• Proceedings of the KSME Conference
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• 2001.06b
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• pp.747-753
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• 2001

This paper presents a dynamic modeling and a robust PID controller design process for the wire bonder head assembly. For the modeling elements, the system is divided into electrical system, magnetic system, and mechanical system. Each system is modeled by using the bond graph method. The PID controller is used for high speed/high accuracy position control of the wire bonder assembly. The Taguchi method is used to evaluate the more robust PID gain combinations. This study makes use of an L18 array with three parameters varied on three levels. Computer simulations and experimental results show that the designed PID controller provides more improved signal to noise ratio and reduced sensitivity than the conventional PID controller.

• Transactions of Materials Processing
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• v.16 no.2 s.92
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• pp.144-149
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• 2007

The superplastic forming/diffusion bonding(SPF/DB) is widely used in the automotive and aerospace industry because it has great advantage to produce complex, light and strong parts. But the superplastic forming process requires much forming time and generates excessive thinning in the thickness distribution of formed part. It is necessary to minimize trial and error for SPF/DB Process. Finite element analysis using $L_{18}$ orthogonal may table of Taguchi method for 3-Sheet D/B process is carried out. Through the study, effect of process parameters, such as DH region size, thickness and friction coefficient, is evaluated and the optimum condition is derived.

• Journal of the Korea Safety Management & Science
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• v.3 no.1
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• pp.117-125
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• 2001

Polyacetal resin is usually used to make molds, but it is difficult to achieve dimension accuracy during molding. Therefore it is usually necessary to cut the polyacetal resin after a molding process. Polyacetal resin is easily machining by standard machine tool. Acetal is also a thermal stable material which can be totted without coolant Another concern about the use of polyacetal resin is that it absorbs water easily, which also results in problems with dimension accuracy Therefore, in this study, the cutting resistance of water-absorbed polyacetal resin and its surface roughness after cutting in order to achieve the highest degree of accuracy in the cutting of polyacetal resin were investigated. Also, The Robust Design method uses a mathematical tool called orthogonal arrays to study a large number of decision variables with a small number of experiments. It also uses a new measure of quality, called signal-to-noise (S/N) ratio, to predict the quality from the customer's perspective. Thus, we have taken Taguchi's parameter design approach, specifically orthogonal array, and determined the optimal levels of the selected variables through analysis of the experimental results using S/N ratio.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.4A
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• pp.269-277
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• 2012

When there are mismatches between the beamforming steering vector and the array response vector for the desired signal, the performance can be severely degraded as the adaptive array attempts to suppress the desired signal as well as interferences. In this paper, an robust method is proposed for the adaptive array in the presence of both direction errors and random errors in the steering vector. The proposed method first finds a signal-plus-interference subspace (SIS) from the correlation matrix, which in turn is exploited to extract an interference subspace based on the structure of a uniform linear array (ULA), the effect of the desired signal direction vector being reduced as much as possible. Then, the weight vector is attained to be orthogonal to the interference subspace. Simulation shows that the proposed method, in terms of signal-to-interference plus noise ratio (SINR), outperforms existing ones such as the doubly constrained robust Capon beamformer (DCRCB).

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.6
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• pp.16-21
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• 2012

Magnesium alloy has been focussed as lightweight material owing to its high strength even though low density with aluminum alloy, titanium alloy and plastic material. Friction stir welding technique was performed by rotating and plunging a shouldered tool with a small diameter pin into the joint line between two butted plates and useful to join magnesium alloy. In this paper, the experiments of friction stir welding were done to investigate the joint characteristics of AZ31 magnesium alloy. For its evaluation, the orthogonal array method$(L_{27}(3^{13}))$ was applied with four factors of pin diameter, shoulder diameter, travel speed and rotation speed of tool and also three levels of each factor. Nine tools were worked through shoulder diameter of 9, 12, 15mm and pin root diameter of 3, 4, 5mm. In addition tensile tests were excuted for the assessment of mechanical properties for joint conditions. From the results, pin diameter, shoulder diameter, and rotating speed of tool influenced on the tensile strength meaningful, but welding speed did not influence on that by the variance analysis. Beside of that, optimum condition of tensile strength was estimated as following ; shoulder diameter:15mm, welding speed:200mm/min, rotating speed:200rpm.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.38 no.4
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• pp.177-183
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• 2015

Incremental sheet metal forming is a manufacturing process to produce thin parts using sheet metals by a series of small incremental deformation. The process rarely needs dedicated dies and molds, thus, preparation time for the process is relatively short as to be compared to conventional metal forming. Spring back in sheet metal working is very common, which causes critical errors in dimensions. Incremental sheet metal forming is not fully investigated yet. Hence, incremental sheet metal forming frequently produces inaccurate parts. This paper proposes a method to minimize dimensional errors to improve shape accuracy of products manufactured by incremental forming. This study conducts experiments using an exclusive incremental forming machine and the material for these experiments are sheets of aluminum AL1015. This research defines a process parameter and selects a few factors for the experiments. The parameters employed in this paper are tool feed rate, tool diameter, step depth, material thickness, forming method, dies applied, and tool path method. In addition, their levels for each factor are determined. The plan of the experiments is designed using orthogonal array $L_8$ ($2^7$) which requires minimum number of experiments. Based on the measurements, dimensional errors are collected both on the tool contacted surfaces and on the non-contacted surfaces. The distances between the formed surfaces and the CAD models are scanned and recorded using a commercial software product. These collected data are statistically analyzed and ANOVAs (analysis of variances) are drawn up. From the ANOVAs, this paper concludes that the process parameters of tool diameter, forming depth, and forming method are the significant factors to reduce the errors on the tool contacted surface. On the other hand, the experimental factors of forming method and dies applied are the significant factors on the non-contacted surface. However, the negative forming method always produces better accuracy than the positive forming method.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.45-50
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• 2011

Hot-Press-Forming (HPF), an advanced sheet metal forming method using stamping at a high temperature of about $900^{\circ}C$ and quenching in an internally cooled die set, is one of the most successful forming process in producing crash-resistant parts such as pillars and bumpers with complex shape, ultrahigh strength, and minimum springback. To optimize conditions of a forming quality in HPF process and secure a safe product without any failures, such as fractures and wrinkling, the simulations based on the coupled thermo-mechanical analysis for a hot-press-formed lower control arm are applied with Taguchi's orthogonal array experiment. Three factor variables - the friction coefficient, blank shape, and hole location for burring - are selected to be optimized. The most effective condition of a forming quality for a hot-press-formed lower control arm is suggested. The simulation results are confirmed with experimental ones.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.4
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• pp.64-69
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• 2011

Magnesium alloy has been known as lightweight material in automobile and electronic industry with aluminum alloy, titanium alloy and plastic material. Friction welding is useful to join different kinds of metals and nonferrous metals they are difficult to be joined by such as gas welding, resistance welding and electronic beam welding. In this study, friction welding was performed to investigate optimization process of Mg alloy with a 20mm diameter solid bar. For that, the orthogonal array $(L_{9}(3^{4}))$ was used that contained four factors and each factor had three levels. Control factors were heating pressure, heating time, upsetting pressure and upsetting time. Also tensile tests were carried out to measure mechanical properties for welded conditions. The levels of heating pressure and upsetting pressure used were 15, 25, 35MPa, and 30, 50, 70MPa, respectively. In addition those of heating time and upsetting time were 0.5, 1, 1.5 sec and 3, 4, 5 sec., respectively, rotating speed of 2000rpm. From the experimental results, optimization condition was estimated as follows; heating pressure=35MPa, upsetting pressure=70MPa, heating time=1.5sec, upsetting time=3sec.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.4
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• pp.179-185
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• 2008

The purpose of this paper is to propose a systematic method on the weld pitch design of a vehicle sub-frame considering the fatigue life of spot welding points. The input data, which perform the fatigue analysis on the spot welding nuggets, are obtained by both the dynamic analysis of the multi-body vehicle model passing through the virtual proving ground of a typical Belgian road and the quasi-static analysis with the finite element model of the vehicle sub-frame. By utilizing the life cycle data obtained from the fatigue analysis, the welding points to perform the pitch change are determined. The sensitivity analysis on the fatigue life of the welding points is carried out by using the three-level orthogonal array design, and through the results of the sensitivity analysis, the best combination on the welding pitch is determined. This study shows that as compared with the baseline design, the sub-frame redesigned by the proposed technique improves the fatigue life about 7 percent while reducing the number of welding points about 19 percent.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.3
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• pp.184-192
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• 2014

The resistance of a high speed monohull can be dramatically increased at the high speed range due to the severe stern trim, spray formation and hull bottom pressure irregularity etc. In order to avoid these demerits associated with this resistance increase, various appendages such as the stern wedge, vertical wedge, stern flap, spray strip etc. have been studied. Each of appendage can control the trim angle and/or improve the resistance performance. If these appendages are combined for finding the maximal resistance reduction, there are enormous combination selections. This paper presents the DOE(Design of experiment) using an orthogonal array in order to decrease the model tests finding the optimum appendage combination. And we evaluate that the method introduced in this paper makes the optimal combination of appendages efficient and time-saving by applying to high speed semi-planing monohull. Here, the maximum speed and the least fuel expense are adopted as the decision criteria.