Example of a response optimization experiment for response surface designs
main topic     interpreting results     session command     see also  

You need to create a product that satisfies the criteria for both seal strength and variability in seal strength. Parts are placed inside a bag, which is then sealed with a heat-sealing machine. The seal must be strong enough so that product will not be lost in transit, yet not so strong that the consumer cannot open the bag. The lower and upper bounds for the seal strength are 20 and 32 lbs., with a target of 26 lbs. For the variability in seal strength, the goal is to minimize and the maximum acceptable value is 1.

Previous experimentation has indicated that the following are important factors for controlling the strength of the seal: hot bar temperature (HotBarT), dwell time (DwelTime), hot bar pressure (HotBarP), and material temperature (MatTemp). Hot bar temperature (HotBarT) and dwell time (DwelTime) are important for reducing the variation in seal strength.

You goal is to optimize both responses: strength of the seal (Strength) and variability in the strength of the seal (VarStrength).

You do not need to analyze these response surface design models. The worksheet contains the models for the response optimizer.

1    Open the worksheet RSOPT_MODEL.MTW.

2    Choose Stat > DOE > Response Surface > Response Optimizer.

3    For VarStrength, choose Minimize.

4    For Strength, choose Target and enter 26.

5    Click Setup. Complete the columns of the table as shown below, then click OK.

Response

Goal

Lower

Target

Upper

Weight

Importance

VarStrength

Minimize

0.8

0.8

2.3354

1

1

Strength

Target

24

26

28

1

1

6    Click OK in each dialog box.

Session Window Output

Response Optimization: VarStrength, Strength

 

 

Parameters

 

Response     Goal     Lower  Target    Upper  Weight  Importance

VarStrength  Minimum            0.8   2.3355       1           1

Strength     Target      24    26.0  28.0000       1           1

 

 

Solution

 

                                               VarStrength  Strength     Composite

Solution  HotBarT  DwelTime  HotBarP  MatTemp          Fit       Fit  Desirability

1         225      0.449575  0        115.826     0.800000   26.0000       1.00000

 

 

Multiple Response Prediction

 

Variable  Setting

HotBarT   225

DwelTime  0.449575

HotBarP   0

MatTemp   115.826

 

 

Response       Fit  SE Fit      95% CI          95% PI

VarStrength   0.80    2.33  (-4.13,  5.73)  (-4.70,  6.30)

Strength     26.00    8.95  ( 7.03, 44.97)  ( 4.86, 47.14)

Graph Window Output

Interpreting the results

The individual desirability of both the seal strength and the variance in seal strength is 1.0. Therefore, the combined or composite desirability of these two variables is 1.0.

To obtain this desirability, you would set the factor levels at the values shown under Solution. That is, hot bar temperature would be set at 225.000, dwell time at 0.449575, hot bar pressure at 0, and material temperature at 115.826.

If you want to adjust the factor settings of this initial solution, you can use the plot. Move the vertical bars to change the factor settings and see how the individual desirability of the responses and the composite desirability change. For example, you may want see if you can reduce the material temperature (which would save money) and still meet the product specifications.

The response optimizer uses model equations. Ensure that your models are adequate before you interpret the results.