Shunmugam M S

High-aspect-ratio high-quality microholes are required in turbine blades to improve cooling performance. These cooling holes are drilled by pulsed laser and hence dimensional as well as geometrical tolerances like circularity and cylindricity are important. The measurement of geometrical features of the microholes is a very challenging task without destroying the components. In the present work, the microholes are produced on Ti6Al4V alloy by ultra-short pulse laser. The geometrical features of microholes are then captured using a non-destructive technique, namely computed tomography. CT-scanned 3D data is directly used for geometrical analysis using open-source software, GOM Inspect. Since algorithms used in the GOM Inspect are proprietary in nature, the extracted coordinate data are also analyzed using the computational methods developed by the authors based on least squares technique. The dimension, circularity, and cylindricity of microholes are compared with the results obtained from GOM Inspect software and a close match is found.

An automated planning system extracts data from design models and processes it efficiently for transfer to manufacturing activity. Researchers have used face adjacency graphs and volume decomposition approaches which make the feature recognition complex and give rise to multiple interpretations. The present work recognizes the features in prismatic parts considering Attributed Adjacency Matrix (AAM) for the faces of delta volume that lie on rawstock faces. Conceptually, intermediate shape of the workpiece is treated as rawstock for the next stage and tool approach direction is used to recognize minimum, yet practically feasible, set of feature interpretations. Edge-features like fillets/undercuts and rounded/chamfer edges are also recognized using a new concept of Attributed Connectivity Matrix (ACM). In the first module, STEP AP-203 format of a model is taken as the geometric data input. Datum information is extracted from Geometric Dimension and Tolerance (GD&T) data. The second module uses features and datum information to arrive at setup planning and operation sequencing on the basis of different criteria and priority rules. Copyright © 2013.

Kinematic accuracy of path traced by a chosen point of a given mechanism is affected by manufacturing errors that cause variation in link lengths and joint clearances. Tolerance analysis in mechanisms refers to a process of finding out deviation from nominal path of the given point in the mechanism due to the manufacturing errors. In this paper, a new application of screw theory is proposed to analyze the kinematic accuracy of the mechanisms with variations in link lengths and joint clearances. Potential of the proposed approach is demonstrated by its application to the tolerance analysis of four-bar planar mechanisms. Following the intent of the international standard, the deviation from nominal path is quantified in normal direction which is more meaningful from a practical perspective. Applicability of the proposed approach to a spatial mechanism is demonstrated using a serial manipulator with three-revolute joints and having one joint-error. The unified framework presented in this paper can be applied conveniently for closed as well as open loop serial manipulators. Designers can use the results of such analysis to specify the tolerances to achieve a desired degree of kinematic accuracy. © 2013 Elsevier Ltd.

Free-form surfaces and micro features are finish machined by a micro ball end mill by removing steps left behind by flat end mill in the previous operation. For effective machining, off-centre ball end milling is employed in such a way that rubbing zone near ball tip is avoided. After confirming the limits of angular immersion from full-slot experimental results, both down and up off-centre milling experiments are conducted on edges of steps created on a test piece. The micro milling forces in off-centre mode are also investigated theoretically using a mechanistic model that considers the geometry of micro ball end mill and basic mechanics of cutting. The amplitudes of predicted forces match well with experimental values and the deviations in the experimental values arise out of micro level unevenness in the step edge. The up milling with lower transverse force is found to be more suitable for machining of thin features.

The study aims at developing a predictive analytical force model for the micro end-milling operation taking into account the material strengthening as well as the edge radius effects that come into play at the micro level. The mechanistic models for macro end-milling process have been extensively reported in literature and such models predominantly use milling force coefficients which are empirically determined from end-milling experiments. The proposed model for micro end-milling is based on determination of milling force coefficients from fundamental oblique cutting approach. The edge radius effect has been accounted by analyzing the rubbing action similar to the rolling of a cylinder over work surface. Johnson-Cook material model has been modified based on the strain gradient plasticity theory incorporating the increase in material strength with decreasing uncut chip thickness. From the micro orthogonal cutting experiments, a good agreement between the experimental and predicted shear strength values is observed. The force model is validated against measured forces in end-milling experiments carried out on the KERN Evo 5 axis micro machining center. The feed and lateral forces are predicted within 10% deviation on an average. © 2012 Copyright Taylor and Francis Group, LLC.

Coordinate measuring machines (CMMs) equipped with continuous scanning probes are widely used in the measurement of sculptured or freeform surfaces. The complex nature of such surfaces requires suitable sampling strategies to ensure adequate measurement. Sampling strategy involves the identification of number of isoparametric scan lines and their locations over the entire surface. When the number of isoparametric scan lines is assumed, the sampling strategy is expected to distribute them so as to ensure the measurement adequacy. A new sampling strategy has been proposed in the present work, considering the complexity of isoparametric scan lines. Freeform surfaces of varying complexities have been used to compute the effectiveness of the proposed sampling strategy, which is measured in terms of lower positional deviations with fewer isoparametric scan lines. The results obtained are compared with uniform and curvature-based isoparametric lines sampling strategies. Copyright © 2013 Inderscience Enterprises Ltd.

Metal cutting is an important machining operation in the manufacture of almost all engineering components. Cutting technology has undergone several changes with the development of machine tools and cutting tools to meet challenges posed by newer materials, complex shapes, product miniaturization and competitive environments. In this paper, challenges in macro and micro cutting are brought out. Conventional and micro end-milling are included as illustrative examples and details are presented along with discussion. Lengthy equations are avoided to the extent possible, as the emphasis is on the basic concepts.

Aerospace, automobile and medical industries extensively use carbon fabric laminate due to their superior physical and chemical characteristics and, from performance point of view, micro-features are provided on certain components. In this work, an attempt has been made to drill micro-holes in carbon fabric laminate composites using 320 μm diameter carbide drills. Based on a preliminary study, drilling strategy with peck cycle is chosen for through-hole drilling in carbon fabric laminate. Micro-drilling experiments are conducted according to full-factorial design using five levels for both speed and feed with three trials for each condition. Thrust force and torque generated during machining are measured and power law based regression models are developed. Though the material is anisotropic and non-homogeneous in nature, the models developed follow the trend in the experimental results. Delamination damage, roundness error and diameter of these drilled holes are measured and analyzed with variation of the process parameters. The results indicate that the good quality micro-holes can be produced by selecting proper process parameters. © 2012 The Author(s).