Innovative Fixturing and Tooling

The production of freeform components is challenging, not only from the point of view of process optimization but also when it comes to the selection and design of the fixturing systems. Currently, most commercially available fixturing systems are difficult to conform to geometrically complex components; while the systems that manage to provide industrially feasible solutions (such as encapsulation techniques) present several limitations (e.g., high complexity, limited reliability, and risk of elastic deformation of the part). In this context, the present work proposes a simple, yet efficient, concept of a fixture capable of holding complex components through the use of compliant/deformable diaphragm elements. The fundaments of this innovative system (i.e., freeform diaphragm-based fixturing system) have been simulated through an experimentally validated finite-element (FE) model, with results showing a good agreement between numerical and measured data (displacement average error av¼4.04%). The main interactions of the system with a workpiece (e.g., contact area and clamping force) have been numerically and experimentally studied, confirming the system’s capacity to generate distributed clamping forces in excess of 1000 N. Based on the modelling activities, an advanced prototype for holding a “generic” freeform component was developed. Using this prototype, a repeatability study then showed the capacity of the system to deterministically position and hold complex geometries. Finally, the proposed fixturing system was thoroughly evaluated under demanding machining conditions (i.e., grinding), and the results showed the ability of the fixture to maintain small part displacement(dx<10 lm) when high cutting forces are applied (Max.FR¼1021.24 N). Design limitations were observed during the grinding experiments, and the lineaments are presented in order to develop improved further prototypes. Overall, the proposed fixturing approach proved to be a novel and attractive industrial solution for the challenges of locating/holding complex components during manufacture.

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Milling of large thin walled casings with complex features needs appropriate damping solutions toachieve required workpiece surface quality when utilising aggressive machining parameters. In thispaper a novel surface damping solution composed of a thin flexible layer mounted with distributeddiscrete masses attached with viscoelastic layer is presented. Damping of higher frequencies through aflexible layer and subsequent lower frequencies through added masses enables damping over a widebandwidth. Finite element modelling and validation of the proposed solution showed a significantdamping of workpiece and corresponding reduction in machining vibration by more than four times.

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Chatter free thin wall machining requires knowledge of the dynamics of a machine-tool system and workpiece either for designing damping solutions or for modelling impact dynamics. Previous studies on thin wall milling mostly focussed on stability studies. However studies on the interaction between the tool and workpiece responses in thin wall machining are scarce in the literature. In this work, the coupled dynamic response of tool and workpiece is presented both for an open (thin wall straight cantilever) and for closed (thin wall ring type casing) geometry structures. Experiments were carried out for different tool overhangs and depths of cut and the machining vibration signal was analysed in time–frequency domain to study the interaction, i.e. coupling, of tool–workpiece dynamic response at various cutting tooth engagement/idle times. The findings from this study highlight the importance of tool's frequency, particularly torsional and first bending modes, in impact dynamics of thin wall milling. Moreover, the differences in dynamic response interaction between a cutting tool and thin wall plate and a cylinder are identified. While the analysis of the open geometry structure showed the presence of tool and workpiece responses for any depth of cut, results on closed geometry structure exhibited a complete dominance of tool mode at higher depths of cut. These findings are of critical importance in understanding the impact dynamics in thin wall milling and also of effectiveness of passive damping solutions.

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The fixturing of large segmented-ring assemblies is of importance to a number of key high value industries such as the aerospace and power generation sectors. This study examines methods of optimising the circularity of segmented-ring assemblies, and how the manufacturing variation within each element (i.e. segment wedge) contributes to overall assembly variability. This has lead to the definition of two original assembly methodologies that aim to optimise an assembly, so that circularity errors are minimised for a given set of components. The assembly methods considered during this study include a radial Translation Build (TB) and a Circumscribed Geometric (CG) approach, both of which are compared to a traditional Fixed Datum (FD) build method. The effects of angular, radial, parallelism/flatness and chord length variability within the component geometry, and their effect on the circularity of the final annular assembly are examined mathematically and experimentally. Furthermore, the inherent loss of assembly circularity due to differences between component and assembly sagitta is also considered, along with the stepping caused by dissimilar adjacent component radii as a result of manufacturing variation. Experimental results show that the CG build method offers a significant improvement in circularity in most situations over the benchmark FD build method. This contrasts the TB results that proved to be the least consistent in terms of circularity, but better in the control of angular breaking errors within the assembly.

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Adhesive fixture systems have several advantages over conventional fixturing methods due to the following key capabilities:(1) can hold components with increased workpiece accessibility for processing, (2) can hold delicate componentswhile avoiding excessive clamping forces, and (3) can hold and support complex or variable geometry parts.

The developmentof high-strength structural adhesives that can be rapidly and controllably cured now offers much greater scopefor holding complex parts than the traditionally used low-strength adhesives, waxes, or low-melt alloys currently used inniche applications and ad hoc fixture systems. This article first evaluates the workholding performance, capability, andsuitability of an ultraviolet-activated adhesive fixture system to hold aerospace-type components; this includes quantifyingthe mechanical properties of the adhesive bond and assessing the influential factors (surface finish, contamination, geometriesof bonded surfaces, and adhesive-curing time).

Then the article presents concepts of adhesive fixture system forrapid location and bonding/de-bonding for enhanced accessibility on machine surfaces. A set of fixture demonstratorsand their effectiveness are evaluated in terms of maximum reaction forces, dynamic performance, and ease of use. Fromthis research, it becomes apparent that the adhesive fixture system approach provides new opportunities for workholdinggeometrically complex components for high-demanding applications (e.g. manufacture of aerospace parts).

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