Product innovation for sustainability: on product properties for efficient disassembly

Abstract

Due to increasing societal awareness, nowadays companies need to consider environmental issues in their business activities. A requirement that has entered the agenda is the design of products to support efficient end‐of‐life management. However, though previous research has addressed various disassembly aspects there is a need for more understanding on which product properties are essential for efficient disassembly processes. Better understanding is also required regarding when, during the product development process, these properties are established. On the basis of empirical studies of disassembly of electrical and electronic equipment and vehicles, this paper suggests a number of product properties that are essential for efficiency of the disassembly process. Furthermore, the paper analyses when these properties are set in the product development process. Four product properties, denoted disassembly properties, have been identified: ease of identification; accessibility; ease of separation; and ease of handling. The analysis shows that these properties are affected during all product development phases. Especially in the early phases it is crucial to consider the disassembly properties in order to avoid unnecessary and costly design changes that may occur in the later development phases if the design solutions are pulled in the wrong direction.

Keywords:

• product development
• product properties
• disassembly

1. Introduction

Due to increasing awareness and concern in society, nowadays companies need to include environmental issues in their business activities. There is a general agreement amongst industrial practitioners and researchers that environmental requirements must be introduced in the product development process and the term Design for Environment (DfE) is widely used for denoting these efforts (Boks and Stevels 2007). Adopting an integrated approach to DfE is preferable, because then the environmental requirements are not seen as purely add‐on constraints but as triggers for improvements of the products' overall attractiveness and quality, leading to new market opportunities and financial gains (Kaebernick et al. 2003). Originating from the various phases of a product's life cycle, different environmental requirements must be addressed in the product development process. Examples of requirements are: avoidance of hazardous substances, low emission levels, energy efficiency, etc. One requirement that has been put high on the agenda is the design of products to support efficient end‐of‐life management. Two targeted product groups are electrical and electronic equipment (EEE) and vehicles because of the high volumes of such products put on the market (Zhang 1999, Zheng 2005, US Environmental Protection Agency 2006). The importance of these product types is manifested by the End of Life Vehicle (ELV) and the Waste from Electrical and Electronic Equipment (WEEE) directives launched within the European Union (Official Journal of the European Communities 2000, 2003). The directives are examples of Extended Producer Responsibility (EPR) initiatives aimed at reducing the amount of discarded products. Research is, however, somewhat inconclusive regarding such initiatives' impact on industry. Some studies have indicated that they have not yet had a great impact on the DfE efforts in industry (Gottberg et al. 2006, Yu et al. 2006), whereas other studies point out that manufacturers acknowledge their influence on the efforts to reduce product environmental impacts (Tojo 2004).

Nevertheless, studies on the feasibility of different end‐of‐life strategies have entered the research agenda and disassembly is considered part of such strategies (Cui and Forsberg 2003). A question mark has though been raised whether disassembly is relevant for small products of low value, whereas it may be more appropriate for medium‐ to large‐sized products (Willems et al. 2006a). A specific concept that has been presented in the literature to facilitate disassembly of end‐of‐life products is active disassembly (Suga and Hosoda 2000, Chiodo et al. 2001, Chiodo and Boks 2002, Hosoda et al. 2004, Hosoda and Suga 2005). The basic idea underpinning the concept is the use of ‘smart materials’, for example shape memory alloys (SMAs) and shape memory polymers (SMPs), which undergo a specific change when exposed to an external trigger such as a temperature that exceeds the transformation temperature (Chiodo et al. 2001). The concept was originally applied to EEE, but recent research has also demonstrated its potential for vehicles (Jones et al. 2003). Acknowledging the need for management of end‐of‐life products, other research has focused more directly on how to consider end‐of‐life aspects in the product development process rather than presenting technological solutions supporting ease of disassembly (e.g. Lee and Ishii 1998, Furuhjelm 2000, Sundin 2004). The underlying argument for focusing on the product development process is that a product's environmental impacts are defined by its basic properties, which are set during the product development process (Rounds and Cooper 2002). Disassembly efficiency is hence associated with the properties of the product and a few such properties have been outlined in the literature. Most of these properties originate from conceptual discussions rather than empirical studies (e.g. Luttropp 1997) and they are often poorly related to the complex context of other product properties as addressed in the literature on conventional product development. Furthermore, literature provides little insight regarding when during the product development process the disassembly properties are established. Specifically addressing disassembly of EEE and vehicles this paper therefore presents empirically derived product properties that are critical for efficiency of disassembly processes and discusses these properties in the light of existing theory on product properties. Furthermore, the paper analyses when these properties are set during product development.

The paper is structured as follows. The next section addresses theory on product properties, followed by a section presenting the empirical material and the research method. Thereafter a number of product properties supporting efficient disassembly are identified. Next the establishment of these properties in the product development process is analysed. Finally, the paper ends with some concluding remarks.

2. Theory on product properties

In essence, a product is developed to fulfil specific functions. Roozenburg and Eekels (1995) define the function of a product as the intended and deliberately caused ability to bring about a transformation of a part of the environment of the product. Other requirements set for a product include low price, nice appearance, reliability, etc. All requirements should be fulfilled by giving the product its various properties. Hubka and Eder (1988) define a property as any characteristic of an object that belongs to and characterises it. They argue that the requirements set for a product are ultimately determined by a few elementary design properties: product structure, form, material, dimension, surface quality, tolerances, and manufacturing method. These elementary design properties constitute the basics of a layered model of different classes of product properties as illustrated in Figure 1. The different requirements set on a product can be translated into external properties, which in turn can be translated into internal properties and finally into the elementary design properties. External properties are the relationship of a product to its surroundings. The internal properties consist of the relationship between the elements in a product, and the properties of those elements. With the elementary design properties as the only means, the designers should fulfil all the requirements set on a product by giving it the necessary internal and external properties. Thus, the requirements set on a product must basically be achieved by a good combination of the elementary design properties.

Figure 1 Relationships between various types of product properties(based on Hubka and Eder 1988).

Researchers have addressed product properties from different perspectives. Product properties associated with design of components and complex products (Ringstad 1996, Liedholm 1999), reverse engineering (Zhongwei 2004, Corbo et al. 2004), and design for manufacturing (Wagne 1995, Herbertsson 1999, Eskilander 2001) are examples that have been considered by researchers. Specifically within the design for manufacturing and assembly (DFMA) area, certain properties are assumed to be vital for achieving efficient manufacturing and assembly processes. Manufacturing systems efficiency depends on the fit between the product and the manufacturing system (Adler 1995) and a number of critical product properties that affect a manufacturing system's performance have been suggested. Examples are bending/torsion stiffness, ease of maintenance, ease of fault diagnosis, component durability, component finish, etc. (Fabricius 1994). More recent studies also support the notion that the product properties affect a manufacturing system's performance. In a study of factors that are critical for the interface between product development and manufacturing, it was found that one such factor is analysis of the product's manufacturability (Lakemond et al. 2007). This implies that the product properties have an impact on manufacturing system efficiency. In other words, this finding supports that the product's manufacturing properties (internal properties) affect the manufacturability (external property), which in turn influence the fulfilment of the product requirements in terms of cost, quality, etc. Another study, which addresses manufacturing ramp‐up performance, has identified properties that directly or indirectly relate to the product design (Berg 2007). An example of such a property is product complexity.

Some research has also addressed product properties decisive for a product's ease of disassembly. Luttropp (1997), for example, suggests one such property based on conceptual discussions inspired by the Theory of Functional Surfaces (Tjalve 1989) and the Theory of Technical System (Hubka and Eder 1988). The disassembly property primarily suggested by Luttropp (1997) is ease of separation. Related to this property, he further proposes the concepts of sorting borders, separation surfaces, and resting load cases. A sorting border is an imaginary surface which encloses something that can be identified and cleaned or purified, a subassembly, a labelled piece of material, etc. At a separation surface the actual separation takes place. A separating surface should be located to and follow the sorting borders in order to facilitate sorting and recovery. A resting load case can appear when a certain stress limit is exceeded or it can be activated by a stress applied in a new direction which does not occur during normal usage. The ease of separation property is also indicated by the experimental research on active disassembly (e.g. Chiodo et al. 2001).

3. Empirical material and research method

The empirical material originates from two case studies on disassembly of end‐of‐life products. The case study approach was adopted, because it is appropriate for exploratory studies of complex phenomena and makes it possible to collect comprehensive, systematic, and in‐depth information about each case of interest (Eisenhardt 1989, Patton 1990, Merriam 1994). Electrical and electronic equipment and automotives were selected as the product types to study, because the implementation of the WEEE and ELV directives pose challenges for manufacturing companies supplying the EU market.

The first case study (Case Alpha) concerned EEE and was carried out at a Swedish company specialising in EEE disassembly. The second case study (Case Beta) was conducted at a car disassembly plant in Sweden. In both case studies video recording analysis was used to study the disassembly processes for each product type. The products disassembled in Case Alpha were computer screens and TV‐sets, whereas in Case Beta two different Volvo cars were disassembled. Data collection also included observations at site and interviews with disassembly operators. Analysis basically followed the three‐phase procedure suggested by Miles and Huberman (1994); data reduction, data display, and drawing conclusions and verification. In the first phase, the video recorded disassembly processes were studied separately. The films were studied several times and for each of the product groups the disassembly activities for individual components were observed, listed and classified into basic operations. Furthermore, the fundamental order of these basic operations were observed and noted. In the second phase, the basic operations and their order of performance were modelled into tables for each type of products respectively. In the third phase, the two sets of tables were compared and combined into a composite model representing the disassembly process. This model was then used to identify product properties that are assumed to be preferable in order to facilitate the basic disassembly operations and hence the disassembly process.

It is acknowledged that the disassembly process is modelled based on a limited number of case studies. Therefore, the findings presented in this paper should be considered with some care. Further studies addressing disassembly of different types of products are required to validate the findings.

4. Essential product properties for ease of disassembly

As was described earlier, contrary to most literature that is based on conceptual discussions this paper adopts an empirical approach to identifying the disassembly properties. Empirical studies of EEE and car disassembly were used to model the disassembly process. The model consists of a number of basic disassembly operations arranged in two sequences; one connector removal sequence and one part removal sequence. For identification of product properties affecting disassembly efficiency this model of the disassembly process has been used. Four product properties decisive for a product's ease of disassembly can be identified. These product properties affect the ease or difficulty of performing individual disassembly operations. Figure 2 illustrates the model of the disassembly process and how the product properties, denoted disassembly properties, are derived from the operations in the process.

Figure 2 Empirically identified disassembly properties.

The disassembly properties are:

1. Ease of identification: The ease of identification property determines how easily a part (i.e. subassembly or component) that is to be disassembled can be identified, i.e. how easily the part can be recognised and how easy its location in the product can be found. A precondition for the possibility of identifying a part is that it has a sorting feature, for example, magnetic properties or colour. Hence, the ease of identification property is related to the location of a part in the product structure as well as to the form, dimension and material of the part. It must be possible to identify not only the part to be disassembled, but also the connectors used.

2. Accessibility: The accessibility property determines how easy a part or a connector to be disassembled can be accessed. The accessibility is related to the product structure and depends on the physical location, part orientation and hierarchical depth of the part in the product.

3. Ease of separation: The ease of separation property determines how easily a part or a connector can be separated from other parts of the product. The ease of separation property is related to the connecting methods used and the number of separable, collision‐free directions.

4. Ease of handling: The ease of handling property determines how easily a part can be handled in the disassembly process. Handling refers to how easy it is to grasp and transfer various parts and connectors. It is also related to the product itself concerning how easy it can be handled as regards orientation and fixation. The ease of handling property is related to the form, dimensions and material of the components and connectors.

Relating the disassembly properties to the different classes of properties presented in Figure 1, they may be considered as internal product properties (cf. Hubka and Eder 1988). These properties affect a product's ease of disassembly, which can be classified as an external product property. Hence, the disassembly properties constitute the intermediate properties between the elementary design properties and the ease of disassembly property. The ease of disassembly property has to be designed into a product (together with the other external properties necessary for fulfilling all the product requirements) with the elementary design properties as the means at hand for a product design engineer. The ease of disassembly property constitutes the interrelationship between a product and the disassembly process, i.e. this property ultimately defines the efficiency of the disassembly process. In order to achieve efficient disassembly, the ease of disassembly property is essential. This property must be translated into characteristics of the elementary design properties which are preferable from an ease of disassembly point of view. Figure 3 illustrates how the different properties associated with disassembly (marked in italics ) relate to the different classes of properties.

Figure 3 The properties essential for efficient disassembly related to the classes of product properties.(Based on Hubka and Eder 1988).

Figure 3 clearly illustrates that the disassembly properties are only part of all properties a product needs to possess in order to fulfil the diverse range of requirements it has to meet. Therefore, trade‐off situations between the disassembly properties and other properties will occur in a product development project. However, if efficient disassembly is striven for as an end‐of‐life option, the disassembly properties must be addressed during product development. The elementary design properties are the means that designers have at hand to design the disassembly properties into a product. Thus, basically efficient disassembly is achieved by a suitable combination of the elementary design properties.

5. The establishment of the disassembly properties in the product development process

A product's ease of disassembly is determined by the disassembly properties. The disassembly properties are, in turn, determined in the product development process. Therefore, it is relevant to analyse where in the product development process the disassembly properties are established.

Several different models of the product development process can be found in both management and engineering literature (Engwall et al. 2005). The models range from sequential phase models to interactive and improvisional models (Roozenburg and Eekels 1995, Pina e Cunha and Gomes 2003, Bishop and Magleby 2004, Trott 2005, Ulrich and Eppinger 2008). Sequential phase models generally present product development as a series of phases with well‐defined milestones and decision gates at which it is decided whether or not to proceed with a development project. Planning and control are supposed to be essential means to reduce the inherent product development uncertainties. Interactive and improvisional models, on the other hand, are based on a contingency perspective on product development. These models presume that actions should be improvised as real‐time responses to a problem or opportunity and executed with the available resources. Though sequential models can be criticised as regarding their potential to represent real product development processes, such models dominate in the literature as well as in industry (Cooper et al. 2004). One of the most widely adopted models in the engineering literature is presented by Pahl and Beitz (1996) and this model will be used to represent the product development process in this paper. The model encompasses four basic product development phases:

	Planning and clarifying the task – specification of information.
	Conceptual design – specification of principle.
	Embodiment design – specification of layout (construction).
	Detail design – specification of production.

The degree to which it is important to address ease of disassembly is related to the recycling infrastructure on a specific market, especially how the infrastructure is assumed to be constructed at the time the products reach their end‐of‐life. Thus, decisions should be taken whether a product is aimed at being landfilled or recycled, and if recycling is aimed at, whether disassembly is likely to become part of the end‐of‐life treatment of the product. If disassembly is likely to be a part of the end‐of‐life scenario, it becomes essential to design the products for ease of disassembly in order to support low cost end‐of‐life treatment. Thus, in the phase of planning and clarifying the task the importance of designing the disassembly properties into a product is determined, even though the properties themselves are not established at this phase. The ultimate result of the activities in the planning and clarifying of the task phase is a design specification. This specification will influence the following development phases significantly because, in principle, the specification can be seen as a simple model of the product, i.e. a description of the product in words and figures. If it has been found in the ‘planning and clarifying the task’ activities that ease of disassembly should be considered, then the design specification must include explicit statements about the goals concerning disassembly in terms of cost, disassembly time, etc.

The establishment of the product structure in the conceptual design phase affects the disassembly properties. The location and orientation of components in the product structure is vital for the accessibility property. Accessibility is supported by a shallow product structure, i.e. a product structure consisting of few hierarchical levels. This is especially important if selective disassembly is aimed at, i.e. only certain parts of the product are disassembled; not the entire product. Components that may be reused as well as components that may contain valuable material or hazardous substances should be located so that they can easily be accessed. Thus, to support easy access to these components they should not be located deep down in the product structure. In the case of complete disassembly it is of less concern where such components are located in the product structure. The ease of identification property is also affected by the product structure, because the ease of identifying a component to be removed is related to where in the product structure it is located. The component should be visible and not hidden behind other components. As the ease of separation property is related to the number of separable, collision‐free directions for the separation, this property must also be considered when the product structure is defined. Due to the limited information on the product at hand in the conceptual phase it is only possible to evaluate a design concept's ease of disassembly roughly. However, using sketches or rough drawings as representations of the different concept variants, a first evaluation of their disassembly properties can be made in the conceptual phase. The possibility of evaluating the design concepts' disassembly properties depends on how detailed the representation of the concept variants is concerning: total number of components, the location of the components in the product structure, the components' form and dimensions, etc.

In the embodiment design phase the product structure is completely determined. This is very important for the product's ease of disassembly because, as was discussed previously, the product structure affects the accessibility property as well as the ease of identification and the ease of separation properties. Furthermore, in the embodiment design phase the individual components' form and dimensions as well as their material are first determined. The form and dimensions of individual components are vital for the ease of identification property. As was mentioned earlier, it must be possible to identify a component to be removed from the product and this is related to the form and dimensions of the component. If the components to be removed from the product are to be automatically identified with a vision system the ease of identification property is especially important. The components need to have significant forms in order to be easily identified with such a system. The components' form and dimensions are also essential for the ease of handling property. The form should be simple so that no special disassembly tools are needed, but standard tools can be used. The dimensions of the components are important because very small components may be hard to handle. Also very big components may be difficult to handle. Components of low weight are preferable from an ease of handling point of view, because they are usually easier to handle than heavy components. Furthermore, in the embodiment design phase the connecting methods are usually determined. The choice of connecting methods depends, among other things, on the force and torque the product will be subjected to during use and how efficient the connectors are in the assembly process. From a disassembly point of view, the connectors affect the ease of separation property. Therefore the ease of separation of the connectors must be taken into account when they are chosen. The material choice affects the ease of identification when the disassembled parts are to be sorted. If parts disassembly is practiced simply to support material recycling, then it is important to consider the sorting properties, which are related to the material choice. This aspect of the ease of identification is probably more important when a product is mechanically processed, i.e. shredded, than if it is disassembled. Nevertheless, the material choice is very important also concerning disassembly because a product consisting of few material variations means that the need for disassembly is reduced. Ideally a product should consist of a single material, a mono‐material product. In this case if material recycling is the aim, the need for disassembly would be eliminated because it would not be necessary to separate mono‐material parts. However, if reuse is the aim it is necessary to use disassembly to separate the reusable subassemblies and components from the product.

Also in the detail design phase the disassembly properties are affected, but to a lesser degree. Still, some aspects related to the ease of disassembly can be identified. For example, the choice of tolerances may affect the ease of disassembly in the sense that tight tolerances can result in the parts to be separated being hard to separate from each other, i.e. the ease of separation property is affected. If components are designed with some kind of grasping surfaces this may simplify the disassembly process in that the ease of handling is facilitated. The definitive material choice made in the detail design phase affects the ease of identification for sorting. However, the most important aspect of the detail design phase affecting a product's ease of disassembly is how complete the documentation of the product is. Documentation about which components include potentially valuable material or hazardous substances, for example, is of utmost importance for the ease of disassembly, and thus for the efficiency of the disassembly process.

6. Concluding remarks

Efficient management of end‐of‐life products is a continuing concern within society and many countries have launched various initiatives aimed at reducing the environmental impacts associated with such products (Yu et al. 2006). Treatment of end‐of‐life products may include processes such as remanufacturing, reuse, material recycling, and incineration. Remanufacturing and reuse require product disassembly to some degree. Moreover, disassembly may be needed in order to reach the weight‐based recycling percentages stipulated by EU directives (Boyce et al. 2002, Boks and Stevels 2007). If disassembly will be part of end‐of‐life management, designing the products for ease of disassembly becomes of importance in order to support an efficient disassembly process.

In this paper four generic product properties, denoted the disassembly properties, which determine a product's ease of disassembly have been empirically identified: ease of identification; accessibility; ease of separation; ease of handling. These properties are relevant regardless of how a product is disassembled in practise; be it manually or by active disassembly technology. For example, active disassembly technologies have to a large extent focused on ease of separation by using SMA and SMP fasteners (Chiodo et al. 2001, Willems et al. 2006b). Even though such technologies facilitate separation, the sub‐assemblies and/or components need to be identified and handled for further processing. Selective disassembly, i.e. disassembly of certain components instead of disassembly of the entire product, also requires that sub‐assemblies and/or components can be easily accessed.

The analysis of the disassembly properties reveals that they are affected during the entire product development process. In the phase of planning and clarifying the task the degree to which disassembly issues should be addressed in the design process is determined, and thus, the disassembly properties are affected indirectly. In the late conceptual design phase and the early embodiment design phase the overall product structure is established. This influences the disassembly properties to a great degree. Later in the embodiment design phase the component designs are established, which also determines the disassembly properties. In the detail design phase the amount of documentation of the product is critical for the efficiency of the disassembly process. Even though a product's ease of disassembly is affected during all product development phases it is paramount to consider the disassembly properties in the early process phases in order to avoid unnecessary and costly design changes that may occur in the later development phases if the design solutions are pulled in the wrong direction.

In the literature several Design for Disassembly (DfD) guidelines to assist the product design engineers can be found. It has, however, been claimed that the number of DfD guidelines should preferably be reduced in order not to restrict the product design engineers' creativity (Willems et al. 2005). The disassembly properties presented in this paper constitute the bottom line for efficiency of the disassembly process. Having the disassembly properties in mind may therefore encourage product design engineers to search for solutions that are favourable from an ease of disassembly point of view. Instead of being familiar with the extensive amount of design guidelines that exist, the product design engineers need only to be aware of the disassembly properties to be able to design a product for ease of disassembly.

As the disassembly properties are only part of the complex set of properties that a product need to possess in order to become attractive, one interesting direction for future studies would address the interrelationships and conflicts that may exist between the disassembly properties and other properties. Such studies are essential in order to identify how trade‐offs between different properties should be managed in product development projects.