整体叶轮五轴侧铣加工的铣削力预测模型研究

为了对整体叶轮等复杂曲面的半精或精加工过程进行仿真和铣削力预测,提出了采用锥度球头铣刀五轴侧铣加工叶片型面的刀轴运动和铣削力计算模型。将锥度球头铣刀沿刀轴方向分解成一定数量的微元,为每个微元创建独立的进给坐标系,并将各微元的总进给速度朝垂直刀轴和平行刀轴等两个方向进行分解,进而得到水平和垂直方向的进给量,由此精确建立微元的总切屑厚度模型。通过斜角切削的正交实验计算相应的摩擦角、剪切应力和剪切角等参数,得到各微元被作用的铣削力,即可预测刀具和工件接触的总铣削力。仿真计算和实验结果对比表明:所建立的铣削力预测模型仿真计算结果与实测一致性好,基本符合实际加工规律。     

五轴铣削加工刀具磨损状态监测研究

随着加工零件的日益复杂,加工要求的不断提高,实际加工时的刀具状况已经成为限制加工质量进一步提高的重要因素.在五轴铣削加工时为了更好的监测刀具的磨损状况,文章对目前的刀具监测方法进行了分析,并建立了五轴铣削加工时平头立铣刀磨损状态监测系统.最后通过实验提出了用刀具的径向力与切向力比值作为监测刀具磨损状态的方法.     

加工误差建模与切削用量选用的研究

为解决数控加工中切削用量选用对加工精度影响的问题,以立铣刀为研究对象建立了铣削力模型,通过建立立铣刀铣削力模型和刀具受力引起的变形模型,推导出刀具z方向误差表达式,并建立了误差模型实验系统。最后通过正交切削实验验证了模型的可靠性,并将切削用量对加工误差的影响权重进行了排序,为切削用量选用提供了参考。     

基于斜角切削的铣削力三维数值模拟

采用有限元软件建立反映金属切削过程中高温、大应变、大应变率的模型,模拟了A16061 - T6铣削加工中刀具微元的斜角切削过程,得到了微元切削力的变化曲线.利用不同切削厚度的仿真结果,分析了切削力、切削力系数与厚度的关系,建立了切削力系数与切削厚度的函数关系模型.利用此模型,模拟了瞬时铣削力.通过铣削试验获得了相同铣削条件下的铣削力,与模拟铣削力比较,发现两者具有良好的一致性,证明了模型的正确性.为复杂工况下铣削力的研究、工件变形预测以及铣削工艺参数优化奠定了基础.     

高速铣削中刀具偏心跳动参数辨识

针对高速铣削中刀具偏心跳动对切削厚度、加工精度以及刀具寿命等的影响问题,通过力学建模建立瞬时切削模型与偏心跳动模型、分解出由偏心跳动引起的铣削力,确定偏心跳动参数辨识过程,以平头立铣刀为例通过试验论证该方法的正确性,为高速铣削中铣削力参数的精确确立奠定基础。     

一种采用动态补偿的五轴机床铣削力预测方法

对五轴数控机床的铣削力进行精准预测,有利于提高工件的加工质量。因此,提出一种采用动态补偿的五轴机床铣削力预测方法。分析五轴数控加工中心结构,研究五轴数控铣削加工中心的进给传动动力学;通过测量切削扭矩,计算电机传递的总转矩,在冲击力激励的作用下,计算它与测量扰动频率响应间的传递函数。将实际切削扭矩分解成直流(静态)分量和交流(谐波)分量,在此基础上采用卡尔曼滤波器衰减噪声,并补偿结构动态模式对间隔采样的切削力矩的影响,从而减少结构动态模式引起的测量值失真。引入Denavit-Hartenberg方法,通过雅克比矩阵求取工件框架中刀具上的切削力和扭矩与驱动框架中驱动力和扭矩的转换关系,进而将刀尖力映射为驱动力矩,以实现对铣削力的预测。结果表明：所提方法预测的力信号与实测的力信号几乎一致,说明该方法能较精准地预测五轴机床的铣削力。     

数控机床多轴联动铣削加工轨迹快速跟踪研究

数控机床多轴联动铣削加工运动学参数变化较大,导致加工轨迹跟踪误差与用时增加。提出新的数控机床多轴联动铣削加工轨迹快速跟踪方法。构建数控机床多轴联动铣削刀具和加工工件瞬时坐标系,实现二者之间的转换,根据坐标系转换结果建立数控机床多轴联动铣削加工运动学模型,结合运动学模型和强跟踪卡尔曼滤波轨迹跟踪方法实现铣削加工过程中运动轨迹的快速跟踪。实验结果表明：该方法可实现铣削刀刃上任意目标点的轨迹跟踪,轨迹跟踪误差低于0.1μm,跟踪平均用时低于1.2 ms,可快速实现高精度的铣削加工轨迹跟踪,为提升铣削加工质量提供保障。     

钛合金铣削刀具的磨损对工件表面沿主轴方向粗糙度的影响

采用硬质合金立铣刀对Ti6Al4V进行高速铣削正交试验,将新刀具所加工的工件表面粗糙度和后刀面磨损至0.05 mm左右时的刀具所加工出来的工件表面粗糙度值进行对比分析,研究磨损后的刀具对工件表面粗糙度的影响。利用粗糙度仪对工件表面粗糙度进行测量,使用超景深显微镜对加工后的工件表面形貌以及刀具磨损情况进行观察,并利用测力仪测量铣削加工过程中刀具产生的铣削力。结果表明:当刀具后刀面磨损至0.05 mm时,其切削参数对工件表面的粗糙度影响大小与刀具崭新时的不一样,这是由于刀具的磨损导致在加工时刀具发生了振颤,从而影响到了工件沿机床主轴方向的粗糙度使其粗糙度增大。     

铝合金薄壁零件铣削力模型的研究

针对Kline铣削力模型变化幅度大的问题,考虑为变形切削厚度的尺寸影响、有效前角、刀具偏心对切削厚度的影响和刀具和工件倾斜的影响,建立了新的铣削力模型,对新的铣削力模型的变化规律进行仿真分析,并通过实验验证。结果表明,新的铣削力模型更接近于实际测定值,验证了该铣削力模型的正确性。     

航空薄壁件铣削加工铣削力预测方法研究

铣削加工中铣削力是导致加工变形的直接原因,而航空薄壁件加工中,加工变形是加工误差产生的主要因素.本文以航空薄壁件铣削加工过程的铣削力为研究对象,通过确定铣削力模型和切削系数参数,建立了刚性和考虑刀具工件变形耦合的柔性预测两种模型.在柔性模型中,采用预扭Timoshenko梁单元的刀具/工件独立建模的方法建立有限元模型,利用Python语言在通用有限元软件Abaqus下迭代求解.实验验证表明预测模型具有很高的准确性和有效性.     

Mechanistic modeling of five-axis machining with a general end mill considering cutter runout

The accurate and fast prediction of cutting forces in five-axis milling of free-form surfaces remains a challenge due to difficulties in determining the varying cutter-workpiece engagement (CWE) boundaries and the instantaneous uncut chip thickness (IUCT) along the tool path. This paper proposes an approach to predict the cutting forces in five-axis milling process with a general end mill considering the cutter runout effect that is inevitable in the practical machining operations. Based on the analytical model of cutting edge combined with runout parameters, the expression of the rotary surface formed by each cutting edge undergoing general spatial motion is firstly derived. Then by extracting the feasible contact arc along the tool axis, a new arc-surface intersection method is developed to determine the CWE boundaries fast and precisely. Next, the circular tooth trajectory (CTT) model is developed for the calculation of the IUCT with a slight sacrifice of accuracy. In comparison with the true IUCT calculated by the trochoidal tooth trajectory model, the approximation error introduced by the circular assumption is negligible while the computational efficiency improves a lot. Finally, combining with the calibrated cutting coefficients and runout parameters, comprehensive formulation of the cutting force system is set up. Simulations and experimental validations of a five-axis flank milling process show that the novel CTT model possesses obvious advantages in computing efficiency and accuracy over the existing approaches. Rough machining of a turbo impeller is further carried out to test the practicability and effectiveness of the proposed mechanistic model.     

A three-dimensional analytical cutting force model for micro end milling operation

In the present day manufacturing arena one of the most important fields of interest lies in the manufacturing of miniaturized components. End milling with fine-grained carbide micro end mills could be an efficient and economical means for medium and small lot production of micro components. Analysis of the cutting force in micro end milling plays a vital role in characterizing the cutting process, in estimating the tool life and in optimizing the process. A new approach to analytical three-dimensional cutting force modeling has been introduced in this paper. The model determines the theoretical chip area at any specific angular position of the tool cutting edge by considering the geometry of the path of the cutting edge and relates this with tangential cutting force. A greater proportion of the helix face of the cutter participating in the cutting process differs the cutting force profile in micro end milling operations a bit from that in conventional end milling operations. This is because of the reason that the depth-of-cut to tool diameter ratio is much higher in micro end milling than the conventional one. The analytical cutting force expressions developed in this model have been simulated for a set of cutting conditions and are found to be well in harmony with experimental results.     

Feedrate scheduling for indexable end milling process based on an improved cutting force model

In CNC machining, an optimal process plan is needed for higher productivity and machining performance. This paper proposes a mechanistic cutting force model to perform feedrate scheduling that is useful in process planning for indexable end milling. Indexable end mills, which consist of inserts and a cutter body, have been widely used in the roughing of parts in the mold industry. The geometry and distribution of inserts compose a discontinuous cutting edge on the cutter body, and tool geometry of indexable end mill varies with axial position due to the geometry and distribution of inserts. Thus, an algorithm that calculates tool geometry data at an arbitrary axial position was developed. The developed cutting force model uses cutting-condition-independent cutting force coefficients and considers run out, cutter deflection, geometry variation and size effect for accurate cutting force prediction. Through feedrate scheduling, NC code is optimized to regulate cutting forces at given reference force. Experiments with general NC codes show the effectiveness of feedrate scheduling in process planning.     

A unified instantaneous cutting force model for flat end mills with variable geometries

A new and unified instantaneous cutting force model is developed to predict cutting forces for flat end mills with variable geometries. This model can routinely and efficiently determine the cutting properties such as shear stress, shear and normal friction angles (SSSNFAs) involved in the cutting force coefficients by means of only a few milling tests rather than existing abundant orthogonal turning tests. Novel algorithms are developed to characterize these properties using following steps: transformation of cutting forces measured in Cartesian coordinate system into a local system on the normal plane, establishment of explicit equations to bridge SSSNFAs and the transformed cutting forces, determination of SSSNFAs by solving the equations and fitting SSSNFAs as functions of process geometries. Results definitely show that shear stress can be treated as a constant whereas shear and normal friction angles should be characterized by Weibull functions of instantaneous uncut chip thickness. Experiments verify that the proposed unified model is effective to predict the cutting forces in flat end milling in spite of cutter geometries and cutting conditions.     

Modeling of three-dimensional numerically controlled end milling operations

A computer-aided cutting simulation system was developed to model three-dimensional numerically controlled (NC) end milling operations. In the developed system, varying axial and radial depths of cut in an NC tool path were identified by a solid modeling system using constructive solid geometry and boundary representation techniques. Once the axial and radial depths of cut were calculated, the dynamic cutting force was calculated from an end milling process model. As a result, the cutting performance in three-dimensional NC end milling operations can be verified and optimized through this approach.     

Closed form formulation of cutting forces for ball and flat end mills

In this paper, a set of basis functions for the calculation of cutting forces in milling are introduced. It is shown that the cutting force at any tool position can be determined by the linear combination of the force basis functions. The method is based on the projection of the chip load area onto the reference coordinate planes. Due to the analytical integration of the cutting forces along the cutter edge, the developed closed form equations provide a fast means of calculating the cutting forces. The validity of the method is experimentally verified for both flat and ball end mills.     

Cutting force prediction in ball end milling of sculptured surface with Z-level contouring tool path

This paper presents an approach to predict cutting force in 3-axis ball end milling of sculptured surface with Z-level contouring tool path. The variable feed turning angle is proposed to denote the angular position of feed direction within tool axis perpendicular plane. In order to precisely describe the variation of feed turning angle and cutter engagement, the whole process of sculptured surface milling is discretized at intervals of feed per tooth along tool path. Each segmented process is considered as a small steady-state cutting. For each segmented cutting, the feed turning angle is determined according to the position of its start/end points, and the cutter engagement is obtained using a new efficient Z-map method. Both the chip thickness model and cutting force model for steady-state machining are improved for involving the effect of varying feed turning angle and cutter engagement in sculptured surface machining. In validation experiment, a practical 3-axis ball end milling of sculptured surface with Z-level contouring tool path is operated. Comparisons of the predicted cutting forces and the measurements show the reliability of the proposed approach.     

High-quality machining of CFRP with high helix end mill

Side milling tests of CFRP (Carbon Fiber Reinforced Plastics) without coolant are carried out by DLC (Diamond-Like Carbon)-coated carbide end mills. Four types of DLC-coated end mills are chosen: UBMS (UnBalanced Magnetron Sputtered) and AIP (Arc Ion Plated) coatings having different helix angles, respectively. The surface integrity is evaluated in terms of 3D profiles of the machined surface, generation of fluffing, delamination and pull-out of the carbon fiber. The cutting force and tool wear with respect to the fiber orientation are also examined. The inclination milling with high helix angle end mill is proposed in which the end mill is tilted in such a way that the resultant cutting force acts parallel to the work surface. This unique approach enables to reduce tool wear and to improve surface integrity of machined surface of CFRP.     

Cutting force estimation in sculptured surface milling

Cutting force milling models developed up to now are mostly used for planar milling using end-mills. Only a reduced number of models applying ball-end mills have been developed. Furthermore these models usually only consider horizontal surface machining, even though the main application of ball-end mills is sculptured surface machining. This article proposes a model that is able to estimate the cutting forces in inclined surfaces machined both up-milling and down-milling. For this purpose a semi-mechanistic model has been developed that calculates the cutting forces based on a set of coefficients which depend on the material, the tool, the cutting conditions, the machining direction and the slope of the surface.A coordinate transformation has been included in order to consider the slope milling case with different cutting directions.The model has been tested on two materials, an aluminum alloy Al7075-T6 and a 52 HRC tool steel AISI H13. Validation tests have been carried out on inclined planes using different slopes and different machining directions.The results provide errors below 10% in most of the cases and both the value and shape of the predicted forces adjust the measured cutting force.     

High-speed five-axis milling of hardened tool steel

This paper investigates critical issues related to high-speed five-axis milling of hardened D2 tool steel (hardness HRc 63). A forging die cavity was designed to represent the typical features in dies and molds and to simulate several effects resulting from complex tool path generation. Cutting tool materials used were coated carbide for the roughing and semi-finishing processes and polycrystalline cubic boron nitride (PCBN) for the finishing process. The effects of complex tool paths on several critical machining issues such as chip morphology, cutting forces, tool wear mechanisms, tool life and surface integrity were also investigated. The main tool failure mode was chipping due to the machine tool dynamics. A five-axis analytical force model that includes the cutter location (CL) data file for computing the chip load has been developed. The effect of instantaneous tilt angle variation on the forces was also included. Verification of the force model has been performed and adopted as a basis for explaining the difficulties involved with high-speed five-axis milling of D2 tool steel.