Basic Approach to a Prediction System for Burr Formation in Face Milling

Geometric parameters and material properties are the two major categories of factors affecting burr formation in the milling process. Geometric parameters such as tool geometry, workpiece geometry, or process condition influence workpiece edge quality at the tool-chip interface. This study identifies a unified criterion to analyze burr formation for different tool engagements. The criterion exploits the exit order of cutting edges of the tool along the workpiece edge, which essentially includes the 3-D nature of the process. The criterion correlates the cutting mechanism and burr formation using the exit order sequence (EOS) as an approximation of chip flow angle. The impact of different possible exit order sequences on burr formation is analyzed. Previously observed phenomena are explained based on the EOS. Also, experiments are done with three different materials (with different ductilities) to analyze the impact of material properties on burr formation for a given EOS. Although burr sizes are different quantitatively with different material, the ranking of burr size for different EOS remained the same. An algorithm for the prediction of burr formation in face milling based on EOS is developed and tested and validated on two different profiles of an automotive part.     

Innovative micro hole machining with minimum burr formation by the use of newly developed micro compound tool

The study focuses on the efforts for minimization of burr formation and improvement of hole surface roughness in micro through-hole machining. It deals with the development of micro compound tool which is consisting of a micro flat drill as the drilling part and a micro diamond-electroplated-grinding part for hole finishing. The finishing diameters of each drilling and grinding parts of the fabricated micro compound tool are 90 μm and 100 μm, respectively. The study focuses mainly on the effect of drill point angle and ultrasonic vibration applied during micro hole machining to the hole entrance and exit burrs formation. The used workpiece is made of stainless steel (SUS304) with a thickness of 100 μm. From the experiment, it was found that the tool having drill point angle of 118° resulted in a smaller burr formation although hole machining was conducted for 600 holes. Furthermore, the application of ultrasonic vibration during hole machining could improve the performance of the developed micro compound tool and decreased the burr size, especially the exit burr.     

Burr Formation in Drilling Intersecting Holes with Machinable Austempered Ductile Iron (MADI™)

This paper presents an investigation of the burr formation for a new material, machinable austempered ductile iron (MADI™), while drilling intersecting holes in the presence of tool wear. A factorial design is used to evaluate the effects of drill point angle and helix angle as well as feed rate and cutting speed on the burr width and height at both curved and flat hole exit conditions. The result indicates the presence of a complex interrelationship among these four variables, particularly the interaction between helix and point angle and its influence on drill corner wear and, hence, burr geometry. Burrs are considerably larger at the flat exit condition. Further experiments were conducted in a central composite design scheme to develop second-order polynomial models of the burr width and height. The result suggests that burr width and height can be reduced by using larger helix and smaller point angles. The result further demonstrates that the somewhat unique work-hardening characteristic of MADI™ during machining can lead to smaller burrs when smaller chiploads are used, regardless of the drill helix and point angles.     

An Approach to Theoretical Modeling and Simulation of Face Milling Forces

A new approach to theoretical modeling and simulation of face milling forces is presented. The present approach is based on a predictive machining theory in which machining characteristic factors in continuous cutting with a single-point cutting tool can be predicted from the workpiece material properties, tool geometry, and cutting conditions. The action of a milling cutter is considered as the simultaneous work of a number of single-point cutting tools, and the milling forces are predicted from input data of workpiece material properties, cutter parameters and tooth geometry, cutting condition, cutter and workpiece vibration structure parameters, and types of milling. A predictive force model for face milling is developed using this approach. In the model, the workpiece material properties are considered as functions of strain, strain rate, and temperature. The ratio of cutter tooth engagement over milling is taken into account for the determination of temperature in the cutting region. Cutter runout is included in the modeling for the chip load. The relative displacement between the cutter and workpiece due to the cutter and workpiece vibration is also included in the modeling to consider the effect on the undeformed chip thickness. A milling force simulation system has been developed using the model, and face milling experimental tests have been conducted to verify the simulation system. It is shown that the simulation results agree well with experimental results.     

Machining efficiency of powder mixed near dry electrical discharge machining based on different material combinations of tool electrode and workpiece electrode

Powder mixed near dry electrical discharge machining (PMND-EDM) is a novel electrical discharge machining (EDM) process. It is proposed to further improve the machining efficiency of dry EDM. The principle of material removal in PMND-EDM is illustrated and its deionization principle is proposed. The influence of residual heat on MRR is analyzed. The concept of superfluous residual heat is proposed. The material removal rate (MRR), the main index of machining efficiency for PMND-EDM process, is researched. Single factor experiments are performed to get effect of peak current, pulse on time, pulse off time, flow rate, tool rotational speed, air pressure and powder concentration on MRR under different material combinations of tool electrode and workpiece electrode. Thermal phenomena in PMND-EDM are illustrated. Effect of each process parameter on MRR of PMND-EDM is gotten and analyzed based on the deionization principle of PMND-EDM. Differences in MRR under different material combinations are found out. Brass tool electrode and W18Cr4V workpiece gain higher MRR under most of discharge conditions, while the superiority of copper tool electrode and 45 carbon steel workpiece in MRR arise when there is improper heat dissipation. The difference is analyzed based on the deionization principle of PMND-EDM.     

An experimental technique to detect tool–workpiece contact in micromilling

There is a need for simple, accurate, and low-cost techniques to detect tool–workpiece contact (or tool touch-off) in micromilling operations. This paper presents a method that is based on monitoring changes in the power spectral characteristics of the spindle vibration signal. The accuracy of this contact detection method is evaluated under different conditions by measuring the overshoot of the tool into the workpiece surface. Specifically, the effects of tool geometry, workpiece surface roughness and hardness, tool wear, step size, and contact detection threshold on the overshoot are analyzed through experiments carried out on a 3-axis micromilling machine. The results show that the method is capable of sub-micron contact detection accuracy depending on the workpiece hardness, roughness, and contact detection threshold.     

Laser tempering based turning process for efficient machining of hardened AISI 52100 steel

Cost-effective machining of hardened steel components such as a large wind turbine bearing has traditionally posed a significant challenge. This paper presents an approach to machine hardened steel parts efficiently at higher material removal rates and lower tooling cost. The approach involves a two-step process consisting of laser tempering of the hardened workpiece surface followed by conventional machining at higher material removal rates with lower cost ceramic tools to efficiently remove the tempered material. The laser scanning parameters that yield the highest depth of tempered layer are obtained from a kinetic phase change model. Machining experiments are performed to demonstrate the possibility of higher material removal rates and improved tool wear behavior compared to the conventional hard turning process. Tool wear performance, cutting forces, and surface finish of Cubic Boron Nitride (CBN) tools as well as low cost ceramic tools are compared in machining of hardened AISI 52100 steel (~63 HRC). In addition, cutting forces and surface finish are compared for the laser tempering based turning and conventional hard turning processes. Experimental results show the potential benefits of the laser tempering based turning process over the conventional hard turning process.     

Prediction of polycrystalline materials texture evolution in machining via Viscoplastic Self-Consistent modeling

The crystallographic orientation or anisotropy is one of the main microstructural attributes strongly affecting the mechanical properties of materials. It is also an influential parameter to be considered during the manufacturing process especially for ultra-precision machining since it affects part quality, tool performance, and process productivity through material properties. In this study, a prediction toolset constituted of a Viscoplastic Self-Consistent model and machining process mechanics model is used to predict the texture evolution on the machined surface. The VPSC (Viscoplastic Self-Consistent) methodology which uses the mechanisms of slip and twinning that are active in single crystals of arbitrary symmetry was used. For this, an analytical model for the process mechanics is derived to understand the forces and stresses generated by the cutting tool at each workpiece point, then the strain and strain rate to capture the rate at which the material is deforming and finally the crystallographic orientations under various machining conditions. Experiments were performed on the orthogonal cutting of aluminum alloy AA-7075-T651 and the texture results were compared to model predictions.     

Measurement of tool internal temperatures in the tool–chip contact region by embedded micro thin film thermocouples

Sensors capable of providing fast and reliable feedback signals for monitoring and control of existing and emerging machining processes are an important research topic, that has quickly gained academic and industrial interest in recent years. Generally, high-precision machining processes are very sensitive to variation in local machining conditions at the tool–workpiece interface and lack a thorough understanding of fundamental thermomechanical phenomena. Existing sensors to monitor the machining conditions are not suitable for robust in-process control as they are either destructively embedded and/or do not possess the necessary spatial and temporal resolution to monitor local tool internal temperatures during machining at the cutting tip/edge effectively. This paper presents a novel approach for assessing transient tool internal temperature fields in the close vicinity of less than 300 μm of the tool cutting edge. A revised array layout of 10 micro thin film micro thermocouples, fabricated using adapted semiconductor microfabrication methods, has been embedded into polycrystalline cubic boron nitride (PCBN) cutting inserts by means of a modified diffusion bonding technique. Scanning electron microscopy was used to examine material interactions at the bonding interface and to determine optimal bonding parameters. Sensor performance was statically and dynamically characterized. They show good linearity, sensitivity and very fast response time. Initial machining tests on aluminum alloys are described herein. The tests have been performed to demonstrate the functionality and reliability of tool embedded thin film sensors, and are part of a feasibility study with the ultimate goal of applying the instrumented insert in hard machining operations. The microsensor array was used for the acquisition of tool internal temperature profiles very close to the cutting tip. The influence of varying cutting parameters on transient tool internal temperature profiles was measured and discussed. With further study, the described instrumented cutting inserts could provide more valuable insight into the process physics and could improve various aspects of machining processes, e.g. reliability, tool life, and workpiece quality.     

Options for broadening and deepening the LCA approaches

Life Cycle Assessment (LCA) has matured over the past decades and become part of the broader field of sustainability assessment. To strengthen LCA as a tool and eventually increase its usefulness for sustainability decision-making, it is argued that there is a need to expand the ISO LCA framework by integration and connection with other concepts and methods. This paper explores the potential options for deepening and broadening the LCA methodologies beyond the current ISO framework for improved sustainability analysis. By investigating several environmental, economic and social assessment methods, the paper suggests some options for incorporating (parts of) other methods or combining with other methods for broadening and deepening the LCA.     

车库出入口坡道噪声影响因素及预测

选取城市居住区中典型地下车库,在优化其出入口噪声采样点布置和同步采样点分组基础上,通过对噪声样本的声学分析,研究了车库出入口坡道噪声与坡道结构、坡度、线形、上下坡等相关因素的关系.通过对平直混凝土路面车库出入口噪声影响预测值的修正,建立了车库出入口坡道噪声影响预测模式.     

Design and fabrication of a laminated thermoforming tool with enhanced features

Thermoforming is a popular manufacturing process for creating useful shapes out of heated thermoplastic sheets using a porous tool under differential pressure. For large, heavy-gauge parts, thermoforming tools are typically made by CNC machining a billet of material or sand casting from an inexpensive master pattern. Although these tooling methods are well established, it is difficult to incorporate enhanced tool functionality such as conformal cooling channels, embedded sensors, unimpeded vacuum channel placement, and customized thermal mass. Profiled Edge Laminas (PEL), a rapid tooling method based on profiling, assembling, and clamping an array of thick layers, is ideally suited for tools used for thermoforming large, heavy-gauge parts and requiring enhanced features. This paper describes how the PEL tooling method can be applied to the design and fabrication of a thermoforming tool and demonstrates the entire process through a case study. Tooling design guidelines and analytical models for predicting conformal channel and vacuum line performance are included. The ease with which multiple-zone conformal cooling/heating channels, vacuum lines, and temperature sensors are incorporated into the tool is also highlighted. Specifically, a 46-layer aluminum PEL tool clamped together with bolts is successfully designed, fabricated, and demonstrated for thermoforming a 0.3×0.4×0.4 m part made from a PVC/Acrylic blend based on the outlined method. The tool incorporates three independent cooling zones sealed by a polymer sealant, three embedded temperature sensors, and an elaborate matrix of vacuum channels. All tool features and the basic geometry were machined into each individual lamina in the same set-up by 2D abrasive waterjet machining, and the final tool surface was CNC-machined. The PEL tooling method is successfully applied to the manufacture of a large, heavy-gauge thermoformed part intended for production.     

The development of a novel process planning algorithm for an unconstrained hybrid manufacturing process

The application of state of the art manufacturing processes has always been constrained by the capabilities either from technical limitations such as limited materials and complex part geometries or production costs. As a result, hybrid manufacturing processes – where varied manufacturing operations are carried out – are emerging as a potential evolution for current manufacturing technologies. However, process planning methods capable of effectively utilising manufacturing resources for hybrid processes are currently limited. In this paper, a hybrid process, entitled iAtractive, combining additive, subtractive and inspection processes, along with part specific process planning is proposed. The iAtractive process aims to accurately manufacture complex geometries without being constrained by the capability of individual additive and subtractive processes. This process planning algorithm enables a part to be manufactured taking into consideration, process capabilities, production time and material consumption. This approach is also adapted for the remanufacture of existing parts. Four test parts have been manufactured from zero and existing parts, demonstrating the efficacy of the proposed hybrid process and the process planning algorithm.     

3D numerical investigation of thermally assisted high efficiency ductile machining of nanocrystalline hydroxyapatite

This study investigates the effects of four different variables (initial workpiece temperature, side rake angle, edge radius/feed rate, and nose radius/depth of cut) on ductile regime machining of a bioceramic material known as nanohydroxyapatite (nano-HAP) using 3D numerical simulation. AdvantEdge FEM Version 5.9 is used to conduct turning simulations of the nano-HAP workpiece. Tecplot 360 is used to analyze the results of the simulations. Because the workpiece is thin, the entire workpiece is set to a uniform initial temperature to simulate laser preheating of the material. Initial workpiece temperature, rake angle (side rake angle), edge radius, and nose radius are varied, and the effects of these operating conditions on critical feed are investigated. It is found that critical feed increases as initial workpiece temperature increases, and also as negativity of rake angle increases. For the edge radius, it is concluded that an initial increase causes an increase in critical feed – however, at some value of edge radius, critical feed shows no further increase; for the nose radius, critical feed appears to show no significant dependence.     

Effect of Tool Edge Geometry on Workpiece Subsurface Deformation and Through-Thickness Residual Stresses for Hard Turning of AISI 52100 Steel

An experimental investigation was conducted to determine the effect of tool cutting edge geometry on workpiece subsurface deformation and through-thickness residual stresses for finish hard turning of through-hardened AISI 52100 steel. Polycrystalline cubic boron nitride (PCBN) inserts with “up-sharp” edges, edge hones, and chamfers were used as the cutting tools in this study. Examination of the workpiece microstructure reveals that large edge hone tools produce substantial subsurface plastic flow. Flow is not observed when turning with small edge hone tools or chamfered tools, and the workpiece microstructure appears random for these cases. Examination of through-thickness residual stresses shows that large edge hone tools produce deeper, more compressive residual stresses than are produced by small edge hone tools or chamfered tools. Explanations for these effects are offered based on assumed contact conditions between the tool and workpiece.     

Effect of fluid concentration in titanium machining with an atomization-based cutting fluid (ACF) spray system

The aim of this work is to investigate the effect of metal-working fluid (MWF) concentration on the machining responses including tool life and wear, cutting force, friction coefficient, chip morphology, and surface roughness during the machining of titanium with the use of the ACF spray system. Five different concentrations from 5 to 15% of a water-soluble metalworking fluid (MWF) were applied during turning of a titanium alloy, Ti–6Al–4V. The thermo-physical properties such as viscosity, surface tension and thermal conductivity of these concentrations were also measured. The test results demonstrate that the tool life first extends with the increase in MWF concentration and then drops with further increase. At low concentration (e.g., 5%), a lack of the lubrication effect causes to increase in a higher friction at the tool–chip interface resulting in severe chipping and tool nose/flank wear within a short machining time. On the other hand, at high concentration, the cooling effect is less. This increases cutting temperature and a faster thermal softening/chipping/notching of the tool material and higher friction at the tool–chip–workpiece interaction zones resulting in early tool failure. A good balance between the cooling and the lubrication effects seems to be found at the 10% MWF concentration as it offers the best machining performance. However, machining with flood coolant is observed to perform the best in the range of 5–7%.     

基于地理分区及神经网络的湖泊水库富营养化研究

构建了一个基于地理分区及神经网络的湖泊水库富营养化综合评价体系.以美国环境保护署Nutrient Criteria Database数据库为参照对象,有针对性地研究我国湖泊水库的情况,首次提出了基于地理分区的简易评价标准,对不同地理特征的水体富营养化临界值进行了定量研究.同时本研究还建立了基于神经网络的富营养化评价模型...     

Micro dimple milling on cylinder surfaces

The paper presents a micro dimple machining on a cylinder surface with a two-flutes ball end mill. When the cutter axis is inclined and the depth of cut is less than the tool radius, non-cutting time, during which neither of the two cutting edges contacts the workpiece, appears in a rotation of the cutter. The rotation of the workpiece and the feed of the tool are controlled so that the cutting areas do not overlap each other. In order to incline the tool with respect to the tangential direction on the cylinder surface, the tool is located at a position oriented at 45° from the top of the cylinder. An analytical model is presented to control the shapes of the dimples with the cutting parameters. The presented machining is verified in cutting tests with measuring the shape and the profile of the dimples. Pre-machining operations are conducted to have a high cylindricity of the workpiece in longitudinal turning and polishing. The cutter runout of the tool is also eliminated by adjusting the orientation and the position of the tool in the collet chuck with measuring the cutting force. The micro dimples are machined accurately as they are simulated.     

Experimental investigation of the machining induced residual stress tensor under mechanical loading

Residual stress induced by machining is complex and difficult to predict, since it involves mechanical loads, temperature gradients or phase transformation in the generation mechanism. In this work, an experiment with a statistical design for the residual stress tensor was performed to investigate the residual stress profile on a machined surface. In order to understand the generation mechanism of residual stress in machining, three variables and workpiece materials were carefully selected to focus on the mechanical loads and avoid the temperature gradients and phase transformation on the machined surface. The mechanical loads considered here included the chip formation force at the primary shear zone and the plowing force at the tool tip–workpiece contact. Depths of cut and rake angles were selected to alter the chip formation force, and the tool tip radius was designed to emphasize the plowing effect. The workpiece material was aluminum 3003. The experimental results showed that the chip formation force provides basic shapes of the residual stress profile for a machined surface. It decides the depth of the peak residual stress below the surface. However, the plowing force was the dominating effect on the surface residual stress, causing high stresses on the surface. The plowing force can shift the surface stress from tensile to compressive. Additionally, the measured stress tensor proved that in-plane shear stress exists for the machined surface.     

Cryogenic Machining of Tantalum

A new approach for the machining of tantalum is presented. The new approach is a combination of traditional turning and cryogenically enhanced machining (CEM). In the tests, CEM was used to reduce the temperature at the cutting tool/workpiece interface, and thus reduce the temperature-dependent tool wear to prolong cutting tool life. The new method resulted in a reduction of surface roughness of the tantalum workpiece by 200% and a decrease of cutting forces by approximately 60% in experiments. Moreover, cutting tool life was extended up to 300% over that in the conventional machining.