Optimal tool orientation in 3 + 2-axis machining considering machine kinematics

A physically-based model for global collision avoidance in 5-axis point milling

Machining large complex industrial parts with a high accuracy often requires tens, hundreds of thousands, or even millions of cutter location points and hundreds of hours of machining. That is why reducing the machining time is one of the most important topics in the optimization of CNC codes for 5-axis milling machines. We propose and analyze a new method of constructing curvilinear tool paths which partly or even entirely align with the direction of the maximum material removal rate. The alignment based on the curvilinear elliptic grid generation allows minimization of the machining time while keeping the convenient zigzag-like topology of the path. The method is applicable to a variety of cost functions such as the length of the path, the machining speed, the material removal rate, the kinematic error, etc., generating different machining strategies. The method has been combined with a new version of the adaptive space-filling curves. The approach has been tested against the standard iso-parametric zigzag, MasterCamX5, “Follow Periphery”/“Helical or Spiral” options of Unigraphics as well as the conventional space-filling curves. The material removal rate cost function has been tested against the tool path length minimization. The numerical and machining experiments demonstrate a considerable advantage of the proposed method.

Numerical Modelling of Electro-Discharge Machining Process Using Moving Mesh Feature

Drilling is one of the conventional methods of producing a hole of the desired shape by removing material with the help of a cutting tool named drill bit. The process of drilling a hole usually leaves behind an undesirable burr at the exit surface of the workpiece. In this experimental work, the design of experiment (DOE) has been carried out as per Taguchi’s L27 orthogonal array with an objective to minimize the height of burr (exit side) of stainless steel (SS) workpieces. The effect of process parameters like varied cutting speed, changes in feed and cutting fluid on burr height as well as machining time has been explored and the optimum condition for minimizing burr height under normal condition, using adhesive and with a backup support is determined by the entire experimental analysis. Response surface methodology and analysis of variance (ANOVA) have been performed to find out the optimum process parameters on burr height and machining time. With the progress of experiment, it has been observed that burr height is greatly influenced by the variation of speed, feed and cutting fluid whereas, cutting fluid has less impact on machining time reduction as compared to the varied speed and feed with adhesive and backup material condition.

This paper describes a development of 5-axis dry electrical discharge machining (dry EDM). The machining characteristics in the processing of a spherical cavity were compared between 3-axis and 5-axis machining in order to investigate the effect of the 5-axis dry EDM. It was found that the processing time of 5-axis machining was nine times shorter than 3-axis machining. Since the end surface of pipe electrode was uniformly worn in 5-axis machining, it was easy to compensate for the tool electrode wear and improve the machining accuracy. Error of the processed shape from the target shape increased when the pitch used in finishing was larger than 60% of the tool electrode diameter due to the edge wear of the tool electrode. Hence, the machining accuracy was improved by optimizing the pitch of the tool path and compensating for the tool electrode wear using the simulation developed.

Reduced machining time and increased accuracy for a sculptured surface are both very important when producing complicated parts, so, the step-size and tool-path interval are essential components in high-speed and high-resolution machining. If they are too small, the machining time will increase, whereas if they are too large, rough surfaces will result. In particular, the machining time, which is a key factor in high-speed machining, is affected by the tool-path interval more than the step size. The present paper introduces a ‘system software’ developed to reduce machining time and increased accuracy for a sculptured surface with Non-Uniform Rational B-Spline (NURBS) patches. The system is mainly based on a new and a powerful artificial intelligence (AI) tool, called artificial immune systems (AIS). It is implemented using C programming language on a PC. It can be used as stand alone system or as the integrated module of a CNC machine tool. With the use of AIS, the impact and power of AI techniques have been reflected on the performance of the tool path optimization system. The methodology of the developed tool path optimization system is illustrated with practical examples in this paper.

A new approach is developed in this paper to predict the three-dimensional gear surface topography in the process of gear generating grinding, and a parametric equation is derived to describe the trajectory on the tooth surface of gear left by each ideal sphere grain. To determine the final three-dimensional gear surface topography generated by thousands of single abrasive grain with randomly distributed locations and protrusion heights, an algorithm for geometrical analysis is developed to systematically process the gear surface profile. There are two steps for this method: the first step is to map the cutting path to the tooth profile in each generating stroke, and the second stage is to combine these generated surface topographies together and trim them in an appropriate manner to create a whole tooth surface. The simulation results show that the surface roughness is increasing monotonously along the tooth profile direction, which is confirmed by the experiment. In order to get uniform surface roughness, a non-uniform generation method is introduced by dividing the entire arc length into isometric n segments. With the use of this method, the surface roughness in each part is essentially equal. Besides, the surface roughness improves about 16.3 % when the machining time is the same, and the reduction of machining time is 42.8 % when the surface roughness of addendum is equal.

This paper presents a methodology and algorithms of optimizing and smoothing the tool orientation control for 5-axis sculptured surface machining. A searching method in the machining configuration space (C-space) is proposed to find the optimal tool orientation by considering the local gouging, rear gouging and global tool collision in machining. Based on the machined surface error analysis, a boundary search method is developed first to find a set of feasible tool orientations in the C-space to eliminate gouging and collision. By using the minimum cusp height as the objective function, we first determine the locally optimal tool orientation in the C-space to minimize the machined surface error. Considering the adjacent part geometry and the alternative feasible tool orientations in the C-space, tool orientations are then globally optimized and smoothed to minimize the dramatic change of tool orientation during machining. The developed method can be used to automate the planning and programming of tool path generation for high performance 5-axis sculptured surface machining. Computer implementation and examples are also provided in the paper.

Multi-axis machining of a complex surface is not only efficient but also reduces workpiece set-up errors. However, engineers usually rely on experience when determining set-up orientation and often cannot finish complex surfaces in one set-up. In this paper, a rational evaluation method for workpiece orientation and configuration of machine tool before tool path planning is proposed to increase the efficiency and reliability of process planning. By incorporating the visibility cone into workspace analysis, a software module is constructed in this research for optimum workpiece orientation and configuration of machine tool. First, the configurations of three-, four- and five-axis machine tools were synthesised, and the workspace was then analysed using form-shaping function. Both position vector and normal vector of each point along the u and v directions in the machining surface were employed to calculate the visibility range as the point of the visibility cone. In 3-axis machining, all normal vectors of the surface were projected on a unit sphere. All normal vectors were ensured to be within the visibility range of the ball-mill cutter as the workpiece set-up orientation changed. In 4-axis machining, the intersection between the visibility cone of each point and the workspace was obtained by changing the set-up orientation. In 5-axis machining, according to different workspaces of 5-axis machine tools, the visibility range of the machining surface was determined to yield the intersection between the visibility cone and the workspace by changing the workpiece orientation. The proposed method for evaluating manufacturability has been demonstrated to generate optimum workpiece set-up orientation and the suitable configuration of machine tools. Tool interference with workpiece surface can be avoided, which can help improve the planning of tool path.

This study proposes a hybrid optimization method which can help users to find optimal cutting parameters which will provide better efficiency and lower power consumption for a milling process. Empirical models including performance-power consumption characteristic curves of servo motors were built, and an optimization algorithm adopting the empirical models with procedure guiding function was developed. The empirical models were built based on the measurements from planned machining experiments with different combination of machining parameters including spindle speed, feedrate, and chip load, etc. After integrating the models and algorithm, an optimization system with human machine interface, which has procedure guiding function, was developed. The system can recommend optimal machining parameters for a milling process for shorter machining time and lower electricity costs based on the original machining parameters. Finally, cutting experiments were conducted to verify the proposed system, and the results showed that the proposed method can effectively enhance efficiency by 42.06% and save 34.74% in machining costs through reducing machining time and electrical power consumption.

Reducing machining time is one of the ways to improve the global competitiveness and productivity. The objective of this paper is to optimize feedrates of milling operation via process modeling, numerical experiments, and an intelligent algorithm under multiple constraints. The approach proposed attempts to overcome drawbacks of human error and computer-aided manufacturing (CAM) software through efficient cutting parameters of given toolpaths. First, machining simulations were performed with the support of CAM system in order to generate the NC program. The milling process was analyzed and re-simulated using the experimental platform to calculate material removal rates and instantaneous forces at the specific time. To obtain the machined accuracy, a new mechanism for milling process has been considered. The cutting force and acceleration as well as deceleration time were considered as machining constraints and integrated into the developed system. The optimizing strategy is the feedrates scheduling, which increases the feedrates to an allowable level to make the process more efficient, taking into consideration the required constraints. Subsequently, an intelligent algorithm was proposed to find real-optimal feedrates and generate more-efficient toolpaths. Finally, machining simulations using optimal values were conducted to evaluate time saving potentials. The results indicated that machining time could be reduced approximately 22%, compared to un-optimal case. Consequently, this work is expected as a contribution to make the milling process more efficient

High-speed machine tools typically provide high spindle speeds and feedrates to achieve an effective material removal rate (MRR). However, it is not possible to realize the full extent of their high-speed capabilities due to the sharp corners of toolpaths which are introduced by conventional machining strategies, such as contour- and direction-parallel toolpaths. To address this limitation, spiral toolpaths that can reduce the magnitude of sudden direction changes have been developed in previous researches. Nevertheless, for some pockets, the average radial cutting width is significantly decreased while the total length of the toolpath is significantly increased as compared to contour- and direction-parallel toolpath. In this situation, spiral toolpath may take more machining time. To overcome these drawbacks, an aggressive spiral toolpath generation method based on the medial axis (MA) transformation is proposed in machining pocket without islands inside, which refers to no additional material inside the counter. The salient feature of this work is that it integrates the advantages of both conventional contour-parallel machining strategy and the existing spiral toolpath machining strategy. The cutting width at each MA point is determined based on the diameter of the locally inscribed circle (LIC) of the MA point and the topological structure of MA. A distance-constrained contour determination algorithm is utilized to calculate the toolpath for each pass. Finally, a circular arc transition strategy is used to transform all the isolated passes into a spiral toolpath. Experiments are conducted to show the effectiveness of the proposed method.

Optimal workpiece setups for 4-axis numerical control machining based on machinability

The kinematical behavior of 5-axis machine tool introduced by toolpath calculation has a close relation with processing efficiency and quality of parts. For the category of sculptured surface parts with abrupt curvature, such as turbine blade and fixed guide vane, the most commonly utilized spiral contouring toolpath modes usually encounter some trouble during actual machining, the reason lies in the difficult tool orientation control near the edge of such parts. However, the global optimization for the spiral toolpath means increased computation burden, and so it is time consuming. In this paper, an efficient 5-axis toolpath optimization algorithm is presented, and the objective is to smooth the rotary axes’ motion caused by drastically changed tool orientation on spiral toolpath for abrupt curvature parts machining. To reduce the computation burden, only path segments on the spiral trajectory-owned weak kinematic performance are selected for further optimizing. To obtain smoother motion for rotary axes, the specific optimization computation for the selected path segments is conducted in the Machine Coordinate System (MCS) instead of the Part Coordinate System (PCS). The optimization model is constructed and a related solution method is presented to ensure the high-performance optimization. The complete optimization algorithm is demonstrated on a spiral 5-axis toolpath for the turbine blade finish machining, and the result shows that only 25.9% optimization computation is needed compared with global optimization algorithm. And then, the actual machining experiments are carried out by using paraffin as cut material, and the machining time with optimized toolpath is decreased by 19.7% compared with initial toolpath. In addition, the surface quality of parts is significantly improved after conducting the optimization. This study proves that the proposed algorithm can significantly improve the processing efficiency and surface quality of parts with abrupt curvature and provides an efficient method to optimize the spiral 5-axis toolpath used for finish machining parts with abrupt curvature.

Machining time is a major performance criterion when it comes to high-speed machining. CAM software can help in estimating that time for a given strategy. But in practice, CAM-programmed feed rates are rarely achieved, especially where complex surface finishing is concerned. This means that machining time forecasts are often more than one step removed from reality. The reason behind this is that CAM routines do not take either the dynamic performances of the machines or their specific machining tolerances into account. The present article seeks to improve simulation of high-speed NC machine dynamic behaviour and machining time prediction, offering two models. The first contributes through enhanced simulation of three-axis paths in linear and circular interpolation, taking high-speed machine accelerations and jerks into account. The second model allows transition passages between blocks to be integrated in the simulation by adding in a polynomial transition path that caters for the true machining environment tolerances. Models are based on respect for path monitoring. Experimental validation shows the contribution of polynomial modelling of the transition passage due to the absence of a leap in acceleration. Simulation error on the machining time prediction remains below 1%.