GlossaryKind of term: Manufacturing termOperation sequence
What is the operation sequence?
The operation sequence is the order of setups and operations from stock to finished part; it shapes stiffness, references and where burrs end up.
It settles which side comes first, which operations go in which setup, roughing before finishing and drilling before tapping, and where heat treatment, deburring and inspection come in. Each step provides the clamping faces and references for the next. The sequence is a choice within the routing: for the same part on the same machines, several sequences are often defensible.
What does the operation sequence depend on?
Which sequence works depends on the datums on the drawing, the tolerances between features, the stiffness of the part at each step, residual stress, clamping options and tool access. A common approach is to fix the final setup first, with the tight mutual dimensions and clamping on machined faces, and to work back from there. Rules of thumb apply alongside: make datum faces early, take heavy cuts while the part is still stiff, keep features with a tight location or orientation tolerance between them in one setup, and bring thin walls to size as late as possible.
How does the operation sequence work in practice?
A different sequence can change time and risk without the part changing. A thin wall brought to size early leaves the part less rigid for the rest of the machining and forces lighter cutting data. Burrs on a face that is already finished need handwork; on a face still to be machined they can disappear in a later pass. Stress relieving between roughing and finishing needs stock left on and usually an extra setup. A sequence with one setup fewer saves setup time per batch, but only where tolerances and access allow it. For a frame in EN AW-6082, for example, a common sequence is to machine the underside flat and to size first as the reference, then turn the part over onto that face for the pockets and holes on top.
What is the operation sequence often confused with?
The operation sequence is not the routing: the routing is the series of steps with machines and subcontractors from sawing to inspection; the sequence is the order of setups and operations within it, and the reason for that order. The process plan records both, with tools and inspection points. Scheduling is something else again: it places orders in time, while the sequence orders the steps within one part.
Frequently asked questions
How do you decide the operation sequence?
Often by starting at the final setup: which tight dimensions and datums have to come together, and which machined faces you clamp on then. Work back to the stock. Rules of thumb follow: roughing before finishing, drilling before tapping, thin walls to size late.
Why finish thin walls last?
Because a wall that reaches its thickness early lacks stiffness through every later operation. It can chatter, deflect under clamping or distort. Leave material on until the end and the part stays rigid while the heavy cuts run.
Why machine datum faces first?
Because later setups clamp on them or probe from them. A datum face finished early and accurately limits the position error between setups. If it comes late, earlier features were made without that reference.