The methods of measurements and snapshots processing have been given and described in detail. In order to estimate an accuracy of tool-edge radius measurement electron microscopy principles has been studied in detail. An error equation has been obtained as a result of these investigations. It is important to note that humans can make out only 5% contrast, which corresponds to 10% accuracy of this method. Therefore, it is computer aid processing of the snapshots which is strongly needed for the method accuracy increasing.
The method has been tested by measuring of copper wire 0.1 mm in diameter.
According to the measurements performed tool edge radius of carbide inserts with the following chemical composition WC=91.5%, Co=8%, Cr3O2=0.5% was about 40 mm with an error less than 7%.
Chapter five. An Example of the Simulation
In this chapter an example of the simulation results has been given. The skiving simulation of carbon steel by carbide tool Haas been performed and simulation results have been demonstrate. It is worth noting that predicted UCT variation has been assumed in this simulation.
According to the reported results some skiving features have been demonstrated, proved and described. They are: the plastic strain and work material hardening which increases by the end of MC, rather constant maximum shear stress, the high magnitude cutting temperature and maximum temperature which may reach work material melting point, the flow of maximum contact temperature position etc.
Some disadvantages of the represented solution procedure have been shown and discussed. The ways of further improvement have been also given.
In this thesis an attempt to advanced cutting modeling has been made. The skiving has been chosen as an object of investigations. The skiving seems to be one of the overall machining process and therefore can be applied to the comprehensive cutting model and software development. This process can also be applied to automatic machines and allows designing rotary scheme automatic lathes, which has both a high volume and flexibility and also needs much less working area than conventional ones do.
The skiving is unsteady-state process with a rather high cutting speed that provides rather high accuracy and machined surface quality. As it has been proved it is closely allied to milling and grinding from kinematics and physics points of view. But some skiving features such as long cutting length and sophisticated undeformed chip thickness and cutting angles variation complicate its theoretical investigations. It has been substantiated that no coolant is needed under skiving and that is why the skiving can be considered as a dry-cutting technology which is becoming more and more popular in foreign industry today. Two interesting features have emerged from the literature observation represented in this study. Firstly, current tool life is comparatively low because of thermal tool stress oscillations. Secondly, the fact is that there are two slipping parts in the machining cycle with no cutting and high frictional forces. According to the reported literature and machine builder’s experience these features usually result in a low tool life under skiving . These are the flaws of skiving application in Ukraine.
The FE model of skiving process has been developed, programmed and validated. In the first development step general solution procedure proposed has been simplified to a semi-experimental scheme. Both deformation and heattransfer simulation problems have been proposed to compute simultaneously by incremental algorithm. The material properties temperature dependency has been taken into account. The general FE-code has been used.
According to the designed procedure, both workpiece and tool geometrical models have been proposed to design by experimental data at a certain amount of calculation points. FE mesh has been generated in a specified tool and workpiece geometrical models independently with subsequent merging. To advance of numerical stability a special method for FE mesh generation has been proposed and programmed.
The deformation simulation problem is based on elasto-plastic with linear hardening material model. FE mathematical model has been deduced in Lagrangian formulation and has been described in detail. The boundary conditions have been specified. The friction contact has been also taken into account. Such loads as a cutting and feed forces have been imposed on the tool.
The heattransfer problem is based on general unsteady-state heattransfer equation. It has been converted to a FE formulation by Crank-Nicholson scheme using a general Galerkin method. The heat sources have been intended to determine by conventional analytical method. The boundary conditions have been specified according to dry-cutting scheme.
It is worth noting that the stress, strain and temperature fields can be obtained from the proposed simulation model, which can help to understand skiving better and completely.
In order to validate skiving simulation model analytical methods of both cutting deformation variables and temperature has been developed.
Experimentally determined forces, cutting length ratio and real undeformed chip thickness variation as well as real tool edge radius are strongly needed. The original methods for the parameters determination have been developed and tried out. A scanning electron microscope and special designed pick-up equipment have been employed.
It has been shown that represented FE simulation models require a further development in order to increase numerical stability and accuracy of the results as well as to develop a valuable predictive model. Moreover the software improvement is also needed for more convenient and faster research performing. Thereby the results of this study can be applied to skiving mechanics investigations and optimization but the software needs further development and drastic validation.
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