Lesson #4 - Tool #1 - Check Sheet

Tool #1 - The Check Sheet As previously mentioned, the intent and purpose of collecting data is to either control the production process, to see the relationship between cause-and-effect, or for the continuous improvement of those processes that produce any type of defect or nonconforming product. A Check Sheet is used for the purpose of collecting data to compile in such a way as to be easily used, understood and analyzed automatically. The Check Sheet, as it is being completed, actually becomes a graphical representation of the data you are collecting, thus you do NOT need any computer software, or spreadsheet to record the data. It can be simply done with pencil and paper! Check sheets have the following main functions: 1. Production process distribution checks - where the distribution lies. 2. Defective item checks - to determine what kind of defects exist in the process. 3. Defect location checks - to determine where the common defects on a part are located. 4. Defective cause checks - type of defect and thus validate the cause thereof. 5. Check-up confirmation checks - final phase of assembly to check the finished product or work. The methods that we will concentrate on and utilize here will be for Production Process distribution and defective item checks. We will discuss the use and relevance of each individually. Defective Item Check Sheet In order to reduce the number of defectives produced, it is necessary to know what kind of defects were produced and the percentage in relation to production. Since every defect has a different cause, it is useless to just list the total number of defects, therefore, we have to find the number of defects caused by each category, and then we have to decide the appropriate action to take to resolve those defects. The appropriate action to take is to pick the top two or three problem areas, and then focus to resolve them. In our example, we have charted some defects from an alternator production line. (To view our example iplease click HERE).    Whenever a defect was discovered, the operator would make an entry in the appropriate column, an "X", check mark or merely a single line for each occurrence. At the end of the day, it can be easily determined what the main problem was for that day just by looking at the graph that was created from the recorded marks. If this is done every day, and on every shift, over the course of a week we can tell what the common problems were, and what problems seemed to be our biggest headache that requires our primary focus. However, it is worth noting that the defects attained on one line, may not be the same as those encountered on another line and similar production line. It may also be that the defects experienced on the day shift, may not be the same defects experienced on the night shift, on the same line and with the same product. Different people, different products, time and temperature are all factors that could cause a different set of circumstances for defects to occur. For that reason, each shift or each line, should have it's own study performed. Once the shift was over and the totals are tallied, you can see from our example that we had two main problems to focus on. These totals, taken from the 8 main categories, will be charted in a Pareto chart, as you will see when you visit the Pareto lesson. Production Process Distribution The size, weight, or diameter of parts, for example, are known as "continuous data". In a process where these types of data are gathered, the distribution they provide will often resemble a Histogram (Histogram is Tool #3). A histogram can be used to investigate the distribution of the process characteristics, and the average value can be calculated. If you click HERE, you can see a sample Production Check Sheet. In this sample sheet, we measured torque readings. The spec limit is 2.2Nm ± .5. From the example sheet, you should see two dark vertical lines, on the left side it is labeled LSL (Lower Spec Limit) which indicates the 2.2 - .5, or 1.7. On the right side, another dark line marked USL (Upper Spec Limit) which indicates the 2.2 + .5, or 2.7. All product readings, or torque readings in this example, that conform (actually good product), need to fall within these limit boundaries. Anything that is measured outside these limits is termed "Non-Conforming" since they are not within proper specification limits. Every time a measurement was taken, an "X", or check mark, was made on the check sheet. From this sample sheet, you can see where most of the torque readings lie, the consistency of the distribution, and how many are actually outside the spec limit. What has also been created here on this Check Sheet is a "Histogram". We will discuss Histograms in a later lesson. Right now, what is important to note from this example chart is that we do not have a good stable process. The distribution is widespread and not well centered between the specification limits. The distribution has dual peaks, or is what is known as "bi- modal". Bi-modal means that there are two points where most of the readings taken are charted, or that is has two peaks. This means the frequency of readings rises and falls twice, rather than a more proper and even distribution with one peak. To illustrate further, I have taken the same data and plotted that in a bar graph to show you the physical appearance just as if it were plotted using Excel. You can see that this looks much like the hand drawn chart that was made in our example. Notice also that you can see two distinct "peaks" separated by less frequent readings in the middle of the two peaks. For a Blank copy of the Defective Item Check Sheet in Excel, Click ON THIS LINK. For a Blank copy of the Production Process Check Sheet in Excel, Click ON THIS LINK