Thesis Type: Postgraduate
Institution Of The Thesis: Bursa Uludağ University, Fen Bilimleri Enstitüsü, Fen Bilimleri Enstitüsü, Turkey
Approval Date: 1999
Thesis Language: Turkish
Student: Ayhan ÖZKÖK
Supervisor: Mustafa Cemal ÇakırAbstract:
The rationalisation of chip formation process which had been beginning in 1900 years by Taylor and had been continued in 1940' s by Merchant is developing very intensively at the last time. The most important matter in the rasyonalisation is a selection of cutting parameters on the base of scientific and research results. Scientific results may be given in analytical or optimisation forms. These results are used more and more easily in computer programmes, CAM systems and NC programmes at the our time. Therefore at first, rationalisation is a reason for increasing of productivity and product quality and for reducing production costs. However influence of cutting factors on chip formation is not known so far certainly. The most important reason is that very complicated an operation with solid mechanics and mechanical energy; elesticity and plasticity, breaking, friction, wear and lubrication, thermal energy formation, transferring for chip formation process. The result of it's having a less rational knowledge's about high alloy and stainless steels using in the conditions of high temperature and loads. The researchs in this thesis explain rationalisation of chip formation process. Therefore to have been examined following : The Chapter two of the thesis named as "significance of chip formation and topic of thesis " is explaining the significance of chip formation and the methods of developements chip formation process are divided in two groups. The first group is studying a theory of thin shear plane and the second group is studying a theory of thick shear zone especially in that chapter the topic of the thesis has been explained and concentrated attention on chosen questions. There was made a physical and theoretical analysis and chip formation process. There the chip formation models were researched and explored necessary postulates. Taking into consideration significance of shape- changing in chip formation process, was given information about slip lines field theory. Afterwards analysis of Merchant's thin plane theory, which is very important for chip formation process development was done.HI There were researched cutting foces, cutting ratio and cutting angle, slip shape- changing, chip formation speed, slip shape-changing speed, friction's in chip formations and sticky friction, dispersion of chips torsion on tools and were given necessary equations and correlation's. The cutting angle value and spent energy of chip formation process were analysed with the help of criterion of minimum energy. Analytical and experimental determinations of cutting forces are explored. Here the comparison of the chip formation models with the true turning has been made, and, leaning on thin plane theory and oblique cutting models, equetions for cutting forces had been determined and shown that equations can not be using at real conditions. Afterwards, theoretical proportions, based on true turning models had been found. This proportions had been done the basic formulas for experimental working. Also on half-analytical methods, cutting forces equations were the up-to-date information on using dynamometers, their varieties and methods of measurements of cutting forces. Information on experiment, experimental factors and devices turning are presented in Chapter three. In that chapter are explaned using lathe, measuring devices, dynamometers for measuring forces and working principles. Information on material, tools, tools geometry, cutting speeds, feeds, layer thickness are given in Chapter three too. In the end of chapter necessary explanation about calibration of devices is given. Direction of experiments, experimental data are given in Chapter four. The experimental results on cutting forces shown on tables and diagrams had been drawn. In the Chapter five contains coclusions and proposes. The most important results which makes in that chapter has been written below: The most important result of experiments is a plastic form-changing of a material which effects on the chip formation process. The principle of the plastic form-changing that if a long time or high energy have been spending, cutting forces will have increased. If spent time is a less, cutting forces will have decreased. In opposite if a hardness or a tensile resistance have been increasing, cutting forces will have increased, because stresses will have increased too. On account of that reason if. a hardness or a tensile resistance will have taken only; hardness or tensile resistance while increasing, cutting forces increases too.IV The another important result of thesis it's a changing of materials form-changing behaviour in consequence of cutting factors. If layer thickness is a large, a plastic form will be changing less; but in the case of thin layer thickness the plastic form will be changing considerably. Therefore if having a karge layer thickness the changes from cutting forces depends on main formulas; but if using a thin layer thickness it can to give a contradictory results. Here, the materials plastic form-changing capability means an important role. In the chip formation fields, that peculiarity form-changing which effected on cutting forces and technological solution can be taken into consideration. The biggest form- changing is taking place in spot contact of the cutting edge of tool with material. It's a pressure form- changing. Afterward, a chip will be begun flow from dolls face. It's a bending form-changing. In metal cutting, at some intermediate speed, shearing takes place along a nose of stationary material attached to the tool face. This so-called built-up edge acts like an extension of the tool: Shear takes place along the boundary of the built-up egde; hence the effective rake angle becomes quite large and the energy consumption drops. However, an advantage is paid: dimensional control is last and, because the built-up edge becomes periodically, it leaves occasional lumps of metal and damaging cracks behind, and the surface finish is poor.