Workpiece Contour Research Articles

Analysis of Cutting Forces and Mechanism of Chip Formation in Ball End Milling of Inclined Surface (4th Report)

In milling with ball end mills of die and mold having various inclined or curved surfaces, tool paths are adopted along an axis of workpiece coordinate system or contour line on workpeice surface. In this paper, a cutting model proposed in previous paper is applied to the milling along the contour line of inclined surface, and cutting forces and chip formation under various inclined angles of the surface are predicted. In the milling of inclined surface in which the left side surface of feed direction of the tool rises, it is obtained analytically that the variation of cutting forces with rotational angle becomes large and rapidly changes. This phenomenon is caused by difference of geometric quantities such as tool-workpiece contact region and undeformed chip thickness along the cutting edge with feed direction of the tool on inclined surface. Predicted results are good agreement with experimental results. From 1st to 4th reports of this investigation, it is confirmed that the cutting forces in various milling process in which both cutting edges of sphere and cylindrical portions engage with the workpiece can be predicted well by using the cutting model proposed and energy method.

A Tool Path Modification Approach to Cutting Engagement Regulation for the Improvement of Machining Accuracy in 2D Milling With a Straight End Mill

In two-dimensional (2D) free-form contour machining by using a straight (flat) end mill, conventional contour parallel paths offer varying cutting engagement with workpiece, which inevitably causes the variation in cutting loads on the tool, resulting in geometric inaccuracy of the machined workpiece surface. This paper presents an algorithm to generate a new offset tool path, such that the cutting engagement is regulated at a desired level over the finishing path. The key idea of the proposed algorithm is that the semi-finish path, the path prior to the finishing path, is modified such that the workpiece surface generated by the semi-finish path gives the desired engagement angle over the finishing path. The expectation with the proposed algorithm is that by regulating the cutting engagement angle along the tool path trajectory, the cutting force can be controlled at any desirable value, which will potentially reduce variation of tool deflection, thus improving geometric accuracy of machined workpiece. In this study, two case studies for 2D contiguous end milling operations with a straight end mill are shown to demonstrate the capability of the proposed algorithm for tool path modification to regulate the cutting engagement. Machining results obtained in both case studies reveal far reduced variation of cutting force, and thus, the improved geometric accuracy of the machined workpiece contour.

DESIGN OF SECURITY INSPECTION SYSTEM OF MEASURING MACHINE FOR CONTOUR OF PROTOTYPE WORKPIECE

In order to adapt the development of modem advanced manufacturing, the study on intelligent coordinate measuring machine (CMM), which can perform online automatic measurement with non-contact, high accuracy method, has been an inevitable trend in the development of manufacturing industry, in which utilizing machine vision inspecting methods will provide technical support for automatic measuring free-form sculptured surfaces. The operating principle of this measuring machine for contour of prototype workpiece is introduced, and the function of a rotary table and an auto-centering module in the whole system for measuring revolving workpieces are discussed. By using appropriate image processing techniques, an image identification system is devised which includes detection of foreign body in working space, identification of model number of workpiece and detection of riding position of workpiece.

Integrated inspection and process control for machining a circular contour on a two-axis vertical turning lathe

This paper examines the integration of readily available commercial hardware into a simple methodology for machine tool performance enhancement through process-intermittent inspection, process stability monitoring, and tool path compensation. Workpiece-specific process-intermittent inspection is performed on-machine and is calibrated using a simple spherical artifact. The developed methodology focuses on integrating the use of readily available commercial hardware. The on-machine probe is used for process-intermittent workpiece inspection and for process monitoring, while the ball bar is used for preliminary assessment of machine tool's ability to compensate for motion and positioning errors. The methodology uses on-machine inspection of initial machining operations to generate compensation trajectories, which are then implemented during the second machining operation. Cutting tests using the developed methodology are performed on an Okuma & Howa V40R two-axis vertical turning centre. The results show that the average absolute deviation of the machined contour of a hemispherical workpiece (90° circular tool path) is reduced to 2.54 µm (0.0001 in) as verified by a coordinate measuring machine.

Research on an intelligent manufacturing system based on an information-localizing machining mode

To raise the response speed of manufacturing enterprises to the dynamic change of market, this paper presents a new machining mode of information-localization and an intelligent manufacturing system based on that mode. Feasible solutions to the key problems involved in this mode and system, such as the acquirement of workpiece contour information, fast calculation of workpiece state, and adaptive machining control based on the actual state information of the workpiece, etc. are given. Experimental verification has been carried out. The theoretical analysis and experimental results show that the proposed method is feasible. It provides a new effective approach to the fast-response manufacturing of complex parts with small lot size.

Hybrid vision/force control at corners in planar robotic-contour following

The accuracy and execution speed of a force controlled contour-following task is limited if the shape of the workpiece is unknown. This is even more true when the workpiece contour contains corners. The paper shows how a hybrid vision/force control approach at corners in planar-contour following results in a more accurate and faster task execution. The vision system is used to measure online the contour and to watch out for corners. The edge is correctly located by compensating the compliance of the tool/camera setup which affects the contour measurement. A simple corner-detection algorithm is presented. Once a corner is detected, the finite-state controller is activated to take the corner in the best conditions. Experimental results are presented to validate the approach.

Application of MRAC theory for adaptive control of a constrained robot manipulator

This study presents the compliance control of a robot manipulator under a constrained environment. Considering the impact of frictional force allows us to more accurately simulate the relationship between the manipulator and environmental contact forces. The controller design proposed herein is based on the adaptive control scheme. In this design, the feed forward and feedback controllers control the position and the contact force of end-effector. Applying these controllers allows us to adapt the manipulator to the unknown surface of the surrounding environment and to have close contact with the curved surface. A Lyapunov function ensures the stability of the system. For an unknown contour, most controllers fail since the desired trajectory can not be obtained, and the parameters of the manipulator are unknown and may varied with the contact force and position. However, in this study, when performing compliant motion, the desired trajectory is generated from the controller based on the tangential direction of the measured contact force. This tangential direction changes according to the operating point. We approach the original nonlinear system with a second order linear system at each instantaneous operating point. Correspondingly, the contour of workpieces can be measured. Experimental results conform the feasibility of the proposed adaptive control scheme. Without knowledge of the contour of workpiece and gains of the controller in advance, the adaptive controller performs well for various unknown contours.

Ｘ線ＣＴスキャナを用いた３次元ＣＡＤデータに基づく内部形状評価

The study deals with X-ray CT technology to inspect the inside parts of workpiece without destroying them. At present, there is few softwares capable of processing X-ray CT scanned data. Therefore, the function was developed to treat the data to evaluate geometric elements such as straight lines, circular arc and others, based on 3-dimensional CAD data as the standard of inspection. After the coordinate system of scanned data is automatically related with the 3-dimensional CAD data, the system evaluates geometric elements considering that a workpiece contour consists of a cluster of segments. Thus, the system cuts the contour of 3-dimensional CAD data on the appointed cross-sectional planes and classifies them into geometric elements. To compare 3-dimensional CAD data with the X-ray CT scanned data, the system calculates the straightness, angle deviation from the direction vector, length and its error of a straight line, and, roundness, deviation of center point, radius and its elTor. In addition, the system offers a visualization interface to display them so that the users utilize the evaluated result comfortably. As a result, the system is found effective to evaluate 2-dimensional geometric elements.

Variation in material removal in Gaussian removal processes

In previous experiments involving ion figuring of optical components, repeated machining resulted in little to no improvement in workpieces due to a variation in the removal. We demonstrate that the variation in removal is due to insufficiently large machining limits and that such variation is common to all Gaussian removal processes. Once larger limits are chosen, successive machining iterations improves workpiece contour significantly.

An algorithm for converting the contour of a 2D workpiece into a rectilinear polygon

This paper presents an algorithm for converting the contour of a 2D workpiece into a rectilinear polygon. The purpose of providing such a conversion is to model the global shape information of the workpiece. Using an existing algorithm, the rectilinear polygon can further be modeled by a tree structure of line segments, known as the simplified skeleton, which can concisely model the global shape information of a workpiece. That is, workpieces with similar global shape can be classified into the same group by considering the similarity among their simplified skeletons. This algorithm is helpful to enhance the modeling capability of the traditional group technology coding schemes.

Force-controlled fuzzy-logic-based robotic deburring

In this paper a three-step active deburring strategy is proposed based on fuzzy logic and force feedback control. A strategy for automatic contour following is developed to identify unknown workpiece contours, to automatically generate desired robot motions, and to detect unknown burr sizes and positional inaccuracies. Under the deburring strategy the robot motion and force control are planned actively according to the detected burr sizes and positional inaccuracies. A fuzzy man-machine interface is built to make use of the knowledge of human operators to simplify the burr detection. A fuzzy model of the deburring process is developed to support the planning of deburring procedures. Implementation of and experiments with the proposed strategies are described.

Automatic programming of grinding robot restoration of contours

A new programming method has been developed for grinding robots. Instead of using the conventional jog-and-teach method, the workpiece contour is automatically tracked by the robot. During the tracking, the robot position is stored in the robot control system every 8th millisecond. After filtering and reducing this contour data, a robot program is automatically generated. The contour data contain different types of noise due to small vibrations and overshoot when the robot is tracking the workpiece. To remove the noise, a new filtering algorithm is proposed. The Look Ahead filter removes outliers from the data. After that, the data is smoothed by the Nadaraya-Watson estimator. The system is tested out by a Multicraft 560 robot. Experimental results show that the filtering algorithm efficiently removes the noise without reducing the accuracy of the contour data. This makes it easy to automatically restore the contour by a robot program.

Force-Controlled Robotic Deburring

In this paper a three-step active deburring strategy is proposed based on force feedback control. Strategies for automatic contour following are developed to identify unknown workpiece contours, to automatically generate desired robot motions, and to detect unknown burr sizes. Under the active deburring strategy burr size variations are identified through contour following and different sizes of burrs are removed with a specification of a variable desired deburring force. Implementation of and experiments with the proposed strategies are described.

Quantitative error-assessment between upset-test data and a computer-code simulation

A quantitative analysis of axial-force, internal radial displacement and workpiece contour histories for upset-tests are presented in this paper. Discrete internal deformations are measured by using the technique of “tracer particles”. Vertical arrays of tracer particles, aligned in the longitudinal direction of the upset cylinders, permit internal radial deformations to be both visualized and measured as a function of axial die-displacement. Statistically quantitative axial-force, radial-contour and internal radial deformations vs axial displacement of the die are obtained via two-factor, replicated-pair, tests. These experimental results can be used to verify computer-simulations and provide the necessary information for improving simulations. Also, these results are useful for calibrating, or “back calculating”, various input parameters associated with computer-simulations. Lastly, the paper presents a quantitative comparison between the experimental results and a computer-code simulation of the forging force and internal radial displacements.

Checking for tool collisions in turning

A tool selected for a turning operation must have the right geometry so that it does not interfere with the workpiece or machine. This paper describes a method that enables any possible interference to be detected automatically and efficiently. It takes into account not only the geometry of the tool and workpiece but also the surrounding surfaces such as chuck, tailstock, and tool turret. The method is based on sliding the tool against the workpiece and machine, determining the locus of the tool-nose centre, and then calculating the intersection between the locus and the area to be machined. In most cases, interference can be detected by only checking the direction angles of the elements of the tool and workpiece contour. When interference is detected, the method also determines the exact area that the tool cannot machine. The method can also determine the minimum safe tool length required for certain operations and, in the case of boring, the minimum depth of cut to avoid interference.

THE PRINCIPLE OF INTERPOLATION IN NUMERICAL CONTROL——FEEDING AT THE MINIMUM ERROR

The principle of interpolation operation has been presented, the fundamental concept of which is to feed a tool in the best direction so that the tool may reach the closest point to the workpiece contour curve. We call the principle as feeding at the minimum error.

The optimal method of interpolation operation in NC—Feeding according to the closest distance

A new method of interpolation operation is put forward in this paper. The fundamental idea about the method is that the tool feeds in the best direction of all possible directions so that the point which the tool will reach is the closest to the workpiece contour curve, thus the error of interpolation is the least. We call the method feeding according to the closest distance (FCD). In another paper it will be mathematically proved that when a tool feeds by unit step the accuracy of interpolation of the FCD is the highest. So the FCD is the optimal method of interpolation operation.