A key aspect of Production & Inventory Control (P&IC) is planning and controlling production operations. The principal objective of Shop Floor Control (SFC) or, as it is often called, Production Activity Control (PAC) is to maximize plant throughput with the fewest resources. For this measurement it is best to show throughput in dollars and resources (materials, labor and overhead) in dollars.
Don’t get distracted by work center throughput. It is total plant throughput (or the throughput of the constraining work center) that is the true measure. Maximizing a non-constraining work center is “sub-optimization”; and it doesn’t pay the bills; although, it does make the cost accountants happy.
An important part of PAC/SFC is the management of the production capacity. Whether you use the total plant or a constraining work center as your measurement point, you will never produce more than maximum capacity. If you release more work to the production floor than can be produced (in a given time period) you are guaranteed to build up Work –In- Process (WIP). Having too much work in front of a work center forces the supervisor to pick and choose which jobs to complete. No first line production supervisor has the information to decide which customer is the most important. Forcing them to make priority decisions without a clear set of rules is a recipe for frustration and high costs.
It is wise to hold work orders in a release queue ahead of the first work center. The scheduler can release work orders based on two criteria:
1. All materials are available and ready for issue to the work order.
2. The order priority is up to date.
Once a work order goes onto the production floor, it must move as rapidly as possible to each work center. If a critical order comes up, it should be inserted in the release queue and sent to the production floor when it meets the two criteria above.
Work orders should be prioritized at each work center based on the priority discipline used at the plant. There will be more in dispatching priority rules in a later article. Many first line supervisors take it upon themselves to groups work orders in their work centers to minimize the time spent in set ups. This is a false economy. If there are problems with long set up times these issues should be addressed with Set-Up Time Reduction kaizens. Don’t work around the problem, fix it!
As work orders move through the plant you can expect to see overloaded work centers from time to time. If this is a chronic problem, where the same work centers are more commonly overloaded, you have a capacity problem to be addressed at that work center. This work center may be the constraint for the plant. There are various ways to expand work center capacity. If the overloaded work centers are in a seemingly random pattern and move around from work center to work center, you may resort to moving equipment or personnel to the temporary overload to quickly reduce it. It is no crime to shut down an under-used work center to move personnel to a bottleneck.
Work center capacity data is an important factor in PAC/SFC. Capacity is a measure of the output that can be expected from a work center in a unit of time. To calculate capacity you must know available time, utilization and efficiency at the work center. Utilization is the percentage of time a work center is active. It is the hours actually worked divided by the available hours. Efficiency is the measure of the productivity of the work center. It is calculated by dividing the standard hours of work produced by the hours actually worked in the work center. If you don’t have the resources or time to collect this data and perform the calculations, you can develop reliable capacity numbers from past history.
You can calculate the average capacity by using the actual output (measured in labor units or hours) from past history. Collecting data for a month will give you a surprisingly accurate capacity number to use in loading and measuring the work center.
Knowing your plant capacity is critical to sending a controllable amount of work through the facility. By keeping the work load in balance with production capacity, you will reduce the confusion and excess WIP. The end result will be higher throughput and usually better quality. It makes practical sense, and I’ve applied these principals in many plants with positive results.
You must log in to post a comment.