At present, monocrystal diamond tools are widely used in ultra-precision cutting. The tool tip geometry of the monocrystal diamond tools is usually made into two forms: linear cutting edge and circular cutting edge. Under the condition of ultra-precision cutting, the length of the straight cutting edge, the radius of the circular cutting edge and the sharpness of the cutting edge all have great influence on the physical phenomena in machining.
Influence of tool tip geometry on machining quality
The geometric shapes of natural diamond tools commonly used include pointed edge, multi-edge edge, linear cutting edge and curved cutting edge (mainly arc cutting edge). In ultra-precision cutting, the linear cutting edge is the linear trimming edge, and the circular cutting edge is the circular trimming edge. In the several point geometry of diamond tool, pointed blade knives, multi cutter blade precision processing surplus hard surface, circular arc cutting edge cutter while machining residual area is lesser, but difficult, grinding, and on the premise of accurate installation, linear cutting edge tool processing residues of the smallest, the highest machining surface quality.
Straight cutting edge
Compared with the circular cutting edge, the linear cutting edge has less cutting resistance, is easy to control the dimensional accuracy and surface roughness, and is easy to manufacture and convenient to grind. Its advantages in high quality and high precision machining are difficult to be replaced by other cutting edges. The linear cutting edge should not be too long, otherwise it will increase the radial cutting force, and too much friction between the cutting edge and the workpiece surface will increase the roughness value of the machined surface and accelerate tool wear.
Arc cutting edge
Arc cutting edge diamond tools are easy to use, but difficult to manufacture, grinding tools, high price. Arc cutting edges are commonly used in foreign diamond tools. The recommended radius of arc of cutting edge tip is Rε = 015 ~ 3mm or smaller, and the feed amount is very small in ultra-precision cutting. In general, the feed amount is F <0102mm/ R. In cutting depth under the same conditions, with the decrease of the blade arc radius, the surface roughness of the workpiece increases, this is because when arc cutting edge processing residue left by the area changes as the point of arc radius, arc radius are decreased when the tip of the cutting edges are getting smaller and smaller, residues of workpiece in cutting area is larger and larger.
Influence of the radius of blunt cutting edge on machining quality
Since the cutting edge cannot be made into a sharp geometric line, there will always be a blunt cutting edge circle. The smaller the radius of the cutting edge blunt circle, the sharper the cutting edge, the larger the radius of the cutting edge blunt circle, the more blunt the cutting edge. The degree of extrusion and friction of the blunt cutting edge on the machined surface is related to the sharpness of the cutting edge. The blunter the cutting edge is, the greater the deformation of the machined surface is, the greater the machining error is, and the worse the machining quality is.
From this point of view, in order to achieve ultra-precision cutting, very small removal must be carried out, that is, the cutting edge of the tool must be extremely sharp or the radius of the cutting edge dull circle is very small, so as to ensure that the cutting thickness removed is small enough. Therefore, the minimum cutting thickness which can guarantee the stability of ultra-precision cutting has a certain relationship with the radius of the blunt circle of the cutting edge of diamond tool. When the parameters of cutting depth, feed, cutting speed and cutting edge vary within the range of ultra-precision cutting conditions, the sharper the cutting edge (i.e. the smaller radius of the blunt circle of the cutting edge), the better the machining surface quality will be.