Sub-assembly Lines Research Articles

The Effectiveness of a Vehicle Manufacturing Line Using Probabilistic Process Timing

Abstract: Automotive manufacturing involves several steps, starting with the casting of components and moving on to the machining and assembly processes. The assembly system, particularly for the Single Cylinder S.I. Engine, will be the only emphasis of this project. A considerable number of components must be integrated throughout the engine assembly process. The creation of a decision assistance system based on a discrete event simulation model is discussed in the work provided in this paper. The four closed-loop network arrangement of vehicle assembly and preassembly lines connected by conveyors is targeted at a particular type of manufacturing lines. The design and execution of such industrial processes frequently include simulation. This simulation research aims to select the process throughput for the Single Cylinder S.I. Engine Assembly line. Any possible machine bottlenecks will be identified by the simulation study to avoid blockages and starvation and increase process throughput. Machine cycle times for various processes should be included in the input data for the research. The Arena simulation program will be utilized in this investigation. The goal is to use existing equipment to boost output on the present Head Assembly Line and Sub-Assembly Lines to an anticipated capacity. The outcomes of the simulation will be used to pinpoint the assembly-line procedures that may have an impact on the S.I. Engine's manufacturing schedule. By contrast the study's findings with the actual process throughput, the findings will be illustrated. Additionally, statistical analysis will be done to boost performance.

Material distribution method in discrete manufacturing systems and a case study from engine builders

In a discrete manufacturing enterprise, it is difficult to satisfy the fast matching and accurate supply of production materials or the demand of modern dynamic production systems using passive material supply. With a focus on engine builders, this study explores the active material configuration and systematic material distribution approaches. Due to the material characteristics and the granularity of logistics demand, the material distribution is arranged in reverse chronological order, and the corresponding mathematical modeling of the distributing period is proposed to achieve lean manufacturing. To ensure exact material distribution time, the allocation material configuration model that works best for the dynamic manufacturing system is presented by means of system modeling. Next, a production material distribution method for the general assembly line and the sub-assembly line with a closely related production sequence is proposed to achieve the exact match of manufacturing and material resources through the analysis of data fusion and logistics resource matching. Finally, a simulation is conducted using production data gathered from engine builders. The results indicate the effectiveness of the proposed active material configuration method. The outcome of this study can be used as a guide for the time planning of material flow in a dynamic manufacturing system and can provide a new research perspective on production logistics or distribution in a production line.

Enhancement of Production in Subassembly Line of a Medium Scale Industry Using Different Lean Tools and Flexsim Simulation Software

In recent engineering practices, the manufacturing industries are more technically able to produce product with high quality to desire the customer needs. For accomplishing customer needs many lean tools are used to improve the methods of manufacturing practices in industries. The aim of this research work is enhance the productivity of spool casing assembly used in horn armature core per shift by using method study, time study and VSM. Cycle time for each operation of the product is determined by time study and the value added, non-value-added activities and transportation wastes occurred in the current state process identified and plotted in the current state VSM. The future state VSM was developed to reduce unnecessary wastes such as transportation, inventory, waiting which occurred in the current state VSM. Both current and future state time study are simulated using Flexsim simulation software. From the observed results it was found that, P3 and P5 model productivity was improved by about 5.5% and 6.5% respectively after implementation of appropriate lean tools.

Assembly systems in Industry 4.0 era: a road map to understand Assembly 4.0

The 4th industrial revolution (Industry 4.0, I4.0) is based upon the penetration of many new technologies to the industrial world. These technologies are posed to fundamentally change assembly lines around the world. Assembly systems transformed by I4.0 technology integration are referred to here as Assembly 4.0 (A4.0). While most I4.0 new technologies are known, and their integration into shop floors is ongoing or imminent, there is a gap between this knowledge and understanding the form and the impact of their full implementation in assembly systems. The path from the new technological abilities to improved productivity and profitability has not been well understood and has some missing parts. This paper strives to close a significant part of this gap by creating a road map to understand and explore the impact of typical I4.0 new technologies on A4.0 systems. In particular, the paper explores three impact levels: strategic, tactical, and operational. On the strategic level, we explore aspects related to the design of the product, process, and the assembly system. Additionally, the paper elaborates on likely changes in assembly design aspects, due to the flexibility and capabilities that these new technologies will bring. Strategic design also deals with planning and realizing the potential of interactions between sub-assembly lines, kitting lines, and the main assembly lines. On the tactical level, we explore the impact of policies and methodologies in planning assembly lines. Finally, on the operational level, we explore how these new capabilities may affect part routing and scheduling including cases of disruptions and machine failures. We qualitatively assess the impact on performance in terms of overall flow time and ability to handle a wide variety of end products. We point out the cases where clear performance improvement is expected due to the integration of the new technologies. We conclude by identifying research opportunities and challenges for advanced assembly systems.

조립공법과 이송정책을 고려한 자동차 차체공장에서 혼류생산이 미치는 영향

The role of body shop in an automotive factory is to assemble parts which are produced in press shop or supplied by outside supplier using welding operations. Generally, the body shop is divided into 15~20 sub-assembly lines and there is no buffer in sub-assembly lines. The decoupled sub-lines are connected by the various conveyor systems which have the function of transportation and buffer space as well. Recently, it is popular that multiple types of cars are produced in a body shop by changing welding jigs or fixtures. Then, the cycle times in welding stations are different with the types of cars. In the initial designing phase of body shops, the estimation of production rate is important for continuing the next design phases such as line balancing. In this study, we investigate the effects of mixed-model production on the performance measures using simulation when the assembly methods, part transfer policies, various isolated efficiency of station are considered.

A novel artificial bee colony algorithm for the workforce scheduling and balancing problem in sub-assembly lines with limited buffers

In this study, a workforce scheduling and balancing problem is solved in unpaced sub-assembly lines with buffers feeding the paced body assembly line of a car manufacturer. The goal is to determine the minimum workforce required to process split lots at sub-assembly stations to feed the paced line over a periodic time window. Limited by a given buffer capacity at each station but with flexible start times for each split lot, an efficient workforce scheduling is possible to prevent shortages in downstream stations. Therefore, a stock-continuity equation has been proposed yielding the size of those split lots. Next, a single-objective Mixed Integer Programming (MIP) model is formulated for the problem as a combination of two implicitly weighted goals to minimise the workforce and the unbalanced workloads. The problem is a variant of workforce scheduling and routing problem with time windows and negligible walking distances. Due to the non-deterministic polynomial-time-hardness of the problem, we proposed an improved Artificial Bee Colony (ABC) algorithm named as discrete ABC with solution acceptance rule and multi-search (SAMSABC). The proposed algorithm is compared with different variants of ABC and other well-known metaheuristic algorithms such as Particle Swarm Optimisation and Differential Evolution on generated test cases. The computational results demonstrate the superiority of the proposed ABC algorithm and reveal that the SAMSABC can achieve accurate results within short computational times.

Transportation of part supply improvement in agricultural machinery assembly plant

This research focused on the problem caused by the transportation of part supply in agricultural machinery assembly plant in Thailand, which is one of the processes that are critical to the whole production process. If poorly managed, it will affect transportation of part supply, the emergence of sink cost, quality problems, and the ability to respond to the needs of the customers in time. Since the competition in the agricultural machinery market is more intense, the efficiency of part transportation process has to be improved. In this study, the process of transporting parts of the plant was studied and it was found that the efficiency of the process of transporting parts from the sub assembly line to its main assembly line was 83%. The approach to the performance improvement is done by using the Lean tool to limit wastes based on the ECRS principle and applying pull production system by changing the transportation method to operate as milkrun for transportation of parts to synchronize with the part demands of the main assembly line. After the transportation of parts from sub-assembly line to the main assembly line was improved, the efficiency raised to 98% and transportation process cost was saved to 540,000 Baht per year.

Quality and productivity improvement through spot welding process optimisation in automobile body shop

Optimised geometry weld spot distribution for different configurations of automobile body sub-assemblies, is a critical activity in any automobile body shop process planning. For an ideal body shop planning, it has to be planned in a systematic approach so that the maximum productivity with high quality is being achieved. For this, the optimised planning has to be made for number of spots welded in a geometry station. The lesser the number of spots, the higher will be the dimensional variations of the assembly; the greater the number of spots, the lesser will be the productivity of the sub-assembly lines. The aim of this paper is to identify an optimised spot quantity for different sizes of parts with different surface contacts. To identify the optimum spot quantity, an industrial experiment was conducted using Taguchi method (L27 OA). Dimensional variations of the samples were recorded in two stages: 1) post-geometry spot welding; 2) post re-spot welding; and the measured data was thoroughly analysed. Recommendations for the optimised number of spots for geometry spot weld stage were made for different assembly configurations. These recommendations are discussed in detail. This study will aid the process planners to distribute the appropriate number of spots in the geometry welding stations.

Modeling and solving assembly line design problems by considering human factors with a real‐life application

AbstractErgonomics has been playing an important role in assembly system design (ASD) that contains not only the main assembly line balancing problem but also the subassembly line balancing and assembly layout problem. The ergonomics in ASD has an impact both on productivity and on workers’ health, especially when frequent changes in the product mix occur. In this study, we propose a systematic approach in order to handle ASD, which consists of three subproblems, while considering ergonomic risk factors. The first two subproblems are solved simultaneously using the proposed rule‐based constructive search algorithm, where ergonomic risks are evaluated by OCRA method. Later, layout problem is solved under transportation constraints using local search methods with various neighborhood structures. To provide the applicability and evaluate the performance of the proposed systematic approach, a real‐life case study in a harness manufacturing company is solved and prototype productions are performed.

Sub-assembly detection and line balancing using fuzzy goal programming approach

This study suggests a mathematical modelling approach to sub-assembly detection and assembly line balancing problems. The sub-assembly detection problem involves two issues as follows: 1 determine which components of products are assembled in sub-assembly area; 2 determine which components of the products are assembled directly in the line. In assembly line balancing problem tasks are assigned to the workstations. The main motivation of this study is to determine the best compromised assembly line structure by solving the sub-assembly detection and the line balancing problems jointly. A multi-objective mathematical model is developed to formulate the above mentioned problems in which two conflicting costs of sub-assembly generation and assembly line labour cost are involved. Since the applications in real life are imprecise, fuzzy goal programming is adapted to the developed model to determining the vague goal. Then the model is implemented in a real life automotive manufacturers assembly line balancing.

Implementing the Gantt chart in Europe and Britain: the contributions of Wallace Clark

Purpose The purpose of this paper is to trace the European and British activities of Wallace Clark and his consulting firm with public sector agencies and private firms implement Henry L. Gantt’s chart concept. Design/methodology/approach Archival records and secondary sources in English and French. Findings Developed to meet the shipbuilding and use needs for the Great War (World War I), the Gantt chart was disseminated through the work of Wallace Clark during the 1930s in numerous public sector and private organizations in 12 nations. The Gantt concept was applied in a variety of industries and firms using batch, continuous processing and/or sub-assembly lines in mass production. Traditional scientific management techniques were expanded for general management, such as financial requirement through budgetary control. Clark and his consulting firm were responsible for implementing a managerial tool, the Gantt chart, in an international setting. Research limitations/implications Some firms with which Clark consulted could not be identified because the original records of the Wallace Clark Company were disposed of by New York University archival authorities. Industries were identified from the writings of Pearl Clark and Wallace Clark, and some private or public organizations were discerned from archival work and the research of French and British scholars. Originality/value This is the first study of the diffusion of a managerial tool, developed in America by Henry L. Gantt, into Europe and Britain through the contributions of Wallace Clark.

An Approximate Analytical Method to Evaluate the Performance of Multi-product Assembly Manufacturing Systems

The automotive industry is characterized by the continuous and frequent adoption of cutting edge technologies in manufacturing. The introduction of new technology often entails a system level investigation to determine whether it meets expected production requirements. Many system design alternatives are usually considered at this stage, and a fast performance evaluation tool is desired to quickly obtain the optimum system configuration. In this paper, we introduce an analytical tool that was developed for this specific purpose.The investigated manufacturing system is a multi-product, automated, assembly production line composed of unreliable machines decoupled by finite buffers. Each product is an assembly of two components that are produced in sub-assembly lines before being assembled at an assembly machine. The performance of this system needs to be evaluated for different configurations that arise mainly due to the integration of a remote laser welding technology. This new technology promises, among other advantages, a much faster assembly than existing technologies. This makes it feasible to share assembly among many products with different possible production policies. The processing machines including the assembly machine are liable to fail randomly in operation thereby necessitating an evaluation method capable of accounting for stochastic behavior.To solve this problem, we develop a decomposition-based approximate analytical method. We use the continuous material flow approximation, which allows to model machines having deterministic but inhomogeneous processing times as in the investigated real system. We also account for multiple machine failure modes and introduce new techniques to incorporate the assembly of multiple products with different policies of switching between products. Comparison with simulation results shows the good accuracy of the model in estimating system throughput and work-in-progress. The model has been successfully utilized to evaluate the performance of an automotive door assembly manufacturing system and the main results of this case study are reported.

Realizing Lean Concept in Automotive Parts Production: Child Parts in Sub-Assembly Line

This paper addresses the application of a promising and concept known as Lean Manufacturing (LM) concepts that can be used to prevent incorrect parts size at subassembly 1 and 5. In the context of size versus volume, the possibility of small parts to encounter defects is much greater compare to huge size. This undesirable circumstance will lead to the financial deficits in terms of waste. At this stage, this paper will identify and investigate the sources of inputs that cause the failure in the manufacturing system. The finding of the failure will be analysed and extending to the problem solution by suggesting the lean approach at the allocated area. By adapting some of this approach, it will deliver to the performance of production line that includes an assessment of fulfilling the objectives in terms of preventing parts incorrect size, reducing related cost from waste and providing customer with quality products. Taking into account of the objectives, the implementation of this approach in the sub assembly line is then described. Nevertheless, further investigations are necessary to improve the proposed applications which currently function with limitation due to small area of production line.

Design rules for implementing the Toyota Production System

The Toyota Motor Company has risen to a place of world prominence in the automotive industry by redesigning the mass production system into the Toyota Production System (TPS), or what is now known worldwide as lean production. In redesigning the mass production system, they changed the final assembly into a mixed model final assembly system to level the demand on their suppliers, converted the linear subassembly lines into U-shaped subassembly cells and redesigned the job shop into manufacturing cells. Final assembly operates with a takt time, and the cells are designed to have a cycle time slightly less than the takt time and to operate on a ‘make one, check one and move one on’ (MO-CO-MOO basis). Single-cycle machine tools are used with built-in devices to check parts (poka-yokes). Between the machines are devices (decouplers) designed to assist the standing, walking workers producing the parts in the manufacturing cells. This paper will discuss four design rules for implementing the TPS.

Bucket brigades on in-tree assembly networks

In a network of subassembly lines, balance becomes more difficult to achieve as it requires that all subassembly lines be synchronized to produce at the same rate. We show how to adapt the “bucket brigade” protocol of work-sharing so that balance emerges spontaneously.

A Modeling and Simulation of Production Process in Subassembly Lines at a Shipyard

In order to simulate material flow in a subassembly line at a shipyard, the product, process, and resources are modeled for the subassembly process. The subassembly line is selected from a large shipyard and consists of several subprocesses, such as base joining, piece alignment, tack welding, and robot welding processes. The analysis and modeling procedure were carried out using the Unified Modeling Language (UML), an object-oriented modeling methodology, and Integration Definition (IDEF), a functional modeling tool. Initially, the characteristics of the shop resources were analyzed using the shipyard data and the layout of the subassembly line was designed with the resources. A production process was then modeled using the resources and the layout. The production process modeling of the subassembly lines was performed using the discrete event simulation method. Using the constructed resource and process model, the productivity and efficiency of the line were investigated. Variations in the resource performance, such as a new welding robot and the number of workers, were examined to simulate changes in productivity. It can be seen that bottlenecks occur in different places according to the nature of new resources. The proposed model is viewed three-dimensionally in a virtual environment so that space allocations for the resources and interferences between objects can be easily investigated.

Designing an assembly line for modular products

To respond to the challenge of agile manufacturing, companies are striving to provide a large variety of products at low cost. Product modularity has become an important issue. It allows to produce different products through combination of standard components. One of the characteristics of modular products is that they share the same assembly structure for many assembly operations. The special structure of modular products provides challenges and opportunities for operational design of assembly lines. In this paper, an approach for design of assembly lines for modular products is proposed. This approach divides the assembly line into two subassembly lines: a subassembly line for basic assembly operations and a subassembly line for variant assembly operations. The design of the subassembly line for basic operations can be viewed as a single product assembly line balancing problem and be solved by existing line balancing methods. The subassembly line for the variant operations is designed as a two-station flowshop line and is balanced by a two-machine flowshop scheduling method. A three-station flowshop line for a special structure of modular products is proposed and illustrated with an example.

CAD/CAM Welding Robot System in Steel Bridge Panel Fabrication.

Recently, the serious problems facing heavy industries such as the increase in the average age of employees, shortage of skilled workers and environmental problems in the workplace are being addressed. The bridge panel fabrication system we have developed is such an approach to solve these problems. It consists of two parallel box girder panel sub-assembly lines, one exclusively for web panels and the other for flange. Each line is made up of stages for fitting, welding, re-forming, drilling and finishing. All of the line equipment is controlled by the line computer in the central control room.The box girder panel is reinforced by the stiffeners and the fillet welding is the objective of each welding stage. In total, 14 articulated-type arc welding robots are applied in the welding stages. In the web panel welding stage, 8 robots are hung from stationaly transverse girders with 2 m span in longitudinal direction and can be used for operations up to 4 m wide by 16 m long. In the flange panel welding stage, 2 welding robots are hung from each of the 3 transverse sliding units that are arranged under the mobile gantry. In total, 6 welding robots cover the 5 m wide by 16 m long work area.By adopting the High Speed Rotating Arc welding process, we have doubled welding efficiency as compared with conventional processes. Furthermore, this process is more effective to reduce panel deformation because of the lower welding heat input. The welding robot system is stabilized with precise accuracy by newly developed joint end and bead end sensing techniques as well as a seam tracking arc sensor system based on the High Speed Rotating Arc.All of the welding robot is linked with LAN to the newly developed, teachingless CAD/CAM system that is based on the computerized design fabrication system for bridge fabrication. This system is especially effective for bridge panel fabrication where almost all the panels are of different shapes.Thus, a step towards computer-integrated manufacturing (CIM) in steel structure fabrication has been achieved.

The CAM System for the Arc-welding Robot for Hull Sub-assemblies

In order to extend the applicable range from the parallel parts to the non-parallel parts of hull structures, a new CAM system for the arc-welding robot has recently been developed.When automatic arc-welding is extended to all the non-parallel hull part workpieces of different shapes, the new CAM system is required to respond flexibly to the alterations of production order, shapes and the laying positions of related workpieces, without taking much time for programming. Satisfying these needs, the following means has been studied for the new system.(1) The new CAM system supplies a task level welding program to the robot controller, which, simultaneously generates every robot motion. Consequently, when it becomes necessary to alter the laying positions of workpieces due to the change of the production order, the robot can react freely to the alterations.(2) For saving programming time and for simplifying the operation, the system of a human interface with an interactive mode is adopted using graphic displays. Operation guides of the system and those commands for selection are both shown on the graphic displays.(3) For saving time and avoiding errors, the data-base of the hull structures is used for programming.(4) A micro computer is provided at the control room in the sub-assembly shop for editing, alterating and maintaining the welding programs.This new function enables the system to react flexibly to the alterations of design and production order.It is estimated that utilization of the new CAM system reduces programming time by 2/3.Experimental calcurations on the economy of the robot based on the actual record of programming and welding time has confirmed that it is possible to maintain an economical advantage even in the case of the robot being applied to workpieces of various shapes.The arc-welding robot for hull sub-assemblies can be effectively used on non-parallel parts of hull structures by employing the new CAM system.This new system offers full automation potential for every welding activity on the sub-assembly line of hull structures.

Increasing the production rate of a just-in-time production system with variable operation times

Abstract This paper examines a just-in-time (JIT) system with kanbans with three subassembly lines feeding a final assembly station. Variability in operation times exists and variability effects are reduced by increasing work in process levels or by unbalancing the subassembly lines through assignment of work content at each station. Of the several unbalancing methods that were analysed in this study, only the high-medium-low showed a consistent improvement in the output rate of the JIT production system. The output rates with unbalanced stations were always superior to the output rate of the perfectly balanced configurations used as controls. The extent of improvement over the output rate of balanced systems increased directly with the variability in operation times in final assembly and subassembly stations and inversely with the interstage buffer capacity allowed in the system.