How to set ideal cycle time, and what it does to OEE

The manufacturing or process engineer who owns the operation should set the ideal cycle time, from cycles timed at the machine on a good day. When it is wrong, OEE is wrong by the same proportion: an ideal 10% too fast cuts reported performance and OEE by 10% and raises the shift goal by 11%, on a shift where nothing on the floor changed.

This guide is for engineers and plant managers who set these numbers or inherit them. It works one hypothetical shift through four different ideals, compares the bases you can set an ideal from, and ends with an audit you can run this week.

What is ideal cycle time?#

A cycle is one repeat of the operation, from the same point to the same point. One cycle can make more than one part: a 4-cavity mold makes four parts per shot, so its ideal is stated per shot and the parts per cycle are a separate number. The glossary entry for cycle time lists the three cycle-time figures a monitoring system shows.

Vorne’s OEE primer defines the ideal as the fastest cycle time your process can achieve in optimal circumstances.^[1] The word that matters is process: the ideal belongs to one operation on one machine, not to the part or the machine alone. For example, the same bracket can have a 90-second ideal on a 5-axis machining center and a 140-second ideal on an older 3-axis mill.

Four different numbers get called a cycle time on the shop floor, and each one has a different job.

The Lean Enterprise Institute defines cycle time as the time to produce a part or complete a process, as timed by actual measurement,^[3] and takt time as available production time divided by customer demand.^[4] Keep the four apart. A plant that types its routing standard into the ideal field measures the machine against its own quote, and a plant that types takt measures it against demand.

What the ideal cycle time decides#

Four numbers are calculated from the ideal, and none of them can be more accurate than it. The first is performance, the OEE factor for speed:

Vorne gives this form, along with a short form of OEE that skips the three factors entirely:^[1]

Read the second formula slowly. Good count and planned production time are facts about the shift, so OEE moves in exact proportion to the ideal. Change the ideal by 10% and OEE changes by 10%, with no change on the floor.

The third number is the shift goal, the part count a shift is expected to finish. It divides the time the machine is expected to run by the ideal:

The fourth is the planned length of a job, which multiplies the other way. For example, 500 parts at a 90-second ideal is 12.5 hours of machine time.

Every second between the ideal and the actual cycle is booked as reduced speed, a performance loss in OEE’s six big losses.^[2] Vorne lists dirty or worn equipment, poor lubrication, substandard material and operator inexperience among its common causes.^[2] A wrong ideal adds a loss to that list that doesn’t exist, or deletes one that does.

What a wrong ideal does to OEE#

Work one shift through with the ideal it should have, then change only the ideal.

Now keep every fact about the shift and swap in the ideals a plant might have on file instead:

The same shift reads anywhere from 69.3% to 91.0% OEE. Three things follow from the table.

• A too-fast ideal invents a speed loss. At 80 seconds the shift shows 10 points of performance loss that nobody can find, because no cycle on this machine runs that fast. People chase it for a week, then stop trusting the gauge.
• A too-slow ideal hides one. The 95-second ideal reads a plausible 95.0%, and nobody questions a 95. Only the 105-second row gives itself away by passing 100%, which Vorne says means the ideal cycle time is set incorrectly.^[1]
• Availability and quality don’t notice. The whole error lands in performance, so a plant comparing factors across machines with mixed bases sends its improvement effort to the wrong factor.

How to calculate OEE works all three factors through for a full shift, including the planned-time choices that move availability.

What a wrong ideal does to the shift goal#

The goal moves the opposite way to performance, which is what makes a fast ideal expensive. Take an 8-hour shift with 60 minutes of expected downtime, so 420 minutes, or 25,200 seconds, of expected running. The machine from the example makes a part every 100 seconds, or 252 parts in that time.

With an 80-second ideal, the goal is 315 and the machine falls behind from the first hour, every shift. Operators learn that the number is never green and stop looking at it.

With a 105-second ideal, the machine reaches its goal of 240 with 20 minutes of running time to spare, and the last 12 parts feel like a bonus. Nobody looks for the 10 seconds a cycle that the machine loses against its real 90-second best.

A fast ideal lowers performance and raises the goal at the same time, so the machine is penalized twice for one wrong number. Fix the ideal before you discuss the goal with anyone on the floor or track the shift against it. The shift goal reference shows how a monitoring system derives the goal from the ideal and the machine’s own downtime history.

Planning uses the same number. A 500-part job planned at the 80-second ideal books 11.1 hours, and at the 100 seconds the machine really averages it needs 13.9. Production scheduling on real run rates covers which rate to plan with.

Which basis should you set it from?#

Four sources supply ideal cycle times, and each one errs in a predictable direction.

Vorne’s convention is the theoretical fastest time to make one part, the inverse of the speed it calls the ideal run rate or nameplate capacity.^[2] That choice shows the full gap to design speed, which suits a line whose speed is set by a dial. On a machine whose cycle depends on the program, a theoretical ideal reports a performance loss nobody can act on.

You don’t need a separate ideal per operator or per shift. The ideal describes the process, and the differences between operators are exactly what performance should show.

Who should own the ideal cycle time?#

One person owns each ideal: the manufacturing or process engineer responsible for the operation. Others supply data or use the number, and none of them should edit it.

The ideal changes when the process changes, and only then. Use this table when someone asks to edit one.

Record every ideal with its basis, the date it was timed and who approved it. A number with no history gets edited by whoever is closest to the keyboard.

Set the ideal cycle time step by step#

1. Pick one operation on one machine

   Choose a part with a settled program or mold, not a first article. For example, OP20 on a bracket, run on one machining center.

2. Choose a good shift

   Pick a shift with sharp tools, good material and an experienced operator, and start after warm-up.

3. Time 10 to 20 consecutive cycles

   Time each cycle from the same point to the same point, such as door close to door close. Include load and unload when they happen on every cycle.

4. Drop cycles with a stop inside them

   A cycle with a chip clear or a jam inside it is a stop plus a cycle. Leave it out, because the stop belongs to availability or to the micro-stop count.

5. Average the rest and enter it per cycle

   Enter the average as the ideal, per cycle and not per part. A 4-cavity mold keeps its shot time and records four parts per cycle.

6. Compare with the measured cycle for a week

   Read the actual cycle time against the new ideal before anyone acts on the performance figure.

The fastest of the twelve was 88 seconds. Using it would set the ideal 2.2% fast and charge every shift for a cycle the machine hit twice.

Check the count before you trust any performance figure. A count matched to ten parts counted by hand, as in validating a production count, rules out a doubled or halved count posing as a cycle-time problem. Counting parts and cycle times on CNC mills and lathes covers the CNC case.

Set ideal cycle times in IoTFlows#

In IoTFlows, the ideal is the Ideal Operation Cycle Time on each operation in the Parts List. You enter it per cycle, with parts per cycle in its own QTY/OP field.

The parts gauge measures performance against it. The Calculated Goal on Shift Production is the shift duration less the expected downtime for that operation and machine, divided by the ideal, so you move a goal by fixing the ideal. The cycle-time setup guide walks through each field.

The sensor measures the actual cycle from the machine’s own signal, and the Production Rate column on Shift Production shows the ideal, goal and actual cycle side by side. OEE tracking reports availability, performance and quality factor by factor, so an ideal that is off shows up in performance alone.

Audit the ideals you have now#

Run these checks on your five highest-volume operations this week.

• Performance over 100% on any shift. The ideal is too slow, or the count is wrong. Hand-count ten parts, then re-time.
• Performance that never moves. A figure pinned between 97% and 99% shift after shift points to an ideal copied from a typical shift rather than timed.
• A goal that is never met. Compare the ideal with the best actual cycle from the last month. If no shift came within 5% of it, the ideal is too fast.
• One ideal shared by different machines. Unless the machines are identical, at least one of them is measured against the wrong number.
• An ideal nobody can explain. With no basis, date or owner on record, re-time it.

Jesel, a valvetrain manufacturer in Lakewood, NJ, runs a version of this check every day on its CNC machines, comparing actual cycle times with the times in its bills of material.

I use the dashboard every day to compare and validate actual cycle times against the times listed in our bills of material.

A deviation in either direction is worth a look. A cycle running long points at tooling or setup, and one running consistently short points at a standard that needs re-timing.