5.14 - Levelled Schedules
To get competitive performance from cellular modules, workloads must be managed on a dynamic rolling basis to exploit their flexibility. Workloads must be structured for maximum output and product mix.
Levelled Scheduling is the process of producing schedules where both the production volume and the changes due to product mix have been smoothed out over short time intervals by varying the mix manufactured to fully utilise capacity whilst allowing mixed small batch flow (see guides 5.13 & 5.16).
Sell Daily - Make Daily
An ideal levelled schedule would organise the manufacture of products to take place in the same periods that they are sold in. For example, if products are sold monthly, they should be made monthly and if they are sold daily they should be made daily (i.e. a mix of products every day of every month). Such Levelled Scheduling procedures lead to a repeating pattern of similar events.
It is important to note that Levelled Schedules cannot exist in isolation and that they must be supported by measures such as changeover reduction programmes and the use of FMEA, machine capability development and planned maintenance.
Benefits of Levelled Scheduling (see 5.13, 5.16 & 7.17)
- Less inventory
- Shorter lead times
- Increased responsiveness
- Mixed mode product manufacture - giving economy of scale
- A pattern of repeating / similar events means that problems associated with schedules, quality, maintenance, etc., become familiar, predictable and hence more easily solved.
- Control systems can be tailored, simplified and made more effective where a consistent pattern of events occurs.
Two Organisational Requirements for Levelled Scheduling
- Medium to long term forward planning of the load pattern on three month to two year horizon to support procurement from suppliers by orders placed at defined time-horizon milestones. A Sales and Manufacturing mixed skill team is required.
- A weekly levelled scheduling team with Sales and Manufacturing skills to produce detailed weekly plans, rolled forward each week for manufacture, balancing the load on manufacturing resources - one team for each distinct product unit or module.
An Example
The diagram shows an ‘Old Style’ schedule, consisting of large batches driven by high setup time and uncertain lead times. As cellular redesign work progresses these causes can be overcome and smaller more frequent batches can be handled.
‘Old Style’ Large Batch Schedule
Item |
Weekly Volume |
Day 1 |
Day 2 |
Day 3 |
Day 4 |
Day 5 |
A |
100 |
27 |
27 |
27 |
19 |
|
B |
27 |
|
|
|
8 |
19 |
C |
5 |
|
|
|
|
5 |
Load |
132 |
27 |
27 |
27 |
27 |
24 |
Capacity |
135 |
27 |
27 |
27 |
27 |
27 |
A levelled Schedule
Item |
Weekly Volume |
Day 1 |
Day 2 |
Day 3 |
Day 4 |
Day 5 |
A |
100 |
20 |
20 |
20 |
20 |
20 |
B |
27 |
|
6 |
7 |
7 |
7 |
C |
5 |
5 |
|
|
|
|
Load |
132 |
25 |
26 |
27 |
27 |
27 |
Capacity |
135 |
27 |
27 |
27 |
27 |
27 |
Categorise products into runners (A), repeaters (B), and strangers (C). Runners should be placed in the schedule first and strangers fitted last to arrive at a levelled load making high volumes daily and low ones weekly.
A high level committee with representatives from Sales and Manufacturing should ensure that priorities are maintained.
Note: it is only the use of simple cells with relatively small numbers of machines that makes levelled scheduling possible.
Sell Monthly - Make Monthly
Sell Weekly - Make Weekly
Sell Daily - Make Daily