Sivasrinivasu Devadula

Kerf profile generated by abrasive waterjet (AWJ) machining process has always been an interesting area as it dictates the quality of the part. However, due to the non-deterministic nature of the process, it is a challenging task to predict it. On the other hand, understanding and controlling the kerf profile in multi-layered structures (MLSs) is a further difficult task as various layers made of different materials respond to erosion in a different manner and results in a completely different kerf shape (barrel or x-shaped kerf profile) due to the material removal mechanisms dependency on the material property of the specific layers, jet divergence and position of specific layer. Therefore, it is important to understand and develop predictive models of resulting kerf profile in MLSs so that they can be used in controlling the accuracy of the resulting kerf which in turn dictates the final part accuracy. The attempts in this direction are very limited although some modeling efforts are reported in homogeneous materials (metals, ceramics). For the first time, an analytical model for predicting the kerf profile generated in MLS machining with AWJ was presented in this research work. Discretized form of Hashish model was used for determining depth of cut. The effect of jet divergence from the experimentally obtained values, upon passing through the upper layer has been considered. The developed predictive model was validated by the kerf shapes obtained from the experimental trials on metal-adhesive-rubber MLS. Kerf profiles obtained from the simulations have captured the resulted convergent-divergent (X-shaped) profile, while cutting metal-rubber laminate composite, effectively. Furthermore, the effectiveness of the proposed analytical model was demonstrated by generating the various kerf shapes generated at various jet traverse rates.

The CMS experiment will change it’s silicon tracker completely during phase-II upgrade. There is need to develop light and high precision and durable mechanical structure for silicon modules. The prime purpose of this should also be reducing material in the silicon tracker detector. The group at IIT Madras is involved in R&D of production of this structures. We have produced high precision bridge made of AL-CF material and carbon fiber stiffener.

The CMS experiment will change its silicon tracker completely during phase-II upgrade. There is need to develop light and high precision and durable mechanical structure for silicon modules. The prime purpose of this should also be reducing material in the silicon tracker detector. The group at IIT Madras is involved in R&D of production of this structures. The prime purpose of this should also be reducing material in the silicon tracker detector. We have produced high precision Al-CF bridges, stumps and Pipe connector 47 degrees for HgCAL detector.

In high-value industries (aerospace, automobile, defense, etc.), various applications like assembly, engine cylinder bores, etc., require hole making with target size/shape, tolerances, and surface quality. The present study investigates the potential of the micro-AWJs (df = ~300 µm) in trepanning holes by considering Aluminum 6061-T6 alloy, as a case study. However, the stochastic, non-deterministic, and flexible nature of the AWJs result in holes with deviated form and dimensional characteristics that lead to part rejection. As the waterjet pressure (P) is the most significant parameter in dictating jet energy, material removal, and productivity, trepanning studies were carried out to investigate the waterjet pressure’s influence on the hole form, dimensional, and surface characteristics. Furthermore, the effect of P on productivity measures in terms of material removal rate (MRR) is investigated. From the results, the edge radius of the hole at the entry plane improved with a higher P by 30.19%. With the increase in the P, the hole diameter deviation from the nominal diameter and circularity error decreased by 10 and 58.88% at the top plane and 11 and 65.2% at the bottom plane. Cylindricity error and taper angle decreased by 11.84 and 15.23% at higher P. Uncut material size and burr length at the exit plane decreased by 43.48 and 24.77% at higher P and the MRR increased by 52.71%. Surface morphology was studied concerning the pressure, with the increases in the jet pressure surface roughness improves, and waviness increases. Micrographs were taken with the help of HRSEM to analyze the effect of P on material removal mechanism, it is observed that at lower P abrasive embedment is a visible phenomenon.

This paper presents a neuro-genetic approach proposed to suggest the process parameters for maintaining the desired depth of cut in abrasive waterjet (AWJ) cutting by considering the change in diameter of focusing nozzle, i.e. for adaptive control of AWJ cutting process. An artificial neural network (ANN) based model is developed for prediction of depth of cut by considering the diameter of focusing nozzle along with the controllable process parameters such as water pressure, abrasive flow rate, jet traverse rate. ANN model combined with genetic algorithm (GA), i.e. neuro-genetic approach, is proposed to suggest the process parameters. Further, the merits of the proposed approach is shown by comparing the results obtained with the proposed approach to the results obtained with fuzzy-genetic approach [P.S. Chakravarthy, N. Ramesh Babu, A hybrid approach for selection of optimal process parameters in abrasive water jet cutting, Proceedings of the Institution of Mechanical Engineers, Part B: J. Eng. Manuf. 214 (2000) 781-791]. Finally, the effectiveness of the proposed approach is assessed by conducting the experiments with the suggested process parameters and comparing them with the desired results. © 2007 Elsevier B.V. All rights reserved.

Two primary heat-generation sources in motorized machine tool spindles are (i) friction in spindle bearings, and (ii) losses in the motor components. The difference in heat generation and heat dissipation rate from the high-speed motorized milling machine tool spindle cause structural deformation, resulting in part inaccuracy. Several research groups used thermo-mechanical and data-based modelling of high-speed motorized spindles to predict and compensate thermal deformation and improve machining accuracy. In real-time thermal compensation, selection of optimal number of thermal hotspots to place the temperature sensors on the spindle is crucial. The present work proposes an approach to select the optimal number of temperature sensors that can be employed to predict the thermal deformation while maintaining required prediction accuracy. For this purpose, the experiments were conducted to evaluate the thermal heat flux across the spindles at different rotational speeds. Furthermore, a finite element analysis (FEA) was performed to simulate the thermal deformation at the tool center point (TCP). The input parameters considered for predicting the simulated deformation were different temperature sensor data on the motorized spindle and the ambient temperature. This work uses the thermal deformation results obtained from FEA to build an improved second-order polynomial regression model. The model reduces the requirement of temperature sensors from three to one to predict the TCP deflection. Results show that the proposed model accuracy was 86.72% with two temperature sensors and 85.99 % with one temperature sensor. It indicates that one temperature sensor is sufficient to predict the TCP deflection with a compromise of 0.73% prediction accuracy level.

Abrasive waterjet (AWJ) is an effective tool for manufacturing parts from multi-layered structures (MLSs) due to its capability in machining a wide range of materials. However, the challenge in employing AWJ in producing the desired kerf geometry in MLS can be attributed to the complex nature of the jet's interaction with multiple layers that possess different material properties. Hence, a model that captures the interaction of the jet with MLS, and predicts the whole kerf geometry is required to gain control over the kerf quality. On the other hand, the kerf generated in a layer is affected by the presence of preceding-/following- layers. In this context, it is essential to develop a comprehensive model for the prediction of kerf profile during the penetration of the jet in each layer. Although, several models exist to predict the process response (erosion depth, top (wt), and bottom kerf width (wb), kerf taper), very limited models available on kerf profile prediction. Further, neglecting the actual jet characteristics limits their ability to predict accurately. By considering the above, this work proposes a model for the prediction of the kerf geometry (profile and characteristics) in a single layer of MLS along with its kerf characteristics apart from considering the non-linearities, such as jet characteristics and the effects of AWJ process parameters. A discretized form of the jet, abrasives mass flow distribution, and their velocity in the jet plume to realize a more realistic model for predicting kerf geometry. Further, a new parameter, 'depth of damaged region’ was defined towards realizing the wt. The model was evaluated by comparing the kerf geometry formed on mild steel (MS) and aluminum (Al) materials by using root mean square and mean absolute error. The proposed model was found to predict the kerf geometry accurately.

Machining complex surfaces on difficult-to-cut materials by conventional methods is challenging due to the issues that arise from both the ‘freeform surface generation’ and the ‘machining difficult-to-cut materials’. On the other hand, abrasive waterjets (AWJs) have proven their unique capabilities in machining a wide range of materials and 3D shapes by maneuvering the jet strategically. In realizing 3D shapes through AWJ milling, the cross-sectional profile (CP) of the kerf, i.e. (i) trench — formed in a single pass erosion and (ii) cavity — formed in an overlapped pass erosion, need to be predicted apriori. However, the stochastic and aggressive behaviour of the AWJ, and the lack of complete understanding of the kerf generation, make the accurate prediction of its CP a difficult task. Furthermore, the cavity generated (by overlapping two trenches) is not a simple linear combination of trenches generated in two single AWJ passes. Also, the modelling efforts that consider both the dynamic jet characteristics and the non-linearity in the kerf formation are very limited. In this work, analytical models are proposed to predict CP the kerf (trench and the cavity) milled by the AWJs by considering the experimental understanding gained on the kerf generation in single and overlapped pass erosion. The modelling strategy evaluates the local erosion volume and sweeps this over the CP along the top width of the kerf. This strategy enables the incorporation of region-wise physical phenomenon in the material removal. Furthermore, it considers the (i) aggressive and stochastic nature of the AWJ, and (ii) particle erosion theories applicable to ductile materials, which pose multiple challenges during conventional machining. The model developed for the trench considers the effective jet divergence, spatial abrasive mass- and velocity-distributions in the jet plume, as inputs. Towards capturing the non-linearity in the cavity generation, the non-flat surface from the previous pass and its effect on the variation of local particle impact angles, uneven jet deflection during subsequent passes around the jet axis, and the degree of overlap were considered. From the experimental validation, it was observed that in the single pass and overlapped passes at different degrees of overlaps (5 %–80 %), the proposed model predicts the kerf geometry with a maximum mean absolute error (MAE) of 36 μm and 49 μm, and the maximum depth of CP with a maximum error of 7 % and 11 %, respectively.

Abrasive waterjet (AWJ) can be used to realize holes of any size and shape in difficult-to-machine ductile materials with negligible heat-affected zone by simply changing the jet path. In this study, the influence of various process parameters, such as waterjet pressure (P), jet traverse speed ((Formula presented.)), abrasive mass flow rate (m a) on the AWJ-trepanned hole’s geometrical features (diameter, taper angle, profile), form characteristics (circularity error, cylindricity error), quality measures (damage region, edge radius, burr formation, uncut material, surface morphology), and material removal mechanism in Al-6061 alloy is studied. The results show that higher P and m a at lower (Formula presented.) are desirable for achieving nominal geometrical features, minimal form error, burr length, and uncut material. Damage region reduces with the decrease in P and m a at higher (Formula presented.). Edge radius reduces with the increase in P at lower (Formula presented.) and m a. The micrographs showed that the initial damage region is uniform at higher P and lower (Formula presented.). Better surface quality is obtained at higher P and m a as lip formation and material pile-up are minimum. Material fracture and cracks in the vicinity of the burr are observed. Based on the mean response analysis, near-optimal parameters are suggested for efficient trepanning.

Abrasive waterjet technology is favored over solid cutting tools for cutting of multi-layered structures in view of its non-contact nature and its ability to cut a wide range of materials. However, the stochastic nature of abrasive water jet (AWJ) interacting with a multi-layered structure (MLS) produces a non-uniform kerf geometry. This non-uniformity depends on the characteristics of jet i.e. jet energy, the duration of interaction of jet with the material, and the nature of material exposed to the jet during cutting. This paper attempts to cover a study that systematically analyses the geometry of kerf generated in MLS and a stack of multiple materials with each material having different mechanical properties. It also covers a study to analyse the role of interfacial adhesive layer on kerf profile variation, and the preferential orientation of multi-layered structure and stacked materials, with its top layer, having an appropriate mechanical resistance (MR), in order to arrive at a strategy to present the structure or a stack of materials to AWJs for producing near uniform kerf profile. Hence, AWJ cutting experiments were carried out over a single- and double- layered structures (SLSs, DLSs) with two different materials such as aluminum (Al), mild steel (MS), which showed a completely different kerf geometry when these materials are stacked in different ways. Stacking of these materials in different ways produced kerf of different geometry not only in the materials but also at their interface. This systematic study enabled to suggest the correct presentation of MLS and also a stack of multiple materials with a suitable material in top layer, to AWJ, for producing near uniform kerf in them. Further, this study also suggested several hypotheses like the importance of relative MR of adjoining layers, critical jet traverse rate, pseudo focusing nozzle, and the choice of layer placement in producing near uniform kerf on MLS and a stack of materials, so as to minimize the efforts in post machining of AWJ cut surfaces. Finally, the relevance of the proposed hypotheses was validated by analyzing the kerf formed over MS-rubber-MS and rubber-MS-rubber configured three-layered structure.