某钢铁企业精益策略解决多机排产转运问题

以某钢铁加工企业多机连续生产为研究对象,针对在制品多、过程周期长的问题,应用精益方法对计划、调度和操作作业进行改善,实现多机生产均衡化及物料同期化,降低了在制品数量和过程周期时间.为保证生产准时化运行,对现场进行作业改善及目视化.实施改善方案后,该工厂的在制品库存降低33％,变质损失成本减少为0.     

基于精益生产的某民营企业继电器生产线改善研究

以某民营企业JZX-22F系列继电器生产线为研究对象,针对现场调查发现的库存堆积多、生产周期长、物料配送紊乱等问题,运用工作抽样法明确了生产线的库存状况及其产生原因.通过减少生产线的料盒数量、制定标准作业三票、降低转运批量等方法进行生产线改善.结果显示,生产线的在制品库存与完工检成品库存均减少了一半以上,精益生产对于继电器生产线改善有很好的实用价值.     

基于价值流的胖轴精益生产分析

为提高胖轴作业效率,通过调查,首先应用价值流图技术,绘制当前状态图,分析胖轴加工过程中存在的生产计划、在制品库存、生产方式等问题,区分胖轴加工中的增值和非增值部分;然后,依据精益思想和工业工程的基本手法,提出平衡物流、合并工序、拉动生产等改善措施,绘制未来状态图作为改善的路标。实施后,胖轴批量加工时间比原来减少54％,形成均衡、拉动生产,减少了在制品库存,使生产过程大为精简。     

基于均衡拉动的DAM产品族精益生产改善研究

针对X-DAM的生产系统,通过其物与信息流动图发现生产过程中存在的问题,依据精益生产的思想和原则,提出了基于均衡拉动的改善方法.运用生产改善实践,缩短了X-DAM的过程周期,降低了在制品库存数量,提高了设备换产效率,使得生产过程更加稳健和安定,能及时应对需求的波动.     

基于工序分析方法的企业生产流程优化研究

运用工序分析方法对GL公司核心产品的加工平面布局和生产流程进行优化和再设计,分析加工车间布局的现状图,构建其优化图,优化设计生产流程。提出通过调整工序顺序、优化平面布局、加强作业人员规范操作培训等措施,来消除制造过程中的信息阻塞,使得工序总数减少了7个,搬运的距离缩减了74.9m,作业人员减少了5人,停滞的时间减少了138min,日产能提升108件。实践结果表明:在企业产品制造流程优化过程中,工序分析方法是消除信息阻塞、降低库存、产能提升、实施精益制造的一个有效工具。     

基于整流化的生产线精益改善方法研究

针对某数字相控阵雷达的核心部件数字阵列模块生产线存在的产能不足、物流路径混乱、生产线不平衡、操作人员疲劳强度高等问题,提出了基于整流化理论的精益改善方案.通过秒表测时、工序内作业拆分、生产线布局调整、瓶颈工序改善、节拍确定和全工序流动等方法实现了在减人缩时的情况下产能提升了50％、日增值工作时间比率从73.9％提高到87.9％.生产线平衡率由原来的55.8％提高到90.3％、在制品数量从76件降低到16件.并应用元单位量份配送方式进行生产线各工位的消耗物料补充,通过带有标签的空盒回收实现对线下准备区作业的看板拉动.     

基于价值流视域下的AIP公司生产流程改善研究(上)

以提高企业运作效率为核心,选取AIP公司轮胎生产线的优化作为本次研究案例,首先,通过绘制现状价值流图,达到生产线的现状可视化,分析工艺布局与物流和信息流的活动,找出当前生产模式中存在的增值与非增值环节;其次,运用精益思想和工业工程的方法,对生产流程进行分析与改善,引入看板拉动式和连续式生产等方法,以节拍平衡方式进行生产,压缩非增值时间、消除信息阻碍、减少作业人员和在制品库存等,使生产周期及产能得到有效改善;再次,采取工序重组、流程优化等改善手法,对生产流程进行精简,并绘制未来价值流图作为重点改善方向,从而实现生产线的再设计;最后,通过价值流图的前后对比发现:企业产能、设备利用率及生产周期改善显著,在提高产品质量的同时有效地降低了生产成本。     

X公司工时与作业方法研究

基于流水线不平衡的现状,运用流程作业分析方法对工时定额和作业方法进行了分析,通过测时、工序同期化等工作来调整流水线负荷,规范作业线形图,给出了具体的基于工时定额的装配线作业指导书.通过这些工作,为企业提高生产能力,组织工时定额合理的装配线,提高工作效率提供了途径.     

基于价值流视域下的AIP公司生产流程改善研究(下)

本文以提高企业运作效率为核心,选取AIP公司轮胎生产线的优化作为本次研究案例:首先,通过绘制现状价值流图,达到生产线的现状可视化,分析工艺布局与物流和信息流的活动,找出当前生产模式中存在的增值与非增值环节;其次,运用精益思想和工业工程的方法,对生产流程进行分析与改善,引入看板拉动式和连续式生产等方法,以节拍平衡方式进行生产,压缩非增值时间、消除信息阻碍、减少作业人员和在制品库存等,使生产周期及产能得到有效改善;再次,采取工序重组、流程优化等改善手法,对生产流程进行精简,并绘制未来价值流图作为重点改善方向,从而实现生产线的再设计;最后,通过价值流图的前后对比发现:企业产能、设备利用率及生产周期改善显著,在提高产品质量的同时有效地降低了生产成本。     

插口组装线的产能分析和平衡改善

基于生产线平衡原理和基础工业工程(IE)手法,以作业测定为依据研究插口组装线的产能和平衡状况,针对产能过剩工序和瓶颈工序,分析工艺流程及操作,提出了持续改善方案.并对改善结果进行分析,在减少了一道工序的基础上使产能满足需求,平衡率达到预期目的.     

酒品包装生产中动态缓冲管理机制

考虑存在资源约束的流线式酒品包装生产车间,为了减少企业生产成本,提出了一种以控制在制品(WIP)库存为主要参考指标的动态缓冲管理方法。本方法通过实时监控缓冲区的WIP库存,根据在监控窗口中缓冲区出现WIP库存由高于安全下限变化到低于安全下限的频率以及随后是否出现WIP库存耗尽的情况,对库存安全上下限进行动态调节进而实现对缓冲的动态管理。为了验证方法的有效性,安排了3组不同的仿真实验。实验结果表明：与传统的缓冲管理策略相比,基于动态缓冲管理策略的控制方法在WIP库存控制方面存在22%以上的优势,采用该方法可以有效的控制生产系统中的在制品库存。     

光通讯产品在制品数量目标研究

以实际的光通讯生产线在制品数量为研究对象,研究生产线在制品数量的设定方法。分别运用分段计算方法和排队论的［M/M/s］∶［∞/∞/FCFS］ 模型以及［M/M/s］∶［N/∞/FCFS］模型研究其目标值,分析结果表明： ［M/M/s］∶［N/∞/FCFS］模型建立的目标值切合实际,故以此为目标,提出生产管理改善措施,实现在制品数量目标控制,使在制品数量降低50%,生产周期减少50%,流动资金占用减少1875万元,很好地验证了该方法的合理性和科学性。     

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.     

Critical WIP loops: a mechanism for material flow control in flow lines

Critical WIP loops (CWIPL) is a proposed material flow control mechanism for a balanced flow line environment aiming at improving throughput and lead time. The mechanism establishes critical loops which their WIP identifies the time of releasing raw material to the line. So, through control of WIP level of critical loops the material flow is managed. The proposed mechanism releases the raw material to the line if the ‘total WIP of the line’ or ‘the WIP of the last machine’ is less than the limit. Besides the aforementioned condition, the necessary condition for releasing the raw material to the line is ‘idleness of the first machine’. Simulation is used to compare the performance of the CWIPL, CONWIP and G-MaxWIP. Different line characteristics such as number of machines, processing time distributions and the maximum WIP level of the line are considered in numerical examples. The results show that CWIPL improves both throughput and lead time compared with CONWIP, while CWIPL has better results than G-MaxWIP with respect to both throughput and lead time in the flow line that has less than nine machines.     

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.     

Petri Net model of repetitive push manufacturing with Polca to minimise value-added WIP

A common simplifying assumption used in the literature is to minimise average Work In Process (WIP), while achieving maximum production rate, which does not consider the fact that the value of WIP increases down the stream of a production process as labour, time, energy and resources are added to it. This paper aims at minimising queues of parts waiting downstream of production process and in turn minimising value-added WIP by constraining more and more inventory of unfinished products at the earlier stages of production. For this reason, generic black token closed loop Petri Net (PN) model of Flexible Flow Shop (FFS) with Paired-cell Overlapping Loops with Card Authorisation (POLCA) is developed. Tokens in the control loops represent Polca cards to control the flow of material from order release till finished products. Marking of PN is done through Mix Integer Linear Programming after the computation of semi-positive P invariants. Simulation is being done to obtain queues of parts, waiting at each station during demand variation. Results were compared with PN model of FFS without Polca. Results showed the constriction of unnecessary WIP towards the initial stage of production instead of at bottlenecks, with proposed model, and in turn minimisation of value-added WIP.     

A dynamic WIP control strategy for bottlenecks in a wafer fabrication system

The performance of a wafer fabrication system is constrained by its bottlenecks, which are difficult to detect and improve due to the complexity within the system. To weaken the negative effects of bottlenecks, a work in process (WIP) strategy is proposed in this paper which focuses on offline target WIP level setting and online WIP control simultaneously. First, bottlenecks are detected and classified based on the constraint weights which are decided by the sensitivity of the system performance to the machine's fluctuant availability. Second, the target WIP level is allocated to the bottlenecks to avoid the process fluctuation caused by unpredictable events. Third, in real time scheduling, the upstream machine of the bottlenecks modifies its dispatching order to adjust the deviation of the WIP levels at the bottlenecks. Finally, a simulation platform is developed to validate the effectiveness of the proposed method.     

Improved customer satisfaction with a hybrid dispatching rule in semiconductor back-end factories

On-time delivery is a vital factor for customer satisfaction in the competitive semiconductor manufacturing industry, and to optimize on-time delivery manufacturers must continuously improve their management of work-in-progress (WIP). However, in undertaking to optimize WIP, managers are also concerned with short cycle times, high throughput, and high utilization. In an attempt to find the most satisfactory solution to these potentially conflicting requirements with regard to WIP, the present study employs fuzzy analytic hierarchy process (AHP) to determine an appropriate set of acceptable WIP deviation levels (AWDLs). These AWDLs are then used in a proposed hybrid dispatching rule to determine the operational priorities of jobs. A simulation model using real-world data is then constructed to examine the proposed mechanism for improving customer satisfaction. The findings of the study confirm that the proposed mechanism is capable of simultaneous consideration of various goals and the achievement of enhanced performances with respect to due-date delivery from semiconductor back-end processes.     

Takt Time Grouping: implementing kanban-flow manufacturing in an unbalanced,high variation cycle-time process with moving constraints

One-piece flow and kanban/pull methods have been used to reduce work-in-process (WIP) and flowtime in manufacturing flow processes; however, these methods have limitations. For example, one-piece flow does not work well when there are relatively large set-up times required between different components. One-piece flow also requires operations to be well balanced with a minimum of variability in processing times at each operation. Unfortunately, these conditions often do not exist. The theory of constraints drum-buffer-rope (DBR) method is designed for unbalanced processes, and it has been shown to be effective for products with large operation time variation. However, DBR does not generally optimise flowtime and cannot handle a process with moving constraints (bottlenecks). We have developed a method called Takt Time Grouping (TTG) for implementing kanban-flow manufacturing, when one-piece flow or DBR do not provide good results. TTG combines one-piece flow manufacturing, transfer-batch sizing and DBR concepts through the use of a constraints-based transfer-batch sizing formula. Using a discrete event simulation model, it is shown that TTG increases throughput rate as compared to one-piece flow, CONWIP and DBR approaches, with much lower WIP inventory and faster flowtime than CONWIP and DBR.     

Lean-pull strategy in a re-entrant manufacturing environment: a pilot study for TFT-LCD array manufacturing

The increase of a panel's size in thin film transistor – liquid crystal display (TFT-LCD), results in an increase in stock space and increased cost from work-in-process (WIP). This paper proposes a lean-pull strategy, combining buffers with CONWIP (CONstant work-in-process), which results in shared resources to a re-entrant process in TFT-LCD manufacturing. The buffer size and CONWIP levels are the decision variables and are solved by simulation optimisation. The proposed procedure is applied to a factory that manufactures TFT-LCD. The study shows that the proposed lean-pull strategy can reduce the cycle time and achieve a reduction of 34.57% in WIP. The automated material handling systems (AMHS) stocker utilisation can be reduced from 62.13% to 18.49% without additional investment or facilities. Sensitivity analysis indicates the maximum daily throughput will achieve over 10% improvement. The empirical results from this pilot study provide useful managerial insights for the production control of array manufacturing.