(Illustration) Optimize the results

Optimize the results.

Instructor : Welcome to Step Two. In Step One we narrowed the vital X's down to three. The nut type, the installation torque force, and the interaction between those two factors. Here in this Step , we'll determine the actual changes to be made in the process, primarily by quantifying the continuous variable, the Installation Torque Force, and its relationship to the Nut Removal Time, or Y.

Instructor : Let's look at the learning objectives for this step. When you finish this step , you will be able to perform Optimizing experiments in order to develop the deliverable, which is the proposed solution.
Instructor : Describe considerations and potential trade-offs involved in reducing the number of experiments.

Instructor : Once you know what you are going to change, you can narrow your focus to determine what the precise changes will be. Let's return to the Rockledge case and see how that exercise plays out.

Instructor : Screening DOE provided enough information for us to determine that we will change to the new Torque-Master nut. The question now arises as to what our optimum torque force setting should be used during installation. We received some indication in previous step , but not enough.
Instructor : In order to determine this information, we will run an experiment using the both the regular nuts and the Torque Master nuts installed with a larger number of torque settings covering a broad range. To interpret the data we will run a Regression Analysis. Each analysis will be a one factor, multi level analysis designed to optimize the torque force for each nut.

Instructor : Let's briefly discuss our experimental parameters:
Instructor : We will conduct a total of thirty runs
Instructor : Fifteen runs will use the current nuts
Instructor : and fifteen will use the Torque Master nuts
Instructor : Each nut will be installed either two or three times at torque settings of fourteen, fifteen, sixteen, seventeen, eighteen, and nineteen thousand foot pounds.

Instructor : Before we continue, let's briefly discuss some issues which may impact your experimental design.
Instructor : While exhaustive testing may be desirable, budgetary considerations may require you to reduce the number of experiments. There are statistical approaches such as the fractional factorial design which can assist you in this task.
Instructor : It will take a certain number of person-hours to run each experiment. This may be another limiting factor.
Instructor : In a situation like the Rockledge case, a solution must be implemented in a timely fashion, or the project objectives will not be met. Your experimental design must take this into account.
Instructor : Depending on your process, there may be a number of other resources which can limit your experimental design. You will have to accommodate them when you reach this stage of the project.
Instructor : As discussed earlier, the full factorial test may require a large number of runs as the number of factors and levels increase. If you need to reduce the number of experiments, you can use a fractional factorial design, which involves,
Instructor : selecting and testing an appropriate sub-set of all possible combinations of factors. This design may also be applicable in the screening process of step one as well.
Instructor : A trade off in using only a sub-set of possible combinations is that we will lose some information about the interactions among factors. Techniques and tools to aid you in selecting the appropriate design will also be covered in further training.

Instructor : At this point, we have run the thirty tests and entered the data into MiniTab. If you look at the worksheet, you will see that
Instructor : Columns C four and C five refer to the test performed with the original nuts, and
Instructor : Columns C six and C seven address the tests performed on the Torque Master nuts. Now we are ready to perform the actual analysis
Instructor : As a preliminary, we will first do a simple plot of the data and see if it shows any discernable trend or curvature. This will determine the specific regression analysis we perform.
Instructor : From the MiniTab menu, select the Graph Menu and then Plot.
Instructor : The dialogue box for plot allows you to generate multiple X Y graphs at one time.
Instructor : Each graph is entered on one line in the Graph Worksheet. The next step is to define the two graphs.
Instructor : Our first graph will look at varying torque levels with the current type of nut.
Instructor : The Y axis is the nut removal time with the current nut,
Instructor : and the X axis is the torque force used.
Instructor : Likewise, the second graph covers the Torque Master nut.
Instructor : With the Y axis showing nut removal time,
Instructor : and the X axis the torque force.
Instructor : Now, when you click on OK, the following graphs are generated.
Instructor : As you can see, the two graphs are similar in shape. The shape is what we're interested in right now.
Instructor : It's obvious that there is no way a straight line could come close to intersecting all of the points on any one of these graphs. So what does this mean?
Instructor : The fact that the relationship is not linear determines which tool will give you the most accurate and usable results when you generate your solution.

Instructor : From the stat menu, choose Regression.
Instructor : From the Regression sub-menu, choose Fitted Line Plot. This is the decision driven by the apparent curvature of the relationship shown in the initial plot.
Instructor : By now, the MiniTab selection menu should be very familiar. First, we will test the Torque-Master nuts at varying levels of torque.
Instructor : Select Column C seven, the Torque-Master removal time for the response variable, or Y.
Instructor : Select Column C six, torque two, for the predictor, or X
Instructor : Select a Quadratic plot to account for the expected curvature of the line and
Instructor : then click on Options
Instructor : From the Options menu, make sure that all of the boxes in the Transformations section are unchecked.
Instructor : Make sure your Confidence Level is set at ninety five point zero, or ninety five percent. This is the accepted convention, and we will commonly accept it as our default.
Instructor : Click on O K to return to the Fitted Line Dialogue Box and then O K from there to generate the graph.
Instructor : Click Next to see the results.

Instructor : The regression plot shows the actual transfer function directly above the graph. In this case, is a quadratic equation that describes the curve of the graph. This transfer function is this Step deliverable which is used in next Step to set the implementation parameters.
Instructor : The lowest point on the graph, which corresponds to the lowest nut removal time, is at an installation torque of seventeen thousand foot pounds. So based on the transfer function, the torque set at seventeen thousand foot pounds will provide us with the lowest removal time.
Instructor : This reading is also well below the upper specification limit of thirty minutes, and even exceeds our target of fifteen minutes.
Instructor : Just to validate our impression, we ran the same exact test with the regular nuts. Click next to see the results.

Instructor : The shape of this graph is similar to that for the Torque-Master nuts. The difference is that none of these readings are below the
Instructor : upper specification limit. This tells us that even if we optimize the installation torque force, it will be impossible to meet our project objectives without changing the nut.
Instructor : Click Next and we'll look at the results of this step.

Instructor : On the left hand side of the screen are two columns. The left hand column represents information that was present at the beginning of this Step and the right hand column represents information that was produced during the Step. At the right are four different pieces of information. Please drag each of the four to the appropriate column. When you are finished, click on DONE to submit.

Instructor : So the summary of the Step is that we accept the Vital X's identified in Step one and determine what actual changes in those Vital X's are necessary to meet our project objectives.

Instructor : Remember when we looked at the process capability of the Nut Installation process and determined that it was already a six sigma process? So we concentrated on improving the Nut Removal process and have determined what changes are required.
Instructor : However, the changes required to improve the Nut Removal process must all be implemented in the Nut Installation process!
Instructor : While our experiments measure the Nut Removal time as the Y factor,
Instructor : The experimental variables, or X factors,
Instructor : Were all implemented in the Nut Installation process.
Instructor : So another valuable lesson learned from this case was
Instructor : Keep the big picture; the entire process map, in mind even as you concentrate on improvements targeted at a single sub-process. So the concept of process mapping discussed in the Define and Measure Phases, becomes a critical element when we implement our improvements in order to impact the CTQs and meet our project goals.

Instructor : So what are our conclusions at the end of Step ? They consist of a proposed solution to our project task.
Instructor : In this case, the first of these deliverables is the requirement to change from the standard nuts to the Torque-Master nuts.
Instructor : The other change requires that the Torque-Master nuts be installed to a torque of 17,000 foot pounds. This was confirmed by our regression analysis earlier. With these changes implemented, we expect to reduce our average nut removal time to less than twenty minutes.
Instructor : We're almost done with the Improve Phase. There's only one thing left to do, and that's to provide the tolerancing information necessary to translate these changes into procedure documents for the shop floor.
Instructor : Be cautious when using the preliminary transfer function. It is limited in that it will not reveal any curvature. We use it to help identify a Vital X, but not to optimize the actual setting.
Instructor : You can use optimization DOE or other tools to optimize the setting of a Vital X.