Shrinkage Error Research Articles

Investigation For Shrinkage Deformation In The Desktop 3D Printer Process By Using DOE Approach Of The ABS Materials

Nowadays, 3D printing (3DP) has become a popular personal approach as it being able to produce a product more quickly and increased accessibility. 3DP was also known as Rapid Prototyping (RP) where it builds three-dimensional (3D) products using layer by layer method from a Computer Aided Design (CAD) files. However, dimensional accuracy (DA) was one of the major problems of these technologies. Thus, it is important to evaluate the best parameter in order to find out the best adjustment to avoid the dimensional error. The objectives of this study were to find the best parameter setting and to evaluate the influence of the changing parameter in 3D part shrinkage error. This study only focused on desktop 3D printer machines, which was the Odyssex Designex X2 and the material used was Acrylonitrile Butadiene Stryrene (ABS). In investigate which factors that most significant to shrinkage, DOE approach was used with parameters such as layer thickness (LT), nozzle temperature (NT), print speed (PS), infill density (ID) and bed temperature (BT). Minitab software has been used for analysis purposes. The significant process parameter effect and the best setting of parameter were determined from ANOVA, Main Effect Plot (MEP) and regression method. Finally, from the results of this study, BT was the most significant effect to shrinkage (SK) and the best setting for achieving less value in SK in ABS materials was LT = 0.25mm, NT = 235°C, PS = 55mm/s, ID = 25% and BT = 100°C. The validation runs was conducted based on the best setting value and it shows that the different between predicted value and actual value was 2.56%. This means that the model was reasonably accurate and the best parameter setting was highly recommended. The results also proved the quality of products was improved by using the DOE approach.

Compensating additional optical power in the central zone of a multifocal contact lens forminimization of the shrinkage error of the shell mold in the injection molding process.

This study aims to develop a compensating method to minimize the shrinkage error of the shell mold (SM) in the injection molding (IM) process to obtain uniform optical power in the central optical zone of soft axial symmetric multifocal contact lenses (CL). The Z-shrinkage error along the Z axis or axial axis of the anterior SM corresponding to the anterior surface of a dry contact lens in the IM process can be minimized by optimizing IM process parameters and then by compensating for additional (Add) powers in the central zone of the original lens design. First, the shrinkage error is minimized by optimizing three levels of four IM parameters, including mold temperature, injection velocity, packing pressure, and cooling time in 18 IM simulations based on an orthogonal array L18 (21×34). Then, based on the Z-shrinkage error from IM simulation, three new contact lens designs are obtained by increasing the Add power in the central zone of the original multifocal CL design to compensate for the optical power errors. Results obtained from IM process simulations and the optical simulations show that the new CL design with 0.1 D increasing in Add power has the closest shrinkage profile to the original anterior SM profile with percentage of reduction in absolute Z-shrinkage error of 55% and more uniform power in the central zone than in the other two cases. Moreover, actual experiments of IM of SM for casting soft multifocal CLs have been performed. The final product of wet CLs has been completed for the original design and the new design. Results of the optical performance have verified the improvement of the compensated design of CLs. The feasibility of this compensating method has been proven based on the measurement results of the produced soft multifocal CLs of the new design. Results of this study can be further applied to predict or compensate for the total optical power errors of the soft multifocal CLs.

Study on Injection Molding of Shell Mold for Aspheric Contact Lens Fabrication

This study aims to propose a method to reduce the shrinkage error of shell molds in the injection molding process. The shell molds are used for casting bi-aspheric soft contact lens with HEMA material. Moldex3D R13.0 is used to simulate and analyze the shrinkage of the front contact lens curve on the front shell mold in Z-axis direction. First, the design of experiment (DOE) method is applied to obtain the optimal setting parameters (melt temperature, injection velocity, and packing pressure). Amount of the shrinkage error is used to compensate the original design curve to improve the shrinkage error in the next simulations. The simulation result after compensation shows that the shrinkage error is reduced as 80.8%. The adding value to compensate the original design curve should be optimized to minimize shrinkage error. Result of this study can effectively improve the shrinkage error before fabricating the shell molds of the soft aspheric contact lens.

Impact of inventory inaccuracies on products with inventory-dependent demand

We explore the impact of inventory inaccuracy on the product whose demand is dependent on inventory level based on a general, stochastic demand model. The shrinkage error and misplacement error are considered simultaneously in our paper. To assess the impact of inventory inaccuracy and the benefits of RFID, we consider the following three approaches of inventory decisions: (1) the retailer is not aware of the inventory inaccuracies; (2) the retailer considers the inventory errors when making inventory decisions; (3) RFID technology is adopted to reduce the inventory errors. The comparison between the first two approaches is used to assess the consequence of ignoring inventory inaccuracies, while the comparison between the second and the third approach reflects the benefits of RFID. We derive the optimal ordering quantity and expected profit analytically, and investigate the variation of available for sales quantity, optimal service level and expected optimal profit with the inventory inaccuracies explicitly. A necessary condition that the tag price should be satisfied to guarantee RFID implementation beneficial is derived. By analyzing the variation of the benefits of integrating error information and adopting RFID with the inventory inaccuracies numerically, our results imply the retailers should pay more attention to inventory inaccuracy errors when the product is characterized with high demand sensitivity.

Rapid manufacturing of plastic aspheric optical lens

AbstractThis paper presents a new process to rapid manufacture the plastic aspheric optical lens. A bridge tooling was developed for fabricating the mold inserts of an aspheric lens using silicone rubber materials. Epoxy‐based composites were used to fabricate mold inserts of an aspheric optical lens. Z‐axis shrinkage error was investigated after plastic injection molding and compensated to the designed aspheric lens. In comparison with conventional method for fabricating a pair of mold inserts of a new plastic lens, a cost reduction of 75.02% and a time saving of 77.78% can be achieved. The deformation improvement percentage is about 92.48%. This technology can be used to compensate the z‐axis deformation efficiently due to shrinkage error of plastics in molding aspheric lens. Aspheric optical lens can be produced rapidly and cost‐effectively.

Generalized shrinkage F-like statistics for testing an interaction term in gene expression analysis in the presence of heteroscedasticity.

BackgroundMany analyses of gene expression data involve hypothesis tests of an interaction term between two fixed effects, typically tested using a residual variance. In expression studies, the issue of variance heteroscedasticity has received much attention, and previous work has focused on either between-gene or within-gene heteroscedasticity. However, in a single experiment, heteroscedasticity may exist both within and between genes. Here we develop flexible shrinkage error estimators considering both between-gene and within-gene heteroscedasticity and use them to construct F-like test statistics for testing interactions, with cutoff values obtained by permutation. These permutation tests are complicated, and several permutation tests are investigated here.ResultsOur proposed test statistics are compared with other existing shrinkage-type test statistics through extensive simulation studies and a real data example. The results show that the choice of permutation procedures has dramatically more influence on detection power than the choice of F or F-like test statistics. When both types of gene heteroscedasticity exist, our proposed test statistics can control preselected type-I errors and are more powerful. Raw data permutation is not valid in this setting. Whether unrestricted or restricted residual permutation should be used depends on the specific type of test statistic.ConclusionsThe F-like test statistic that uses the proposed flexible shrinkage error estimator considering both types of gene heteroscedasticity and unrestricted residual permutation can provide a statistically valid and powerful test. Therefore, we recommended that it should always applied in the analysis of real gene expression data analysis to test an interaction term.

Development of a low cost high precision fabrication process for glass hybrid asphericaldiffractive lenses

The hybrid aspherical diffractive singlet achromat design can be used to reduce chromaticaberration in compact optical systems. In this paper, the development of a compressionmolded, low cost and high precision hybrid diffractive glass lens is described. Specifically,an aspherical diffractive lens designed to compensate for chromatic aberration wasfabricated by precision glass molding. The diffractive features are integrated on theaspherical surface to avoid mold alignment during fabrication. As part of the effort to lowermanufacturing cost, the diffractive profiles were directly fabricated by single-pointdiamond turning without polishing. A thin layer of platinum–iridium coatingwas applied to the mold surfaces to protect the mold inserts from degradationduring the molding process. In order to reduce thermal shrinkage error, the hybridlens was fabricated using a two-step precision molding process on a commercialglass molding machine. The geometry of the molded hybrid aspherical diffractivelens was measured using an optical profilometer and the results demonstrated amatch to the design mold profile with a replication error of 0.16% in the radialdirection and 6.3% in the axial direction. In addition, an optical metrology system toevaluate the diffraction efficiency and chromatic focal shift was constructed andthe measured results showed that the hybrid lenses indeed function as designed.

Efficient mold manufacturing for precision glass molding

Precision glass molding is an efficient near net shape fabrication method for high volume production of aspherical optical glass components. Up until now, the mold manufacturing is still the most cost- and time-consuming process partly due to the fact that the shrinkage error of glass has to be compensated for by means of multiple molding trials and mold modifications (this process is sometimes called mold iteration). The main reason for shrinkage is the different thermal expansions of mold and glass materials during forming and cooling, many other factors such as uneven cooling speed and stress relaxation affect molding process and thus lead to complex form deviation in final geometry. In this paper, an efficient mold manufacturing process with integrated numerical simulation is presented in the form of a case study of an industrial molding example. Taking into account the shrinkage error predicted by process simulation, revised molds are manufactured directly with compensated design. After molding test with the compensated molds, the surface figure of the molded glass lenses was in good agreement with the desired shape within ±1 μm, which matched the original accuracy requirement and no further mold compensation was needed. Based on the result of this work, it is clear that numerical simulation can be used as an efficient tool to predict the final geometrical shape of precision molded glass components, which leads to an efficient mold manufacturing with lower production cost and a shorter cycle time.

Elimination of film shrinkage error in Weissenberg photographs

Elimination of film shrinkage error in Weissenberg photographs