How Overlapping Operations Shorten Delivery on Big Orders

Lot streaming lead time reduction comes from a single change in permission: the downstream operation is allowed to start on the first finished sublot instead of waiting for the entire order. Instead of 1,000 pieces sitting at the mill until the last one is cut, the first batch moves to drilling while milling keeps running. EDGEBIC by User Solutions expresses that overlap as a field on the routing step, and on a documented order it turns a 52-hour serial handoff into roughly 37 hours on the same two machines.

This post is about the delivery outcome. For the three overlap models and when each applies, see lot streaming explained. This post sits under the EDGEBIC results guide.

The Waste of the Serial Handoff

Most scheduling systems treat a routing as a relay race. Operation 20 cannot begin until operation 10 reports complete, because that is the simplest rule to code. It is also wrong on the shop floor, where the first finished pieces have been sitting in a tote for hours.

The waste is easy to see once you look for it. A 26-hour machining run feeding a 4-hour deburring bench occupies 30 hours of calendar under a serial rule. Physically it needs closer to 27. That extra day is not a capacity problem, a staffing problem, or a routing problem. It is a permission problem: nothing in the schedule ever told deburring it was allowed to start. Multiply that across a routing with six operations and a large lot, and the delivery you quote is inflated by handoffs that never had to happen. For where lead time hides in general, see reduce manufacturing lead time.

The Overlap Made Concrete

Lot streaming grants the permission with a rule instead of a phone call. The piece-count model is the one most job shops want. You state a number of pieces, and the engine computes when that many will exist:

flow time = setup + min(transfer batch, order quantity) x hours per piece

Take a 100-piece shaft order. Turning runs at 0.5 hours per piece with a 2-hour setup, and the transfer batch is 20 pieces with a half-hour move time. Twenty pieces exist at 2 + 20 x 0.5 = 12 hours after the lathe starts, plus 0.5 hours of handling, so drilling is cleared at hour 12.5. The full turning run is 52 hours. Under a serial rule drilling waits all 52. The overlap pulls the job's elapsed time down to roughly 37 hours on exactly the same two machines. See the lot streaming overlap walkthrough for the arithmetic run end to end.

That 15-hour recovery cost nothing. No machine was added, no shift was worked. A field on the routing step told the second operation it could start when the work was physically ready.

Three Models, One Outcome

Delivery compression takes a different form depending on what "ready to move" means at the station:

The continuous-process case matters because plenty of shops have processes with no discrete pieces to count. A paint booth running 08:00 to 12:00 with a one-hour lag clears the curing oven to start at 09:00 instead of noon: three hours of compression, no counting required. See what is lot streaming for the concept and what a transfer batch is for the piece-count term.

Overlap Versus Parallel: Not the Same Lever

Lot streaming is often confused with running jobs in parallel, and the difference decides which one you reach for. Lot streaming overlaps sequential operations on the same routing: drilling starts on the first pieces while turning finishes the rest. Parallel processing runs one operation across several machines at once, which is a capacity play. See splitting a large order across parallel work centers for that mechanism.

They stack. A long routing can overlap its sequential steps and split its heaviest single operation across machines, and the delivery gains compound. But they answer different questions, and lot streaming has the lower cost of the two because it adds no iron, only permission.

What Overlap Cannot Do

It cannot exempt the downstream step from capacity. Overlap grants an early start; it does not create free hours on the second machine. If the drill is loaded, drilling begins at the later of the transfer-batch time and the drill's next open window. The plan tells you that honestly rather than pretending the overlap is free.

It cannot help where the handoff is already tight. A short upstream operation feeding a long downstream one has little serial waste to recover. The gain is largest where a long operation feeds a shorter one, which is exactly the shaft case, and it shrinks toward zero as the two run times converge.

It cannot be configured on a process it does not fit. Piece-count streaming is ignored on continuous-process work centers by design. Putting a piece count on a paint line does nothing, and the start-to-start lag is the model that belongs there instead. Choosing the model is a work center question, not a matter of taste.

It cannot substitute for a real bottleneck fix. Overlap compresses the handoff between operations; it does not add capacity at the machine that is genuinely the constraint. Where the constraint is the limit, protect it first. See protecting the constraint to lift plant output.

Want to know how much serial waste is inflating your quoted lead times? Bring a long multi-operation routing to a demo and we will run it serial and overlapped on your own numbers.