Tales from the real world: Finding The Weakest Link

Here is a ‘Tales from the real world’ extract from our book ‘Manufacturing Money’

Today our tale provides you with a real world example of the ‘Five Focusing Steps’ to improvement. In particularly ‘Step 1: Identify the constraint’ and ‘Step 2: Maximising the constraints output’.

This is a time when i looked at a problem for months before i finally figured out where the constraint was. I hope you enjoy the tale.

“A large grey iron foundry, that I used to run, largest in the southern hemisphere at the time, had a massive green sand casting line. At our peak we made over 3000 engine blocks a day, along with crankshafts, flywheels, disc brakes, and other automotive components. The line ran from a basement to two stories in the air and had a few kilometres of conveyor chain, belts, flat bed conveyors and four massive twenty tonne furnaces. Lifting the rate of production out of this system was essential. We used to run the line for 2 shifts, ideally 6 days a week if we could get the people to work, and still had shortages. The line ran at about 135 moulds an hour and had been commissioned in the early sixties. The ground did shake when it ran, which wasn’t often enough or fast enough.

Our maintenance department completed a massive study about downtime for each of the many machines and sections of conveyor that made up this massive integrated system. We had data on downtime occurrences in each area, their duration, their causes, and plan of fixes. Over a nine day shutdown encompassing an Easter weekend we spent about $100,000 on replacing worn component, modifying downtime causes, replacing switches, lubricating system, and generally given the entire system a major upgrade. We were all confident that this was the game changer we needed to lift our performance and breakout of the scrambling pattern the team had been in for years.

We restarted production and the mould line speed stubbornly remained stuck in the mid 130’s. My boss asked me, nicely, but pointedly, when were we going to see the returns for all the money we had spent. A week later, no change, another week, still no real change. I was at a loss, we all were. At our downtime reduction meeting where we looked at the data every week we started to ask what was the piece of equipment that shut the line down most often.

We added some sensors to try and see what was really going on (this was 1960’s technology remember so data capture was non-existent until we built it) and what we discovered was that the main conveyor drive motors were being turned off and on every half second or so by some part of the system. The main mould line never reached full speed as it was being flicked on and off continuously. Because this was happening so often and the sheer mass of the conveyor system meant that momentum kept the whole thing moving no-one noticed that the line was being turned off and on. The most common piece of equipment sending out a ‘stop the line’ signal was the weight transfer machine.

When you pour molten metal into a sand mould the air that is already inside the mould becomes superheated as it escapes. So that the mould is not disturbed by the force of this escaping air a large weight (700kg+) is placed on top of each mould before the metal is cast. After the metal has been poured this weight is then removed and placed onto another mould. This process occurs using a very simple, if rather robust, ‘pick and place’ style piece of machinery. This piece of equipment was what was actually stopping the line.

We were all confused as to how it was that this machine could be the problem. It never showed up on our manual downtime logs as a significant cause. The maintenance group and the production supervision went to investigate. The machinery was pneumatically powered (compressed air) and there was a large 2” air line going to the machine. Sometime previously a rubber air hose that connected the main line to machine must have broken. It appears that no 2” hose must have been available so a series of reducing nipples had been fitted and it was actually a 1” air hose that fed the machine. The machine was being fed about one quarter of the air it should have been. It was starved of air, and was running slower than it should have been. No one had noticed. That night we replaced the 1” hose and all of the nipples and fitted a 1.5m length of the correct 2” diameter hose.

The result was instantaneous, the mould line rate jumped to about 145 in the next month and we peaked at a monthly rate of 170 before I left. With the motor being allowed to actually hit full speed the noise and speed of the system jumped dramatically. All of our downtime reduction efforts became focused on what was stopping the motor from running at high speeds.

Over the next few months we gradually went to a five day week then a nine day fortnight as we could reliably run more production with less cost and time. Our weakest link was actually a piece of 1” hose.

The $100,000 did give us value as these items needed to be fixed to support the increased speeds but it wasn’t the weakest link at that time and I wish we had fixed the hose first.”

If you would like to read our book Manufacturing Money, you can buy a hard copy here, or alternatively download a kindle version here.

Comments are welcome.

Have an Awesome Day!


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