In our third blog we considered scheduling in the context of a manufacturing planning process; now, let’s explore how both planning and scheduling enable the execution of a plan, noting their respective roles and analyzing their interdependencies.
We plan/schedule to help us execute: to do the right things at the right times in the right ways to efficiently achieve an objective. But in a dynamic world we’re constantly adjusting plans/schedules to reflect reality, which begs a key question: What parts of a manufacturing plan/schedule can we change without sacrificing productivity?
We want our plan/schedule to reflect reality as much as possible, but we also need sufficient plan stability to avoid inefficiency, where we prepare for one task and end up doing something else. So, inside this lead time we don’t re-plan (except for major disruptions, when such waste is warranted); we work with older data. This first part of the manufacturing plan belongs to execution; it defines a frozen period, a boundary enabling us to consistently re-align our plans with reality without sacrificing efficiency.
Planning/scheduling workflows need an accurate picture of the conditions expected at the execution boundary, at the end of the frozen period. Given this starting condition, re-planning/scheduling can realign plans/schedules with execution, closely reflecting reality without destabilizing our work environment. When a major disruption occurs, requiring a relaxation of all or part of the frozen period to enable more complete re-planning, execution and planning/scheduling workflows and interfaces should be designed to provide this capability.
Though planners may request visibility into frozen plan details within planning/scheduling workflows, such detail is irrelevant for planning/scheduling purposes. In fact, providing it can actually be problematic, encumbering and possibly destabilizing planning/scheduling workflows, since plans/schedules approximate reality, not fully considering real-time constraints that affect execution-level detail. The plan may be executed in ways that violate simplistic assumptions inherent in the plan/schedule, making accurate representation very difficult or impossible.
Having explored planning theory and analyzed the relationships and interdependencies between the planning, scheduling and execution processes, in our final blog we’ll take a step back and look at the big picture, summarizing what we’ve found and why it’s important.
For additional information, read the rest of the blogs in this series:
- Part 1 – Supply Chain Planning Basics: Plan, Schedule, Execute
- Part 2 – Supply Chain Planning Basics: A Planning Paradigm
- Part 3 – Supply Chain Planning Basics: Planning to Schedule
- Part 5 – Supply Chain Planning Basics: Implications