Applied Mechanics and Materials Vol. 197

Abstract: We perfect Product-Process Matrix theory of Hayes and Wheelwright and propose a more generalized theoretical strategic model. In this paper, the data from International Manufacturing Strategy Survey in 2009 is used to examine the new model by hierarchical regression analysis. The results show that, different matches between flexible production capacity (manufacturing strategy), speed of product update and product customization (market strategy) will lead different business performance. The results improve the Product-Process Matrix theory, and provide theoretical and practical guidance to manufacturing enterprises for strategies choice.

Abstract: Small data set approach is used for the estimation of Largest Lyapunov Exponent (LLE). Primarily, the mean period drawback of Small data set was corrected. On this base, the LLEs of daily qualified rate time series of HZ, an electronic manufacturing enterprise, were estimated and all positive LLEs were taken which indicate that this time series is a chaotic time series and the corresponding produce process is a chaotic process. The variance of the LLEs revealed the struggle between the divergence nature of quality system and quality control effort. LLEs showed sharp increase in getting worse quality level coincide with the company shutdown. HZ’s daily qualified rate, a chaotic time series, shows us the predictable nature of quality system in a short-run.

Abstract: When thin metal plates are excited by a high-power ultrasonic transducer, superharmonic and high-order subharmonic vibration phenomena of the plates are observed in our experiments. However, the nonlinear mechanism in the system is still not fully understood. In this paper, a finite element model is established based on the experimental conditions and numerical simulations are performed to explore the generation mechanism of the nonlinear vibration. By comparing the waveforms and frequency spectra of the vibration velocity of the plate to these of the contact force between the ultrasonic horn tip and the plates, it can be found that waveform distortion of the contact force is the main reason for generating the superharmonic vibration, while the intermittent contact-impact between the horn tip and the plate is the reason for subharmonic vibration in the plate. The FEM simulation results can explain reasonably the observed experimental phenomena, which are useful to help to improve the effects of the nonlinear phenomena occurred in ultrasonic processing.

Abstract: Closed repetitive gapped sequential pattern mining has been gained more and more attention in recent years, in this paper, we propose a novel method MRCGP(mining closed repetitive gapped sequential pattern based on repetition linked WAP-Tree). In the first step of MRCGP, the given sequential database is transformed into a new database in which every item is expressed by its landmark; then a positional information table(PIT) which includes all of the position information of 1-frequent items is constructed, all of the repetitive gapped 2-sequential patterns of different items (RPDI) can be obtained through searching the positional information table; following, a repetitive linked web access pattern tree (RLWAP-Tree) is built, in RLWAP-Tree, the 1-frequent items are stored as header table, the items in header table will be linked to their same items which appear earliest in each sequence corresponding to RLWAP-Tree with solid line, all of the items in RLWAP-Tree are linked to their same items in the same sequences with broken line; through mining projection tree of the existing repetitive gapped pattern recursively, we can obtain the repetitive gapped sequential pattern; at the end, we get the closed repetitive gapped sequential pattern by checking inclusion relation of any two patterns. The experiment result shows MRCGP has better time efficiency.

Abstract: Flow-induced vibration (FIV) of a head gimbals assembly (HGA) in hard disk drives (HDDs) limits the positioning accuracy of magnetic head in the HGA for higher HDD magnetic recording density. The pressure fluctuations characterize turbulent fluctuations exciting the HGA off-track vibration (HGA-OTV). In this paper, experimental studies have been carried out to investigate the spectrum characteristics correspondence between pressure fluctuations around an HGA and the simultaneous HGA-OTV under different HDD rotation speeds. A practical and effective experimental setup has been implemented to enable the simultaneous measurements on both the pressure fluctuation and HGA-OTV signals, where pressure fluctuations are measured with a pressure transducer through a small hole on the HDD top cover and the direct HGA-OTV signals are detected through a laser Doppler vibrometer. Results under conditions of three different HDD rotation speeds of 7200, 9000, 10800 rpm have been investigated and compared. It is shown that the HGA off-track vibration spectra are highly associated with those of the pressure fluctuations in terms of principal peaks in four frequency bands around 1.8 kHz, 2.5-3.5 kHz, 7-7.5 kHz and 11.5-12.5 kHz. With increasing HDD rotation speed, it is shown that the spectrum magnitudes of both the pressure fluctuation and the HGA off-track vibration increase correspondingly, while the principal peak positions in spectra of either pressure fluctuation or the HGA off-track vibration always hold the line. This study demonstrates a causal nexus from the pressure fluctuation to the HGA off-track vibration and suggests the feasibility of controlling the HGA-OTV through suppression of pressure fluctuations around the HGA.

Abstract: Laser tube bending is a kind of plastic forming method with high flexibility, and is suitable for the low ductility material and thin thickness tube. This paper proposes a systematic scheme for three-dimensional tube bending, which forms the tube by varying the bending position and bending direction continuously. The bending part is simplified as a three-dimensional curve and then the curve is divided into segments and substituted with line sections. The scheme takes the angle between two adjacent segments as the laser bending angle at each bending position and the angle between two adjacent bending plane as the variation of bending direction. The effectiveness of proposed scheme is verified with the forming of a helical tube experimentally. The dimension errors of the formed helical tube are 6.25% in diameter and 7.59% in pitch respectively.

Abstract: The high resolution curves could be transformed to low resolution curves by wavelet analysis. A new method for boundary preserving of the low resolution curve by modify the knot vector and the control points is represented. The definition of the deviation curve is proposed, and the discrete deviation curve method is represented to estimate the deviation between the low and high resolution curves. Wavelet-based tool path is generated for the contour NC machining by using the low resolution curves as the references. The experimental results demonstrate that the wavelet-based tool path has less information and is smoother than the traditional method’s. So it could reduce the calculating amount and improve the machining efficiency.

Abstract: The boundary-layer theory explains very well the steady-state flow over a flat plate at zero incidence angle known as the Blasius flow. It is long known that the appearance of boundary layers is not restricted to the canonical problem of the motion of a body through a viscous fluid. Several other technologically important sources of boundary-layer behavior are the flows behind expan- sion and shock waves travelling over smooth surfaces and the flow above a moving conveyor belt. In fluid mechanics, to obtain the multiple solutions in ordinary differential equations is always a concerned and difficult problem. In this paper, a novel RNA genetic algorithm (NRNA-GA) inspired by RNA molecular structure and operators is proposed to solve the parameter estimation problems of the multiple solutions in fluid mechanics. This algorithm has improved greatly in precision and the success rate. Multiple solutions can be found through changing accuracy and search coverage and multi-iterations of computer. At last, parameter estimation of the ordinary differential equations with multiple solutions is calculated. We found that the result has great accuracy and this method is practical.

Abstract: A V-norm Decoupling internal model control (IMC) method with filters based on inverted decoupling for multivariate stable object is proposed in this paper. The actual industrial process is very difficult to obtain an accurate model, which makes the control effect not satisfactory. To solve this problem, the V-norm decoupling controller is designed on the basis of the inverted decoupling, and a filter is added in front of the controller to reduce coupling and increase robustness. Compared with traditional multivariable controller designed method, the method of designing the internal model controller in this paper is simpler and less calculation. Finally, the Wood/Berry model is taken as the simulated object to verify the controller design method is reasonable. The results show that V-norm decoupling internal model controller method is effective and feasible, even the system model is mismatched.

Abstract: Reducing energy usage is an essential consideration in sustainable manufacturing. This paper presents a multi-objective optimization model based on the trade-offs between sustainability, productivity and machining quality, which aims for reducing the cutting energy in machining processes. Three objectives, surface roughness, material removal rate and energy consumption, are simultaneously optimized. Additionally, a method to determine the weight factors is proposed to calculate grey relational grade of multiple responses. Experiment used Taguchi design method was performed to verify the optimization model and promising results reducing the energy consumption of machining processes were achieved.