How to use Nakazawa Method

If you have following problems, why not use Nakazawa Method.


1. Speed up the pace of research and development
2. Improve the quality and performances of products
3. Reduce products cost keeping quality

This method was given a US patent in 1999 and Japanese patent in 2002. Yet you may use this method in every field except selling the calculation software and/or products incorporated this method.

Full explanation of the method is given in the book "A Trump for Production Nakazawa Method" in Japanese. Also the calculation software is provided, using this software you can obtain the optimal values easily.
Now explain how to use this method briefly in step wise below.

Taking an example of a horizontal injection machine shown below, the processes of the method will be explained.



Process of Nakazawa Method is as follows:
1. Decide the purpose of the job
2. Decide the functional requirements (FRs) and the target value/range for each FR
3. Select design parameters (DPs) against the FRs
4. Allot them to an orthogonal array
5. According to the orthogonal array experiment and take data for each FR
6 .Using the calculation software the optimum values for parameters that satisfy all the FRs sufficiently are obtained
7. Making the product incorporating the above optimum values and confirm that the FRs are satisfied, then the development ends

Let us explain details about the processes.l

1. Decide the purpose of the job
Specifically indicate the purpose of the Method application, such as creation of new technology, development of new product, improvement of a product, optimizing of production conditions so on. Here take "the improvement of an injection machine" as an example


2. Decide the functional requirements (FRs) and the target value/range for each FR
Three FRs are chosen in this case. They areabrasion at some points (mm),
material flow rate (productivity)(g/min) and power consumption(kWh).
Next determine the target value/range for each FR, such as that abrasion must be less than certain amount (mm), material flow rate is more than certain amount (mm) and power consumption is less than certain amount (kWh). These values are inputted into the software. These values are called design ranges (DRs).
The DRs can be chosen to be higher performance than that of the products made in own company and/or currently used one.
If specific value needs not to be determine, the mean value calculated from all the experimental data obtained through Nakazawa Method may be used. The provided software calculate automatically the mean value to designate it as a DR.

3. Select parameters (DPs) against the FRs
Select the most effective DPs against the FRs. Here the four DPs are selected such as the inner diameter (mm) and length (mm) of the screwhead ring, revolution of the screw (rpm) and temperature of the barrel heater (degrees C).Then decide three levels for each DP which are presumed cover the optimum value.

4. Allot them to an orthogonal array
These DPs and levels (for instance A1, A2 and A3 to the parameter A) are inputted into the software. Since the number of DPs are four, the smallest orthogonal array L9 (Table1) is chosen. If the number of DPs is more than four then larger size orthogonal array must be chosen.

                     Table 1. L9 orthogonal array

No  DP FR
 Inner diameter
of ring 
 Length
of ring 
Revolution
of screw
Temperature
of barrel heater
 Abrasion
amount 
Flowrate Power
consumption
1 A1 B1 C1 D1 data ・・・・
2 A1 B2 C2 D2
3 A1 B3 C3 D3
4 A2 B1 C2 D3
5 A2 B2 C3 D1
6 A2 B3 C1 D2
7 A3 B1 C3 D2
8 A3 B2 C1 D3
9 A3 B3 C2 D1 ・・・・ data


5. According to the orthogonal array experiment and take data for each FR
According to the L9 orthogonal array the nine sets of experimental conditions in rows are set and data are obtained experimentally or from calculations for each FR. Then those data are inputted in the corresponding cells in the row positions. In each cell a number of data exist, because experiments are done repeatedly under the same conditions and/or under different outside conditions. When data are saved in Excel form, they can be easily imported into the software.

6 .Using the calculation software the optimum values for parameters that satisfy all the FRs sufficiently are obtained
The recsat curve for each DP of each FR are calculated in the software and shown on the monitor. The recsat function is explained in detail in the book
"A Trump for Production Nakazawa Method" (sorry! it is written in Japanese). Then a sum of the recsat curves of all the FRs for a DP, which is called "total recsat curve", is obtained and shown. The corresponding point of the DP to the minimum total recsat is the optimum value of the DP which satisfies all the FRs. The optimum values of all the FRs are determined one after another. Using the software you can easily obtain these results.


7. Making the product incorporating the above optimum values and confirm that the FRs are satisfied , then the development ends
Once confirmed with the final product which is made from the optimum values of DPs that all the performances are in the design ranges, the development ends. Final results of the above injection machine is shown in Table 2. Actually Abrasions were measured at three points.

Table 2. Final results of development

Abrasion (mm) Power consumption
(kWh)
Flow rate
(productivity)
(g/min)
Ring Screw head
Inner
diameter
Length Length
New type 0.001 0.148 0.247 15.3 130
Currently used type 0.005 0.234 0.533 32.3 54

This table shows that all the items are drastically improved.

When a performance or some are not obtained, please take the following three steps.
1. When an optimum point is located at either end of the total recsat curve ( for example A1 or A3 ), experiment again reconstructing the orthogonal array of new levels of the DP which covers the expecting optimum point.
2. If that process does not succeed, another important DP may exist and find it, and experiment again.
3. Nevertheless good results could not be obtained, the fundamental structure ( that idea ) must be thrown away to create other structures. You must not cling to that idea to loose money and time.

How do you think this method? Isn't it easy to use? About sixty Japanese well-known companies introduced this method to gain much benefit.

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