Multi-point Machining Research Articles

Optimization of responses in single and multi-point machining processes using Dragon-fly algorithm coupled with TOPSIS and VIKOR decision-making approaches

Due to complex production practices, it is becoming crucial to provide greater thermal management and friction reduction in manufacturing processes. Lubricants play a crucial role by effectively reducing friction, minimizing wear and tear thereby extending the lifespan of the tool. It is observed that there is a shortage of studies associated with the machining of hard materials like Ti-6Al-4V. The present work has therefore focused on the machining of high-grade Titanium alloy under dry and Neem oil aerosol-mist spray wet conditions. The machining is performed on two kinds of machining processes, such as plain facing with single point tool and co-axial turn-mill facing with multi-point cutting tools on computer numerical controlled Turn-mill machine tool. Furthermore, there are very few articles reported on usage of Neem oil (AzadirachtaIndicaL.) as a lubricant. This has motivated the authors to use Neem oil in a mist condition to minimize the quantity of coolant, without compromising on the tool temperature, surface quality, and tool-wear. The responses obtained are subjected to regression analysis to evolve the fitness functions. Multi-objective optimization of these functions is than adopted using Dragon-fly algorithm (MODA) under the constraints of the machining parameters. A set of pareto optimal solutions for each of the machining cases are obtained and are further evaluated using TOPSIS and VIKOR decision-making approaches to achieve the optimal values of the cutting parameters. The optimum parameters for single point cutting under wet conditions were observed as speed (592 rpm), feed (0.058 mm rev−1) and depth of cut (1.00 mm).The corresponding values of responses were tool temperature (37.05 °C), surface roughness (0.128 μm) and tool wear (155.19 μm). The equivalent values for multi-point cutting were determined as 510 rpm, 0.086 mm rev−1 and 0.25 mm. The responses for these optimal conditions are 32.17 °C, 0.725 μm and 45.72 μm in that order.

A new approach to find gouge free tool positions for a toroidal cutter for Bézier surfaces in five-axis machining

We implement and test a multi-point machining tool positioning technique that positions the tool using only a variation on gouge checking. The result is a method that is roughly twice as fast as an earlier method that performed a numerical search to find a tool position with multiple points of contact with the design surface. A GPU implementation provides an additional factor of ten speedup. Verification of the method was done via simulation and machining and measuring physical parts.

Numerical implementation of drop spin and tilt method for five-axis tool positioning for tensor product surfaces

This paper presents an extension of multipoint machining technique, called the Drop Spin and Tilt (DST) method, that spins the tool on two axes, allowing for the generation of multiple contact points at varying distances around the first point of contact. The multiple DST second points of contact were used to manually generate a toolpath with uniform spacing between the two points of contact. The original DST method used a symbolic algebra package to position the tool on a bi-quadratic surface; our extension is a numerical solution that allows positioning a toroidal tool on a tensor product Bézier surface, which we tested on bi-degrees 2, 3, 4, and 5. On the three bicubic surfaces we tested, the average number of initial seeds for our numerical method was less than 5 across all three surfaces, and the average number of Newton iterations was less than 20 except when the curvature of the tool closely matches the local surface curvature (in which case more iterations were required). Furthermore, we investigate the spread of possible second points of contact as the tool is spun around these two axes, demonstrating the feasibility of using the method to control the machining strip width.

Locator Placement Optimization for Minimum Part Positioning Error During Machining Operation Using Genetic Algorithm

Fixture design is one of the main factors which affect the final product quality. Proper design of fixture plays an important role in ensuring the required tolerance of the product. Proper placement of locators is one of the prominent factors in fixture design. Locators are elastic: they deform under clamping and machining forces causing rigid body displacement of the workpiece which in turn affects the part quality. In this article, a 3-2-1 type of fixturing system having elastic locators around a considerably rigid rectangular workpiece is considered. A genetic algorithm is proposed, which uses a fitness function that evaluates the positioning error of the workpiece under external forces and torque. Among several variables, 12 variables, which define the placement of locators, are chosen to be optimized while minimizing the positioning error of the workpiece at the point of action of machining force. The proposed algorithm optimizes the 12 interlinked variables, within the specified region, for machining force and torque at a single point. However, when the cutting tool moves to any other point on the workpiece, it is observed that either the workpiece loses its contact with any one of the locators or the positioning error increases by a large value. To overcome this issue, the proposed algorithm is further modified for placement optimization to cater for multi-point machining, and the isostatism of the workpiece is ensured by checking the magnitude and direction of displacement (of what?) at each point of workpiece-locator contact. Finally, the original and modified GA algorithms are explained through a case study where the single point optimized placement shows loss of contact when machining force is applied at other points. The placement optimized from the modified algorithm shows that the isostatism of the workpiece remains intact while all four positioning errors are converged towards the same value. The results obtained from the proposed and modified algorithm are verified using ANSYS simulation.

Analysis of Different Tool Path Strategies for Free Form Machining with Computer Aided Surface Milling Operations

Free form surfaces are commonly used to generate aesthetic parts. These parts can be manufactured directly by material removal techniques or indirectly with molding or forming techniques. In any case, these surfaces must be commonly machined with traditional processes, at least until certain degree of surface finishing, and the tool path must be generated with computer aided applications. In doing so, developers are implementing new theoretical strategy operations for controlling tool path and trajectories. These new options have so many combinations that it is difficult to know which is the best one to choose when defining the tool movements. Apart from the traditional strategies fixed angle method, principal axis method and multipoint machining, combined with tool orientation, there are many other strategies to explore due to machine tool and numerical control improvements. What is need now is a validation of these new strategies in computer aided applications regarding time minimizing and how the cutting parameters affects in the surface final result.

A method for generating multiple solutions for multipoint five-axis tool positioning

Multipoint machining (MPM) strategies are a class of methods that use the flexibility of a five-axis machine to position a tool in close proximity of the desired surface so that the tool touches the surface on at least two points of contact. However, existing multipoint methods cannot control the spacing between the two points of contact. This paper presents a new technique, called the Drop, Spin, and Tilt (DST) method that can generate multiple contact points at varying distances around the first point of contact. The multiple DST second points of contact were used to manually generate a toolpath with uniform spacing between the two points of contact. While a uniform space could be attained at most tool positions, problem cases were encountered demonstrating that more work is required for an algorithmic version of this process. The proposed method was implemented in a symbolic algebra system and verified on a variety of surfaces.

PSO_PI Controller of Robotic Grinding Force Servo System

When an industrial robot is used to grind a curved surface ,as marine propeller surface, contact force and feed movement must controlled together at the similar time in order that the grinding tool would machine the work-piece, with required force, at the right position in right posture. A passive wrist system is advanced, in this paper, to conform the shape of the machining propeller by altering its posture along with the surface. Grinding force is controlled under a simple new PSO-PI controller at a steady value in the normal direction of the mentioned machining point by multi-point machining, while the grinding tool moving along the curved surface of the propeller. It means that the model of the passive wrist system and the surroundings could be used in force controlling when robots grind marine propeller surface by a grinding tool with multi-point machining. PSO_PI controller policy is being assembled and compared with a PI controller to obtain a controller that provides grinding with higher quality. The compared controllers have been optimized together with the parameters of the Two-Phase Hybrid Stepping Motor. The particle swarm optimization (PSO) method was selected from several methods to optimize of Proportional-Integral controller parameters in order to give better performance with improved step response for robotic grinding force servo system and overshoot are reduced. This control method was simulated using MATLAB/SIMULINK.

PSO_PI Controller of Robotic Grinding Force Servo System

When an industrial robot is used to grind a curved surface ,as marine propeller surface, contact force and feed movement must controlled together at the similar time in order that the grinding tool would machine the work-piece, with required force, at the right position in right posture. A passive wrist system is advanced, in this paper, to conform the shape of the machining propeller by altering its posture along with the surface. Grinding force is controlled under a simple new PSO-PI controller at a steady value in the normal direction of the mentioned machining point by multi-point machining, while the grinding tool moving along the curved surface of the propeller. It means that the model of the passive wrist system and the surroundings could be used in force controlling when robots grind marine propeller surface by a grinding tool with multi-point machining. PSO_PI controller policy is being assembled and compared with a PI controller to obtain a controller that provides grinding with higher quality. The compared controllers have been optimized together with the parameters of the Two-Phase Hybrid Stepping Motor. The particle swarm optimization (PSO) method was selected from several methods to optimize of Proportional-Integral controller parameters in order to give better performance with improved step response for robotic grinding force servo system and overshoot are reduced. This control method was simulated using MATLAB/SIMULINK.

The edge–torus tangency problem in multipoint machining of triangulated surface models

This paper presents a method for computing the tangency between an edge and a torus. This tangency is used in positioning a toroidal tool on an edge that is part of a triangulated surface. This method is easier to implement and faster to execute than earlier solutions to this problem. The method was tested on a triangulated surface modeling a pyramid and on a triangulated tensor product Bezier patch.

Optimising tool positioning for achieving multi-point contact based on symmetrical error distribution curve in sculptured surface machining

The multi-point tool positioning algorithms produce much larger machining strip width than the single-point algorithms and apparently reduce the actual machining time. This paper presents a tool positioning algorithm for multi-point machining of sculptured surface, which is excellent at dealing with both of concave and convex surfaces. The proposed method is based on the middle-point error control (MPEC) method, which means the connection point between cutter and surface corresponds to the middle point of error distribution curve. Usually, only one cut contact (CC) point can be obtained with this method. Thus, the proposed method improved the MPEC method for achieving two CC points. At first, the shape of error distribution curve is investigated, and its asymmetry is evaluated. Secondly, the error distribution curve becomes symmetrical after the cutter is rotated with a roll angle, and the cutter is separated with surface at the same time. Finally, the minimum tilt angle is found, and two CC points are obtained without gouging. Machining experiment is conducted to verify the proposed method, and the result reveals that the machining strip width is increased apparently and the tool position is almost unchanged after the adjustment with proposed method. Simulation, measurement, and analysis are also given in the part of the experiment.

A multipoint method for 5-axis machining of triangulated surface models

In this paper, we present a multipoint machining method for the 5-axis machining of triangulated surfaces with radiused end mills. The main idea is to drop the tool onto the surface to find an initial point of contact, and then rotate the tool while maintaining tangency with this initial point of contact until a second point of contact is found. The proposed procedure ensures a gouge-free position with two points of contact, allowing for a larger side step than a single point of contact method. This proof of concept paper presents the mathematical equations that must be solved to position the tool with two points of contacts on an STL surface. The paper further verifies the concept with simulations and presents experimental results to confirm the simulations.

Rotary Contact Method for 5-Axis Tool Positioning

In this paper, a new 5-axis tool positioning algorithm called the rotary contact method (RCM) for open concave surface machining using the toroidal cutter is developed. The RCM comes from the reverse thinking of multipoint machining (MPM) method and apparently distinguishes the traditional tool positioning principles, as it determines the optimal tool positions based on the offset surface instead of the design surface. The basic idea of the RCM is to determine the initial tool location first and then rotate the tool for required contact. The RCM can not only guarantee gouge-free tool positions without the additional local gouge checking and correction process but also effectively produce big machined strip width for open form surface machining just like the MPM. Besides, this new method is simple to implement. Machining simulation was performed to verify the validity of the RCM.

Study on the Fuzzy-PID Policy for Force Control in Free-Form Surfaces Polishing by Robots

When a robot is used to polish or finish a curved surface, both feed movement and contact force have to be controlled at the same time so that the polishing tool would machine its work-piece at the right position in right posture with required force. In this paper, a passive wrist system is developed to adapt the shape of the machining curved surface by changing its posture along with the surface. And under the Fuzzy-PID policy, polishing force is controlled at a stable value in the normal direction of the named machining point while the polishing tool moving along the curved surface by multi-point machining. It means that the passive wrist system and the model of the surroundings could be used in force controlling when robots polish free-form surfaces with multi-point machining by a grinding ring.

Dual Drive Curve Tool Path Planning Method for 5-axis NC Machining of Sculptured Surfaces

The problem of finished surface being not first-order continuous commonly exists in machining sculptured surfaces with a torus cutter and some other types of cutters. To solve this problem, a dual drive curve tool path planning method is proposed in this article. First, the maximum machining strip width of a whole tool path can be obtained through optimizing each tool position with multi-point machining (MPM) method. Second, two drive curves are then determined according to the obtained maximum machining strip width. Finally, the tool is positioned once more along the dual drive curve under the condition of tool path smoothness. A computer simulation and cutting experiments are carried out to testify the performance of the new method. The machined surface is measured with a coordinate measuring machine (CMM) to examine the machining quality. The results obtained show that this method can effectively eliminate sharp scallops between adjacent tool paths, keep tool paths smooth, and improve the surface machining quality as well as machining efficiency.

Basing precision of disk and bush blanks in multipoint machining

In mass production, multipoint machining of disk and bush blanks is often employed, on the basis of multipoint mandrels. At the same time, the bases and basing systems for such machining is not considered in the relevant literature and in State Standard GOST 21495–76 [1]. Their basing is assumed to be analogous to the basing of individual blanks. However, this is clearly erroneous, not only in view of the formal aspects of the problem (which geometric elements are technological bases and how they should be repre� sented in theoretical basing systems) but in fundamen� tal respects (the basing precision for such blanks). In the present work, we analyze the bases and basing sys� tems for such blanks in multipoint parallel and serial machining, as well as the basing errors in terms of the dimensions and mutual position (lack of concentric configuration) of cylindrical surfaces. We employ the terms and concepts in [2–4].

Basing precision of disk and bush blanks in multipoint machining

Basing precision of disk and bush blanks in multipoint machining

Analyses on the Solution Areas of Multi-Point Machining Constraints

Hermite method and MPM method were studied. Multi-point machining constraints with the cutter tilting forward and backward were derived respectively. So the number of the solutions of the two Multi-point machining methods was doubled than before. To derive some general conclusions about solution areas of Multi-point machining constraints, structure of neighborhood region close to a given point on a surface was used to substitute the surface in the Multi-point machining error calculation. A computational example was also given in the paper. With the theoretical analyses and computational example, it was proved that, for an open and slightly curved surface machining with Multi-points method, without regard to interference, there were four branch areas satisfying Multi-point machining constraints and distributing radically nearby the first tangent contact points respectively on condition that the cutter was tilted forward or backward. And they extended basically in the directions along the principal curvatures at the first tangent contact point.

SECANT ALGORITHM IN MULTI-POINT CONTACT MACHINING

In order to acquire a universal multi-point contact machining alogrithm and reduce the computation cost, the prin ciple of algorithm realizing multi-point contact between the toroidal outter and the machining surface is analyzed. And the method positioning the toroidal cutter is derived. A novel algorithm, for machining error controlling in multi-point contact machining, is proposed. In the algorithm, a function equation having the radius of the circle of the parameter difference between two contact points as the independent variable is constructed to control the maximal undercut error occurring within the two contact points in multi-point contact machining. The secant algorithm is utilized to solve the equation after iterations , and then the optimal value of the circle radius and cutter location is derived. It is proved by a computational example that very wide path intervals can be acquired when secant algorithm is applied in tool position calculation with multi-point method. The time cost of secant algorithm is much less than that of Hermite method. And it is more effective in the application on the sculpture surface machining.

MULTI-POINT MACHINING WITH ANTI-GOUGING AND SCALLOP HEIGHT CONTROL

Multi-Point Machining (MPM) is a tool positioning strategy for 5-axis machining of complex surfaces. A multi-point tool position results in tangential contact between the tool and the design surface at several points. By machining at several points on the tool simultaneously, material removal rates can be improved. In this paper several issues regarding multi-point machining are resolved. First, a much faster method for solving the equations governing multi-point contact is presented. Second, a method of estimating scallop height is described. This estimator makes it possible to produce constant scallop height tool paths. Finally a method of eliminating interference between the tool and the surface has been developed and integrated into the MPM tool positioning strategy.

Multi-point tool positioning strategy for 5-axis mashining of sculptured surfaces

Multi-point machining (MPM) is a tool positioning technique used for finish machining of sculptured surfaces. In this technique the desired surface is generated at more than one point on the tool. The concept and viability of MPM was developed by the current authors in previous works. However, the method used to generate the multi-point tool positions was slow and labor intensive. The objective of this paper is to present efficient algorithms to generate multi-point tool positions. A basic multi-point algorithm is presented based on some assumptions about the curvature characteristics of the surface underneath the tool. This basic algorithm is adequate for simple surfaces but will fail for more complex surfaces typical of industrial applications. Accordingly, tool position adjustment algorithms are developed that combine the basic algorithm with non-linear optimization to achieve multi-point tool positions on these more complex surfaces.