Tool Path Length Research Articles

New criteria for tool orientation determination in five-axis sculptured surface machining

The problem of optimal tool orientation determination in five-axis flat-end milling of sculptured surfaces is examined in this paper. The optimal tool orientation avoids local and global gouging of the tool and maximises a specific criterion related to machining efficiency. Two new criteria are introduced in this paper to quantify the tool orientation quality at a cutter contact point: infinitesimal machining volume (IMV) and infinitesimal machining area (IMA). The IMV criterion is used to maximise the material removal at the cutter contact point. The IMA criterion attempts to identify tool orientations that would lead to minimised overall tool path length. Using one of these criteria, an optimisation problem can be formulated to determine the optimal tool orientation among feasible gouge-free orientations. It is shown that the commonly adopted criterion of machining strip width in the determination of the optimal tool orientation cannot contribute towards maximising the material removal and does not really result in minimum overall tool path length. Results from various case studies have indicated that the newly introduced criteria can be used to generate optimal tool orientations that significantly increase machining efficiency.

Process planning for corner machining based on a looping tool path strategy

A corner is an elemental machining feature for internal pockets that is difficult to plan and execute. During machining of a corner, there is continuous variation in radial depth of cut and frequent changes in magnitude as well as direction of the feed rate. These result in inconsistent machining leading to machine tool jerk, excessive cutting force, and poor surface finish. In this paper, an integrated process planning approach for optimal corner machining has been proposed that combines the tool path generation and machining parameter selection tasks. As a first step a looping tool path strategy was implemented to progressively remove material in multiple loops in order to keep the radial depth under a permissible limit. The tool path consists of G1 continuous biarc and arc spline segments which allow a constant feed rate to be held over the entire tool path. The geometries of the corner and cutting tool and the kinematics of the machine tool structure were considered in the calculation of the allowable constant feed rate. In the next step, the machining time was minimized by iteratively adjusting the feed per tooth value under cutting force constraints. The constraint ensured that the tool deflection was always under a tolerance limit. The resulting tool paths for different test cases indicated the ability of the tool path generation strategy to minimize the number of loops. A comparison of the results on machining times based on initial and optimal feed values and their corresponding tool path lengths indicated the potential for the improvement in productivity of corner machining. The proposed integrated approach that combines both geometric and machining parameters can generate more optimal process plans than approaches that consider these parameters separately.

Hybrid genetic algorithm for minimizing non productive machining time during 2.5 D milling

Minimization of non-productive time of tool during machining for 2.5 D milling significantly reduces the machining cost. The tool gets retracted and repositioned several times in multi pocket jobs during rough machining which consumes 15 to 30% of total machining time depending on the complexity of job. The automatic CNC program commonly generates contour parallel tool path. Optimization of tool path length during on-productive time can be modeled on Traveling Salesman Problem (TSP) which belongs to family of non-deterministic polynomial (NP) hard problem. In the present work, a Hybrid Genetic Algorithm (HGA) has been proposed to optimize the non-productive tool path in which the initial seed solution is generated by special heuristic and combined with random initial solution generated by simple genetic algorithm (SGA). A defined performance index known as Relative percentage deviation (RPD) has been used for analyzing the results by varying the size of the jobs. From the analysis, it is found that HGA shows superiority over SGA for same computation time limit as the stopping criteria.

Gaze training enhances laparoscopic technical skill acquisition and multi-tasking performance: a randomized, controlled study

BackgroundThe operating room environment is replete with stressors and distractions that increase the attention demands of what are already complex psychomotor procedures. Contemporary research in other fields (e.g., sport) has revealed that gaze training interventions may support the development of robust movement skills. This current study was designed to examine the utility of gaze training for technical laparoscopic skills and to test performance under multitasking conditions.MethodsThirty medical trainees with no laparoscopic experience were divided randomly into one of three treatment groups: gaze trained (GAZE), movement trained (MOVE), and discovery learning/control (DISCOVERY). Participants were fitted with a Mobile Eye gaze registration system, which measures eye-line of gaze at 25 Hz. Training consisted of ten repetitions of the “eye-hand coordination” task from the LAP Mentor VR laparoscopic surgical simulator while receiving instruction and video feedback (specific to each treatment condition). After training, all participants completed a control test (designed to assess learning) and a multitasking transfer test, in which they completed the procedure while performing a concurrent tone counting task.ResultsNot only did the GAZE group learn more quickly than the MOVE and DISCOVERY groups (faster completion times in the control test), but the performance difference was even more pronounced when multitasking. Differences in gaze control (target locking fixations), rather than tool movement measures (tool path length), underpinned this performance advantage for GAZE training.ConclusionsThese results suggest that although the GAZE intervention focused on training gaze behavior only, there were indirect benefits for movement behaviors and performance efficiency. Additionally, focusing on a single external target when learning, rather than on complex movement patterns, may have freed-up attentional resources that could be applied to concurrent cognitive tasks.

Enhancing Incremental Sheet Forming Performance Using High Speed

Flexible sheet metal forming processes represent one of the most relevant industrial issues of the scientific research. Incremental Sheet Forming is one of the most promising answers for many production scenarios. In particular, it becomes competitive when the production lot size decreases and the production variability increases. The process is basically set up on numerically controlled machines: a blank is clamped at its border and progressively deformed by a punch that moves according to a proper tool path program, reproducing the final part shape. Thus, the manufacturing time is directly dependent on the tool path length. Up to now, this aspect is one of the reasons why a systematic industrial application is not permitted. To overcome this drawback, an experimental investigation was planned in order to evaluate how the process is affected changing the cycle time. More in detail, an extended experimental investigation on the influence of process speed (i.e. tool rotation speed, tool feed) and other process parameters was executed taking into account a relatively simple 3D component. An accurate analysis of the obtained parts was performed, with particular attention to the thinning distribution that, of course, influences the material failure. Finally, the surface quality was also measured as an output variable.

Integrated method for tool path generation in five-axis sculptured surface machining

Five-axis machining allows continuous adjustment of cutter orientation along a tool pass. Unfortunately, the flexibility has not been fully exploited due to the separate consideration of tool path generation and cutter orientation in current machining methods. This paper presents an integrated method (IM) for tool path generation, which is tightly integrated with the orientation strategy, to minimise tool path length under the constraint of smooth cutter orientation. Distinctively, cutter orientation along a tool pass is optimised by balancing considerations of maximum material removal and smoothness of cutter movement. Further, the intervals between successive tool passes are maximised according to the optimised orientation. In the paper, the IM is combined with the quadric method, a recently developed cutter orientation strategy, for iso-parametric machining with a flat-end cutter. However, the method could be applied to other orientation strategies with different machining mechanisms and cutter types. Simulated examples illustrate that the IM is more efficient in machining than established methods.

A Neural Network Based Approach to 5-axis Tool-path Length Estimation for Optimal Multi-cutter Selection

Computer-Aided Design and Applications is an international journal on the applications of CAD and CAM. It publishes papers in the general domain of CAD plus in emerging fields like bio-CAD, nano-CAD, soft-CAD, garment-CAD, PLM, PDM, CAD data mining, CAD and the internet, CAD education, genetic algorithms and CAD engines. The journal is aimed at all developers and users of CAD technology to ptovide CAD solutions for various stages of design and manufacturing. The journal publishes all about Computer-Aided Design and Computer-Aided technologies.

Selection of optimal set of cutting tools for machining of polygonal pockets with islands

Selection of the optimal set of cutting tools is one of the most important steps in process planning for 2.5-D pocket machining. Conventional CAM software requires considerable input from the user in terms of selection of tool sizes and machining strategy. This trial-and-error procedure to determine the optimal process sequence tends to generate conservative and suboptimal results. This paper presents a methodology for optimal selection of a sequence of tools to minimize the total time required to end mill a non-convex polygonal pocket with or without islands using the staircase milling strategy. The algorithm decomposes the pocket geometry into convex regions and mills each region independently by selecting a sequence of tools based on the accessibility of various tools to the region. Strategies have been developed for machining the main pass and the subsequent leftover areas in order to obtain the final pocket geometry. Subsequently, the machining times for each decomposed area are aggregated while accounting for the need to use multiple passes, non-cutting time, and the tool change time. A dynamic programming approach is used to determine the optimal set of tools which minimizes the total processing time. The effect of varying the non-cutting speed and tool change time on the tool path length and number of tool selection is studied.

Advanced process planning for subtractive rapid prototyping

PurposeSubtractive rapid prototyping (SRP) uses layer‐based removal from a plurality of orientations in order to create geometry in a highly automated manner. However, unlike additive means, the method can be inefficient due to redundant cutting operations on previously machined regions. The purpose of this paper is to present process planning methods for SRP, specifically dealing with stock material management in multiple setup operations.Design/methodology/approachAnalysis of remaining stock material was performed by considering slices of respective stereolithography (STL) models. Further, an initial approximation was made of accessibility to enable iterative visibility analysis. The combination of these approaches led to efficient and fast algorithms. After analysis, the slices could be converted back to useful STL models through polyhedral reconstruction.FindingsThis method of approximation yields results similar to exact geometry. Using remaining stock data from this approach leads to a significant reduction in tool path length and processing time in SRP.Originality/valueThis paper presents novel methods of geometric representation and inaccessible volume calculation for four‐axis layer‐based machining and shows a successful implementation in an SRP system.

Voronoi-diagram-based linking of contour-parallel tool paths for two-and-a-half-dimensional closed-pocket machining

Contour-parallel tool paths for machining milling features are formed by linking the offsets. Determination of links between offsets and the sequence in which the offsets should be traversed is a major problem. Results of efforts to link tool paths from academic researchers and developers of commercial computer-aided manufacturing (CAM) systems have shortcomings which include the fact that the linking strategies (a) are not based on clear geometric principles, (b) are not optimal, (c) do not consider technological factors such as the amount of slotting, overmilling, mode of cutting, and (d) are either not gouge-free or use tool retractions to avoid gouging. To overcome these shortcomings, this paper presents a linking algorithm which employs segments on the Voronoi diagram as links. The technological factors, hitherto ignored in previous research are considered and their optimality is ensured by employing guidelines which were mostly developed through observations of tool paths generated from a general test bed. Multiple solutions obtained after pruning out unfeasible solutions can be evaluated by users using geometrical (total tool path length) and technological (amount of overmilling, slotting, etc.) considerations or a combination of the criteria. The implementation of the algorithm is tested by generating tool paths for two two-and-a-half-dimensional (2½D) milled features. When compared with those obtained from some commercial CAM systems, they are shorter by 5 to 31 per cent.

The processing time optimization of printed circuit board

PurposeThe purpose of this paper is to demonstrate the optimization of printed circuit board (PCB) manufacturing by improving drilling process productivity.Design/methodology/approachTwo different ways are explored to increase the productivity of the PCB drilling operation. The first way involves the minimization of the cutting‐tool path length. The second way to achieve the objective explores the efficiency of processing stacked PCBs.FindingsTo reduce the tool path length between the holes of a PCB, a heuristic hybrid algorithm to solve the traveling salesman problem (TSP) is briefly described. Also, a mathematical model to calculate the total processing time is proposed. Based on this model, the paper shows the optimal number of stacked PCBs that can be profitably processed, while high processing productivity does not always mean high number of stacked PCBs.Research limitations/implicationsThe paper does not treat the optimization of the drilling process parameters, even if reduction of the drilling time using optimized cutting parameters also represents an efficient method for improving the productivity.Originality/valueThe paper shows the influence of the algorithm performance for solving the TSP on the processing time minimization, by decreasing the component of drill movement time along the drill path between holes. Additionally, the conditions in which stacking a specific number of PCBs is advantageous are also investigated. Furthermore, the paper shows how to determine the optimum number of stacked PCBs.

Mechanistic approach to predict real machining time for milling free-form geometries applying high feed rate

An accurate estimate of machining time is very important for predicting delivery time, manufacturing costs, and also to help production process planning. Most commercial CAM software systems estimate the machining time in milling operations simply by dividing the entire tool path length by the programmed feed rate. This time estimate differs drastically from the real process time because the feed rate is not always constant due to machine and computer numerical controlled (CNC) limitations. This study presents a practical mechanistic method for milling time estimation when machining free-form geometries. The method considers a variable called machine response time (MRT) which characterizes the real CNC machine’s capacity to move in high feed rates in free-form geometries. MRT is a global performance feature which can be obtained for any type of CNC machine configuration by carrying out a simple test. For validating the methodology, a workpiece was used to generate NC programs for five different types of CNC machines. A practical industrial case study was also carried out to validate the method. The results indicated that MRT, and consequently, the real machining time, depends on the CNC machine’s potential: furthermore, the greater MRT, the larger the difference between predicted milling time and real milling time. The proposed method achieved an error range from 0.3% to 12% of the real machining time, whereas the CAM estimation achieved from 211% to 1244% error. The MRT-based process is also suggested as an instrument for helping in machine tool benchmarking.

Improving endmilling surface finish by workpiece rotation and adaptive toolpath spacing

Free-form surfaces are being used in a growing number of engineering applications, especially in injection molding of consumer products. Decreasing the manufacturing cost and time of these molds will improve the efficiency of manufacturing injection molded consumer products. This paper is motivated by the need for simple strategies to improve the quality of and decrease the time required to machine free-form surfaces. We present two methods to improve the surface finish of parts finished with ball-nose endmilling. In the first method the surface finish is improved by finding an optimal orientation angle for the workpiece relative to the machining axis. In the second method finish is improved by adaptively varying the step-size when using raster toolpaths. The adaptive variation is controlled by a user-defined finish improvement factor, where the spacing density is increased only if the improvement in surface finish is greater than the finish improvement factor. These methods are implemented using an analytical model of the workpiece surface finish based on the mean scallop height of the machined surface. Results from the analytical model are verified with machining experiments, and we show that the adaptive spacing strategy can improve the surface quality by more than 50% with a small increase in the toolpath length. To achieve a similar improvement in surface quality by uniformly decreasing the path spacing results in a much larger increase in the toolpath length. The strategies discussed in this paper allow process planners intuitive control over the toolpath layout and spacing and improve the efficiency of machining high quality parts.

The optimization of printed circuit board manufacturing by improving the drilling process productivity

With the rapid growth of printed circuit board technology today, board density is becoming an important concern. In every aspect of production, productivity and cost are crucial matters. The aim of this research is the optimization of printed circuit board manufacturing by improving the process productivity. Attention was focused on reducing tool path length and processing time. The paper is divided in two main parts. First part presents an original hybrid heuristic algorithm, for solving traveling salesman problem. The algorithm is based on the structure of a general optimization procedure, and is used to reduce the tool path length. Also, it is developed a practical mathematical model for printed circuit board processing time calculation. The case study on the second part of the paper shows basically the efficient use of the above algorithm in finding the optimal length of the tool path. It is shown the influence of stacked printed circuit board on process productivity. By means of its concepts management, the paper represent a real guide for optimal design of printed circuit board drilling technology.

A study of user performance employing a computer-aided navigation system for arthroscopic hip surgery

Object Computer-aided technology can decrease the difficulty associated with arthroscopic hip surgery. Our computer-aided system helps to navigate in the hip joint during arthroscopy by (1) tracking tool position with a linkage of encoders, and (2) using 3D computer graphics to indicate the tool position relative to the patient anatomy. This paper presents a study of user performance to verify the effectiveness of this computer-aided system for hip arthroscopy as a part of continued work on this project. Materials and methods A user study was completed to determine if the computer-aided system could help reduce task completion time and tool-path length. The time and path length provide a measure of operation time and potential tissue damage, respectively. Ten participants completed a simple navigation task with and without the assistance of the computer-aided system. Results A time reduction of 38% and a path length decrease of 72% were achieved with the computer-aided system, confirming its effectiveness. A user survey provided overall positive feedback regarding the system. The survey information also suggested areas of improvement for continued research. Conclusion The proposed computer-aided system can be used to address the challenges of arthroscopic hip surgery by reducing operation time and improving patient safety.

Five-axis machining time estimation algorithm based on machine characteristics

Abstract In this paper, we present a machining time estimation algorithm for five-axis high-speed machining. Estimation of machining time plays an important role in process planning and production scheduling of a shop. In contrast to the rapid evolution of machine tools and controllers, machining time calculation is still based on simple algorithms of tool path length divided by input feedrates of NC data, with some additional factors from experience. We propose an algorithm based on five-axis machine behavior in order to predict machining time more exactly. For this purpose, we first investigated the operational characteristics of five-axis machines. Then, we defined some dominant factors, including feed angle that is an independent variable for machining speed. With these factors, we have developed a machining time calculation algorithm that has a good accuracy not only in three-axis machining, but also in five-axis high-speed machining.

Telementoring versus on-site mentoring in virtual reality-based surgical training

Telementoring can be an adjunct to surgical training using virtual reality surgical simulation. Telementoring is hypothesized to be as effective as a local mentor for surgical skills training. In this study, 20 Romanian medical students trained using a virtual reality surgical simulator (LapSim) with a telementor or local mentor. All the students watched an instructional module at the beginning of the exercise. The telementor, in the United States, interacted by videoconferencing. Before and after training sessions, tool path length and time for task completion were measured. Instructional media and training with mentoring resulted in similar levels of performance between locally mentored and telementored groups. Right- and left-hand path length and time decreased significantly within each group from the initial to the final evaluation (p < 0.05) for most tasks (grasping, cutting, suturing). No significant difference was achieved for clip-applying. Integration of instructional media with telementoring can be as effective for the development of surgical skills as local mentoring.

Virtual CNC system. Part II. High speed contouring application

This paper presents a trajectory planning strategy for maintaining the tool positioning accuracy in high speed cornering applications. A 3D contour error estimation algorithm is presented for determining the geometric deviation from arbitrarily shaped toolpaths. Two spline fitting strategies are developed for smoothening sharp corners. The under-corner approach reduces the toolpath length, and therefore the cornering time. This technique yields successful results when used with a high bandwidth servo controller (such as sliding mode control), capable of accurately tracking the commanded toolpath. The over-corner approach is based on stretching out the sharp corner with a smooth curve, which counteracts the ‘undercut’ caused by the large phase lag in low bandwidth servo controllers (such as P–PI control). The cornering feedrate is adjusted in the Virtual CNC platform, developed in the first part of this article, to ensure that contour error violation does not occur. The achieved cornering accuracy is verified in experiments, which are in close agreement with predictions obtained with the Virtual CNC.

Optimal tool selection for 2.5D milling, part 2: a Voronoi mountain approach for generalized pocket geometries

Cutter selection is a critical subtask of machining process planning. In part 2 of this two-part series, we develop a robust approach for the selection of an optimal sequence of milling cutters. We rely on the Voronoi mountain construction algorithm developed in part 1 to support generalized pocket geometries containing multiple obstruction regions and contours consisting of circular arc and linear segments. Open edges are supported in both the original pocket contours as well as the intermediate edges that bound removal regions for subsequent tools in the optimal sequence. Exact tool-path lengths are computed for the multiple tool sequences rather than relying on area-based estimates of machining time and cost. An externally supplied table of machining technology data is required to drive the tool selection algorithm.

Corner optimization for pocket machining

The aim of this paper is to propose a pocketing tool path improvement method by adapting the geometry of the tool path to the kinematic performance of high speed machining machine tools. The minimization of the machining time is a major objective, which should be taken into account for the tool path computation. In this way the tool path length can be reduced or the real feedrate increased. The described method proposes modification of the values of the corner radii in order to increase real feedrate. In the same way, this method checks the radial depth of cut variations along the tool path. The computed tool path presents a smaller length and the machine tool produces a higher average feedrate at the same time. In addition, the use of Bspline for the tool path computation is a significant improvement compared with straight lines and circle arcs for the machining time reduction. Several tests are realized on various machine tools in order to quantify the benefits: the proposed method can reduce the machining time by approximately 25% compared with classical tool paths computed using a CAM system.