Sequence metal fabrication operations by estimated duration and dependencies, then estimate the job's production schedule and completion time.
The calculator uses operation durations and finish-to-start dependencies. An operation with no dependency can begin at the start of the job. An operation with a dependency starts after its required predecessor has finished.
When multiple operations do not depend on one another, they can be placed in parallel. This can reduce the overall completion time compared with simply adding every operation duration.
A fabrication job schedule is an ordered plan showing when individual operations should begin and finish. Typical operations can include cutting, drilling, forming, fitting, welding, grinding, inspection, coating and packing.
The correct sequence depends on the physical manufacturing process. Some operations must wait for previous operations, while others can be performed simultaneously if the necessary resources are available.
A useful schedule therefore considers both duration and dependency instead of simply sorting operations from shortest to longest.
Dependencies prevent an operation from starting before its required predecessor is complete.
For example, welding generally cannot begin until the required parts have been cut and fitted. Painting may need to wait until fabrication and required inspection are complete.
Incorrect dependencies can produce an unrealistic schedule, so the result should always be reviewed against the actual fabrication process.
If two operations are independent, they may be performed at the same time. For example, material preparation for one component can sometimes occur while another component is being fabricated.
Parallel work can significantly reduce elapsed job time even though the total amount of work remains unchanged.
The difference represents the benefit obtained from overlapping independent operations.
The critical path is the chain of dependent operations that determines the minimum completion duration represented by the entered schedule.
If an operation on the critical path is delayed, the final completion time can also be delayed unless the schedule has enough available float.
Critical-path analysis is particularly useful when deciding which fabrication operation deserves the closest scheduling attention.
How does this calculator sequence fabrication operations?
It calculates the earliest possible start of each operation based on its dependency and duration, then orders the resulting operations by their calculated start and finish times.
Can two fabrication operations run at the same time?
Yes, when neither operation depends on the other. Actual resource availability must still be checked.
What is the critical path?
It is the dependency chain that determines the calculated minimum completion time.
Does the calculator account for machine capacity?
It uses the operation sequence and durations but does not automatically prevent two simultaneous operations from using the same machine or worker.
Why is the calculated schedule shorter than the total work hours?
Independent operations can overlap, reducing elapsed time even though their individual work durations remain unchanged.
Should setup time be included?
Yes. Include setup and changeover time in the operation duration when they materially affect the schedule.
Can this schedule welding jobs?
Yes. Welding can be entered as an operation with its estimated duration and the appropriate preceding fabrication dependency.
Is this a replacement for production scheduling software?
No. It is a practical planning calculator for sequencing a single fabrication job. Complex shops may require resource-constrained scheduling software.