Week 2: Inventory Turns, Executive Shirts, Process Re-engineering, Worker flexibility and productivity, Queuing Model
Names: ___________________________________
Executive Shirts Company Assignment, write name/names
Please use Pages 2 to 9 of this document (have questions and some partial answers) to write your answers to the questions and to show your work. In preparing your answers, assume little or no variation in operation times and that a management system is in place that is capable of maintaining average inventories as described in the cu
ent and proposed systems.
Executive Shirts Company Assignment
Review the HBS case Executive Shirts Company and answer all nine Assignment Questions in this document. (Please ignore the questions on the last page of the case.) Note that this document provides a few partial calculations to assist you with this HW. Please make sure to state any assumptions you make in answering questions.
A. Flow Diagram (or Process map): See Case for details
Note 1: WIP inventories are not shown.
Note 2: The two numbers in
ackets for each stage (labor time per shirt, number of workers) are from Exhibit 3 in the case. Where there are multiple workers assigned to a stage, assume that the workers work in parallel independently of each other. For example, for Make Collar, (3.9, 8) means there are 8 workers assigned to this stage, and each can make collar for one shirt in 3.9 minutes. Thus, 8 of them can make collars for 8 shirts in 3.9 minutes.
Note 3: The first stage (Cut Patterns) performs the following tasks: (i) roll out layers of fa
ic (one layer at a time, up to 60 layers, could be a mix of different colors) on the cutting table, and (ii) layout patterns (for up to 8 different sizes, a pattern has all different pieces for a shirt), cut and move the pieces from the table. This operation is performed by 4 workers who work as a team. It means, all 4 workers work together to perform a task. For example, it takes 1.5 minutes for team of all 4 to layout one layer of fa
ic. It takes 30 minutes for team of 4 to cut.
B. Analysis of the Cu
ent Cutting Operation (Exbt.2): Capacity
60 layers of cloth (“L=60”)
Patterns for 8 shirts (8 shirts per layer, may be of different sizes)
Takes 1.5 minutes to roll out each laye
Takes fixed 30 minutes to cut, takes same amount of time regardless of the number of layers
Cutting takes: (1.5 x L + 30) minutes for L layers
Number of shirts in L layers = 8L shirts
Cutting takes: (1.5 L + 30) minutes to cut pieces for 8L shirts
Cutting takes: (1.5 L + 30)/60 hours to cut pieces for 8L shirts [Note 60 minutes per hour]
Hourly production capacity with L layers =
8
(1.530)/60
L
L
æö
ç÷
+
èø
shirts per hou
Hourly production capacity for L equal to 60 =
8*60
(1.5*6030)/60
æö
ç÷
+
èø
= 240 shirts
Daily production capacity for L equal to 60 = 240 (shirts/hour) x 8 (hours/day) = 1,920 shirts per day
Assignment Question 1: Assume that the company policy requires that number of layers L must be an integer multiple of 5 but cannot exceed 60; that is, L can take any value in the set (5, 10, 15, 20, ...,60). Show that the minimum L needed is 10 to get the daily production capacity of 800 shirts per day?
Answer: (Show your calculations to support your answer.)
C. Analysis of post-cutting stages (15 stages, from Make Collar to Package):
Assignment Question 2: Calculate the daily production capacity of each post-cutting stage. (Please fill in the numbers in the table below). Which stage is the bottleneck? What is the process capacity?
Stage
Description
Daily Capacity (show your calculations), assume 480 minutes/day
1
Make Colla
480 (min/day)
8 workers
3.9 (worker-min/shirt)
x
= 984.61
2
Make Cuffs
(480/2) x 4 = 960
3
Make Sleeves
4
Make Front
5
Make Back
6
Join Shoulders
7
Attach Colla
8
Attach Sleeves
9
Stich Sleeves
10
Sew Seam
11
Attach Cuffs
12
Hem Bottom
13
Inspect
14
Iron
15
Package
Q2.a: Which stage is the bottleneck (the stage with the lowest daily production capacity)?
Q2.b: What is the daily capacity (shirts per day) of the process?
Assignment Question 3: What is the average flow time in days (from the start of Cutting to the completion of Packaging) given the production rate of 800 shirts/day and the inventory data in Exhibit 3 of case?
Inventories (Three batches per worker except for Cutting, 60 shirts per batch; Exhibit 3)
Type of
Operation
Number of
Workers
Number of
Machines
Average WIP
(number of 60 shirt batches)
Cutting
4
1
16 batches
Sewing
48
48
144 batches
Inspect
4
-
12 batches
Iron
4
4
12 batches
Pack
4
-
12 batches
Total WIP Inventory = 196 batches x 60 shirts
atch = 11,760 shirts
Hint: Refer to the Toy Manufacturing Example to understand how to find the average flow time given the inventory and the flow rate.
D. Planning for Custom Shirts: Increasing the capacity of Cutting
Management requirements for custom shirts
Delivery: Within 5 days
Amount (Production/day): 100 shirts / day
Order Quantity: 1 to 5 shirts of a size per order
Assignment Question 4: (The purpose of the analysis in this question is to demonstrate that the existing cutting machine does not have enough time to cut pieces for 100 shirts per day of custom shirts. Note that each custom shirt order is for one size and for up to 5 shirts per order). In the cutting operation for custom orders, assume that it still takes 1.5 minutes per layer and fixed 30 minutes for cutting. Each layer will have a pattern for only one shirt and there could be up to 5 layers depending on the order size.
How many minutes of cutting time per day is needed on the existing cutting machine to cut fa
ic for 100 custom shirts per day? To answer this question, assume L = 5 and one shirt per layer.
Insight: If your answer to the above question is more than 480 minutes, then clearly we need another cutting machine. Moreover, the fixed component of the cutting time for the new machine should be faster than 30 minutes.
Assignment Question 5: Compute the daily cutting capacity of the new “low play” laser cutting machine assuming: (1) L = 5 and 1 shirt per layer, and (2) L = 1 and 1 shirt per layer. [Note: As the case states, laying out a pattern and cutting takes 2.5 minutes for up to 5 layers. You can assume that the time to roll out layers for this machine is negligible.]
5a. Daily cutting capacity with 5 layers per cut?
5b. Daily cutting capacity with 1 layer per cut?
E. Planning for Custom Shirts: Mike’s and Ike’s Plans
(i) Mike’s Plan: Two cutting machines, a common line for post-cutting stages
Cc
· Post cutting operations: Common line for both products
· For regular cutting: Assume L = 10 and 8 shirts per layer ( 80 shirts per cut
· For custom cutting: Assume L = 5 and 1 shirt per layer ( 5 shirts per cut
· From Regular Cutting to first stage in Post-Cutting: Each batch of 10
oken into 2 batches of 5
· From New Cutting Machine to first stage in Post-Cutting: Shirts moved in batches of 5
· All Post-cutting operations: Shirts handled (stored, moved) in batches of 5 shirts
· Post-cutting inventories: WIP inventories in batches of 5 shirts
· See Exhibit 5 for WIP inventories
Assignment Question 6: Calculate the average flow time (called manufacturing lead time or MLT in the case) for shirts for Mike’s plan. Assume flow rate of 900 shirts per day (800 regular and 100 custom). Please use the numbers in Exhibit 5 to calculate the average inventory.
(ii) Ike’s Plan: Two cutting machines, two separate lines
Regular shirts Line:
· One less worker on each post-cutting stage
· Cutting: L = 60 and 8 shirts per laye
· Batch size of 60 shirts
· WIP data in Exhibit 6
Custom shirts Line:
· One worker per station
· Cutting: 1 shirt at a time (L=1 and 1 shirt per layer)
· Batch size of 1 shirt
· WIP of 2 shirts for Cutting machine and 3 shirts per worker for post-cutting operations
Assignment Question 7: Convince yourself that the daily capacity for regular shirts in Ike’s plan is 720 shirts per day. How much overtime (in minutes) per day is needed to meet the target of 800 shirts per day? Assume that the overtime is in multiple of 60 minutes. [To answer this question, assume that overtime is used for all workers on the line. It is certainly possible to run the line with fewer workers in overtime, and we will discuss this aspect in class.]
Assignment Question 8: (a) Calculate the daily production capacity of the custom line, (b) Calculate the average flow time for the custom line assuming production of 100 shirts per day.
Q8.a: Daily production capacity of the Custom Line:
Q8.b: Average Flow Time (in days) for custom shirts:
F: Recommendation
Assignment Question 9: Compare Mike’s and Ike’s plans in terms of performance [cost, quality, time, flexibility] for both regular shirts and custom shirts and demand forecasts. Which plan would you recommend? Why?
Summary of numerical/short answers: Please write your answers in the table below.
Question
Description
Your Answe
1
Min L
10
2 a
Bottleneck Stage
2
Process Capacity
3
Flow Time in days for the cu
ent process
4
Minutes of cutting Time for customs shirts
5 a
Capacity of new machine with L = 5
5
Capacity of new machine with L = 1
6
Average flow time in Mike’s plan
7
Overtime for regular shirts in Ike’s plan
8 a
Daily Capacity of Custom Line in Ike’s plan
8
Average flow time for custom line in Ike’s plan
Make
Back
Cut
Patterns
Make
Colla
Make
Cuffs
Make
Sleeves
Make
Front
(3.9, XXXXXXXXXX2.0, XXXXXXXXXX65,2 XXXXXXXXXX2.50, XXXXXXXXXX70,4)
Stitch
Sleeves
Attach
Sleeves
Attach
Colla
Sew
Seam
Join
Shoulders
(0.66, XXXXXXXXXX65,4)