Labour productivity in modular assembly: a study of automotive module suppliers

Modular assembly is being applied to an increasing number of vehicles and part manufacturers to manage the ever-changing demands of the automotive industry. In spite of many researches performed on the supply chain management and logistics aspects of modular production, there is no research discussing modular production line concepts used by module suppliers. In this paper, labour productivity of two assembly line concepts including the conveyor line and box assembly line is studied under modular production environment. Both line concepts and respective assembly processes are described in detail. Mathematical models showing the total work faced by these two assembly line concepts are developed and compared. Two productivity scales are defined: the maximum achievable productivity and the actual productivity. The labour productivity rates of these assembly line concepts on above productivity scales obtained from calculations and a simulation are compared as a performance measure.     

Analysis and improvement of multi-product assembly systems: an application study at a furniture manufacturing plant

In this paper, we introduce an application study of modelling, analysis and continuous improvement of an assembly system at a furniture manufacturing plant using production systems engineering methods. Analytical models have been developed to characterise the assembly system making multiple products, and recursive procedures have been derived to evaluate line production rate. Lot size analysis is carried out, and bottleneck analysis methods are introduced to identify the bottlenecks, whose improvement can lead to the largest improvement in system performance. Such methods provide a quantitative tool for plant engineers and managers to operate and improve assembly line with high productivity, and are also applicable to other large-volume manufacturing systems.     

基于启发式算法的电控板装配线线平衡优化

为了解决人员配置不稳定而导致的工位作业负荷不平衡问题,以某电控板装配企业为对象,构建其电控板装配线生产模型和线平衡优化模型。在该优化模型中,将约束条件转化为启发式规则,改进模型的参数设置和处理过程,将该模型转化为可求解的启发式算法。以该企业某电控装配线为例,通过线平衡优化实验证明该模型有效提高产量和线平衡率,说明该模型是有效和实用的。     

Mixed model assembly system with multiple secondary feeder lines: layout design and balancing procedure for ATO environment

The constant research for efficiency and flexibility has forced assembly systems to change from simple/single assembly lines to mixed model assembly lines, while the necessity to reduce inventory has led the transition from single to multi-line systems, where some components are assembled in secondary lines, called feeder lines, connected to the main one by a ‘pull philosophy’. A possible approach to configure such an assembly system is to balance the main line first and use the retrieved cycle time to balance each feeder line separately, which is a questionable solution, especially if operators can perform tasks on both the feeder and the main line. Moreover for its complexity the mixed model balancing problem is usually solved transforming it into a single model by creating a single ‘virtual average model’, representative of the whole production mix. The use of a virtual average model assumes that the processing times of some models are higher or lower than the cycle time, which creates overload/idle time at the stations. This approach, especially in complex multi line production systems, largely reduces the assembly line productivity and increases the buffers dimensions. This paper faces the mixed model assembly line balancing problem in the presence of multiple feeder lines, introducing an innovative integrated main-feeder lines balancing procedure in case of unpaced assembly systems. The proposed approach is compared with the classical one and validated through simulation and industrial applications.     

装配线平衡系统研究与开发

装配线的平衡问题已有大量理论研究,但缺乏应用工具.为了消除该问题理论与实际应用之间的鸿沟,利用有效的算法,开发了一个装配线平衡的系统.简要介绍了装配线平衡问题及其求解算法,阐述了系统的功能及其实现过程.企业界的工程技术人员利用该系统可以有效地解决装配线平衡问题,从而提高装配线的生产效率.     

应用SIMOGRAMS方法解决装配生产线瓶颈

详细介绍了SIMOGRAMS,一种新的人机操作分析、联合操作分析的新方法.针对某轮胎公司现有生产能力无法满足市场需求的实际问题,首先确定瓶颈车间-成型车间,然后运用SIMOGRAMS工具,从该车间装配生产的主要产品装配流程入手,对整个装配过程进行联合操作分析,提出了初步改善方案并分析改善效果.最后将装配线从固定式布置改变为产品式布置,根据各基本工作单元所包含的工作量将其组合成工作量基本相等的工作包,并将这些工作包分派给每个操作者或工作站,形成基于几种产品的细胞单元,大幅度提高了手工装配线的生产能力和灵活性.     

ProModel的服装缝制流水线仿真及应用

对S公司的服装缝制流水线编排情况进行研究,建立了基于ProModel的仿真模型.将仿真模型运行情况与实际情况进行对比,确定模型的有效性,并运用该模型运行结果分析实际流水线生产情况,有针对性地提出改进措施并仿真,根据仿真结果对流水线进行了优化.结果表明,在考虑和处理诸如回修、搬运等因素的影响时,仿真方法相比手工编制方法具有明显的优势,有利于企业更有效地提高流水线的生产效率和实现对生产进度的准确把握.     

A case study evaluating the ergonomic and productivity impacts of partial automation strategies in the electronics industry

A case study is presented that evaluates the impact of partial automation strategies on productivity and ergonomics. A company partly automated its assembly and transportation functions while moving from a parallel-batch to a serial line-based production system. Data obtained from company records and key informants were combined with detailed video analysis, biomechanical modelling data and field observations of the system. The new line system was observed to have 51% higher production volumes with 21% less per product labour input and lower work-in-process levels than the old batch-cart system. Partial automation of assembly operations was seen to reduce the total repetitive assembly work at the system level by 34%. Automation of transportation reduced transport labour by 63%. The strategic decision to implement line-transportation was found to increase movement repetitiveness for operators at manual assembly stations, even though workstations were constructed with consideration to ergonomics. Average shoulder elevation at these stations increased 30% and average shoulder moment increased 14%. It is concluded that strategic decisions made by designers and managers early in the production system design phase have considerable impact on ergonomic conditions in the resulting system. Automation of transport and assembly both lead to increased productivity, but only elements related to the automatic line system also increased mechanical loads on operators and hence increased the risk for work-related disorders. Suggestions for integrating the consideration of ergonomics into production system design are made.     

Sequencing procedure for balancing the workloads variations in case of mixed model assembly system with multiple secondary feeder lines

In order to increase flexibility and reduce costs, assembly systems are changing from simple mixed-model assembly lines, to multi-lines systems, where some components are assembled in secondary lines, called feeder lines, connected to the main line by a ‘pull philosophy’. The production of different models in such a complex multi-lines assembly system, where the tasks to perform could be very different from model to model, impacts the production with very high workload time variations, with the consequence of lack of productivity. If operators can perform tasks on different stations on both the feeder and the main lines these time variations can generally be absorbed. But if working across the stations is not possible (closed stations), the balancing of these workload time variations becomes critical. In such contexts the consolidated approach, that allows to configure mixed-model-multi lines assembly system with a single average model representative of the whole mix, can be very limited and is unable to bring substantial results. This paper aims to introduce an innovative sequencing model for mixed-model-multi-lines system, in the case of closed stations, in which it is possible to obtain, after a first long term configuration, a short term balancing, using an appropriate sequencing, for a given production mix and characteristics of the assembly system. The proposed procedure is applied to un-paced assembly lines and validated through simulation and industrial applications.     

A Methodology to Describe Operating Characteristics of Assembly Systems

A methodology for describing the operating characteristics of low volume (small lot) assembly systems is presented in this paper. Analytical models indicate that the deterministic assembly system is equivalent to a flow shop. A numerical approximation technique is applied to develop measures of performance for probabilistic systems. Results include identification of metering stations which control work flow and of potential inconsistencies between productivity and flow-time objectives. The impacts of scheduling policies that determine the intervals at which “mainframes” are launched into assembly, and the due dates for parts, are investigated. The strategy of setting due dates for parts is shown to have a significant influence over work-in-process levels and schedule performance in probabilistic systems.     

Workers’ rest allowance and smoothing of the workload in assembly lines

Ergonomic aspects have a crucial role in manual assembly systems. They impact on the workers’ health, final product quality and productivity. For these reasons, there is the necessity to integrate them into the assembly line balancing phase as, whereas, only time and cost variables are considered. In this study, human energy expenditures are considered as ergonomic aspects and we integrate them, for the first time, into the assembly line balancing problem type 2 through the rest allowance evaluation. We consider as an objective function the minimization of the smoothness index. Firstly, a new optimal method based on mixed integer linear programming and a new linearization methodology are proposed. Then, a heuristic approach is introduced. To complete the study, a computational experimentation is presented to validate the mathematical model and to compare the methodologies proposed in terms of computational time, complexity and solution. Additionally, we provide a detailed analysis of the impact that rest allowance evaluation can have on productivity comparing the results obtained, taking into account the rest allowance integration before, during and after the assembly balancing process.     

ASRS sizing for recreating automotive assembly sequences

Since a mixed model assembly line's efficiency depends on the sequence of jobs moving down the line, manufacturers spend considerable effort optimizing the sequence of jobs entering the plant. In automotive assembly plants however, repair loops and parallel stations scramble the sequence before it reaches the final assembly stage. Many automotive assembly plants use an automatic storage and retrieval system to revamp the scrambled sequence before final assembly. One plant even goes so far as to reconstruct the original sequence by completely undoing the sequence scrambling. We derive a relationship between the sequence scrambling information, the variety of model-colour configurations, and the size of the automatic storage and retrieval system needed to reconstruct the initial sequence. We enunciate this new ASRS sizing problem actually facing industry, show how to model it, present a solution approach, and demonstrate the approach on actual sequence scrambling data from an automotive assembly plant.     

State-based analysis of labour productivity

Establishing efficient continuous improvement processes requires industrial companies to analyse their productivity quickly on different work system levels and to link productivity losses with suitable improvement measures in the course of productivity management. Common productivity analyses are either narrowed to certain functions of a production process or they do not possess a sufficient level of detail to derive goal-oriented improvement measures. The challenge is to gain production data with a relatively low effort and to gain broad transparency over productivity losses from the work place to the company level at the same time. This paper presents a new methodology for the comprehensive analysis of the various impacts on labour productivity, relying on state-based modelling of worker activities in serial production. Typical application areas include the automotive industry or the production of home appliances. The approach combines straightforward data acquisition methods with a structured evaluation process as foundation for the productivity management on different work system levels, including work stations, production lines, production segments and the plant. An integrated matching procedure processes the analysis results and yields a set of applicable improvement methods from a definable toolset. Compared with existing methodologies, the underlying model promises a reduced data acquisition effort and high usability. Its potential for practical application is shown with two industrial case studies.     

Product quality and plant build complexity

This paper assesses the hypothesis that plant build complexity impacts quality, suggests mechanisms to explain how complexity impacts quality, and offers countermeasures to mitigate this impact. We analyse automotive assembly data that supports the proposition that plant build complexity negatively impacts quality. In addition, this paper provides actual automotive assembly line work instructions and shows how they can be represented by the Gilbreths’ fundamental work elements and plant build complexity impacts these work elements. To highlight complexity's adverse impact on quality, we compare the actual work instructions at two automotive assembly line stations–one with very little complexity and one with extreme complexity. We list common automotive assembly quality lapses and describe how they can be caused or exacerbated by complexity. Finally the paper presents practical countermeasures to mitigate complexity's impact on quality. While based on the automotive industry, the lessons apply to all complex assembly lines.     

基于Witness的某制造车间生产线仿真优化

以某立柱制造车间生产线设计为例,运用TOC约束理论和DBR排程理论,结合Witness软件进行制造系统的建模与仿真,分析影响制造系统生产线的各种影响因素,通过设置各项参数、调整设备数量来优化生产物流,提高机器利用率和生产效率以使企业在市场竞争中获得优势。     

Production control in a complex production system using approximate dynamic programming

Development of an efficient production and inventory control policy for a production system with multiple working stations, intermediate components and end products is difficult. In particular, uncertain demand and large changeover times at the work stations cause significant problems. In this paper, we consider an assembly line for dishwashers which require multiple types of wire racks that must be fabricated and coated at different work centres before supplying the assembly lines. An approximate dynamic programming (ADP) method is proposed to address the complexities associated with such a system. In addition, an Artificial Neural Network model is designed to approximate state values of the system, thus helping the system to make decisions at particular states. A near optimal production and inventory control policy is developed through an ADP algorithm. The proposed method can be extended to any similar system.     

Simulation-based optimisation of logistics distribution system for an assembly line with path constraints

The design of logistics distribution system for an assembly line with given layout is usually constrained by various factors such as the vehicles for the distribution of assembly components and the paths on the shop floor for the vehicle movement. Since design optimisation of these production systems with such constraints is hard to solve by mathematic approaches, simulation-based approach is mostly used. In this paper, simulation-based analysis and optimisation of a logistic distribution system is performed combined with a heuristic algorithm to obtain a solution that most suits the practical requirements of an assembly line. The proposed simulation-based method builds a model that satisfied various complicated real-world problems at the work site of an investigated factory. Meanwhile, a dynamic dispatching method for vehicle movement is also presented which can adjust the control strategy and decision parameters dynamically in the process of simulation and contributes significantly to form a more fruitful design scheme. Experimental results show that proposed method performs better than the analytical model-based approach and some other methods, and the dynamic vehicle dispatching method presented performs better than some existing common strategies used in literature.     

玩具厂装配流水线的瓶颈分析与平衡改善

运用工作测定与作业分析的方法,分析了某玩具厂装配流水线的工作过程与平衡状况,针对整条流水线中存在问题,结合生产实际提出了解决装配流水线瓶颈环节、改进流水线平衡的方案.通过实施改进方案,工序总数减少了3道, 瓶颈工作时间降低了4 s,装配流水线负荷效率提高了34.7%.     

基于标准作业时间和仿真的装配线规划

在分析装配线规划内容的基础上,提出了基于标准作业时间及系统仿真的装配线规划方法并开发了相应的原型系统。通过建立装配操作树,定义装配操作约束,规划合理平衡的装配工位,同时生成装配作业表。以此作业表为输入,建立装配线的仿真模型,为装配线系统布置中的流参数等优化提供环境。通过这些工作,为企业制定工时定额合理的装配线,提高自主规划生产系统的能力提供途径。     

Structural equations modelling for relational analysis of JIT performance in maquiladora sector

This paper analyses the process of implementing a just-in-time (JIT) methodology in maquiladora assembly plants in Mexico, through 20 activities undertaken in the areas of administration, supervision and production. The proposed approach uses a factor analysis of each group of variables (validating their feasibility through an analysis of the correlation matrix) by sections, activities and benefits obtained. A structural equations model is proposed to show how key factors in the success of the implementation of JIT associated with productive activities interrelate with factors linked to benefits. The results forthcoming from the study show that the benefits obtained through the proper administration by senior managers of their powers are directly reflected in the plant’s productivity indices, such as increases in output, quality and the operational flexibility of production systems. Furthermore, a good relationship with and management of suppliers guarantees an acceptable level of control over inventories, regarding both work in process and the end product, and likewise impact upon productivity indices.