The combination of the two results in the removal of the PCD material.

PCD cutting tool grinding requirements for tooling

Based on the above grinding characteristics of PCD, the requirement of cutting equipment for PCD grinding with diamond grinding wheel is much higher than that of general tool grinding machine.Mainly include:

(1) the machine tool has good rigidity of process system

Due to the high hardness of PCD material, the grinding machine must have high resistance to deformation, especially spindle system and tool clamping system.The grinding force of PCD cutting tool can reach 100 ~ 500N.Therefore, it is required that the axial diameter of the machine tool is large, and the axial rigidity and strength of the bearing are high.

(2) the machine has short swing mechanism with adjustable stroke and adjustable speed

PCD grinding ratio is extremely low, the grinding mechanism of PCD diamond grinding wheel is the main of PCD material as the impact of the formation of the micro mechanical action such as crushing, abrasion, fall off, cleavage and thermal chemical oxidation and graphitization mixed results.Therefore, the short - range swing mechanism can improve the grinding efficiency and the quality of tool edge.Generally, the swing distance is 0 ~ 50mm, and the swing speed is 20 ~ 60 times/min.

(3) the tool holder of the machine tool has high precision rotary function and on-line detection device

As the PCD material is hard, brittle and wear-resistant, its blade tip is usually designed as an arc shape to reduce the amplitude of relative vibration of the tool and workpiece.In order to realize the machining of the tool tip arc, the tool holder of the machine tool should have high precision revolving function and on-line measuring device for the size and quality of the tool tip arc radius.In this way, it can avoid the positioning error caused by multiple loading and clamping, and increase the machining efficiency multiple times.