What is sequence-dependent setup time?

It is setup time that depends on which job ran before. Running an aluminum job after another aluminum job might need 10 minutes; running it after a steel job might need 45 minutes for full coolant and chip cleanout. Schedulers that ignore this systematically underestimate total setup hours.

How much setup time can sequencing actually save?

In typical high-mix CNC shops, intelligent sequencing recovers 15–30% of total setup hours per machine per week. On bottleneck machines that is a direct throughput gain. The recovery is largest where families of similar parts exist but are not grouped by the current scheduling method.

Should setup time always be minimized?

No. Minimizing setup at the cost of missing customer due dates is a bad trade. The right objective is a weighted sum of due-date adherence and changeover minimization, with weights that depend on whether the resource is a bottleneck and how tight the customer commitment is.

Setup Sequencing — Manufacturing Scheduling Glossary

Definition

Setup sequencing is the practice of ordering operations on a machine so that consecutive jobs share as much fixture, tooling, and material as possible, minimizing total changeover time across a batch. It is a sequence-dependent optimization problem: the setup time for job B depends on which job ran before it. A good sequence can reduce total setup hours per week by 20–40% on bottleneck machines.

Why it matters

Setup is pure non-value-added time. On a CNC machining center running 30-minute setups twelve times a day, that is six hours of lost throughput. Reordering the same jobs to group similar fixtures can recover two to three hours of spindle time per day per machine without buying anything. At the bottleneck, those hours are direct throughput.

Common failure mode

Jobs run in due-date order, which scatters fixture changes across the day. Operators flip the same fixture on and off three times. Total setup time doubles. Throughput drops without anyone noticing because the planner only tracked due-date adherence, not changeover hours.

How Skody approaches it

Skody scores each candidate sequence on a combined objective: due-date adherence plus changeover minimization, weighted by whether the machine is a bottleneck. The scheduler will deliberately bend due-date order on non-critical jobs to keep the bottleneck running, and will surface the trade-off to the planner.

Bottleneck

The resource whose limited capacity governs the throughput of the whole factory.

Finite Capacity Scheduling

Scheduling that respects the real, limited capacity of each machine, operator, and tool.

Dispatching

Telling each operator and machine which job to run next, in what order, right now.

Lights-Out Machining

Running CNC machines unattended outside of staffed shift hours.

Queue Time

The time a job waits in front of a work center before it actually starts processing.