Papers by Author: Yu Han Wang

Abstract: A high-precision and efficient machining method of plane double enveloping hourglass worm is proposed. The worm tooth surface is first created and analyzed based on meshing theory. The analysis reveals that the worm tooth surface is a developable ruled surface. This provides the ability of precise flank milling of the worm tooth surface. The meshing lines on the worm tooth surface indicate the contact lines of the worm tooth and the cutter. The five-axis tool path of flank milling is then generated according to the meshing lines. The flank milling has obviously advantages in machining efficiency and surface quality, compared with the conventional end milling method. The cutting simulation and experiment validate proposed method.

Abstract: NC tool paths of digital CAD models are currently generated as a set of discrete data points. The CNC interpolator must convert these points into continuous machine tool axis motions. In order to achieve high-speed and high-accuracy machining, the development of a real-time interpolation algorithm is really indispensable, which can deal with a large number of short blocks and still maintain smooth interpolation with an optimal speed. In this paper, a real-time local cubic B-spline interpolator with look-ahead scheme is proposed for consecutive micro-line blocks interpolation. First, the consecutive micro-line blocks that satisfy the bi-chord error constraints are fitted into a C1 continuous cubic B-spline curve. Second, machining dynamics and tool path contour constrains are taken into consideration. Third, local cubic B-spline interpolator with an optimal look-ahead scheme is proposed to generate the optimal speed profile. Simulation and experiment are performed in real-time environment to verify the effectiveness of the proposed method. Compared with the conventional interpolation algorithm, the proposed algorithm reduces the machining time by 70%.

Abstract: In order to exploit the advantages of five-axis flank milling method for space free surface machining to the full, a definition of non-equidistant dual-NURBS tool path is presented first. On this basis, the constraint of velocity of points on the tool axis and the constraint of scanning area of the tool axis are deduced. Considering both of these constraints, an adaptive feed five-axis dual-NURBS interpolation algorithm is proposed. The simulation results show that the feedrate with the proposed algorithm satisfies both of the constraints and the machining time is reduced by 38.3% in comparison with the constant feed interpolator algorithm.

Abstract: NURBS interpolation has many advantages over the traditional linear or circular interpolation in high-speed machining. The existing work in this regard focuses on adaptive feed interpolation considering the chord error constraints and tangent acceleration limits. However, regardless of the dynamic characteristics of individual axis, performance will inevitably suffer when the system is called upon to execute a complex trajectory beyond the range of its capabilities. The intent of the present work is to provide an optimal feed interpolation method respecting both the chord error constraint and the drive constraint of each axis. A look-ahead scheme is applied with a moving window to augment the calculation efficiency for real-time application. Simulations are performed to verify the resulting feedrate, acc/dec profiles and the real-time performance of the proposed interpolator.

Abstract: Self-affine and stochastic affine transforms of R2 Iterated Function System (IFS) are investigated in this paper for manufacturing non-continuous objects in nature that exhibit fractal nature. A method for modeling and fabricating fractal bio-shapes using machining is presented. Tool path planning algorithm for numerical control machining is presented for the geometries generated by our fractal generation function. The tool path planning algorithm is implemented on a CNC machine, through executing limited number of iteration. This paper describes part of our ongoing research that attempts to break through the limitation of current CAD/CAM and CNC systems that are oriented to Euclidean geometry objects.

Abstract: In free-form surface machining, it is essential to optimize the feedrate in order to improve the machining efficiency. Conservative constant feedrate values have been mostly used since there was a lack of physical models and optimization tools for the machining processes. The overall goal of this research is the integration of geometric and mechanistic milling models for force prediction and feedrate scheduling for free-form surface machining. For each tool move a geometric model calculates the cutting geometry parameters, then a mechanistic model uses this information with the constraint force to calculate desired feedrates. The feedrate is written into the part program. When the integrated modeling approach was used, it was shown that the machining time can be decreased significantly along the tool path. Production time in machining propeller example was reduced to 35% compared to constant feedrate cases.

Abstract: Five-axis NC machining tools can improve the efficiency and accuracy obviously in today’s machining industries, but the machining errors and tool interference are likely to happen due to the complexity of tool motion. So the verification of the tool path is very important and necessary before machining the part. A new algorithm for 5-axis machining verification based on the swept volume has been presented in the paper. Based on the machine tool path and the cutter geometry, the cutter’s instantaneous swept profile is determined. By integrating the intermediate swept volume, the cutter’s swept envelope can be constructed and applied to NC verification. The algorithm has been implemented through Visual C++ and OpenGL language on Windows XP platform; a few examples are to verify the reliability of the proposed algorithms effectively. The experiment results indicate that the proposed method is superior to the traditional methods on the processing time and image quality. This proposed algorithm can be further applied to machining error analysis, collisions interference and NC path optimization, etc.

Abstract: This paper presents a reasonable method for generating the tool-path of free-form surface polishing using the fractal curves. Free-form surface polishing processes as a finishing process are used to reduce the roughness of surfaces and smooth the surface form by eliminating the surface waviness left by tool marks, EDM spark erosion and so on. In the interest of realizing this aim without introducing undesirable surface waviness and time efficiency, a tool-path should provide even coverage of free-form surface during polishing. A fractal curve is suitable to cover the free-form surface uniformly at any complexity due to its plane-filling and self-similar characteristics. A method of generating the fractal path for free-form surface polishing is presented, and also an automatic polishing system is installed to confirm the path planning method’s validity.

Abstract: To overcome the acceleration discontinuity and feed fluctuation of the conventional five-axis grinding interpolator, a jerk-limited acceleration is utilized and two aspects of constraints is taken into account: (1) the machining dynamics, including the constraints of power, velocity, acceleration and jerk represented by upper bounds for each axis (2) the contour constraints of linear segments, including the linear distance of the segment and sharp corner at the segment junctions. With the analysis of these constrains, the optimal feed for each segment and the joint feed at the segment junctions is derived. The corresponding adjusted interpolation algorithm with jerk-limited acceleration is presented such that a smooth motion during the machining can be maintained. The presented algorithm is demonstrated by the simulation result.

Abstract: To alleviate the feed fluctuation and maintain a smooth feed in five-axis machining, this paper takes the following two constraints into account: (1) the machining dynamics, including the constraints of power, velocity and acceleration represented by upper bounds for each axis (2) the contour constraints of the tool path, including the linear distance of the segment and sharp corner at the segment junctions. With the analysis of these constraints, the optimal feed is derived and the corresponding adjusted interpolation algorithm is presented such that a smooth motion during the machining can be obtained. The presented algorithm is demonstrated by the simulation result.