Conventional Tool Paths Research Articles

Investigation of stochastic toolpath strategy in three-axis ball-end milling of 2D and free-form surfaces

The machining of free-form components by ball-end milling inherently produces surface error in the form of scallops. The objective of any free-form toolpath strategy is to balance productivity while minimizing scallop height to reduce surface error. Conventional machining strategies produce repeatable material patterns (constant scallop height) that may limit workpiece function in areas such as lubricity, directional anisotropy, and aesthetic appearance. These strategies also involve steady-state cuts, which allow accumulation of temperature, restrict the permissible depth and speed. In the present paper a novel complex stochastic toolpath strategy has been proposed that comprises pseudo-random circular contours concatenated into a smooth path. The approach enables continuous variation of chip load, force, and direction, and avoids conditions of continuous, periodic high cutting loads and heat accumulation. Based on initial testing, it has been observed that stochastic toolpaths are longer than conventional toolpaths. However, a decrease in average cutting loads enable reduction in cutting time with feed optimization. Additionally, the proposed strategy resulted in lower scallop height than conventional machining, thereby improving surface condition.

Random adaptive tool path for zonal optics fabrication.

Deterministic optics fabrication using sub-aperture tools has been vital for manufacturing precision optical surfaces. The fabrication process requires the tool influence function and the tool path to calculate the dwell time that guides the tool to bring surface quality within tight design tolerances. Widely used spiral and raster paths may leave excess waviness from the tool path, and the unavoidable constant removal layer is added to obtain positive dwell time. This waviness can be removed by either using smaller tools sequentially or randomizing the tool path. However, the existing tool-path solutions can hardly adapt to different surface aperture shapes and localized surface errors. Process efficiency and accuracy are also not well considered in tool-path planning. We propose an innovative zonal Random Adaptive Path (RAP) to solve these problems in this study. Firstly, RAP can be flexibly adapted to different surface aperture shapes by introducing part boundary. Secondly, an average threshold strategy is used in the RAP planning to improve efficiency, enabling the surface errors to be selectively corrected. Finally, the threshold is performed in several passes within one processing cycle, each with its RAP, until the desired residual is achieved. The performance of the proposed RAP is studied by comparing it with the conventional tool paths. The results demonstrated that RAP takes the least processing time and achieves the best surface quality, which verifies the effectiveness of RAP in deterministic optics fabrication.

Reprint of: Residual stress inclusion in the incrementally formed geometry using Fractal Geometry Based Incremental Toolpath (FGBIT)

Single Point Incremental Sheet Forming (SPISF) is a well-known flexible alternative to conventional generative manufacturing processes. In SPISF, the geometry to be formed is fragmented into series of 2D slices and the plastic deformation is achieved through layer by layer movement of a Numerically Controlled (NC), hemispherical or ball end forming tool. The whole plastic deformation is the sum of all localized strains developed during each increment. Spiral, constant z incremental toolpaths, and their variants are common conventional toolpaths for SPISF. Several researchers have investigated these toolpaths extensively. Fractal Geometry Based Incremental Toolpath (FGBIT) is a recently developed toolpath for SPISF that improves the process formability and stress distribution. Unlike conventional toolpaths, FGBIT deforms the base region of the formed geometry which induces work hardening and residual stresses into the work piece. This may lead to the forming of high strength components. The residual stress distribution over the base region of the formed component (square cup) has been investigated in this study. Further, a comparison based on residual stress distribution between FGBIT and conventional incremental toolpaths is presented. Residual stresses have been measured by using nanoindentation technique. Pile up generation near the periphery of the indent is investigated for conventional and FGBIT based toolpaths. It has been observed from the experimental results that, the strength of the formed component increases due to induced compressive surface residual stresses while using FGBIT hence, metal components with high fatigue life and better strength-to-weight ratio can be formed.

Optimizing the numerical algorithm in Fast Constant Engagement Offsetting Method for generating 2.5D milling tool paths

In the case of 2.5D rough milling operations, machining efficiency can significantly be increased by providing a uniform tool load. This is underpinned by the fact that uniform load has a positive effect on both tool life and machining time. Unfortunately, conventional contour-parallel tool paths are unable to guarantee uniform tool loads. However, nowadays there are some advanced path generation methods which can offer a constant tool load by controlling the cutter engagement angle. Yet, the spread of these non-equidistant offsetting methods is hindered by their dependence on complex calculations. As a solution to this problem, the Fast Constant Engagement Offsetting Method (FACEOM), developed in the scope of our previous study, is seen to be taking a step towards reducing computational needs. In this paper, suggestions for further improvements of FACEOM are presented. Decreasing the number of path points to be calculated is made possible by implementing adaptive step size and spline interpolation. Through simulation tests, it was also analysed which of the numerical methods utilized for solving boundary value problems can be applied to obtain the shortest calculation time during tool path generation. The practical applicability of the algorithm has been proved by cutting experiments. With respect to research results, this paper also describes how a tool path created by the algorithm can be adapted to controllers of CNC machine tools. Solutions presented in this paper can promote a wider application of a modern path generation method that ensures constant tool loads.

Investigation of a radial toolpath in single point incremental forming

Single point incremental forming (SPIF) is a sheet material forming process recognized for its potential performance in low to medium volume production due to precluding the need for high-investment stamping dies. This process forms blanks instead through the use of local deformations, traditionally imposed utilizing a hemispherically-shaped tool. The dieless nature of this process makes it ideal at low volumes; however, several drawbacks of the process currently inhibit its widespread use in industry, including difficult-to-predict springback and poor surface finish.Another perceived drawback of SPIF is overall low formability. Conventional toolpaths form the blank through a series of successive passes in which the tool is generally constrained to the XY plane. Here a novel toolpath is proposed and tested experimentally and through simulation to determine its viability of improving formability. The toolpath investigated travels radially through the center of the workpiece, rather than along its periphery, in order to generate a more uniform thickness profile. A formability improvement of 21% was found utilizing this strategy.

Residual stress inclusion in the incrementally formed geometry using Fractal Geometry Based Incremental Toolpath (FGBIT)

Abstract Single Point Incremental Sheet Forming (SPISF) is a well-known flexible alternative to conventional generative manufacturing processes. In SPISF, the geometry to be formed is fragmented into series of 2D slices and the plastic deformation is achieved through layer by layer movement of a Numerically Controlled (NC), hemispherical or ball end forming tool. The whole plastic deformation is the sum of all localized strains developed during each increment. Spiral, constant z incremental toolpaths, and their variants are common conventional toolpaths for SPISF. Several researchers have investigated these toolpaths extensively. Fractal Geometry Based Incremental Toolpath (FGBIT) is a recently developed toolpath for SPISF that improves the process formability and stress distribution. Unlike conventional toolpaths, FGBIT deforms the base region of the formed geometry which induces work hardening and residual stresses into the work piece. This may lead to the forming of high strength components. The residual stress distribution over the base region of the formed component (square cup) has been investigated in this study. Further, a comparison based on residual stress distribution between FGBIT and conventional incremental toolpaths is presented. Residual stresses have been measured by using nanoindentation technique. Pile up generation near the periphery of the indent is investigated for conventional and FGBIT based toolpaths. It has been observed from the experimental results that, the strength of the formed component increases due to induced compressive surface residual stresses while using FGBIT hence, metal components with high fatigue life and better strength-to-weight ratio can be formed.

Trochoidal toolpath for the pad-polishing of freeform surfaces with global control of material removal distribution

A trochoidal toolpath has an advantage in automated polishing owing to its multidirectional characteristic. Compared to most conventional toolpaths, a trochoidal toolpath has increased flexibility in its pattern control by involving more control parameters. In this work, the flexibility of a trochoidal toolpath has been applied in the pad-polishing of freeform surfaces using a tilted elastic disk, with global control of material removal distribution over part surfaces. Using the proposed approach, a novel mesh conformal parameterization-based algorithm is developed to simplify the complex trochoidal toolpath generation from freeform surfaces to a 2D domain, while considering mapping distortion. The material removal variation along the guide-line of the trochoidal toolpath is addressed by using optimized trochoidal step and radius, after precisely calculating the effect of overlapped toolpath trajectories. Moreover, adaptive feedrates for partitioned local regions are further proposed to address the material removal variation along the direction perpendicular to the trochoidal guide-line. Simulation and experimental studies are conducted and show that the fluctuation of removal depth can be considerably reduced with the global control of material removal distribution.

Time-Efficient Trochoidal Tool Path Generation for Milling Arbitrary Curved Slots

Trochoidal (TR) tool paths have been a popular means in high-speed machining for slot cutting, owing to its unique way of cyclically advancing the tool to avoid the situation of a full tool engagement angle suffered by the conventional type of slot cutting. However, advantageous in lowering the tool engagement angle, they sacrifice in machining efficiency—to limit the tool engagement angle, the step distance has to be carefully controlled, thus resulting in a much longer total machining time. Toward the objective of improving the machining efficiency, in this paper, we propose a new type of TR tool path for milling an arbitrary curved slot. For our new type of TR tool path, within each TR cycle, rather than moving circularly, the tool moves in a particular way such that the material removal rate is maximized while the given maximum engagement angle is fully respected. While this type of TR tool path works perfectly only for circular slots (including straight ones), by means of an adaptive decomposition and then a novel iso-arc-length mapping scheme, it is successfully applied to any general arbitrarily curved slot. Our experiments have confirmed that, when compared with the conventional TR tool paths, the proposed new type of TR tool path is able to significantly reduce the total machining time by as much as 25%, without sacrificing the tool wear.

Spiral tool paths for high-speed machining of 2D pockets with or without islands

Abstract We describe new methods for the construction of spiral tool paths for high-speed machining. In the simplest case, our method takes a polygon as input and a number δ>0 and returns a spiral starting at a central point in the polygon, going around towards the boundary while morphing to the shape of the polygon. The spiral consists of linear segments and circular arcs, it is G1 continuous, it has no self-intersections, and the distance from each point on the spiral to each of the neighboring revolutions is at most δ. Our method has the advantage over previously described methods that it is easily adjustable to the case where there is an island in the polygon to be avoided by the spiral. In that case, the spiral starts at the island and morphs the island to the outer boundary of the polygon. It is shown how to apply that method to make significantly shorter spirals in some polygons with no islands than what is obtained by conventional spiral tool paths. Finally, we show how to make a spiral in a polygon with multiple islands by connecting the islands into one island. Highlights It is described how to construct a spiral to be used for pocket machining. The spiral respects a user-defined maximum stepover distance between neighbouring revolutions. The algorithm can create a spiral that morphs an island to the boundary of the pocket. The obtained spirals are in some cases much shorter than previously described spiral toolpaths. The algorithm is fast and a popular industrial strength implementation has been created.

Optimal space filling for additive manufacturing

Purpose In additive manufacturing (AM) process, the physical properties of the products made by fractal toolpaths are better as compared to those made by conventional toolpaths. Also, it is desirable to minimize the number of tool retractions. The purpose of this study is to describe three different methods to generate fractal-based computer numerical control (CNC) toolpath for area filling of a closed curve with minimum or zero tool retractions. Design/methodology/approach This work describes three different methods to generate fractal-based CNC toolpath for area filling of a closed curve with minimum or zero tool retractions. In the first method, a large fractal square is placed over the outer boundary and then rest of the unwanted curve is trimmed out. To reduce the number of retractions, ends of the trimmed toolpath are connected in such a way that overlapping within the existing toolpath is avoided. In the second method, the trimming of the fractal is similar to the first method but the ends of trimmed toolpath are connected such that the overlapping is found at the boundaries only. The toolpath in the third method is a combination of fractal and zigzag curves. This toolpath is capable of filling a given connected area in a single pass without any tool retraction and toolpath overlap within a tolerance value equal to stepover of the toolpath. Findings The generated toolpath has several applications in AM and constant Z-height surface finishing. Experiments have been performed to verify the toolpath by depositing material by hybrid layered manufacturing process. Research limitations/implications Third toolpath method is suitable for the hybrid layered manufacturing process only because the toolpath overlapping tolerance may not be enough for other AM processes. Originality/value Development of a CNC toolpath for AM specifically hybrid layered manufacturing which can completely fill any arbitrary connected area in single pass while maintaining a constant stepover.

A numerical study of multi-pass design based on Bezier curve in conventional spinning of spherical components

Bezier curve has been widely used as the roller path in conventional spinning. In this paper, Finite Element model with parameterized 2-pass conventional spinning tool paths based on quadratic Bezier curve is developed to explore the influence on the wall thickness reduction of spherical components. The results show that the first path has significant effect on wall thickness distribution and the selection of parameter values in tool path is crucial for thickness distribution.

A curvature optimal sharp corner smoothing algorithm for high-speed feed motion generation of NC systems along linear tool paths

Conventional tool paths for computer numerical-controlled (CNC) machine tools or NC positioning systems are mainly composed of linear motion segments, or the so-called G1 commands. This approach exhibits serious limitations in terms of achieving the desired part of geometry and productivity in high-speed machining. Velocity and acceleration discontinuities occur at the junction points of consecutive segments. In order to generate smooth and continuous feed motion, a geometric corner smoothing algorithm is proposed in this paper, which fits quintic B-splines to blend adjacent straight lines together. The proposed transition scheme ensures G 2 continuity transitions and optimal curvature geometry delivering fast cycle time without violating the axis acceleration limits. The cornering error is controlled analytically allowing the user to set the desired cornering tolerance. The feed profile along the corner-blended tool path is generated based on S-curve-type acceleration profile, and it is scheduled for minimum cycle time. At last, the corner-blended tool path is interpolated in real-time with minimum feed fluctuation for accurate and smooth feed motion. Proposed algorithms are implemented, and their effectiveness is tested on a CNC machine tool.

The Optimal Model of Tool Paths Generation for Pocket Milling

This paper describes an integrated method to determine optimal cutting parameters for milling pocket based on minimum cutting time. The main constraints entailed in real cutting, such as chatter free, uncut free tool paths, cutter and machine tool limitations, are included into the optimal model. The optimal parameters (depth of cut, width of cut, spindle speed) are inserted into the tool paths generation directly for four kinds of conventional cutting modes (Zig and Zig-Zag parallel cutting mode, inwards and outwards spiral pattern modes). According to the fact that the first cut in every cut level is slotting milling, the milling areas are divided into slotting milling area and general milling area. This dynamically corrected tool paths generation method changes the order of conventional tool paths, so different cutting parameters are used in slotting milling and general milling areas. The case study has demonstrated that the proposed methods can identify the optimal milling conditions and generate tool paths automatically and result in minimum milling time.

Efficient five-axis machining of free-form surfaces with constant scallop height tool paths

Generation of efficient tool paths is essential for the cost-effective machining of parts with complex free-form surfaces. A new method to generate constant scallop height tool paths for the efficient five-axis machining of free-form surfaces using flat-end mills is presented. The tool orientations along the tool paths are optimized to maximize material removal and avoid local gouging. The distances between adjacent tool paths are further optimized according to the specified scallop height constraint to maximize machining efficiency. The constant scallop height tool paths are generated successively across the design surface from the immediate previous tool path and its corresponding scallop curve. The scallop surface, an offset surface of the three-dimensional design surface based on the specified scallop height, is used to establish accurately the scallop curve with the constant scallop height. The present method was implemented and validated through the five-axis machining of a typical free-form surface. The results showed that the conventional isoparametric tool paths were over 36% longer in the total tool path length and less efficient than the constant scallop height tool paths generated by the present method.