This is a guide to help you use calendars in planning and scheduling.
It will be useful because capacity is constrained by the availability of resources. Calendars can define when those resources are on shift, available to do work and when they are off-shift or down.
In a manufacturing business, resources are better known as workers and machines. So the calendars that people and machines use are central to concept of capacity planning.
If you understand this simple idea, and follow the steps below, you will have an effective way to fix capacity and compare with demand.
What Are Calendars?
Planning asks “how are we going to meet demand with the time and resources available?”
Scheduling asks “when and in what sequence are are we going to execute the plan?”
“How”, “when”, “time” and “resources available”. To define them all, you need a calendar. A calendar tells us the beginning and end time of each shift as below.
You can have as many shifts as you like in a day, and holidays are simply left out. If you add over-time, change the begin and end times for the day in question. Remember that this is a formatted view.
The real values that Excel stores are like this:
Decimal days, starting from 1 Jan 1900. This table will list every date over the period you want to do planning. Set it for a year and you will have a long list of begin and end times with all the shifts and working days.
In just two columns, we can precisely set the shifts for any group of production resources. Let’s call this group of resources a work center.
Each work center will operate to a calendar and can be assigned accordingly. If we add another column, then we now have a simple three column calendar that lists every working shift for every day and every shift pattern.
Then all we need to do is allocate the work center to a calendar in a separate table and define how many resources it has. Each resource is part of a work center; each work center works to a calendar.
So in two simple tables, you have the capacity for every resource available to production.
How To Use Calendars in Planning?
So here is what you need to do to use calendars in capacity planning.
- Group each production resource into a work center. This is likely to be done already- your process routing that defines standard work will allocate an operation to a work center to perform.
- Choose the time period for calendars. Take a long range. You do not want to be building calendars every month. Start with a couple of years and be sure to include all the dates that could possibly come up as a projected due-date or start-date in a planning system. Adjust the calendars as holidays, over-time and shifts get added and changed.
- List different shift patterns in a long table with the begin and end times for each shift. Identify each shift pattern by a code, usually one shift pattern for a group of work centers. If you find yourself with more than 4 or 5, you may be setting yourself up with too much overhead to maintain the calendars.
- Allocate each work center to a shift pattern and specify the number of resources for each work center.
- Maintain the calendar and work center tables in the master data. This can be in Excel, or derived from the MRP system data.
You can see an example of this in action with our Capacity Planning Tool. This post describes how it works and provides a download link.
Take a look at how this calendar concept works in this functional capacity planning tool. You can load up your own data and adjust to fit your shift pattern. Then add capacity by changing the calendar and see the impact to available capacity to production.
Let us know how you get on with our calendar concept. Leave us a comment below, we really like to have your feedback.