Line Balance Optimisation

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How to set up Recovery Speeds (V Curve) for different Bottleneck Machines on the Line

Almost all automated production lines are designed around a Critical Machine (this is the designed constraint or bottleneck of the line). By having a designed constraint enables it to be managed such that the line throughput can be determined by this machine. All other equipment should have the ability to run faster. Typically the designed constraint of the production line is the most expensive asset which is normally the Filler or Blower.

Overtime, there may be additional product types that are added to the production line, which create a new bottleneck on the line. If the volume of these new product types is high there needs to be an analysis carried out to determine if it makes sense to upgrade the equipment that has become the new bottleneck. In most cases the typical volume is small so it is not possible to justify the machine upgrade and therefore the throughput of the line is now dictated by this machine which has become the new constraint for the line.

To enable the line to run as previously that is to keep the original constraint machine as the designed Critical Machine it is not untypical for the whole line to be reduced in speed to maintain the original V Curve with the Filler being at the bottom of the V Curve. In this case the line is losing volume output even greater than maximum speed of the new Bottleneck. It would make more sense to change the configuration of the production line such that the new bottleneck machine is made the Critical Machine. This would ensure that the volume output is maximised at the rate at which the new bottleneck can produce at its maximum speed.

Example with fictional data shown below:

Machine Original Configuration Maximum Speeds in units per hour New Format Maximum Speeds in units per hour
Blower 42,000 42,000
Filler 40,000 40,000
Labeller 44,000 44,000
Packer 48,000 38,000
Palletiser 52,000 52,000

Consider the data in the table above. In a number of cases to maintain the Filler as the Critical Machine and still attempt to have a line V Curve the maximum speeds of the machines are set as below (assuming an approximate 10% over speed for downstream machines):

Machine New Format Maximum Speeds to maintain Filler as Critical Machine
Blower 42,000
Filler 32,000
Labeller 36,000
Packer 38,000
Palletiser 52,000

In this case, the production line is losing 6,000 units per hour in speed (38,000 – 32,000) compared to the maximum possible speed of the Packer. Also, another program for the blower may have to be defined or it will stop/start constantly.

To maximise the throughput of the line at the rate of the new bottleneck machine capability, the line configuration should be changed so that the Packer now becomes the new Critical Machine of the line and the other machines ensures that this is always fed with product. Therefore the V curve (maximum speeds) of the line should be as follows:

Machine New Format Maximum Speeds to make Packer the Critical Machine
Blower 42,000
Filler 40,000
Labeller 40,000
Packer 38,000
Palletiser 52,000

This set up will ensure that the overall throughput of the line is only reduced by 2,000 units per hour compared of the original configuration and not 8,000 units per hour if Filler is kept as the Critical Machine. The Filler should be set to modulate the speed like all the other variable speed equipment so when the line is full on outfeed it reduces its speed to that of the maximum speed of Packer which would be 38,000 units per hour in this case. This ensures that the equipment run at the Critical Machine speed in nominal state.

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