| Polycrystalline cubic boron nitride(PCBN)is a new type of tool material.With the further development of automobiles,large machine tools and the aerospace industry,its application prospects are getting wider and wider.Due to the high hardness and brittleness of PCBN tools,they usually needs to be sharpened and chamfered in order to meet the cutting processing requirements.At present,the negative chamfer is mainly ground by special indexable cutter CNC precision grinders imported from abroad,or on ordinary grinders with special negative-chamfer fixtures.The grinding accuracy of the first way is better than the latter way,but the grinding cost is higher;and the quality of negative-chamfer grinding is poor by the latter way,which is inconvenient to operate.Therefore,it is necessary to design a tool negative-chamfer grinding device which can effectively and conveniently grind various tool negative chamfer without the help of expensive foreign tool precision CNC grinders,and realize low cost and good quality tool negative-chamfer grinding processing.The specific work content is as follows.First of all,The structural characteristics,working principle and working process of original fixture are analyzed,and the advantages and disadvantages of original fixture and their causes are explored.Following by relevant parameters of PCBN tool negative-chamfer grinding,three types of negative-chamfer fixtures with different principles or structures are designed and manufactured,and the negative chamfer of three groups PCBN tools are ground by those fixtures.Secondly,the two methods,quantitative appearance quality and cutting performance,are used to compare and evaluate the grinding quality of three negative-chamfer fixtures.The quantitative appearance quality evaluation method is to use overall negative-chamfer arc degree to quantitatively evaluate negative-chamfer appearance quality,the smaller overall negative-chamfer arc degree,the more uniform negative-chamfer grinding.The evaluation results show that Scheme three negative-chamfer grinding fixture is better than other fixtures in terms of uniformity of negative chamfer in quantitative appearance quality evaluation and the roughness of processed workpiece surface in the evaluation of cutting performance.Then,through comparative analysis of two evaluation results,the relationship between negative-chamfer arc degree of tool and cutting performance is explored,so as to predict thecutting performance of different quality negative-chamfer tools.The analysis results show that: the negative-chamfer arc degree at actual cutting point can quantitatively describe the relationship between quality of negative chamfer and cutting performance of tool;as negative-chamfer arc degree at actual cutting point increases,the roughness of processed workpiece surface follows increases;but it has less effect on cutting force and tool wear.Finally,according to evaluation result of negative-chamfer fixture’s grinding quality,the overall design idea of negative-chamfer grinding device is proposed based on negative-chamfer grinding fixture of scheme three.And through the analysis of movement and dynamic process of fixture part,the reasonable selection of rotating shaft motor and angle control motor is completed.In addition,the main functions,arrangement methods and structural characteristics of negative-chamfer grinding device’s other parts are also explained.The actual manufacturing of negative-chamfer grinding device provides a design basis to achieve the independence and specialization of grinding device and reduce the equipment cost. |
