The six big losses
One of the major goals of the OEE and TPM (Total Productive Maintenance) programs is to reduce and / or eliminate the six major losses. These are the most common causes of loss of manufacturing efficiency. The following list shows the 6 Great Losses, and relates them to the OEE categories:
MANAGEMENT OF THE SIX MAJOR LOSSES
Now that we know they are the Six Big Losses and some of the events that contribute to these losses, we can focus on ways to monitor and correct them, many of them in Real Time. Categorizing these losses makes corrective analysis much easier, and a key objective should be to collect data quickly and efficiently, instead of waiting for the time to perform the analysis (end of shift, day or even worse) , at the end of the week).
1. Unscheduled Stops
Eliminating or minimizing Dead Times by Unscheduled Stops is critical in improving the OEE. Other factors of the OEE should not be analyzed if the machine is stopped by any of these shutdowns. Not only is it important to know how much downtime is being taken in the process (and when), but also the causes attributable to specific sources of Loss Reasons (Reasons for Unemployment). Once dead time and stop reasons are tabulated in a table such as XL Lean Tool, it is easier to apply Root Cause Analysis to the most severe cause in this category.
2. Product Changes and Adjustments
Product changes (Set Up) and adjustments are generally measured as the time between the last good unit produced before the Product Change to the first consistently produced good unit that meets the requirements and quality standards.
Taking the preparation time for Product Change is critical to reduce this loss. Next to the measurement a program must be activated to reduce this time (the most popular one is the SMED program: Single Minute Exchange of Dies)
Many companies use creative methods to reduce the Time of Change including previous assemblies, carts with tools and necessary parts for the change in a place, tools pre-adjusted with marks to avoid adjustments in the site, and use of prefabricated meters.
ALWAYS take programs such as SMED the same as Formula 1 cars take PITS. The XL Lean Tool is like the stopwatch that helps improve times.
3. Small Stops and Reduction of Speed
Small changes and reduced production speed are the most difficult losses to monitor and record. The Time Cycle analysis should be used to identify these types of losses. In many processes, recording data for Time Cycle Analysis needs to be automated since the cycles are very fast and the events are very repetitive, so they do not leave the adequate time to keep a manual record.
Comparing all the completed cycles with the Ideal Time Cycle and filtering the data with the Small Stop threshold and the Reduced Speed threshold of the XL Lean Tool it is very easy to automatically categorize these stops to analyze them. The reason for analyzing the Small Paros separately from the Reduced Speed is that the root cause is typically very different, as can be seen in the examples of Events in the Previous Table.
4. Rejects at startup and during production
Rejects at start-up and during production must be differentiated, as the root cause is often different between start-up and stabilized production. The parts that require re-work of any kind must be considered as rejections. Recording these rejections during a shift or work can help identify potential causes and, in many cases, you can discover certain patterns.
Often a Six Sigma program can be used, where a common metric is to reach a defect ratio of less than 3.4 defects per million, and focus attention on a goal to achieve near-perfect quality.