Lot cycle time prediction in a ramping-up semiconductor manufacturing factory with a SOM–FBPN-ensemble approach with multiple buckets and partial normalization

“Ramp-up” is the process of increasing the production rate of a semiconductor manufacturing factory from the first lot to whole volume. Lot cycle time estimation and control during production ramp-up in a semiconductor factory is even more important. However, in addition to the large fluctuation, there are also trends and jumps (sudden increases) in the lot cycle time, which makes it a very challenging task. A SOM–FBPN-ensemble approach with multiple buckets and partial normalization is therefore proposed in this study for lot cycle time prediction in a ramping-up semiconductor manufacturing factory, which was seldom investigated in the past studies. The proposed methodology is composed of two parts. In the first part, the multiple-bucket approach is applied to consider the ramp-up plan of the semiconductor manufacturing factory. Subsequently, the SOM–FBPN-ensemble approach is applied to predict the cycle time of every lot in the ramping-up semiconductor manufacturing factory. The buckets obtained in the first part become additional inputs to the SOM–FBPN, and every parameter is normalized into a range narrower than [0, 1] to reflect the difference between the future and the past. To evaluate the effectiveness of the proposed methodology, a production simulation model was employed in this study. According to experimental results, the prediction accuracy of the proposed methodology was significantly better than those of many existing approaches.     

半导体重入加工过程自动组合装置的建模与分析

利用面向资源的着色赋时Petri网,对半导体业中自动组合装置的可重入加工过程进行了建模,描述了具体的加工过程,同时从定性和定量的角度出发,分别分析单手机器人和双手机器人自动组合装置模型的死锁问题和产能,研究了避免死锁的控制策略,以及初始特性、稳态特性和结束特性。     

The practices of integrating manufacturing execution systems and Six Sigma methodology

Currently, manufacturing execution systems (MESs) are widely used in the aerospace, automotive, semiconductor, optoelectronic, pharmaceutical and petrochemical industries, as well as other sectors. An MES can link with automation equipment to record relevant information automatically and control the quality of work in process (WIP), statistics analysis, production scheduling and the maintenance of equipment and instruments, etc. In recent years, the manufacturing industry has successfully applied the Six Sigma methodology to projects. However, due to insufficient data or a misunderstanding of the Six Sigma methodology, some of the projects failed. This paper aims to discuss the define, measure, analyse, improve, control (DMAIC) phases of integrating an MES with Six Sigma methodology, detailing the phases to improve the above situation and to avoid the extra time and cost of sourcing data. It will improve the process performance and capability, cycle time, rolled throughput yield and operating costs significantly, which, in turn, improves the quality of implementing the Six Sigma methodology quickly and precisely.     

Discovery of hidden maintenance opportunities in automotive assembly lines: MOW and GMOW

In manufacturing systems, many maintenance tasks require equipment to be locked out for safety. However, such stoppage might directly cause short-term production losses although maintenance is performed to increase the long-term system reliability. In this paper, we investigate how long we can strategically stop equipment for maintenance during production operating without affecting system throughput. We extend the concept of maintenance opportunity windows (MOWs) to various system configurations and introduce a new concept of group maintenance opportunity windows (GMOWs). GMOW is the maximum time window that allows to perform a group maintenance without jeopardizing the flow of a production line. Moreover, we also provide how to calculate MOW and GMOW via simulations which can deal with uncertainties in production lines, such as random machine failures, starvations, blockages, etc.     

两种多层穿梭车系统的性能比较分析

物流配送中心订单响应速度的加快,对订单拣选系统提出了更高的要求。多层穿梭车系统因其柔性强、效率高等特点,近年来得到了广泛应用。多层穿梭车系统具有两种形式--基于转载车和基于环形输送线,二者均可实现货物的快速拣选,但在系统吞吐量和订单完成周期方面存在差异,致使企业决策者难以进行系统选择。基于上述原因,本文比较两种多层穿梭车系统的性能差异。建立两个系统的开环排队网络模型,然后求解系统吞吐量、订单完成周期,通过仿真验证了排队论模型的准确性,通过试验对两种系统的性能进行对比分析。结果表明,系统吞吐量与层数、巷道数相关,层数越多,巷道数越少,转载车系统相对于环线系统优势越显著;订单完成周期与层数、订单到达率相关,层数越多,订单到达率越低,转载车系统相对于环线系统越具优势。     

Sandglass-type product specification management method for supporting modular design of semiconductor manufacturing equipment

The product life cycle for semiconductor manufacturing facilities has been significantly reduced as a result of the technological advancement of the semiconductor manufacturing process and the expansion of its demand. To ensure long-term market competitiveness under this environment, many companies attempt to convert their systems into mass customization production systems. In general, the specification management for semiconductor manufacturing equipment has adopted the method of making the bill of materials structure of the existing equipment into a new one based on the same physical structure and then customizing it according to a customer’s demands in the detail design phase. However, this method results in longer lead times and difficulties maintaining data consistency due to frequent design changes in connection with various derived products. We suggest a sandglass-type product specification management method to efficiently reflect varying and versatile requirements in product development and shorten the design lead time. In addition, we propose a method to support the modular design of semiconductor manufacturing equipment by classifying the standard specifications for a final product into product component and part component specifications. Finally, we develop a closed-loop product specification management system called NEXUS using our method, and apply this system to semiconductor manufacturing processes.

     

Dispatching of overhead hoist vehicles in a fab intrabay using a multimission-oriented controller

The semiconductor manufacturing system has become one of the most important manufacturing systems in recent years. Intrabay automation for wafer transport is in high demand in a 300 mm foundry fab. The control of the transport system plays an important roles in manufacturing efficiency and the satisfaction of production strategy. In general, efficiency is the most important issue that has appeared in most research of automated transport systems. However, how to dynamically adjust the transport policy to meet the production strategy and to increase the transport efficiency as well seems to be more crucial to modern semiconductor manufacturing systems. In this paper, a fuzzy-logic-based multimission-oriented overhead vehicle dispatcher is developed. The vehicle dispatching rule is assigned in real-time according to the statistics of the manufacturing performance. In this manner, the dispatching rules can be adjusted according to possible high-risk lots so that most of the production strategies can be satisfied. If all of the lots meet the prescribed production strategies, then the nearest-job-first rule can be used to offer higher transport efficiency. In addition, the proposed vehicle dispatcher is also capable of deadlock-free operation, collision avoidance, and blockage prevention. Finally, this paper uses AutoMod simulation software to construct and evaluate the manufacturing models. By evaluating the simulation results, the proposed intelligent multimission-oriented vehicle dispatcher performs better performance than the others, and all of the production strategies are satisfied .     

Optimization and implementation of cellular manufacturing system in a pump industry using three cell formation algorithms

In recent years cellular manufacturing has become an effective tool for improving productivity. Attainment of full benefits of cellular manufacturing depends firstly on the design of the machine cells and part families and secondly on the method of operation which take full advantages of cell properties. Inappropriate methods of loading and scheduling can even lead to the failure of cellular manufacturing systems (CMS), however efficiently the cell is designed. This paper examines three array-based clustering algorithms, namely rank order clustering (ROC), rank order clustering-2 (ROC2) and direct clustering analysis (DCA) for manufacturing cell formation, with a real-life example to demonstrate the effectiveness of various clustering algorithms. The machine cell formation methods considered in this comparative and evaluative study belongs to the cluster formation approach of solving the MCF problem. The most effective method is selected and used to build the cellular manufacturing system. The comparison and evaluation are performed using four published performance measures and compares the improvements with the existing conventional system and the cellular manufacturing system. The above algorithms were written in the C++ language on an Intel/Pentium III-PC-compatible system.     

Machine loading in flexible manufacturing systems considering routeing flexibility

The key competitive strength of a manufacturing system lies in its flexibility, which represents the ability to respond effectively to changing circumstances. Flexible manufacturing systems (FMSs) react appropriately to change. The relevance of a particular type of flexibility depends upon the system and problem being considered. In this paper, the machine loading problem in a flexible manufacturing system is addressed. The loading problem is concerned with the allocation of part operations and required tools to the machines, so as to optimise some objective(s) subject to some technological constraints. Several objectives have been considered in the past such as maximisation of the utilisation of resources, minimisation of processing and tooling costs and maximisation of throughput rates. In such procedures, it is quite probable that a rigid loading schedule is obtained and in cases of machine breakdowns and tool failures alternate routeings are often not available. Therefore, in this paper, we develop a mathematical model which considers maximisation of the production routeings available for the parts and hence increases the routeing flexibility. The model is illustrated by examples.     

CIMS软件可靠性保证技术

软件已成为计算机集成制造系统(CIMS)的关键组成部分,其可靠性直接影响到CIMS的性能、运行和维护成本.本文从软件生存周期的角度,论述了在各个阶段中保证软件可靠性的技术.     

Cycle time variance minimization in dynamic scheduling of single machine systems

In this paper, we study the minimization of variance of cycle times in a dynamic single machine system where jobs arrive continuously over time. Numerous production systems give rise to single machine models, and a multiple-machine environment where the performance of a bottleneck machine determines the performance of the entire system reduces to a single machine problem [16]. Minimizing cycle time variance helps in safe predictions of the completion of job production and thus in providing the same quality of service to the customers. This allows an improved ability to meet the due dates reliably, and thus the greater coordination with further downstream operations on the jobs, as highly preferred in semiconductor manufacturing. Scheduling the bottleneck process to minimize the time of presence of the jobs in process minimizes the deterioration of cycle time-related performance measures. Low values of cycle time-related measures are also preferred for low risk of wafer contamination associated with it during processing. New scheduling rules are developed to minimize both the cycle time variance and the maximum cycle time for single machine system, wherein the machine/process is always utilized to the maximum extent and in the extreme case is heavily loaded with jobs for processing. The performance of the proposed rules is compared with the rules available in the literature and the results are presented for the objectives of minimizing cycle time variance and maximum cycle time at higher levels of machine utilization.     

Reliability Optimisation of FMS with Spare Tooling

Tool reliability plays an important role in the performance and justification of flexible manufacturing systems (FMS). Failure of a single tool can cause downtimes over the entire system. This results in missing due dates, and inferior products. Therefore, in order to justify the large capital investment associated with FMS, the system must perform in a reliable manner to give an acceptable or expected rate of return on capital. FMS reliability should be studied at the planning and design stages, as tool failures pose a major obstacle to achieving this objective. In this paper, a mathematical model has been developed to determine the spares requirement of the tooling system in an FMS, so that the desired system reliability is achieved and the cost is minimised. The influence of tool sharing on cost, reliability, spares requirement, and tool magazine capacity of the FMS are analysed. The tools and tool transporter are subject to general failure distributions.     

物与信息混合驱动的带返修生产系统性能分析

聚焦物与信息两流混合驱动的含返修闭环异步串联生产系统,在综合考虑加工设备和信息控制设备随机故障的基础上研究了生产和信息控制参数对复杂生产系统稳态性能的影响。基于工件加工与信息的交互作用关系,采用重叠分解法将该系统拆分成多个混合驱动的装配和拆卸子系统。建立了前向和反向递归迭代算法来估计系统稳态生产率。数值实验与工业缝纫机数字化生产线案例验证了迭代算法在识别系统瓶颈和估算系统稳态性能等方面的有效性。     

基于模糊Petri网推理的半导体生产线动态调度研究

针对动态调度的特点,为了综合优化半导体生产线性能指标,尝试使用基于模糊Petri网推理的方法进行动态调度。首先分析了影响动态调度决策的生产线状态信息;然后建立了模糊Petri网形式化推理机,继而构建了面向半导体生产线的模糊Petri网推理模型;最后使用实际半导体生产线模型,将提出的方法与FIFO、EDD和CR策略进行了仿真比较。结果表明基于模糊Petri网推理的动态调度方法能够改善半导体生产线多种性能指标。     

Estimation of Part Waiting Time and Fleet Sizing in AGV Systems

As manufacturing systems have grown in size and complexity, material flow control has become one of the key issues for system efficiency, and determination of the number of vehicles required is an important issue in the design of the AGV (automatic guided vehicle) systems for automated material flow control. In an AGV system, a part issues a delivery request for its transportation, and then an empty vehicle is assigned based on a pre-determined vehicle selection rule and provides delivery service. This research presents a fleet sizing procedure for an AGV system with multiple pickup and delivery stations. A queueing model is used to estimate part waiting times. The fleet sizing procedure estimates the minimum number of vehicles needed to ensure a predefined part waiting time limit. While most stochastic models assume first-come-first-served or random vehicle selection rules for the selection of an empty vehicle, this model considers such additional rules as the nearest vehicle selection rule, which is the most popular among all vehicle selection rules. The performance of the proposed model is examined through computational experiments. This work was supported by Korea Research Foundation Grant (KRF-2003-042-D20136).     

Reliability Optimisation of Flexible Manufacturing Systems with Spare Tooling

Tool reliability plays an important role in the performance and justification of flexible manufacturing systems (FMSs). Failure of a single tool can cause downtimes over the entire system. This would cause due dates to be missed and can result in inferior products. Therefore, in order to justify the large capital investment associated with FMSs, the system must perform in a reliable manner to give an acceptable or required rate of return on the investment. In order to arrive at this objective, FMS reliability must be studied at the planning and design stages, tool failures pose a major obstacle to achieving this objective. In this paper, a mathematical model has been developed to determine the spare tooling requirement for the tooling system in an FMS, so that a desired system reliability is achieved and the cost is minimised. The influence of tool sharing on cost, reliability, spares requirement, and tool magazine capacity of the FMS are analysed. The tools and tool transporter are subject to general failure distributions.     

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.     

Reliability analysis of flexible manufacturing systems

High productivity is the primary goal of flexible manufacturing systems (FMSs) in which semi-independent workstations are integrated using automated material-transport systems and hierarchical local networks. Availability of various subsystems and of the system as a whole is a prerequisite for achieving functional integration as well as high throughput. An FMS also has inherent routing and operation flexibilities that provide it with a certain degree of fault tolerance. A certain volume of production can thus be maintained in the face of subsystem (i.e., machines, robots, material handling system, etc.) failures. In this article, we propose two reliability measures, namely, part reliability (PR) and FMS reliability (FMSR) for manufacturing systems and present algorithms to evaluate them. We also consider the dynamic or time-dependent reliability analysis as a natural generalization of the static analysis. The methods outlined use an algorithm that generates process-spanning graphs (PSGs), which are used to evaluate the reliability measures.     

Actuarial calculation of the squareness errors for ultra-precision micro v-groove machine tools

Automation is a powerful way to reduce production costs. The growing market demand for a wide set of models and small batch production make flexible automated production systems an emerging need in several industries. The aim of this paper is to analyze and to maximize the performance of robotized flexible production systems consisting of a robot, feeder, working station, and unloading station, where the operations of the working cycle are scheduled using a sequencing algorithm based on priority rules. Since the working cycle is not predefined, the cycle time is strongly influenced by the parameters characterizing the workcell such as the workcell layout, the robot transfer movements, the feeder, the working operations, and the presence of a buffer between stations. In this work, we modeled the working cycle of a simple but representative layout of an industrial robotized flexible production system with and without buffer, and we implemented a recursive algorithm to estimate the cycle time. The analytical model derived was compared to the experimental results, obtained by using a prototype of the flexible production workcell. The results show that the analytical model is a powerful tool to estimate the performance of the workcell and to identify the design variables or their combinations that maximize the throughput.     

Simultaneous scheduling of machines and vehicles in an FMS environment with alternative routing

Scheduling of flexible manufacturing systems is a well-known NP-hard problem which is very complex, due to additional considerations like material handling, alternative routing, and alternative machines. Improvement in the performance of a flexible manufacturing system can be expected by efficient utilization of its resources, by proper integration and synchronization of their scheduling. Differential evolution is a powerful tool which proved itself as a better alternative for solving optimization problems like scheduling. In this paper, the authors addressed simultaneous scheduling of both machines and material handling system with alternative machines for the makespan minimization objective. The authors proposed a machine selection heuristic and a vehicle assignment heuristic which are incorporated in the differential evolution approach to assign the tasks, to appropriate machine and vehicle, and to minimize cycle time.