Application of QFD for enabling environmentally conscious design in an Indian rotary switch manufacturing organisation

Abstract

Many businesses are recognising that environmental consciousness is an important concept for survival in today's highly competitive market. This paper presents a project in which quality function deployment (QFD) for environment (QFDE) has been applied to an Indian rotary switch manufacturing organisation to enable environmentally conscious design at the early stage of product development. QFDE consists of four phases. QFDE phases I and II are concerned with the identification of the rotary switch parts that are important in enhancing environmental consciousness. QFDE phases III and IV are concerned with the evaluation of the effect of design improvement on environmental quality requirements. The results obtained from the case study revealed that QFDE could be applied in the early stage of rotary switch product development as it identified the vital components from an environmental perspective and enabled the options for design improvement to be effectively evaluated. The managerial implications of the case study have also been presented.

Keywords:

• quality function deployment
• environmentally conscious design
• environmental product design
• design for environment
• rotary switches

1. Introduction

Increasing competition between manufacturing organisations has highlighted environmental consciousness as an important concept for survival in the competitive world (Giancarlo 2005, Padma et al. 2008, Sakao 2009). Organisations have been adopting practices designed to maintain environmental safety and minimise energy utilisation (Pun et al. 2002, Hervani et al. 2005). Modern organisations have been focusing on reducing environmental problems that are recognised as the eighth deadly waste. Environmental friendliness has become the focus of the contemporary product design scenario (Prahalad and Hamel 1994). Many design tools are available for evaluating a product's impact on the environment, but the drawback is that most tools require detailed data which cannot be used at the early product design stage. Quality function deployment (QFD) is a tool that analyses the functions of a product that can be used at the early product development stage (Akao 1990). QFD is aimed at translating consumers' demands into design targets and major quality assurance points to be used throughout the production phase. A sustainable product will impart little impact on the environment during its life cycle. In this context, QFD for environment (QFDE) proposed by Masui et al. (2003) has been used in this research project. QFDE consists of four phases. QFDE phases I and II are concerned with the identification of components that are focused on product design considering both environmental and traditional requirements. After this process, design engineers will improve the design of their product from an environmental perspective. QFDE phases III and IV enable design engineers to examine the possibility of design improvements for components and to determine the improvement effect of design changes. This paper reports a case study on the application of QFDE to rotary switches being manufactured by an Indian rotary switch manufacturing organisation.

2. Literature review

Dr Yoji Akao is regarded as the father of QFD, and he has contributed the widely used definition for QFD (Besterfield et al. 2004). QFD provides the need for translating consumer demands into appropriate technical requirements during each stage of a product/process development (Sullivan 1986). It enables the development of customer friendly and high-quality products. QFD has its origin at Mitsubishi's Kobe Shipyard in Japan (Pardee 1996). QFD emphasises quality in the design process to prevent the likelihood of defects at the earliest stages thereby reducing cost and improving productivity (Chan and Wu 2002, Akao and Mazur 2003). Other benefits of QFD include reduced design changes, increased market share and improved market quality (Chan and Wu 2002, Akao and Mazur 2003). One limitation is that QFD is a complicated process which requires the expertise of qualified professionals to develop the House of Quality (HOQ) (Olhager and West 2002). Problems exist in decomposing the tables separately from HOQ. Some of the advanced models of QFD are ‘Q’ model analysis (Dijkstra and van der Bij 2002), house of flexibility (Olhager and West 2002), enhanced QFD (Witter et al. 1995), total QFD (Devadasan et al. 2006), innovative total QFD (Vinodh et al. 2006), intelligent QFD (Myint 2003) and dynamic QFD (Adiano and Roth 1994, Raharjo et al. 2006). QFD has been widely applied in various industrial sectors (Karsak 2008; Miguel and Carnevalli 2008). Some authors have integrated QFD with the Theory of Inventive Problem Solving (TRIZ) for enabling the systematic creation of technical innovation for new products (Yamashina et al. 2002). Fung et al. (2002) have optimised product design resources using a nonlinear fuzzy QFD model. They have presented a case study to illustrate how the proposed fuzzy model and the optimisation routine can be applied to help decision makers in a company to deploy their design resources towards gaining better overall customer satisfaction. Reich and Levy (2004) have developed a simple, intuitive method, formulated as constrained nonlinear programming for managing product development to obtain the best quality product under dynamic resource constraints. Chen et al. (2005) have proposed a novel fuzzy expected value operator approach to model the QFD process in a fuzzy environment, and two fuzzy expected value models are established to determine the target values of engineering characteristics in handling different practical design scenarios. Bhattacharya et al. (2005) have proposed an integrated model combining analytic hierarchy process (AHP) and QFD for the industrial robot selection problem by considering several technical requirement factors.

Some researchers have been working on incorporating environmental aspects into QFD. Pun (2006) has presented the determinants of environmentally responsible operations and suggested green QFD as one of the tools for environmentally responsible operations. Cristofari et al. (1996) introduced the concept of green QFD by integrating QFD with a life-cycle approach to product development. This is useful for evaluating different product concepts and deploys environmental requirements throughout the development process. Zhang et al. (1999) developed a method called GQFD-II that includes the integration of life-cycle assessment (LCA) and life-cycle costing (LCC) into QFD. They integrated LCC into QFD matrices and suggested the deployment of quality, environmental and cost requirements throughout the entire product development process to evaluate different product concepts. Masui et al. (2003) presented a concept called QFDE in which QFD was applied to an environmentally conscious design. Sakao (2007) has presented a QFD-centred design methodology for an environmentally conscious product design. He combined LCA, QFDE and TRIZ and applied the combination to a hair dryer to effectively support the product planning and conceptual design stages.

Though researchers have contributed certain techniques for enabling environmental consciousness, few have explored the feasibility of deploying such techniques in an industrial scenario to ensure practical validity. In this context, the QFDE contributed by Masui et al. (2003) has been utilised in this research for infusing environmental aspects into the early design stage for rotary switches manufactured by an Indian organisation.

3. Research methodology

The methodology followed during this project is shown in Figure 1. As shown in Figure 1, the project started with a literature review on QFD and its application on environmentally friendly aspects. This was followed by the adoption of the QFDE model suggested in the literature. A suitable organisation for conducting the case study was identified which demonstrated the aspiration to attain world class status by means of implementing environmentally friendly strategies. Phase I was concerned with the application of QFDE for the rotary switches. Phase II was concerned with the deployment of engineering metrics (EMs) items to product components. In phase III, the effect of a set of design changes on EMs items was estimated. The goal of phase IV was to translate the effect of design changes on EMs into environmental quality requirements. This was followed by the derivation of practical inferences.

Figure 1 Research methodology.

4. Case study

This section presents the details of the application of QFDE for rotary switches.

4.1 The company

The case study was conducted at XYZ electronics limited, a rotary switch manufacturing organisation located in Coimbatore, Tamil Nadu, India. The company manufactures cam-operated rotary switches and has implemented various world class strategies such as 5S and an ISO quality management system.

4.2 Identification of the environmental voice of customer (VOC) and environmental EMs

This section describes the requirements and attributes considered from an environmental perspective throughout the life cycle of the product. Recyclers and government are considered as customers. The voice of recyclers and government regulations are expressed by means of engineering terms.

4.2.1 Environmental VOC

Environmental VOCs represent the quieter, safer operation of switches: comfortable to hold switches easily, increased lifetime of the switches, portability, reduced material use, easy to transport, reduced energy consumption, increased durability, easy to reuse as a product, easy to disassemble during the maintenance stage, easy to clean, easy to sort the products, harmless to living environment and to the users during manufacturing, and use and ease of disposability.

4.2.2 Environmental EMs

Environmental EMs include the technical/engineering characteristics of rotary switches. It also includes ease of application of torque, reduced weight and volume, reduced number of parts, reduced material types, increased hardness, increased lifetime, reduced amount of energy, rate of materials being recycled, biodegradability and toxicity of materials, and improved insulation strength.

4.3 Identification of target for design improvement

4.3.1 QFDE phase I

Phase I describes the application of QFDE to the design of rotary switches. Table 1 shows the deployment of VOC to EMs. VOC items in Table 1 include the environmental VOC such as ‘easy to transport and retain’ as well as traditional requirements such as ‘number of parts’ and ‘number of types of materials’. Generally, VOC items are weighted based on a market survey to reveal the ‘customer weights’. A rating of ‘9’ indicates that it is very important, ‘3’ indicates it is important and ‘1’ indicates it is relatively important. The degree of importance of environmental VOC is dependent on the concept of product life cycle. On the other hand, EM items include new items such as ‘Insulation strength’ as well as traditional items such as ‘Balance (Torque)’. The mapping points between VOC items and EM items are indicated by means of numbers indicating both factors called ‘relational strength’ determined by the designer. Similar to the weighting of VOC item, ‘9’ indicates a strong relationship, ‘3’ indicates a medium relationship and ‘1’ indicates certain strength. Here, at the mapping points between the environmental VOC items and environmental EM items, the values of relational strength are provided for the designer to enable decision making. The total sum multiplied by ‘customer weights’ and ‘relational strength’ is the ‘raw score’ for each EM item. ‘Relative weight’ for each item is obtained by dividing the raw score by the sum of the raw score. For example, EM values such as ‘number of parts’, ‘weight’ and ‘amount of energy’ with raw scores of ‘0.27’, ‘0.22’ and ‘0.15’, respectively, are relatively important to satisfy the customer requirements of: ‘easy to process and assemble’, ‘easy to transport and retain’ and ‘less material use’.

Table 1 QFDE phase I of rotary switches.

	EM
VOC	Customer weights	Balance (torque)	Weight	Volume	Number of parts	Number of types of materials	Hardness	Physical lifetime	Amount of energy	Rate of recycled material	Biodegradability	Toxicity of materials	Insulation strength
Quiet	1	3	1
Operates safely	9
Operates easily	9	3			3								1
Comfortable to hold	9		3	1			1
Reliable	9												3
Portable	9
Less material usage	9		9	3	9	1		1	3	3	1		3
Easy to transport and retain	9		3	3	3				3
Easy to process and assemble	9		9		9
Less energy consumption	1		1	1	3		3		9	3			3
High durability	3
Easy to reuse	3									9	3	3
Easy to disassemble	3		1	3	9				3	3
Easy to clean	9									9
Easy to sort	3				9
Harmless to living environment	3									1	9	9
Possible to dispose of at ease	1									3	3	9
Raw score		30	221	73	273	9	12	9	72	153	48	45	66
Relative weight		0.029	0.22	0.072	0.27	0.089	0.011	0.089	0.071	0.151	0.047	0.044	0.065

4.3.2 QFDE phase II

Phase II is concerned with the deployment of EM items to product components. The relative importance of each product component is obtained in a similar manner as phase I. As shown in Table 2, it is found that ‘contact stages’ and ‘knob shaft’ are the important components. To improve existing systems environmentally, the results obtained are concerned with the QFD results without the environmental VOC and environmental EM items.

Table 2 QFDE phase II of rotary switches.

		Component characteristics
EM	Phase I relative weight	Knob/ handle	Knob shaft	Front assembly	Mounting plate	Contact stages	Cover plate
Balance (torque)	0.029	9	9	3	9	9
Weight	0.22	3	1	3	3	3	3
Volume	0.072	1	1	3	1	3	1
Number of parts	0.27			3	3	9
Number of types of material	0.089			3		9
Hardness	0.011		9			3
Physical lifetime	0.089	9	9			9
Amount of energy	0.071		9			9
Rate of recycled materials	0.151
Biodegradability	0.047
Toxicity of materials	0.0445
Insulation strength	0.056		9			9
Raw score		1.794	2.596	2.04	1.803	5.841	0.732
Relative weight		0.121	0.175	0.137	0.121	0.394	0.0494
Note: The numbers in italics indicate that the relative weights of these component characteristics are higher.

The results of phase II show that the important components are contact stage, knob shaft and front assembly.

4.4 Evaluation method of design improvement

QFDE phases III and IV are concerned with the evaluation method of design improvement.

4.4.1 QFDE phase III

When design engineers improve their product from the viewpoint of the environment, evaluating the effects of candidate design changes on environmental aspects is an effective process after identifying the important components. In phase III, the effect of a set of design changes on EM items is estimated. In general, design engineers can make several alternative plans. There are two options for design engineers to decide their focus. One method originates from target VOC. If they already have a target of ‘less material usage’, VOC, for example, they should look for parts with less material usage. Another method is to examine the most important components identified in phase II. Tables 3 and 4 show examples of phase III. Here, priority has been assigned to the environmental aspects, and the design improvement plan has been set mainly from the viewpoint of the environment. The two design options proposed with consideration of the results of phases I and II include the following combinations of components and EMs.

Table 3 QFDE phase III of rotary switches for option I.

		Component characteristics
EM	Phase I relative weight	Knob/handle	Knob shaft	Front assembly	Mounting plate	Contact stages	Cover plate	Score	Improvement rate of EM
Balance (torque)	0.029		9		9			18	0.46
Weight	0.22							0	0.00
Volume	0.072							0	0.00
Number of parts	0.27							9	0.60
Number of types of material	0.089							0	0.00
Hardness	0.011							0	0.00
Physical lifetime	0.089	9						9	0.33
Amount of energy	0.071		9					9	0.50
Rate of recycled materials	0.151							0	0.00
Biodegradability	0.047							0	0.00
Toxicity of materials	0.0445							0	0.00
Insulation strength	0.056							0	0.00

Table 4 QFDE phase III of rotary switches for option II.

		Component characteristics
EM	Phase I relative weight	Knob/handle	Knob shaft	Front assembly	Mounting plate	Contact stages	Cover plate	Score	Improvement rate of EM
Balance (torque)	0.029							0	0.00
Weight	0.22					3		3	0.18
Volume	0.072							0	0.00
Number of parts	0.27			3		9		12	0.80
Number of types of material	0.089							0	0.00
Hardness	0.011							0	0.00
Physical lifetime	0.089							0	0.00
Amount of energy	0.071							0	0.00
Rate of recycled materials	0.151							0	0.00
Biodegradability	0.047							0	0.00
Toxicity of materials	0.0445							0	0.00
Insulation strength	0.056					9		9	0.50

Option I:

•	Make the knob/handle from a material with high friction coefficient to increase the physical lifetime.
•	Choose a material for the knob shaft that is capable of withstanding the torque (force) applied to it.
•	Choose a material for the mounting plate that will bear the torque applied to it.
•	Choose a material for the knob shaft that can dissipate a high amount of energy in the form of heat.

Option II:

•	The materials used in the contact stages should have high insulation strength.
•	The number of parts used in the contact stages should be the minimum possible.
•	The weight of the contact stages should be reduced as much as possible.
•	The number of parts used in the front assembly should be a minimum.

The numbers indicating the relational strength in phase II of Table 2 at mapping points between the target EMs and parts remain as shown in Tables 3 and 4. The improvement rate to each EM item ‘mr _j ’ is obtained from the equation:

where K is the index number of component, J the index number of EMs, b _j,k the relational strength between EM item j to compo, c _j,k the improvement rate of EM item j to component k and originally allowed to take the real numbers from 0.0 to 1.0.

Hence, for simplicity, c _j,k can take the binary numbers: c _j,k  = 1 (improvement possible) and c _j,k = 0 (improvement impossible) (Masui et al. 2003).

Examples of the improvement rate calculations for options I and II for selected EMs are presented in the following sections.

4.4.1.1 Improvement rate calculations for option I

1.	For EM ‘balance torque’: from phase III, (9 × 0.029+9 × 0.029) = 0.522; from phase II, (9 × 0.029+9 × 0.029+3 × 0.029+9 × 0.029+9 × 0.029) = 1.131. Improvement rate = 0.522/1.131 = 0.46.
2.	For EM ‘number of parts’: from phase III, (9 × 0.27) = 2.43; from phase II, (3 × 0.27+3 × 0.27+9 × 0.27) = 4.05. Improvement rate = 2.43/4.05 = 0.6.

4.4.1.2 Improvement rate calculations for option II

1.	For EM ‘weight’: from phase III, (3 × 0.22) = 0.66; from phase II, (3 × 0.22+1 × 0.22+3 × 0.22+3 × 0.22+3 × 0.22+3 × 0.22) = 3.52. Improvement rate = 0.66/3.52 = 0.18.
2.	For EM ‘number of parts’: from phase III, (3 × 0.27+9 × 0.27) = 3.24; from phase II, (3 × 0.27+3 × 0.27+9 × 0.27) = 4.05. Improvement rate = 3.24/4.05 = 0.8.

4.4.2 QFDE phase IV

The objective of phase IV is to translate the effect of design changes on EMs into environmental quality requirements. Tables 5 and 6 show an example of phase IV for rotary switches. In Tables 5 and 6, the values of customer weight and relational strength between VOC items and EM items are the same as shown in phase I (Table 1). The improvement rate for EM items obtained in phase III is shown at the bottom of Tables 5 and 6. The improvement rate for each environmental VOC ‘vr _i ’ is obtained from the following equation:

where J is the index number of EM item, I the index number of a VOC item and a _i,j the relational strength between VOC item I and EM item j.

Table 5 QFDE phase IV of rotary switches for option I.

	EM
VOC	Customer weights	Balance (torque)	Weight	Volume	Number of parts	Number of types of materials	Hardness	Physical lifetime	Amount of energy	Rate of recycled material	Biode- gradability	Toxicity of materials	Insulation strength	Improvement rate of customer requirement	Improvement effect of customer requirement
Quiet	1	3	1											0.345	0.345
Operates safely	9													0.000	0.000
Operates easily	9	3			3								1	0.050	0.450
Comfortable to hold	9		3	1			1							0.000	0.000
Reliable	9												3	0.000	0.000
Portable	9													0.000	0.000
Less material usage	9		9	3	9	1		1	3	3	1		3	0.024	0.216
Easy to transport and retain	9		3	3	3				3					0.052	0.468
Easy to process and assemble	9		9		9									0.033	0.297
Less energy consumption	1		1	1	3		3		9	3			3	0.273	0.273
High durability	3													0.000	0.000
Easy to reuse	3									9	3	3		0.000	0.000
Easy to disassemble	3		1	3	9				3	3				0.121	0.363
Easy to clean	9									9				0.000	0.000
Easy to sort	3				9									0.200	0.600
Harmless to living environment	3									1	9	9		0.000	0.000
Possible to dispose of at ease	1									3	3	9		0.000	0.000
Improvement rate of EM		0.46	0.00	0.00	0.60	0.00	0.00	0.33	0.50	0.00	0.00	0.00	0.00
Amount														1.098	3.012

Table 6 QFDE phase IV of rotary switches for option II.

	EM
VOC	Customer weights	Balance (torque)	Weight	Volume	Number of parts	Number of types of materials	Hardness	Physical lifetime	Amount of energy	Rate of recycled material	Biode-gradability	Toxicity of materials	Insulation strength	Improvement rate of customer requirement	Improvement effect of customer requirement
Quiet	1	3	1											0.045	0.045
Operates safely	9													0.000	0.000
Operates easily	9	3			3								1	0.046	0.414
Comfortable to hold	9		3	1			1							0.008	0.720
Reliable	9												3	0.000	0.000
Portable	9													0.000	0.000
Less material usage	9		9	3	9	1		1	3	3	1		3	0.034	0.306
Easy to transport and retain	9		3	3	3				3					0.027	0.243
Easy to process and assemble	9		9		9									0.054	0.486
Less energy consumption	1		1	1	3		3		9	3			3	0.177	0.177
High durability	3													0.000	0.000
Easy to reuse	3									9	3	3		0.000	0.000
Easy to disassemble	3		1	3	9				3	3				0.129	0.387
Easy to clean	9									9				0.000	0.000
Easy to sort	3				9									0.266	0.798
Harmless to living environment	3									1	9	9		0.000	0.000
Possible to dispose of at ease	1									3	3	9		0.000	0.000
Improvement rate of EM		0.00	0.18	0.00	0.80	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.50
Amount														0.786	3.576

Examples of the improvement rate calculations for options I and II for selected customer requirements are presented in the following sections.

4.4.2.1 Improvement rate of customer requirement calculations for option I

1.	For the customer requirement ‘quiet’ operation: from phase IV, (3 × 0.46+1 × 0.00) = 1.38 (relational strength × improvement rate) and (1+3) × 1 = 4 (sum of relational strength × customer weight). Improvement rate of customer requirement = 1.38/4 = 0.345.
2.	For the customer requirement ‘operates easily’: from phase IV, (3 × 0.46+3 × 0.60+1 × 0.00) = 3.18 and (3+3+1) × 9 = 63. Improvement rate of customer requirement = 3.18/63 = 0.050.

4.4.2.2 Improvement effect of customer requirement calculations for option I

Improvement effect = improvement rate of customer requirement × customer weight.

1.	For the customer requirement ‘quiet’ operation: improvement effect = 0.045 × 1 = 0.045.
2.	For the customer requirement ‘operates easily’: improvement effect = 0.05 × 9 = 0.45.

The improvement effect for the environmental VOC considering customer weight is obtained by multiplying vr _i and customer weight i.

4.4.3 Evaluation of design for environment options

The improvement effect for the VOCs with their weights was calculated for each design from an environment perspective through phases III and IV. In this case study, the scores 3.012 and 3.576 were obtained for options I and II, respectively, and it was concluded that option II was the best.

5. Results and discussion

QFDE enables design engineers to select the most effective plan involving design changes. In order to practically validate the effectiveness of applying QFDE, a questionnaire-based validation was conducted with the Company executives. The format of the questionnaire is shown in Figure 2.

Figure 2 Format of questionnaire.

The responses of the executives are presented in Table 7. The respondents were executives of the design, production and quality control departments. These executives possess excellent knowledge about the Company's manufacturing practices.

Table 7 Responses of the executives.

		Response in Likert's scale					Average response in Likert's scale
S.No.	Question	E1	E2	E3	E4	E5	(1, not all possible; 5, partially possible; 10, completely possible)
1	To what extent is the concept of QFDE practically understandable by the executives of your organisation?	8.5	9	8	8.5	8.5	8.5
2	To what extent are the options generated by QFDE practically feasible?	9	9	9	10	8	9.0
3	To what extent does QFDE enable design engineers to select effectively the design changes?	9	9	10	9.5	10	9.5

5.1 Impact of QFDE at XYZ electronics

As a result of the QFDE process, changes were made to embed environmental consciousness at the early stages of rotary switch product development. An alternative material with high insulation strength is currently being evaluated for contact stages and efforts have been taken to minimise the number of parts in the contact stages and front assembly to obtain weight reduction.

5.2 Managerial implications

Although researchers have established that environmental consciousness is a promising characteristic for enabling modern companies to achieve core competitiveness, practitioners have to realise the importance of environmental consciousness. In order to bridge the gap between lack of awareness and the potential for successful implementation of QFDE, a systematic roadmap was suggested to the practitioners. Accordingly, the experiences of conducting the implementation study on QFDE have been used to develop the roadmap shown in Figure 3.

Figure 3 Roadmap for implementing QFDE.

As shown in Figure 3, exposure programmes on environmental consciousness have to be conducted for the managers. These programmes must convey the basics and benefits of environmental consciousness. At this juncture, the managers should have developed enthusiasm to bring out environmental consciousness. They would also have understood the benefits of embedding environmental consciousness in the early product design stages. Next, an orientation programme on QFDE must be conducted for the managers. They have to be informed about the steps to be followed and about the resources required for its successful conduct. Then, the features of the QFDE technique have to be explained to the employees in an orientation programme. These steps are not only aimed at creating awareness on environmental consciousness but also at laying the strong foundation for successfully anchoring QFDE in the organisation.

After creating awareness on QFDE, VOCs and EMs have to be identified. Depending on the opinions expressed by the management, a QFDE team may be formed. The entire QFDE programme may be coordinated by a QFDE coordinator. Followed by that, meetings shall be conducted to develop the QFDE phases. At the end of these meetings, outputs have to be derived. These outputs need to be implemented. The impact of this implementation shall be studied after a gestation period. Depending on the impact on environmental consciousness, the QFDE programme may be expanded to different levels.

6. Conclusions

Contemporary manufacturing organisations are focusing on reducing production costs and preventing environmental problems. Green manufacturing systems integrate product and process design issues with manufacturing planning and control in an effective manner to identify, quantify, assess and manage the flow of environmental wastes with the goal of reducing environmental impacts (Hutchinson 1996, Maxwell et al. 1997). In this context, QFDE has been used to handle environmental and traditional quality requirements of the product. QFDE can be used in the early stages of product design for enabling sustainability (Masui et al. 2003). Phases I and II of QFDE enabled the design engineers to evaluate rotary switch components from an environmental perspective. Phases III and IV of QFDE analysed the design changes and various candidate designs of rotary switches from the perspective of environmental improvement. The managerial implications of the case study were also presented.

6.1 Limitations and future research directions

The case study was conducted for a single manufacturing organisation. In future, case studies could also be conducted at other manufacturers of rotary switches. Also, to further improve the validity of the approach, case studies could be conducted at different industrial sectors in which QFDE could be applied for the development of new products.