John B. Morehouse

Thin-Film PVDF Sensor-Based Monitoring of Cutting Forces in Peripheral End Milling

A sensor module that integrates a thin film polyvinylidene fluoride (PVDF) piezoelectric strain sensor and an in situ data logging platform has been designed and implemented for monitoring of the feed and transverse forces in the peripheral end milling process. The module, which is mounted on the tool shank, measures the dynamic strain(s) produced in the tool and logs the data into an on-board card for later retrieval. The close proximity between the signal source and the PVDF sensor(s) minimizes the attenuation and distortion of the signal along the transmission path and provides high-fidelity signals. It also facilitates the employment of a first principles model based on the Euler–Bernoulli beam theory and constitutive equations of the piezoelectric sensor material to relate the in situ measured PVDF sensor signals to the feed and transverse forces acting on the tool. The PVDF sensor signals are found to compare well with the force signals measured by a platform-type piezoelectric force dynamometer in peripheral end milling experiments.

Thin-Film PVDF Sensor Based Monitoring of Cutting Forces in Peripheral End Milling

A sensor module that integrates a thin film Polyvinylidene Fluoride (PVDF) piezoelectric strain sensor and an in situ data logging platform has been designed and implemented for monitoring of feed and transverse forces in the peripheral end milling process. The module, which is mounted on the tool shank, measures the dynamic strain(s) produced in the tool and logs the data into an on-board card for later retrieval. The close proximity between the signal source and the PVDF sensor(s) minimizes the attenuation and distortion of the signal along the transmitting path and provides high-fidelity signals. It also facilitates the employment of a first principles model based on Euler-Bernoulli beam theory and the constitutive equations of the piezoelectric sensor material to relate the in situ measured PVDF sensor signals to the feed and transverse forces acting on the tool. The PVDF sensor signals are found to compare well with the force signals measured by a platform type piezoelectric force dynamometer in peripheral end milling experiments.Copyright

Predictive modeling of machining residual stresses considering tool edge effects

The surface integrity of machined components is defined by several characteristics, of which residual stress is extremely important. Residual stress is known to have an effect on critical mechanical properties such as fatigue life, corrosion cracking resistance, and dimensional tolerance of machined components. Among the factors that affect residual stress in machined parts are cutting parameters and tool geometry. This paper presents a method of modeling residual stress for hone-edge cutting tools in turning. The model utilizes analytical cutting force models in conjunction with an approximate algorithm for elastic–plastic rolling/sliding contact. Oxley’s cutting force model is coupled with a slip line model proposed by Waldorf to estimate the cutting forces, which are in turn used to estimate the stress distribution between the tool and the workpiece. A rolling/sliding contact model, which captures kinematic hardening, is used to predict the machining residual stresses. Additionally, a moving heat source model is applied to determine the temperature rise in the workpiece due to the cutting forces. The model predictions are compared with experimental data for the turning of AISI 52100. Force predictions compare well with experimental results. Similarly, the predicted residual stress distributions correlate well with the measured residual stresses in terms of magnitude of stresses and depth of penetration.

Interfacial Burr Formation in Drilling of Stacked Aerospace Materials

Interfacial burr formation during through-hole drilling in stacked aluminum sheets is a common problem in aircraft assembly operations. Burrs formed at the interface of the sheets are removed through non-value added de-stacking and deburring operations that increase the overall assembly time and costs. This paper presents experimental work aimed at understanding the impact of drilling parameters including drill geometry, cutting conditions, clamping configuration and drill wear on interfacial burr formation. Specific conclusions regarding the influence of these parameters on burr sizes and drilling forces are presented.

On-Line Monitoring of End Milling Forces Using a Thin Film Based Wireless Sensor Module

A sensor module that integrates a thin film PVDF piezoelectric strain sensor and a wireless data processing/transmitting platform has been designed and implemented for wireless monitoring of the feed force in the slot end milling process. The module, which is mounted on the tool shank, measures the dynamic strain produced in the tool and transmits data wirelessly to the receiver connected to a data acquisition computer. A first principles model based on the Euler-Bernoulli beam theory and constitutive equations of the piezoelectric sensor material is used to transform the wirelessly obtained data into the feed force acting on the tool in a slot milling operation. The wireless PVDF sensor signal is found to compare well with the expected (or theoretical) sensor signal computed from the measured feed force in slot milling experiments.Copyright

Design of thin-film polyvinylidene fluoride sensor rosettes for isolation of various strain components

Thin-film polyvinylidene fluoride piezoelectric sensors have long been recognized as a promising alternative to traditional metal foil strain gauges in applications where only dynamic or quasistatic signals are of interest. Compared to metal foil strain gauges, polyvinylidene fluoride sensors feature high sensitivity, high dynamic range, and broad frequency bandwidth. However, transverse sensitivity of the polyvinylidene fluoride sensor is higher than that of a metal foil strain gauge, making it more difficult to isolate a particular strain component or a deformation mode when the host structure is under complex loading. In addition, polyvinylidene fluoride films are sensitive to changes in ambient temperature due to the pyroelectric effect. In this article, three temperature-compensated polyvinylidene fluoride sensor rosette designs are proposed for isolating specific strain component(s) and deformation mode(s) of interest. First-principles based models are derived to relate the polyvinylidene fluoride sensor rosette output to the actual elastic strain component of interest. Experimental validation is conducted to verify the proposed models and to compare the performance of the polyvinylidene fluoride sensor rosettes with their metal foil strain gauge counterparts.

A METHODOLOGY FOR ECONOMIC OPTIMIZATION OF PROCESS PARAMETERS IN CENTERLESS GRINDING

Centerless grinding is an abrasive machining process commonly used in the aerospace and automotive industries for shaping axisymmetric components that require a high dimensional accuracy and a smooth surface finish. For this high volume manufacturing operation, process parameters have historically been selected conservatively using machining data handbooks or on a trial-and-error basis according to operator experience without explicit consideration of how the selected settings affect the productivity or cost of the operation. To improve operation efficiency, a science-based approach for selecting the optimum process parameters must be developed to replace traditional industrial practices. In this article, a methodology combining several analytical and experimental techniques is presented for optimizing the key process parameters in plunge centerless grinding of Inconel 718 and Ti-6Al-4V superalloy fasteners in two phases: (i) modeling of process constraints using experimental design and statistical regression, and (ii) determination of optimum grinding conditions in the feasible operating region using a simulation algorithm based on classical machining economics theory. The results show that the implementation of optimum material removal rates can lead to an appreciable reduction in the cost of the operation while satisfying the constraints imposed on the machine tool and the workpiece quality.

Handling constraints for manufacturing process optimisation using genetic algorithms

Handling constraints is a common challenge to all optimisation methods. To no exception is the planning and optimisation of manufacturing processes that often involves a number of constraints reflecting the complicated reality of manufacturing to which the pursuit of the best operation condition is subject. Mathematical models describing todays manufacturing processes are generally discontinuous, non-explicit, and not analytically differentiable; all of which renders traditional optimisation methods difficult to apply. Genetic Algorithm (GA) is known to provide an optimisation platform method capable of treating highly nonlinear and ill-behaved complex problems, thereby making it an appealing candidate. However, several issues in regard to the handling constraints must be rigorously addressed in order for GA to become a viable and effective method for manufacturing optimisation. In this paper, a new constraint handling strategy combined with (α,μ)-population initialisation is proposed. Twelve numerical test cases and one surface grinding process optimisation are presented to evaluate its optimisation performance.