What is CT, TT, LT, and ST

For those working in automotive quality and production, these terms are part of our daily lives. However, even for experienced professionals, it’s surprisingly common to get tongue-tied when someone suddenly asks for a clear definition.

Let's break down these confusing terms once and for all.

1. Cycle Time (CT)

Cycle Time is the time required to produce one unit of a product within a minimum production lot. It represents the total time elapsed from the moment materials are fed into the process until a finished product is produced.

• Example: To find the actual productivity for a lot of 1,000 units, you divide the total time (from material input to packaging) by 1,000. This serves as the basis for setting production targets.

2. Takt Time (TT)

Takt Time is the "heartbeat" of production—the pace at which you must produce a product to meet customer demand.

• Example: While Standard Time (ST) is the theoretical time for each process, TT is the actual time taken per process in a real production environment, often determined by the slowest (bottleneck) process.

3. Lead Time (LT)

• General Definition: The time elapsed between a customer placing an order and the delivery of the product.
• Production Lead Time: The duration from the moment production is planned and started until the product is completed and entered into the finished goods warehouse.

4. Standard Time (ST)

The time required for a qualified worker, working at a normal pace under defined conditions and methods, to produce a unit of specified quality and quantity. It is the sum of Basic Time and Allowances.

• Example: Calculated by multiplying the standard work time (from material input to the next process) by an Allowance Rate (usually 10–15%). ST represents the theoretical maximum productivity. Since ST is defined per process, any improvements in productivity or process changes must be reflected in an updated ST.

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Key Formulas & Practical Examples

• Takt Time = Total Operating Time / Required Quantity
  • Example: If 2 people make 5 items in an 8-hour shift: $(480 \text{ min} \times 2) / 5 = 192 \text{ min/EA}$.
• Lead Time = The total duration from material input to output.
  • Example: The time from kneading flour to the moment the bread is ready to eat.
• Cycle Time = Since materials are fed continuously, this is the time interval between one finished unit and the next.
• Observed Time (Net Time): Pure work time, including material preparation.
• Standard Time: Observed Time + Allowances.
  • (Allowances: Unavoidable delays or fatigue factors, which vary by company and product.)

Pro Tip: If a product goes through processes A (10'), B (30'), and C (20'), the total Takt Time or Cycle Time for the finished product is 60'. However, while Process A's Cycle Time is 10', you cannot say its Takt Time is 10'.

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Boosting Productivity through CT and TT

Productivity improves when you align these concepts. In a car factory, if a car rolls off the line every 3 minutes, it's because the target time (Takt Time) was set to 3 minutes.

Process	Before	After
A	1 person / 3 min	1 person / 3 min
B	2 people / 1.5 min	1 person / 3 min
C (Bottleneck)	1 person / 6 min	2 people / 3 min
Total Output	80 units (480/6)	160 units (480/3)

The Lesson: To increase productivity, you must analyze the Cycle Time of all processes and balance them (Line Balancing).

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What is Standard Pitch Time?

This is the time required per person to achieve the production goal.

• Calculation: Total Operating Time / Production Target
  • Example: $28,800 \text{ sec} / 900 \text{ units} = 32 \text{ seconds per unit}$.

To hit the 900-unit goal, each person’s work must take 32 seconds. If a process takes 85 seconds, you must add more people to that stage to bring it closer to the Pitch Time.

As a manager, you shouldn't just tell supervisors to "do their best." You must provide the specific target (e.g., units per hour) and the method to achieve it. (If you leave it to them to "figure it out," it usually won't happen! ^^)

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A Personal Perspective on Terms

1. Working Hours: The time you are paid for (e.g., 08:00–17:00; 8 hours excluding lunch).
2. Operating Hours: 8 hours if breaks are included, or 7 hours 40 minutes if 20 minutes of breaks are excluded. If you subtract 10 minutes for cleaning, it becomes 7 hours 30 minutes.
3. Actual Operating Time: The time spent actually working, excluding model changes, equipment breakdowns, training, or power outages. (Note: Morning briefings and material staging should be handled before or outside of this time.)
4. Effective Operating Time: The time spent producing good units (non-defectives).
5. Productivity:
   • (1) Actual Good Units / Production Target
   • (2) Man-Hours (M.H) of Effective Operating Time / M.H of Total Operating Time
6. Equipment Availability: Actual Operating Time / Planned Operating Time
7. ST (Standard Time):
   • (1) Total Product ST: Sum of STs for each process.
   • (2) Bottleneck ST: Used to distinguish before and after Line of Balance (LOB).
8. Man-Hour Productivity (UPPH): Units produced per person per hour.
   • Calculated based on the Bottleneck ST (or CT for automated equipment).
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