Tool Deflection Research Articles

A predictive model on surface roughness during internal traverse grinding of small holes

The surface roughness of nozzles has important influence on the quality of fuel atomization. The diameter of nozzles in aero engine is generally less than 1 mm. Because of the smaller diameter of the grinding wheel used, its stiffness is poor and thus the wheel tends to deflect under the grinding force. The deflection of grinding wheel has great influence on the actual feed, which ultimately affects the roughness. Therefore, a predictive model of the roughness during internal traverse grinding (ITG) is thus needed. Such a predictive model was established in this paper, in which the deflection of tool and interference of grooves were taken into consideration. In addition, the relationship between roughness and various input variables, namely, the rotating speed, the oscillation speed, the radial feed speed, the feed time, and the spark-out time, was established. Then several groups of experiments with different input variables were carried out to calibrate and validate the model, which demonstrated that the predictive model of surface roughness of ITG in small-hole nozzles has good accuracy, and provides guidance for the optimization of processing parameters.

Theoretical analysis and experimental study of offset error of ultra-precision micro-spindle caused by cutting load

ABSTRACT The existing ultra-precision micro-spindles fail to achieve the machining requirement of sub-micron precision because of its large radial error. In this study, the calculation model of radial offset error caused by cutting load is established for ultra-precision micro-spindle and an example design is carried out. The study finds that the offset of the tool tip increases with the increase of tool overhanging length and decreases with the increase of the span of spindle rotor. Bearing stiffness has the greatest effect on the tool tip offset, followed by the tool deflection deformation while the deflection deformation of spindle rotor has the smallest effects on the tool tip offset. The thrust bearing restrains the increase of tool offset error to some extent. The supporting centre of the aerostatic bearing shifts under the acting of cutting load due to its small bearing stiffness. Finally, the testing was conducted on a prototype micro-spindle, which shows the rationality of the established model.

A study on material removal mechanism of ultramicro-grinding (UMG) considering tool parallel run-out and deflection

Micro-grinding is capable of machining complex structures in a wide variety of hard and brittle materials when compared to other micro-machining processes. In recent years, more attentions have been paid to micro-grinding field, but not much even little has been paid to ultramicro-grinding (UMG). What usually be called UMG is a kind of micro-grinding process, during which grinding tool is extremely small, usually less than 50 μm. In this scale, tool parallel run-out and tool deflection have a big effect on grinding results. In view of the abovementioned facts, the exact prediction of grinding force in UMG is still not fully developed, especially when considering tool parallel run-out and tool deflection. In order to better explain the grinding process and the material removal mechanism in UMG, this paper proposes an analytical grinding force prediction model considering the related cutting parameters, tool parallel run-out, tool deflection, size effect, and the exact trochoidal trajectory of single grain. In this prediction model, final undeformed chip thickness is computed by considering tool parallel run-out and tool deflection, then forces are calculated based on the final undeformed chip thickness. In order to study the special characteristics of UMG, a series of UMG single-factor experiments have been conducted, and the parameters of tool parallel run-out and tool deflection were measured during the experiment. The proposed grinding force model is validated through UMG orthogonal experiment with grinding tool about 40 μm diameter, and the workpiece is single-crystal silicon. During the experiment, the total indicated run-out (TIR) and grinding forces in both x and y directions are measured and analyzed, and the relationship between grinding forces and cutting parameters, between TIR value and cutting parameters, and between grinding forces and TIR value are investigated. Relative to the general cutting condition, a sliding situation (cutting depth is extremely low) is found and analyzed. Based on the experiment results, an empirical formula for cutting parameters and TIR is obtained. To verify the model, comparisons among experimental result, the proposed model and the previous three force models are made, and the final comparison result shows that the proposed model agrees better with the experimental results than other three previous models, only a few mismatched points (E > 10%) are found, and the biggest error for Fx is 18.12% and for Fy is 20.91%, indicating the effectiveness and accuracy of the proposed model. The proposed grinding force model is not only expected to be meaningful to optimize grinding parameters but also anticipated to be powerful to provide the basis for the more accurate grinding force prediction.

INCREASING PRODUCTIVITY OF CUTTING PROCESSES BY REAL-TIME COMPENSATION OF TOOL DEFLECTION DUE TO PROCESS FORCES

The Internet of Production (IoP) describes a vision in which a broad range of different production data is available in real-time. Based on this data, for example, new control types can be implemented, which improve individual manufacturing processes directly at the machine. A possible application scenario is a tool deflection compensation. Although the problem of tool deflection is well known in the industrial field, a process-parallel compensation is not common in industrial applications. State-of-the-art solutions require time and cost consuming tests to determine necessary cutting parameters. An NC-integrated compensation that adapts the tool path in real-time will make these tests obsolete and furthermore enables higher chip removal rates. In this paper, a control-internal real-time compensation of tool deflection is described, which is based on a process-parallel measurement of process forces. The compensation software is designed as an extension to the NC kernel and thereby integrated into the position control loop of an in-series NC. The compensation movements are generated by manipulating the reference values of the feed axes. The approach is investigated by experiments with linear axis movements. During these tests, a significantly reduction of geometrical machining errors is possible.

Integration of tool error identification and machining accuracy prediction into machining compensation in flank milling

In a flank milling process, the tool rotation profile error induced by its radial dimension error, setup error, tool deflection, and wear has a great influence on the dimensional accuracy of the machined components. In this paper, we present an integrated identification of tool error, prediction of machining accuracy, and compensation methodology for tool profile error to improve the machining accuracy. Firstly, the tool errors are divided into static and dynamic errors based on the error characteristics and the corresponding error identification methods are established to recognize the tool error parameters. Secondly, the machining accuracy is predicted by a prediction model, and the tool error parameters are input into this model. Thirdly, a new tool error compensation method is developed and incorporated in the corresponding NC codes. Finally, some machining experiments have been carried out to validate the proposed identification-prediction-compensation methodology, and the results show that this methodology is effective.

Modification of Tool Orientation and Position to Compensate Tool and Part Deflections in Five-Axis Ball End Milling Operations

Tool-workpiece deflection is one of the major error sources in machining thin walled structures like blades. The traditional approach in industry to eliminate this error is based on modifying tool positions after measuring the error on the machined part. This paper presents an integrated model of cutting force distribution on the tool–blade contact, automatic update of blade static stiffness matrix without resorting to time-consuming finite element solutions as the material is removed, the prediction and compensation of static deflection marks left on the blade surface. The main focus of the paper is to compensate the deflection errors by respecting the maximum form errors, collision of tool/machine/workpiece, cutting speed limit at the tool tip, and ball end—blade surface contact constraints. The compensation has been carried out by two modules. The first module adjusts the tool orientation along the path to reduce the error by constructing an optimization problem. This module is computationally inexpensive and results in about 70% error reduction based on the conducted experiments. The modified tool path resulted from the first module is fed to the second module for further reduction of the form errors if needed at the violated cutter locations; hence it takes less computational time than the stand alone approach proposed in the literature. The proposed algorithms have been experimentally validated on five-axis finish ball end milling of blades with about 80% reduction in cutting force induced form errors.

Monitoring of Cutting State in End-Milling Based on Measurement of Tool Behavior Using CCD Image

To date, various in-process monitoring and measuring techniques for milling have been proposed; these are based on factors such as spindle power, cutting force, and vibration. However, the spindle power and cutting force in small-diameter milling processes are too small, thereby rendering these methods ineffective. This study aims to develop an in-process monitoring system of the cutting state, and thus, prevent tool breakage in milling when using a small-diameter tool. Our previous study showed that this monitoring technique is based on the analysis of the tool projection image by a CCD camera. It enables a precise measurement of tool deflection during high-speed milling. In this study, we apply this system to the measurement of tool deflection in end milling under different cutting conditions, including tool type, machining shape, workpiece, and feed rate. Moreover, we examine the relationship between tool deflection and cutting conditions. The results clarify that this system enables in-process monitoring of tool deflection. The measured tool deflection with this system is influenced by the cutting condition. In addition, the tool deflection shows a periodical change in one turn, which seems to be related to the number of tool edges.

Modelling and analysis of tool deflections in tailored micro end mills

The deflection of micro end mills has a detrimental effect on surface quality of the machined micro components and adversely affects the achievable dimensional and geometrical tolerances. In this paper, the analysis and modelling of tool deflections of tailored micro end mills have been considered. The tool deflections are obtained using analytical models as well as finite element simulations and verified using a dedicated measurement setup, which uses a capacitive sensor with a nanometre resolution for static tool deflection measurements. The optimisation of the micro end mill geometry has been performed to determine optimum neck taper angle and transition radius of the single edge micro end mill to have minimum tool deflections. With the developed model, tool failure predictions for a given process parameter set can be performed and it can be used for better micro milling process planning.

Modelling and analysis of tool deflections in tailored micro end mills

The deflection of micro end mills has a detrimental effect on surface quality of the machined micro components and adversely affects the achievable dimensional and geometrical tolerances. In this paper, the analysis and modelling of tool deflections of tailored micro end mills have been considered. The tool deflections are obtained using analytical models as well as finite element simulations and verified using a dedicated measurement setup, which uses a capacitive sensor with a nanometre resolution for static tool deflection measurements. The optimisation of the micro end mill geometry has been performed to determine optimum neck taper angle and transition radius of the single edge micro end mill to have minimum tool deflections. With the developed model, tool failure predictions for a given process parameter set can be performed and it can be used for better micro milling process planning.

Influence of cutting ratio and tool macro geometry on process characteristics and workpiece conditions in face milling

This paper presents the influences of the inverse cutting ratio (width-to-thickness b/h<1) and the macro cutting geometry on the chip formation, milling forces, tool deflection, as well as on the workpiece surface integrity in face milling. The investigations are based on the DoE method using finite element simulation and practical experiments. A significant decrease of the cutting force by up to 65%, was achieved using inverse cutting ratio. Accordingly, the mechanical tool deflection from its axis was reduced. At the same time, the residual tensile stresses of the workpiece surface increase applying the inverse cutting ratio.

Forces, form deviations and surface roughness in micro-milling of CoCr alloys for dental prostheses

Micro-milling, besides selective laser melting, is commonly used for the manufacture of dental prostheses. Demands to the application of these prostheses require hard and tough materials like cobalt-chrome alloys or ceramics. The cutting process is governed by static as well as dynamic interactions between the process and the structure of the workpiece. These interactions deteriorate the work result, especially the shape accuracy. The deflection of the milling tool is one effect, which has a significant influence. However, the deflection can be minimised by optimising the manufacturing strategy, by an adjustment of the process parameters or by optimising the tool path, which leads to an increased quality of the final product. The work presented in this paper aims to establish a connection between tool deflection and resulting form deviations during micro-milling of defined geometries in CoCr alloys. This is achieved by measuring the active forces while machining an defined test geometry with different feed rates and radial infeeds and a subsequent evaluation of the resulting form. Furthermore, the influence of the workpiece geometry on the forces and form deviations is analysed to serve as a foundation for future optimisation steps. In order to quantify the surface quality, white light interferometry is applied to measure the surface roughness Sa and Sq and the influence of feed rate vf and radial infeed ae on the surface roughness is derived.

Development of a model to compensate overcut during Electro Discharge Boring process

Electro discharge boring (EDB) process is novel concept of machining through X-Y tool actuation applied for boring of hard and difficult to machine materials. Unlike conventional boring machining, EDB process is free from vibration, cutting forces or tool deflection. Since, the removal of material takes place due to the action of repetitive sparks therefore overcut is observed in the bored cavity produced during EDB process. In the present study, an effort has been made to predict and reduce the overcut generated during EDB process. Effect of process parameters on overcut have been studied using Taguchi's experimental method and then significant process parameters have been identified using analysis of variance method. Further, a prediction model has been developed using multiple regression analysis for prediction of overcut produced during boring process on Inconel 718 material. Finally, an algorithm has been developed in MATLAB software for compensation of overcut by suggesting compensating orbital radius for specified target diameter of cavity. The test results obtained using proposed algorithm show that the cavities generated are very close to the specified target cavities. [Submitted 3 September 2016; Accepted 24 July 2018]

Experimental and finite element investigation of over-bending phenomenon in Double-Sided Incremental Forming (DSIF) of aluminium sheets

Abstract Double-Sided Incremental forming (DSIF) is a flexible sheet forming method with increasing research interest in the last decade. It offers improved formability and accuracy over the conventional single point incremental forming (SPIF) although it accompanies with the possibility of tools losing contact during the forming process. Mounting a pneumatic supporting tool is an efficient solution. However, the tools may squeeze and over-bend the material when forming for a high wall angle. A possible reason may be due to inaccurate prediction of material thinning or the effect of tool deflection. This work uses a modified finite element (FE) model with dedicated toolpath design incorporated with simplified stiffness of tools and machine in order to reproduce the effect of system elasticity to the DSIF process with hydraulic supporting tool and evaluate the root causes of the over-bending problem. The numerical results are compared with experimentally produced components, focusing on the thickness evaluation and development of the tool deflection throughout the process. This comparison demonstrates the effect of the tool deflection upon the formed parts, including the geometric error and excessive deformation on the wall region. The conclusion suggests a need for a compensation based approach in the design of DISF toolpath and machine systems.

Study on Instantaneous Tool Deflections Considering Tool Run-out in Micro Milling Process

Study on Instantaneous Tool Deflections Considering Tool Run-out in Micro Milling Process

Optimization of complex cutting tools using a multi-dexel based material removal simulation

Multi-dexel based material removal simulations provide a fast and flexible way to compute process forces and tool deflections for milling and turning operations. This allows an advanced process planning including detection of collisions for complex toolpaths. However, using dexel simulations for designing cutting tools has rarely been investigated. Especially the position of individual cutting edges is not considered, because current approaches only subtract the sweep volume of the tool envelop instead of the rake face. This paper presents a new method to design cutting tools using material removal simulations and a detailed tool geometry representation. The discretization of the tool allows an efficient calculation of the engagement conditions of individual cutting edges. The method is used to optimize novel porcupine milling cutters with round indexeble inserts, which produces a geometry analogous to serrated end mills. Based on the calculated forces, the positions of individual indexable inserts are adjusted to minimize the maximum radial force. An optimum has been found that reduces radial force by 12% compared to conventional porcupine milling cutters with squared inserts.

Optimization of manufacturing complex-shaped gas turbine blades

In mechanical manufacturing, parts containing complex surfaces are extensively used to meet specific necessities such as performance, appearance and lightweight. However, dimensional and geometric non-conformities related to the cutting parameters were found.Thus, the aim of this paper is to introduce an experimental study conducted on workpieces obtained from AISI 304 stainless steel to control the milling process in terms of tool deflection, tracking error and surface roughness. To achieve this objective, a 3-axis CNC machine and an end-ball tool were used to manufacture the work pieces. The shape and dimensions of each specimen were inspired from the components of gas turbine blades containing complex shapes. A L27 Taguchi standard was adopted as a Design of Experiment (DOE) grouping three factors (cutting speed, feed speed, axial depth) with three levels.The obtained results show how much the tool deflection and the tracking errors are mainly influenced by the feed speed and the cutting speed.Combining experimental and analytical models, an empirical model of the cutting force perpendicular to the tool axis, grouping tool stiffness and cutting parameters, is proposed in this study. The increase of the axial depth conduces to an increase in tool deflection, the tracking errors and the cutting force.

Self-optimizing tool path generation for 5-axis machining processes

This paper presents a self-optimizing process planning approach for 5-axis milling that allows an automatic compensation for tool deflection. For this purpose, process conditions are obtained from a process-parallel material removal simulation and merged with shape error measurements. Using machine learning methods, the resulting shape error is predicted and the tool path adapted automatically. The system has been implemented on a 5-axis CNC machine centre. It is shown that the resulting shape error can be reduced by 50%. Moreover, the article highlights the behaviour of the learning process and the transferability to other workpiece geometries.

A Finite Element Modeling Prediction in High Precision Milling Process of Aluminum 6082-T6

This study investigates micro-end-milling machining prediction using three-dimensional finite element modeling method. The FE model was developed for contouring up-milling operation for prediction of chip flow, burr formation, cutting temperature and cutting forces in an integrated model. The flow stress behavior of the workpiece was modeled by the Johnson–Cook material constitutive model. Different cutting conditions were simulated to consider the effect of the process variables that might be difficult or impossible to follow in the physical experiments at this scale. The tool was precisely 3D modeled to describe the detailed geometry of the tool which is one of the critical aspects of the model and is characteristic of the cutter tool micro-geometry design. Furthermore, the tool deflection was studied using a FE model under the experimental cutting forces measured in the different cutting conditions in order to consider the micro-end-mill deviation from the nominal position. 3D simulations of chip flow and temperature distribution are compared in various cutting conditions. The results of the burr formation, temperature distribution and cutting forces in three directions predictions are compared against the experiments. Simulations were able to predict the burr height with an accuracy between 1 and 4 µm depending on cutting parameters settings. The results of this study are beneficial to comprehend the micro-end-milling chip and burr formation to increase the machinability of the workpiece and to understand the influence of cutting parameter in order to prevent several experimental tests prior to the final machining.

Investigating the impact of tool inertia on machinability of a β-titanium alloy using tool deflection and acoustic emission

Finding sustainable ways of machining exotic materials is gaining more and more importance in the manufacturing industry. Application of advanced measuring instruments for quantifying performance measures is a crucial requirement for making machining processes viable. The presented work aims to ameliorate machining of a high-strength β-titanium alloy using information from measurements of key responses, such as cutting energy consumption, tool deflection, and tool damage. Acoustic emission data and tool’s acceleration data are utilized to work out the magnitudes of energy consumed and deflection undergone by the tool, respectively. The article focuses on quantifying the effects of tool’s inertia, strength of work material, and two cutting parameters on the aforementioned responses. A total of 54 continuous cutting experiments are performed in which a fixed volume of material per experimental run is removed. Tool deflection method helped to determine the significant effects of varying tool inertia, work material strength, and cutting speed on the machining process. Likewise, acoustic emission method highlighted the strong effects of material strength and cutting speed caused on the cutting energy consumption. The effect of feed rate is found to be significant regarding tool wear only. Finally, the tool wear data are tested for correlation against the corresponding data sets of the other two responses. It is found that both tool deflection and cutting energy possess strong uphill relationships with tool wear.

Investigation of tool deflection during milling of thread in Cr-Co dental implant

Milling is a good option for manufacturing internal threads in hard-to-cut dental components due to lower cutting forces. In the case of a very small drilled diameter, the tool cannot be large enough to reduce tool deflection nor sufficiently small to avoid the influence of the tool penetration. As a consequence, both situations need to be considered and no other research study dealt with this aspect for the modeling of thread milling forces. This article deals with the analysis of forces, deflection, and undercutting during machining of one typical internal thread geometry used for implants in a chrome-cobalt dental alloy. The geometry is analyzed considering the influence of tool penetration and it is presented new equations to identify the regions where it occurs. Machining experiments are conducted acquiring cutting forces and tool axis position in order to calculate the tool radial forces and estimate tool deflection. Manufactured threads geometry is measured to evaluate dimension quality. It can be claimed that the tool trajectory should consider one extra revolution around the drilled hole in order to machine the undercut material due to tool deflection for this small tool diameter.