Surface roughness analysis and improvement of PMMA-based microfluidic chip chambers by CO2 laser cutting

For the microfluidic chip, the surface roughness of the chamber sidewall is an important parameter in estimating its quality. In this work, the chambers of the polymethyl methacrylate (PMMA)-based microfluidic chip were fabricated by CO₂ laser cutting, and then the surface roughness of the sections cut using different laser parameters and ambient temperature was studied by a non-contact 3D surface profiler. Our observation shows that the surface roughness results primarily from the residues on the laser-cut edge, which are produced by the bubbles bursting. To reduce the surface roughness of the cut section, a new approach is proposed, that is preheating the PMMA sheet to a suitable ambient temperature during laser processing. The results indicate that at a preheat temperature of 70-90 °C, the surface roughness resulting from the cut would be reduced. In our experiment, the best result was that the arithmetical mean roughness is R_a = 100.86 nm when the PMMA sheet was heated to 85 °C.     

Study of the parameters in electrical discharge machining through response surface methodology approach

Whereas the efficiency of traditional cutting processes is limited by the mechanical properties of the processed material and the complexity of the workpiece geometry, electrical discharge machining (EDM) being a thermal erosion process, is subject to no such constraints. The lack of correlations between the cutting rate, the surface finish and the physical material parameters of this process made it difficult to use. This paper highlights the development of a comprehensive mathematical model for correlating the interactive and higher order influences of various electrical discharge machining parameters through response surface methodology (RSM), utilizing relevant experimental data as obtained through experimentation. The adequacy of the above the proposed models have been tested through the analysis of variance (ANOVA). Optimal combination of these parameters was obtained for achieving controlled EDM of the workpieces.     

Modeling of flow separation of assist gas as applied to laser cutting of thick sheet metal

The present paper describes the results of mathematical modeling of supersonic flows of a viscous compressible gas, obtained by numerically solving three-dimensional full Navier–Stokes equations, and also the results of experiments with visualization of gas jet flows in channels geometrically similar to the laser cut. Separation of the gas flow from the cut front is predicted numerically and then validated by experiments on a model setup. The gas flow structure arising in a narrow channel behind a sonic (conical) or supersonic nozzle is described. Specific features of originating in the flow separation on a smooth surface in a narrow channel are examined, and mechanisms controlling the separation are proposed. Flow separation directly affects the changes in the shape and structure of striations and is the one of main reason for the worse quality of the laser cut surface. It is shown that the changes in the structures of striations over the thickness of the sheet being cut are closely related to aerodynamic features of jet flows of the assisting gas in the cut channel.     

A heuristic for the one-dimensional cutting stock problem with usable leftover

A heuristic algorithm for the one-dimensional cutting stock problem with usable leftover (residual length) is presented. The algorithm consists of two procedures. The first is a linear programming procedure that fulfills the major portion of the item demand. The second is a sequential heuristic procedure that fulfills the remaining portion of the item demand. The algorithm can balance the cost of the consumed bars, the profit from leftovers and the profit from shorter stocks reduction. The computational results show that the algorithm performs better than a recently published algorithm.     

Cutting optimization of structural tubes to build agricultural light aircrafts

In this study we deal with the one-dimensional cutting of metallic structural tubes used in the manufacturing of agricultural light aircrafts. The problem is modeled by mixed integer linear formulations aiming to minimize material trim losses and considering the possibility of generating remainders (leftovers) with enough size to reuse. To validate the application of the models in practice, we carried out experiments with real data of order lists from Ipanema, an agricultural airplane produced by a Brazilian aeronautical company. The models were solved using a modeling language and an optimization software. The computational results show that the models are useful in supporting decisions in this cutting process.     

少无废料激光板材切割技术

采用少无废料激光板材切割技术,可以大幅度地提高材料利用率,缩短切割时间,提高生产效率。激光切割路径优化算法和板材的无搭边排样技术是少无废料激光板材切割的关键技术问题。文章研究了少无废料激光切割路径优化原则,在此基础上,研究了少无废料激光切割编程技巧,并结合纺机板材的激光切割实践,进行了少无废料激光板材切割技术研究,结果表明,采用少无废料激光切割技术,材料利用率可10%~30%,切割长度可减少5%~10%。     

紫外激光切割Si片的实验研究

报道了用193nm准分子激光切割硅片的实验结果。采用柱透镜光学系统及“热劈裂法”获得小于15μm的切缝及小于5μm的切面不平整度。     

Constraint decomposition algorithms in global optimization

Many global optimization problems can be formulated in the form min{c(x, y): x X, y Y, (x, y) Z, y G} where X, Y are polytopes in ^p , ⁿ , respectively, Z is a closed convex set in ^p+n, while G is the complement of an open convex set in ⁿ . The function c: ^p+n is assumed to be linear. Using the fact that the nonconvex constraints depend only upon they-variables, we modify and combine basic global optimization techniques such that some new decomposition methods result which involve global optimization procedures only in ⁿ . Computational experiments show that the resulting algorithms work well for problems with smalln.     

激光切割工艺参数的智能选择系统

提出用试验设计与人工神经网络相结合的方法,建立了一个激光切割工艺参数的选择优化的智能系统.通过试验设计的方法,只需做少数几次切割试验,将试验结果输入人工神经网络中进行训练和学习,系统便可经过自学得到切割结果与切割参数之间的隐含的定量关系,获得切割知识.在实际切割时,系统根据学到的切割知识,可以对任何给定的切割条件进行推理,对切割参数进行结果预测和优化.这种方法既不需要做大量的工艺试验,也不是单纯的专家经验,而是结合了两者的优点,使结果预测建立在既有试验数据又有专家知识的基础上,因而更加可靠、准确.该系统在激光方位切割的具体应用表明,系统能够准确给出定量的加工参数.     

Viscous fingering induced flow instability in multidimensional liquid chromatography

Viscous fingering is a flow instability phenomenon that results in the destabilisation of the interface between two fluids of differing viscosities. The destabilised interface results in a complex mixing of the two fluids in a pattern that resembles fingers. The conditions that enhance this type of flow instability can be found in coupled chromatographic separation systems, even when the solvents used in each of the separation stages have seemingly similar chemical and physical properties (other than viscosity). For example, the viscosities of acetonitrile and methanol are sufficiently different that instability at the interface between these two solvents can be established and viscous fingering results. In coupled chromatographic systems, the volume of solvent transported from one separation dimension to the second often exceeds the injection volume by two or more orders of magnitude. As a consequence, viscous fingering may occur, when otherwise following the injection of normal analytical size injection plugs viscous fingering would not occur. The findings in this study illustrate the onset of viscous fingering in emulated coupled chromatographic systems and show the importance of correct solvent selection for optimum separation performance.