A Lean upgrade for Die Casting-Case of Axiomatic Design
Wen-Kuei Chen, Ph.D.1, Yu-Ming Kuo 2, Yi-Li Chang3
1Department
of Finance, I-Shou University,
1, Section 1, Hsueh-Cheng Rd., Ta-Hsu Hsiang, Kaohsiung County, Taiwan 840, R.O.C.
rexchen@isu.edu.tw
2Department
of Industrial Engineering & Management, I-Shou University,
1, Section 1, Hsueh-Cheng Rd., Ta-Hsu Hsiang, Kaohsiung County, Taiwan 840, R.O.C.
kuo-min@yahoo.com.tw
3Department
of Industrial Engineering & Management, I-Shou University,
1, Section 1, Hsueh-Cheng Rd., Ta-Hsu Hsiang, Kaohsiung County, Taiwan 840, R.O.C.
Kangta0177@hotmail.com
Abstract
A product that has good reputation usually meets the customers’ ends. However, the design of a product,
which is the base of good quality, still can’t be systematically evaluated.
Fortunately, “Axiomatic
Design,” an analytic method brought up by Dr. Suh, professor of MIT, just compensates for the
deficiency.
It is applied to qualitative and quantitative verification.
The method is based on the
procedure in which the Design Parameters, supposed to reflect the functional requirements, are verified
step by step downwards in Z procedare.
During the process, the effectiveness of a product can be
evaluated by practicing Design Matrix and Design Equation.
On the other hand, Reangularity and
Semangularity are used to analyze the mutual interference between parameters and the functional
contribution of each parameter.
process should be reversed.
The study finds out that in order to improve production technology, the
In the case of Die Casting of shock absorber, the fundamental reasons of the
flaws are first considered, through the interrelationship diagram.
avoid the flaws.
Accordingly, strategies are sought to
Then, the procedure is followed step by step upwards.
and product yield of the case in our study are tremendously improved.
keywords：Axiomatic Design、Uncoupled Design、Die Casting
At last, the machine’s capacity
1. Introduction
Dr. Nam P. Suh, professor of Massachusetts Institute of Technology, did research for a very
long time in order to establish the theory of Axiomatic Design.
He also provided many
examples. Based on the theory of Axiomatic Design, design is dealt with as a solid frame.
Everything related to product design is in its own order and can be checked and evaluated
whenever necessary during the process. Dr. Suh claimed that the designing team should reflect
the product requirements on Design Parameters. Besides, they should try their best to keep the
parameters form interfering each other, step by step downwards during the process.
In Chapter Two, we are going to explain the concepts of Axiomatic Design, and how to
evaluate Uncoupled Design
. In Chapter Three, based on the production of Die Casting of shock absorber, we are going to
analyze the relation between process parameters and production requirements, and bring up
some strategies that can attain Decoupled Design
. The procedure is from the bottom and then step by step upwards and is repeated over and
over again. In Chapter Four, we conclude this thesis in brief.
2. Axiomatic Design
Only few cases in Taiwan apply the theory of Axiomatic Design. Ms. Wu Shu-Ying applied this
theory to evaluate the product design of mobile phones.
Mr. Liu Zhi-Xing, Mr. Wang
Ren-Qing and Mr. Chen Jia-Hao cooperated and applied TRIZ and Axiomatic Design to design
mousse for computers. What worth recommendation here is that Mr. Ye Yong-Zan applied
Axiomatic Design to the product design and evaluation of back-lighted module.
There are three types of Dr. Suh’s design matrix：Uncoupled design, Decoupled design and
Coupled design. Diagonal matrix belongs to Uncoupled Design
design in which there is no interference between the parameters. Triangular matrix belongs to
Decoupled design in which there is only little interference between the parameters. Other
matrixes, however, belong to Coupled design in which parameters seriously interfere with each
other.
Dr. Suh divided the issue of design into four areas：usage, functions, substance, and
process. In order to make the transformation of the above four areas effective, Dr. Suh brought
up Independent Axion and Information Axion as the guidelines. Independent Axion is applied
to make sure that each function is independent from each other and will be attained. On the
other hand, Dr. Suh advocates Reangularity and Semangularity, the two evaluation indexes.
The former evaluates how well the parameters are not interfered with each other while the latter
evaluates how well the functions contribute. When all the parameters are not interfered with
each other and the Semangularity is upmost, the design matrix appears as a diagonal one.
In
addition, Mr. Huang Yao-Kun’s self-made function of EXCEL can directly calculate the
angularity between these two indexes.
Figure-1 Zig-Zag
Axiomatic Design is applied to carry out the product design through the reflective
transformation of two adjacent areas in Z procedare, as detailed in Diagram-1. Take the
process development as an example. We start with DP, a design parameter in the substance
area, and then access the area of process. Then, we decide PV, a corresponding variable of
process. Afterwards, we go back to the substance area and determine the design parameters of
the lower layer.
3. The process of Die Casting
In the shock absorber’s factory before, they used the method that one person operated two
machines, so each of the four operators should operate two machines.
There are two stages of
casting a shock absorber：pre-production and production. Before daily primary production,
they started at the pre-production stage and all the related staff got ready the mold in the casting
machines. They smeared some protective agent over the mold surface and the rising head, and
then the pattern was heated from the middle of the mold. The protective agent was smeared
over the mold in order to prevent from adhering to mold, and over the rising head in order to
keep the temperature of it. The production stage included four steps which are（1）Pouring
（The heated aluminum liquid was poured into the mold.），
（2）Solidification（Starting the procedure of pattern solidification）
，
（3）Separating the mold
（Taking out the pattern which is done）
，
（4）Reuniting the mold（Putting the mold together and
waiting to pour the liquid again）. When the operator took out the pattern which is done, he
should eye-check the quality, but if necessary, he should examine the surface of the mold, or
even arrange it.
In order to measure the wasted time, we defined four variables. They are X1（Pouring
Time），X2 （Solidification Time）
，X3（Separating Time）
，and（Closure Time）.
X1
Pouring Time（closure timing–pouring timing）：The interval between closure and
pouring the aluminum liquid. We observed that the operator often didn’t pour the liquid
after the closure.
X2 Solidification Time（pouring timing-solidification timing）
：The interval between pouring
the liquid
and pressing the solidification button. Because one operator should be in charge of two
machines, he usually had to wait for the solidification of patterns. Therefore, some time
was wasted.
X3 Separating Time（solidification timing-separating timing）
：The interval between taking out
the pattern and pressing the closure button. During the casting, if the operator spotted any
raised dots, he would arrange the mold. Therefore, the other machine will be delayed and
therefore it can’t be operated in time.
X4 Closure Time（separating timing-closure timing）
：The interval between completing the
pattern and pressing the closure button. Usually, after the operator took out the pattern, he
won’t immediately press the closure button and therefore wasted some time.
PouringTime
Time
Pouring
Pouring
Pouring
SolidificationTime
Time
Solidification
Solidification
Solidification
Separating
Separating
SeparatingTime
Time
Separating
surface of
the mold
Arrange
Arrange
ClosureTime
Time
Closure
Closure
Closure
Figure-2 Waste time and Die casting
As shown at Diagram-2, these four variables are used to measure how much machine’s capacity
had been lost. The less their mean and standard deviation is, the better. In order to collect data
effectively, the software EXCEL is applied to design many stopwatches. We used the
stopwatches to record the beginning and ending time of each procedure. We design formulas
to automatically calculate the working time and related statistics. The solidification time of each
mold is 90 seconds but we found out that the means of the wasted time are 35.4, 22.0, 20.8 and
15.0 seconds respectively. All of them are higher than average, so there are a lot to be improved
in the process.
In the process of casting, the temperature of the mold while taking out the pattern is the
critical factor that determined whether the solidification is good or bad. The ideal temperature
is 380±10oC with which the pattern would be solidified. However the diagram of temperature
showed that the temperature is getting higher and higher after each mold. There are two kinds of
flaws：raised dots on the pattern surface and crooked rising head. The former is caused by the
peeling of the protective agent while the latter is caused by the ineffective solidification.
Accordingly, crooked rising head is classified as “quality of mold temperature” and raised dot
on the pattern surface is classified as “quality of mold surface.” Moreover, the procedure
operated by the operator also affects the machine’s capacity, so we classify it as “operator’s
work.”
3.1 Quality of Mold Temperature
The rising head of some patterns are crooked. It is caused by separating the mold while the
temperature is still high. If the operator pours the aluminum liquid while the mold is still hot,
then solidification won’t be completed in time, and the pattern will be soft. According to our
observation, experienced operators will postpone to press the solidification button in order to
prolong the solidification time. As the analysis in reversed Z procedure shown in Diagram-3, we
first define PV11, natural heat dissipation, and PV12, postponement of pressing the
solidification button. Then we trace back to the previous PV1, appropriate mold temperature.
Furthermore, we define the process parameter DP11, lowering the temperature to solidify, and
DP12, adjusting mold temperature. Then we trace back to the previous DP1, excellent pattern.
After examination, we now find out that natural heat dissipation seriously interferes with
postponement of pressing the solidification button. To lower their independence is necessary. In
order to ensure that the temperature of the mold can be stably lowered, we practice two
strategies:
（1）to increase heat dissipation devices and（2）to increase the monitors which show mold
temperature. We redefine PV11, controlling heat dissipation and PV12, immediately starting
solidification. Besides, we define the process parameter DP11, solidification at fixed time, and
DP12, the mold temperature while taking out the pattern.
Figure-3 Quality of Mold Temperature Zig-Zag Improve Chart
3.2 Quality of Mold Surface
The raised dots on the surface of some patterns are caused by the low temperature of the rising
head and the peeling of protective agent. Therefore, the flow of the aluminum liquid can’t be the
same and some aluminum will stick to the mold. As the analysis in reversed Z procedure shown
in Diagram-4, we define PV21, smearing protective agent, PV22, heating the core of the mold,
and PV23, protective agent by hand. We trace back to previous PV2, proper pre-production.
Furthermore, we define process parameter DP21, preventing sticking to the mold, DP22,
pre-heating the mold, and DP23, keeping warm of the rising head. Then, we trace back to
previous DP2, appropriate casting. After examination, we find out that “smearing protective
agent,” “heating the core of the mold,” and “protective agent by hand” actually seriously
interfere with each other. In order to ensure the flow of aluminum liquid is smooth and the
aluminum won’t stick to the mold, we practice three strategies：using highly-effective protective
agent, heating the outer shell, and protective agent by pen. We redefine PV21, smearing
protective agent, PV22, heating the outer shell, and PV23, protective agent by pen.
Figure-4 Quality of Mold Surface Zig-Zag Improve Chart
3.3 Operator’s Work
The production is originally designed as “one operator, two machines,” it meant to let the
operator be responsible for their own effectiveness. According o the survey of wasted time, the
production method causes many waits. As shown in Diagram-5, we first define PV31, pouring
the liquid after putting together the mold, PV32, taking out the pattern after separating the mold,
and PV33, putting together the mold after taking out the patterns. We trace back to PV3,
self-production and self-examination. We furthermore define process parameter DP21, pouring
at fixed time, DP22, taking out the pattern at fixed time, and DP23, putting together the mold at
fixed time. We trace back to DP2, high effective machine’s capacity. After examination, we find
out that “pouring at fixed time”, “taking out the pattern at fixed time”, and “putting together the
mold at fixed time” interfere with each other because of a lot of waits. The independence
between people and machine should be lowered. The new policy is to recruit two operators in
one group. They take turns to pour the liquid and take out the patterns. Based on the policy of
“two people, four machines,” the operator in charge of pouring only needs to patrol the four
machines, fetching the liquid, pouring the liquid, and pressing the solidification button. On the
other hand, the operator in charge of taking out the patterns only need to take out the patterns,
eye-check them, and if necessary, arrange the mold and press the button to put the mold
together.
Figure-5 Operator’s Work Zig-Zag Improve Chart
3.4 Outcome Improvement
Throughout the whole study, Axiomatic Design is applied as the guiding principle. We try our
best to eliminate the independent condition between each procedure parameter and process
variable of Die Casting. After the improvement, temperature of the mold, from which the
pattern has been taken out, has turned stable.
It shows that preheating the mold can be
effectively controlled and therefore reached a 33% decrease in the rate of invalid patterns.
When it comes to the wasted time, as shown in Diagram-6, all of the eight machines have
obviously improved. The product capacity has been surely 100% improved.
Figure-6 Improvement Chart
4. Conclusion
In our study, we take the Die Casting of shock absorber as an example in order to realize the
process variable behind each product flaw, through interrelationship diagram. We demand that
the casting should be based on the process parameters and we seek improving strategies to
upgrade angularity. Then, we analyze layer by layer upwards. At last, both the machine’s
capacity and product yields are tremendously improved.
This study only relies on the qualitative verification of information but still realizes that
Dr. Suh’s Axiomatic Design is an excellent guide. Generally, the process is followed step by
step downwards in Z procedare. While we are seeking for improving strategies, however, a
reverse procedure is appropriate.
Reference
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學位論文：
2. 黃耀琨，
「FMEA 與公理設計關聯之研究」
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書籍：
5. Suh, Nam P., The Principles of Design, New York: Oxford University Press, (1990).
6. Suh, Nam P., Axiomatic Design: Advances and Applications, New York: Oxford University
Press (2001).
7. Suh, Nam P., Complexity: Theory and Applications, New York: Oxford University Press
(2005).