I’m a controls systems validation engineer who is doing a part-time degree in
mechatronics. My project is on exploring the replacing of the FIRO (First In / Random Out) buffers we have at work on our filling/packaging line (Bottles) for FIFO (First In / First Out) buffers and then looking at how that helps us with maintaining traceability etc.

This is a fantastic question and one I thought I understood until I started thinking about it. I also like the term FIRO, which I have to admit I never heard before. Most accumulation systems I’ve used are generally either FILO or FIFO with some randomness thrown in. A few are near perfect FIFO.

The answer to her question starts with a definition of traceability. Traceability in packaging is the power to locate when a particular product was packaged in order to isolate a problem. In the event of a recall, packagers want to minimize losses and the more traceability they have the less product gets scrapped and the more confident they are that the public is protected from sickness (or worse). Raising the precision of your traceability has significant operational and efficiency costs, so companies must select the level that makes sense for them.

What type of accumulation system you needdepends on the level of traceability you're looking for.

Here are acceptable ways to use accumulation under various levels of traceability:

Traceability by Day
If you need a product to be traceable back to a specific day, then any accumulation style will work (FIFO, FILO, FIRO, etc.). All you have to do is make sure all buffers, hoppers, and reject collectors are cleared out between shifts. Have an inspector walk the line and make sure no product has been taken off the line and set aside during production. When stacked in pallets, make sure each pallet is wrapped and marked in a way that no products can easily be removed or have their documentation tampered with. Pallets should be stored so they are not mixed with other days’ pallets.

Traceability by Hour
Keeping track of a specific hour’s production requires more rigorous procedures. All buffers should have a maximum dwell time that when added to the total production time, is no more than 30 minutes (ie. 2 buffers with 10 minutes of maximum dwell time, plus 10 minutes of total production time makes the maximum amount of time on the line 30 minutes). If the OEM cannot provide a maximum dwell time that is low enough to achieve this, then periodically you will have to artificially introduce down time to empty the buffer if it has not emptied on its own before the alloted time. This has a significant impact on efficiency.

Traceability by Case or Product
The highest level of traceability goes down to an individual product or small group (ie. case). In this scenario, no product should ever be able to pass each other on the conveyor system or in buffers, which requires tamper proof conveyors with overhead covers. Constant monitoring is required to make sure no products are removed from the packaging line unless recorded by an automatic rejector. Rejected products should be dropped into a locked box that can’t be opened in the packaging area. At that point all these extra measures begins to make RFID tracking an economical solution, which would allow you to once again use any accumulation system, even FILO ones.

Check out our selection of accumulation tables.

Remember that game show the Weakest Link?

The first step in maximizing your throughput is identifying your constraint, or bottleneck. Take the efficiency of each machine and multiply it by its maximum rate. This will give you the net rate of each machine. The machine with the lowest net rate is your constraint and your goal should to keep it running as fast and as often as possible.

Example:
A simple packaging line: (ppm = products per minute)

Some interesting notes:

• Each machine runs 92% or higher, but the line net efficiency is only 83.9%. This is because downtime on just one machine shuts down the whole line (ie. if the Casepacker jams, the Filler and the Labeler also shut down). The net efficiency of the line is calculated by multiplying the efficiencies of each machine in sequence:
  0.94 * 0.97 * 0.92 = 0.839 = 83.9%
• To get the overall line speed, multiply the net efficiency by the max rate of the slowest machine: 0.839 * 200 = 167.7 ppm
• The machine with the lowest net rate is the labeler (194 ppm), making it the constraint. 194 ppm is the upper limit of what we can achieve on this line.

So how do you achieve the upper limit of 194 products per minute? By making sure downtime on the Filler and Casepacker don’t ever cause the Labeler to shut down. By adding an accumulation table in between the Filler and the Labeler, you are segregating the line into two separate systems. This breaks the compounding effect of the machine efficiencies.

Since the line is now in two sections, we have to calculate their throughput separately. The throughput of the first section is 282ppm (0.94 * 300 ppm = 282 ppm). The throughput of the second section is 178.5 ppm (0.97 * 0.92 * 200 ppm = 178.5 ppm). We are still limited by the bottleneck of the second section, so the throughput of this line is 178.5 ppm, a 6.4% increase over our previous line.

Since we haven’t reach our upper limit of 194 ppm we should add another buffer between the Labeler and the Casepacker.

Now we’ve broken the line into three sections with each machine running independently. We have no compounding of efficiencies, so all we have to do is pick the lowest net rate of the machines. In this case, the Labeler’s net rate is 194 ppm and this is throughput of the line, a 15.7% increase over our original throughput of 167.7 ppm.

What does 15.7% mean to a company’s bottom line?

If you are having trouble meeting market demand for a product it could be huge.
Let’s say the line is running:
2, 8 hour shifts per day
7 days a week
Profit is a conservative 50 cents per product

2 shifts * 8 hours * 60 minutes / hour * $0.50 cents * 26.3 extra products per minute = $12,624.00 per day in additional revenue

Over six months it generates $2,203,880.00