TWI Knowledge Summary
Manufacturing - discrete event simulation
Discrete event simulation involves modelling a system as it progresses through time and is particularly useful for analysing queuing systems. Such systems are common in the manufacturing environment and are obvious as work in progress, buffer stocks, and warehouse parts. They are also widespread in everyday life often noticeable at supermarket check outs, road traffic junctions, and airport baggage handling systems.A major strength of discrete event simulation is its ability to model random events and to predict the effects of the complex interactions between these events. Experimentation is normally carried out using the software model to answer 'what-if?' questions. This is achieved by changing inputs to the model and then comparing the outcomes. This type of simulation is primarily a decision support tool.
Current status
Discrete Event Simulation was first used in the 1950s to study a range of business problems. The objective was to improve efficiency, reduce costs and increase profitability. These business problems mainly involved analysing the queuing of objects that had a small number of operations carried out on them and followed a limited number of routes from start to finish (e.g. mass production of products). The models created in the 1960s and 1970s were usually computer programmes written specifically for the scenario in question and the output was given as lists of numbers. By the 1980s, the models were enhanced by the addition of 2D animations that mimicked the system and provided a visual representation of the problem. Animations proved particularly useful for assessing and confirming the validity of the model and, in the 1990s, simulation software was further enhanced to give 3D visualisation. These programs now allow the users to recognise and compensate for spatial constraints. Increases in computational processing power have enabled the software to include texture mapping and third person viewing bringing them to the point of virtual reality.Benefits and risk
To enter the field of discrete event simulation requires significant financial commitment. The company is required not only to purchase the software and hardware to run it on, but also to maintain an operator skilled in its use. The price of a 'seat' has been falling over recent years. Software can vary dramatically in price and capability. While the numbers of people with the necessary simulation skills (e.g. design, software engineering, manufacturing, business) are increasing, they are becoming more sought after due to increasing use of these tools.The benefits of discrete event simulation are both diverse and valuable. In short, models should be used as a quick method of analysing and solving complex problems. The knowledge this provides reduces the risk associated with important decision making, and increases confidence by supporting the decision with forecasted data. One-off and regular financial gains can be realised by optimising performance of studies.
The success of simulation in reducing the risk and uncertainty associated with the manufacturing environment has been realised by many companies in all industrial sectors. Some companies are now using simulation to drive and forecast their business.
Areas of development
Driven by the need to quickly introduce new products, and to tailor to specific customer requirements, organisations are moving away from mass production and towards mass customisation. This presents greater challenges for discrete event simulation, because of the increased number of processes and products. These issues mean that models will become even more complex, imposing the need to trace products throughout the system, and include more rules and logic.Other areas of development also stem from this trend. There is a requirement for smoother integration with design tools and more rapid validation of the model (to the point of real time comparison and integration with shop floor data capture systems).
Further information
Related information on this topic can be found in the following content items:Computerised factory layout - a guide to best practice. Section 1. Introduction and contents
FAQ: What is simulation
TWI aerospace industry case study - Manufacturing simulation
Further information
If you have a query on this subject please email TWI's Manufacturing Support Department. manufacturing.support@twi.co.uk
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