Hyunjune Yim

Identification of dimensional variation patterns on compliant assemblies

This paper presents a methodology to diagnose sources of dimensional variation for compliant parts from the measurement data of final assemblies. The method is developed for a single-station assembly process. The proposed diagnosis tool is based on applying a predictive variation propagation model to determine the part-to-part and tooling interaction in the assembly system. The variation propagation model allows identifying the impact of different faulty component patterns in the final assembly product. Using the predictive assembly fault patterns and the designated component analysis, the contribution of each fault in the total system variation may be identified. The methodology incorporates an optimal sensor placement algorithm to determine the key measurement points in the assembly. Two case studies were conducted to illustrate that the methodology is capable of identifying part variation patterns from assembly measurement data, even under significant levels of noise. Although the methodology is presented for a single assembly station, it can be extended to a multiple-station assembly scenario using a multistation variation propagation model.

Kinematics-Based Determination of the Rolling Region in Roll Bending for Smoothly Curved Plates

This paper proposes and develops a kinematics-based, systematic approach to determine the region of a plate to be rolled, in order to fabricate smoothly curved plates. The approach includes a kinematic analysis to calculate the plates curvature distribution, and, in addition, a linear regression analysis to determine the initial and final locations of the roller during the roll bending process. Three artificial cases and two real cases have been studied, and the results are in good agreement with field practices. This approach will play an important role in the automation and optimization of the plate forming process.

Sensor Placement for Effective Diagnosis of Multiple Faults in Fixturing of Compliant Parts

This paper presents a new sensor placement methodology for effective fault diagnosis in an N-2-1 locating scheme used in compliant sheet metal assembly processes. The proposed approach is based on the effective independence (EfI) sensor placement method. The EfI method is a computational algorithm that starts with all feasible sensor locations and reaches the desired number of locations, by progressively eliminating those having the least contributions to the linearly independent manifestation of the fixture faults. The least squares method was adopted to identify fixture faults from the measurement data. An automotive panel part was considered to illustrate the suggested methodology. The sensors placed by the EfI method enable the effective identification of multiple fixture faults even in the presence of moderate measurement noise.Copyright

Mechanics of Die-less Asymmetric Rolling for Fabrication of Compound Curved Plates

The mechanics of die-less asymmetric rolling has been investigated in depth, for the first time, using a two-dimensional analytical model and a three-dimensional finite element model. In doing so, the physical understanding of mechanics underlying die-less asymmetric rolling has greatly been enhanced. Moreover, the asymmetry in roller radii was found to be the most effective parameter for curvature control, in the considered ranges of various parameters.

Tolerance Design for Parts of a Sliding-Type Mobile Phone to Improve Variational Quality of Its Side Gap

Received 10 September 2012; received in revised form 6 November 2012; accepted 7 November 2012ABSTRACTThis paper investigates the tolerance stack-up in a commercial sliding-type mobile phone modeldeveloped by a Korean electronics company, with focus on the dimensional quality of the gapbetween the sliding top and the main body. The tolerance analysis in this study is done using acommercial software package, which runs Monte Carlo simulations to produce the statistical dis-tributions of the gap size at desired locations. Such an analysis revealed that the original designdid not yield the desired dimensional quality of the gap. Through a series of systematic analy-ses and syntheses, an improved design is proposed for the nominal dimensions and tolerances ofselected features of the parts. The proposed design was validated, through tolerance analysissimulation, to meet the desired requirement of the gap quality.Key words:Computer-Aided Tolerancing (CAT), Datum Flow Chain (DFC), Gap, Mobile phone,Tolerance analysis, Tolerance design

Construction of a Verified Virtual NC Simulator for the Cutting Machines at Shipyard Using the Digital Manufacturing Technology

Digital manufacturing is a technology to simulate the real manufacturing process using the virtual model representing the physical schema and the behavior of the real manufacturing system including resources, processes and product information. Therefore, it can optimize the manufacturing system or prevent the bottleneck processes through the simulation before the manufacturing plan is executed. This study presents a method to apply the digital manufacturing technology for the steel cutting process in shipyard. The system modeling of cutting shop is carried out using the IDEF and UML which is a visual modeling language to document the artifacts of a complex system. Also, virtual NC simulators of the cutting machines are constructed to emulate the real operation of cutting machines and NC codes. The simulators are able to verify the cutting shape and estimate the precise cycle time of the planned NC codes. The validity of the virtual model is checked by comparing the real cutting time and shape with the simulated results. It is expected that the virtual NC simulators can be used for accurate estimation of the cutting time and shape in advance of real cutting work.

Tolerance Analysis Considering Weld Distortion by Use of Pregenerated Database

A general and efficient methodology has been developed to analyze dimensional variations of an assembly, taking into account of the weld distortion. Weld distortion is generally probabilistic because of the random nature of welding parameters such as the welding speed, maximum welding temperature, ambient temperature, etc. The methodology is illustrated by a very simple example of two perpendicular plates fillet-welded to each other. Two steps comprise the methodology: establishment of a weld-distortion database, and tolerance analysis using the database. To establish the database, thermo-elasto-plastic finite element analyses are conducted to compute the weld distortion for all combinations of discrete values of major welding parameters. In the second step of tolerance analysis, the weld distortion retrieved from the database is used in addition to the dimensional tolerances of the parts. As a result of such an analysis, sensitivities of the assembly’s dimensional variations to the part tolerances and weld distortion are obtained, which can be help improve the dimensional quality of the assembly.Copyright