Setting WIP levels with statistical throughput control (STC) in CONWIP production lines

We develop a simple adaptive production control method for setting WIP levels to meet target production rates in a pull production operating under the CONWIP (Constant work in process) protocol. This method, termed Statistical Throughput Control (STC), uses real-time data to automatically adjust WIP levels (via kanban cards) in the face of noisy estimates of throughput. Because STC does not rely on a steady-state model, it is well-suited to systems subject to environmental changes such as those induced by continuous improvement efforts. Using simulation, we demonstrate the effectivness of STC under a variety of conditions, including single and multiple products, simple flow lines, routeings with shared resources and assembly systems.     

Optimal cost design of flow lines with reconfigurable machines for batch production

Modular reconfigurable machines offer the possibility to efficiently produce a family of different parts. This paper formalises a cost optimisation problem for flow lines equipped with reconfigurable machines which carry turrets, machining modules and single spindles. The proposed models take into account constraints related to: (i) design of machining modules, turrets, and machines, (ii) part locations, and (iii) precedence relations among operations. The goal is to minimise equipment cost while reaching a given output and satisfying all the constraints. A mixed integer programming model is developed for the considered optimisation problem. The approach is validated through an industrial case study and extensive numerical experiments.     

Effect of scrapping on the performance of multistage automatic transfer lines

Many analytical and simulation models have been developed to study the behaviour of automatic transfer lines. Most of these models, however, have neglected the important phenomenon of scrapping of workpieces. In this paper we study the effect of this phenomenon on the performance of automatic transfer lines.     

Production control and combined discrete/continuous simulation modeling in failure-prone transfer lines

In this paper, we consider a production system consisting of multiple tandem machines subject to random failures. The objective of the study is to find the production rates of the machines in order to minimize the total inventory and backlog costs. By combining analytical formalism and simulation-based statistical tools such as design of experiments (DOE) and response surface methodology (RSM), an approximation of the optimal control policy is obtained. The combined discrete/continuous simulation modeling is used to obtain an estimate of the cost in a fraction of the time necessary for discrete event simulation by reducing the number of events related to parts production. This is achieved by replacing the discrete dynamics of part production by a set of differential equations that describe this process. This technique makes it possible to tackle optimization problems that would otherwise be too time consuming. We provide some numerical examples of optimization and compare computational times between discrete event and discrete/continuous simulation modeling. The proposed combination of DOE, RSM and combined discrete/continuous simulation modeling allows us to obtain the optimization results in a fairly short time period on widely available computer resources.     

Effect of discrete flow distribution on heat transfer at a vertical surface in natural convection

The influence of a discrete distribution of injection and suction of air on heat transfer at a vertical flat surface under free convection has been investigated experimentally. The results are presented together with empirical formulas for the heat transfer coefficients.     

A review of the literature on the use of SPC in batch production

The major concern of this paper is to provide a review of the use of SPC techniques in batch production. Data transformation is considered as one of the most important activities when implementing SPC in such an environment. Other activities include focusing attention on the process rather than on the product and the use of standardized control charts (SCCs) in place of traditional charts. Aspects of data transformation are dealt with especially with regard to explaining the mechanism of data transformation and selecting as well as evaluating several transformation techniques. In addition, a method of sensitivity analysis for SCCs is also included.     

Effect of bio-sludge concentration on the efficiency of sequencing batch reactor (SBR) system to treat wastewater containing Pband Ni

The removal efficiency of sequencing batch reactor (SBR) system with synthetic industrial estate wastewater (SIEWW) containing Ni²⁺ or Pb²⁺ was increased with the increase of mixed liquor suspended solids (MLSS). But, the sludge volume index (SVI) of the system was increased up to higher than 100 mL/g under MLSS of up to 4000 mg/L. Also, the effluent NO₃⁻ was decreased with the increase of MLSS. The heavy metals (Ni²⁺ or Pb²⁺), BOD₅, COD and TKN removal efficiencies of SBR system with SIEWW containing 5 mg/L heavy metal (Ni²⁺ or Pb²⁺) under MLSS of 3000 mg/L were 83–85%, 96–97%, 95–96% and 83–94%, respectively. The increase of heavy metal (Ni²⁺ or Pb²⁺) concentrations of SIEWW from 5 to 50 mg/L were not significantly effected to both COD and BOD₅ removal efficiencies (they were reduced by only 4–5%), but they were strongly effected to both TKN and heavy metals removal efficiencies (they were reduced by 15 and 20–30%, respectively). Both Ni²⁺ and Pb²⁺ could repress the growth of both nitrification and denitrification bacteria. And Ni²⁺ was more effective than Pb²⁺ to reduce the heavy metals removal efficiency. The SBR system could be applied to treat the industrial estate wastewater (IEWW) containing both Pb²⁺ and Ni²⁺ even the heavy metals concentrations was up to 5 mg/L, but the removal efficiency was quite low and excess bio-sludge did not produce. However, the system efficiency could be increased with the increase of BOD₅ concentration of the wastewater. The Pb²⁺, Ni²⁺, COD, BOD₅ and TKN removal efficiencies of the system with IEWW containing 500 mg/L BOD₅, 5 mg/L Ni²⁺ and 5 mg/L Pb²⁺ under HRT of 3 days were 85.68 ± 0.31%, 87.03 ± 0.21%, 86.0 ± 0.5%, 94.04 ± 0.4% and 90.5 ± 0.9%, respectively. And the effluent SRT, SS and SVI of the system were 44.7 ± 0.6 days, 150 ± 6 mg/L and 100 mL/g, respectively.     

Cool-down studies on vacuum insulated cryogenic transfer lines

Analytical and experimental studies on the cool-down of vacuum insulated cryogenic transfer lines have been carried out. An expression for estimating the cool-down history is derived taking into account the gas conduction effects. Experiments were carried out for LN₂ flow in glass lines. The cool-down time decreases with increasing vacuum up to 10^?2 torr. Beyond this there is no significant change in cool-down time. The outer jacket size has no appreciable influence on the cool-down process. Higher mass flow rates result in faster cooling of the pipe line. The experimental and theoretical cool-down curves agree well, particularly at higher jacket vacuums and at higher mass flow rates.     

Optimal design of production lines

A model is presented for jointly determining the profit-maximizing number of workstations and interstation buffer capacities for stochastic unpaced lines. Several important implementation issues are discussed and system sensitivities examined, providing the line designer with new and important tools and insights.     

The effect of breakdowns on U-shaped production lines

Consider a synchronized line performing assembly or fabrication tasks. Tasks are grouped into stations and stations are positioned on a line that is U-shaped. Stations may break down and be repaired. Small buffer inventories may be placed between stations to lessen the effect of breakdowns at one station on production at other stations. This paper investigates the effect of the U-shape of the line on the line effectiveness. We find that effectiveness increases when the line is U-shaped, compared with the traditional straight line shape.     

Analysis and solution to the single-level batch production smoothing problem

Many companies use mixed-model production systems running under the Just-in-Time philosophy in order to efficiently meet customer demands for a variety of products. Such systems require demand be stable and production sequence be leveled. The production smoothing problem aims at finding level schedules in which the appearances of products are dispersed over the horizon as uniformly as possible. In this paper, the production smoothing problem is extended to a more general manufacturing environment where a single machine can be identified as either the final or the bottleneck stage of the system and products may have arbitrary non-zero setup and processing time requirements on this single machine. An optimization model is built for the problem and a two phase solution methodology is developed. The first phase problem is shown to be NP-hard and a parametric heuristic procedure is proposed for its solution. In contrast, the second phase problem is shown to be efficiently solvable and currently available solution methods are adopted from the literature. A computational study is designed to test the proposed two phase solution methodology and also the parametric heuristic procedure. Computational results show that the proposed two phase solution methodology enables effective and efficient control of the studied manufacturing system, and the heuristic procedure developed for the first phase problem is time efficient and promises near optimal solutions for a variety of test instances.     

基于市场和生产效率的排产研究

就生产而言,若能维持单品种长期生产,效率肯定是最高的,但考虑了市场因素以后,又是不现实的,因为生产必须随市场而动。如何更科学地编排每月的生产日计划并组织实施,尽量延长每台卷包设备生产同一品种或规格相似品种的时间,减少设备改动和换牌频次,同时又要满足上述市场的要求,这就需要在市场和生产效率间找到较佳的平衡点。     

Effect of discrete structure of “continuous” phase of heat transfer in a fluidized bed

The heating of a semi-infinite layer of particles adjacent to a heated surface is investigated analytically in a one-dimensional approximation. The conditions in which such a system can be regarded as a homogeneous isotropic medium are found.     

Lockout/tagout and optimal production control policies in failure-prone non-homogenous transfer lines with passive redundancy

This paper considers a production problem for a transfer line subject to random failures and repairs, and differs from other studies on transfer lines. It considers a manufacturing system consisting of three machines (two machines with passive redundancy, and one in series with the previous ones) producing one part type. The control problem is subject to non-negative constraints on work-in-process (WIP). The decision variables are the production rates of two main machines and a standby machine, and influence the WIP levels, the inventory levels and the system's capacity, which is assumed to be described by a finite-state Markov chain. The objective of this paper is to minimise WIP and finished goods inventory costs; it also aims to respect the essential space–time during intervention on machine down, in order to minimise the possibility of the circumvention of protection devices or of the retraction of lockout/tagout procedures through a passive redundancy system. This paper therefore verifies the effect of passive redundancy on optimal stock levels. Given that an analytical or even a numerical solution of the problem is very difficult to find, and that we want to have a more realistic model for industries, we present a combined approach, which is presented based on a combination of analytical formalism, simulation modelling, design of experiments, and response surface methodology to optimise a transfer line with passive redundancy, producing one part type. The usefulness of the proposed approach is illustrated through a numerical example and a sensitivity analysis.     

低温传输管线的设计与研究

以北京正负离子对撞机二期改造项目(BEPCⅡ)第一对撞厅液氮传输管线与液氮、液氦多通道传输管线为例,介绍低温传输管线的结构设计,有限元分析与实验结果表明,它是合理、可靠的,为国内今后大型低温系统的设计和实施提供了成功的范例。