Standard work combination table

How the combination table is calculated

The standard work combination table puts one operator’s round on a time line, element by element, together with the machines the operator starts. It is part of standard work as commonly practised (from the Toyota Production System), not a standard; the lines and checks here are the usual ones.

Formulas

• Operator cycle = Σ manual time + Σ walk time; element i starts where element i − 1 ended its walk.
• Machine time runs from the end of the element’s manual time; the operator is back at the element one cycle after its start.
• Late = machine end − back, when the machine is not done yet. The operator waits once per cycle, for the latest machine; after that wait the other machines are ready in time, so the cycle becomes the operator cycle + the longest lateness.
• Over takt: the cycle with the wait is longer than the takt.

Worked example (the tool’s example)

1. Manual 4 + 8 + 10 + 6 + 9 = 37 s, walk 3 + 4 + 2 + 3 + 5 = 17 s: operator cycle 54 s.
2. The welder is started at 7 + 8 = 15 s and runs 48 s, to 63 s; the operator is back at 7 + 54 = 61 s and waits 2 s: the cycle becomes 56 s.
3. 56 s is within the takt of 58 s; the press (37 to 49 s, operator back at 85 s) is never waited for.

Common mistakes

• Using the machine’s cycle time as the operator’s: the operator only loads and starts it.
• Leaving out walking: on a spread layout it is a large part of the cycle.
• Timing one round only: take the repeatable time of several rounds, without the odd disturbances.
• Filling the cycle exactly to takt: without some margin every disturbance stops the line.

Input and files

• Numbers may use a decimal comma or point; the machine and walk columns may be empty.
• Excel: the elements with start, machine end, return, lateness and cycle as formulas. Print / PDF puts the chart and the table on A3 landscape; the blank form has a wide column to draw the lines by hand.
• Files: CSV, TSV and TXT are read as if pasted (UTF-8, UTF-16, otherwise Windows-1257). XLSX: choose the sheet and the columns or a cell range; formula cells use the value Excel last saved, dates are kept as text. Files up to 20 MB are read in this browser only and never uploaded.
• XLSX files are read with SheetJS Community Edition 0.20.3, Apache License 2.0 (license text at the end of this file).

Questions

What is a standard work combination table?

A chart of one operator’s work elements on a time line: manual work as a solid line, the time a machine runs on its own as a dashed line, walking as a wavy line, and the takt as a line across. It shows at a glance whether the operator’s cycle fits the takt and whether the machines are ready when the operator comes back to them.

Why does the operator wait for a machine?

A machine started in one element runs while the operator does the rest of the round. If its machine time is longer than the time until the operator comes back, one cycle later, the operator stands and waits. The table shows for every machine how late it is; the operator waits once per cycle, for the latest machine (after that wait the others are ready in time), so the cycle becomes the operator’s cycle plus the longest lateness.

Is walking time waste?

It adds no value, but it is part of the cycle as long as the layout needs it. Showing it as its own line makes it visible: moving a rack or a machine closer often shortens the cycle more than working faster.