G.H. Lim

Pricing used products for remanufacturing

Remanufacturing is one of recovery options for used products. As remanufacturing requires a continuous supply of used products, the economic incentive is required to attract customers to return their used products (called cores) and the problem of pricing a core becomes an important issue. Such a pricing problem is analogous to pricing an option, which can be used to sell the remanufactured cores (called core products). As sales price of core products follows a geometric Brownian motion, we propose a model here to evaluate the acquisition price of cores. This model links core acquisition price with the sale price of core product but assumes other costs such as logistics and remanufacturing to be deterministic. We have presented a numerical example to show its applicability. Since the model proposed here is generic, it is believed that the proposed model can be used in setting the core prices in many situations.

Vibration reliability characterization of PBGA assemblies

Abstract Generally, the low-cycle fatigue induced by thermal cycling is the major concern in the reliability of surface mount technology for electronic packaging, but the high-cycle fatigue induced by vibration can also contribute significant effect, especially for applications in automobile, military, and avionic industries. To assess vibration induced fatigue failures, the dynamic properties of printed circuit board (PCB) assemblies play a very important role. In this paper, the dynamic properties of a plastic ball grid array (PBGA) assembly were characterized by using experimental modal testing and finite element analysis. The bare PCB and PCB assembly with PBGA modules mounted were tested and analyzed separately, so that the influence of PBGA modules on the PCB’s dynamic properties could be identified. It was found that mounting PBGA modules to PCB increased the stiffness of the PCB. Results of constant-amplitude vibration reliability testing of the PBGA assembly are also reported. It was found that the PBGA assembly was vulnerable to vibration, and fatigue failure always occurred at the corner solder balls of the PBGA module.

Reliability of PBGA assemblies under out-of-plane vibration excitations

Vibration testing of plastic ball grid array (PBGA) assemblies to assess the reliability of the solder joints under external vibration excitations was reported in this paper. The test vehicle was an assembly with four 256 I/Os PBGA modules assembled on a printed circuit board (PCB). During the test, the assembly was clamped at two opposite sides to a vibration shaker. It was found that the dynamic displacement of the assembly under external out-of-plane sinusoidal vibration excitations was highly nonlinear. In order to determine the reliability of the solder joints, the resistance of each module was continuously monitored during the test. Under an out-of-plane sweep sinusoidal excitation with a constant acceleration amplitude of 2.5 G within a narrow frequency band around the fundamental resonant frequency of the assembly, the first-time-to-failure and mean-time-to-failure of the solder joints were found to be 0.46 and 6.19 million vibration cycles respectively. The failed solder joints were at the corners of the PBGA module. Most failures were due to cracks near the copper pad on the PCB side.

An approach to design reverse logistics networks for product recovery

Shortened product lifecycle has resulted in increasing number of obsolete products, leading to growing environmental concerns. Product recovery, which is a way of reducing waste, is gaining popularity in recent years. To effectively implement product recovery activities, a reverse logistics network design that can facilitate reverse flow of used products in an efficient way is required. In this paper, an approach to design reverse logistics network for product recovery, incorporating multi-objective functions, multi-period planning horizons, and uncertainties is presented. This approach consists of both mathematical and simulation models; the former utilizes mixed integer programming (MIP) to model the multi-objective, multi-period problem of network design, whereas the latter is employed to incorporate uncertainties. Due to its complexities, spanning-tree based genetic algorithms are utilized to find non-dominated solutions. The preferred non-dominated solutions are simulated under several scenarios of uncertainties to determine the best-preferred reverse logistics network design.

Experimental modal analysis of PBGA printed circuit board assemblies

In order to understand the dynamic properties and develop a valid finite element model of a plastic ball grid array (PBGA) PCB assembly, a series of experimental modal tests have been conducted and reported in this paper. Firstly, the purpose and importance of conducting these experimental modal tests are discussed. Secondly, detailed test results of our PBGA PCB assembly are presented, which can serve as a valuable reference for those who are interested in the vibration fatigue reliability of PBGA PCB assemblies. Lastly, some factors which have an important influence on the modal test results of the PCB assembly are discussed.

Feature Extraction, Optimization and Classification by Second Generation Wavelet and Support Vector Machine for Fault Diagnosis of Water Hydraulic Power System

Abstract The work described in this paper investigates the fault diagnosis of water hydraulic motor by the optimization and automatic classification of the feature values. The second generation wavelet for the vibration signals analysis of the water hydraulic motor was proposed to extract the feature values. The new optimization method by bi-classification support vector machine (SVM) was proposed to select the optimal feature values based on a rank criterion and the algorithm was developed here. In order to classify the conditions of the pistons used in the hydraulic motor, a two-level structure based on the multi-classification was developed in this work. The multi-classification method of SVM for the fault diagnosis of a piston crack was investigated. The winner-takes-all scheme was studied. The results of the classification were found to be successful.

Fault diagnosis of water hydraulic actuators under some simulated faults

Abstract Water hydraulics captured the imagination of engineers some 2500 years ago and recently it has revived to become a powerful alternative in areas where the environment and health are of great concern. Previously, this field of knowledge suffered some setbacks as technology was still at its developing stage, but with better tolerances and the availability of better materials, this technology is now a reality. This paper focuses on the fault diagnosis of the condition of hydraulic actuators working on the principle of tap water hydraulic power systems. Two common actuators were explored, namely a water hydraulic cylinder and a water hydraulic axial piston motor. Possible real-life faults were simulated on the actuator’s internal component. The cylinder was operated with worn piston or rod seals whereas the motor has worn capstan and piston shoes in place. These actuators were operated to capture their unique vibration signals in their faulty states to be compared with their ‘healthy’ condition state. Both actuators were loaded in steps for trend observation in the vibration signatures. Results show that, in general, there is a change in vibration signals, flow rate and average operation duration when more load is added to the actuators. If a fault has occurred internally, it will also correspond to another change in the above parameters in the spectra plotted. With this knowledge, LabVIEW software can be written to set warning levels that will trigger an alarm when a fault is impending.

Test and reliability analysis of PBGA assemblies under random vibration

To understand the high-cycle reliability of plastic ball grid array (PBGA) interconnections under external random vibration loading, a series of vibration test of PBGA assemblies were conducted. The test vehicle has four PBGA modules assembled on a printed circuit board. The assembly was clamped at two opposite sides on a fixture, which was bolted to a vibration excitation. Firstly, the dynamic properties of the assembly under external random vibration excitation were characterized. The resonant frequencies of the assembly were identified, and the maximum dynamic deflection was estimated. Then the reliability test were carried out. In the reliability tests, the electrical resistance of PBGA modules was continuously monitored, so that any failure could be detected. This paper describes the test procedures, and shows the typical vibration fatigue failures in the PBGA interconnections. Test results will be analyzed in detail.

Designing reverse logistics network for product recovery

Shortened product life cycles result in increasing number of obsolete products, with adverse environmental impact. Manufacturers are facing increasing pressures from consumers and government regulators to become environmentally responsible, and have begun to setup networks to implement product recovery. This paper proposes an approach to design reverse logistics network for discrete product recovery, considering multiple objective functions (maximising net revenue and minimising environmental impact), multi-period planning horizon and uncertainty. The approach makes use of both optimisation and simulation models: mixed integer programming (MIP) to model the multi-objective, multi-period problem of network design, and simulation to handle uncertainty. Spanning-tree based genetic algorithms are utilised to find non-dominated solutions for the multi-objective model, and preferred non-dominated solutions are re-evaluated under several scenarios of uncertainty to determine the best-preferred network design. The approach is applied to a case study of part recovery implementation at a computer manufacturer.

Testing and evaluation of water hydraulic components by acoustic emission and wavelet analysis

In condition monitoring and fault diagnosis of machinery, vibration analysis is the major method and wavelet analysis is widely implemented. The acoustic emission (AE) method is another important and effective signal in fault diagnosis of mechanical systems. In this paper, the AE signal is applied to diagnose the piston condition of the water hydraulic motor in a water hydraulic system. The AE signal is obtained under different flow rates and torques. The wavelet-based signal processing technique is used to analyze the fluid-borne vibration and structure-borne vibration (acoustic signal). The spectrum based on wavelet analysis is effective in analyzing the acoustic signals under specific frequency ranges, compared with the conventional power spectrum density (PSD). The results show root mean square (RMS) of the wavelet-based acoustic signal analysis is very effective for the fault diagnosis of piston cracks under the different flow rates and torques.