| Titanium alloy is widely used in the field of aviation and aerospace with the property of high-strength, corrosion resistance and high temperature resistance. As the development of technology of our country satellite, the accuracy of some key titanium parts has achieved sub-micron level so that the processing system is requested for strong manufacturing capability.Titanium alloy is a kind of difficulty processing material because of good chemical activity and lower thermal conductivity. So the processing of titanium alloy is easier to make tool wear which decreases manufacture accuracy. Therefore, to meet requirement of high-precision titanium alloy part, research on tool wear and machining error compensation during machining titanium alloy part is done so as to make dimensional accuracy, form and position accuracy of titanium alloy part achieve sub-micron level and surface roughness on nanometer scale.Because of the property of difficulty processing for titanium alloy, a methodology of tool condition monitoring is used to monitor the condition of tool and make surface roughness achieve nanometer scale. Based on acoustic emission, an indirect method was used as tool condition monitoring. To establish the mapping relations between acoustic emission and tool condition, an experimental platform was firstly established to acquire abundant acoustic emission and measure VB of insert in a range of different cutting parameters. Secondly, based on wavelet transform, an analytical approach was applied for extracting eigenvectors, which is corresponding to tool condition, from acoustic emission. Thirdly, the use of BP neural network is to map eigenvector onto tool condition. Finally, based on acoustic emission, a tool condition monitoring system was established by integrating above research.A method of machining error compensation is utilized to bring accuracy of machine tool up to required level to guarantee the accuracy requirement of high-precision titanium alloy part. The technique of machining error compensation is the fusion of static error compensation and the strategy of open-loop control. Based on accomplished hardware platform, the research on the technique of machining error compensation is as follows. Firstly, error pretreatment methods were studied to merge different kinds of error data and to scheme compensation path. Secondly, motion control for error compensation was studied to make compensation actuator follow preset path to compensate machining error. Finally, hardware device and above research were integrated to build a machining error compensation system with compensation actuator, which is called micro-feeding tool holder.The performances of two techniques were validated experimentally and results proved the effectiveness of above techniques and two systems. The recognition accuracy of tool condition monitoring system is 73.44% in the range of some cutting parameters. Machining error compensation system has improved positioning accuracy of Z-axis of the lathe from 2μm to 0.2μm. And the system has capacity to compensate horizontal straightness error of Z-axis and tapper error of workpiece. The horizontal straightness error of Z-axis is decreased from 2.025μm/210 mm to 0.448μm/210 mm with the cutting of 77.89%. The CNC lathe equipped with machining error compensation system has manufactured high-precision titanium alloy. Its diameter is Φ199.999 6mm, roundness is 0.000 46 mm, cylindricity is 0.000 68 mm and surface roughness is Ra0.048μm. Above two techniques and two systems, which have brought the performance of machining system up to make the lathe manufacture high-precision titanium alloy, have met the requirement of aerospace and have an important value and potential application. |
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