|Nutek, Inc. Quality Engineering Seminar, Software, and Consulting ( Since 1987) Site: Examples|
Case Study 1: Vane Pump Cylinder Block Process Parameter Study
|Review and print Sample Problem Solving Project Reports: Report-I, Report-II|
About the Case Studies
The DOE application case studies included above are all actual experiments conducted by industrial practitioners. Because of proprietary nature of the projects, the names of owner companies and the specific objectives have been purposely altered. Each experiment adhered to the application steps and attempted to satisfy the purpose of the studies. The description of the case studies listed above, include project specifics in each of the application steps outlined here. (All experiments were designed and analyzed using Qualitek-4 software)
If you are starting out with your first DOE application, read the case studies to see how it is done typically, but stick to the following guidelines and seek out answers to questions posed in each of the steps. The guidelines presented below are intended for readers who have either completed a course (seminar) on DOE/Taguchi Approach or otherwise familiar with the technique.
I. PLANNING - This is the most important step in the application process. For better results, planning must be done with the project team and all things must be decided by consensus. The project objectives, how the objectives are evaluated, factors involved in the project, etc. are determined in this session. (See below for a detailed agenda of discussions)
II. DESIGNING EXPERIMENTS - Based on the factors and levels identified in the planning session, the experiment is laid out for the project. In the Taguchi approach, most experiments can be designed using the Orthogonal arrays (L-4 through L-64) prescribed Dr. Genechi Taguchi. Some situations with mixed level factors can be designed by minor modification of the standard Orthogonal array.
III. RUNNING EXPERIMENTS - The designed experiments
are carried out as per the recipe prescribed by the Orthogonal array. When the project
objectives includes seeking ROBUST design, experiments must be carried out by exposing
them to the conditions of the Noise factors as specified by the Outer array, In all cases,
a random order is preferred for carrying out the experiments.
IV. ANALYSIS OF RESULTS - The first thing to do
before analyzing results is to decide what to do about multiple criteria of evaluation.
The thing to remember is that, as far as DOE analysis is concerned, you are only allowed
one numeric data for each sample. So, in case there is more than one objective, you will
have the option to analyze each criteria at a time, or combine them all into one single
Overall Evaluation criteria (OEC). You need not worry about this
task if you are after only one thing and there is only one type of result you recorded.
VI. CONFIRMATION OF IMPROVEMENT - This includes running a number of samples at the optimum condition and comparing the average result with the expected performance. If the mean of the sample performance falls within the C.I. on the expected performance, Running confirmation experiment is a must even if you have a strong background in DOE and have a high degree of confidence in the conclusions. It is a necessary verification exercise that enhances your confidence in the technique, and may even help you earn some credibility with your team members.
I. PROCEDURE FOR EXPERIMENT PLANNING (Brainstorming)
Experimental designs produce most benefits when they are planned carefully. For proper planning it is necessary that a special session is dedicated to discuss various aspects of the project with the project team and that all decisions are made by the group consensus. The project leader should arrange for the planning session, and when possible, have someone who is not involved in the project, facilitate the session. Following are general guidelines for contents and nature of information sought.
a) Project Objectives ( 2 - 4 hours)
b) Factors (same as Variables, Parameters, or Input, 1 - 2 hours)
c) Levels of the Factors ( 1/2 hours)
d) Interactions (between two 2-level factors, 1/2 hours))
e) Noise Factors and Robust Design Strategy ( 1/2 - 1 hour)
f) Experiment and Analysis Tasks Distribution (1/2 hours)
(Details of other four steps in applications tend to be specific to the project and can be found in the individual case studies presented earlier)