METHODS FOR ESTIMATING THERMFISICAL PROPERTIES OF THE "TOOL - STEEL WORKPIECE" CONTACT PAIR AND THE POSSIBILITY OF THEIR USE IN CALCULATION OF THE PARAMETERS OF THE TURNING PROCESS

The analysis of methods for assessing the properties of contact pairs "hard alloy tool - steel workpiece" with the aim of improving the reliability of the choice of turning modes in generations of CNC systems equipped with technical intelligence. The models for calculating the cutting speed, the cutting force, the value of roughness Ra, have been corrected by introducing into their structure an additional informative value about the properties of each contact pair - the thermoEMF of the trial cut.

Cutting speed setting at steel machining with hard-alloy tool and with wear-resistant coating based on preliminary rapid definition of contact pairs

A fundamentally new method for cutting speed setting at structural and carbon steel machining with tools having coatings based on a corrected analytical model is offered into which an additional information parameter on contact pair properties is introduced: thermo-EF of a test cut. The model allows solving a direct problem of cutting speed choice and an inverse one on a definition of tool life.

ANALYSIS AND SELECTION OF RATIONAL CUTTING MODES WHILE USING HARD-ALLOY TOOL FOR SHAFT TURNING

Turning machining of such parts as shafts is considered as the most widely-spread method formanufacturing units, mechanisms and machinery. While doing so it is necessary to ensure high quality of shaft turning with the help of a hard-alloy tool (accuracy and roughness, stability and predictability of steel edge dimensional wear), maximum tool durability, resource of its service life and productivity. As it is known all these operational parameters of the tool depend very heavily on cutting speed. However absence of an analytical dependence for determination of optimum cutting speed value does not per permit to prescribe optimum operational modes at the stage of technology design process. The cutting tool can be subjected to mechanical, anrasive, adhesive, oxidation (chemical), thermal-fatigue and diffusion wear types depending on turning conditions. In this case wearing process consists of two wear types and one of them influences at a certain point on wearing process to a greater extent than the other one. Methodology for prescription of rational turning modes for medium and high cutting speeds ensuring maximum resource of the tool operation has been developed in the paper and it has been based on the analysis of the existing viewpoints about changes in the hard-alloy tool durability due to cutting speed while turning shafts. The range of cutting speed changes has been determined in the paper and it leads to an increase of the tool durability period and, correspondingly, turning productivity of 45 steel grade shafts while using the tool with T15K6-hard-alloy replaceable inserts.

The mechanism of wearing of the hard alloy tool under ultrasonic reinforcing finishing treatment

The working capacity of indenters prepared from hard alloy VK8 under conditions of reinforcing finishing treatment by ultrasonic tools was investigated. It was found that under normal treatment conditions, normal wear of the hard alloy takes place. An electron microscopic study of the morphology of the surface of the wear area and its state after the etching of cobalt (Co) using replicas was performed. X-ray microanalysis of the wear area was performed. No obvious traces of adhesive, diffusion, abrasive wear were detected. It was shown that the deterioration of the hard alloy tool VK8 mainly occurs as a result of fatigue failure, which leads in the investigated speed range of the part 10...120 m/min to the precipitation of individual carbide grains and whole groups of them. The non-linear nature of the wear-velocity curve is due to allotropic transformations of cobalt. It was found that at cobalt speeds of 10...50 m/min, the first allotropic transformation from the initial β-Co state to α-Co occurs, and then the second partial allotropic conversion of α-Co to β-Co occurs at a velocity of more than 50 m/min. The presence of a β-Co phase, which is more brittle, leads to an intensification of wear. The WC-WC boundaries and the deformation of WC carbides are not responsible for the formation of the wear surface microrelief and the integral wear of the carbide tool.

Improving the cutting tool durability by applying multi-layer coatings

The interrelation between the stress values in the cutting tool and the working efficiency of the instrument materials, particularly the durability period is considered. The possibility of applying the cutting force as a parameter for assessing the efficiency of using one or another hard-alloy tool, including the choice of the optimal coating is shown. It appears possible because the cutting force, on the whole, reflects the value and the distribution of stress. The graphical illustration of the results obtained is presented.