螺旋铣孔工艺的切削稳定性及工艺参数规划

以螺旋铣孔工艺时域解析切削力建模、时域与频域切削过程动力学建模、切削颤振及切削稳定性建模为基础,研究了螺旋铣孔的切削参数工艺规划模型和方法。切削力模型同时考虑了刀具周向进给和轴向进给,沿刀具螺旋进给方向综合了侧刃和底刃的瞬时受力特性;动力学模型中同时包含了主轴自转和螺旋进给两种周期对系统动力学特性的影响,并分别建立了轴向切削稳定域和径向切削稳定域的预测模型,求解了相关工艺条件下的切削稳定域叶瓣图。在切削力和动力学模型基础之上,研究了包括轴向切削深度、径向切削深度、主轴转速、周向进给率、轴向进给率等切削工艺参数的多目标工艺参数规划方法。最后通过试验对所规划的工艺参数进行了验证,试验过程中未出现颤振现象,表面粗糙度、圆度、圆柱度可以达到镗孔工艺的加工精度。     

Prediction of cutting forces in helical milling process

The prediction of cutting forces is important for the planning and optimization of machining process in order to reduce machining damage. Helical milling is a kind of hole-machining technique with a milling tool feeding on a helical path into the workpiece, and thus, both the periphery cutting edges and the bottom cutting edges all participated in the machining process. In order to investigate the characteristics of discontinuous milling resulting in the time varying undeformed chip thickness and cutting forces direction, this paper establishes a novel analytic cutting force model of the helical milling based on the helical milling principle. Dynamic cutting forces are measured and analyzed under different cutting parameters for the titanium alloy (Ti–6Al–4V). Cutting force coefficients are identified and discussed based on the experimental test. Analytical model prediction is compared with experiment testing. It is noted that the analytical results are in good agreement with the experimental data; thus, the established cutting force model can be utilized as an effective tool to predict the change of cutting forces in helical milling process under different cutting conditions.     

Effect of tool stiffness upon tool wear in high spindle speed milling using small ball end mill

Longer tool life can be tentatively achieved at a higher feed rate using a small ball end mill in high spindle speed milling (over several tens of thousands of revolutions per minute), although the mechanism by which tool life is improved has not yet been clarified. In the present paper, the mechanism of tool wear is investigated with respect to the deviation in cutting force and the deflection of a ball end mill with two cutting edges. The vector loci of the cutting forces are shown to correlate strongly with wear on both cutting edges of ball end mills having various tool stiffnesses related to the tool length. The results clarified that tool life can be prolonged by reducing tool stiffness, because the cutting forces are balanced, resulting in even tool wear on both cutting edges as tool stiffness is lowered to almost the breakage limit of the end mill. A ball end mill with an optimal tool length showed significant improvement in tool life in the milling of forging die models.     

考虑左旋切削刃切削连续性的碳纤维增强树脂基复合材料铣削研究

采用右旋切削刃铣刀加工碳纤维增强树脂基复合材料（CFRP）时,纤维层受单向轴向力作用而易产生分层、毛刺等损伤,采用左右旋切削刃共存的多刃微齿铣刀对纤维层施加双向轴向力能有效抑制损伤,但如何保证每层纤维都受到左右旋切削刃的切削作用成为抑制损伤的关键。以多刃微齿铣刀为研究对象,通过设计不同的分屑槽螺旋角,获得左旋切削刃切削面积连续、重叠及未连续三种类型的铣刀。通过实验研究发现：切削面积连续时,CFRP加工表面有少量毛刺及翻边;切削面积重叠时,CFRP加工表面无毛刺及撕裂损伤,效果最好;切削面积未连续时,加工表面有大量毛刺和撕裂损伤;此外,表面粗糙度值会随着分屑槽螺旋角的增大而增大。     

微细铣削切削力正交实验研究

在自行研制的三轴联动微细铣床上,选取典型微三维零件特征进行铣槽和侧铣两种工况正交铣削实验,对微细切削力进行测量和分析。深入研究了主轴转速、轴向切深、每齿进给量等工艺参数对微细切削力的影响规律,以优化加工参数,提高微铣削的加工效率和加工精度。     

基于Pareto遗传算法的螺旋铣加工参数优化

螺旋铣是主要针对航空领域中难加工材料的先进制孔工艺技术。在螺旋铣孔过程中,主轴转速、每齿进给量和每转轴向切削深度是3个最主要的加工参数。以材料去除量和刀具耐用度为优化目标,基于Pareto多目标遗传算法,针对螺旋铣削钛合金材料在稳定性切削条件下的切削参数进行了优化,主要考虑铣削参数对孔表面质量的影响。最终通过切削实验进行了验证。     

基于斜角切削理论的钛合金螺旋铣孔切削力建模

通过分析螺旋铣孔的加工原理和计算加工过程中的运动向量,结合侧刃和底刃对切削力的影响,建立了螺旋铣孔过程的切削力解析模型。提出了基于斜角切削的切削力系数辨识方法,并根据斜角切削过程几何关系推导出摩擦角、剪切角、剪切应力的约束方程。开展切削力系数辨识试验和钛合金螺旋铣孔试验对仿真值进行验证,结果表明,切削力的仿真值与试验值误差较小,平均误差为9.55%,从而验证了斜角切削系数辨识方法的有效性和切削力模型的正确性。     

Prediction of vibration amplitude from machining parameters by response surface methodology in end milling

Decreasing vibration amplitude during end milling process reduces tool wear and improves surface finish. Mathematical model has been developed to predict the acceleration amplitude of vibration in terms of machining parameters such as helix angle of cutting tool, spindle speed, feed rate, and axial and radial depth of cut. Central composite rotatable second-order response surface methodology was employed to create a mathematical model, and the adequacy of the model was verified using analysis of variance. The experiments were conducted on aluminum Al 6063 by high-speed steel end mill cutter, and acceleration amplitude was measured using FFT analyzer. The direct and interaction effect of the machining parameter with vibration amplitude were analyzed, which helped to select process parameter in order to reduce vibration, which ensures quality of milling.     

微铣金属表面微沟槽结构的粗糙度及形貌分析

为了提高和改善微沟槽表面质量,设计了高速微铣削实验,研究了微沟槽底面表面粗糙度和侧壁残留毛刺的变化规律。从理论角度引入了已加工表面的形成机理,建立了微观表面粗糙度理论模型,提出了刀具跳动对侧壁形貌变化影响的规律。利用三轴联动精密微细铣削机床加工微细直沟槽,并选取主轴转速、轴向切深、进给速度、刀具跳动量和材料组织结构为研究因素。采用多因素正交实验和极差分析法,对表面粗糙度值进行数值分析。铝合金,钢和钛合金三类微沟槽底面对应的最佳表面粗糙度值变化范围分别为1.073~1.481 μm,0.485~0.883 μm,0.235~0.267 μm;无刀具跳动钛合金微沟槽壁毛刺的最大高度为7.637 μm,而当刀具存在0.3 μm的径向综合跳动量时对应的微槽壁毛刺的最大高度为21.79 μm。铣削参数对表面粗糙度值的影响按从大到小依次为进给速度、主轴转速、轴向切深,且随着进给速度和轴向切深的增大,表面粗糙度值增大;随着主轴转速的增大,表面粗糙度值先减小后增大;在相同加工条件下,若微圆弧刀刃无磨损,微刀具的跳动量对微直沟槽侧壁表面质量有较大影响。同时,不同金属材料特性也是影响微沟槽表面质量的潜在因素。     

Surface texture generation using high-feed milling with spindle speed modulation

This paper presents a new surface texturing technique using ball-end milling with high feed speed and spindle speed modulation. The ratio between feed-rate and cutting tool radius is in the range of 0.2–0.4, which is much larger than the ratio in conventional milling. Sinusoidal modulation signal is added, so the spindle speed becomes time-varying in order to generate different texture profiles. The cutting tool kinematics are modeled considering the tool-tip run-out and deflection due to cutting forces. The effects of amplitude and frequency of the modulation signal on tool-tip trajectories and surface textures are simulated and analyzed. The relationship between the micro features of the surface texture and the process parameters are investigated. Surface texturing experiments are conducted based on the proposed technique, and tribology tests are performed on the textured surface. It is shown that the textured surfaces present frictional anisotropy, which depends on the process conditions and modulation parameters. The proposed technique is able to achieve fast generation of various surface textures without additional instrumentation, and the final texture geometry is controllable based on the presented kinematics model.     

Development of cutting force prediction model for carbon fiber reinforced polymers based on rotary ultrasonic slot milling

Carbon fiber reinforced polymers (CFRP) have got widely increased applications in aviation, defense and other industries due to their properties of high specific strength/stiffness, high corrosion resistance and low-thermal expansion. The issues like excessive cutting forces and machining damages are encountered in machining due to heterogeneity, anisotropy and low heat dissipation of these materials. The cutting forces are required to be predicted/minimized through modeling. In this article, the novel axial and feed cutting force model has been developed and validated through rotary ultrasonic slot milling of CFRP composites. The variations less than 10% have been found between the measured and corresponding simulated values of the cutting forces. However, some higher variations have also been observed in the few cases mainly due to heterogeneity and anisotropy of such material. The cutting depth is a significant parameter for axial and feed forces, while the feed rate is significant for the axial force. Both the forces decreased with the increase of spindle speed, while they increased with the increase of feed rate and cutting depth. The developed models have been found to be robust and can be applied to optimize the cutting forces for such materials at the industry level.     

高速铣削1Cr18Ni9不锈钢切削力建模及实验分析

采用多因素正交实验法,在五轴高速加工中心上,进行了高速铣削1Cr18Ni9不锈钢的实验。基于概率统计和回归分析原理,对回归方程进行了显著性检验,并建立了1Cr18Ni9不锈钢的切削力经验模型。通过分析正交实验直观图,研究了切削参数对切削力的影响。     

Empirical models and optimal cutting parameters for cutting forces and surface roughness in hard milling of AISI H13 steel

In the present research, an attempt has been made to experimentally investigate the effects of cutting parameters on cutting forces and surface roughness in hard milling of AISI H13 steel with coated carbide tools. Based on Taguchi’s method, four-factor (cutting speed, feed, radial depth of cut, and axial depth of cut) four-level orthogonal experiments were employed. Three cutting force components and roughness of machined surface were measured, and then range analysis and analysis of variance (ANOVA) are performed. It is found that the axial depth of cut and the feed are the two dominant factors affecting the cutting forces. The optimal cutting parameters for minimal cutting forces and surface roughness in the range of this experiment under these experimental conditions are searched. Two empirical models for cutting forces and surface roughness are established, and ANOVA indicates that a linear model best fits the variation of cutting forces while a quadratic model best describes the variation of surface roughness. Surface roughness under some cutting parameters is less than 0.25 μm, which shows that finish hard milling is an alternative to grinding process in die and mold industry.     

Theoretical modelling of cutting forces in helical end milling with cutter runout

A theoretical cutting force model for helical end milling with cutter runout is developed using a predictive machining theory, which predicts cutting forces from the input data of workpiece material properties, tool geometry and cutting conditions. In the model, a helical end milling cutter is discretized into a number of slices along the cutter axis to account for the helix angle effect. The cutting action for a tooth segment in the first slice is modelled as oblique cutting with end cutting edge effect and tool nose radius effect, whereas the cutting actions of other slices are modelled as oblique cutting without end cutting edge effect and tool nose radius effect. The influence of cutter runout on chip load is considered based on the true tooth trajectories. The total cutting force is the sum of the forces at all the cutting slices of the cutter. The model is verified with experimental milling tests.     

The optimal cutting-parameter selection of heavy cutting process in side milling for SUS304 stainless steel

This paper presents an optimal cutting-parameter design of heavy cutting in side milling for SUS304 stainless steel. The orthogonal array with grey-fuzzy logics isapplied to optimize the side milling process with multiple performance characteristics. A grey-fuzzy reasoning grade obtained from the grey-fuzzylogics analysis is used as a performance index to determine the optimal cutting parameters. The selected cutting parameters are spindle speed, feed per tooth,axial depth of cut and radial depth of cut, while the considered performance characteristics are tool life and metal removal rate. The results ofconfirmation experiments reveal that grey-fuzzy logics can effectively acquire an optimal combination of the cutting parameters. Hence, performance in theside milling process for heavy cutting can be significantly improved through this approach.     

HIGH SPEED MILLING OF GRAPHITE ELECTRODE WITH ENDMILL OF SMALL DIAMETER

Graphite becomes the prevailing electrode material in electrical discharging machining (EDM)currently.Orthogonal cutting experiments are carried out to study the characteristics of graph- ite chip formation process.High speed milling experiments are conducted to study tool wear and cutting forces.The results show that depth of cut has great influence on graphite chip formation.The removal process of graphite in high speed milling is the mutual result of cutting and grinding process. Graphite is prone to cause severe abrasion wear to coated carbide endmills due to its high abrasive- ness nature.The major patterns of tool wear are flank wear,rake wear,micro-chipping and breakage. Cutting forces can be reduced by adoption of higher cutting speed,moderate feed per tooth,smaller radial and axial depths of cut,and up cutting.     

Three dimensional cutting force analysis in end milling

The analysis of cutting forces plays an important part in the design of machine tool systems as well as in the planning, optimization, and control of machining processes. This paper presents a three-dimensional model of cutting forces in peripheral end milling in terms of material properties, cutting parameters, machining configuration, and tool/work geometry. Based on the relationship of the local cutting force and the chip load, the total cutting force model is established via the angle domain convolution integration of the local forces in the feed, cross feed, and axial directions. The integration is taken along the cutter axis and summarized across the cutting flutes. The convolution integral leads to a periodic function of cutting forces in the angle domain and an explicit expression of the dynamic cutting force components in the frequency domain. The closed-form nature of the expressions allows the prediction and optimization of cutting forces to be performed without the need of numerical iterations. To assess the fidelity of the analytical model, experimental data from end milling tests are presented in the context of three dimensional time waveforms, power spectra, and phase angles, in comparison to the values predicted by the model.     

钛合金大直径孔螺旋铣削工艺优化研究

本文基于螺旋铣孔技术,采用正交试验和极差值分析方法,在钛合金上进行了19.05mm直径孔的螺旋铣削试验。分析了不同切削参数对轴向切削力、钛合金孔径、粗糙度等的影响,以此为指标优化出最佳工艺参数。在此基础上研究了最佳参数下切削力、加工质量和刀具磨损随加工孔数的变化,发现在大直径孔加工中,螺旋铣孔技术可有效改善加工质量、提高加工效率。     

SURFACE PROPERTIES OF THE MACHINED WORKPIECE FOR HELICAL MILLS

Stability and surface errors are investigated numerically for milling operations with a helical tool. A detailed two degree of freedom mechanical model is derived that includes both surface regeneration and the helical teeth of the tool. The governing delay-differential equation is analyzed by the semi-discretization method. The surface errors are predicted based on the (stable) forced motion of the tool. New surface error parameters were introduced to characterize the properties of the spatial machined surface. The errors were calculated numerically for a given machine tool and workpiece for different axial depths of cut and spindle speeds. It is shown that both good surface properties and large material removal rate can be achieved by appropriate axial immersion in case of helical fluted tool. This phenomenon was proved analytically by means of the Fourier transformation of the cutting force.