The design for dismantling (also known as design for recycling, or design for disassembly) includes the practices to optimize the way how a product will be treated at end of life, and to optimize the separation of components and materials for their recovery (repair, recycling, energy recovery). The design for dismantling applies equally to a product to be disassembled as for products intended to undergo a grinding step. Considerations are particularly related to choice and combination of different materials that compose a product but also to the assembly and mechanical connections between components and subassemblies of the product.
Objectives of design for dismantling
The main objective of design for dismantling is to integrate, issues related to the end of life of a product already in the design stage. It is actually more effective to adapt a product based on a chain of dismantling steps (recycling) which might be applied to treat it at end of life phase than the other way around. It is not possible for economic or technical reasons to separate and recycle all of the components of a product (M.A. Reuter & al), it is therefore appropriate that the choice of materials and assembly are best suited for dismantling.
The objective of dismantling is also to facilitate the repair. This allows to extend the lifespan “in use” of a product (several lives through several different users), and avoids the direct production of waste.
The design for dismantling therefore aims to facilitate:
– The upgrade / restore;
“Reuse, reemploy, upgrade / restore, recycling” what’s the difference?
- “Upgrade / restore”, the product is not the end of life:
- “Reuse, reemploy”, the product has reached the end of his first life (e.g. the owner wants to discard it):
- “Recycling”, the product does not work and cannot be repaired. In this case, the product will be recycled.
– It can be upgraded, for example: we change one or more components of a computer (RAM, processor, graphics card, etc..) to continue using it.
– It can be refurbished, it is the case of a return of a product during its warranty period. Refurbished, it can be used again.
– It is in working order, it may be reemploy. This is the case of computer parks of some companies that are renewed at regular intervals.
– It no longer works, but it can be repaired. After repair, the product can be reused. Example: a mobile phone which is going to change the battery, a washing machine with the belt should be replaced, etc…
The technical choices made during the design phase of a product are key to the “performance” of a product during its dismantling. It is estimated that only 10-20% of the costs and benefits of recycling are due to the optimization of the recycling process, while 80 to 90% of these costs are determined by design (Desai, A., Mitak A.).
More generally, the challenges of designing for dismantling are:
– Preserve the raw material resources,
– Reduce the amount of non-recyclable waste send to landfill,
– Facilitate the achievement of recycling regulations requierements.
The principles of the design for dismantling
The design for dismantling revolves based on three key principles:
Use and materials selection
– Consider the amount of recyclable material in a product and the redemption price of recycled material:
Recycling of a product will only be relevant if it is possible to separate it (manually or mechanically) in sufficiently pure material flow (M.A. Reuter and A. van Schaik (2012)).
The choice of materials is conditioned in particular by the type of treatment that will be applied at the product at end of life. Depending on the redemption price of recycled materials, the choice for manual or mechanical removal will be more appropriate. This choice will depend on the amount of the different materials that can be extracted from a product, but also the possible rate of extraction of these materials.
The table below gives an order of magnitude for some materials, of the quantity (in grams per minute) of material to be extracted from a waste stream to make the activity economically viable.
Table 1: Extraction of economic quantities of some materials (in g / min)
Example: In order to make ABS recycling profitable, it must be possible to sort 800g of ABS in a minute from a waste stream. In contrast, to make extraction and recycling of gold content in waste profitable, just 50mg (0.05g) should be extracted in the same period of time.
– Parts marking (plastic):
Concerning plastic parts, one of the key design measures for dismantling is the marking of parts. This marking is defined by ISO 11469 and ISO 1043-1 to ISO 1043-4.
- Permit the identification and allow quickly (hand) sorting of a part depending on the type of plastic used.
- Contain a significant number of information such as flame retardant, fillers or any other type of additives.
- Adapt to the combined parts plastics.
To be practically effective, marking must remain visible throughout the life of the part that wears it, this is why it is recommended that the marking is carried out during molding of the part, or by etching. Labels are especially to be avoided because they can cause contamination during recycling. As well, painting may disappear during use.
The ISO standards do not define a specific location for the marking of plastic parts. However, to be relevant/usable, it agrees that it can be visible at anytime of the product life cycle and especially during the phases of manufacturing, repair or end of life of product. It is therefore possible to produce several markings in various locations. Obviously this should not compromise the aesthetic considerations of the product.
– Choose materials with physical properties that can be separated:
Regarding the choice of plastic, to allow separation by densimetric sorting of different polymers, the polymers should have a differencein density of at least 0.15 g/cm3 (see Table 2).
Table 2: density of different polymers
Moreover, laminated materials are to be avoided because of the difficulty of separating the materials used. Finally, in cases where the materials cannot be separated, they have to be compatible for recycling (see sheet design plastic parts).
– Use surface treatments wisely:
For metals, the design rules for dismantling are to avoid the use of surface coatings, especially when they reduce the recyclability of materials (reduced performance of the recycled material, cf. Table 3). Moreover, the alloys are bringing addition elements into the recycled material which may be undesirable: it is therefore necessary to limit their use (eg selective surface treatments).
|Considered metal||Contaminants during recycling|
|Steel||Copper, tin, zinc, lead, aluminum
|Aluminium||Cast iron, steel, chrome, zinc, lead, copper, magnesium|
|Zinc||Cast iron, steel, lead, tin, cadmium
Table 3: Examples of contaminants for metals recycling
Parts design and structure of products
The second axis (first is material usage and selection) for the design for dismantling is the structure of the product. The rules for the structure of a product adapted to disassembly are:
– Create a hierarchical structure.
– Create a modular design.
– Gather wear parts for their simultaneous replacement.
– Reduce the number and type of operation required for the dismantling of the product (see § 3.3 selection and use of fasteners).
– Standardize / Reduce the number of components.
– Reduce the number of materials in an assembly.
– Divide the product into functional modules, and subassemblies (replaceable, repairable).
– Do not paint plastic parts (identification problems or contamination during recycling).
– Avoid as much as possible the use of parts with laminated materials.
Selection and use of fasteners
The third area of design for dismantling is the choice and use of fasteners and connection types. The choice of fasteners relates both to the ability of a product to be repaired (time and associated cost) in its ability to be dismantled or crushed at end of life (separation and release of different materials).
|Factors affecting the dismantling||Improvement opportunities|
|The type and number of fasteners||✔ Select fasteners easy to disassemble|
|✔ Provide access to linking elements|
|✔ Reduce the number of fasteners|
|✔ Use standard fasteners|
|✔ Prefer snap fit fasteners|
|✔ Reduce the number and type of fasteners in an assembly|
|✔ If metal fasteners are used, prefer ferromagnetic metals to allow a magnetically sorting during dismantling (but beware of corrosion that could make disassembly difficult)|
|The visibility of fasteners||✔ Facilitate access to fasteners (e.g. through holes)|
|✔ Mark not visible links|
|✔ Avoir using hidden links|
|The conditions of disassembly||✔ Permit an automated disassembly|
|✔ Favour the use standard tools|
|✔ The use of materials with shape memory allows an active disassembly (e.g. depending on temperature)|
|✔ The presence of fluid or gas can disrupt the operations of disassembly|
Whatever the fasteners used, the disassembled parts must have the following characteristics:
- Good accessibility,
- Low volume,
- Low weight,
- Not dangerous.
Fasteners must take into account the end-use of the parts in order to choose the most appropriate ones:
- Reemployed / reused,
The following table compares different types of fasteners in terms of their behavior against recyclability, disassembly, accuracy of the link or loading capacity:
Table 4: Ability of several types of connections applying to different criteria (recyclability, disassembly, junction, charging) – Source VDI 2243
The next table shows liberation behavior after a shredding operation some connection types:
Table 5: Characteristics of connection types related to their specific degree and non-randomness of liberation behaviour after a shredding operation (continuing from Van Schaik and Reuter, 2007) with examples for different connection complexities, properties of connected materials, homo/heterogeneity of connection, etc (Van Schaik and Reuter, 2012)
Synthesis of rules of design for dismantling
The diagram below provides list points to assess the difficulty of disassembling a product:
The design for dismantling mainly consist to integrate end of life issues at the early stage of design of the product to adapt products to technical and economic limits of dismantling system whatsoever. We may summarize main rules:
– Use of recyclable materials / compatible (if not recycled, and avoiding materials prohibited by regulations).
– Streamline the number of materials.
– Using materials with characteristics that allow their separation easily during recycling.
– Reduce component number by integrating many functions into one component.
– Reduce the number and standardize the fasteners used.
– Design of seperable components:
- Choose materials with different properties (magnetic / nonmagnetic, heavy / light) for easy sorting,
- Keep a gap of 0.15 g/cm3 between the density of polymers.
– Facilitate access to components / fasteners (if possible to have only one way to access all components).
– Avoid painting (especially plastic parts) and coatings / surface treatments.
Further, design methods such as TRIZ method permit to solve contradictions that may occur during the design. The use of CAD can also help to anticipate problems by simulating the removal operation virtually. All these rules must be considered taking into account other functional specifications of the product.
– TRIZ applied to innovate in Design for Disassembly. (2005) – Daniel Justel et al.
– Systematic integration of design for recycling into product design. (1995) A Kriwet, et al.
– Design for disassembly (2005) – Jesse Miller
– Evaluation of disassemblability to enable design for disassembly in mass production. (2003) Desai, A., Mitak A
– VDI 2243 : Recycling-oriented product development – 2002 – German/English
– M.A. Reuter and A. van Schaik (2012): Opportunities and Limits of recycling – A Dynamic-Model-Based Analysis, MRS Bulletin, 37(4), pp. 339-347
– Schaik, A. van and Reuter, M.A. (2012). Shredding, sorting and recovery of metals from WEEE – Linking design to resource efficiency. In: Waste electrical and electronic equipment (WEEE) handbook.
– M.A. Reuter and A. van Schaik (2012). Opportunities and Limits of WEEE Recycling – Recommendations to Product Design from a Recyclers Perspective. In: Proceedings of Electronics Goes Green 2012+, 9-12 September 2012, Berlin, Germany. In press. 8 p.