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Manufacturing Processes—Production and Business: Reducing Cycle Time, Part 4

Manufacturing Processes—Production and Business: Reducing Cycle Time, Part 4

By Bob Sproull

Review of Reducing Cycle Time, Part 3

In Part 3 of this series, I discussed the implications of Little’s Law for cycle time and throughput. I explained that Little’s Law implies that reducing cycle time is essentially the same activity as reducing WIP, as long as throughput remains constant. I also expounded that reducing WIP without reducing variability will cause throughput to decrease. I concluded with five reasons for keeping cycle times as short as possible, especially in the constraint operation.

Batch Production versus One-Piece Flow

Part 4 continues this discussion on Little’s Law and its implications to cycle time and throughput when comparing batch production versus one-piece flow. As I have previously mentioned, much of what I am presenting in this series of posts is taken from my second book, The Ultimate Improvement Cycle—Maximizing Profits Through the Integration of Lean, Six Sigma and the Theory of Constraints.

I mentioned in my last post that the “batch and queue” production system is the most inefficient scenario for a company, but that isn’t exactly true. If a company practices “batch and store production,” whereby instead of processing the material to the next process, they move the material to a storage location, then the cycle time becomes even more protracted!

Continuing on, let’s suppose that instead of producing material in batches (when a part is completed in one station), it moves immediately to the next station and then on to the next until it is completed (see figure below). This type of production is referred to as single-piece or one-piece flow. One-piece flow refers to the concept of moving one work piece at a time between individual work stations. One-piece flow has several distinct benefits including keeping WIP to low levels and encouraging work balance and improved quality.

But in a system like this, what happens to cycle time? Let’s take a look.

cycle time diagram

Looking at the above figure, the processing time is one minute. The first part is processed through work station A and takes one minute. The first part continues immediately to station B while the next part enters station A. After one minute, the first part continues to station C, the second part moves to station B, and a new part enters station A. After another minute, the first part moves to station D, the second part moves to station C, the third part moves to station B, and a new part enters station A. After another minute, the first part has been completed in station D, so that the total time the first part remained in the process was exactly four minutes.

The throughput is one part every four minutes or 0.25 parts per minute (15 parts per hour).

Batch Performance vs. WIP, C/T and T

Batch Size

(WIP)

Cycle Time

(Minutes)

Throughput

(Parts/Minute)

Throughput

(Parts/Hour)

1

4

0.25

15

2

4

0.50

30

3

4

0.75

45

4

4

1.0

60

5

5

1.0

60

6

6

1.0

60

7

7

1.0

60

8

8

1.0

60

9

9

1.0

60

10

10

1.0

60

So what would happen if we increased WIP to 2 instead of 1?

Coming in the next post

In the next post, we will answer the question I just posed above.

Until next time.

Bob Sproull

Bob Sproull

About the author

Bob Sproull has helped businesses across the manufacturing spectrum improve their operations for more than 40 years.

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