Flexible manufacturing and automation allow a system to run lean and adapt to daily part mix variations, but increased flexibility with more pallet-machine combinations provides challenges for quality control. Without proper management, this tension between quality and operations risks either drastically reducing OEE or sacrificing quality. With proper tracking, analysis, and tools we can achieve high quality parts while maintaining great machine utilization.
Flexibility and Quality
From a daily operations perspective, full flexibility with every pallet allowed to every machine is the simplest design since it allows the machines to always be cutting material. From a programming, inspection, and quality perspective, restricting each part to a single pallet-machine combination is the simplest design since only a single program, offsets, and tools need to be checked and improved. As mentioned in the flexibility tactic, with the right techniques the day-to-day operation of the cell can run efficiently with less than full flexibility; typically we see that about 20% of the work needs to be flexible (although each system is different). We therefore advocate for a design where first the flexibility plan is developed where the flexibility is reduced as much as possible without impacting the daily machine OEE. (A small safety margin of flexibility should also be added.) Once the flexibility plan is implemented, tools and tracking can help the inspection operators and quality engineers understand and iteratively improve the part-programming to ensure that parts are consistently produced with high quality.
Paths and Inspection Frequencies
A path for a part type is a combination of pallet and machine for each
process. For example, if process 1 could be on pallets 1 or 2 and go to machines
1, 2, and 3 and process 2 could be on pallets 3 or 4 and go to machines
4, 5, or 6, there are 36 possible paths: 6 choices for process
1 (P1-MC1, P2-MC1, P1-MC2, P2-MC2, P1-MC3, P2-MC3) and similarly 6 choices for process 2.
The flexibility plan might restrict that if process 1 is on pallet 1 then process 2
is on pallet 3 and if process 1 is on pallet 2 then process 2 is on pallet 4, reducing the number of paths to
6 * 3 = 18.
(Although simulation should be used to ensure this flexibility restriction does not impact OEE.)
Inspections and quality analysis should be focused on ensuring that each path
produces a quality part. To do so, once material is
tracked, SeedTactic: OrderLink and SeedTactic: FMS
Insight are aware of paths and incorporate them into inspection signals. The
quality engineer can enter an inspection frequency per-path. For example, say
that we want every fifth part inspected. FMS Insight will track each path and
every fifth part on the path will be signaled for inspection. That is, say that
a part was just completed and used path
P1-MC2;P3-MC4 (process 1 on pallet
1 to machine 2, process 2 on pallet 3 to machine 4). FMS Insight will check
past completed parts that used this specific path
P1-MC2;P3-MC4 and find
the last time a part on this path was signaled for inspection. If 4 parts on
this path have been machined and not inspected, the part being unloaded is
the 5th part on this path, is signaled for inspection, and FMS Insight
displays a message to the operators. This tracking happens for each of the
possible paths automatically.
To account for rare paths, OrderLink and FMS Insight also support a maximum time since the previous inspection per-path. For example, say we want to ensure that each path is inspected at least every 5 days. When a part is completed, FMS Insight searches for past parts produced on the same path. If it has been more than 5 days, the part is automatically signaled for inspection (even if the part has been produced on a different path within 5 days).
For quality review, FMS Insight provides statistics and reports per-path. The quality engineers can view the paths that are used, the total number of parts machined on each path, the inspected parts on each path, and importantly the parts failing inspection on each path. This allows the quality engineers to identify if a problem is path/offset specific or if a problem is general to the program irrespective of pallet and machine. Quality engineers can also run experiments by adjusting the inspection frequencies individually for each path and having the new inspection frequencies automatically implemented on the factory floor.
We encourage inspections to happen at a separate location and not at the load/unload station. Inspections at the load station increase load/unload time and have the potential to cause pallet traffic jams by preventing the pallets from flowing properly. While using simulation it is possible to design a system with inspections included as part of the load/unload process, it is simpler to inspect at a separate stand located near the cell. FMS Insight's serials and part tracking ensure that the data about the specific material to be inspected is retained even if the part sits on the floor at the inspection inbound for a while.
At the inspection stand on the factory floor, a computer/tablet and handheld barcode scanner should be installed. The inspection operator can then scan the barcode (or manually enter the serial) and FMS Insight will bring up the production history for this material and any inspections that have been signaled. FMS Insight then allows the operator to mark the inspection as successful or failed.
Quarantine Bad Parts
When an inspection fails, you might want to find and quarantine similar parts
that might also exhibit the problem. FMS Insight supports this by allowing
you to enter a serial or scan a barcode and then search for parts produced at
similar times on the same path. For example, say that a part with serial
ABCD is marked as failed. FMS Insight will search for serial
the date and time that it was machined, find the specific path that it used,
and then search for all parts produced within 3 days of the date and time
ABCD was machined (the time window can be expanded beyond 3
days as well). The parts from this 3-day window are sorted by the path that
they used and their serials are displayed, allowing you to see exactly which
serials should be quarantined.
Simple approaches to high machine utilization and quality have disparate approaches, but properly managing flexibility to implement high OEE together with tools to track paths allow machines to operate with high utilization while producing quality parts.