A kanban-based simulation study of a mixed model just-in-time manufacturing line

The kanban-based operation of a mixed model manufacturing line is studied. Features of the hypothetical manufacturing line modelled are presented in terms of general structure, major components and operational characteristics. Simulation model developed is described and parameters of the base model are given. Experimental design features are discussed with respect to simulation related issues, performance measures, statistical analysis and experimental design clusters. Statistical findings are summarized in tabular format. Non-intuitive behaviour observed in each experiment set is interpreted.     

A branch-and-bound approach for machine selection in just-in-time manufacturing systems

Equipment selection issues are very important in the early stages of implementation of just-in-time (JIT) manufacturing systems. This paper addresses the problem of determining the number of machines for each stage of a JIT system by minimizing production, imbalance and investment costs. The problem is modelled as a mixed-integer nonlinear optimization program and a branch-and-bound algorithm is developed for its solution. This algorithm guarantees the global optimum of the problem and is enhanced by simple, yet very effective, upper bounding heuristics. The solutions obtained by the developed branch-and-bound approach are compared to solutions that have appeared in the literature using heuristic approaches. The comparisons indicate that the proposed algorithm leads to significant economic savings, averaging 17% on a set of problems from the literature. The paper also considers the application of the algorithm to large-scale, industrially-relevant, problems with up to 10 stages and 200 products. Even for the largest of these problems, the search for the integer optimum requires modest computational times. This demonstrates the potential practical impact of the proposed methodology.     

A note on ‘Economic manufacturing quantity in a just-in-time delivery system’

This comment is made on a paper by Golhar and Sarker who showed that it is economically advantageous for a supplier to participate in the just-in-time delivery system. Although the general conclusions are correct, one of the conditions under which the results are obtained is not necessary. Also, the optimal production quantity is not independent of delivery quantity though their interdependency is in a rather indirect manner.     

A graph-based model for manufacturing complexity

This paper presents a graph-based model to measure the relative manufacturing complexity of and the manufacturing similarity of products in job shop manufacturing systems. This model depicts the impact of the complexity factors on the profit realisable from products based on their manufacturing process and required resources/skills. These resources deal with the process required for a component to reach assembly, the process of assembling the components to a whole product. This relative manufacturing complexity measure not only can support assembly and production cost estimation, but also can provide a guideline for creating a product with the most effective balance of manufacturing and assembly. Also, the results of this study can help improve budgeting and resource allocation, and the product life cycle cost estimation for future products. A numerical example is also presented to demonstrate the application of the proposed approach.     

Tolerancing for manufacturing: A three-dimensional model

This paper proposes a three-dimensional (3D) model on manufacturing tolerancing for mechanical parts. The work presented relies on research conducted at the LURPA on the computation of 3D tolerance chains for mechanisms. Starting from these works, the authors propose a formalization of the problem within the more specific context of manufacturing tolerances. Models of the workpiece, the set-ups and the machining operations are provided. The main originality is to model the machining set-up as a mechanism. The concept of the small displacements torsor (SDT) is used to model the process planning. It opens up the way for the 3D integration product/process because of the similarities between the concepts used in both points of view. The first part recalls the principle of the modelling of surface variations with SDT as well as its application to the modelling of mechanisms. The second part introduces the use of the concept in the case of manufacturing tolerancing. A third part shows the modelling of the problem with the help of an example. At last, a detailed computer implementation is described.     

Optimization-based planning for the stochastic lot-scheduling problem

We describe a finite-horizon stochastic optimization model for the stochastic lot-scheduling problem and procedures for finding near-optimal solutions. Several different products are produced by a single-stage process with significant changeover times and costs, and the demand for these products is random. The deterministic version of this problem, the economic lot-scheduling problem, is the subject of a great deal of research. However, the problem with random demand for the products is commonly found in practice but is not as well researched. The models developed in this paper address the problem of dynamically planning the timing and size of production runs in this kind of production environment. We also report some computational results that indicate the quality of the resulting production schedules.     

A manufacturing control model

Be it teaching or discussing logistic target attainment with practitioners, there is often a confusing gap between the manufacturing control methods applied on the one hand and the logistic objectives on the other hand. Which method is appropriate to increase on-time delivery, which to decrease the WIP? When configuring manufacturing control the discussion often quickly turns to choosing one method over the other and too often the results are disappointing. In order to provide a framework for a more systematic approach, a model has been developed that links the tasks of manufacturing planning and control with the logistic objectives.     

Determination of fault-tolerant fabric-cutting schedules in a just-in-time apparel manufacturing environment

In apparel manufacturing, accurate upstream fabric-cutting planning is crucial for the smoothness of downstream sewing operations. Effective and reliable fabric-cutting schedules are difficult to obtain because the apparel manufacturing environment is fuzzy and dynamic. In this paper, genetic algorithms and fuzzy-set theory are used to generate fault-tolerant fabric-cutting schedules in a just-in-time production environment. The proposed method is demonstrated by two cases with production data collected from a Hong Kong-owned garment production plant in China. Results of the two cases preliminarily show that the genetically improved fault-tolerant schedules effectively satisfy the demand for downstream production units, guarantee consistent and reliable system performance, and also reduce production costs through reduced operator idle time. More cases will be conducted in order to further validate the effectiveness of the proposed method.     

Hybrid genetic algorithm for the economic lot-scheduling problem

The economic lot-scheduling problem (ELSP) is an important production scheduling problem that has been intensively studied over 40 years. Numerous heuristic algorithms have been developed since the problem is NP-hard. Dobson's heuristic has been regarded as the best in its performance. The present paper provides a hybrid genetic algorithm based on the time-varying lot sizes approach in the ELSP literature. Numerical experiments show that the hybrid genetic algorithm outperforms Dobson's heuristic.     

A model for labour pooling in batch manufacturing

Cross-training workers to perform multi-skilled jobs is one of the modern trends in job design. As companies engage in downsizing, the remaining workforce is expected to do more and different tasks. This paper presents a formal definition and a practical solution for optimizing the size and cost of the pool of multi-skilled workers for production units operated under batch manufacturing. The pool size is optimized through a search procedure applied separately to just-in-time (JIT) and level production plans, which are derived from the stones heuristic. The method allows direct calculation of the cost savings from labour pooling. This paper was inspired by consulting in the food industry, where implementation of these results has significantly reduced labour costs.     

A capacitated vehicle routing problem for just-in-time delivery

This paper focuses on the formulation and solution of the problem of planning vehicle routes for material delivery within the premises of a plant working under a just-in-time production system. The unique characteristic of this problem is that the quantity to be delivered at each of the demand nodes is a function of the route taken by the vehicle assigned to serve that node. The problem is modeled by adding a non-linear capacity constraint to the standard vehicle routing model, such that vehicle idle times and inventories at the customer locations are minimized. A heuristic solution procedure is outlined, and the formulation of a lower-bound relaxation is suggested. The performance of the heuristic solution procedure is evaluated in comparison to the lower-bound relaxation, and the heuristic procedure is shown to provide generally good results.     

A simple non-associated flow model for sand

 This paper proposes a simple non-associated plasticity model for sand. The yield surface is taken to be a member of a recently derived family of yield loci, requiring the specification of a single parameter in addition to the stress ratio at the peak value of deviatoric stress on the yield surface in deviatoric:mean effective stress space. This simple equation, can easily be fitted to given sand data. The flow rule also has a simple equation, such that the critical state is not at the top of the yield locus in stress space. The equation of the flow rule requires the specification of the critical state dissipation constant, plus one additional parameter. This permits realistic modelling of the undrained behaviour of sand in states looser and denser than critical. The parameter controlling the flow rule can, for convenience, be taken to be equal to the parameter governing the shape of the yield surface. However, since the two parameters are not required to be equal, the flow rule can easily be adjusted to model more accurately the rate of change of direction of the plastic strain increment vector with changing stress ratio around the yield surface. The model resembles more complex models based on the mathematical theory of envelopes, but the equations of the yield loci and flow rules are much simpler. The contribution in this paper is therefore to provide a model similar to those derived based on micro mechanical considerations, but which is more useful to geotechnical engineers, in that the number of parameters is kept to a minimum, the constitutive equations are simple, and the flow rule can easily be controlled. The model is easy to apply in geotechnical analysis, and would be easy to implement in a finite element program. Received: 11 January 2002     

A topological model of limitations in design for manufacturing

Design for manufacturing (DFM) is a methodology that requires the use of specific manufacturing information at all stages of design. The method relies on a collection of informal and often controversial principles that seem to have eluded the benefits of formal analysis. The transition from design to manufacturing can be modeled as a mathematical mapping, and it has been previously shown how the discontinuity of this mapping formally captures the folklore that small design changes can lead to significantly increased manufacturing cost. We study the properties of the transition map in the presence of design and manufacturing variations, and show that its continuity is closely related to the structure of design and manufacturing topological spaces. The main result of this paper establishes conditions on these spaces under which design for manufacturing cannot be described by any continuous transition map. In practical terms, our study reveals the limitations of many DFM systems and approaches in their ability to relate design and manufacturing knowledge, and explains these limitations in terms of a basic incompatibility between the underlying design and manufacturing representations. We discuss how our model applies to DFM relative to traditional manufacturing methods (such as casting and stamping) and we speculate what changes might occur for alternative manufacturing technologies (such as electrical discharge machining (EDM), stereolithography, laser machining, and particle deposition).     

设计与制造中的统计几何公差建模及应用

几何与尺寸公差(形位公差GD&T)广泛用于机械工程设计与制造中重要几何特征的偏差控制.相对较成熟和简单的尺度公差建模与分析,几何公差统计建模与分析更具挑战性,是当前CAD技术中尚未但亟待解决的课题之一.现提出采用统计几何模态模型(SMA)方法解决这一问题.SMA可识别刻划与解释测量数据中的几何特征信号模式及其变化,从而服务于制造中的(公差)质量检验、诊断及变化模式的统计建模.在设计中SMA可进行模态重组综合,从而再现或仿真几何特征偏差的随机变化进行统计几何公差分析.     

A simple ballistic material model for soda-lime glass

Various open-literature experimental findings pertaining to the ballistic behavior of glass are used to construct a simple, physically based, high strain-rate, high-pressure, large-strain constitutive model for this material. The basic components of the model are constructed in such a way that the model is suitable for direct incorporation into standard commercial transient non-linear dynamics finite-element based software packages like ANSYS/Autodyn [ANSYS/Autodyn version 11.0, User documentation, Century Dynamics Inc. a subsidiary of ANSYS Inc.; 2007.] or ABAQUS/Explicit [ABAQUS version 6.7, User documentation, Dessault systems, 2007.]. To validate the material model, a set of finite element analyses of the Edge-on-Impact (EOI) tests is carried out and the results compared with their experimental counterparts obtained in the recent work of Strassburger et al. [Strassburger E, Patel P, McCauley JW, Kovalchick C, Ramesh KT, Templeton DW. High-speed transmission shadowgraphic and dynamic photoelasticity study of stress wave and impact damage propagation in transparent materials and laminates using the edge-on impact method. In: Proceedings of the twenty-third international symposium on ballistics. Spain: April 2007, and Strassburger E, Patel P, McCauley W, Templeton DW. Visualization of wave propagation and impact damage in a polycrystalline transparent ceramic-AlON. In: Proceedings of the twenty-second international symposium on ballistics. Vancouver, Canada: November 2005.]. Overall, a good agreement is found between the computational and the experimental results pertaining to: (a) the front-shapes and propagation velocities of the longitudinal and transverse waves generated in the target during impact; (b) the front-shapes and propagation velocities of the “coherent-damage” zone (a zone surrounding the projectile/target contact surface which consists of numerous micron- and sub-micron-size cracks); and (c) the formation of “crack centers”, i.e. isolated cracks nucleated ahead of the advancing coherent-damage zone front. Relatively minor discrepancies between the computational and the experimental results are attributed to the effects of damage-promoting target-fixturing induced stresses and cutting/grinding-induced flaws located along the narrow faces of the target and the surrounding regions.     

Optimizing production smoothing decisions via batch selection for mixed-model just-in-time manufacturing systems with arbitrary setup and processing times

This paper is concerned with the production smoothing problem that arises in the context of just-in-time manufacturing systems. The production smoothing problem can be solved by employing a two-phase solution methodology, where optimal batch sizes for the products and a sequence for these batches are specified in the first and second phases, respectively. In this paper, we focus on the problem of selecting optimal batch sizes for the products. We propose a dynamic programming (DP) algorithm for the exact solution of the problem. Our computational experiments demonstrate that the DP approach requires significant computational effort, rendering its use in a real environment impractical. We develop three meta-heuristics for the near-optimal solution of the problem, namely strategic oscillation, scatter search and path relinking. The efficiency and efficacy of the methods are tested via a computational study. The computational results show that the meta-heuristic methods considered in this paper provide near-optimal solutions for the problem within several minutes. In particular, the path relinking method can be used for the planning of mixed-model manufacturing systems in real time with its negligible computational requirement and high solution quality.     

Multicriteria models for just-in-time scheduling

Just-in-time manufacturing consists of organising the production of elements in order to meet a certain number of objectives or requirements according to the so-called ‘Just-in-Time philosophy’. Just-in-time has been studied extensively in the literature for many years due to the large number of real-life situations where it can be applied. This paper aims at revisiting Just-in-Time principles and detailing how they can be applied to the scheduling stage of a manufacturing process. Therefore, new models that are multicriteria models by their very nature are presented and discussed. The conclusions highlight the fact that most of the existing models presented in the scheduling literature happen to be incomplete regarding Just-in-Time principles.     

A mathematical programming model for reconfiguration of flexible manufacturing cells

In flexible manufacturing cells, changes in demand size, product mix, part variety, existing routings and set-up/operation times may require reconfiguration of the cells. In this study, an approach is developed to decide when and how such a reconfiguration should be carried out for existing cells. This study considers reconfiguration in terms of changing part routings, adding a new machine type in a cell, duplicating an existing machine type, removing an existing machine from a cell and transferring a machine to another cell. The study also shows the total number of tools of each type on each machine located in each cell after reconfiguration. To make the optimal reconfiguration decisions, a mathematical programming model to minimize the total reconfiguration cost is developed. The developed model considers the lower and upper bounds on machine utilizations and the time limits on machine cycle times to decide when to reconfigure the system.