切削难加工材料刀具失效机理及其材质优选的试验研究

对不同牌号(组织结构)的硬质合金刀具,进行断续切削难加工材料3Cr-1Mo-1/4V钢的对比试验,通过对所选的刀具产生的粘结破损和破损区域大小以及刀具在断续切削过程中粘结破损的机理进行比较分析,优选出适合加工3Cr-1Mo-1/4V钢的刀具材料,提高加工效率,改善切削条件,提高刀具性能及使用寿命。

MILLER WEAR IN MILLING Ti ALLOY WITH NITROGEN GAS MEDIA

Milling Ti alloy is a very difficult technology. The primary problem is that the miller wear is very rapid and makes the miller break or rapture. Although cutting fluid is mainly used to reduce friction and temperature in cutting area to enhance tool life, it is the largest source of environmental pollution. To develop a technology for the clean and efficient milling Ti alloys, nitrogen gas is used as a cutting media in this paper. Based on lots of experiments and researches, the tool life and wear mechanism of high speed steel miller is analyzed. A conclusion is drawn that, milling with nitrogen gas media yields much longer tool life than dry milling. Tool life equations (Taylor′s equations) are derived for both milling types.

曲轴车-车拉加工系统刀夹寿命分析研究

一个完整的切削加工系统不仅仅包括切削刀片,还包括机床与刀具连接系统。车-车拉是目前曲轴加工主要加工工艺,其刀具系统包括刀片与刀夹,而车-车单元切削刀夹往往由于侧壁容易在交变载荷的作用下引起疲劳断裂而失效。本文围绕刀夹寿命的影响因素为研究对象,通过金属材料的疲劳寿命与应力的数学关系式,测得实际切削时刀夹所受的切削力,应用三维造型软件建立刀夹模型,然后利用ANSYS有限元加载切削力,模拟仿真实际切削过程中刀夹侧壁所受到的应力随侧壁厚度的变化情况,最后利用MATLAB拟合建立刀夹寿命与侧壁厚度的关系式。鉴于实际加工中刀夹侧壁厚度与切削刃有效切削长度的关系,为了平衡切削效率与刀夹寿命之间的矛盾,因此选择最佳的刀夹侧壁厚度为3～3.5 mm。

Machinability Investigation and Optimization of Process Parameters in Cryogenic Assisted Sustainable Turning of AISI‑L6 Tool Steel

The application of cutting fluid is significantly increased in the machining sector to improve productivity.However,the inherent characteristics of cutting fluids on ecology,environment,and society shift the interest of researchers to work on environmentally friendly cooling conditions such as cryogenic cooling.Here,the effect of cutting speed and feed rate on the machining performance of the AISI‑L6 tool steel is investigated under cryogenic cooling conditions.Then,the L9 Taguchi based grey relational analysis(GRA)is conducted to investigate the essential machining indices such as cutting energy,surface roughness,tool wear,and material removal rate(MRR).The results indicate that the cutting speed of 160 m/min and feed rate of 0.16 mm/r are the optimum parameters that significantly improves the machining performance of AISI‑L6 tool steel.

Layout design for disc cutters based on analysis of TBM cutter-head structure

Studies to date have failed to consider gage disc cutters’variable cutting depth and the constraints of cutter-head welds,and have ignored the coupling mechanism between the profile of the full-face rock tunnel-boring machine(TBM)cutter-head and the assembled radius layout of the disc cutters.To solve these problems,an adaptive design method for studying cutter layout was proposed.Taking the bearing stress of the outermost gage disc cutter as an index,the profile of the cutter-head was determined.Using a genetic algorithm and based on the principles of equal life and equal wear,the assembled radii of the cutters were optimally designed.Boundary conditions of non-interference between the cutters,manholes,muck buckets and welding lines were given when a star layout pattern was used on cutters.The cutter-head comprehensive evaluation model was established by adopting relative optimization improvement degree of evaluation indices to achieve dimensional consistency.Exemplifying the MB264-311-8030 mm tape TBM cutter-head,the calculations show that compared with the original layout scheme,among the 51 disc cutters,the largest gap of the cutters’assembled radiuses is only 25.8 mm,which is 0.64%of the cutter-head’s radius and is negligible.The cutter-head’s unbalanced radial force decreases by 62.41%,the overturning moment decreases by 33.22%,and the cutter group’s centroid shift increases by only 18.48%.Each index is better than or approximately equal to the original cutter-head layout scheme,and the equivalent stress and deformation are both smaller;these results fully verify the feasibility and effectiveness of the method.

Modeling of Transient Thermal Conditions in Cutting

The thermal conditions like the temperature distribution and the heat fluxes during metal cutting have a major influence on the machinability, the tool lifetime, the metallurgical structure and thus the functionality of the work piece. This in particular applies for manufacturing processes like milling, drilling and turning for high-value turbomachinery components like impellers, combustion engines and compressors of the aerospace and automotive industry as well as energy generation, which play a major role in modern societies. However, numerous analytical and experimental efforts have been conducted in order to understand the thermal conditions in metal cutting, yet many questions still prevail. Most models are based on a stationary point of view and do not include time dependent effects like in intensity and distribution varying heat sources, varying engagement conditions and progressive tool wear. In order to cover such transient physics an analytical approach based on Green＇s functions for the solution of the partial differential equations of unsteady heat conduction in solids is used to model entire transient temperature fields. The validation of the model is carried out in orthogonal cutting experiments not only punctually but also for entire temperature fields. For these experiments an integrated measurement of prevailing cutting force and temperature fields in the tool and the chip by means of high-speed thermography were applied. The thermal images were analyzed with regard to thermodynamic energy balancing in order to derive the heat partition between tool, chips and workpiece. The thus calculated heat flow into the tool was subsequently used in order to analytically model the transient volumetric temperature fields in the tool. The described methodology enables the modeling of the transient thermal state in the cutting zone and particular in the tool, which is directly linked to phenomena like tool wear and workpiece surface modifications.