Total Flow Time

Total flow time is the total time a job spends moving through all stages of a process, from release to completion. In Intro to Industrial Engineering, it includes processing, waiting, and delay time in job shop scheduling.

What is Total Flow Time?

Total flow time is the amount of time a job takes to move from the moment it enters a system until it finishes every required step in Intro to Industrial Engineering. That total includes actual processing time, time spent waiting in queues, setup or transfer delays, and any other pauses between workstations.

In a job shop, this is not just a stopwatch on one machine. A part may be cut at one station, wait for a drill press, sit in line behind other jobs, and then move again. All of that time counts, which is why total flow time is usually much larger than the pure processing time alone.

The idea matters because job shop systems have different routes for different jobs. One job might visit three machines, another might visit six, and each one may face different waiting times. When schedules are crowded or machine times vary a lot, total flow time can grow quickly even if each individual operation looks short.

A common way to think about it is as the full life of one job inside the shop. If a job enters at 8:00 a.m. and is finished at 3:00 p.m., its total flow time is seven hours, regardless of how much of that time was active work. That makes it a better measure of the customer-facing speed of the system than processing time by itself.

In scheduling problems, you often try to reduce total flow time by changing the order of jobs, balancing loads across machines, or removing bottlenecks. The goal is not just to make one machine fast, but to keep jobs moving so they do not stack up in queues. In a job shop, that is usually where the biggest time losses happen.

Why Total Flow Time matters in Intro to Industrial Engineering

Total flow time shows whether a production system is actually moving jobs efficiently or just keeping machines busy. In Intro to Industrial Engineering, it connects scheduling decisions to real outcomes like customer wait time, work-in-process, and shop congestion.

It also gives you a way to compare different schedules. Two schedules can use the same machines and the same processing times, but one may produce much shorter flow times because jobs are sequenced better. That is why the term shows up in job shop problems where you are asked to judge which order is better, not just which order finishes eventually.

You will also see total flow time tied to bottlenecks. If one workstation slows everything down, jobs spend more time waiting before and after that station, which pushes the total upward. So the term helps you spot where a process is losing time, not only where work is being done.

It connects directly to bigger course ideas like lead time and throughput. If you lower total flow time, you often reduce how long jobs sit in the system and improve how quickly the shop can deliver completed work. That makes it a useful metric any time you are analyzing a manufacturing or service process with multiple steps.

How Total Flow Time connects across the course

Lead Time

Lead time is the broader customer-facing wait from request to completion, and total flow time is the in-system portion from entry to finish. In job shop problems, these two can overlap a lot, but lead time may also include time before the job is released into production. If a question asks what happens inside the shop, total flow time is usually the cleaner metric.

Cycle Time

Cycle time usually means the time between completed units coming out of a process, while total flow time tracks one job’s full trip through the system. They are related, but they answer different questions. If you are analyzing one custom order moving through several machines, total flow time is the better fit. If you are watching output rate, cycle time is more useful.

Bottleneck Analysis

Bottleneck analysis helps explain why total flow time gets long in a job shop. A slow or overloaded machine creates queues, and those queues add waiting time to every affected job. When you identify the bottleneck, you can target the step that is stretching total flow time the most instead of guessing.

Critical Ratio

Critical ratio compares the time left until due date with the time left to process the job, so it helps with dispatching decisions. Total flow time is different because it measures how long the job actually spends in the system. In sequencing problems, you may use a rule like critical ratio to decide the order, then evaluate how that order affects total flow time.

Is Total Flow Time on the Intro to Industrial Engineering exam?

A problem set or quiz item may give you a route sheet, machine times, and waiting times, then ask for the total flow time of a job. You add every processing segment plus any delays between steps, not just the active work time. If the question compares two schedules, look for the one that keeps jobs waiting less, since that usually lowers total flow time.

In a case-based question, you may also explain why a shop with the same machines performs worse under one sequence than another. The best answer points to queue buildup, bottlenecks, and job movement through the system. If a work-in-process chart or schedule is shown, total flow time is the metric that tells you how long a specific job stays in the system from start to finish.

Total Flow Time vs Lead Time

Lead time and total flow time overlap, but they are not always identical. Total flow time usually means the time a job spends inside the production system from release to completion, while lead time can include time before release, ordering delays, or other outside-the-shop waits. If the problem is about shop-floor scheduling, total flow time is the more precise term.

Key things to remember about Total Flow Time

• Total flow time is the full time a job spends moving through a production process, including processing, waiting, and delays.

• In a job shop, it is usually much longer than the pure processing time because jobs often queue between machines.

• Shorter total flow time usually means smoother scheduling, less congestion, and better use of the system.

• The term is useful when comparing schedules because it shows how long one job actually stays in the shop.

• If a question gives multiple operations, count every step and every wait before you call the job finished.

Frequently asked questions about Total Flow Time

What is total flow time in Intro to Industrial Engineering?

Total flow time is the total amount of time one job spends in a production system from entry to completion. In Intro to Industrial Engineering, that includes processing time plus waiting time, transfer time, and any delays between operations. It is a common metric in job shop scheduling because it shows how smoothly jobs move through the shop.

Is total flow time the same as processing time?

No. Processing time is only the time a job is actively worked on at a machine or station. Total flow time includes processing time plus all the time the job waits or sits idle between steps. That difference matters a lot in job shops, where queues can be longer than the work itself.

How do you calculate total flow time for a job?

Add every time segment from the moment the job enters the system until it leaves. That means each operation time, plus any waiting or delay between operations. A common mistake is to add only the machine times and forget the queue time, which gives you a number that is too low.

Why does total flow time matter in job shop scheduling?

It shows whether your schedule keeps jobs moving or leaves them sitting in line. A schedule that minimizes total flow time usually reduces congestion and improves delivery speed, even if the machine runtimes stay the same. That is why it is a useful way to compare sequencing choices.