Descriptive Study I: Understanding Design
4.8 Drawing Overall Conclusions
4.8.2 Completing the Reference Model and Updating the Initial Impact Model Model
During DS-I the Initial Reference Model (see Figure 3.10) is continuously updated using the findings from the literature and one’s own empirical studies. Once the empirical studies have been completed, the Reference Model can be finalised and the Initial Impact Model updated, as will be illustrated using our reliability example.
Reliability Example
Figures 4.7 and 4.8 show the upper and lower part of the final Reference Model for the reliability example. Compared to the Initial Reference Model, the Key Factor has moved from ‘product reliability’ to ‘embodiment reliability’ due to an increased understanding of causes and effects. A possible link between early failure detection (upper part of the figure) and early assessment (in this case reliability of embodiment rather than of detail design) is not included for reasons of clarity and because this link was considered less relevant. The aim is to focus on the chain of causes and effects associated with improving product reliability product quality, customer satisfaction and market share, and not on the chain of effects associated with a reduction of iterations and lead time.
Based on the Reference Model, the Initial Impact Model can be further detailed.
Figures 4.9 and 4.10 show the resulting upper and lower part of the Initial Impact Model for our reliability example. As discussed earlier, clarity had the largest effect, simplicity had an effect but is not an absolute measure, and unity is relevant but not found to be a problem in the cases investigated. The support should therefore focus on clarity and simplicity, with an emphasis on clarity. Furthermore, it is assumed that when the embodiment is more reliable, the number and size of modifications needed after the use of the Design for Reliability methods in the detailed design stage will be reduced and the amount of time left sufficient. The factors ‘quality of components’ and ‘quality of production’ were considered not to be problematic within the company, and ‘motivation of use’ as a factor that cannot be influenced by the researchers, so that those factors are not considered (shown with dashed lines). Note that at this stage, the Impact Model is still an Initial Impact Model, which will be finalised in the PS stage.
Figure 4.7 Upper part of the Reference Model resulting from the DS-I stage
Figure 4.8 Lower part of the Reference Model resulting from DS-I Success Factor
product reliability market share
+ + +
[1]+
_ + _ 0
[2] [A]
[1]
[1]
_ +
quality of product
quality of production
__
[1]
maintenance cost
_ + ++ +
+
[4]
[3,4]
[3]
++ + _
[3]
[5]
Measurable Success Factor early failure detection &
analysis
lead time project cost
profit
+ _
+ + ++
+ +
+ +
+ _ + +
+ 0
+ _
Lower part of Reference Model (Fig. 4.8) number of
iterations
customer satisfaction
product cost price
other factors
operating cost warranty
cost Success Factor
product reliability market share
+ + +
[1]+
_ + _ 0
[2] [A]
[1]
[1]
_ +
quality of product
quality of production
__
[1]
maintenance cost
_ + ++ +
+
[4]
[3,4]
[3]
++ + _
[3]
[5]
Measurable Success Factor early failure detection &
analysis
lead time project cost
profit
+ _
+ + ++
+ +
+ +
+ _ + +
+ 0
+ _
Lower part of Reference Model (Fig. 4.8) number of
iterations
customer satisfaction
product cost price
other factors
operating cost warranty
cost
product reliability _ _ _
+ +
+
+ +
+ + Reliability of
embodiment
_ _
_ _
_ _
+ +
_ +
+
use of DfR methods other factors
0
+ % of
project time left to improve _
product- specificity of DfR
methods _ 0
+
Key Factor Upper part of Reference Model (Fig. 4.7)
level of unity level of
simplicity
quality of product use
clarity of instruction
motivation of use quality of production
quality of bought-in components level of clarity
reliability of detail design quality of concept
product reliability _ _ _
+ +
+
+ +
+ + Reliability of
embodiment
_ _
_ _
_ _
+ +
_ +
+
use of DfR methods other factors
0
+ % of
project time left to improve _
product- specificity of DfR
methods _ 0
+
Key Factor Upper part of Reference Model (Fig. 4.7)
level of unity level of
simplicity
quality of product use
clarity of instruction
motivation of use quality of production
quality of bought-in components level of clarity
reliability of detail design quality of concept
Figure 4.9 Upper part of the updated Initial Impact Model resulting from DS-I
Figure 4.10 Lower part of the Initial Impact Model resulting from DS-I, focusing on improving the levels of clarity and simplicity, emphasising clarity as one of the main factors
_ _
+
_
Success Factor
product reliability customer
satisfaction market share
+ + +
other factors +
_
quality of product quality of
production
++
+ _ _
warranty cost _ _
_
_
operating
_ cost
_ _
Measurable Success Factor early failure
detection &
analysis
lead time number of
iterations project cost
profit
+ _
_ _ _ __
_ + +
_
+ _
Lower part of Impact Model (Fig. 4.10)
product cost price
maintenance cost
_ _
+
_
Success Factor
product reliability customer
satisfaction market share
+ + +
other factors +
_
quality of product quality of
production
++
+ _ _
warranty cost _ _
_
_
operating
_ cost
_ _
Measurable Success Factor early failure
detection &
analysis
lead time number of
iterations project cost
profit
+ _
_ _ _ __
_ + +
_
+ _
Lower part of Impact Model (Fig. 4.10)
product cost price
maintenance cost
product reliability
quality of bought-in components quality of production quality of
product use
clarity of instruction reliability of
detail design
+ +
+ +
_ _
+ _
+
motivation of use
_ +
use of DfR methods
+
+ +
+
Upper part of Initial Impact Model (Fig. 4.9)
level of unity level of
simplicity level of
clarity
+ +
+ +
+ +
Key Factor number of
iterations
+_
reliability of embodiment
support early
embodiment % of
project time left to improve
product reliability
quality of bought-in components quality of production quality of
product use
clarity of instruction reliability of
detail design
+ +
+ +
_ _
+ _
+
motivation of use
_ +
use of DfR methods
+
+ +
+
Upper part of Initial Impact Model (Fig. 4.9)
level of unity level of
simplicity level of
clarity
+ +
+ +
+ +
Key Factor number of
iterations
+_
reliability of embodiment
support early
embodiment % of
project time left to improve