Total Machining Time Research Articles

Optimal iso-planar cutting direction based on machine kinematic metric: A differential geometry method for freeform surface finishing tool path computation

ABSTRACTWhile machining width is an important factor of the machining time of freeform surface finishing operations, in reality the kinematic capability of the machine tool is usually the bottleneck of achieving higher feed speed and optimal machining time. The purpose of this paper is to conveniently (and approximately) determine the optimal cut direction considering the speed kinematic capability of the machine tool, without having to compute the actual tool path. We propose a mathematical instrument, called Machine Kinematic Metric (MKM), to easily evaluate infinitesimal machining time on a freeform surface based on machine kinematic consideration. It's a tensor field similar to the metric tensor in differential geometry. MKM is integrated over the part surface to approximate the cut-direction-dependent total machining time, and used to determine the optimal cut direction that minimizes the machining time. To validate the accuracy of the prediction using MKM, we apply the method and compute the machini...

Optimal Workpiece Setup for Time-Efficient and Energy-Saving Five-Axis Machining of Freeform Surfaces

Energy consumption in five-axis machining of freeform surfaces can be considerably large for large-size parts. This paper presents a study on how to setup the workpiece in order to minimize the energy consumption without modifying the toolpath itself. For an arbitrary freeform workpiece, the way how it is setup on the working table highly affects the machine's kinematic behavior, which dominates the overall processing time and energy consumption. Taking into account the speed and acceleration limit of each axis of the machine, we first establish the energy consumption model as a function of the workpiece setup. However, this original model involves certain critical physically pertinent coefficients (such as the moment of inertial of a rotary table) which are usually unavailable in practice. Instead, by exploring insightful geometric characteristics of the five-axis machine, an alternative energy consumption model is established which is independent of those hard-to-obtain coefficients. A simple algorithm is then designed to optimize this model. Both computer simulations and physical cutting experiments demonstrate that, when compared with an arbitrary setup, the optimized workpiece setup is able to achieve a significant saving (as much as 50%) in both energy consumption and total machining time, both using a same tool path.

Post-processor development of a five-axis machine tool with optimization tool radius compensation

The post-processor is an important interface that transforms cutter location data into numerical control (NC) data. The data compensation in a five-axis machine is quite complex, because of a variety of the machine centers and the computerized numerical control (CNC) system. Since most work on the five-axis post-processor method has dealt primarily with the generation of NC code, this study breaks with tradition and introduces a post-processor with optimization tool radius compensation and a general machine configuration. Furthermore, a practical method for optimizing the NC code is presented that is based on further study of tool compensation and tool wear. The proposed post-processor is validated for various five-axis machine centers using a generalized kinematic model and various cutting tool models. The results of the verification tests showed that proposed post-processor approach can be used to accurately convert the cutter location into NC codes, and the optimized NC code generated by the optimization tool radius compensation method demonstrates the practical value of the proposed approach for improving processing quality and reducing the total machining time and cost.

Tools and Strategies for Grinding of Riblets on Freeformed Compressor Blades

A major goal in the design of turbomachinery is the increase of efficiency. To attain this increase, the flow losses must be reduced. A substantial proportion of the losses is generated by skin friction between compressor blades and working fluid. With respect to smooth surfaces, micropatterns (riblet-structures) reduce skin friction in turbulent flow by up to 10%. Grinding with multiprofiled wheels is an effective method for the manufacturing of riblet-structures on large plane surfaces. However, the grinding wheel wear affects the accuracy of the riblet geometry and the efficiency of the manufacturing process. Therefore, this paper shows the potential of different grinding wheel types for the manufacturing of riblet structures on an industrial scale with regard to tool wear. The results show that vitrified bonded tools are not suitable for the structuring of compressor blades. Here, axial forces lead to high profile wear. In contrast, grinding wheels with a metal bond are more wear resistant. However, the dressing process of metal bonded tools is time-consuming and causes 80% of the total machining time. As a consequence, just one blade can be structured per day. To increase the efficiency, a new grinding wheel was developed, which is bionically inspired by beaver teeth. The tool is constructed of alternating layers consisting of metal bonded diamonds and pure resin respectively. With this layer-by-layer setup, the tool does not have to be dressed and enables structuring of up to 50 compressor blades per day.

Effect of Machining Parameters and Optimization of Machining Time in Facing Operation using Response Surface Methodology and Genetic Algorithm

Optimum selection of machining parameters and its cutting conditions plays a major role in increase of productivity and minimization of total machining time. A significant improvement in process may lead to increase the process efficiency and low cost of manufacturing. In this research, Spindle speed, Feed rate, Depth of cut and End relief angle is considered as an input parameter for facing the A22E Bimetal bearing material using M42 HSS tool material. A second order mathematical model is developed using Design of Experiments (DoE) of Response Surface Methodology (RSM) to predict machining time on bimetal bearing material using special Industrial type of CNC lathe. The Analysis of Variance (ANOVA) was used to study the performance characteristics in facing operation. The values of Prob>F less than 0.05 indicate model terms are significant. Design Expert software is used to analyze the direct and interaction effects of the machining parameter. The genetic algorithm (GA) is trained and tested using MATLAB 7.0. The GA recommends 1.169 seconds as the best minimum predicted machining time value. The confirmatory test shows the second order regression predicted values and experimental values were very close and good agreement.

On scheduling with non-increasing time slot cost to minimize total weighted completion time

This paper addresses a recent open scheduling problem which aims to minimize the summation of total weighted completion time and the total machine time slot cost. Focusing on the case of non-increasing time slot cost with non-preemptive jobs, we show that the problem can be solved in polynomial-time when the time slot cost decreases with certain patterns, including linearly decreasing, decreasing concave, and decreasing convex cases. Different methodologies are used for three cases. For the linearly decreasing case, we can classify all the jobs into three categories and schedule the job sets one by one. For the decreasing concave case, we calculate each job's worst starting time and try to make them far away from their worst starting times. For the decreasing concave case, we calculate each job's best starting time and let them start close to their best starting times. Finally, we show that the problem is NP-hard in the strong sense when the time slot cost decreases in an arbitrary way.

EXPERIMENTAL STUDY OF DOUBLE POINT CUTTING TOOL ON CHIP – TOOL INTERFACE TEMPERATURE IN TURNING

A special type of a tool is designed and made to have two cutting points for turning long workpieces and it may be termed as the double point cutting tool. The double point cutting tool has two cutting points which has the height difference of 0.5 mm and the distance between them is 6 mm. So that when the first cutting point takes 0.5 mm depth of cut and next to that the second cutting point also takes 0.5 mm depth of cut as the tool proceeds for turning. Hence the total machining time is reduced considerably. Chip – Tool Interface Temperature takes very important role in metal cutting which decides the dimensional accuracy, mechanical properties of the workpiece and the tool life. Investigation on Chip – Tool Interface Temperature in HSS Double Point Cutting Tool during turning of Mild Steel for different cutting conditions is presented in this Research article.

Five-axis tool path generation based on machine-dependent potential field

Traditional methods for improving machining efficiency in five-axis machining mainly concentrate on two frontiers. One seeks to minimise the total length of the tool path, while the other aims at maximising the feedrate. These two optimisations are carried out independently at different stages of a machining process and often conflict each other. Explicitly, a tool path with minimum total tool path length may turn out to be inferior when the specific machine tool’s capacities are considered, and, in order not to exceed the limits of those capacities, the machine’s controller has to keep the feedrate under an inordinately low level, thus actually prolonging the real machining time. In this article, by considering the local geometry of the part surface and the speed and acceleration limits of the machine’s axes, a vector field called machine-dependent potential field is proposed to characterise the relationship between the material removal rate and the feed direction. Based on this introduced potential field, and combined with the well-known iso-cusp height expansion method, a new five-axis tool path generation algorithm is proposed. Preliminary experiments show that this new algorithm can sometimes achieve substantial savings in total machining time over the existing methods.

A Study on Tool Allocation Method Considering Load Balancing and Optimization of Transportation Based on Mathematical Programming

A new tool allocation method is proposed in this paper to consider both the load balancing and optimization of a transportation based on a mathematical problem. The proposed tool allocation method consists of two steps. In the first step, the individual tools are divided into tool sets based on 0-1 programming problem in order to balance a total machining time by using the individual tool sets and reducing a total number of transportation processes. In the second step, the individual tool sets are allocated to the Machining Centers (MCs) based on a quadratic assignment problem in order to minimize transportation total distances of jobs.

English

The growth of Indian manufacturing sector depends largely on its productivity & quality. Productivity depends upon many factors, one of the major factors being manufacturing efficiency with which the operation /activities are carried out in the organization. Productivity can be improved by reducing the total machining time, combining the operations etc. In case of mass production where variety of jobs is less and quantity to be produced is huge, it is very essential to produce the job at a faster rate. This is not possible if we carry out the production by using general purpose machines. The best way to improve the production rate (productivity) alongwith quality is by use of special purpose machine. Usefulness and performance of the existing radial drilling machine will be increased by designing and development of twin spindle drilling head attachment. Human force is required to drill the hole, drilling depth cannot be estimated properly, job may spoil due to human errors, and different size holes cannot be drilled without changing the drill bit. Consumes lot of time for doing repeated multiple jobs, these all are the drawbacks. To overcome all these problems, this automated drilling machine is designed which is aimed to drill the holes automatically over a job according to the drilling depth. The main concept of this machine is to drill the holes over particular jobs repeatedly at different depths, sequence is maintained. As the machine contains drill motor, the movement is controlled accurately. This paper deals with such development undertaken for similar job under consideration alongwith industrial case study

Development of a CAD-CAM Interaction System to Generate a Flexible Machining Process Plan

A unique machining knowledge has led to several different perspectives between planners and operators as regards in designing a machining process plan. All precedents have shown the need to maintain a suitable machining process plan. Commercial Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) systems have facilitated the manipulation of 3D models to generate a machining process plan. The open Advanced Programming Interfaces (APIs) are also helpful in tailoring decision support systems to determine process plans. This study proposes an emergent system to generate flexible machining process plans. The proposed system considers the integration between design and manufacturing perspective to produce relevant machining process plan. The generation of process plans begins by considering the total removal volume of the raw material, estimating the removal features, thus analyzing and ordering several candidates of machining process plans. The total machining time and number of setups from each machining process plan candidate is analyzed and evaluated. Eventually, the proposed system is tested using several prismatic 3D models of a workpiece to show the outcomes.

Research on inverse evaluation mechanism in toolpath generation based on global interpolation simulation

Free form surfaces are primarily designed and manufactured by CAD/CAM/CNC system. In traditional way, toolpath generation approaches always consider machining precision and efficiency by constraining scallop height and toolpath lengths. However, toolpath lengths do not exactly reflect the actual machining time because the feedrate usually fluctuates along different toolpath during CNC interpolating period, which indicates that the total machining efficiency is coupled with both toolpath generation and interpolation. Therefore, the toolpath generation and interpolation systems should not be independent, and the conventional unidirectional information flow from CAM to CNC should be replaced by a new mechanism with information exchange and mutual optimization. This paper proposes an inverse evaluation mechanism with feedback information from CNC to CAM system. The feedback information is obtained by off-line interpolation simulation for each toolpath and evaluation of the total machining time for the entire surface. With the feedback information, CAM is able to optimize the toolpath or choose the best one among candidate solutions. As the evaluation mechanism should be under the same interpolation algorithm, an interpolation algorithm with axis kinematic/dynamic constraints is also introduced. The simulation results with different free form surfaces show that the proposed mechanism can economically improve the machining efficiency without increasing system cost.

A novel acc-jerk-limited NURBS interpolation enhanced with an optimized S-shaped quintic feedrate scheduling scheme

This paper presents a new adaptive acc-jerk-limited nonuniform rational B-spline (NURBS) interpolation method based on an optimized S-shaped C2 quintic feedrate planning scheme. At first, the modified quintic feedrate profile for each sharp corner during the acceleration/deceleration (acc/dec) stage is constructed. To this end, two feedrate slope correction coefficients (FSCC) are introduced for zero end point acceleration and jerk conception in acc/dec stage of each sharp corner. Also, a new algorithm is recommended to compute the acc/dec stage traverse time with respect to the deceleration starting time in this paper. Then, the modified quintic feedrate scheduling scheme equipped with the FSCC is improved for the tool path containing several sharp corners. The FSCC and the deceleration starting times corresponding to all sharp corners are evaluated using an optimization method such that the total machining time to be minimized. In this paper, the pattern search algorithm equipped with the nonlinear constraint function including the acceleration and jerk limitations Matlab code is used for obtaining the optimized parameters to accomplish the acc-jerk-limited feedrate scheduling scheme along the tool path. The proposed interpolation method is performed for several case studies and compared with the previously published methods to evaluate the effectiveness of the designed adaptive acc-jerk-limited feedrate scheduling scheme. The simulation results demonstrate that the proposed interpolation algorithm is capable for providing a smooth feedrate transition for all stages of motion along the tool path and yields satisfactory performances such as total machining time and the interpolation steps.

The Tightening Accuracy of Workpieces in the Multiple Clamping Devices

Fixtures are used for orientation-positioning-tightening of workpieces during machining on machine tools. Multiple clamping fixtures are intended to clamp several workpieces for simultaneous or successive machining. Multiple clamping is characterized by a series of economical advantages, due to the reduction of total machining time. These advantages are more important once the number of workpieces is higher or if the machining is made with compound tools. Due to the complexity, overall size and the high number of components, the multiple clamping fixtures have diminished accuracy than simple fixture due to elastic and contact deformations of fixtures housing, of supports etc. Also, multiple clamping fixtures present diminished rigidity and dynamic stability. From the analysis of the specialized literature results that there are a few paper on the subject of multiple clamping. In the paper there are presented the causes that can lead to the diminish of the accuracy of multiple fixture. The modalities for the determination of fixtures precision are presented, also, for the parallel and serial multiple clamping fixtures.

An integrated optimization of cutting parameters and tool path generation in ultraprecision raster milling

This paper provides a new methodology for the integrated optimization of cutting parameters and tool path generation (TPG) based on the development of prediction models for surface roughness and machining time in ultraprecision raster milling (UPRM). The proposed methodology simultaneously optimizes the cutting feed rate, the path interval, and the entry distance in the feed direction to achieve the best surface quality in a given machining time. Cutting tests are designed to verify the integrated optimization methodology. The experimental results show that, in the fabrication of plane surface, the changing of entry distance improves surface finish about 40 nm (Ra) and 200 nm (Rt) in vertical cutting and decreases about 8 nm (Ra) and 35 nm (Rt) in horizontal cutting with less than 2 s spending extra machining time. The optimal shift ratio decreases surface roughness about 7 nm (Ra) and 26 nm (Rt) in the fabrication of cylinder surfaces, while the total machining time only increases 2.5 s. This infers that the integrated optimization methodology contributes to improve surface quality without decreasing the machining efficiency in ultraprecision milling process.

Five-axis tool path and feed rate optimization based on the cutting force–area quotient potential field

Feed rate assignment in five-axis surface machining is constrained by many factors, among which a particularly critical one is the deflection cutting force on the tool: while a larger feed rate increases the machining productivity by shortening the total machining time, it nevertheless inevitably enlarges the deflection cutting force as well, which will cause the tool to be more prone to bending and the machine more prone to vibration, thus adversely degrading the surface finish quality. In this paper, we present a new five-axis tool path generation algorithm that strives to globally maximize feed rate for an arbitrary free-form surface while respecting a given deflection cutting force threshold. The crux of the algorithm is a new concept of the (cutting) force–area quotient function—at any cutter contact point on the surface, the maximal effective material removal rate (with respect to the deflection cutting force threshold) is a continuous function of the feed direction. This function induces a potential field on the surface and based on which an efficient tool path generation algorithm is designed. Preliminary experiments show that substantial reduction in total machining time can often be achieved by the proposed algorithm.

Multi-Objective Optimization for Milling Operations using Genetic Algorithms under Various Constraints

In this paper, the parameter optimization problem for face-milling operations is studied. A multi-objective mathematical model is developed with the purpose to minimize the unit production cost and total machining time while maximize the profit rate. The unwanted material is removed by one finishing pass and at least one roughing passes depending on the total depth of cut. Maximum and minimum allowable cutting speeds, feed rates and depths of cut, as well as tool life, surface roughness, cutting force and cutting power consumption are constraints of the model. Optimal values of objective function and corresponding machining parameters are found by Genetic Algorithms. An example is presented to illustrate the model and solution method.

Parallel Machine Selection and Job Scheduling to Minimize Sum of Machine Holding Cost, Total Machine Time Costs, and Total Tardiness Costs

This paper is concerned with scheduling of a set of single-operation tasks on a set of parallel machines where subcontracting is allowed. The objective is to choose a subset of machines/subcontractors from a set of available machines/subcontractors to perform all jobs to minimize sum of several costs. Processing time of jobs is assumed to be equal. Lower and upper bound for number of jobs assigned to a machine/subcontractor is considered. We first present a comprehensive survey of applications and models. We show special case of the problem when lower bound for number of jobs assigned to each machine/subcontractor is equal to zero is equivalent to single-sink fixed-charge transportation problem (SSFCT). This proves NP-hardness of the problem. Efficient dynamic programming algorithm for this special case is presented. Complicating issues regarding the general case with nonzero lower bounds for number of jobs assigned to machines/subcontractors is discussed. We transfer the general problem to multiple choice knapsack problem (MCKP) that can be solved efficiently using available algorithms. Several new problems are introduced. Complexity of each problem is resolved. Transformation to MCKP is provided that allows available algorithms to solve the problems. The main contribution of this paper is to establish theoretical results regarding the solution of these difficult problems.

Fast Production of Gear Prototypes – A Comparison of Technologies

The time-to-market for automotive and other gear-involved products is still reducing. This demands new production technologies for the manufacturing of functional gear prototypes. At the moment gear prototypes are made using classical series production technologies, such as gear hobbing and grinding. However, these technologies require design specific dedicated tools, making the production of a functional gear prototype expensive and time-consuming. This paper presents an experimental investigation and comparison of different alternative production technologies for the manufacturing of functional gear prototypes. Wire-EDM, Selective Laser Melting and milling using standard milling tools, have been compared for the production of a spur gear out of 16MnCr5 steel. A strategy for the wire-cutting of a spur gear was developed, resulting in a total machining time of 22h – with very good gear quality in terms of geometrical accuracy and surface roughness. This same gear has been produced by SLM, with a total machining time of 17h. Two different milling strategies have been developed on a milling machine, resulting in a total machining time of 14h15min. The shape accuracy and surface roughness were compared using a CMM and a surface profiler. Taking these results into account and considering the fact that it is impossible to make helical gears or machine micro flank corrections using wire-EDM, it was concluded that the milling is the most promising production technology for functional gear prototypes. The fact that functional prototypes could be made without the current lead time (± 10 weeks) is a great improvement for the production of gear prototypes, meeting the shorter time-to-market requirements of today's industry.

Optimization of Makespan in Job and Machine Priority Environment

This paper analyses a specific case of permutation flow shop scheduling problem with job and machine priority. Sometimes, a particular job has to precede or succeed another job; or a set of jobs are to be together for a specific reason. Within the set of jobs also, there may be a condition that a particular job has to precede or succeed another job. In such case, the scheduling is done in two or more phases to optimize the makespan. In many occasions, the percentage utilization of a particular machine has to be increased due to several reasons. The machine may be costlier, rented, and highly precise or needs to be operated continuously. In the context of the permutation flow shop scheduling, the percentage utilization is calculated in terms of machining time compared with the makespan. For a fixed number of jobs, the total machining time for each machine is also fixed and reduction in the makespan only can increase the percentage utilization. On the other hand, splitting the machining times and regrouping may also help for achieving the objective. The problem is demonstrated with numerical examples. For trial purpose, the machining time of all the jobs that come before and after the priority machine are split (25% and 50%) individually and also in toto, and combined with the critical machine. The number of jobs and machines is kept the same. Consequently, the makespan and percentage utilization have been computed and compared with the original case.