When a manufacturing process stops for an unplanned event (e.g., a motor failure) it accumulates down time. While down time is most often associated with equipment failures (breakdowns), it actually encompasses any unplanned event that causes your manufacturing process to stop. For example down time can be triggered by material issues, a shortage of operators, or unscheduled maintenance. The unifying element is that although production is scheduled, the process is not running due to an unplanned stop.
By way of contrast, a planned stop is any event where the process is unavailable to run due to a preplanned activity, such as a changeover or scheduled maintenance.
Defining Down Time
In order to measure down time accurately it is important to create a clearly defined standard and then consistently apply that standard (over time and across equipment). It is particularly important to define the difference between down time (an OEE Availability Loss) and small stops (an OEE Performance Loss). A good way to do this is to define a time-based threshold that differentiates between down time and small stops, based on the idea that a reason should be captured for every down time event, whereas it is not expected to capture a reason for every small stop. This time-based threshold can be based on absolute time or relative time.
For down time we recommend the following simple definition based on absolute time:
Down time events are unplanned stops that are long enough that we assign a reason for each occurrence. In practice, we define down time as any unplanned stop that is five minutes or longer.
An alternative definition, based on relative time, integrates Ideal Cycle Time (the theoretical minimum time to produce one piece) into the definition. For example:
Down time events are unplanned stops that last for more than 100 manufacturing cycles (i.e., are 100 times longer than the Ideal Cycle Time).
Effects on Manufacturing Productivity
For most manufacturers down time is the single largest source of lost production time. It receives a high level of attention since equipment failures and breakdowns are highly visible (nothing is more frustrating than watching manufacturing equipment standing idle). As visible as down time is, an amazing number of companies significantly underestimate their true down time – especially when they estimate their down time or manually record down times for each occurrence. Fortunately, this is an easy problem to fix (through simple automation as described later).
If your manufacturing process includes multiple pieces of equipment (such as in a packaging line) it is very important to focus attention on the constraint of the process. In particular, focus on down time:
- At the constraint itself (e.g., in a bottling line the constraint is often the filler)
- At upstream equipment that does down and starves the constraint
- At downstream equipment that goes down and blocks the constraint
Focusing improvement efforts on the constraint ensures optimal use of resources and is the most direct route to improved productivity and profitability.
From the perspective of Overall Equipment Effectiveness (OEE) and Total Equipment Effectiveness (TEEP), down time is captured as an Availability Loss. From the perspective of the Six Big Losses, down time is captured as an Unplanned Stop.
Manufacturing Best Practices
The ultimate best practice for reducing down time is Total Productive Maintenance (TPM). TPM emphasizes proactive and preventative maintenance to maximize the operational efficiency of equipment. It blurs the distinction between the roles of production and maintenance by placing a strong emphasis on empowering operators to maintain their equipment. TPM has many elements: 5S, Autonomous Maintenance, Planned Maintenance, Quality Integration, Focused Improvement, New Equipment Management, Training, Education, Safety, and more. In fact, both OEE and the Six Big Losses are originally from the world of TPM.
Implementing TPM is a substantial task that involves high levels of support from executive levels of an organization. If you don't currently have the resources to commit to a TPM program, here are four proven best practices that are very effective as quick wins for reducing down time.
Four Great Strategies
Four highly effective strategies for reducing down time are:
- Track Down Time Accurately
- Categorize Down Time with Reasons
- Expose Down Time in Real-Time
- Attack the Largest Sources of Down Time
Track Down Time Accurately
Problem: We are not sure if our down time numbers are accurate. As a result, when we're reviewing our losses we don't know if we're working on the right things.
Strategy: Replace manual tracking of down time with automated tracking of down time (track down time based on equipment inputs rather than operator tick sheets).
Solution: XL automatically detects down time using a single input from your equipment (usually an existing sensor that counts parts or equipment cycles). XL records every down time event with sub-second accuracy. The XL scoreboard shows down time in real-time on the plant floor and XL provides down time information to employees everywhere using patented technology and its integrated web server.
Categorize Down Time with Reasons
Problem: We are having trouble prioritizing improvement actions because we don't have good enough information about why our equipment isn't running.
Strategy: Capture reasons for each down time event.
Solution: It is essential to capture a reason for every down time event to help you prioritize actions. XL makes this very easy – simply type in your down time reasons and XL automatically generates a barcode sheet. Your operators scan barcodes to indicate reasons for each down time event and XL automatically “snaps” reasons to the appropriate down time event. We recommend starting simple – no more than 25 reasons, one of which should be ‘All Other Losses’.
As a best practice, make sure that every reason is clear (when looked at in the context of other reasons) and describes a symptom (as opposed to attempting to diagnose a root cause). Remove reasons that are rarely used and add reasons as needed to ensure that ‘All Other Losses’ is not in the top ten losses.
Expose Down Time in Real-Time
Problem: We have multiple manufacturing lines, so it's hard for us to know where to focus our attention. We have reports about what happened in the past but we want to know where our biggest problems are right now – so we can fix them before they affect our numbers for this month.
Strategy: Create a dashboard that shows you the instantaneous “right-now” status of your entire plant (including which lines are down).
Solution: XL tracks the current state of every monitored production asset. Any combination of real-time metrics can be shown to give you whatever context you need for effective decision-making. Information can be viewed hierarchically (e.g., by department), and color is used to show the real-time “right now” status of each production asset.
Attack the Largest Sources of Down Time
Problem: Now that we are accurately tracking our down time (with reasons), we want a simple but systematic approach to reducing down time.
Strategy: Use top loss information to systematically attack your largest sources of down time.
Solution: XL provides rich reporting and strong insights about where you are losing the most productivity. Use the Top Losses report to identify which down time reason to attack next. Here's how:
- Set the Date Range to Last 30 Days.
- Set the View to the appropriate shift and select Show Only Down Time Losses.
- Identify one loss within the top five that the team feels confident they can improve.
- Agree on an improvement target and any external resources needed to reach that target.
Post the report in the area. Review progress by monitoring Top Losses information.
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