appearance and distribute regulation for grinding-cracks of solid carbide cutting tools

Solid carbide cutting tools in the aerospace, mold manufacturing, automobile manufacturing, machine tool manufacturing, and other fields to get more and more widely used, especially in an increasingly important position in the field of high speed cutting. In the field of high speed cutting, due to the high standard request tool, security, reliability, durability, solid carbide cutting tools inner and surface quality requirements are more strict. And with the hard alloy bars especially ultrafine cemented carbide material inner quality enhances unceasingly, the quality of the surface of solid carbide cutting tools is more and more attention. As is known to all, the service life of carbide cutting tools in addition to related to its abrasion resistance, and is often seen in the collapse edge, broken blade, non-normal failure aspects, such as fracture after grinding tool grinding cracks and surface defects is one of an important reason for abnormal failure. These surface defects including when they are exposed to the surface after grinding hard alloy bar internal powder metallurgy manufacturing defects such as delamination, crack, not pressed, holes, etc.) and grinding process caused by unreasonable grinding on the grinding surface grinding crack defects, and grinding cracks are more common. These grinding cracks, the Baptist oil to the naked eye, magnifying glass, blowing sand, a stered microscope tool microscope and conventional tend to cause leak detection methods, residual tool when use, especially in high speed cutting may cause serious consequences, so solid carbide cutting tools products to the harm of the grinding crack defects. For solid carbide tool grinding cracks reasons were analyzed and discussed, and put forward effective prevent grinding-cracks of process improvement measures has very important practical significance.

 

Manufacturing carbide cutting tools by using diamond grinding processing can make the surface layer of physical - mechanical properties deterioration or improvement. Basic parameter in determining the quality of surface layer is: the microstructure (i.e., the surface roughness), the structure of the surface layer and the structure, the first Ⅰ kind of residual stress value and distribution. After sintering of hard alloy is usually has no less than Rz5? M's surface roughness, Rz not less than 2 diamond processing can guarantee? M in the Rz = 1 ~ 5? M within the scope of the depth of the microscopic roughness in fact does not affect the service life of cemented carbide. In grinding hard alloy grain internal fine crystal structure parameters are changed, the embedded crystal pieces of broken (coherent scattered area), its value decreases, an order of magnitude by (10 ~ 15) x 10 - to 5 mm (10 ~ 15) x 10-6 mm. Grain microscopic distortion values (Δ d/d, the first class Ⅱ stress) change, surface layer properties also change accordingly.

 

But, in fact, fine crystal structure parameters and found no direct relationship between carbide life. So under the cyclic load (such as milling force) the service life of cemented carbide with both the structure and the structure of surface layer is not directly related, and in the first place is not determined by the surface roughness, but depends on surface residual stress state, namely the first Ⅰ kind of residual stress value and its distribution along the cross section strength and life of the carbide plays a decisive factor. The formation of surface residual compressive stress fracture source migration leads to a deeper load smaller distance surface level, inhibit the initiation and propagation of cracks, this makes the strength and life; At the same time as the hard alloy surface layer depth distribution of the residual compressive stress layer increases, the strength and life gradually improve. While surface layer formation of the residual tensile stress promote the initiation and propagation of crack, crack is necessary condition, and results in lower strength and service life. But after grinding surface often there are both residual compressive stress and tensile stress, therefore, the ideal state of grinding surface layer should be the surface residual compressive stress value, the higher the better, the deeper the better distribution of the residual compressive stress layer; Near surface residual tensile stress value is lower, the better, the residual tensile stress in the thinner the better, the deeper the maximum tensile stress in the distance from the surface, the better. On the other hand, the surface shallow high compressive stress distribution and the near surface layer of the tensile stress value is the main reason of grinding crack initiation. So, in the process of grinding should be reduced as far as possible and avoid the generation of residual tensile stress.