Research On Chip Formation Mechanism Of Hard Cutting High Strength Steel 42CrMo

Machine parts consisting of hardened steel are high performance components which are often loaded near their physical limits, high strength steels are widely used. The functional behavior of machined parts is decisively influenced by the fine finishing process which represents the last step in the process chain and can as well be undertaken by cutting as grinding. The hard cutting technology instead of grinding materials has greatly developed, and is used as the final machining process widely instead of grinding more and more. Although the cutting force, cutting heat, adiabatic shear theory and chip formation mechanism of hard cutting have been extensively studied and valuable results obtained, as a new technology, hard cutting chip formation mechanism is not very clear and has not formed a systematic scientific system. In today’s scientific research and industrial production, cutting of hardened steel is a topic of high interest.The main works and results of this dissertation’s researches are list below:1. The tool stop speed and acceleration of the spring type Quick Stop Device are studied by high speed camera. The work performance of the QSD can fully meet the research needs of hard cutting chip formation mechanism experiments. The samples obtained by the QSD experiment are reliable.2. The cutting of hardened steel, dynamic behavior under high stress, high strain & strain rate, high temperature, and the material removal mechanism under mul ti-fields effects are studied by the QSD specimens.Metallographic specimens are made by chip root and observed by the microscope to research the instantaneous state of cutting process when the tool stops. Then on these bases, the dynamic change behavior of materials in the 4 deformation areas of the work piece through the chip formation processes is analyzed to reveal the mechanism of physical and mechanical behavior. The chip formation model is established in order to describe and predict the cutting chip formation process.It’s shown that during chip formation process of 42 Cr Mo hard cutting, adiabatic shear zone forms near the tip of the tool and expands to the internal material during the cutting process. The crack initiation of segmental chip generates form the free surface and expands to the inside material. The main preseason leads to the chip separation finally is crack expand effect.3. Based on the Abaqus finite element simulation/analysis results of the hard cutting, the cutting force, cutting temperature and stress field, strain field, temperature field of the chip formation stages are analyzed. The chip formation mechanism of the hard cutting of 42 Cr Mo steel is revealed and the physical model of the chip formation process is improved by comparing the simulation results with the experiment results.Through researching on cutting area stress field, strain field, temperature field of a complete segmental chip formation cycle, the periodical and dynamical characteristics of the parameters of the hard cutting chip formation processes are revealed.4. The hard cutting experiment platform of cutting force, cutting temperature, chip morphology, chip flow, processed surface quality is set. Study on the hard cutting 42 Cr Mo white layer and the segmental chip formation physical mechanism and their influence. Study on the transient state, strong impact and adiabatic shearing of the material removal process.5. Experimental research on the cutting force and the machined surface roughness of the cylindrical hard turning. The cutting force and the machined surface roughness are highly affected by the reasonable combination of the cutting parameters. A cylindrical hard turning cutting force, surface roughness prediction model is established by orthogonal cutting experiments.Through this dissertation’s research, the high strength steel 42 Cr Mo hard cutting chip formation mechanisms, the multi-field effect, the chip formation mechanism under cutting force- thermal coupling effect are studied by simulation and experiment analyses. The chip deformation mechanism is studied and the chip formation model is established. The relationship between cutting force, cutting temperature, the chip morphology and processed surface roughness are studied. The results can be a reference for the hard cutting research and practice.