Srichand Hinduja

Convex hull-based feature-recognition method for 2.5D components

Abstract The automation of process planning requires the implementation of a feature-recognition procedure, so that decisions relating to tool selection and machining operations can be made. Described within this paper is a feature-recognition technique that is applied to 2.5D components created from a boundary-representation solid modeller. The method involves the determination of the convex hull for the components faces. The edges within the convex hull belong to faces that form a feature. In addition to this, inner loops of edges and concave edges are also detected, because they give rise to some faces that belong to a feature. The feature recognizer, in some cases, merges two or more features together, provided they have some common geometric characteristics. Information regarding the possible directions of approach for the cutter and the depth to be machined is also determined by the feature recognizer. The main advantage of the proposed method is that by considering one face at a time rather than the whole component, the complexity of the problem is reduced drastically.

Recognition of rough machining features in 2D components

In this paper, two methods are used to recognize the roughing features in an intermediate workpiece, which is obtained by gluing the finishing features onto the original component. The first method is based on the physical states of equilibrium and hence is referred to as the equilibrium method. This method recognizes features originating from convex inner loops. The second method, referred to as the concavity method, uses the concavity of vertices, edges and faces to detect features and the interactions between them. The features are represented as volumes and are classified according to a feature taxonomy. In this taxonomy, a new class of features, i.e. free features, is included. Examples of such features are blend, edge and vertex volumes. Edge and vertex volumes are combined with face volumes to form face machining features. The methodology is illustrated by recognizing the features in two industrial components.

Automatic tool selection for rough turning operations

Abstract A method of automatically selecting cutting tools for rough turning operations on a CNC lathe is presented. While the selection procedure can deal with various economic objectives, only the minimum cost per component is considered in this paper. Selection is made from an appropriate tool library and in order to reduce the search time a heuristic method is employed. The cost of machining with a given tool is estimated following the determination of the cutting conditions consistent with the constraints acting on the process. From a detailed examination of the constraints it is possible to ascertain whether the next tool in the library will give improved cutting conditions and the possibility of a lower cost. This procedure eliminates the need for an exhaustive search of the library and results in a very fast and efficient algorithm. The results of ten tool selections are presented. In all cases the computation time for the heuristic approach was less than 5% of that for the exhaustive search. In eight out of ten cases the heuristic method selected the same tool as the exhaustive search; in the two cases where the tools selected were different, those selected by the heuristic method produced only a marginal increase in the operation cost.

Voronoi diagram-based tool path compensations for removing uncut material in 2-D pocket machining

This paper solves the problem of uncut areas, which can arise when 21/2D pockets are machined with radial widths of cut greater than half the cutter diameter. Using the Voronoi diagram approach, three types of uncut areas are defined i.e., corner, centre and neck uncut regions. The corner uncut area is further subdivided into five different types, the centre uncut area into four and the neck uncut area into two. Techniques for detecting each type as well as algorithms for generating the tool paths for removing them are developed based on a singularity-free Voronoi diagram approach. These efficient and robust algorithms ensure that no uncut material is left behind even for complex-shaped pockets containing islands. The proposed algorithms even permit the radial width of cut to be increased to its limiting value of tool diameter. Three examples are included to illustrate the procedures for detection and removal of the different types of uncut areas.

Construction of feature volumes using intersection of adjacent surfaces

An algorithm is presented for the construction of feature volumes using the topology and geometry found in the 3D boundary representation of a solid object. The concavity of faces, edges and vertices is used to detect features and any interactions between them. Faces adjacent to the feature faces are intersected to create new edges which can be used to create totally new construction faces. These construction faces are then used to complete the feature volume. Simple rules have been developed which allow the intersection of quadric surfaces. This algorithm is modular in nature and can be used in conjunction with any feature detection module. The basic principle is established using the simplest of examples. The technique is then tested on several benchmark parts taken from the NIST design repository.

Determination of optimum cutter diameter for machining 2-O pockets

Abstract Tool paths in milling are calculated using user-defined values of the radial width of cut (b) and the cutter diameter (D). When calculating the other cutting parameters, most researchers and practising engineers assume that the ratio of the radial width of cut to the cutter diameter i.e. b/D remains constant over the entire tool path length. However, in practice, when machining pockets and many other features with window-frame type toolpaths, b/D does not remain constant. In this paper, the optimum cutter diameter is chosen following a consideration of the variation of b/D throughout the cutter path. It is shown that while a smaller cutter diameter gives a more favourable variation, it leads to a longer toolpath. Hence the final optimum cutter diameter is a compromise between the increased costs of a larger diameter with a shorter toolpath and the lower costs of a smaller diameter with a longer toolpath.

A tool-regulation and balancing system for turning centres

The tool-balancing system described in this paper regulates the selected tools for the machining of a certain component on a turning centre and optimises the tool-changing strategy on a machining-cost basis.The regulation of the tools represents a correlation between the total number of tools selected and the available tool positions on the machine tool. When there are free tool positions on the turret, duplicates of the high-wear tools can be used in order to reduce the number of interruptions for tool changing. When the number of tools is greater than the number of turret positions, some tools are automatically replaced by others which are already being used for different operations and which offer geometrical suitability and compatible performance.Further, the tool-changing strategy is optimised by modifying the optimum tool life and/or the cutting data. The system has been successfully tested for a variety of applications and it has resulted in increased productivity and machinetool utilisation.

Checking for tool collisions in turning

Abstract 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.

Development and evaluation of a low-cost computer controlled Reconfigurable Rapid tool

AbstractThis paper describes the development of a low-cost rapid tool that is easily re-configurable by a single computer-controlled actuator or conventional CNC machine. The bed-of-pins concept used in popular pin-art toys and by other researchers is enhanced with a novel approach of positioning and clamping the pins in a simple, low-cost and time-saving manner which is scalable to large size products. Different tool path strategies for positioning the pins by using a CNC machine are proposed and evaluated to obtain an optimal strategy. The position of the pins, and the NC code, is automatically derived from the 3D CAD model of the part. The concept has been tested on parts made from carbon fibre and thermoplastic moulding, and sheet metalforming. The scalability of the concept to large size objects is also demonstrated.

Modelling turned components with non-axisymmetric features

This paper describes a hybrid method for modelling turned components with non-axisymmetric features. It allows the user to create a turned component using either a feature-based library or traditional modelling tools (i.e. Boolean and sweeping operations), or both. Features created by the latter method are recognized by a novel 3D feature recognition algorithm which is based on the three states of equilibrium of physics namely stable, unstable and neutral. This method is capable of recognising non-axisymmetric (depressions, protrusions, flats, cross-holes, etc.) and axisymmetric (grooves, recesses, etc.) features. Once the faces belonging to a feature are detected, the system determines the machining volume and then an artificial intelligence module assigns the feature an appropriate name and a machining operation. The equilibrium method is general in nature and requires, as its input, a solid model of the turned part in boundary representation form. The recognition technique takes into account the existence of the blank, be it a bar, casting or forging. As an example, the features present on a stub axle of an automobile are recognized.