RELAZIONE PER IL CONSEGUIMENTO DELLA LAUREA MAGISTRALE IN INGEGNERIA GESTIONALE
Development of a Method for Modelling Manufacturing
Structures to Enable a model based Multi-Criteria
Analysis
RELATORI IL CANDIDATO
Prof. Ing. Gino Dini Giulia Farina
Dipartimento Di Ingegneria Civile e Industriale [email protected]
Dr.-Ing. Gunther Reinhart
Institute for Machine Tools and Industrial Management TUM, Munich
Dipl.-Wirt.-Ing. Christian Plehn
Institute for Machine Tools and Industrial Management TUM, Munich
Sessione di Laurea del 30/04/2014 Anno Accademico 2012/2013 Consultazione NON consentita
Method for modelling
manufacturing structures to enable
their model-based multi-criteria
analysis
Verfasser:
Farina, Giulia
Betreuer:
Plehn, Christian
Zeitraum:
01.10.2013 bis 31.03.2014
iwb-Nr.:
2013/029-MT
strutture manifatturiere,infatti, abbiano una forte influenza sulla changeability. Gli obiettivi di questo lavoro di tesi sono la revisione e valutazione dei più promettenti metodi esistenti per modellare le strutture manifatturiere, e partendo da questi risultati, lo sviluppo di un metodo per modellare le strutture manifatturiere, che consenta un’analisi multi-criteria delle stesse. L’analisi consentita dal metodo sviluppato permette di identificare gli effetti causati dalle interdipendenze all’interno delle strutture manifatturiere sulla loro changeability. Le interdipendenze considerate sono le relazioni tra gli elementi delle strutture manifatturiere e le proprietà che consentono e influenzano il miglioramento della loro changeability. I risultati più rilevanti di questo metodo mostrano l’importanza di ridurre la complessità delle strutture manifatturiere per facilitare il miglioramento della loro changeability, e la possibilità di trarre vantaggi dalle influenze positive esistenti tra le proprietà, in modo da innescare un effetto domino che comporti il miglioramento della changeability delle strutture manifatturiere.
Abstract
In the last years, changeability of manufacturing structures became one of the crucial challenges in manufacturing planning, to stay competitive. Manufacturing structures are believed to have a strong influence on changeability. The objectives of this thesis work are the review and the evaluation of the most promising existing methods for modelling manufacturing and factory structures, and starting from these results the development of a method for modelling manufacturing structures to enable their model based multi-criteria analysis. The analysis enabled by the method developed allows to identify the effects caused by the interdependencies within manufacturing structures, on their changeability. The interdependencies considered are the relations between the elements of manufacturing structures and the properties which enable and influence the improvement of their changeability. The most relevant results of this method show the importance to reduce the complexity of manufacturing structures to facilitate the improvement of their changeability, and the possibility to take advantages from the positive influences existing among the properties to trigger a domino effect which allows the improvement of manufacturing structures changeability.
Task description
Title of Master Thesis:
Development
of
a
Method
for
Modelling
Manufacturing Structures to Enable a model based
Multi-Criteria Analysis
Iwb-Nr.: 2013/029-MT
Author: Giulia Farina Supervisor: Christian Plehn
Start: 01.10.13 End: 31.03.14
Situation:
In the last years, changeability of manufacturing systems and structures became one of the crucial challenges in manufacturing planning. To improve changeability, different enablers have been identified, e.g. modularization of machines and manufacturing structures or concepts for mobilization of manufacturing resources within factories. Manufacturing structures, determined by the spatial arrangement, interdependencies and properties of manufacturing resources, are believed to have a strong influence on changeablity.
Objective:
Main objective of this thesis is the review, categorization and evaluation of existing types of modelling and structuring techniques for manufacturing and factory structures respectively. Beside a thorough literature review within engineering science, promising approaches from business science and operations research should also be taken into closer consideration. Based on these results, a method for modelling manufacturing structures is to be developed to support their analysis and the generation of alternative adaptation paths.
Approach:
Review and characterization of modelling techniques for structure modelling within engineering science, business science and operations research
Definition of requirements for the analysis of manufacturing structures Definition of criteria for evaluation of structuring methods and techniques Comparison of the most promising structuring methods and techniques
Development of a method for a model based multi-criteria analysis of manufacturing structures
Agreement:
By the academic supervising of Mrs. Giulia Farina by Mr. Dipl.-Wirt.-Ing. Christian Plehn intellectual property of the iwb became part of this thesis. Publication or dissemination of this thesis to third parties requires authorization by the head of iwb. I agree, that this thesis is archived as pdf file in the digital thesis database of the iwb and in stock in the iwb-owned library, which is only accessible for iwb-employees.
Garching, 31.03.2014
Table of Content
1. Definition of project scope – Chapter 1………..
1.1 The context……… 1.2 The manufacturing structure……….. 1.3 Thesis objective………
2 Review and characterization of modelling techniques for structure modelling with engineering science, business science and operations research – Chapter 2………...
2.1 Introduction………... 2.2 Traditional Manufacturing Systems……….. 2.3 Reconfigurable Manufacturing Systems – RMSs………... 2.4 Comparison of Manufacturing Systems………... 2.5 Systematic of Changeability……….. 2.6 Types of Factory Changeability……….... 2.7 Transformability………... 2.7.1 Objects of Tranformability………... 2.7.2 Enablers of transformability……… 2.7.3 Methods and Principles for the planning of Transformability………... 2.7.4 Example of a Transformable Factory………... 2.8 Methods and Approaches for modelling Manufacturing Structure………..
2.8.1 State of the art………... 2.8.2 RAS Design Method………...
2.8.2.1 Introduction………... 2.8.2.2 Description……… 2.8.2.3 Industrial case-study………... 2.8.3 A generic Model for Reconfigurable and Agile Manufacturing System
(RAMS)………... 2.8.3.1 Introduction………... 2.8.3.2 Description………. 2.8.3.3 Industrial case-study………... 2.8.4 Method for Multi-Scale Modelling and Simulation of Assembly
Systems……….. 2.8.4.1 Introduction………... 2.8.4.2 Description………. 2.8.4.3 Example……….. 2.8.4.4 Conclusion and roadmap………...
3 Definition of requirements for the analysis of manufacturing structures –
Chapter 3………...
3.1 Introduction………... 3.2 Motivation of changeability………. 3.3 Elements of changeable manufacturing……….. 3.4 Factory levels………... 3.5 Changeability objectives………. 3.5.1 Manufacturing level………. 3.5.2 Assembly level………. 3.5.3 Factory level………. 3.5.4 Summary of changeability objectives………...
1 1 2 2 2 2 3 4 5 6 7 8 8 9 11 12 13 13 14 14 14 15 16 16 17 25 27 27 27 29 30 30 30 31 32 33 34 35 35 36 37
3.6 Changeability enablers……….. 3.6.1 Manufacturing level………... 3.6.2 Assembly level………. 3.6.3 Factory level………. 3.7 Changeability process………... 3.8 Requirements for the analysis of manufacturing structures………....42
4 Definition of criteria for evaluation of structuring methods and techniques and evaluation of the most promising ones – Chapter 4……….
4.1 Introduction………... 4.2 Definition of criteria for the evaluation………. 4.3 Evaluation of the most promising structuring methods and techniques…... 4.3.1 Evaluation of RAS Design Method………... 4.3.1.1 Summary………... 4.3.1.2 Critical appraisal………... 4.3.2 Evaluation of RAMS Generic Model………. 4.3.2.1 Summary………... 4.3.2.2 Critical appraisal………... 4.3.3 Evaluation of Method for Multi-Scale Modelling and Simulation of
Assembly Systems………... 4.3.3.1 Summary………... 4.3.3.2 Critical appraisal……….. 4.4 Conclusion………..
5 Development of a method for a model based multi-criteria analysis of manufacturing structures – Chapter 5……….……….
5.1 Introduction……….. 5.2 Preparation………... 5.3 First Modelling and Analysis Level……….. 5.4 Second Modelling and Analysis Level……… 5.4.1 First Step………... 5.4.2 Second Step………. 5.4.3 Third Step………. 5.4.4 Summary………... 5.5 Third Modelling and Analysis Level ………... 5.6 Fourth Modelling and Analysis Level………. 5.7 Summary………. 6 Conclusion – Chapter6………... 7 References………... 37 38 39 39 40 42 44 44 44 45 45 45 45 46 46 46 47 47 48 48 50 50 51 55 56 57 69 70 74 75 78 81 82 84
1
1 Definition of project scope – Chapter 1
This chapter aims to briefly describe the context in which the project is developed, explain the thesis’s objective and the importance of manufacturing structures to face the increasing complexity in engineering development.
1.1 The context
The traditional competitive advantages of European manufacturing companies (T. Bauernhansl, J. Mandel, S. Diermann, 2012, p.364), such as quality, a high level of reliability, and innovative technologies are no longer drivers of sustainable business success on globalized and ever volatile markets. The trend towards more and more volatile and unpredictable demand fluctuations opens up new opportunities to differentiate from competitors. Previous flexibility approaches prove to be insufficient today: they focus too much on individual operations, on machines and their technical and logistical periphery, and on their integration into the information processing environment. Flexible manufacturing was directed at small and medium quantities and maximizing technical application and extending the period of use. It was all about technological developments. Future competitive opportunities go together with a comprehensive structural changeability of the entire production system. In the last years, changeability of manufacturing systems and structures became one of the crucial challenges in manufacturing planning. To improve changeability, different enablers have been identified, e.g. modularization of machines and manufacturing structures or concepts for mobilization of manufacturing resources within factories. Manufacturing structures are believed to have a strong influence on changeability. To face such complex and strict requirements (E. Carpanzano, F. Jovane, 2007, p.435) adaptive knowledge based production systems have to be developed. In particular, the conception and development of a new generation of automation solutions, that integrate all factory levels from machines controls up to shop-floor supervision and production planning in a unique real time framework, is mandatory. Future factory automation systems have to be modular, open, agile and knowledge based in order to promptly self-adapt themselves to changing exogenous conditions, like consumer expectations, market dynamics, design innovation, new materials and components. Nowadays, there are not universally accepted reference models, standards, methodologies and software tools for adaptive factory automation systems development. Thus, many different methods and technologies are adopted in industrial practice, and many different new approaches and solutions are proposed in recent scientific literature.
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1.2 The manufacturing structure
Manufacturing structures are determined by the spatial arrangement, interdependencies and properties of manufacturing resources, in fact the definition of manufacturing structure is: “Structure which describes the spatial arrangement, the relations and the life cycle dependent properties of manufacturing resources in a separable part of a factory, considering available space and infrastructure.
1.3 Thesis objectives
The main objective of this thesis is review, categorize and evaluate the existing types of modelling and structuring techniques for manufacturing and factory structures respectively. Beside a thorough literature review within engineering science, promising approaches from business science and operations research should also be taken into closer consideration. Based on these results, a method for modelling manufacturing structures has to be developed to support their analysis and the generation of alternative adaptation paths.
2 Review
and
characterization
of
modelling
techniques
for
structure
modelling
with
engineering science, business science and
operations research – Chapter 2
2.1 Introduction
Responsiveness is an attribute enabling manufacturing systems to quickly launch new products (Anatoli I. Dashchenko, 2006, p.30) on existing systems and to react rapidly and cost-effectively to:
1. market changes; 2. customer’s orders;
3. government regulations (safety and environment);
4. system failures (keep production up despite equipment failures). Market changes include:
1. changes in product demand; 2. changes in current products; 3. introducing new products.
These changes are driven by aggressive economic competition on a global scale, more educated and demanding customers, and a rapid pace of change in process
3
technology. To survive in this new manufacturing environment, companies must be able to react to changes rapidly and cost-effectively. This can be done by a manufacturing system that is designed for changing production capacity as market grows, and adding functionality as product changes.
In this chapter Traditional Manufacturing Systems are briefly described and compared with The RMSs (Reconfigurable Manufacturing Systems); then the types of Factory Changeability are discussed and some methods and approaches for modelling Manufacturing Structure are presented.
2.2 Traditional Manufacturing Systems
Dedicated manufacturing lines (DML) (Anatoli I. Dashchenko, 2006, pp.28-29), or transfer lines, are based on fixed automation and produce a company’s core products or parts at high-volume. Each dedicated line is typically designed to produce a single part (e.g., specific engine block) at high production rate. When the volume is high, the cost per part is relatively low. Therefore, DMLs are cost effective as long as market demand matches the supply; but with increasing pressure from global competition, there are many situations in which dedicated lines don’t operate at full capacity, and thereby create losses. Of course, producing product variety is impossible with a DML, and therefore their role in modern manufacturing is decaying. Flexible manufacturing systems (FMS) consist of computer numerically controlled (CNC) machines and other programmable automation and can produce a variety of products on the same system. However flexible systems haven’t been widely adopted, and many of the manufacturers that bought FMSs aren’t pleased with their performance. Drawbacks of FMSs are that they require more expensive machines than DMLs, and because of the single-tool operation of CNC machines, the production rate of FMSs is very small compared with DMLs. In addition, the production capacity of FMSs is usually lower than that of dedicated lines, and they aren’t designed for a quick change in their capacity, namely, they aren’t responsive to market changes. The picture below (Fig.1) depicts a comparison between DML and FMS.
Advantages Limitations
DLM Low cost
Fast – multi-tool operation
Not flexible – for a single part Fixed capacity – not scalable
FMS Convertible
Scalable capacity Expensive Slow – single-tool operation Fig.1 Comparison between DML and FMS.
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2.3 Reconfigurable Manufacturing Systems – RMSs
A cost-effective response to market changes (Anatoli I. Dashchenko, 2006, p.31) requires a new manufacturing approach that not only combines the high throughput of DML with the flexibility of FMS, but also is able to react to changes quickly and efficiently. This is achieved by designing systems according to two principles:
1. Design of a system and its machines for adjustable structure that enable system scalability in response to market demands and system/machine adaptability to new products; structure may be adjusted at the system level (e.g., adding machines) and at the machine level (changing machine hardware and control software).
2. Design of a manufacturing system around the part family, with the customized flexibility required for producing all parts of this part family (this reduces the system cost).
A Reconfigurable Manufacturing System (RMS) is a system designed at the outset for rapid change in structure, as well as in hardware and software components, in order to quickly adjust production capacity and functionality within a part family. Building a system with adjustable structure, scalability, and flexibility focused on a part family (Anatoli I. Dashchenko, 2006, p.32) creates a responsive reconfigurable system. Highly productive, cost-effective systems are created by:
1. part family focus;
2. customized flexibility that enables the operation of simultaneous tools (similar to a dedicated machine).
The flexibility of RMS provides all the flexibility needed to process the part family, and therefore is less expensive than the general flexibility of FMS.
RMS is being recognized today (Anatoli I. Dashchenko, 2006, p.27) as a necessary tool for increasing productivity and sustaining profits despite of abrupt global market changes. A typical RMS may include an array of flexible equipment, such as CNC machines, and special reconfigurable equipment comprehensive of machine tools, robots, and in process inspection machines. RMS may have two levels of reconfigurability: the first level consists in the arrangement and connections of machines at the system level, and the second level consists in some of the system’s machines that are reconfigurable. Both levels are designed according to a set of principles, and possess special characteristics, which are:
modularity; integrability; customization; scalability; convertibility; diagnosability.
5
Reconfigurable systems are focused on achieving the responsiveness at low cost and rapid time.
2.4 Comparison of Manufacturing Systems
Traditional manufacturing systems can hardly meet the requirements (Anatoli I. Dashchenko, 2006, pp.28-29) dictated by the new, competitive global environment. Dedicated manufacturing lines (DMLs) are based on inexpensive fixed automation and produce a company’s core products or parts at high volume and for a long run time. Therefore, the FMS production capacity is usually lower than that of dedicated lines and their initial cost is higher. While DML and FMS are limited in capacity-functionality, RMS capacity and functionality change over time as the system reacts to changing market circumstances. The following pictures (Anatoli I. Dashchenko, 2006, pp.32-33) show respectively, a global comparison of DML, RMS and FMS (Fig.2), and a comparison of capacity and functionality allocation of DML, RMS and FMS (Fig.3).
DML RMS FMS
System Structure Fixed Adjustable Adjustable
Machine Structure
Fixed Adjustable Fixed
System focus Part Part Family Machine
Scalability No Yes Yes
Flexibility No Customized General
Simultaneously operating tool
Yes Yes No
Productivity High High Low
Lifetime Cost
Low for a single part when fully
utilized
Medium for production at medium to high
volume of new parts and variable
demand during system lifetime
Reasonable for simultaneous production of many
parts (at low volume), otherwise
high
6
Fig.3 Comparison of capacity and functionality allocation of DML, RMS and FMS.
2.5 Systematic of Changeability
Changeability is called for on all levels of a company. Five structuring levels of a company can principally be identified (Anatoli I. Dashchenko, 2006, pp.385-386), each of which can be considered in terms of process and space (Fig. 4).
Fig.4 Structuring levels of a company from the process and space viewpoint.
From the process viewpoint, the centre of attention on the highest structuring level is the production network in which the company’s own network is embedded. From the space viewpoint, the site and the infrastructure are considered here. The next level
7
down that of general site development, relates to the structuring of the entire factory site. Here, from the process viewpoint, the arrangement of and the relations between the individual production areas and the layout of the factory buildings are decided upon. On the next level, the individual building with its structure and distribution of supporting columns is defined and the structures, layout and work organization for production and logistics are developed. On the level of group workstations, the arrangement of the workstations and the principles of manufacture and assembly for the individual structural units are defined along with the whole transport technology. The main concern on the bottom level is with the single workstations, their operating technology and the ergonomics and safety for the employees at the individual work-places. Below that level are the technological processes located, which are given from the point of factory planning.
2.6 Types of Factory Changeability
If the five structuring levels are combined with the associated product levels (Anatoli I. Dashchenko, 2006, pp.386-387), a field emerges that allows the definition of five types of changeability. Any type on a higher level subsumes all the types below it (Fig. 5).
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Changeover ability designates the operative ability of a single machine or work
station to perform particular operations on a known work piece or subassembly at any desired moment with minimal effort and delay.
Reconfigurability describes the operative ability of a manufacturing or assembly
system to switch reactively and with minimal effort and delay to a particular family of work pieces or subassemblies through the addition or removal of single functional elements.
Flexibility refers to the tactical ability of an entire production and logistics area to
switch reactively and with reasonably little time and effort to new – although similar – families of components by changing manufacturing processes, material flows and logistical functions.
Transformability indicates the tactical ability of an entire factory structure to switch
reactively or proactively to another product family. This calls for structural interventions in the production and logistics systems, in the structure and facilities of the buildings, in the organization structure and process, and in the area of personnel.
Agility means the strategic ability of an entire company – mainly proactively – to open
up new markets, to develop the requisite products and services, and to build up the necessary production capacity.
2.7 Transformability
A factory's ability to undertake changes reactively or proactively (foreseeing future evolution) to the so-called objects of change (Anatoli I. Dashchenko, 2006, p.387), thus modifying structures at all structural levels of the factory, may be defined as transform-ability. Characteristic of this change is a modification or adjustment of all relevant objects of change, triggered by the existing demand for innovative products and services. The objects of change characterize a factory's structural elements to which a modification might be effected.
2.7.1 Objects of Transformability
Every transformation object (Anatoli I. Dashchenko, 2006, pp.387-388) can be uniquely assigned to one of the four considered structuring levels. In addition, the transformability of a factory can be classified by three forms of transformability: spatial, organizational and technical (Fig.6).
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Fig.6 Examples of transformation objects, sorted by form of transformation and planning level.
Spatial transformability denotes the scope for the expansion and contraction of the factory. The element of what is known as breath-ability plays an important role here in respect of floor and ground areas and principally concerns the factory site, the works layout and the production layout. Organizational transformability enables the alteration and adaptation of organizational structures and processes. Technical transformability refers to the configurability and reconfigurability of operational resources, processes and buildings. It embraces all the technical systems in a factory. Every transformation object can be assigned to one of the transformability and planning level.
2.7.2 Enablers of transformability
The change of the objects itself can mainly take place through five so-called transformation enablers. By its existence, an enabler (Anatoli I. Dashchenko, 2006, pp. 388-389) contributes to the fulfilment of a transformation process. Furthermore, the enablers characterize the potential of the ability to transform, and become active only when needed. The characteristic of an enabler influences positively or negatively a factory’s ability to adapt. Figure 7 illustrates the main five enablers that the factory planner may use for purposes of attaining transformability.
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Fig.7 Enablers of transformation.
Universality represents the characteristic of factory objects to be dimensioned and
designed in their composition for diverse tasks, demands, purposes and functions. This enabler stipulates an over-dimensioning of objects to guarantee independence of function and use.
Mobility ensures the unimpeded mobility of objects in a factory. It abolishes the
classical division between immobile and mobile things, and covers all production and auxiliary facilities including buildings and building elements, which can be placed, as required, in different locations with the least effort.
Scalability provides technical, spatial and personnel extensibility or reduces ability. In
particular this enabler provides for spatial degrees of freedom, regarding expansion, growth and contraction of the factory layout.
Modularity follows the idea of standardized, pre-tested units and elements and also
concerns the technical facilities of the factory, (e.g. buildings, production facilities and information systems) as well as the organizational structures, (e.g. segments or function units). Modules are autonomously working units or elements that ensure a high interchangeability with little cost or effort (so called Plug and Produce Modules).
Compatibility allows various conditions and interactions within and outside the
factory. It especially concerns all kinds of supply systems for production facilities, materials and media. It also facilitates diverse potential materials, information and personal relationships. This enabler provides – besides the ability to detach and to integrate facilitates – incorporating or disconnecting products, product groups, and
11
parts, components, manufacturing processes or production facilities in existing production structures and processes with little effort, by using uniform interfaces. For the factory planner, in addition to the great variety of a structure’s transformability, the speed at which changes might be effect the factory is very important. As a requisite for a change process, and as a result of the considerable pressure exerted by the competition, it might also be asserted that both planning and the realization of the change process must take place at the speed required by the market.
2.7.3 Methods and Principles for the planning of Transformability
Future factory planning projects will have to deal with the following challenges (Anatoli I. Dashchenko, 2006, 389-391):
drastic increase of the planning frequency with shorter planning horizons at the same time;
highest speed in planning; unclear database;
target oriented integration of all disciplines along the planning cycle of a factory (architects, civil engineers, investors, operators, producers, suppliers, manufacturing technicians, logistics experts, etc…).
Nine success-promised planning principles of the factory planning have been outlined (Fig.8).
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They are aligned to the goals of efficiency, transformability and attractiveness, which are imperative objectives for factory planning and operating. By means of a planning scenario, main effects on the production and their probable development in the future should be transferred to consistent future pictures, the so-called scenarios. This, in turn, allows for the planning of factory structures in such a way that their conversion might be suitable for potential, future changes in the scenarios. These scenarios allow to derive the needed transformability a factory would need. An important planning principle for the future proves to be the consideration of future life cycles. The different life cycles of buildings, of products and manufacturing processes must be better balanced than at present. Beside economic potentials, this opens the possibility of a higher reaction ability of the factory to future changes. On the basis of the necessity of an economic production, the consistent alignment during the planning on the value added-chain is significant. The consistent avoidance of waste as a principle should consequently lead to short throughput times and, as a result thereof, to increasing delivery reliability in the sense of a quick response to customer wishes. Basically, for each factory-planning task many possible solutions exist. The premature preference of one single solution should, however, be avoided. Instead, a planning of variants should be performed. The layout planning on the other hand should always start with an ideal solution that is later transformed by the consideration of restrictions into several real variants. The principle of the iteration follows a stepwise planning that becomes increasingly concrete and considers the return on prior planning steps. The effects of individual planning steps on the project can be checked easily and, if necessary, corrected immediately.
2.7.4 Example of a Transformable Factory
Figure 9 shows a brief example (Anatoli I. Dashchenko, 2006, pp.391-392) of an implemented transformable factory. This is the result of a “Green-field”- planning project for a manufacturer of pumps. The modular building structure, consisting of a lightweight steel construction with few columns, enables easy expansion or reduction if necessary. Furthermore, the building is highly universal and allows to be expanded, as might be required. The organizational structure is foreseen so as to allow for the easy integration of new components or products, while efficiently dealing with increasing quantity demands. The concept of the factory layout ensures a high scalability, especially in case of the above mentioned possible changes in quantity demand. The factory's layout is furthermore well aligned with the material and information flows. The offices have been integrated in the manufacturing sector, allowing for better communication between the employees. This factory type also presents the features of a quick response factory. The logistic control principle is a mixture of a ConWip-System and a Kanban System.
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Fig.9 Example of a Transformable Factory.
2.8 Methods and Approaches for modelling Manufacturing
Structure
2.8.1 State of the art
The methods described in this paragraph are the only ones which can be useful for the development of this thesis, because for the development of a method for modelling manufacturing structures to enable their model based multi-criteria analysis, aiming to the evaluation of manufacturing structure changeability, the interesting methods are only those which allow the modelling of manufacturing structures changeability. None of these methods derives from the field of operations research, because the latter offers, above all, methods to improve the scheduling, instead the methods researched have to be useful for the modelling of manufacturing structure’s changeability. The research of the methods has been carried out by means of ScienceDirect and Google Scholar, using and combining the following key words for the research:
methods, techniques, approaches; modelling, changing, modifying; changeability, transformability;
manufacturing structures, manufacturing systems, layouts, production structures, production systems.
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2.8.2 RAS Design Method
2.8.2.1 IntroductionIn several manufacturing systems which handle a larger product portfolio, fluctuating production volumes and “end-of-life-cycle” products require frequent revision of the production structure applied (D. Gyulai, Z. Vén, A. Pfeiffer, J. Váncza, L. Monostori, 2012, pp.579-584) in order to gain shop-floor space and to level between capacity and throughput of the system. An effective solution to handle the fluctuation in the order-stream is the application of reconfigurable systems (RMS), since they respond to changes by offering focused flexibility on demand by physically reconfiguring the structure of the system. The method presented below is a RAS (Reconfigurable Assembly System) design method that separates the low and high volume product families dynamically and by assigning to them the appropriate reconfigurable or dedicated production lines, respectively.
2.8.2.2 Description
RAS design method defines the boundaries and the components of a reconfigurable assembly system. It aims to solve two main issues:
1. Definition of an appropriate product mix for a given time horizon which could be produced in the Reconfigurable Assembly System at a balanced utilization level and throughput.
2. Definition of the equipment requirements, the configuration, and the operational conditions of the reconfigurable Assembly System.
For solving the first problem it’s necessary, first of all, describe clearly the main assumptions and constraints about the whole manufacturing system, which are:
there are production lines (assembly lines), each consisting of workstations; the number of workstations is limited;
the number of the applied fixtures is unlimited;
at each workstation one or more processes can be executed; the workstations are operated by human operators;
any process can be started only if an operator with specified skill is available; the assembly lines meet the requirements of a flow-shop system;
the production orders are known in advance for the given period;
lines can be dismantled and reassembled, thus workstations aren’t necessarily stored in the resource pool.
Regarding the product mix, the decision is based on the combination of the production volume or revenue and the technology requirements of the production, following the steps given as follow:
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2. Calculate the resource demand for each element of this set by multiplying the sum of production orders by the total work content (including the setups and assembly time of the line) for the given element.
3. The set of products included into the RAS is filled by starting with the product having the smallest intensity resulted.
4. Feed the given order-stream into the RAS and calculate the operation time of each line assembled in the system for producing a certain product.
5. By iteratively removing the product with the highest intensity from the RAS, and repeating the calculation of the operation times will result in a final set of products, which could be produced in a balanced way in the RAS.
The second problem can be solved by a systematic search for an appropriate configuration of the RAS.
The most important results of the simulation of this method show the effect of the number of operators and the number of workstations available in the resource pool on utilization and throughput.
2.8.2.3 Industrial case-study
In this paragraph is presented an industrial case-study to facilitate the understanding of the method.
The as-is state of system considered has got the following characteristics:
the prototype simulation system is a real production facility in the automotive industry;
the reorganization of the company’s production requires a new assembly segment for the low-volume products;
there’s only a relatively small shop-floor space for this segment;
the main requirements are that the lines have to meet customer orders while occupying the smallest area;
the assembly process at lines are manual, supported by various pressing-machines and screwing-pressing-machines;
the material flow of the lines is linear;
all the assembly tasks of the products are sequential.
The problem is that it’s impossible to assemble each product in a dedicated, highly automated system, therefore the objective of this project is aiming to reduce the required space of all the low-volume lines and to reorganize their operation by making them reconfigurable. In other words the number of workstations and of operators necessary to perform the production in face of changeable order demands and limited shop-floor space has to be established.
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During the reorganization process of the low-volume segment, within the conceptual system design, the questions which had to be answered were:
1. How to separate effectively the low-volume and the high-volume product families and assign the appropriate assembly system?
2. Which are the equipment requirements of the proposed reconfigurable assembly segment, so as to perform continuous production in face of changeable order demands and limited shop-floor space?
The basic concept of the new system design was the reconfigurability which is supported by modular assembly lines, and steps executed to solve the issues are:
1. Systematic categorization of the assembly tasks of each product within the mapping process of the production lines.
2. Identification of the main assembly tasks.
3. Standardization of the main tasks in terms of their equipment and technological requirements.
The result obtained using the RAS design method is that the simplified operation of the reconfigurable system is:
1. The assembly lines are built-up by means of the standard workstations by moving them next to each other.
2. The operator does the necessary setup tasks (plugs-in the air connectors, places the necessary fixtures on the workstations,…).
3. The operator prepares the necessary parts by using the kits. 4. The operator assembles the products in the required volume.
5. After the assembly process is finished, the operator dismantles the lines by moving back the workstations to the resource pool.
2.8.3 A generic Model for Reconfigurable and Agile Manufacturing
System (RAMS)
2.8.3.1 Introduction
Global economic competition (Imad Chalfoun, Khalid Kouiss, Anne-Lise Huyet, Nicolas Bouton, Pascal Ray, 2013, pp.485-490) and rapid social and technological changes have forced manufacturers to face a new economic objective: manufacturing responsiveness. A new type of manufacturing system, a Reconfigurable Manufacturing System (RMS), has been developed in order to provide exactly the capacity and functionality needed, exactly when it is needed. In recent years, the evolutionary progress and paradigm shifts of manufacturing systems have been moving towards agile manufacturing systems. A generic model for Reconfigurable and Agile Manufacturing Systems (RAMS), which permits the modelling of real manufacturing systems and allows a good description of reconfiguration activities, is described below.
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2.8.3.2 Description
The following picture (Fig.10) shows the organization of the RAMS generic model.
Fig.10 Organization of the RAMS generic model.
The horizontal axis describes the system structure and its configurations, instead the vertical axis distinguishes the logical part from the physical part. The structure defines the system elements and its capabilities as resources and products and the connections between them; the configuration describes how the structure elements are used and how they are organized. The logical part describes the functions to perform and the physical part describes the organization of the different material elements which will carry out these functions.
Logical structure is composed of products and functions which must be performed on the product and also defines the process plan which leads to the final product.
Physical structure describes the arrangement of the different material elements which compose the system as the stationary resources (machines, buffers, etc…), the transport resources (robots, conveyors, etc…) and the different connections between them; the connections represent the potential transfer links between the stationary resources and they are associated with the transport resources.
Reconfiguration is the ability to modify the number of resources, capabilities and organization to meet the needs of production and it can be obtained through the logical and physical configuration.
Logical configuration (software) is the implementation of control programs for each component of the structure.
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Physical configuration represents the resources and the capabilities required for each resource.
The operations play a key role in the model, in fact they combine the functions with the resources and they connect the structure to its configurations and the physical part to the logical part.
This method comprises three main steps: 1. Definition of the structure:
structure formalization; structure meta-model; structure connections. 2. Configuration: configuration formalization; configuration meta-model. 3. Definition of the operations:
operations formalization; operations meta-model.
The structure formalization is the representation of the structure by the pair:
S : {Sp , Sl} , where
Sp = physical structure;
Sl = logical structure.
Sp is described by the triplet:
Sp : {R, Capab, Conn} , where
R = set of structure resources;
Capab = capabilities of each resource; Conn = connection application.
The connection application links two stationary resources together through a transport resource which carries out the transfer and it can be represent in the following way:
Conn : R_s×R_s×R_t→{0,1} , where
R_s = stationary resource; R_t = transport resource.
Sl is represented by the quintet:
Sl : {F, G, Pr, Prec, Affec} , where
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G = set of logical sequences; Pr = set of product types;
Prec = precedence relation between functions within a logical sequence; Affec = assignment of one or more logical sequences for all product types. The functions set comprises three kind of functions:
F_tr = work functions; F_ts = transport functions; F_st = storage functions.
The precedence relation and the assignment of logical sequences are respectively represented in the following way:
Prec : G×F×F→{0,1};
Affec : G×Pr×→{0,1}.
The structure meta-model illustrates the modular components to be built and the network of relationships which ensures the data flow between these components. The Systems Modelling Language (SysML) provides the Block Definition Diagram BDD which allows to represent the structure into modular components, or blocks, with relations between them. The goal of the structure meta-model is to build the RAMS structure in a modular manner to facilitate system reconfiguration and to collaborate with other components to perform the agility required. An example of a structure meta-model is depicted in picture below (Fig.11).
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Fig.11 Example of a structure meta-model.
The system structure comprises:
The physical structure which is composed of resources, capabilities and connections; the types of resources considered are stationary resources (machines, emergency machines, buffers), transport resources (conveyors, robots, loaders/unloaders), and Automated Guided Vehicles (AGV).
The logical structure which is characterized by work functions (involved in the realization of products), transport functions (associated with connections), and storage functions (they connect the loader/unloader to the buffers).
The structure meta-model is represented by using seven different blocks: System block which represents the structure;
Port block which defines the characteristic locations for transfers;
Connections block which represents the connections that link machine ports via a conveyor or a robot;
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Products block which represents the product types; Plan block which describes all types of products;
Precedence block which defines precedence relations between functions; Assignment block which assigns one or more process plans (function
sequences) to each type of product.
The connections represent potential transfer links between machines and are associated with the transport resources that can run them. The application of this method requires as assumption a configuration already given which defines the following information:
number of movable machines (N); IN/OUT buffers;
number of stages (m) with two IN and OUT stages; number of machines in each stage (np[m]);
machines arrangement;
connections between machines;
Cartesian coordinates (xi, yi) for each machine at the workshop level;
the coordinates of the IN and OUT buffers are respectively (xin, yin) and (xout,
yout);
the connections are defined in the workshop considering that X_Y means that X is connected with Y.
Aiming to integrate the concept of agility with the reconfiguration function, the connections are represented in the following way:
P[i, j] represents the machine at stage i and local number j, and it’s an element of the transposed matrix of P = (pi, j) 1 ≤ i ≤ m, 1 ≤ j ≤ max (np[m]), where max
(np[m]) is the maximum between the number of machines in each stage.
P[i, j].coordinates = (xi, yi) are the Cartesian coordinates of P[i, j].
R[i, j] is the transport resource associated with P[i, j].
P[i, j].FollowingMachines is a vector that represents the following machines of P[i, j].
size[P[i, j].FollowingMachines] is the number of following machines of P[i, j]. The loader performs the connections between IN and the first stage (m=1):
For i=1 to np[1]
IN_P[1, i] performed by the loader.
The unloader performs the connections between IN the last stage m and OUT:
For i=1 to np[m]
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The transport resources associated with machine P[i, j] perform the connections between the first stage m=1 and the last stage m:
For i=1 to m-1 For j=1 to np[i]
For K=1 to size[P[i, j].FollowingMachines]
P[i, j]_P[i, j].FollowingMachines[k] performed using R[i, j] which is associated with the P[i, j].
In this way the connections are modelled in a manner to move and connect easily the machines from their coordinates and neighbours.
Configurations define the various uses and organizations of the structure elements so that each configuration meets its objective.
The configuration formalization is the representation of configuration by the pair:
C : {Cp , Cl} , where
Cp = physical configuration;
Cl = logical configuration.
The physical configuration Cp is a key indicator to evaluate the configuration in terms
of cost and is described by the pair:
Cp : {R_util, Capab_assoc} , where
R_util = resource set used in the configuration (included in R);
Capab_assoc = defines required capabilities associated with each resource and for each resource, certain modules (tools and/or devices) will be eligible for use.
The method defines the following two applications:
RessUsed : R_util × R →{0, 1} which defines the resources used in the
configuration;
CapabAssoc : Capab_assoc × Capab→{0, 1} which enables the capabilities
associated with each resource in the configuration to be specified.
The logical configuration Cl is represented by the set of control programs
corresponding to products, process plan and configurations:
Cl : {Prog}.
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Implement : Prog × R_util→{0, 1} which allows a control program to be
implemented for each resource used in the current configuration.
In the same way as for the structure, the configuration meta-model represents the configuration in modular block components with relations between them. The system configuration block represents a possible configuration of the system and has three relations, with the physical configuration, the logical configuration and the set of operations; the picture below (Fig.12) shows an example of a configuration meta-model.
Fig.12 Example of a configuration meta-model.
The operations are a key indicator to evaluate the configuration in terms of operating time.
The operations formalizations distinguishes six types of operations at the workshop level:
main operations; transport operations; storage operations;
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activation operations; assignment operations; implementation operations.
The operations meta-model is represented by using different blocks: Main operations block which defines the main operations;
Transport operations block which represents the transport operations; Storage operations block which describes the storage operations;
Sequence operations block which represents the sequence of operations; Activation operations block which represents the activation operations; Assignment operations block which defines the assignment operations;
Implementation operations block which describes the implementation operations.
An example of an operations meta-model is shown in the following picture (Fig.13).
Fig.13 An example of an operations meta-model.
This method defines the following applications:
Op_main : Op × F_tr × R_s →{0, 1} which describes the operations
implementing work functions on associated machines;
Op_transport : Op × F_ts × Conn →{0, 1} which defines the operations
associating the transport functions with the different connections;
Op_storage : Op × F_st × Buffer →{0, 1} which describes the operations
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buffer, and Stj (Prj, OUT) that allows to store the final product (produced on a
machine in stage m) in the OUT buffer;
Op_assignment : Op × R_util →{0, 1} which is used to enable the resources
used in a configuration;
Op_activation : Op × capab_assoc × R_util →{0, 1} which enables to
specify the modules (tools and/or devices) of the resources used according to the configuration requirements;
Op_implementation : Op × Prog × R_util →{0, 1} which allocates
implementation operations in order to implement control programs on each resource used in this configuration.
2.8.3.3 Industrial case-study
In this paragraph is presented an industrial case-study to facilitate the understanding of the method; the case considered is a process of assembling electronic components on printed circuits boards.
The physical structure is represented by:
the stationary resources IN, OUT, M1, M2, M3, M4, M5;
the transport resources loader, unloader, R1 (Robot 1), R2 (Robot 2), Cv1
(Conveyor 1), Cv2 (Conveyor 2);
various connections;
capabilities of each resource (each resource can carry out several operations). The logical structure is represented by:
products;
three types of boards;
five process plans to obtain these products by carrying out work functions; the functions Pr = {Pr1 , Pr2 , Pr3}, G = {G1 , G2 , …, G5}, F = {F_tr , F_ts ,
F_st}.
The conditions of this case are:
1. Each work function is represented by a single operation that must be implemented at least once : F_tr = {F_tr1 , F_tr2 , …, F_tr7}.
2. Each transport function is implemented by a single operation which is linked to a connection : F_ts = {F_ts1 , …, F_ts10}.
3. Each storage function is implemented by a single operation : F_st = {F_st_in ,
F_st_out}.
The steps necessary to model the structure are: 1. Assignment of the process plans to products.
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2. Definition of the precedence relation between functions within each process plan.
3. Start from the product to set up a new configuration. 4. Choose the corresponding process plan.
5. Choose the resources capable of executing all the process plan functions. 6. Definition of an organization of the resources with connections to carry out the
process plan (first part of physical configuration). 7. Definition of the main operations.
8. Assignment of the operations (second part of physical configuration). 9. Implementation operations (logical configuration).
The first configuration defined is depicted in the picture below (Fig.14).
Fig.14 First configuration of the process of assembling.
For example if a failure occurs suddenly on M3 the generic model of RAMS helps to
reconfigure the line quickly and effectively by modifying the currently used resources, coordinates, associated capabilities and control programs for each component of the new structure: the new configuration obtained is shown in the following picture (Fig.15).
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2.8.4 Method for Multi-Scale Modelling and Simulation of Assembly
Systems
2.8.4.1 Introduction
The approach presented below aims (M. Neumann, C. Constantinescu, E. Westkämper, 2012, pp.406-411) at the development of a method for an efficient and scalable modelling and simulation of an assembly system in all its scales, based on a manufacturing resource library, a suitable modelling language and a modelling procedure, that enables a knowledge-driven and continuous optimization of the assembly system as well as scenario analysis.
2.8.4.2 Description
This method is based on the concepts described below and the five pillars depicted in the picture 16.
The basic concepts are the following:
A factory object, of a special scale, is a machine, tool, device, workplace, transport system, manufacturing equipment, or manufacturing resource which is required to fulfil the purpose of manufacturing and/or logistic processes. A factory object is defined through its scale, position and condition (state of a
factory object) over the time.
Two different classes of factory objects can be defined:
temporary (mobile) factory objects, whose scale, position and condition changes over time;
permanent (mainly immobile) factory objects, whose scale and position remains constant, in opposite to their condition, over time (they change their condition in every instant of time).
The model consists of factory objects, their characterization and interdependencies in a transparent and comprehensive way.
Fig.16 The five pillars of the method.
METHOD FOR MULTI-SCALE MODELLING AND SIMULATION OF ASSEMBLY SYSTEMS 4. MODELLING PROCEDURE 5. OPTIMIZATION 3. RESOURCE LIBRARY 2. MODELLING LANGUAGES 1. BASE MODEL “Assembly System”
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Modelling languages: two different modelling languages are used, which are The Value Stream Mapping enhanced with required notions (Graphical Modelling Language), and Ontology Web Language – OWL which enables a semantic characterization of factory objects and a proper modelling of interdependencies between them (Semantic Web Technology Modelling Language).
Resource library: it consists of factory objects for every scale of the assembly system; the factory objects are predefined and/or configurable; it contains interdependencies between factory objects and processes.
Modelling procedure: the modelling is supported through an easy to use drag and drop function and intuitive Graphical User Interface (GUI); the modelling of assembly system is structured according the scales and supported through the employment of flexible workflows and established procedure; the model development is performed in two steps, which are
1. The existing assembly system is modelled on the fly directly in the shop floor, thus the layout and the internally interdependencies of the Factory Object and between the Factory Objects can be modelled.
2. The rough model can be detailed and optimized.
Optimization: an active analysis, configuration and optimization is supported; further more real data from Manufacturing Execution Systems and Product Life Cycle Management Systems can be used for simulations to identify the most suitable planning scenario by employing into the method integrated optimization functions. The focus of the approach is the Assembly System Base Model, which is described below.
The approach considers the SUM (Stuttgart Enterprise Model) scales starting from the production system, production cells up to machines and workplaces. Infrastructure (electricity, gas, hydraulic and pneumatic systems, ICT) and the in-house logistics are even considered. The Assembly System consists of different factory objects, which are required at different scales and purposes of manufacturing; each scale is defined through its purpose in the manufacturing process and through its allocated factory objects, therefore each scale is a unit with specific factory objects. The following pictures (Fig.17 and Fig.18) depict respectively the structure of the Assembly System and the classes of factory objects.
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Fig.17 Structure of the Assembly System.
Fig.18 Classes of factory objects.
Data is processed by suitable processing methods and is subsequently provided to other systems or applications (MES, ERP Digital Factory) and shared between them. Each scale and factory object can be characterized through its infrastructural boundaries and interdependencies; the interdependencies between single factory objects and scales can be described with the language OWL.
The context comprises the position, scale and condition of factory objects, and it’s captured through sensors (RFID, GPS or force) based on the “Smart Factory” approach.
2.8.4.3 Example
In this paragraph an example of the working of the Assembly System Base Model is described.
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Fig.19 Factory objects and their interdependencies.
A planner wants to optimize the assembly line in replacing the permanent factory object 1 (FO1ᴾ) with a newer version. This factory object requires the infrastructural
boundary 9 (IB9), which is the requirement for a hydraulic access, but the scale
Assembly Line doesn’t provide this access yet. The Model will tell the planner that an issue arises, which is assigned through the corresponding lightning (Issue). Thus, the actor has to search for alternatives, like adapting the scale or replacing the machine with another machine.
2.8.4.4 Conclusion and roadmap
The development of the Method for Multi-scale Modelling and Simulation of Assembly Systems is an on-going and complex research topic where future steps are of huge interest. The next steps are as follows:
the development of the knowledge-based manufacturing resource library; analysis of the interdependencies between the assembly system scales and
factory objects;
enhancement of the Value Stream Mapping Method to according the method requirements;
the data exchange with Manufacturing Execution and Enterprise Resource Planning Systems.
3 Definition of requirements for the analysis of
manufacturing structures – Chapter 3
3.1 Introduction
The aim of this chapter is define the requirements for the analysis of manufacturing structures, because the most important objective of this thesis is the development of
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a method for modelling manufacturing structures to enable their model based multi-criteria analysis. Nowadays, to face the complexity of markets, the production structures have to be modelled for adapting themselves to the demand fluctuations, and consequently the changeability of manufacturing systems and structures is a crucial challenge to stay competitive. Changeability is the answer to uncertainty, therefore defining the requirements for the analysis of manufacturing structures means identifying which are the enablers of changeability, because the manufacturing structures and methods for modelling these ones have to enable changeability. In the next paragraphs are described the motivation of changeability, the elements of changeable manufacturing, the changeability objectives and enablers, and finally the requirements for manufacturing structures’ analysis, considering the evaluation of their changeability, are defined.
3.2 Motivation of changeability
Manufacturing systems have evolved over the years in response to many external drivers (Hoda A. ElMaraghy, 2009, pp.3-6) including the introduction of new manufacturing technologies and materials, the constant evolution of new products and the increased emphasis on quality as well as the escalating global competition and pressing need for responsiveness, agility and adaptability. Manufacturing systems paradigms, such as flexible and reconfigurable manufacturing can be viewed as enablers of change and transformation at different levels. Flexible manufacturing allows changing individual operations, processes, parts routing and production schedules; this corresponds to variations in products within a pre-defined scope of a parts family. It also allows adjusting production capacity within the limits of the existing system. Therefore, FMS offers generalized flexibility that permits changes and adaptation of processes and production volumes, within the pre-defined boundaries, without physically changing the manufacturing system itself. Reconfigurable manufacturing allows changeable functionality and scalable capacity by physically changing the components of the system through adding, removing or modifying machine modules, machines, cells, material handling units and/or complete lines. Hence, RMS responds to changes by offering focused flexibility on demand by physically reconfiguring the manufacturing system. The factory buildings have to be adaptable to two and sometime three product generations as well, and even the site must follow new requirements, for example regarding logistics and environmental regulations. The prerequisites for successful participation in dynamic and global production networks require that the production processes, resources, plants structures, manufacturing systems layouts as well as their logistical and organizational concepts be adaptable quickly and with low effort. This ability is necessary for production companies to withstand the continuous changes and the
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turbulent manufacturing environment facing them, and can be described as “changeability”.
3.3 Elements of changeable manufacturing
The scope of changeability (Hoda A. ElMaraghy, 2009, pp.10-11) has to be widened from the manufacturing system that makes various work pieces to encompass the whole factory that produces different products in various variants. It should be noted that the terms “flexibility and reconfiguration” are generally specific to certain factory levels. Therefore, changeability has been proposed as an umbrella concept that encompasses many aspects of change on many levels within the manufacturing enterprise. Changeability can be defined as the characteristics to accomplish early and foresighted adjustments of the factory’s structures and processes on all levels, due to change impulses, economically; but it can even be interpreted according to the factory level. The following figure (Fig.20) depicts the scope of changeable manufacturing.
