Handling disturbances in small volume production

. Robotics and Computer Integrated Manufacturing 19 (2003) 123–134

Handling disturbances in small volume production Monica Bellgrana,*, Emanuela Aresub a

Department of Manufacturing Systems, Royal Institute of Technology, 100 44 Stockholm, Sweden b MacGREGOR (SWE) AB, P.O. Box 4113, 400 40 Gothenburg, Sweden

Received 31 August 2002; received in revised form 10 September 2002; accepted 30 September 2002

Abstract The question of preventing and handling disturbances is often discussed in relation to high-volume production. However, disturbance handling is also relevant in small volume production. In general terms, disturbances could be approached on the basis of which phase of the production system life cycle they occurred in. For example, dealing with production disturbances already in the development phase may be a successful preventive approach. The purpose of the paper is to identify and analyse how disturbances occur and are handled in a situation of producing different product modules in small volumes compared to mass production. The discussion is based on theoretical studies, earlier empirical studies, and a case study performed recently at a Swedish engineering and manufacturing company with small-scale production. A successful product development process is required in order to achieve a product with the desired conditions concerning time, cost and quality, etc. It also implies preparing for a disturbance-free production process. Disturbance elimination should therefore be considered a design criteria when designing. r 2003 Elsevier Science Ltd. All rights reserved.

1. Introduction 1.1. Background Production disturbances occur during start-up of industrial production systems, as well as during full production. In general, the question of reducing and handling production disturbances is often discussed in relation to high-volume production. The reasons for preparing for a smooth production when producing in high volumes is evident, as disturbances and losses are often both time-consuming and costly to handle. However, it is also necessary to discuss production disturbances when producing products in small volumes. The conditions when producing in small and very small volumes similar to handicraft/pilot production (o10 products/year) are quite different from those of producing products in large annual volumes. Consequently, the strategies for handling disturbances in such businesses may differ from the strategies that highvolume companies develop.

*Corresponding author. Tel.: +46-660-57827; fax: +46-660-57805. E-mail addresses: [email protected] (M. Bellgran), emanuela. [email protected] (E. Aresu). URLs: http://www.mh.se, http://www.macgregor-group.com.

The research presented here deals with how disturbances that occur in companies producing different product modules in very small volumes are dealt with, compared with how high-volume production companies handle disturbances. When producing small quantities of many different products, companies may choose whether it is convenient to produce in-house or to outsource. Discussing disturbances occurring outside the company’s product development (PD) is therefore also of interest.

1.2. Theoretical issues on disturbances As a general term, disturbance has a wide meaning and needs specification or classification for different fields. Production disturbances, the main point of discussion here, can be seen from several different perspectives and can also be described with various words, such as disruptions, failures, errors, defects, losses and waste [1]. Ylip.aa. defines production disturbances as ‘‘All the activities that are carried out or should be carried out in correction, prevention, and elimination of production disturbances and potential production disturbances in both existing and future systems during their life cycles’’ [2].

0736-5845/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0736-5845(02)00069-8

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Handling production disturbances on a strategic level means to foresee disturbances and also prevent them from appearing in the production system. This could be done by utilising the development process for efficient design of the production system. As put forward by Blanchard [18], it is for example essential that a system maintenance and support concept be developed during the conceptual design phase. Dealing with the disturbance problem requires measurement of performance, and utilisation of process data and information of production disturbances appearing during different production life-cycle phases. The area of disturbances and disturbance handling are often related to reliability and maintenance and, hence, treated from this perspective. The production perspective on the problem is slightly different from the maintenance perspective and focus. The production and maintenance departments are also often organisationally separated into different departments, indicating their different approaches. A holistic view of the task of achieving high production efficiency and effectiveness by eliminating disturbances could possibly also involve an organisational integration of production and maintenance. Reliability should not only be considered in terms of product reliability, but is also important when it comes to system design, i.e. the process of designing the production system. Unreliable systems are unable to fulfil the mission for which they were designed. In an environment of scarce resources, it is essential that reliability be considered as a major system parameter during the design process. Reliability is a characteristic inherent in design [3, p. 345]. The authors define reliability simply as the probability that a system or product will accomplish its designated mission in a satisfactory manner for a given period when used under specified operating conditions. Elements of probability, satisfactory performance, time (or missionrelated cycle), and specified operating conditions are connected to the reliability definition [18]. Probability is usually stated in quantitative terms representing a fraction or a percent specifying the number of times that one can expect an event to occur in a total number of trials. Satisfactory performance indicates that specific criteria must be established saying what the system must do in order to satisfy the needs of the customer. Time represents the measure against which the degree of system performance can be related. The specified operating conditions under which a system or product is expected to function during operating or nonoperating time (storage, handling and transport modes) include environmental factors [18]. This reliability definition suits large-scale production better than production in very small volumes, as time and quantity are important elements of the definition. Looking at the

reliability elements of satisfactory performance and specified operating conditions, these elements could possibly also be relevant to consider in production systems where small volumes are produced. Thinking in reliability terms, both during the product design work and the production design and preparation phase, may be one way of emphasising the approach of eliminating disturbances already during the early design work, instead of waiting for the disturbances to appear and dealing with the problems as they occur.

2. Research methodology 2.1. Basic approach The research results presented here are founded on research within the manufacturing engineering discipline, concerning the field of design and evaluation of production and assembly systems in particular, performed at the manufacturing engineering department at . Linkoping University of Technology. See e.g. [4–8]. In [5], a model for analysing assembly system design is presented, involving three parts; design process planning (subdivided further into aspects concerning design process management and design process structure), the design process (subdivided further into aspects concerning preparatory design and design specification) and the contextual part. The model is supported with a design method in the form of guidelines on three levels of detail, and separated into eight phases. The research was based on empirical studies; 6 case studies, an interview study with 10 companies, and a survey. Later work presented in [8] aimed at identifying and structuring the performance of assembly systems and their design processes, and proposed a framework for identifying important relationships between the results of specific design projects and influencing factors in the design process. The result was based on an interview study with 15 companies and 3 case studies. Recent research within the field of production disturbances is performed by participation in an ongoing national multi-disciplinary co-operation project called ‘‘TIME’’ [1]. The objective is to develop a methodology for analysing and dealing with production disturbances on both a short-term and a longterm basis, also including the utilisation of software support. A holistic perspective referring to a strategic, tactical and operative level has been chosen in order to deal with production disturbances at a manufacturing company. The research results are based on case studies in Swedish manufacturing industry, and so far, one extensive case study has been performed and another initiated. The research presented in this paper concerns production disturbance handling from a strategic point

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of view. In general terms, disturbances could be analysed on the basis of what phase of the production system life cycle the disturbances occurred in. Identifying and structuring the disturbances into categories are important initial steps in the strategy for how to handle disturbances in both a short-term and a long-term perspective. However, it is also necessary to analyse the reasons behind the disturbances. An interesting approach here is how to deal with production disturbances already in the development phase. Is it possible to find general guidelines for how to prevent or eliminate disturbances when designing both product and production system? These and other related issues are discussed in the paper based on theoretical studies and a case study within a Swedish industrial company. 2.2. The case study methodology The case study methodology was considered appropriate for the research purpose. As put forward by Yin [9], a case study in its original meaning means to investigate the unique case, and is a relevant strategy when the research questions of ‘‘how’’ and ‘‘why’’ are posed. Yin defines a case study as follows: A case study is an empirical inquiry that investigates a contemporary phenomenon within its real-life context; when the boundaries between phenomenon and context are not clearly evident; and in which multiple sources of evidence are used. [9] A case study does not allow making generalisations related to frequencies, the generalisation to theoretical propositions is more relevant. The unique strength of a case study is also to deal with a full variety of evidence such as documents, artefacts, interviews and observation strategy [9]. In the present case study, different data collection methods were chosen for the research purpose such as

Side ramp

observations, studies of documentation, and semistructured interviews with employees from the engineering and production departments at the company. The empirical findings indicate how a company developing and manufacturing products (often customised) in small volumes approaches the problem of disturbances.

3. Description of the case study company’s businesses and processes 3.1. Company description The main issues here, focusing on disturbance handling related to small-volume production, are based on a case study at the MacGREGOR RoRo Ship Division in Gothenburg, providing marine cargo flow engineering solutions. The company is the world-leading supplier of RoRo equipment with a market share of 50–60%. Net sales for 2001 totalled 868 MSEK, and the company employs about 120 people at its Gothenburg headquarters and 1500 worldwide. The facility at Gothenburg focuses on RoRo equipment, developing all kinds of equipment for RoRo vessels. Core products are ramps, car decks, doors, side access, land systems, etc. An example of products for RoRo vessels is illustrated in Fig. 1. 3.2. Product ordering process Products of large sizes are produced in small volumes at the MacGregor RoRo Ship Division. The development and building of the products can be initiated differently, and is also performed through different processes. In a broader perspective the product ordering process at MacGREGOR can be considered as taking place within the ship development process. The process

Car deck

Stern ramp Shell door

Bulkhead door Ramp cover Stern door

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Hoistable ramp

Hydraulic power pack Fig. 1. A vessel with examples of RoRo products.

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3.3. The product development process

Ship development Ship owner

Yard

Partly based on the product ordering process, development activities at MacGREGOR can be divided into two different types of processes: *

Product MCG *

Production

Fig. 2. The product ordering process in a broader perspective.

usually starts with a shipowner demand, and in collaboration with a specific shipyard. Early in the development process of a ship (even before the suppliers have got an order), MacGREGOR is involved in developing equipment. New products are developed based on orders coming from a yard or a ship-owner, and the requirements may be based on a possible ship structure of a ship that does not yet exist. The reason for starting a project at this early point is for concurrent engineering purposes, i.e. to work in parallel with the ship development and building in order to achieve the best possible result in the shortest time. Such a project is thus started although there may be a risk of customerinitiated changes that will affect the early development work. During the early work, MacGREGOR also investigates possible ways to produce the product, i.e. either in-house or outsourced. In this context, MacGREGOR plays the role of the supplier which means that the PD within the company is the last stage of the PD of the whole ship. The process of concurrent engineering is illustrated in Fig. 2. In a later phase when, for example, a new order is received from a customer, the future activities of the Ro-Ro division will be related to what the company calls ‘‘a new project’’ or a ‘‘contract’’. The development activities continue during the whole working process of a new project, and involve many functions such as Contract Management (economical responsible), Production (responsible for purchasing and producing), Installation, New Sales and Engineering. Managing a customer order may also involve development tasks related to other products of the customers, i.e. the customer often asks for help in solving problems with their earlier products as a precondition for future orders. Development activities may, therefore, also be initiated by the customer’s request for a solution to a problem with an existing product.

The company-driven new PD process: Development of an entirely new product from concept to prototype and tests. The order-driven PD process: Development of customer specific products based on an existing concept in the company product range.

The company-driven new PD process is a continuous process, often performed independently from orders, but of course related to market demands. An example of a development project of an entirely new product is the Corex sandwich project, which also included the development of the production system for in-house production. An order-driven PD process starts when there is a customer demand for a specific product. As there are no standard products for these types of marine products, all products are customised. As a starting point for the development, it is investigated whether there are any existing products that can be utilised as a base for the new development project. If not, the R&D department becomes involved in the work of offering the new product. In general, this type of development could be said to be partly company-driven as well since the company decides what products are interesting to develop based on a long-term strategy (affected by the long project duration, for example). The order-driven PD process also occurs if a similar product already exists. Then the design department becomes involved instead of the development department, and an evaluation is made of how similar the existing product and the intended new product are in order to foresee cost and resources needed. Examples of such a type of product are a stern ramp and a car deck. When an order-driven project is initiated, there is a clear procedure to follow. The procedure is described in the Quality Handbook, including for example what type of meetings should be held and guidelines for the information flow. In addition, an informal exchange of information before formal project start has recently been transformed into a formal pre-study, involving not only the sales department but also the engineering department in an early phase. 3.4. Product design In shipbuilding, the general design methodology used when designing a new product can be described as consisting of three main interactive phases: product definition in system terms, basic solution to the product, and material/detailed design [10].

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At MacGREGOR, the actual design of the product starts with the ‘‘basic design’’ where sales engineers draw the basic components of the new product. Only a cost analysis exists at this stage, based on knowledge from earlier projects. When the product is ordered, a design team comprising 5–6 designers and a design leader is formed. Examples of the tasks of the design team are related to mechanics, hydraulics and fittings of the product. Technical solutions are elaborated on, and any kind of problem that shows up must be solved implying that experience and competence are fundamental at this stage. Furthermore, a detailed design of the product is made for purchase and production. The drawings produced must be approved by the classification societies, and consequently requirements for changes may appear. At the end of the technical and detailed design stages, a procedure of design verification has recently been introduced in order to verify that the design output meets the customer requirements defined in the technical specification and that the design team is fully informed of these requirements. The results are discussed and evaluated by the design team before the product design is complete and the production process may start. Technical aspects are highly prioritised in the course of a project, as achieving a technical successful product is a precondition for order—before even talking about costs and delivery. For every project, a design leader is appointed with the task of dealing with the technical aspects of the product. In parallel, the project’s financial aspects are handled by a contract manager who cooperates with the project leader in matters concerning resource investments, etc. Previously, the overall project leader had the double function of being both design leader and contract manager, which implied a good project overview. However, a disadvantage of this dual role was the overload of design tasks, and this was dealt with by a necessary separation of the two roles of design leader and contract manager. This new project management structure has both advantages and disadvantages of its own. One advantage, however, is that contract managers also have the important role of gathering information about the actual ship design. 3.5. Production and product installation The production of MacGREGOR products mainly consists of welding operations, where specialised personnel work more or less intensively depending on the urgency of the delivery requirements. The production of an order-driven product is usually made at second-tier suppliers, while production of new products developed from scratch can be produced in-house (as was the case with the Corex sandwich structure). The quality handbook describes the procedure of the planning of manufacturing and delivery required by the second-tier

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supplier. Although MacGREGOR controls the product quality resulting from the production activity of the second-tier supplier, their involvement in the production system development work is limited. On the other hand, when the product is produced in-house, the production system is developed internally. The last phase of the total PD process is the installation and start-up of the product on board the ship. Experience and competence makes this one of MacGREGOR’s strengths. The time for the development process varies. One example is the development of a stern ramp with a general dimension of 10 m in length and 15 m in width, which can vary from 6 months to a year (from order to delivery) depending on product complexity. The production time usually varies from 2 to 3 months. Quality, time and costs are three fundamental parameters for measuring the success of a project. In addition, functionality, weight, and reliability are other key parameters in the design of products. 3.6. Process guidelines and information flow The PD process is a part of either the ‘‘New Sales’’ or the ‘‘Conversion’’ process, depending on whether it concerns new building or rebuilding. How sales and order processing take place is described in the quality handbook. Here, it is suggested that the information flow should be started at the sales department. Information should be communicated from the sales department to the other departments of the company (CM, Design, Production, Installation and Finance). The information flow is guided by, for example, sales engineers trying to get the necessary information in order to draw up the technical specification for the customer, or by the need for mutual exchange of information among all functions involved in the PD project. Among other things, the quality handbook includes tools for reviewing design projects (e.g. the design review used by the design team, and the contract follow-up used by the contract manager and people involved in the project). For example, a design review should be performed in order to verify that design output meets customer requirements, and that these requirements are well known to the design team. An easy-to-use form is also presented in the quality handbook in order to highlight areas where improvements or modifications are necessary. The contract’s follow-up form provided in the handbook is used to document changes made during the project. This tool is, however, not always utilised as the follow-up of a contract is not made to the extent it should be, for example due to a perceived lack of time. The quality handbook also includes a description of a close-out meeting where all departments are involved in

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order to discuss their contract experiences, and to get feedback from each other. Information such as final time table, capacity used and utilisation of experience from suppliers, production and logistics, are discussed and documented in a standard form called ‘‘nonconformities and suggested improvement report’’.

4.2. Disturbances during production When it comes to production and product installation, disturbances occurring are often due to different reasons such as: *

*

4. Disturbances and reasons for disturbances at the company *

4.1. Disturbances during early phases Disturbances may occur in different phases of a project. In the basic product design stage, problems may appear. For example as a consequence of misunderstanding of the technical solutions that the sales engineers have offered and sold to the customers. Problems that appear in this phase are often the most costly ones, but are in some cases thus expected due to the designers’ experience of the fact that some factors are difficult to foresee. One such example concerns the installation of cables, and the problems that may occur within this process. Experience and competence are again fundamental for solving such problems successfully. Disturbances often show up in the late design phase or during the production and installation phases. The short time available for producing detailed drawings to be approved before product delivery is, for example, a difficulty during the detailed product design. Common disturbances that occur late in the design phase are often due to changes coming from the yard and/or the shipowner, or changes imposed by the Classification Societies’ Rules for approval. To handle these types of disturbances, backtracking and correcting drawings are required, with the consequence of spending more resources than planned. Disturbances in the design phase are also related to implementation and learning of new software for 2D and 3D design. Making decisions about actions to follow in the design phase sometimes creates internal project disturbances and delays. Late design changes may also cause production disturbances. A reason for disturbances may be related to the way a project is considered, i.e. to what degree it is considered to be a ‘‘replay’’ of an older project or product. There are different degrees of ‘‘replay’’ possible depending on how much a product variant differs from the original product design. When requirements for changes appear in a new project that was considered to be equal to a previous project in the first place, this new situation may have both technical and economic consequences. The evaluation of similarities and differences between projects is, therefore, important for the success of an order-driven project.

Material problems caused by lack/delay of material, or by defective material from suppliers. A discrepancy between theory and reality illustrated by tolerance problems, manufacturability deficiencies, etc. Inefficient information flow, e.g. illustrated by difficulties in knowing the reality at the specific location, difficulties in talking about where the errors are, and language communication difficulties.

Examples of disturbances during installation are wrong fittings due to wrong tolerances, or due to a different (unknown) form of the ship. Such problems are either caused by lack of information about the ship, or by lack of control of the design results before it is too late. It is especially difficult to foresee the problems in the case when an existing ship should be converted. In such a situation, the experience and competence of the employees are very important in order to predict and avoid all possible problems. In production, different kinds of disturbances may occur. In the new project for the mentioned Corex product, production implied a development of the laboratory used for the first prototypes. Here, the problems were solved as a result of the knowledge and experience of the people involved in the development of the Corex structure. In the case of order-driven projects when production is outsourced, disturbances during production are the responsibility of the supplier. Other problems that may occur are related to the need for small design changes of the components. These changes are caused by lack of information about the exact ship layout, or what rules apply in a particular country. Changes in general, even if they are of a minor kind, can cause changes in the whole production process, both for production and purchase, as well as for design since the existing product drawings need to be corrected and the new structure approved by the classification societies. 4.3. Classification of disturbances In order to analyse the disturbances occurring within the case study company, a classification could be made according to their appearance in different life-cycle phases. In Fig. 3, a classification of the disturbances is made and related to reasons and the project’s life-cycle phase. One of MacGREGOR’s goals is to record disturbances, and this is made by use of the quality system (e.g. the non-conformities document). Most of the

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Life-cycle phase → Basic Design

Reasons for disturbances

Design

Internal

IT problems, Lack of making decision information about ship design conflicts, lack of time

Changes from yard/ ship-owner

Uncertainty

Changes in ship design

Production and Installation

Design changes Changes at late stage, wrong fittings with the ship

Changes from Classification Societies

Non-conformance Non-conformity in in drawings materials, welding etc.

Changes from suppliers

Changes of e.g. electrical components

Supplier delay

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Non-conformity in materials and components Late deliveries of material

Fig. 3. Classification of reasons for disturbances in different life-cycle phases.

disturbances mentioned in Fig. 3 were, however, collected during the interviews since they were well known but not documented.

5. Handling production disturbances in-house and when outsourced 5.1. Disturbance handling in practice In the exemplified Corex project, MacGREGOR decided to keep the production in-house for the first time. One of the main reasons for this decision was that the in-house competence and knowledge obtained during the development of the new product was considered to be very important for successful production. During this PD process, mainly people working with and responsible for the production developed the machines and process techniques. However, designers and engineering experts from other departments were also involved in addition to external consultants. A smooth production, free from technical problems and component tolerance induced problems from suppliers, was the main goal of the project. However, disturbances occurred anyhow due, for example, to rules laid down by the classification societies. This required changes of a mainly bureaucratic nature in the production process. More effort put into early communication with the classification societies could have been one way to reduce the need for such production changes. In other cases, the development of the production system is not concerned to the same extent since the production is outsourced. When production is outsourced, production disturbances seldom concern MacGREGOR, except for rare cases when a change directly affects the product design or customer delivery time. On

the other hand, high product quality is required which means that the company has chosen to have often longterm relationships with the suppliers, ensuring a good understanding and discussion of possible problems within production as well. Problems occurring in outsourced production could not be completely handed over to the supplier, as it can result in problems during product installation, and as such it becomes a MacGREGOR problem.

5.2. Disturbance handling in theory In general, practical problems such as material and information flow problems may be able to be identified and therefore hopefully also reduced or avoided in the next project. The problem of discrepancy between theory and reality is, however, much harder to solve. A high theoretical education and a positive attitude to new technologies may not be enough. Relevant experience and know-how in the production field as well as applied knowledge in the specific ship-building field, are essential to engineers in general in order to foresee and eliminate possible disturbances during different phases of the PD process. The balance between theoretical knowledge and practical experience in the field, including production, is interesting to discuss when it comes to the task of forming project teams. This may be a specific issue to engineering companies where production is not considered a core activity, and hence is difficult to learn in-house. More conscious learning (i.e. based on formal education and problem solving) rather than unconscious (when learning through experience, through reaction to reward and punishment) would help to avoid repeating others’ mistakes when gaining higher competence and competitiveness, as also highlighted in [11].

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In the shipbuilding industry disturbances are often detected through quality audits in order to identify nonconformities in the quality standard (e.g. ISO). Lloyd’s Register of Shipping found that the highest proportion of deficiencies was in the area of maintenance of the ship and equipment. The reasons for these non-conformities were deficiencies in defining and implementing procedures, and the problems of recording non-conformities. Lloyd’s suggests that using a quality standard is a possible way for making improvements [12]. In both the cases of in-house production and outsourced production, achieving a successful production system presupposes achieving a successful development project. Earlier studies presented in [8] pointed out a number of design factors affecting the success of a production system. Examples of empirically identified success factors are: * * * * *

Creation of an effective information network, Relevance of adopting a long-term strategy, Use of systematic methods in the design process, Integration of production and product design and Co-operation with suppliers.

These factors are relevant preconditions for the prevention of expensive disturbances in the later phases of the PD project as well.

6. Disturbance elimination during the design phase 6.1. General preventive design considerations Preventing and eliminating disturbances is difficult yet necessary. A successful PD process implying the development and production of a product of the required conditions (time, cost, quality, etc.) without disturbances is always the desired goal. However, the difficulty in foreseeing disturbances that may appear both during the design project and during production, requires an awareness of how to deal with these issues. Applied working methods, the use of tools and methods, communication and information procedures, etc. are examples of means for supporting the elimination of disturbances during the design phase. Both the processes of product design and production system design (or choice of production solution) are relevant to focus in order to prevent possible disturbances. In the MacGREGOR case study, the dynamic environment puts high demands on the company and its ability to face new problems in the machines. There is a need for a systematic way of working during the product design, as the context implies a dynamic environment where products are not standardised. MacGREGOR works with a standard system that shortens the development lead time for new projects by the standardisation of components used in the

products. Standardising components implies simplifications in several dimensions. Furthermore, it increases the knowledge about production techniques and operations of these standardised components. However, there are still components designed that could have been made similar to others or been replaced by standard components. Insufficient work in the production design phase is also an important cause of problems and deficiencies when building-up and running-in a production system as well as during full production, as also discussed by Wiendahl et al. [13]. At MacGREGOR, the design phase in general has priority for a variety of reasons, not least its influence on costs. The influence of the design phase on the possibility to prevent disturbances is also relevant to consider, since most design activities control the outcome of both manufacturing process and the final product. One problem, however, is the difficulty when designing of foreseeing disturbances that may occur at different stages in the manufacturing process. 6.2. Design and engineering approaches Wallace and Sackett [14] state that the benefits of integrated design and manufacturing systems in mid to high-volume production are widely accepted. However, in the opinion of the authors, the low production volume, large component size and high complexity product domain is less well served by this technology. This product domain also implies products that are heavily customised for the end-user, and being highly customised to individual user specification makes it unlikely that the opportunity for making a prototype will exist. It is, therefore, vitally important to get a design right the first time in this product domain. Wallace and Sackett furthermore define direct engineering as the process of moving from concept through detail design, to product realisation without prototyping. Repetitive direct engineering is defined as the more usual format of the product realisation process where a substantial unique product customisation is made of a base product design, and may be applied to every customer order [14]. Both engineering definitions suit MacGREGOR’s engineering processes. In the repetitive direct engineering environment reconsideration of a design is less likely to occur, the first product produced will probably go to a customer and there is little likelihood of a prototype being produced. It is possible for the skilled assembler to compensate for a bad design but it makes the task longer, more error prone and increases direct and indirect assembly costs, as also discussed by Wallace and Sackett. Compensating for difficulties and disturbances during production caused by a non-robust design should be handled either produced in-house or outsourced to supplier. The right-first-time philosophy is, therefore,

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important in the direct engineering context. Different DFX methods (DFA, DFM, etc.) could, for example, be used in order to support the right-first-time philosophy. Performing analysis using DFX methods may suggest alternative manufacturing and assembly methods and procedures, eliminating possible production disturbances in a later stage and reducing manufacturing lead times and hence, costs. Due to the short delivery times in shipbuilding (relative to product complexity) which must be fulfilled, the envisaged large-scale orders/projects require parallel production activities. This includes the simultaneity of design, procurement, operations planning, manufacturing and assembly [15]. The DFX methods could be used as tools when working concurrently within development projects. Concurrent engineering (CE) is the consideration of the factors associated with the life cycle of the product during the design phase. The essence of CE is not only the concurrency of the activities but also the cooperative effort from all the involved teams, which leads to higher profitability and better competitiveness [16]. A research study aimed at identifying the critical constraints with respect to global manufacturing and synthesising the best practices of CE in industrial sectors including shipbuilding, identified vital key elements for success. Those elements were effective communication, a systematic involvement of customers, suppliers, and distributors, powerful information infrastructure, and effective use of modern technology [16]. CE could be considered as a way of preventing disturbances, by organising the total PD process efficiently, implying working together and in parallel with product and production development.

For production in small volumes, failures or disturbances could be more easily corrected with experience and competence directly during production. In production of large volumes, the design of the actual production system involves its possibility of producing products of the same quality during the products whole life cycle. A continuous improvement effort is relevant in such a context. The design focus is, therefore, different for production of large volumes compared to production in extremely small volumes, almost handicraft production. As pointed out by the people interviewed at MacGREGOR, risk analyses are seldom made nowadays for the purpose of foreseeing possible disturbances and problems arising during a design project. Such analyses are otherwise one possible way to identify and emphasise relevant problems during the design phase instead of postponing them to other life-cycle phases. One example of a tool that could be used here is ProcessFMEA.

7. A life-cycle perspective on production related disturbances When a production system is not designed properly, problems will most likely appear within the physical system. Examples of such problems or deficiencies for an assembly system where high-volume products are assembled are, according to empirical studies [5]: * * * *

6.3. Production issues Product complexity in the shipbuilding business and decreasing manufacturing penetration in terms of lean production leads to inter-organisational production, and this inter-organisational production necessitates additional efforts for production planning and control, according to Kuhlmann et al. [15]. The result is that the products are produced in parallel to acquisition of production and process information. In mass production, disturbances may occur both during the start-up and ramp-up phase of the production system, as well as during full production. In smallvolume production, the situation is different as there is no specific ramp-up phase. Here, we find the disturbances directly during ‘‘full production’’ and after. The manufacturing of products in very small volumes, down to single products, resembles handicraft rather than the mass customisation that is reality in some companies today. In the case of MacGREGOR the design phase conditions are relevant in a different way compared to the design of a production system for mass production.

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*

* *

Implementation problems. Running-in problems. Production disturbances. Maintenance problems. The fact that the work organisation does not fit the technical system. A need for capacity change. A need for immediate technical and/or work organisational changes.

These problems may also be relevant to some extent for low-volume production, although here, the start-up phase is not separated from the production phase in the same way as in mass-production. Implementation problems and running-in problems are, therefore, different. Maintenance is also an area that involves different preconditions and goals depending on production system for products in low or high volumes. The life-cycle approach to disturbance handling has been mentioned as one way of approaching the problem. It is, for example, possible to consider production disturbances during the whole life cycle of the production system, see Fig. 4. On a more basic level compared to the detailed level of Fig. 4, the general life cycle of a production system for mass production involves the phases of development,

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Project & system System concept Identification of need for change Requirement Preliminary Design Quotation & choice of subcontractors Detailed Design

Analyses Operation Production ramp-up System Component integration, & system personnel testing training

Fig. 4. Production disturbances should be considered during the life cycle of the production system [1].

full production (steady state) and decline, where production system development involves both design and realisation, i.e. building and start-up, of the production system [5]. Related to these five life-cycle phases, disturbances could also be categorised according to their appearance in the production system life cycle: Design: Building:

Start-up:

Production: Decline:

Project disturbances. Project disturbances. Technology problems when realising the physical production system. Project disturbances (take-over procedure from project to line). System start-up and running-in problems (technical and organisational). Production disturbances (line function). Possibly project disturbances (if takeover from line to project). Problems when recycling technical equipment, documentation, etc.

The gradual acceleration of production rates to full volume is depicted in the so-called start-up curve, which is the function of the time required for attaining targeted levels of output (capacity and quality). Measures of change in capacity and quality contribute to differentiate the start-up phase from the steady-state phase. The steady-state phase begins as capacity and quality targets are attained [17]. Separating the start-up phase from the steady state (production), will also facilitate the measurement of running-in problems and production disturbances which may sometimes be difficult. Classification of production disturbances is a question of purpose and viewpoints [2], who regards production disturbances as a discrete or declining, planned or unplanned disrupting event or a change, during the scheduled production time, contrary to the planned or desired stable state which can affect start-up-time,

operational performance, product quality, safety, working conditions, environment, etc. [2]. A production system for a single-product or a lowvolume product is different from the production system of a product that should be produced in a larger volume. Consequently, the process of developing these two types of production system varies greatly. Deficiencies and errors in preceding phases such as engineering and design manifest themselves in the start-up of an assembly system according to Blanchard et al. [3]. Concerning a high-volume product, Almgren [17] states that when analysing efficiency during start-up, the focus should be put on identifying the causes of losses and analysing how these losses affect output and efficiency. A research study in [17] presents four independent variables that affect efficiency during start-up; Work method: the individual-task relation and how the distribution of tasks is co-ordinated. Work pace: the intensity with which the activities that make up the work cycle are performed. Process disturbances: disturbances that decrease the net operating time with underlying variables such as delivery performance of suppliers, competence of operators, status of machinery and equipment. Conformance: the degree to which a product’s or a component’s design and operating characteristics meet the established standards (a deviation - off-line correction). These variables are not influent in the same way on low-volume production (as experience in the Corex production, for example) as on large-volume production. In the Corex project, the work method and pace were already decided in practice by those involved in the production since they were also involved during the development. Concerning the conformance variable, the product functionality could be achieved only with the highest level of quality and therefore conformity to the demands. The variable that could be considered more influent concerned the process disturbance variable, as disturbances came from different parts of the production process. In the above categorisation of disturbances during the production system life cycle, a distinction is made between project disturbances and operating disturbances. Project disturbances occur during both the design process, when building the production system, and during the start-up phase (since the take-over procedure from the project organisation to the line organisation often implies difficulties, see [5]. Project disturbances may possibly also occur during the decline phase. These disturbances are often personnel-related or of an organisational or administrational nature, but could also have to do with for example information flow. The project disturbances are different to those

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operating disturbances that occur when the production system is to be realised based on the design result, although the operating disturbances could be caused by administrational problems for example. The life-cycle oriented approach to disturbances is more easily related to large-volume production than to small-volume production, for the reasons already mentioned, such as non-separation of the start-up and running-in phases, and the actual production phase. In small-volume production where the working cycle of each product is consequently quite long, the different phases, including the actual design, may be integrated to a certain degree. The analysis of the problems and disturbances that appear during the working cycle do not require the same attention as in mass-production, where systematic errors must be prevented. However, recognising and documenting problems and disturbances that may occur also when producing in small volumes, and continuing by analysing the reasons for these disturbances, is a way of drawing general conclusions about typical problems. Such information and knowledge is valuable in the prevention work, when designing new products.

8. Factors affecting disturbance management According to the empirical findings, one of the most important factors for managing disturbances within such a business is knowledge and experience of the personnel, since many problems are difficult to prevent beforehand. In addition, forward thinking and the use of management tools such as risk analysis, are helpful in order to work with the preventive aim of reducing disturbances. Kuhlmann et al. [15] confirm that human capabilities and the accumulated experience of professionals are key resources in shipbuilding in general. To handle such a complex production process combining different manufacturing types at one site (from line manufacturing to construction site assembly), improvisation and flexibility are needed by the employees as well as supporting systems [15]. One important reason for disturbances occurring in the production of single customised products such as those exemplified, is the fact that it is not possible to make a prototype of the product. Here, there is only one chance to successfully manufacture a product of high quality and deliver it on time to the customer. Consequently, much of the knowledge of the product and its manufacture must be developed during the actual production phase, as the time for re-design and rationalisation that continuously improve both manufacturing process and product design is reduced. A strategy emphasising both a holistic view and a preventive attitude for disturbance handling is, therefore, an advantage.

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Problems that occur during the technical design phase may be considered mainly engineering problems. Identifying, documenting and analysing these problems is one way of managing them. A new method for document management is being implemented at the engineering department at MacGREGOR in order to facilitate the internal information flow between designers and the information flow between designers and purchasers. In the same way as mass-production companies, small-volume production companies are under the pressure of fierce competition. Competence, experience and product flexibility are key factors for these companies, and it also means that these companies must manage disturbances by utilising the options that their key factors imply. A potential for better disturbance management implying for example prevention, concerns the utilisation of easy-to-use tools for the improvement of information flow (such as the quality handbook used by the case study company).

9. Discussions and conclusions The special features of customer order processing in shipbuilding lie in the individuality of the product and the required manufacturing processes together with their corresponding dependencies [15]. Customer orders are handled as projects and the simultaneous production processes, their activities and the resource requirements are harmonised with multi-projects in mind. The design process of both product and production process is of utmost importance in order to design for success. The total cost of the product is largely determined already during the design phase, as well as the choice of possible options. Making changes in later phases is costly both in terms of time and financial resources. Consequently, the best possibility to affect the outcome is during the design phase. In a dynamic environment, there is always a risk that competence and knowledge do not develop as quickly as problems do. During design and production of products in small volumes, different problems and disturbances may occur. Preventive and continuous maintenance work is, however, managed differently under such circumstances compared to the maintenance of the production processes when producing in large volumes. In the research project mentioned called the ‘‘TIME’’ project, manufacturing efficiency is concerned starting with the management of production disturbances from an operational, tactical and strategic point of view. It is evident that the management of disturbances is very different in volume production, compared to the disturbance and maintenance management at for example MacGREGOR, who produce RoRo products in very small volumes. One interesting aspect, though, is

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the possibility of comparing the different design and production processes in order to learn from both businesses how to handle disturbances in an efficient way. The economic advantages of reducing disturbances are important motives for emphasising this work, and creating systems for managing disturbances both in the a short term and the long term.

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