Work Study and Processes
Takt time, cycle time, time study, fatigue, learning curves, lead time, capacity, layout, VSM and line balancing: the classic and Lean tools to design and improve a process.
Real case
In a heavy-machinery shop with 14 machines, management estimated that actual cutting time was around 60% of the workday. A work sampling study with about 3,000 random observations (3,024) gave 50.7%, and showed that 9.6% went to setup and 10.8% to tool handling: that is where the opportunity to improve methods was.
Source: Niebel and Freivalds, Ingeniería Industrial: Métodos, estándares y diseño del trabajo. See the article
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Fatigue and rest breaks
A standard time has to include the rest the task requires. How much depends on energy expenditure, posture, force and environment, and on differences between people (age, body size, sex) that are worth understanding in order to design workstations that serve many people, and not to judge anyone by an average.
Flow process chart: the 5 symbols to map any process
The flow process chart (cursograma in Spanish) records everything that happens to a part or a person using just 5 symbols: not only what gets produced, but also every transport, delay, inspection and storage that nobody counts today.
Lead time: how long it really takes for the product to reach the customer
Lead time is the total time that passes from the moment raw material (or the order) comes in until the product goes out. It is not cycle time: most of the lead time is usually waiting, and that is where the improvements are.
Learning curves
When a task is repeated, each unit gets made faster, and that improvement follows a predictable pattern: every time the cumulative quantity doubles, the time per unit drops by a fixed percentage. It is useful for setting standards for new workers and for small batches.
Line balancing
Balancing a line means spreading the tasks of a process across its workstations so that none ends up overloaded or idle. Two simple formulas give you the minimum number of stations you need and how well the real workload ended up distributed.
Plant layout
There are four classic types of plant layout —fixed position, process, cellular and product— and none of them is "the best" in general: each one fits depending on the volume and variety of what you make. Muther's SLP method organizes the decision with data, not by eye.
Production capacity vs. demand and utilization rate
What a plant can make is set by its bottleneck; what it can sell is set by the market. Comparing the two, and measuring how much of the capacity is really being used, keeps you from promising what you cannot deliver and from having idle capital.
Spaghetti diagram: seeing the real path of people, materials or information
The spaghetti diagram draws every movement of a person, part or document on the real floor plan of the plant or office: the tangle of crossing lines that results shows, at a glance, how much a poorly laid-out process makes people walk for nothing.
Stopwatch time study
When you time a task, there are two ways to record the time of each element: let the stopwatch keep running, or reset it to zero at every break point. Each has advantages, limits and typical errors, and the number of cycles to observe depends on the cycle time.
Takt time vs. cycle time
Takt time is the pace at which a part HAS to come out to meet demand; cycle time is the pace at which your process ACTUALLY produces it. Comparing the two numbers, station by station, is the first diagnosis of any line.
Time study: how to calculate the standard time of a task
Timing a task with a stopwatch is only the first step. To reach a fair standard time you have to correct for the operator's pace and add the allowances for fatigue, personal needs and unavoidable delays.
VSM: mapping the value stream from end to end
VSM draws, with standard symbols, the whole path of material and information for a product —from the supplier to the customer— so you can see at a glance where inventory piles up and which process is the bottleneck against takt time.