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Formulas Used In Six Sigma-Define & Pre-Define Phase
In Previous articles I have discussed about the vital DMAIC phase of Six Sigma where I have explained the process in each phase that is Define, Measure, Analyse, Improve and Control (DMAIC), in this context we are going to learn about formulas used in Define phase of DMAIC which are critical to control variation in a process thereby making the process or the product defect free.
We will discuss the First Phase that is given below:
Define and Pre-Define Phase:
Talk time = Available time for production/customer demand.
Available production time = Scheduled time – Break time – Meeting time.
Production time is the time required in producing a product so for example if available production time is 400 minutes and customer demand is 20 units then Takt time = 400/20 =20 minutes so the production has to make 1 unit every 20 Minutes.
Cycle time is split into four components:
•Auto time – Time spent by machines running unattended;
•Manual time – Time spent in loading, unloading, and adding components during the same process;
•Delay time – Time spent waiting for operator or other process to finish, or parts or raw material availability; and
•Machine time – Time spent by machine working on the part.
In an ideal production process, the cycle time must be as close to the takt time as possible.
Lead time is the time between customer order and delivery of the product.
For Example in Delivering a Burger of Mc Donald’s to the customer the company takes 30 minutes so 30 minutes is the lead time.
Reducing lead time should be the target, but to do so, you should reduce cycle time, set up time, and wait time. Lead time will automatically get impacted.
Calculating Batch Size
✓Number of machines – 10
✓Cycle time per part – 2 minutes
✓Average daily demand – 20
✓Work hours – 480 minutes
✓Average changeover time – 60 minutes (Once at the end)
Solution
✓Step 1 – Production time needed
•Production time needed = No. of machines * cycle time per part * average daily demand
= 10 * 2 * 20 = 400 minutes
•Time available for set up = Available production time – production time needed
= 480 – 400 = 80 minutes
✓Step 2 – Calculate EPEI
•EPEI = number of setups possible in the 80 minutes set up time
= (Total set up time calculated)/ (Average set up time provided)
= 80/60 = 1.33
•Number of machines = 10
•If there are 10 machines, there would be 10 changeovers.
•The number of setups of 1.33 means that only 1.33 changeovers are possible, not 10.
•EPEI is the time required to cycle all the parts.
•Working at 1.33 changeovers per day, it would take 7.5 days to complete all changeovers.
That is,
•EPEI = 7.5 days
Batch size = EPEI * Daily demand.
•From the calculation, batch size = 7.5 * 20 = 150.
✓Interpretation: The daily demand is 20, but the batch size is 150. That is over-production.
Crew size is the number of people needed to man the production line.
✓Crew size = Cycle time/Takt time
Example: A product works on a takt of 100 minutes and has production cycle time of 400 minutes. What is the crew size?
✓Solution:
•Crew Size = 400/100 = 4
•4 staff are needed on the line to ensure takt target is met.
I will be discussing the formulas used in Measure Phase in my next article.
The Author Suresh .V. Menon is a Certified Lean Six Sigma Black Belt accredited from IASSC, Trainer& IT Consultant, he can be contacted at sureshmenonr1009@gmail.com for queries and comments
