Pocket Milling Operation Research Articles

An integrated approach for Fixture Layout design and Clamping Force Optimization

Fixture Layout Design (FLD) determines the specific position of locators and clamps to orient and holds the workpiece with respect to a machine tool. The FLD approaches that use Finite Element Analysis (FEA) have been widely used in previous works and have become computationally expensive and specific to a particular problem. Further, the FLD and clamping force optimization were often performed separately by ignoring their interdependence. In the present work, the locators' contact forces are uniformly distributed by suitably varying the fixture layout and clamping force to maximize the part dimensional and form quality. The parametric rigid body model is used to depict the behaviour of the workpiece-fixture system, and it is incorporated with the genetic algorithm to optimize the design variables. A prismatic workpiece with pocket milling operation is considered to validate the proposed methodology. Stability criterion and tool-fixture interference are considered constraints. Subsequently, FEA is used to verify the integrity of the proposed approach. The results infer that the uniform distribution of maximum elastic deformation is achieved due to the uniform distribution of contact forces. The suggested approach is proven effective for designing a milling fixture to manufacture components with high dimensional and form precision.

Computer-aided modelling and experimental evaluation of the pocket milling operation for alloy tool steel (AISI D3)

Computer-aided modelling and experimental evaluation of the pocket milling operation for alloy tool steel (AISI D3)

Optimization of flexible fixture layout to improve form quality using parametric finite element model and mixed discrete-integer genetic algorithm

Dimensional and form accuracy of the workpiece can be improved by effective fixture layout design which shows minimum deformation of the workpiece during machining. Flexible fixtures are inevitable in industries owing to high product variety and shortened production time. Hence, an integrated approach is presented to select the optimum position of locating and clamping elements in a flexible fixture that provide good form accuracy. In this approach, a Parametric Finite Element Model (PFEM) is developed using the information about the workpiece, fixture plan and machining condition. PFEM is used to predict the elastic deformation of the workpiece for the fixture layouts generated using a discrete Genetic Algorithm (GA) with mixed integer-discrete variables. The objective is to minimize the maximum deformation of the workpiece by optimizing fixture layouts. The stability of the workpiece and fixture system is ensured by implementing non-negative reaction force constraints in GA. The proposed approach is applied for a prismatic workpiece to carry out pocket milling operation. The significance of this work is to express the flexibility and computational effectiveness of PFEM to accommodate variation in the workpiece, machining condition and fixture plan while designing flexible fixtures. Further, it highlights a significant reduction in search space due to the use of discrete GA and stability constraint as it takes less objective function calculations. An experimental analysis is performed to study the effectiveness of the proposed approach. Therefore, the proposed approach provides a viable solution to the optimization problem in flexible fixtures.

Machining capability of a 2-D of parallel kinematic machine tool and conventional CNC milling machine

Machining performance of an optimally designed prototype of a 2 degree of freedom PKM (parallel kinematic machine) is optimized in this work. The effect of machining parameters upon the surface quality of machined components is studied. Pocket milling operations are performed at various feed, speeds, and depth of cut on PKM and conventional CNC milling machine. The surface roughness of the machined component is measured, and the results are compared. Taguchi approach is used to design the experiment and analysis of variance is employed to obtain the optimal cutting conditions. The depth of cut is noticed as the most significant parameter that affect the surface roughness. The first version of the PKM prototype shows machining performance similar to the conventional CNC machine. The study establishes the machining capability of PKM and offers scope for developing dynamically superior substitute over the CNC machine tool.

Taguchi-Grey Relational Based Multi-Response Optimization on the Performance of Tool Coating Thickness in Pocket Milling

In this paper, the Taguchi method and Grey relational analysis is used to evaluate the effect of tool coating thickness by machining Titanium Alloy Grade 5 (Ti6Al4V) with Titanium Aluminium Nitrate (TiAlN) Nano coated tools by varying their coating thickness. The pocket milling operation is carried out using the L9 orthogonal array with three levels and four factors design on the CNC vertical machining center. The tool coating thickness, spindle speed, feed rate and depth of cut was selected as machining input parameters for the experiment. The various output parameters such as cycle time, tool wear, surface roughness, material removal rate, micro hardness were found out after machining process. After obtaining all the output parameters the optimization was done by finding out the S/N ratio and grey relation analysis method. According to grey relational grading it was found out that tool coating thickness is the most affected factor for the machining. The confirmation test was done using the optimized value and the results obtained were close to each other.

Modelling of Pocket Milling Operation Considering Cutting Forces and CNC Control Inputs

Machining of large pocket is a key issue for the production of aerospace parts. The optimization of this phase may lead to interesting cost reduction.This paper will study the prediction of the cutting forces acting on a milling tool while machining the corner of a pocket and the impact of the general behavior of the machine tool on the process time.These aspects are combined in a simulation framework at a macroscopic level. Some simulation results are presented and commented. This work can be used to optimize the cutting condition and tested on various toolpath strategies.

TRACKING WORKPIECE STABILITY UNDER VARYING CUTTER POSITIONS, MASS AND COMPLIANCE OF WORKPIECE IN POCKET MILLING

Manufacturing accuracy and surface finish as well as productivity by way of high metal removal rates are mainly restricted by the occurrence of workpiece vibrations and loss of stability. In this paper, dynamic stability of Al-6061-T6 prismatic workpiece located in a milling fixture with 3-2-1 location principle and two hydraulically operated clamps is investigated under spatially varying cutter position and continuously decreasing mass and compliance of a workpiece during pocket milling operation. The mathematical model for the fixtureworkpiece system is based on Hertzian contact theory. The workpiece and fixture elements are considered rigid and the model takes into account the only contact stiffness. A six-dof dynamical model, that includes metal removal effect (MRE), is developed to simulate the dynamical response of the fixture workpiece system in MATLAB Simulink. Finally, the lift-off and macro-slip is calculated and the stability is determined for each contact. The effect of metal removal on the workpiece during machining is considered for 20% and 50% metal removal. For increased metal removal the measured and simulated accelerations are compared and found to have a good agreement with each other. The theoretical model thus developed for dynamic response simulation will be integrated with a Computer Aided Fixture Design (CAFD) system.

Investigation on the Effect of Tool Coating Thickness in Pocket Milling using Austenite Ss316

Objective: This paper presents the research work done in Pocket milling operation using Stainless steel 316 materials. The most critical process parameters namely, Coating thickness (μm), Depth of Cut [DOC] (mm), Spindle Speed [SS] (rev/ min) and Feed Rate (mm/min) are taken into consideration to improve the quality of the output characteristics. The required output characteristics are Cycle time (min), Surface quality measurement, i.e., Roughness of the surface (Ra), Wear of the Tool (mm), Microhardness (HV) and Material Removal Rate (mm3/min). Methods/Analysis: The Taguchi method was used to tabulate the Design of experiments (DOE) of L9 orthogonal array. According to the study, the required Material Removal Rate is considered ‘higher the better’ and other required output characteristics are ‘lower the better.’ To determine to a most significant process parameter, Taguchi’s grey relation analysis is used. To determine the significance and shift of each parameter to the total variation observed, Signal to Noise Ratio (S/N) was used. The contributions of each process parameters to obtain the required output characteristics are studied. Findings: From the grey relation grade, the highest maximum – minimum value shows that the depth of cut is the most influential input parameter for the obtained output characteristics. The optimum input parameters are tool coating thickness of 10 μm, the speed of the spindle being 2500 rev/min, feed rate being 1000 mm/min and depth of cut being 0.7 mm. A verification test was performed conducive to determine the veritableness of the obtained optimal input parameters. The test proves that the optimum input process variables satisfy the required output characteristics for pocket milling operation in AISI Stainless Steel 316 material.

Finite strip modeling of the varying dynamics of thin-walled pocket structures during machining

The structural model of the workpiece is required for modeling, analysis, and avoidance of forced and regenerative (chatter) vibrations in machining of thin-walled parts. Finite element models (FEM) provide a versatile means for modeling the workpiece dynamics, but such models need to be updated frequently as the mass and stiffness of the workpiece varies continuously during machining. The computational time and power that is needed for re-meshing the FEM and then re-computing the natural modes of the workpiece is prohibitive. In this paper, a new approach based on Finite strip modeling (FSM) is presented for modeling the structural dynamics of thin-walled structures during pocket milling operations. The substantially higher computational efficiency of the FSM approach in predicting the varying dynamics of thin-walled pocket structures is verified by comparing its performance against FEM and the multi span plate (MSP) approach presented in (J Manuf Sci Eng 133:021014, 2011). Additionally, the accuracy of the presented approach in analyzing the stability of vibrations and determining the extent of dynamic deflections is verified using experimental results.

Experimental Investigation for Tool Life by Optimizing Machining and Geometric Parameters of CNC End Mill Tool

CNC end milling is a unique adaption of the conventional milling process which uses an end mill tool for the achining process. During the End milling process, the material is removed by the end mill cutter. The effects of machining parameters of end milling process like spindle speed, depth of cut and feed rate and geometric parameter rake angleof a 14 mm diameter HSS end mill tool have been investigated on a AISI 1025 MS plate work material for pocket milling operation to reveal their impact on tool life using Taguchi Methodology. Experimental plan is performed by a Standard Orthogonal Array three times. The results of analysis of variance (ANOVA) indicate that the proposed mathematical odel can be adequately describing the performance within the limit of factors being studied. The optimal set of process parameters has also been predicted to maximize the tool life.

English

Pocket-milling operations are widely used for scooping out materials during the machiningof aircraft components. This paper presents a tool-path planning algorithm for pocket-millingusing zig-zag method. The algorithm consists of basically three modules, viz., generating toolpathelements using pocket geometry entities as input, finding out intersection points (edgepoints), and rearranging points in a zig-zag fashion. OPTPATH algorithm1,2 is used for generatingtool-path elements. These elements thus generated are used to find out the intersection pointswith all entities. The valid points are arranged in a zig-zag way, which are used for machiningany pocket considered. This algorithm works satisfactorily for all the pocket boundaries havingline-line, line-arc, and arc-arc geometry entities.

Neural networks for estimating the tool path length in concurrent engineering applications

This paper deals with the development of a neural computing system that can predict the cutting tool path length for milling an arbitrary pocket defined within the domain of a product design, in a computer numerically controlled (CNC) setting. Existing computer aided design and manufacturing systems (CAD/CAM) consume significant amounts of time in terms of data entry pertaining to the geometries and subsequent modifications to them. In the concurrent engineering environment, where even the designer needs information from the CAD/CAM systems, such time-consuming processes can be expensive. To alleviate this problem, a neural network system can be used to estimate machining time by predicting cost-dependent variables such as tool path length for the pocket milling operation. Pockets are characterized and classified into various groups. A randomized design is described so that the training samples that have been chosen represent the domain evenly. An appropriate network was built and trained with the sample pocket geometries. The analysis of the performance of the system in terms of tool path length prediction for new pocket geometries is presented.

Neural network modeling for tool path planning of the rough cut in complex pocket milling

Abstract This paper presents a new approach to rough-cut tool path planning of pocket milling operations. The key idea is to formulate the tool path problem into a TSP (traveling salesman problem) so that the powerful neural network method can be effectively applied. Specifically, the method is composed of (1) digitization of the pocket area into a finite number of tool points, (2) a neural network method (called a SOM—self-organizing map) for path finding, and (3) post-processing for path smoothing and feed rate adjustment. By the neural network procedure, an efficient tool path (in the sense of path length and tool retraction) can be robustly obtained for any arbitrary shaped pockets with many islands. In postprocessing, (1) the detailed shape of the path is partially modified by eliminating sharp corners of the path segments and (2) any crossovers between the path segments and islands. With the determined tool path, the feed rate adjustment is finally performed for legitimate motion without requiring excessive cutting forces. The validity and powerfulness of the algorithm is demonstrated through various computer simulations and real machining.

Computer-aided generation of optimum chatter-free pockets

This work outlines the development of NC programming subroutines for use in generating the tool path for pocket milling operations in such a way as to avoid the occurrence of chatter. While information is currently available to the programmer about acceptable feeds and speeds, choices of these parameters do not radically affect the part program structure by altering the number of passes or tool path required. For the purposes of chatter avoidance, however, the decisive parameters are the axial and the radial depth of cut, and these parameters are decisive in the program structure. There is almost no information currently available to the programmer about selecting these parameters, and he must use his experience or intuition. A substantial fraction of the productive time of a modern machine tool is therefore spent in verification cuts (the program must be written, tried, and then corrected several times). It is shown that the acceptable (chatter-free) axial and radial depths of cut change depending on the dynamics of the machine and particular tool, the direction of the cut, and the mode of milling (up- or down-milling). The subroutines outlined in this paper select from a database of acceptable cuts the tool path which will result in the maximum metal removal rate. The pockets may have complex 2 1/2 D geometries and may include multiple islands. Several examples are used to illustrate the resulting tool paths, and comparisons are made to tool paths resulting from other available software.

Computer-aided generation of optimum chatter-free pockets

This work outlines the development of NC programming subroutines for use in generating the tool path for pocket milling operations in such a way as to avoid the occurrence of chatter. While information is currently available to the programmer about acceptable feeds and speeds, choices of these parameters do not radically affect the part program structure by altering the number of passes or tool path required. For the purposes of chatter avoidance, however, the decisive parameters are the axial and the radial depth of cut, and these parameters are decisive in the program structure. There is almost no information currently available to the programmer about selecting these parameters, and he must use his experience or intuition. A substantial fraction of the productive time of a modern machine tool is therefore spent in verification cuts (the program must be written, tried, and then corrected several times). It is shown that the acceptable (chatter-free) axial and radial depths of cut change depending on the dynamics of the machine and particular tool, the direction of the cut, and the mode of milling (up- or down-milling). The subroutines outlined in this paper select from a database of acceptable cuts the tool path which will result in the maximum metal removal rate. The pockets may have complex 2 1/2 D geometries and may include multiple islands. Several examples are used to illustrate the resulting tool paths, and comparisons are made to tool paths resulting from other available software.

Operation Planning Based on Cutting Process Models

This paper describes model based operation planning for pocket milling operations. The tool path and cutting conditions are determined based on the geometric model of workpieces and the physical models of the cutting process. The tool path is generated by using the Voronoi diagram of a cutting area. Cutting conditions to achieve the maximum metal removal rate are determined by evaluating the physical models of cutting torque, chatter vibration, and machining error. To maintain a favorable cutting state, the radial depth of cut is controlled by modifying the tool path distance at the circle path segment and by adding additional tool path segments at the corner. Examples are shown to demonstrate the effectiveness of the method.