Determination of optimal coordinates for switching processing cycles on metal-cutting machines

OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 1 Results and discussion Example of determining the optimal coordinates of the tool changeover Here is an example of the effectiveness of the method for selecting speed trajectories and switching processing cycles for longitudinal turning of a shaft with D = 8.0 mm made of 08Kh15N24V4TR steel with non-sharpenable plates made of GC2015 hard alloy by SANDVIK Coromant, the plate shape is “W”. Cutting depth is (0) 2.0 P t  mm; the initial feed is (0) 0.1 P S  mm/rev.; initial cutting speed is 0 1.2 V  m/s. The length along the axis is 38.0 mm, the cutting path of one workpiece is 9.5 m, the total path is 840 L  m. The mathematical expectation of the cutting path to critical wear is 0.8 mm with constant optimal cutting conditions of 20 m. Parameters  that characterize the evolution are  1 0.1   m –1 and  2 0.01   m –1 . The variance value of this parameter is  0,1 i i    . The cost parameters 1 c 2 c are taken in conventional units of cost to a unit of time. For this case, Fig. 3 shows the dependence of the cost ef fi ciency on the number of switches n . Here, the optimal values of the number of switches are highlighted with red circles and a dotted line, depending on the cost of replacing and readjusting the tool 2 1 c sc  . In any real system, the condition 2 1 c c  is usually met, since the cost of operating the machine is included in 2 c . If 2 0 c  , the optimal is n   . Then the costs approach their minimum value of C 0 (shown in blue), determined by the hypothetical case of processing with a non-wearable tool in constant modes: (0) 0.1 P S  mm/rev. = const, 0 1.2 V  m/s . The optimal number of the switching also depends on the parameters  that characterize the change in the wear intensity along the cutting path. As shown earlier [10], the parameter  , being an integral estimate of the evolutionary properties of the cutting process, depends on the dynamic properties of this process including the formed attractors of the tool deformation displacements relative to the workpiece. They change during the development of tool wear. The analysis shows that .., as a rule, it is not an integer, so it is natural to take the optimal number of switches as the nearest integer value. In addition, it is necessary to coordinate the path corresponding to the switching with the length of the tooltip movement when processing a speci fi c part. The given example il- lustrates the optimization of switching processing cycles for the case when the parameters of the evolution- ary trajectories of changing modes are constant and correspond to mathematical expectations  . Since in a real system   ( 3 , 3 ) i           , the set is also characterized by random distribution i l  (l) . In Fig. 4  1,0 ( ) à V      ,  1,0 ( ) b V   ,  1,0 ( ) c V      . According to the proven position (3) and (4), all coordinates i l that provide a minimum cost for manufacturing a batch of parts correspond to constant speeds 1,0 V at which the tool need to be replaced (Fig. 4). Therefore, the replacement of tools must be carried out not in the motion coordinates, but the speed ones 1,0 const V  . Currently, the CNC programs for machining parts remain unchanged when processing a batch of workpieces, regardless of the development of tool wear. The wear development changes the parameters of the dynamic cutting system and, as a result, changes its properties, which affect the intensity of tool wear and the quality parameters of the processed parts. Therefore, the MEUT needs to be coordinated with the evolutionarily changing properties of the cutting process. In this case, the MEUT is determined not on the basis of fi xed technological modes, but on their trajectories consistent with the evolutionarily changing properties of the dynamic cutting system. This coordination allows minimizing the intensity of tool wear when producing parts of the required quality. It requires reducing the speed vector in the direction of the tooltipmotion. Thus, if the elastic-dissipative properties of the tool andworkpiece subsystems are unchanged,