How to Calculate Lead Time for Stitching Process?

For a long time, I did not publish any answer of the questions asked by OCS readers. This week I will post only Question & Answer posts. Keep reading for the latest posts on Q&A series.


The question I am going to ask is the basic of the manufacturing industry. 

Q-1: How can I calculate Lead Time for stitching process? 

Q-2: Should we always consider style category proportion (Basic, semi fashion, Fashion & H fashion) while calculating the Lead time for a stitching facility? Waiting for your prompt response. ... asked by Sohaib Abbas


While I was reading this question, suddenly one of my real life stories came to my mind. A similar question I have faced 7 years ago. I appeared in a job interview for production planning job. The interviewer gave me a problem and I had to solve that. Problem was as following 
"Suppose you receive an order of 5000 pieces. you have two sewing lines to run the style and average production per day per line is 400 pieces. Calculate how many days it would take to complete stitching?"

I was in hurry to answer the question. I thought it is a very simple question. It can be solved easily by mathematical calculation. On a paper, I did a simple calculation and replied it would be 7 days.

My calculation was 
Production per day from two lines = 400 X 2 = 800 pieces
Total production requirement is 5000 pieces
So, production time in days would be = (5000/800) = 6.25 days and rounded off 7 days.

My answer was wrong.

The interviewer explained to me that I couldn't make it in 7 days. 
First reason, from day one I would not get the production of 400 pieces from each line. So need to consider production build-up time.

The second reason, I need to add extra cutting quantity to the order to find total quantity to be stitched. And considering these I had to calculate production time for that order. 

That was the story. Unfortunately, I did not get that job.

Let me explain answers to today's questions. 

Answer to Question #1. 

The same principle you need to apply when you calculate Lead Time of the Stitching Process for your orders. Here is the lead time calculation procedure -

Step#1. Find Production build up time. I mean how much time a line takes to reach pick production. This is also known as a learning curve. If you know learning curve, you can calculate day wise production up to pick production.

Step#2. Calculate average production capacity of your line daily from the garment SAM and average line efficiency.
Step#3. As said above, if you cut extra quantity add that to your total production quantity

Step#4. Finally, calculate the lead time adding days required to complete stitching the full order.

Suppose you got an order of 4000 pieces. No extra cutting. On the 4th day after loading a style, you reach to pick production. Based on learning curve production on 
Day 1- 100 pieces
Day 2- 250 pieces
Day 3- 450 pieces 
Day 4 and onward 500 pieces. 

So in the initial 3 days line you will get production of 800 pieces and later 500 piece/day
So stitching lead time 
= (3 days+(4000-800)/500) days 
= 3+6.4 days = 10 days

Day wise production in initial days (production build-up days) to be calculated from the learning curve.

Answer to Question #2. 

Production build up time varies product to product. So yes, you have to consider product categories while calculating production lead time of an order.

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