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Manufacturing Processes—Production and Business: The Interference Diagram, Part 5

Manufacturing Processes—Production and Business: The Interference Diagram, Part 5

By Bob Sproull

Review of The Interference Diagram, Part 4

In my last post, I demonstrated how to construct an Interference Diagram (ID) by defining our goal or objective, identifying interferences that hinder us from achieving it, and assigning time impact estimates for each interference. As a review, this is the figure of our ID, complete with the time impact for each interference. This graphic is a compelling way of communicating the hindrances in our processes, as well as the extent to which they cause inefficiency.

Figure 1 – Graphic of ID

interference diagram

In today’s post, I will complete this series on the Interference Diagram by explaining what we can do with the information we have collected. Much of what have presented in this series of posts is taken from one of my books, [1] Epiphanized–A Novel on Unifying Theory of Constraints, Lean, and Six Sigma, co-authored with Bruce Nelson.

A Pareto analysis shows the impact of the interferences

One of the tools we can use in conjunction with our ID is the Pareto Chart, so let’s construct one now. A Pareto analysis should be based on available machine time. This will succinctly show the impact of the interferences.

If the available machine time for the XYZ machine is considered to be 8 hours for one shift, then the available time is 480 minutes (60 min X 8 hours = 480 minutes) during an 8-hour period. With 480 minutes as our baseline to measure the impact of the interferences, the results will show the conflict between the time available to work and the time the machine actually spends working.

Figure 2, below, is an example setup of the Excel® input sheet which shows the interference description, the total minutes the interference consumes, and the percentage impact on the total minutes available. The chart reveals that the leading time impact comes from not having parts available to work on at the machine. Fixing this interference alone could provide an additional 90 minutes of throughput time every day.

Figure 2: The Simple Excel Setup

# Description Daily Minutes Percent Interference

1

Parts not available

75

16%

2

Breaks & lunch

60

13%

3

Operator finding part

90

19%

4

Looking for supervisor

45

9%

5

Looking for paperwork

30

6%

6

Machine is broken1

6

1%

 

Total Interference minutes2

306

 
 

Available work minutes3

174

 
 

Total Available minutes

480

 
 

Utilization Percentage

 

36%

116 minutes is calculated from a weekly average of 30 mins (30 mins/ 5 days)
2∑ interference minutes
3Available mins - Interference mins.

A Pareto Chart shows the interferences in descending order of impact

From this spreadsheet setup, we can emphasize the impact of the interferences. With the interference percentage calculated, we can create a Pareto Chart to visually display the breakout and “interference impact.” Figure 3 displays the interference impact for our example.

When the ID is used to analyze and exploit a constraint, it can be a quick and effective tool to generate good ideas quickly. This method, when used in conjunction with Pareto analysis, can quickly provide an ideal visual tool to determine the significant interferences. From there, we can determine the correct actions to provide the highest levels of improvement.

Figure 3 below is the completed Pareto Chart which lists the interferences and their individual time percentages in descending order. Starting on the left side of the Pareto Chart, we can see that the biggest gain comes from eliminating the need for the operator to find his parts, followed by parts not available. This tells us that by fixing the interferences associated with parts, approximately 35 percent (19 percent plus 16 percent) of the wasted time could be recovered. These two interferences on the list should be reduced or eliminated first, if possible, to gain the most benefit.

Continuing on, we see that the next highest interference is the time wasted from breaks and lunches at 13 percent. We all agree that workers are entitled to their breaks and lunches, but do they all have to go on breaks and lunches at the same time? An alternative is to have substitute relief during breaks while the regular constraint operator is away. This will enable our constraint to continue producing without stoppage, which will result in more throughput.

Figure 3: Pareto Chart of Interferences

Pareto chart of interferences

By eliminating just the top three interferences we can reduce our wasted time by 48 percent. This means that we can essentially double our output without adding additional manpower. Think about the impact of such a simple solution to your bottom line!

Coming in the next post

In my next post, I will begin a new series on manufacturing process improvement. As always, if you have any questions or comments about any of my posts, leave a message and I will respond.

Until next time.

Bob Sproull

References:

[1] Epiphanized–A Novel on Unifying Theory of Constraints, Lean, and Six Sigma, 2nd Edition, Bob Sproull and Bruce Nelson, CRC Press, 2015.

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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