What’s a micro-stop, and how is it important to you?
Author – Tim Smith
ei3 Corporation, in their article, “What are micro-stops, and how are they detected?” Interpret micro-stops as “minor stoppage losses that occur when a machine stops for a short time due to a temporary problem.” The short article is quite good in explaining the relationship between a stop affecting utilization. After all, it is associated with a downtime event, or it affects performance because it is considered uptime and therefore extends the cycle time. Users of monitoring systems report that the accumulation of otherwise innocuous and minor stops accounts for hundreds of hours of lost production time.
The challenge with attributing the stop to a downtime event is that these minor stoppages are usually ignored by engineers looking for more significant downtime events with much higher durations. When micro-stops are identified as downtime events, they are generally overlooked as process events affecting cycle time and performance. Many micro-stops are events related to ongoing material conveyance or non-value-add tasks such as blowing chips, changing chip bins, swapping parts, etc. These activities are all necessary, impacting efficiencies, but cannot be eliminated. They affect performance by adding time to cycle time. The traditional method of identifying these performance stealers is to perform a time study on the process. But studies have shown that the very act of performing a time study impacts the study results.
To have an accurate picture of the process, one must collect the process data autonomously through machine monitoring systems. However, almost all such systems only treat these downtime events as an availability impairing metric and not as a necessary performance degrading event. If the system is sophisticated enough, it can be configured to forego recording these events, leaving the cycle time pegged as uptime, thus masking a potentially significant problem. Platforms such as Memex’s MERLIN Tempus are configurable and can be set up to see the micro-stop event. If a time threshold is reached, it can be instructed to change the micro-stop event to another event type. An example is when an operator opens the machining envelope door every ten parts and blows out the chips. The original time study put the procedure at 15 seconds. However, the “door open” event is recorded as an event lasting upwards of two minutes. To classify the event as a downtime affecting utilization is incorrect in that there are fifteen seconds which is considered part of the process or procedure to make parts. The first fifteen seconds of the “door open” event is not a downtime event. However, the following 110 seconds is an unplanned downtime state. MERLIN can be configured to process the first fifteen seconds of the “door open” event as a “remove chips” event set to a neutral category which neither impacts the availability (Utilization) nor the Performance metrics. Then, once the 15 seconds have expired and the machine is still in “door open,” the system will revert the state to “door open” classified as a downtime state, which will now impact utilization.
The value of being able to collect true micro stops and to reclassify stops longer than anticipated allows for the identification of chronic downtime events and validation of previous time study of non-production process events. Each is addressed differently by the CI engineering teams. In the example of blowing chips, if the event is chronically taking longer than expected, an investigation could prove low pressure in the lines, larger chips due to a tooling change, not enough cutting fluid being applied, cutting fluid nozzles plugged, or the operator requires more training. If the chip removal process is based on an active optional stop, switching to door open, possibly there will be a pattern where, even though optional stop is triggered, the door is only opened every other time the machine goes into optional stop, signifying that the operator is kipping a chip removal exercise and therefore accumulating a large number of chips by the time he does remove them, taking more time than usual. Accurate recording of micro stops provides evidence for the identification of the root cause. The system you employ must be flexible enough to be configured to respond to micro stops, re-evaluate them and reclassify them dynamically in real-time, to collect accurate information. Furthermore, the system must be able to trigger real-time responses such as texts and emails and visuals in response to dynamic changes. This is called situational awareness.
Such systems as Memex’s MERLIN Tempus provide this level of comprehensive flexibility right out of the box. The ability of a system to infer a state based on occurring states and standards removes a level of operator dependence. The antiquated operator-centric data collection approach is inherently inaccurate because events are recorded after the fact and are usually very subjective. Realtime operator classifications of machine impacting states are faster, simpler, controlled and accurate because the machine initiates the state change based on an autonomous event and applied logic. The resulting record of the micro stop event, in this case, is easy and requires minimal effort by the operator to respond. Based on rules derived from logic the states accurately reflect the positive, neutral, or negative impact of events, providing dramatically more accurate metrics than simple utilization monitoring packages.
This approach reveals a whole host of potential scenarios which can rob an operation of production time. From blocked and starved conditions to personnel or procedural constraints, through to process impairments or chronic and acute downtime events, the level of detail will provide the needed information to drive impactful continuous improvement within your organization. Micro stops are robbing your organization of valuable production time, resulting in loss of throughput, delayed delivery time, quality issues and loss of customer confidence, all affecting the bottom line. Micro stops and the ability to identify them and remove them should be very important to you.