Balancing printed circuit board assembly line systems

This paper considers the placement of components onto printed circuit boards (PCBs) using surface mount technology. Multiple automatic placement machines, a variety of PCB types and a large volume for each PCB type characterize the environment studied. The problem addressed is that of allocating and arranging the components on several placement machines, organized into one or several assembly lines, while considering a different assembly time if components are located at different feeder locations. The one assembly line problem is equivalent to balancing a multi-model assembly line where models are assembled in small batches without component rearrangement between model changes. The objective is tominimize the weighted sum of each assembly PCBcycle time, which is defined as the maximum time a PCB has to spend on each machine. We solve this problem with Lagrangian relaxation techniques. Industrial case study results are presented. We also compare the global performance of five placement machines if they are organized as a single assembly line or broken down into two or more assembly lines.     

Estimating printed circuit board assembly times using neural networks

Several production planning tasks in the printed circuit board (PCB) assembly industry involve the estimation of the component placement times for different PCB types and placement machines. This kind of task may be, for example, the scheduling of jobs or line balancing for single or multiple jobs. The simplest approach to time estimation is to let the production time be a linear function of the number of components to be placed. To achieve more accurate results, the model should include more parameters (e.g. the number of different component types, the number of different component shapes, the dimensions of the PCBs, etc.). In this study we train multilayer neural networks to approximate the assembly times of two different types of assembly machines based on several parameter combinations. It turns out that conventional learning methods are prone to overfitting when the number of hidden units of the network is large in relation to the number of training cases. To avoid this and complicated training and testing, we use Bayesian regularisation to achieve efficient learning and good accuracy automatically.     

Rolling horizon production scheduling of multi-model PCBs for several assembly lines

The joint task of allocating several PCB assembly jobs to a set of production lines, load balancing of the line machines and job scheduling is considered. The production facility includes a number of assembly lines of different kinds, the PCB jobs are of different types and they should be allocated to suitable (i.e. feasible) lines. Scheduling of the production should respect the predefined release and due dates, and the objective is to minimise the sum of job tardy times. The scheduling is of the rolling-horizon-type where at the beginning of each planning period new jobs are inserted in the current non-preemptive production programme of unfinished jobs from the past planning periods. A mathematical formulation and a two-phase heuristic (including initial job-to-line allocation and schedule improving steps) are given for the problem. Experimental tests with jobs from practice were convincing.     

Workload planning in small lot printed circuit board assembly

The problem of workload planning in small lot printed circuit board (PCB) assembly concerns the determination of the daily mix of production orders to be released into the production system. When switching from one production order (board type) to another, a considerable set-up time is incurred based on the number of component feeders to be replaced in the component magazine of the assembly machines. To support the order-mix decision faced by a major electronics manufacturer, two versions of a linear programming model are developed. The models differ primarily in their degree of aggregation and their computational effort. In order to reduce the aggregational error incurred, a fuzzy approach is developed to estimate the number of component set-ups at automatic SMD placement machines. Our numerical investigation reveals that sufficiently accurate solutions may be obtained from a highly aggregate fuzzy LP-model and this is achieved with considerably less computational effort than with a more detailed LP-model. We also demonstrate the potential suitability of the fuzzy LP-model for implementation within an interactive decision support system.     

A GA-based solution approach for balancing printed circuit board assembly lines

Printed circuit board (PCB) assembly lines consist of a number of different machines for mounting electronic components onto PCBs. While high-speed placement machines are employed to assemble standard components, so-called fine-pitch placement machines are used to mount complex electronic components with high precision and by use of specific nozzles. In this paper, we investigate a typical mass production environment where a single type of PCB is assembled in a line comprising high-speed as well as high-precision placement machines. The PCB assembly line balancing problem consists of assigning component feeders, each holding a specific electronic component type, and the corresponding placement operations to machines in the line so as to minimize the assembly cycle time. To solve this problem, a two-stage solution procedure based on genetic algorithm (GA) is proposed. In the first stage, component feeders are assigned to the placement machines with the objective of balancing the workload within the assembly line. A number of candidate solutions are then transmitted to the second stage, where specific machine optimization algorithms are applied to determine the feeder-slot assignment in the component magazine of the machines and the placement sequence of the various components. As a result, fine-tuned placement operation times are achieved which reflect the individual operation mode and the actual component setup of the placement machines. Finally, from the candidate solutions the one which minimizes the actual PCB assembly time is selected.     

Automatic Petri Net Simulation Model Generation for a Continuous Flow Transfer Line with Unreliable Machines

A production line is studied with several machines in series. The machines are separated with finite buffers. They can break down and have to be repaired. Production is assumed to be continuous, i.e. no individual products can be identified. Analytical models for the performance evaluation of such a system are scarce. Analytical results for the throughput can be obtained only under very restrictive assumptions. The performance study of longer transfer lines requires either approximation or simulation. A Petri net model is developed for an n‐machine ‐buffer system. The rules to design the Petri net transitions are given. The automatic generation of a discrete‐event simulation model from the Petri net model is explained. Finally, some potential applications of the Petri net are illustrated. These applications include the simulation of transfer lines with complex stochastic behaviour, the optimization of buffer size and allocation and the evaluation of approximation models for long transfer lines. Using the simulation model described in this paper, quality and reliability engineers can simulate the performance of a given continuous flow transfer line and evaluate the effect of performance‐increasing measures such as the insertion of extra buffer space or the use of more reliable machines. Copyright © 2004 John Wiley & Sons, Ltd.     

PCB assembly scheduling for collect-and-place machines using genetic algorithms

In printed circuit board (PCB) assembly, collect-and-place machines, which use a revolver-type placement head to mount electronic components onto the board, represent one of the most popular types of assembly machinery. The assignment of feeders to slots in the component magazine and the sequencing of the placement operations are the main optimisation problems for scheduling the operations of an automated placement machine. In this paper, we present different genetic algorithms (GAs) for simultaneously solving these highly interrelated problems for collect-and-place machines in PCB assembly. First we consider single-gantry machines as the basic type of machinery. In the conventional GA approach all placement operations and the feeder-slot assignment are represented by a single chromosome. In order to increase the efficiency of the genetic operators, we present a novel GA approach, which integrates a clustering algorithm for generating sub-sections of the PCB and grouping the corresponding placement operations. It is shown that the proposed GAs can be extended to schedule dual-gantry placement machines, which are equipped with two independent placement heads and two dedicated component magazines. Hence, component feeders have to be allocated between the two magazines. To solve this allocation problem, two different heuristic strategies are proposed. Finally, detailed numerical experiments are carried out to evaluate the performances of the proposed GAs.     

辊板式铝塑泡罩包装机的开发

目的 铝塑泡罩包装机分为DPA系列(辊辊型)、DPP(B)系列(平板或板板型)、DPH(T)系列(辊板型)3种类型,针对过去的泡罩包装机存在着一些如封合后会弯曲、影响美观以及效率低下等问题,需要加大力度对泡罩包装机进行设计开发,使其达到国际先进水平。方法 DPH(T)系列辊板式铝塑泡罩包装机在辊辊式和平板式铝塑泡罩包装机的技术基础上优化并组合,DPH(T)系列辊板式铝塑泡罩包装机采用平板式吹塑成型(也叫正压成型)和辊式封合技术;新研发的DPH辊板型铝塑泡罩包装机采用摆线运动规律来改善凸轮的动力特性。结果 DPH(T)系列铝塑泡罩包装机生产效率高、运行平稳、结构合理、操作简单、性能可靠、消除了刚性和柔性冲击;DPH(T)系列铝塑泡罩包装机广泛用于药品、食品等的包装。结论 DPH(T)系列铝塑泡罩包装机综合性能得到了改善和提高,并且有些机型目前已经达到了国际先进水平。     

A note on ‘balancing printed circuit board assembly line systems’

In a recent paper of (Lapierre, S.D., Debargis, L. and Soumis, F., Balancing printed circuit board assembly line systems. Int. J. Prod. Res., 2000, 38, 3899–3911.), the authors considered the balancing of a PCB assembly line consisting of several pick-and-place machines. The authors claimed that, for the particular machine type they considered, the component placement time is independent of the placement sequence of the components and then concentrated on allocating component types to machines and configuring the feeders on each machine to balance the line. We show that, the placement time is actually dependent on the placement sequence and thus, it needs to be accounted for if a more accurate line balance is looked for.     

Integration of computer simulation in design for manufacturing and assembly

As a reason for competitiveness, the process of product development evolves using, in some situations, improvement methods, e.g. design for manufacturing and assembly (DFMA). In the framework of the product development process, it is desirable that engineers and managers have a systemic view of the effects that changes in local processes will have on the overall performance of the entire production system. This vision of such effects can be achieved with computer simulation. This study aims at assessing how DFMA can be integrated with computer simulation and the benefits from the alternatives identified by such method during production and assembly. Using the electronic voting machine printer as object of study, options to improve design by means of DFMA principles are identified. Five models were developed to represent the current assembly process and two models following the implementation of the changes proposed by the DFMA. The sale price is confidential (exclusive product of the Brazilian government). The company provided data in assembly costs. The results show the production increase in assembly time (9.94%) and average daily sales ($415).     

Development of group setup strategies for makespan minimisation in PCB assembly

Balancing setup effort and actual production time is an important issue in medium-variety, medium-volume printed circuit board (PCB) assembly. By grouping batches of similar PCB types to be processed with a common machine setup, the total time required for setting up the component feeders in the magazine of the placement machine can be reduced. On the other hand, the assembly times per PCB increase, since it is no longer possible to optimise the feeder locations in the magazine for each PCB type individually. In order to balance the savings in setup time and the increase in assembly time and to minimise the global makespan, we propose efficient grouping procedures which include machine-specific algorithms for fine-tuning the machine operations for a group of PCBs. Hence, the actual placement times are reflected much more accurately, compared with conventional grouping procedures which merely analyse the component similarity between pairs of PCBs. Two different agglomerative clustering techniques are proposed. One is based on average linkage clustering, the other on a novel hierarchical clustering approach using an inclusion tree representation of the PCB types. Both take the limited capacity of the component magazine into account. We demonstrate the effectiveness of our approach in an extensive numerical investigation of a single-gantry collect-and-place machine equipped with a rotary placement head and an interchangeable feeder trolley. Compared to conventional methodologies, the proposed group setup strategies reduce the global makespan for a given number of batches significantly.     

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。     

Role of similarity measures in PCB grouping procedures

The problem of grouping printed circuit boards (PCBs) for simultaneous assembly on electronic assembly machines is an extension of the set-covering problem. A general approach based on cluster analysis and measure of similarity between PCBs is suggested as a basis of PCB grouping. The approach is independent of the specific similarity measure used. We show that, due to the analogy between this problem and the problem of machine cell formation in group technology, similarity measures developed for the second problem are useful as building blocks in a general framework that solves the PCB grouping problem.     

Product quality inspection in Bernoulli lines: analysis,bottlenecks, and design

This paper is devoted to serial production lines consisting of producing and inspection machines that obey the Bernoulli reliability and Bernoulli quality models. Such production lines are encountered in automotive assembly and painting operations where the downtime is relatively short and the defects are due to uncorrelated random events. For these systems, this paper develops analytical methods for performance analysis, bottleneck identification, and design. In addition, insights into the nature of bottlenecks in such systems are provided, and an empirical rule for placing an inspection machine that maximises the production rate of non-defectives is formulated.     

Determination of buffer sizes for drum–buffer–rope (DBR)-controlled production systems

The present paper describes an analytical approach based on reliability analysis to determine the sizes of constraint buffer and assembly buffer in a drum–buffer–rope-controlled production system. Every machine in the system is modelled as a two-state named as up and down canonical model. Then, with these canonical models and the relationships between the feeder and fed machines, the models for determining constraint buffer and assembly buffer are constructed. To illustrate the approach's practical usefulness, a numerical example is presented. Based on the data analysis, we find that, for constraint buffer, the more feeder machines, the smaller the buffer size needed. And for assembly buffer, the more feeder machines the larger the buffer size needed. Then, two pieces of advice for the production managers to effectively use production-controlling policies are proposed.     

Capacity planning of serial and batch machines with capability constraints for wafer fabrication plants

Capacity planning is crucial to the investment and performance of wafer fabs. This research proposes a practical procedure to calculate the required number of machines with serial and batch processing characteristics, respectively. Several formulae are first presented. Five heuristic algorithms are then proposed to determine the lower bound, the upper bound, and the near-optimal of the number of machines of the type with capability constraint. Data from real foundry fabs are used in a case study to determine the required number of 64 types of equipment and to evaluate the performance of the proposed procedure. The algorithm using the best ratio of production efficiency and equipment cost to select the machine type with capability constraint results in the least required number of machines, the highest machine utilisation, and the lowest equipment investment. An AutoSched AP simulation model is used to evaluate if a wafer fab using the calculated number of machines of each type can result in a preset monthly output rate. Simulation results indicate that the proposed procedure can quickly and accurately calculate the required number of machines leading to the required monthly production target. Fab managers can use this tool to conduct what-if analysis for equipment investment alternatives.     

Effect of maintenance policies on the just-in-time production system

Using simulation, experimental design, and regression analysis, mathematical models are developed here to describe the effect that maintenance policy, machine unreliability, processing time variability, ratio of preventive maintenance time to processing time, ratio of minimal repair time to preventive maintenance time, and production line size have on various measures of performance, namely total production line output and production line variability of the just-in-time production system. The analysis of the data shows that under different situations, different maintenance policies do not have the same effect on the production line performance. The following conclusions were obtained; when the number of production machines is low (five machines or less), and/or when the ratio of minimal repair time to preventive maintenance time is high, maintenance policy III leads to a higher performance than maintenance policy II. Otherwise maintenance policy II, which is more sensitive to the change of the ratio of minimal repair time to preventive maintenance time, leads to a higher performance. The results of the study can be utilized in choosing a maintenance policy as a function of the production process parameters. Once a policy is chosen, the practitioner can select the most important factors to control under that policy in order to minimize the machine idle time, maximize the production process reliability, improve productivity, and therefore increase the production line performance.     

Component allocation and job sequencing for two series-connected SMD placement machines

The problem of component allocation and sequencing PCB assembly jobs for two series-connected SMD placement machines is addressed. With the allocation of components, a balancing of the workload per PCB for the two machines should be achieved. Furthermore, when switching from one type of PCB to another, setup times must be considered. Two heuristic procedures are developed and tested in extensive numeric analyses of a number of realistic case models. The problem examined and the database used represent a concrete case of an industrial application in which very diversified small jobs are to be processed.     

Aggregate line capacity design for PWB assembly systems

In a multi-product, flexible manufacturing environment, line capacity of printed wiring board (PWB) assembly systems may need to be adjusted at the beginning of each aggregate planning period because of demand fluctuation over multiple periods. A model of production planning and equipment changeover scheduling at the aggregate level is developed. In the described model, three kinds of equipment changeover methods, i.e. adding machine, removing machine and transferring machine, are involved. Because the model is a large-scale integer programming problem, it cannot be solved directly. A solution approach is developed, which first solves a recursive linear programming problem to obtain a rough set of machines to be added and a rough set of machines to be removed for each machine line in each period, then applies a branch and bound heuristic to the rough sets to obtain near-optimal solutions to the equipment changeover scheduling problem. Computational studies show the financial benefit both on capital cost and equipment changeover costs.