淬硬钢模具硬态铣削机理及精加工过程优化

发布时间：2018-03-17 14:33

  本文选题：模具精加工　切入点：硬态铣削　出处：《哈尔滨理工大学》2016年博士论文　论文类型：学位论文

【摘要】：汽车覆盖件淬硬钢模具的制造是汽车生产制造中的重要环节,然而,淬硬钢模具精加工时,由于工件硬度较高,加工余量较小,造成刀具与工件之间经常出现“滑刀”现象,使得模具最终的尺寸精度和表面质量很难保证,增加了后期人工修磨时间。除此之外,淬硬钢模具精加工采用硬质合金刀具加工时,切削效率较低,使得汽车模具的整体制造周期较长。因此,改善淬硬钢模具精加工中的“滑刀”现象,开展新型刀具材料在淬硬钢模具精加工中的应用研究,对提高汽车覆盖件模具的加工质量及加工效率,进而提高汽车制造业水平具有重要意义。切削刀具在制造过程中切削刃存在一定的钝圆,使得切削加工存在最小切削厚度,当精加工余量选择不当导致实际切削厚度小于最小切削厚度时,刀具与工件之间将不能进行正常的切削,而出现“滑刀”现象。考虑切削刃钝圆半径在淬硬钢模具精加工中的影响,在对铣削加工过程中切削层厚度变化规律及工件表面形貌分析的基础上,通过对表面形貌中切削—犁耕—滑擦区域划分,提出一种基于铣削加工方式确定最小切削厚度的方法,通过切削实验及仿真手段对提出的最小切削厚度确定方法的可行性进行了验证。在此基础上,确定了不同硬度淬硬钢Cr12Mo V的最小切削厚度。采用理论推导方法,建立了考虑切削参数、工件曲率及刀具变形等因素的淬硬钢模具凸曲面精加工极限切削深度预测模型,并通过切削实验手段对所建立的模型进行了验证。此研究成果为淬硬钢模具精加工余量的选取提供了一个“最小值”,以避免产生“滑刀”现象。通过实验手段,对比了PCBN刀具与硬质合金刀具在铣削加工淬硬钢方面的切削性能。研究了PCBN刀具断续加工淬硬钢刀具失效机理,将PCBN刀具断续加工淬硬钢中的刀具破损分为低速性破损与高速性疲劳破损,在揭示其破损机理的基础上,给出了避免产生低速性破损的临界铣削条件。通过对切削实验中产生疲劳失效刀具的断口形貌进行观察,揭示热—力耦合作用下PCBN刀具断续加工淬硬钢疲劳失效机制,并给出预防PCBN刀具过早出现疲劳破损的措施。分析了传统球头铣刀在加工淬硬钢模具小曲率型面时的弊端,在此基础上,设计开发了淬硬钢模具小曲率型面精加工专用双圆弧Ⅰ型、双圆弧Ⅱ型、sinⅠ型及sinⅡ型PCBN铣刀,并给出了新型PCBN刀具的使用条件。本文以汽车覆盖件模具常用材料淬硬钢Cr12Mo V为研究对象,采用理论分析、数值模拟及切削实验相结合的方法,对淬硬钢模具精加工中“滑刀”现象以及PCBN刀具断续加工淬硬钢机理等问题进行研究。研究成果为提高淬硬钢模具精加工质量及效率,进一步实现汽车覆盖件淬硬钢模具的高品质加工提供理论依据及技术指导。
[Abstract]:The manufacture of hardened steel dies for automobile panels is an important link in automobile manufacturing. However, due to the high hardness of the workpiece and the small machining allowance, the phenomenon of "slippery knife" often occurs between the tool and the workpiece during the finish machining of the hardened steel die. The final dimension accuracy and surface quality of the die are difficult to guarantee, which increases the time of manual grinding. In addition, the cutting efficiency is low when the die of hardened steel is finished with cemented carbide tools. The whole manufacturing period of automobile die is longer. Therefore, the phenomenon of "slipper" in the finish machining of hardened steel dies is improved, and the application of new cutting tool materials in the precision machining of hardened steel dies is studied. It is of great significance to improve the machining quality and efficiency of automobile panel die, and then to improve the level of automobile manufacturing industry. There is a certain blunt circle in the cutting edge of cutting tool in the manufacturing process, which makes the cutting tool have the minimum cutting thickness. When the actual cutting thickness is less than the minimum cutting thickness due to the improper selection of the finishing allowance, the normal cutting between the tool and the workpiece will not be carried out. Considering the influence of the blunt circle radius of cutting edge on the finish machining of hardened steel dies, on the basis of analyzing the thickness of cutting layer and the surface morphology of workpiece during milling, By dividing the cutting, ploughing and sliding friction regions in the surface topography, a method for determining the minimum cutting thickness based on the milling method is proposed. The feasibility of the proposed method for determining the minimum cutting thickness is verified by means of cutting experiments and simulation. On the basis of this, the minimum cutting thickness of hardened steel Cr12Mo V with different hardness is determined. A prediction model of the limit cutting depth for the finish machining of hardened steel die convex surface considering cutting parameters, workpiece curvature and tool deformation is established. The model is verified by cutting experiments. The research results provide a minimum value for the selection of finish machining allowance of hardened steel dies, in order to avoid the phenomenon of "skid knife". The cutting performance of PCBN tool and cemented carbide tool in milling hardened steel was compared. The failure mechanism of PCBN tool in intermittent machining of hardened steel tool was studied. The tool breakage in the intermittent machining of hardened steel by PCBN tool is divided into low speed damage and high speed fatigue damage. The mechanism of tool breakage is revealed. The critical milling conditions to avoid low speed damage are given. By observing the fracture morphology of the tool which produces fatigue failure in cutting experiment, the fatigue failure mechanism of quenched steel produced by PCBN tool under the coupling of heat and force is revealed. The measures to prevent premature fatigue breakage of PCBN cutters are given. The disadvantages of traditional ball end milling cutters in machining the small curvature surface of hardened steel dies are analyzed. The special double circular arc 鈪，

本文编号：1625173