1. At its most basic, overall equipment effectiveness (OEE) is a simple calculation that can be the foundation of great process analysis. It is used to evaluate one machine, one station, or an entire factory.
2. It’s understandable by operations, engineers and executive management, and it can guide real-time and long-term process improvements.
MEASURING OEE
1. There are three factors that go into calculating OEE: availability, performance and quality.
2. Availability: Is the line/station/machine operating? As an example, consider:
- Planned downtime: Rest and lunch breaks = 90 minutes/shift
- Unplanned downtime: Unexpected maintenance = 60 minutes
- Total downtime: 150 minutes
- Actual run time (330 minutes) / planned run time (480): 68.8 percent availability
3. Performance: What are the product completion rates (throughput)? Performance is based on availability because your throughput is inherently limited by hours available.
- 100 percent performance: 1 can of cola per second: 330 minutes of available time = 19,800 cans of cola
- 66.7 percent performance: 1 can of cola per 1.5 seconds
4. Quality: How many completed products met their specifications?
- Quality Score: 19,800 total production – 4,000 defective products / 19,800 = 79.8 percent
5. The OEE score is 36.7 percent, which is figured as availability (68.8 percent) x performance (66.7 percent) x quality (79.8 percent).
6. According to LeanProduction.com, manufacturers typically fall within the 60 percent range. If you’re scoring 85 percent or above, you’re exceptional!
ISSUES IMPACTING OEE
1. Unplanned stops: equipment failures, starved stations or unplanned maintenance.
2. Planned stops: changeovers, machine cleaning, tooling swap outs, etc.
3. Small stops: minor or idling stops usually less than two minutes that could include things like a sensor obstruction, jams, feeds, etc.
4. Slow cycles: anything slowing the production time from its maximum speed, like a worn out conveyor belt, poorly maintained equipment or an inexperienced machine operator.
5. Process defects: defective parts produced during stable production due to equipment handling errors or incorrect equipment settings.
6. Reduced yield: defective parts produced after an equipment failure until equipment has returned to a steady state.
BENEFITS FROM MEASURING OEE
1. Plants typically work quickly to identify and attack problems, but fail to take the time to understand what’s at the root of the problem. OEE can provide visibility to both the big picture and the details.
2. By measuring OEE, you can identify your potential losses and understand where you’re falling short. Is it performance, quality or availability? From there, you can pinpoint the problem and correct it.
3. OEE provides valuable insight to in-depth process analysis, like root cause, where operational studies are required rather than quick fixes. The following sections provide examples I’ve seen where plants used their OEE data to improve availability and performance.
REDURING DOWNTIME (With station-specific OEE metrics)
1. One automotive manufacturing customers was having unexpected downtime issues that turned out to be related to their assembly line tool track.
2. Using station-specific OEE metrics, they identified an operation that was frequently experiencing small stops. Upon further investigation, they realized that when vehicles advanced beyond a certain point in that operation, the torque tool hose reach was too short.
3. When the torque tool could no longer reach the desired part, the line would stop. This is the kind of thing that’s likely to be accepted as an inherent, structural limitation and ignored. The longer an operator experiences it, the more they’ll take it for granted as an unavoidable stoppage.
4. To eliminate this downtime, we simply rewrote the customer’s automated work instructions to begin torquing the part earlier in the line. This was a quick change that improved availability at minimal cost. Without the station-specific OEE metrics, it might not have been identified as a root cause.
IDENTIFY AND CORRECTING PERFORMANCE SHORTFALLS
1. OEE is also a great tool for gaining larger scale insights, like comparisons of shift productivity.
2. One customers needed to increase line speed from 17 jobs per hour to 23 jobs per hour. One shift had production rates considerably lower than the other. Possible causes included a lack of operator training, lack of just-in-time parts, or machine faults. Without specific data, it was hard to know where to start.
3. OEE was evaluated for operators, machines and operations, and ultimately they were able to determine that the issue was cycle slowing caused by insufficient operator capability on the second shift. Second-shift operators were given additional training and performance targets were reached.
SOLVE REAL-TIME PROBLEMS
1. OEE data is not only valuable for longer-term studies and analysis; it can have real-time and near-real-time impact.
2. Your method of communicating OEE data will influence its effectiveness.
3. Plant floor PLC data blocks can drive machine data to a cloud-based or locally hosted server database.
4. If you’re using the Industrial Internet of Things (IIoT), you’re already gathering that data into your information infrastructure.
CHALLENGES OF MAINTAINING AN OEE FRAMEWORK
1. The deployment of a robust OEE monitoring system cannot be just restricted to putting a data processing and analysis software in place. As a plant expands, the OEE solution needs to organically evolve, with repeated installations and setup procedures being carried out with each evolving, and new machine unit.
2. Caution should also be exercised while amalgamating the OEE solution in existing legacy systems, in order to preserve their security and integrity. A scalable and sustainable OEE monitoring platform will also ensure that minimum support and maintenance is required.
3. Manufacturing often involves recurrent product changeovers, and shift changes, sometimes spanning 24 hours a day, seven days a week. An OEE solution must seamlessly integrate such variable work patterns.
4.In a manufacturing plant, every operation has an available scheduled, along with some planned downtime for equipment and product changes, and maintenance. Time is also spent in in the event of technical breakdowns, apart from idling and minor stoppages.
5. Unplanned time loss affects production speeds and can very well have undesirable effects on production quality. OEE is that singular KPI which factors in all these variables to provide an en courant understanding of overall performance
6. And in a smart manufacturing environment, it holds the potential to supersede fallibilities, achieving near perfect production cycles.
Source:
https://www.automationworld.com/products/software/blog/13316309/how-to-make-use-of-oee
https://www.ltts.com/blog/measuring-oee-automated-manufacturing-environment
