Bottleneck detection of complex manufacturing systems using a data-driven method

Bottlenecks within a production line significantly affect system productivity. Most current bottleneck detection schemes focus on the long-term bottleneck detection problem using an analytical or simulation model. Furthermore, these studies are restricted to serial tandem lines only. This research focuses on extending the newly developed data-driven method for throughput bottleneck detection from a serial line to a manufacturing system with a complex layout. Within these complex systems, two specific layouts are considered: the concurrent process and the closed-loop feedback process. The method is verified using simulation case studies. An industrial case study is examined to demonstrate the practicality of this approach and to validate the efficiency of the proposed bottleneck detection method.     

Detecting bottlenecks in serial production lines – a focus on interdeparture time variance

This work addresses an important problem in industry – locating the bottleneck in a production line – and suggests a practical approach to accomplish that end. We describe and validate, using discrete event simulation, a novel method of bottleneck detection in open, asynchronous serial production lines with finite buffers. The technique uses a single measure – station interdeparture time variance – to locate the system bottleneck. The proposed method is compared to other bottleneck detection approaches and it is shown that the proposed method performs as well and sometimes better than other methods. We conclude that the proposed approach has a number of significant advantages. It is easy to use and implement, not requiring data about failure and repair times, raw process times, buffer sizes, etc., but instead uses a single piece of easily obtained real-time production line data – station work-in-process (WIP) interdeparture time. The proposed method can identify production constraints without the need to build an analytical or simulation model, is well suited for use in industry, and can be readily implemented in standard simulation tools.     

基于精益思想的生产线改造仿真与研究

阐述了企业生产线改造过程中精益思想应用的必要性,以及在生产线改造中需要遵循的精益原则:生产线平衡、连续流、产品混流生产和标准化管理。以水洗机为实例,分析了水洗机装配生产线的现状,基于传统思想与精益思想,使用面向对象的eM-Plant软件,建立相应的离散事件仿真模型,以产量、在制品和对市场的反应速度为绩效指标,研究和分析模型仿真进行的输出结果,对两种不同思想的生产线改造进行比较,为装配生产线实际改造提供依据。     

A data-driven approach to multi-product production network planning

The clearing function models the non-linear relationship between work-in-process and throughput and has been proposed for production planning in environments with queuing (congestion) effects. One approach in multi-product, multi-stage environments has been to model the clearing function at the bottleneck machine only. However, since the bottleneck shifts as the product release mix changes, this approach has its limitations. The other approach is the Alternative Clearing Function formulation, where the clearing function is first estimated at the resource level using piecewise linear regression from simulation experiments, and then embedded into a linear programme. This paper develops an alternative to the Allocated Clearing Function formulation, wherein system throughput is estimated at discrete work-in-process points. A mixed integer programming formulation is then presented to use these throughput estimates for discrete release choices. The strength of the formulation is illustrated with a numerical example and the new approach is compared with the ACF.     

HTBS微耕机包装线仿真与优化

针对HTBS公司微耕机产能提升的紧迫性,分析了微耕机生产线工段——包装线的工位作业及工序流程;依据秒表测时法所测数据,结合Flexsim仿真技术分析包装线瓶颈;运用经验排序法对包装线瓶颈工位工序及其他工位工序进行合理排序,以平衡各工位负荷,并通过Flexsim建立优化后的包装线仿真模型验证其有效性。微耕机包装线优化后,生产线平衡率由66.67%提高到90.77%,日产量由354台提高到436台,平衡优化效果明显。     

Analysis of approximately balanced production lines

This paper develops two analytical formulas for estimating the throughput of a reliable production line with exponential service times and finite intermediate buffers. The formulas apply in the case of an approximately balanced line with identical buffers or near optimal buffer allocations, where the processing times of the machines are close to each other but not necessarily the same. The derivation of the formulas is based on the standard decomposition method. Moreover, it is proved that, in general cases, both formulas provide upper bounds for the throughput obtained by the decomposition method. Numerical experiments show that the proposed formulas achieve good accuracy for approximately balanced production lines. Finally, the formulas are applied to the buffer allocation problem, and two closed-form expressions are obtained for estimating the smallest buffer capacity which is necessary to achieve the desired throughput.     

CWIPL II,a mechanism for improving throughput and lead time in unbalanced flow line

Critical WIP loops II (CWIPL II) is a proposed material flow control mechanism for an unbalanced flow line environment. CWIPL II is based on CWIPL and it determines critical loops in unbalanced lines. The WIP of critical loops identifies the time of releasing raw material to the line. CWIPL II proposed a new classification for unbalanced flow line which is ‘near unbalanced flow line’ and ‘perfect unbalanced flow line’. In near unbalanced line, there is one bottleneck and a raw material release to the line if ‘WIP of the bottleneck’ or ‘WIP upstream the bottleneck’ is less than defined level. In perfect unbalanced line there are multiple bottleneck and a raw material release to the line if ‘WIP upstream the slowest machine’ or ‘WIP between two primary bottleneck’ is less than defined level. Like CWIPL, the necessary condition for releasing the raw material is ‘idleness of the first machine’. CWIPL II is compared with CONWIP and TOC by simulation. Different scenarios are employed in the comparison analysis. The scenarios address variables such as number of machines, processing time distribution, WIP target level. Location of slowest machine and location of two primary bottlenecks are considered in examples. Simulation results and statistical tests of 141 numerical examples show that CWIPL II improves lead time in near unbalanced line and throughput in perfect unbalanced line compared with TOC. Because of the trade off between line throughput and lead time, the mechanism that improves one of them while maintaining the other at previous level is valuable. It is shown that CWIPL II has improved TOC in the cases that TOC hasn’t improved CONWIP.     

Real time production improvement through bottleneck control

Variability is a key characteristic for evaluating the performance of a process. Small variability for a bottleneck machine can generate high production variability. Short-term production analysis and bottleneck identification are imperative for enabling optimal response to dynamic changes within the system. In comparison to the rich and abundant literature available on long-term analysis, only a small section of the literature addresses the dynamic bottleneck control policies, which may be used to maximise sustainable benefits. In this paper, a real time bottleneck control method is introduced to efficiently utilise the finite manufacturing resources and to mitigate the short-term production constraints by using two practical approaches: initial buffer adjustment and maintenance task prioritisation. The objective for real time bottleneck control is to obtain a continuous production improvement towards a balanced-line status to increase the throughput efficiently. The benefits of this method are presented by considering an industrial case study of an automotive assembly line. The results obtained from this case study show significant production improvements as compared to traditional approaches.     

Real-time performance evaluation and improvement of assembly systems with Bernoulli machines and finite production runs

Extensive research has been investigated in the past several decades to evaluate the performance of manufacturing systems under rigid production mode. Based on the deployment of the new manufacturing strategies (e.g. smart manufacturing), real-time performance analysis, continuous improvement and efficient production management of flexible production systems are urgently to be investigated. Therefore, we study the problems of real-time performance evaluation and bottleneck of assembly systems in this paper. The system is assumed to have Bernoulli machines and finite production runs. We first derive the mathematical model of the system and then, derive the analytical formulas for performance evaluation of systems with three Bernoulli machines. In addition, we propose a decomposition and aggregation-based algorithm to approximate the system performances with high accuracy and computational efficiency. The idea is then extended to generalised assembly systems. Finally, the method of bottleneck analysis by using completion time bottleneck indicator is introduced and evaluated by numerical justification.     

考虑系统波动因素的DBR瓶颈缓冲区容量设置

DBR方法中的缓冲区容量设置直接影响产品的生产提前期和系统的有效产出,最终影响产品的市场竞争力。针对静态设置的缓冲区容量不能根据生产系统波动程度进行调整的问题,提出一种动态设置缓冲区容量的方法。首先分析影响缓冲区容量设置的3个因素,采用G/G/1排队模型衡量瓶颈前工序生产自然波动、瓶颈前工序数量和瓶颈工序随机波动对缓冲区容量设置的影响,并考虑避免机器故障和机器维修导致的瓶颈“饥饿”,求解机器故障因素和机器维修因素所需要的最小缓冲区容量。在此基础上,提出一种基于系统仿真的动态调节缓冲区容量的方法。最后通过案例分析,验证了所提方法的有效性和实用性。     

Availability and throughput of unreliable,unbuffered production lines with non-homogeneous deterministic processing times

This paper studies production lines composed of several serial machines which are subject to random operation-dependent failures. The production lines have no intermediate buffers between adjacent machines. Machines have different deterministic processing times. The purpose of this paper is to propose analytical models to assess steady-state availability and throughput of such lines. Thousands of production line configurations have been experimented to compare the performance of the proposed approach to approximate existing techniques. A general simulation model was developed and statistical tests carried out to prove that the proposed approach is exact and robust to model unreliable, unbuffered, and non-homogeneous production lines.     

Quantitative analysis of a transfer production line with Andon

In this paper, analytical models are developed to study the performance of a transfer production line featuring Andon. In addition to providing analytical expressions to evaluate effective production rates, we investigate conditions under which Andon should be introduced and implemented. Some practical rules are derived to guide operations management on the factory floor. We show that when average repair times are short, introducing Andon to stop the line and repair all defects on the line is an effective way to achieve a high throughput of non-defective jobs.     

基于 Witness 轿车焊装车间焊接生产线的仿真与优化研究

通过对某汽车焊接生产线工艺流程的研究,运用 Witness 仿真软件建立层次清晰的系统仿真模型。 根据仿真目标,设计了 2 组仿真试验,依据仿真结果进行焊接生产线的瓶颈分析、设备利用率分析以及设备产能匹配分析,为生产调度计划的制定、生产线的规划与布局提供科学的依据。     

A statistical framework of data-driven bottleneck identification in manufacturing systems

Data-driven bottleneck identification has received an increasing interest during the recent years. This approach locates the throughput bottleneck of manufacturing systems based on indicators derived from measured machine performance metrics. However, the variability in manufacturing systems may affect the quality of bottleneck indicators, leading to possible inaccurate detection results. This paper presents a statistical framework (SF) to decrease the data-driven detection inaccuracy caused by system variability. Using several statistical tools as building blocks, the proposed SF is able to analyse the logical conditions under which a machine is detected as the bottleneck, and rejects the proposal of bottleneck when no sufficient statistical evidence is collected. A full factorial design experiment is used to study the parameter effects of the SF, and to calibrate the SF. The proposed SF was numerically verified to be effective in decreasing the wrong bottleneck detection rate in serial production lines.     

Evaluation of Just-In-Time alternatives in the electric wire-harness industry

This paper investigates some of the theoretical and practical issues for the introduction of Just-in-Time (JIT) techniques into an automotive wire-harness assembly line. Some of the issues explored include the number of production kanbans and the unit load size to be used for every air of subassemblyassembly stations in a production line. An associated probability of stockout for different combinations is also determined. Simulation is used to validate the results obtained through an analytical method and to compare two commonly used strategies: the 'on-line' strategy which uses the subassembly operations adjacent to the assembly stations and the 'off-line' strategy which has the subassembly operation at some distance from the assembly line. Four performance criteria are used to evaluate the strategies: throughput, work-inprocess inventory, lead time, and subassembly equipment utilization.     

装配线仿真流程及其案例研究

针对目前装配线仿真研究缺少模型检验步骤而导致仿真结果不可信的问题,在总结目前装配线仿真研究的基础上,引入两次仿真模型有效性的检验过程,提出完整的装配线仿真流程。为验证该流程的有效性,以实际装配线为例,在分析布局与工艺流程的基础上,考虑物流线布局、瓶颈机器数量、AGV数量和AGV速度对产能的影响,设计并基于Plant Simulation软件建立24种方案。所有方案仿真模型有效性的检验通过后,通过比较各方案的产能与机器利用率得到最佳方案。仿真结果表明,优化后的产能较初始方案提升约227%,瓶颈机器利用率提升约51%,平均机器利用率提升约121%。所提仿真优化流程可行且有效,可为装配线仿真研究与应用提供指导,对其他生产领域的仿真研究也具有借鉴意义。     

G公司生产流程的瓶颈分析与改进

采用瓶颈模型对G公司生产流程的瓶颈进行了分析,并提出改进措施,数据分析表明,所提出的改进方案对提高企业有效产出率有效.     

供应链时间瓶颈及其价值评价研究

供应链整体的时间优化取决于少数的薄弱环节,即供应链上的"时间瓶颈",时间瓶颈包括能力瓶颈、不增值瓶颈、调度瓶颈和界面瓶颈四种形式,分析了形成这些瓶颈的主要因素;为了在多个瓶颈中确定突破重点,以瓶颈消除后供应链的产出速率和供应链总体流程周期的改善率为依据,建立了时间瓶颈的价值评价模型;总结了供应链上时间压缩和瓶颈消除应遵循的结构化程序.     

A novel metric for determining the constraining effect of resources in manufacturing via simulation

This paper provides a novel method for determining the constraining effect of resources in a manufacturing system using discrete event simulation. Traditionally manufacturing systems are constrained by one or more bottlenecks. Eliminating or mitigating the bottleneck will speed up the system throughput. However, bottlenecking resources generally only refer to machines, and primarily focus on flow-shops not job-shops. One important resource we believe that is often overlooked is workers and their associated skills, and we propose that a particular skill could be flagged as a bottleneck resource. We define new metrics known as resource constraint metrics (RCM) for measuring the constraining effect of a resource on the entire manufacturing system. These metrics are flexible and differentiate between the constraining effects of machines and their requested skills. The metrics can also deal with complex workflows with alternative routing, alternative resources, calendars (a necessary consideration when dealing with workers), worker performance, and multiple modes of operation of machines (e.g. run, setup, and maintenance). The use of RCMs in simulation aids in real-world decision-making, by determining which resource should be focussed on and improved to reduce the overall system feeling constrained. This will have the effect of increasing throughput or at least providing the capacity for increased throughput.     

一个改进的单抓钩周期性排序模型及其在自动化学处理线中的应用

计算机控制的抓钩广泛用于自动化学处理线的工件的运送。抓钩的排序直接影响系统的生产率，抓钩排序的目标是对运送进行排序以极大化生产率。当某工序处理时间非常长时，该工序成为瓶颈。为了去除该瓶颈，系统可以为该工序设计多个处理槽，这称为“多重处理槽”问题。本文提出一个改进的混合整数规划模型以求解有“多重处理槽”的单抓钩周期性排序问题的最优解。实例表明所提出的方法是有效的。