Effects of routing flexibility, sequencing flexibility and scheduling decision rules on the performance of a flexible manufacturing system

This paper focuses on a simulation-based experimental study of the interaction among routing flexibility, sequencing flexibility and part sequencing rules in a typical flexible manufacturing system (FMS). Two scenarios are considered for experimentation. Three routing flexibility levels, five sequencing flexibility levels and four scheduling rules for part sequencing decision are considered for detailed investigation. The performance of the FMS is evaluated using various measures related to flow time and tardiness of parts. The simulation results are subjected to statistical analysis. The analysis of results reveals that deterioration in system performance can be minimized substantially by incorporating either routing flexibility or sequencing flexibility or both. However, the benefits of either of these flexibilities diminish at higher flexibility levels. Part sequencing rules such as earliest due date and earliest operation due date provide better performance for all the measures at higher flexibility levels.     

Impact of operation flexibility and dispatching rules on the performance of a flexible manufacturing system

Operation flexibility is one of the eight common types of flexibility that exist in flexible manufacturing systems. Dispatching rules are commonly used in loading the machines. This paper studies the effects of different levels of operation flexibility and various dispatching rules on the performance of a flexible manufacturing system. The system performance considered is mean flow time. Simulation results indicate that the mean flow time cannot be always improved by increasing the level of operation flexibility. Altering the dispatching rules seems to have a more significant effect on the mean flow time performance than changing the level of operation flexibility.     

Machine Sharing in Manufacturing Systems: Total Flexibility versus Chaining

In this paper, we compare the operational performance of two machine-sharing configurations: total flexibility and chaining. We show that chaining captures most of the benefits of total flexibility while limiting the number of part types processed on any individual machine to only two. We examine the relative desirability of the two configurations under varying buffer sizes, loading conditions, number of machines, and setup times, as well as for different control policies. For nonzero setups times, we show that chained configurations can outperform fully flexible ones. This particularly is the case when either the number of machines or length of setup times is high. We also find that the effect of the system size on performance diminishes with the number of machines. This means that multiple smaller chains can perform almost as well as a single long one. Our results are consistent with the recent findings of Jordan and Graves (1995), who examined the economic benefits of chaining relative to full flexibility.     

A genetic algorithm approach to machine flexibility problems in an ion plating cell

For a long time, manufacturing industries have been concentrating on increasing productivity by increasing the size of the workforce, but this scenario has changed in last decade since the introduction of the term flexibility. Now, the manufacturers realize that flexibility of the machine environment can provide a better economic solution for improving productivity due to its quick response to the changing environment in the manufacturing industry. However, only very limited research on machine flexibility in the ion plating (IP) industry has been carried out and most of it has focused on product development and quality of coating. The aim of this paper is to determine the optimal level of machine flexibility in an ion plating cell (IPC) to improve the entire system performance. A machine loading sequencing (MLS) model based on a multi-objective genetic algorithm (GA) is developed and the case study of metal finishing company is discussed to validate the proposed model. Different levels of machine flexibility have been assigned to different machines to determine the optimal level to increase the overall system performance based on on-time delivery, quality of product and production cost. The results demonstrated that machine flexibility level in IPC should be zero under recent IP technology. However, when the IP technology is developed enough so that IP machine has the ability to produce different types of coating in high quality, machine flexibility should be introduced to enhance the overall system performance.     

An operational measure of routing flexibility in a multi-stage multi-product production system

The high degree of variety in customer demands causes mass production to become outdated and flexible production to be favored. Routing flexibility can be found in systems that implement general-purpose machines, alternative or identical machines, redundant machine tools, or the versatility of material handling systems. It is recognized that routing flexibility can be treated as a tool for enhancing system performance, such as lead time and inventory reduction. However, its implementation entails a huge cost of installation of flexible machines, automated tool changers and fixtures, and machine operators possessing multiple skills. Therefore, system managers must determine the appropriate level of routing flexibility for a specific system configuration in order to balance benefits and costs incurred. This paper presents a background to and a rational for a routing flexibility measure for a multi-stage flow shop. Instead of merely counting the number of available routes, this measure takes into account the loading balance between machines. Therefore, a manufacturing system with overloaded machines will have less routing flexibility as compared with one that is not overloaded, when both systems have the same number of available routes. An example for demonstrating the applicability of the proposed measure is also illustrated.     

面向订单型企业ERP中的工作流管理

ERP是一种利用信息技术全面整合企业资源的管理技术，已被越来越多的企业重视和利用。但是，由于ERP是一面向功能的事物处理系统，处理流程固化在系统之中，使得企业(特别是面向定单型企业)在处理不同业务需求时，不能灵活地应对，影响了系统的使用效果。因此，将工作流管理技术引入ERP，对提高ERP技术的实用性和灵活性具有重要的作用。文章通过将角色、权限、任务、资源等作为工作流要素，采用面向对象的方法建立工作流管理模型，并以此支持ERP中的业务处理，从而使ERP系统可灵活地配置其业务流程，提高了ERP的实用性和灵活性。     

A Comparison Between Machine Flexibility and Routing Flexibility

In this paper, we evaluate two types of flexibility, machine flexibility and routing flexibility, in terms of manufacturing performance in various shop environments. A simulation-based investigation was conducted to analyze the impact of these types of flexibility on the average flow time of parts under various job flow pattern conditions, which characterize the shop nature from a random job shop to a flow shop, operation time variance, setup time, and shop load. The experimental results show how these types of flexibility affect the average flow time of parts and which type is superior under what conditions. Management can obtain better insight and guidelines for determining priorities or the scale, or scope, of various decision items relating to design standardization, process and operations improvement, investment in new equipment and tools, and the like.     

Evaluation of routing flexibility of a flexible manufacturing system using simulation modelling and analysis

Routing flexibility is a major contributor of the flexibility of a flexible manufacturing system (FMS). The present paper focuses on the evaluation of the routing flexibility of an FMS with the dynamic arrival of part types for processing in the system. A typical FMS configuration is chosen for detailed study and analysis. The system is set at five different levels of routing flexibility. Operations of part types can be processed on alternative machines depending upon the level of routing flexibility present in the system. Two cases have been considered with respect to the processing times of operations on alternative machines. A discrete-event simulation model has been developed to describe the operation of the chosen FMS. The performance of the system under various levels of routing flexibility is analyzed using measures such as mean flow time, mean tardiness, percentage of tardy parts, mean utilisation of machines, mean utilisation of automatic-guided vehicles, and mean queue length at machines. The routing flexibility for producing individual part types has been evaluated in terms of measures such as routing efficiency, routing versatility, routing variety and routing flexibility. The routing flexibility of the system has been evaluated using these measures. The flexibility levels are ranked based on the routing flexibility measure for the system. The ranking thus obtained has been validated with that derived using fuzzy logic approach.     

Changing the climate [organisational culture for lean manufacturing]

Failure to realize the full benefits of world-class performance can often be attributed to aspects of organizational culture. Many organizations are now looking forward implementing lean manufacturing techniques. However, the employees on whom lean manufacturing is inflicted often frustrates its implementation. Many organizations overlook the importance of organizational culture in the successful implementation of lean manufacturing. It is worth knowing that in order to implement lean, it is vital to understand the culture of the said organization in order to create a cost-effective implementation plan. This paper describes the finding of a study conducted within one organization regarding the implementation of lean manufacturing.     

Simultaneous data acquisition for improved performance in transit time difference ultrasonic flowmeters

Clamp-on ultrasonic transit time difference meters have many benefits for use in industry such as their non-intrusive nature, portability and ability to work with corrosive fluids. However, all transit time difference meters suffer from a sensitivity to changes in the speed of sound or flow profile in the fluid during the ultrasonic measurement. Trigger time jitter in the data acquisition electronics can also contribute to fluctuations in the output of the meter, since the upstream and downstream signals jitter back and forth in time independently of one another. Both of these mechanisms are a product of the method of data acquisition used, where one transducer is used as a generator and the signal is received on the other, then the other transducer is driven to send ultrasound the other way. A new method of performing the measurement is proposed in which the transducers are both driven simultaneously and the signal is received on both transducers at the same time, with the ultrasonic waves having passed through the same volume of fluid with the same flow profile. It is shown that fluctuations in the output of a flowmeter at constant flow rate can be reduced by over an order of magnitude compared to acquisition modes where the generation pulse and the start of data acquisition are not actively synchronised.     

A Study of Non-Recessed Hybrid Flexible Journal Bearing With Different Restrictors

For bearings operating under heavy loads, the elastic deformation of bearing surface induced by fluid film pressures can no longer be neglected as it is comparable to the order of magnitude of fluid film thickness. In the present work a theoretical study describing comparative performance of non-recessed hybrid journal bearing using different flow control devices has been carried out by considering bearing shell flexibility into the analysis. The relevant governing equations have been solved using finite element method. The comparative performance of non-recessed hybrid journal bearings of two separate configurations have been studied for various values of bearing flexibility parameter (([Cbar]_d)). The results have been presented for hole-entry type journal bearings compensated by capillary, orifice and constant flow valve restrictors and for a slot-entry type journal bearing, for the same set of values of operating and geometric parameters. The computed results indicates that in order to get an improved performance of non-recessed journal bearing, a proper selection of bearing flexibility parameter (([Cbar]_d)) along with type of flow control device (i.e., capillary, orifice, constant flow valve, slot etc.) and type of bearing configuration (symmetric/asymmetric) are essential.     

An improved genetic algorithm for integrated process planning and scheduling

Process planning and scheduling are two of the most important functions involved in manufacturing process and they are actually interrelated; integration of the two is essential to improve the flexibility of scheduling and achieve a global improvement for the performance of a manufacturing system. In order to facilitate the optimization of process planning and scheduling simultaneously, a mathematical model for the integrated process planning and scheduling (IPPS) is established, and an improved genetic algorithm (IGA) is proposed for the problem. For the performance improvement of the algorithm, new initial selection method for process plans, new genetic representations for the scheduling plan combined with process plans and genetic operator method are developed. To verify the feasibility and performance of the proposed approach, experimental studies are conducted and comparisons are made between this approach and others with the makespan and mean flow time performance measures. The results show that the proposed approach on IPPS has achieved significant improvement in minimizing makespan and obtained good results for the mean flow time performance measure with high efficiency.     

An empirical research for CNC technology implementation in manufacturing SMEs

The aim of this research is to investigate whether CNC technology affects the firm performance and to determine the manufacturing parameters and competitive priorities that are affected by the adoption of CNC technology. In order to understand the effect of CNC adoption on firm performance, CNC user and non-user firms were investigated statistically to determine any significant difference between them. Then, the investigation was carried out on the effect of CNC technology on manufacturing parameters and competitive priorities. For this purpose a sampling pool including 100 SMEs (small and medium sized enterprises) was investigated. Thirty-eight of these SMEs had previously implemented CNC technology. Our findings show that CNC implementation makes a significant difference on firm performance. Similar results were also found in the analysis on manufacturing parameters and competitive priorities indicating that firms gain significant benefits. However, surprisingly no significant difference was found with respect to delivery performance and volume flexibility between the two groups of firms.     

Design and performance characteristic analysis of servo valve-type water hydraulic poppet valve

For water hydraulic system control, the flow or pressure control using high-speed solenoid valve controlled by PWM control method could be a good solution for prevention of internal leakage. However, since the PWM control of on-off valves cause extensive flow and pressure fluctuation, it is difficult to control the water hydraulic actuators precisely. In this study, the servo valve-type water hydraulic valve using proportional poppet as the main valve is designed and the performance characteristics of the servo valve-type water hydraulic valve are analyzed. Furthermore, it is demonstrated through experiments that a decline in control chamber pressure that follows the change of pilot flow is caused by the occurrence of cavitation around the proportional poppet, and that fundamental characteristics of the developed valve remain unaffected by the occurrence of cavitation.     

柔性液压冲击系统

液压冲击器对工作对象变化的适应能力称为冲击器柔性。现行液压冲击器以行程反馈原理来工作,由于体积及加工工艺的限制,冲击能只能在2-3挡范围内调节,且调节时需要停机。这样既不能提高工作效率,又不能实时、精确地根据冲击对象的物理性质(硬度、块度)来调节冲击参数,其柔性品质很低。研究具有自适应能力和柔性冲击能力的液压冲击器是冲击机械研究中的一个前沿性问题。基于压力反馈的氮爆式冲击器,利用活塞的冲击反弹特性实现对冲击对象性质的判断,并通过计算机控制由柔性配流系统实现冲击能与冲击频率的独立无级调节,可达到柔性冲击的效果。试验表明,柔性液压冲击系统具有时间、空间和环境等多种柔性品质。     

Scheduling of FMSs with information delays: A simulation study

Practitioners and academicians throughout the world recognize the crucial role played by flexibility within manufacturing organizations, especially those engaged in small batch manufacture. However, although the concept of flexibility has begun to attract increased attention, its interaction with information integration and automation has not captured due attention. For example, it almost always has been assumed that a real-time control mechanism is available for exploiting routing flexibility on the shop floor. While this may be true for FMSs, it generally is not so for the vast majority of conventional manufacturing systems with varying levels of information integration and automation. The lack of a fully integrated and automated control mechanism within such semi-automated flexible manufacturing systems (SAFMSs) would eventually cause delays in the availability of shop status information. In this paper, we study the impact that defined modes of information delay have on the performance of a hypothetical SAFMS through detailed simulation experiments. Given that the level of routing flexibility is a controllable design parameter, our interest is in determining the impact that information delays have on decisions pertaining to the selection of appropriate levels of routing flexibility. To highlight the impact of information delays within the SAFMS, the Taguchi experimental design procedure is adopted as a performance evaluation and analysis vehicle, using makespan as a measure of performance. Simulation results indicate the presence of a system specific tolerance limit, operation below which minimizes performance loss.     

Control of an Assembly System with Processing Time and Subassembly-Type Uncertainty

We address the problem of controlling an assembly system in which the processing times as well as the types of subassemblies are stochastic. The quality (or performance) of the final part depends on the characteristics of the subassemblies to be assembled, which are not constant. Furthermore, the processing time of a subassembly is random. We analyze the trade-off between the increase in the potential value of parts gained by delaying the assembly operation and the inventory costs caused by this delay. We also consider the effects of processing time uncertainty. Our problem is motivated by the assembly of passive and active plates in flat panel display manufacturing. We formulate the optimal control problem as a Markov decision process. However, the optimal policy is very complex, and we therefore develop simple heuristic policies. We report the results of a simulation study that tests the performance of our heuristics. The computational results indicate that the heuristics are effective for a wide variety of cases.     

Evaluation of multi-holed orifice flowmeters under developing flow conditions – An experimental study

This study focuses on multi-holed orifice plates, which have superior flow measuring characteristics as compared to their conventional counterparts. However, literature is scant on quantitative parametric investigations. In this experimental study, the performance of a multi-holed orifice plate is evaluated for variable number of holes (n), equivalent diameter ratio (EDR), compactness ratio (C), plate thickness ratio (s/d) and upstream developing length (L/D) in developing flow regimes for the Reynolds number range of 24,500–55,500 by using Central Composite Design. A total number of 324 experiments were performed. It was found that EDR has the most significant effect on pressure loss coefficient, followed by ‘n’ and ‘C’. Moreover, it was found out that single orifice (SO) and multi-holed orifice (MO) have almost the same pressure losses for the same value of EDR/β. However, flow develops quickly for MOs. Higher values of coefficient of discharge were observed in the case of MOs as compared to the SOs with little effect of upstream disturbances. The effect of developing length is significant on the accuracy of orifice meter. However, when the multi-holed orifice plates are installed at 2D upstream length, the effect of upstream disturbances are diminished. This result provides the flexibility of installation, which means that multi-holed orifices can be installed at 2D. The experimental data is in good agreement with literature. Finally, an optimum orifice plate (5,0.4,0.7) was selected for flow developing region with minimum pressure loss coefficient based upon the experimental results.     

Operational flexibility quantification in a make-to-order assembly system

Manufacturing flexibility is becoming a fundamental production objective, along with cost, quality, and delivery time. Current production systems face quick changes in market conditions and they need to adapt in this environment. The supply chain and industrial globalization give an important role for assembly systems. Placed at the end of the value chain, assembly systems must face those quick changes successfully to reach the expected performance. The key performance indicators are normally based on cost, quality, and delivery time objectives. Reducing costs and improving quality are almost universal goals. Delivery time is typically determined by customer demand in the supply chain, planning from make-to-stock to make-to-order, and aspiring to reach a just-in-time manufacturing system. In this context, flexibility could be the differential advantage to tackle uncertainty. Closely related to the rest of production objectives and the overall performance of the system, flexibility must be integrated in the system for successful decision-making in operations. This work presents this approach of flexibility. A brief review of flexibility concepts and measurements in the literature precedes an introduction to flexibility, defined based on the function of utility. This function represents the expectations of system performance. This approach allows the formulation of the taxonomy of operational flexibility in agreement with the classical types identified in former works. Next, an integer model is programmed to simulate the basic behavior of task planning in a make-to-order assembly system. This first application illustrates flexibility quantification based on utility evolution. The use of common industrial parameters to quantify operational flexibility will finally facilitate an integrated interpretation of system performance trends.     

叶顶间隙对轴流式叶轮机械性能及噪声的影响研究进展

在轴流式叶轮机械中转子与机壳之间存在一定的间隙,该间隙的大小对叶轮机械的全压、效率和噪声等均有很大影响。结合近年来在叶顶间隙领域开展的研究,详细综述了国内外在叶顶间隙对轴流式叶轮机械性能及噪声的影响等方面的研究进展,并对叶顶间隙在今后的发展方向进行了展望,为叶轮性能的优化提供参考。