Sam Anand

Feature-based modelling approaches for integrated manufacturing: state-of-the-art survey and future research directions

Abstract Features capture the engineering significance of a part model and serve as an important support tool for integrated manufacturing. Feature-based design systems typically act as ‘interpreters’ between the CAD and the CAM activities. These systems can be classified broadly into human-assisted feature definition systems, automatic feature recognition systems and design by features systems. Researchers have come to realize that the best system architecture for a feature-based system would be a blend of the above-mentioned approaches. This paper reviews the major developments in the field of feature-based modelling with particular emphasis on automatic feature recognition systems. The approaches used for automatic feature recognition systems are systematically categorized and discussed. Automated feature recognition systems are broadly categorized into volume feature recognition systems and surface feature recognition systems, and the published research in each of these categories is critically discus...

Effect of Thermal Deformation on Part Errors in Metal Powder Based Additive Manufacturing Processes

In metal additive manufacturing (AM) processes, parts are manufactured in layers by sintering or melting metal or metal alloy powder under the effect of a powerful laser or an electron beam. As the laser/electron beam scans the powder bed, it melts the powder in successive tracks which overlap each other. This overlap, called the hatch overlap, results in a continuous cycle of rapid melting and resolidification of the metal. The melting of the metal from powder to liquid and subsequent solidification causes anisotropic shrinkage in the layers. The thermal strains caused by the thermal gradients existing between the different layers and between the layers and the substrate leads to considerable thermal stresses in the part. As a result, stress gradients develop in the different directions of the part which lead to distortion and warpage in AM parts. The deformations due to shrinkage and thermal stresses have a significant effect on the dimensional inaccuracies of the final part. A three-dimensional thermomechanical finite element (FE) model has been developed in this paper which calculates the thermal deformation in AM parts based on slice thickness, part orientation, scanning speed, and material properties. The FE model has been validated and benchmarked with results already available in literature. The thermal deformation model is then superimposed with a geometric virtual manufacturing model of the AM process to calculate the form and runout errors in AM parts. Finally, the errors in the critical features of the AM parts calculated using the combined thermal deformation and geometric model are correlated with part orientation and slice thickness.

A genetic algorithm based approach for robust evaluation of form tolerances

Abstract This paper deals with the accurate interpretation of inspection data for various classes of form tolerances. The minimum zone (MZ) method (ANSI Y14.5M-1994) yields the lowest value (most accurate) for all the form tolerance errors. The MZ solution minimizes the maximum deviation of the inspected feature from a reference (normally an ideal state of the evaluated feature). An accurate evaluation of this solution for various form tolerances involves solving a nonlinear optimization problem. Evaluation algorithms incorporated in current coordinate measuring machines deal with minimizing the least-square error for the form feature being evaluated, resulting in higher values for form tolerances. This paper solves a nonlinear optimization problem for form tolerance evaluation by applying genetic algorithms. A unified genetics-based algorithm has been used to estimate the minimum zones of all form tolerance classes, namely straightness, flatness, circularity, and cylindricity. Multiple search zones are formed throughout the data set, simultaneously in each iteration, to arrive at a global optimal solution. This approach takes care of the inherent nonconvexity in the search surface and overcomes problems of local optima. The results of this approach, applied to some examples, are presented in this paper and compared with results from existing methods reported in the literature.

Minimum-zone form tolerance evaluation using particle swarm optimisation

Robust and accurate evaluation of form tolerances is of paramount importance in todays world of precision engineering. Present-day Coordinate Measuring Machines (CMMs) and other optical scanning machines operate at high speed and have a high degree of accuracy and repeatability which are capable of meeting the stringent measurement requirements. However, the evaluation algorithms used in conjunction with them are not robust and accurate enough, because of the highly non-linear nature of the minimum-zone form tolerance formulation. Evolutionary Algorithms (EAs) have proved effective in solving non-linear optimisation problems. In this paper, Particle Swarm Optimisation (PSO) is employed to evaluate various minimum-zone form tolerances. An unconstrained formulation of the minimum-zone form tolerance is used for the optimisation. The methodology is validated by testing on several datasets from published literature and yields equal or better results than other existing minimum-zone algorithms. It is also extremely robust and the quality of the results is not affected by the number of points in the dataset.

Machine understanding of manufacturing features

Automated engineering analysis (AEA) of the solid model of a product is an essential task for the implementation of concurrent engineering. AEA has the potential to analyse several design and manufacturing activities in order to reduce the product development time and the associated costs. This especially has been the goal of many American manufacturing companies facing stiff global competition. AEA involves the use of the CAD data base of the product model for several design and manufacturing activities such as process planning, NC path planning, GT coding, assembly analysis, tolerancing, automated jig and fixture design, FEM analysis, heat transfer analysis, etc. The power of AEA can be fully realized if the output from the CAD data is in a higher-level form, i.e., features. However, CAD systems typically store the product information in a lower-level form such as points, edges, faces, etc. This paper presents a rule/graph-based approach for generating higher-level product definition in terms of manufac...

An integrated machine vision based system for solving the nonconvex cutting stock problem using genetic algorithms

The two-dimensional stock cutting problem is well known and often studied. A genetic algorithm approach to the problem is developed that is capable of handling some of the more intractable forms of the problem: nonconvex parts; nonconvex sheets; multiple irregularly shaped sheets; and so on. An integrated system is developed that incorporates a machine vision module for acquiring the images of irregular (nonconvex) parts and sheets, polygonalizing them, and storing them in a database of parts and sheets. Using the polygonal images as well as the manufacturing schedules and priorities as input, a genetic algorithm is used to generate part layouts that satisfy the manufacturing constraints. The significant features of this approach are (1) the integration of all aspects of the layout process and (2) the flexibility of the genetic algorithm approach, which allows it to be adapted to fit the special requirements of different problems. The proposed methods can be particularly useful in the leather and apparel industries, where nonconvex parts and sheets are commonly used.

Assessment of circularity error using a selective data partition approach

This paper presents a novel and accurate method to estimate the circularity tolerance of a machined part. The selective data partition (SDP) algorithm presented here utilizes the actual measurement points obtained from a CMM to calculate the circularity tolerance. The tolerance zone obtained by this method conforms to the definition of roundness tolerance as specified in the ANSI (ANSI 1994) standards. The data set is sub-divided into quadrants and the basis points are then chosen from among the points in each quadrant. The basis points are then used to fit a pair of concentric circles with minimum radial separation. The circularity tolerance is given by the difference in the radii of the concentric circles. An iterative procedure is followed to arrive at the final circularity tolerance value. Several data sets were tested to illustrate the successful implementation of the algorithm. The results thus obtained are also compared with the existing methods to demonstrate the accuracy and ease of implementatio...

Manual, Hybrid and Automated Inspection Literature and Current Research

Inspection is an activity that controls the outgoing product quality and involves search, detection and measurement or diagnosis. Traditionally, inspection tasks have been allocated to humans. Attempts to automate industrial inspection in order to eliminate errors and alleviate monotony have faced difficulties due to technological limitations and/or prohibitive implementation costs. An occasional compromise is partial automation (hybrid inspection). Reviews published research in manual, hybrid and automated inspection to understand the current research status.

A new Steiner patch based file format for Additive Manufacturing processes

Additive Manufacturing (AM) processes adopt a layering approach for building parts in continuous slices and use the Standard Tessellation Language (STL) file format as an input to generate the slices during part manufacturing. However, the current STL format uses planar triangular facets to approximate the surfaces of the parts. This approximation introduces errors in the part representation which leads to additional errors downstream in the parts produced by AM processes. Recently, another file format called Additive Manufacturing File (AMF) was introduced by ASTM which seeks to use curved triangles based on second degree Hermite curves. However, while generating the slices for manufacturing the part, the curved triangles are recursively sub-divided back to planar triangles which may lead to the same approximation error present in the STL file. This paper introduces a new file format which uses curved Steiner patches instead of planar triangles for not only approximating the part surfaces but also for generating the slices. Steiner patches are bounded Roman surfaces and can be parametrically represented by rational Bezier equations. Since Steiner surfaces are of higher order, this new Steiner file format will have a better accuracy than the traditional STL and AMF formats and will lead to lower Geometric Dimensioning and Tolerancing (GD&T) errors in parts manufactured by AM processes. Since the intersection of a plane and the Steiner patch is a closed form mathematical solution, the slicing of the Steiner format can be accomplished with very little computational complexity. The Steiner representation has been used to approximate the surfaces of two test parts and the chordal errors in the surfaces are calculated. The chordal errors in the Steiner format are compared with the STL and AMF formats of the test surfaces and the results have been presented. Further, an error based adaptive tessellation algorithm is developed for generating the Steiner representation which reduces the number of curved facets while still improving the accuracy of the Steiner format. The test parts are virtually manufactured using the adaptive Steiner, STL and AMF format representations and the GD&T errors of the manufactured parts are calculated and compared. The results demonstrate that the modified Steiner format is able to significantly reduce the chordal and profile errors as compared to the STL and AMF formats. A new Steiner patch based Additive Manufacturing file format has been developed.Steiner format uses triangular rational Bezier representation of Steiner patches.Steiner format has high geometric fidelity and low approximation error.The Steiner patches can be easily sliced and closed form solutions can be obtained.AM parts manufactured using Steiner format has very low profile and form errors.

Vision assisted NC milling path generation

Abstract CAD/CAM software are an interrelated mesh of computer programming systems that serve to monitor, process and control the flow of manufacturing data. Modern day techniques rely extensively on the integration of standards like the initial graphics exchange specification (IGES) with automated path planning modules. The intent of such an integration is to maintain the system as generic as possible. Integration of the various aspects of manufacturing systems provides total automation of the system. A machine vision system was used to generate the NC code to face mill any planar polygonal part. The vision system helps to capture the image of the face of a polygonal object. This image is decoded into edges and vertices by performing computations in software, based on simple image processing rules. Then the software passes the control to a path planning module. This module selects the most efficient tool path and generates the part program to face mill the part. This paper presents a detailed description of the algorithm developed along with its application environment.