Real Machining Process Research Articles

Chatter identification in milling of Inconel 625 based on recurrence plot technique and Hilbert vibration decomposition

In the paper a cutting stability in the milling process of nickel based alloy Inconel 625 is analysed. This problem is often considered theoretically, but the theoretical finding do not always agree with experimental results. For this reason, the paper presents different methods for instability identification during real machining process. A stability lobe diagram is created based on data obtained in impact test of an end mill. Next, the cutting tests were conducted in which the axial cutting depth of cut was gradually increased in order to find a stability limit. Finally, based on the cutting force measurements the stability estimation problem is investigated using the recurrence plot technique and Hilbert vibration decomposition method.

Simulation-based tool development for structuring of surfaces for sheet bulk metal forming tools

A simulation-based development of a high-feed milling tool for structuring sheet bulk metal forming tool surfaces is introduced. Based on a geometrical simulation the development chain will be reversed by designing the milling tool to the requirements of the surface topographies. Taking into account surface parameters, the design of the tool as well as the milling parameter values will be changed and simulated to predict the surface topographies prior to the real machining process. Within this reversed process chain the surface parameters can be adjusted regarding the requirements of the forming process.

Determination of Material Constitutive Laws for Inconel 718 Superalloy Under Different Strain Rates and Working Temperatures

In this paper, a special procedure for the prediction of parameters of the Johnson–Cook constitutive material models is proposed based on the experimental data and specially developed MATLAB scripts which allow advanced modeling of complex 3D response surfaces. Experimental investigations concern two various strain rates of 10−3 and 101 1/s and the testing temperature ranging from the ambient up to 700 °C. As a result, a set of mathematical equations which fit the experimental data is determined. The applicability of the experimentally derived constitutive models to the FEM modeling of real machining processes of Inconel 718 alloy is verified.

Triaxial loading device for reliability tests of three-axis machine tools

Abstract This paper presents a triaxial loading device (TLD), which can apply a triaxial force on the spindle of a three-axis machine tool that is executing a 3-degree-of-freedon feeding motion, aiming at simulating cutting forces applied on the spindle in a machining process. A prototype was fabricated and its kinematics and dynamics were analyzed. An explicit force control system was designed based on a fuzzy proportional-integral (PI) controller, integrating a force and a position feedforward. The effectiveness of the control system was evaluated; results illustrate that the fuzzy PI controller reduces the rising time and overshoots, and the force and the position feedforward eliminate the hysteresis and following errors caused by unknown feeding motions, respectively. Loading experiments were conducted to test the dynamic loading capacity of the TLD. The experimental results illustrate that the device is capable to add a triaxial force, which tracks a reference force with acceptable errors, on a spatially-moving spindle with random trajectories in real time. The TLD can simulate the cutting forces that the spindle encounters in real machining process and provides an efficient and economical loading approach that avoids a costly long-term cutting for the reliability tests of three-axis machine tools.

Technical Drawing Learning Tool‐Level 2: An interactive self‐learning tool for teaching manufacturing dimensioning

ABSTRACTThis work presents an interactive self‐learning tool named Technical Drawing Learning Tool‐Level 2—TDLT‐L2—for teaching manufacturing dimensioning to engineering students. The tool was designed for the students enrolled in the first year of the Bachelor in Management and Mechanical Engineering of the Universities of Brescia and Udine. It consists of a simple interactive tool, based on video and drawing animations, aimed at demonstrating the connection between real and simple machining processes and workpiece dimensions on technical drawing. TDLT‐L2 is currently available in two versions: as a standalone application for Windows or Android based operating systems and as a set of interactive PDF documents. It was conceived as the first module of a package of tools that will be developed, based on the learning levels proposed in the Technical Drawing Evaluation Grid—TDEG. A preliminary evaluation of TDLT‐L2 effectiveness was done involving the Management and Mechanical engineering students of Udine in some dimensioning exercises. The statistically considerations done on the obtained results confirmed the validity of the tool as a self‐learning instrument with an average increase of marks of about 8.8%. © 2016 Wiley Periodicals, Inc. Comput Appl Eng Educ 24:519–528, 2016; View this article online at wileyonlinelibrary.com/journal/cae; DOI 10.1002/cae.21728

Analytical model of temperature distribution in metal cutting based on Potential Theory

Abstract. Temperature fields evolving during metal cutting processes have also been of major interest. Temperatures in the tool influence the wear behaviour and hence costs, temperatures in the work-piece are directly responsible for later product quality. Due to the high significance of temperatures, many modelling attempts for temperature fields have been conducted, however failed to deliver satisfying results. The present paper describes a novel analytical model using complex functions based on potential theory. Relevant heat sources in metal cutting as well as changing material constants are considered. The model was validated by an orthogonal cutting process and different real machining processes.

A solid-analytical-based method for extracting cutter-workpiece engagement in sculptured surface milling

Five-axis milling is used extensively to machine the complex parts with sculptured surfaces in die and mold, automotive, aerospace industries, and so on. Cutting force, a key input in simulating the vibration of cutting tools prior to implementing the real machining process, is mainly determined by the feed rate, spindle speed, cutting depth, and cutter-workpiece engagements (CWE). However, identifying the CWE efficiently and accurately is one of the most challenging problems in milling workpiece with complex geometry. This paper presents a novel and integrated solid-analytical-based approach to extract the CWE data in five-axis milling complex parts with sculptured surfaces. In this method, cutting tool and workpiece are modeled exactly. By performing “Boolean Subtraction” operations between cutting tool and workpiece at any cutting location (CL), the possible CWE is obtained firstly. For first cut and slotting cases, the exact CWE can be extracted easily according to the relationship between feed direction and surface normal direction of cutting tool. For following cut cases, the extra steps are needed because the CWE in these cases is associated with the previous cut. The critical line swept surface is constructed analytically at three continuous cutting locations in a previous cut. After trimming the possible CWE using the critical line swept surface, the exact CWE can be identified finally. The advantages of the proposed method are its robustness and flexibility to cancel the complex steps for constructing tool swept volume and updating in-process workpiece. Validation tests show that the developed method has higher efficiency and accuracy.

Machining Process Simulations with Smoothed Particle Hydrodynamics

Because of its meshless nature, the Smoothed Particle Hydrodynamics (SPH) method is a promising alternative to well-established mesh-based simulation techniques like the Finite Element Method when investigating setups that are characterized by a highly dynamic behavior as well as large deformations of the initial configuration. This is typically the case for machining processes. First, a brief introduction to the basic principle of the SPH discretization formalism is provided. Second, the extensions to the original SPH solid scheme that are necessary to model the process of metal cutting in an appropriate way, i.e., to take into account, among other things, the thermal aspects of the problem, are introduced. Besides, emphasis is placed on the local adaptive resolution strategy that has been developed and helps to improve the accuracy of the simulation results while reducing the required computational cost at the same time. The main focus of this paper is on the capability of the extended SPH solid model to describe real machining processes in simulations. Here, we demonstrate that the employed discretization method is able to reproduce the behavior of a processed workpiece observed in experiments by analyzing and, subsequently, assessing the obtained simulation results in terms of chip morphology, stress and temperature distribution, as well as cutting force. For validation purposes, we compare the results found from both simple two- and fully three-dimensional simulations with experimental data for steel C45E.

Composite error prediction of multistage machining processes based on error transfer mechanism

Nowadays, modern manufacturing enterprises are paying more and more attention to machining process quality control in order to ensure the product quality. Since machining quality fluctuation is performed as composite error, then error control is becoming the key point in product quality assurance. However, as a prevention method, error prediction is not used effectively. In this paper, a new method of composite error prediction based on error transfer mechanism is proposed to help control the error sources (man, machine, material, method, measurement and environment, namely 5M1E) in multistage machining processes in order to improve the product quality. Firstly, the formation process of quality fluctuation is introduced, and the quality fluctuation network is established. Secondly, after two kinds of error are defined, the single process independent error formation process and the multistage error transfer mechanism are then analyzed deeply. Thirdly, the single process independent error prediction model is established by using the LS-SVM method and error separation principle, according to which, the composite error of multistage processes is predicted based on error transfer function. Finally, an example of the real specific machining process is given to illustrate the effectiveness and correctness of this methodology.

Global obstacle avoidance and minimum workpiece setups in five-axis machining

The state-of-the-art tool path computation algorithms for five-axis machining consider only the workpiece and clamping device for collision avoidance. However, in a real five-axis machining process, there are many other types of obstacles beyond workpiece and clamps that the tool assembly must avoid, e.g., sensors and other intrusive devices. In such cases, the only solution at present is by means of computer simulation of the machining process after the tool path has been computed. If collision is found, it requires re-computing the tool path and/or changing the setup of the workpiece. This process is then re-iterated until all the collisions are resolved. As a result, the process is time consuming and requires excessive human intervention. In this paper, we present rigorous analyses of the obstacles in five-axis machining and propose efficient numerical algorithms for calculating and representing them. Using our results, the obstacle-free tool orientations can be determined completely at the tool path planning stage, rather than relying on the simulation afterward. In addition, as a direct application of our mathematical modeling, we present a heuristic-based solution to the optimal workpiece setups problem: finding a minimum number of workpiece setups for an arbitrary sculpture part surface so that it can be machined completely on a given five-axis machine without colliding with the obstacles. We use orthogonal table–table five-axis machines as an example and work out a numerical experiment using the proposed solution.

Identifying the time of change in the mean of a two-stage nested process

Statistical process control charts are used to distinguish between common cause and special cause sources of variability. Once a control chart signals, a search to find the special cause should be initiated. If process analysts had knowledge of the change point, the search to find the special cause could be easily facilitated. Relevant literature contains an array of solutions to the change-point problem; however, these solutions are most appropriate when the samples are assumed to be independent. Unfortunately, the assumption of independence is often violated in practice. This work considers one such case of non-independence that frequently occurs in practice as a result of multi-stage sampling. Due to its commonality in practice, we assume a two-stage nested random model as the underlying process model and derive and evaluate a maximum-likelihood estimator for the change point in the fixed-effects component of this model. The estimator is applied to electron microscopy data obtained following a genuine control chart signal and from a real machining process where the important quality characteristic is the size of the surface grains produced by the machining operation. We conduct a simulation study to compare relative performances between the proposed change-point estimator and a commonly used alternative developed under the assumption of independent observations. The results suggest that both estimators are approximately unbiased; however, the proposed estimator yields smaller variance. The implication is that the proposed estimator is more precise, and thus, the quality of the estimator is improved relative to the alternative.

Towards High-Fidelity Machining Simulation

The main purpose of any machining simulation system is to reveal or mimic the real machining process as accurately as possible. Current simulation systems often use G-code or CL data as input that has inherent drawbacks such as vendor-specific nature, incomplete data, irreversible data conversions and lack of accuracy. These limitations hinder the development of a truthful simulation system. Hence, there is a need for higher-level input data that can assist with accurate simulation for machining processes. In addition, there is also a need to take into account of true behaviour and real-time data of a machine tool. The paper presents a High-Fidelity Machining Simulation solution for more accurate results. STEP-NC is used as the input data as it provides a more complete data model for machining simulations. The status-quo of the machine tool is captured by means of sensors to provide true data values for machining simulation purposes. The outcome of the research provides a smart and better informed simulation environment. The paper reviewed some of the current simulation approaches, highlighted the current simulation problems, discussed input data sources for smart machining simulation and introduced the high-fidelity simulation system architecture.

Modeling Research of Hypoid Gear Based on Real Machining Process

In this paper, two modeling methods, the forming method and the generating method, for hypoid gears with two kinds of transmission ratio are discussed by simulating the actual machining process. In the generating modeling method, the tooth profile of the gear is generated by boolean algorithm step by step after creating the models of the gear blank and the cutter and then rotating around their own axis by certain degrees until the cutter is outside the gear blank completely. In contrast with the generating modeling method, the tooth profile is formed by carrying out the boolean algorithm for one time after creating the models of the gear blank and cutter seperately in the forming modeling method. Then using feature instance, all the teeth are created both in the generating modeling method and in the forming modeling method. Using the two modeling methods given in this paper, the modeling process can be shortened and the modeling precision can be improved.

Chatter prediction based on frequency domain solution in CNC pocket milling

Chatter has been a problem in CNC machining process especially during pocket milling process using an end mill with low stiffness. Since an iterative time-domain chatter solution consumes a computing time along tool paths, a fast chatter prediction algorithm for pocket milling process is required by machine shop-floor for detecting chatter prior to real machining process. This paper proposes the systematic solution based on integration of a stability law in frequency domain with geometric information of material removal for a given set of tool paths. The change of immersion angle and spindle speed determines the variation of the stable cutting depth along cornering cut path. This proposed solution transforms the milling stability theory toward the practical methodology for the stability prediction over the NC pocket milling.

Sensorless jerk monitoring using an adaptive antisymmetric high-order FIR filter

In the computerized numerical controllers (CNC) machine-tool processes many finishing and wear problems are related to jerk (derivative of acceleration). Since jerk sensors are expensive and scarce, a sensorless approach is presented as novelty. By taking the incoming signal from a digital incremental encoder included in the standard servo-loop of a CNC machine, the jerk is calculated with a new digital signal processing technique. The contribution of this work focuses on a simple high-order FIR filter with an adaptive algorithm that makes it possible to extract the jerk from the digital position measurement in a sensorless fashion. The algorithm reaches a good approximation to the expected jerk shape by overcoming the intrinsic quantization noise in the digital measurement and the changing dynamical conditions of a real machining process. The algorithm is tested on simulations and over one real CNC machine achieving great similarity between analytical and monitored jerk. It preserves most of the important jerk characteristics like peaks and coarse shape, getting a maximum of 2% of average jerk error on simulations, and 5% of average jerk error on real experiments. This computational efficient algorithm reaches a processing rate up to 760,000 samples per second in an FPGA implementation, which makes it suitable for high speed applications.

2A2-H11 NC加工シミュレーションの高精度化に関する研究(生産システム・生産機器メカトロニクス)

A NC geometric cutting simulator is widely used software that is enable to verify a tool path without real machining process by executing the machined shape check and the interference check between a tool and a workpiece. The purpose of this study is to develop a high-accuracy NC geometric cutting simulator which is able to predict the tool deflection and wear based on removal volume. This paper describes about calculation algorithm of the tool deflection and wear based on removal volume, and refers to the result of comparison of the tool deflection and wear between NC geometric cutting simulation and machining experiment.

Modeling of Virtual Machining System for Contour Milling of Gear Indexing Cam

Geometrical model of virtual machining system was introduced. Based on the analysis of the machining system, it was divided into workpiece subsystem and tool subsystem. Dynamic models of subsystems have been established by means of simplification of machining system. Dynamic analysis and simulation have been done. Model of virtual machining system is the combination of geometrical model and dynamic model. Based on the dynamic analysis and simulation of virtual machining system, conclusion was drawn: (1) In cutting process, as cutter feeds into cutting zone, vibration appears and becomes stronger and stronger. As cutter tends to leave cutting zone, vibration becomes weaker and weaker and disappears finally. The most violent vibration occurs as cutter has engaged into cutting zone and as cutter tends to leave cutting zone. (2) As machining corresponding to dwell of indexing plate, dynamic response is smooth and steady. (3) Vibration will attenuate sharply after cutter leaving cutting zone. The operation of virtual machining system accords with the appearance in real machining process. Properties of product model are very close to those of real machined cam.

Using Error Equivalence Concept to Automatically Adjust Discrete Manufacturing Processes for Dimensional Variation Control

Traditional statistical process control (SPC) has been widely employed for the process monitoring in discrete part manufacturing. However, SPC does not consider any adjustment preventing the process drift. Furthermore, many in-line adjustment approaches, such as thermal error compensation and avoidance, are designed only for machine tool error reduction. This paper intends to fully utilize the engineering process information and to propose an alternative compensation strategy based on equivalent fixture error (EFE) concept that could reduce overall effect of the process errors. Considering three types of error sources in a machining process, we propose to adjust fixture locators to compensate errors using the EFE model. The dynamic property of EFE is investigated for the feedback adjustment of both static and quasi-static errors in machining processes. A minimum-mean-square-error controller is designed based on the dynamic EFE model. We then evaluate the performance of the controller such as stability and sensitivity. A self-updating algorithm for the controller will track the latest process information to stabilize the controller output. Finally, we simulate this process adjustment using the data collected from a real machining process. The results show that this algorithm can improve the machining quality.

Effects of design dimensions on the driving force variation of a hybrid TRR’XY parallel kinematic machine tool

Using parallel-link mechanism as the basic structure of the parallel kinematic machine (PKM) tool is a new design concept and has become one of the most important research fields, attracting many previous researchers. Research on the actuator driving force variation of a PKM tool is essential for the applications of a PKM tool to real machining processes. For machining a component, the smaller actuator driving force required means that the PKM tool has a higher machining performance. To improve the machining performance, understanding of the required actuator driving is very important. A generalized force analysis of the developed system was obtained using the Denavit-Hartenberg (D-H) notation method. The force reactions on the joints and actuator driving forces are obtained on the basis of various cutter locations and a given external cutting force. The prediction of the cutter location with the singularity condition can be also obtained on the basis of the infinite force of the joints. The geometry relationship between the tool platform and the links is adopted to verify the singularity conditions of the system. The driving force variation of the hybrid TRR- XY five-degree-of-freedom machine tool is further investigated.

Kinematic and Singularity Analyses of a Six DOF 6-3-3 Parallel Link Machine Tool

A parallel link manipulator is considered to be an important construction feature of machine tools in the future. To construct a parallel link machine tool which can be practically applied for machining, the analysis of singularity is essential. A six degrees-of-freedom 6-3-3 parallel link machine tool was considered to investigate the effects of the design parameters on the singularity of the system. The U matrix method, which is based on the Plucker coordinate system, is adopted to investigate the singularity of the machine tool. The results show that a little variation of the orientation of the tool frame can effectively avoid the singular condition during the machining processes. This result is important for the applications of parallel link machine tools in real machining processes.