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THE SIX SIGMA APPROACH TO REDUCE THE PRODUCT
DAMAGES IN THE WAREHOUSE
Assist.Prof.Dr.Nihal ERGİNEL
Prof.Dr.Nimetullah BURNAK
2003
Introduction
The most common complaint of end customers about the defects is the product damages.
This damage can occur to the warehouse in which the products are packaged, stored, and shipped.
Six sigma methodology is applied to eliminate the complaints about the product damages.
Steps
We set process map, and cause – effect diagram to find the effective factors.
Their priorities are assigned via Chi-Square test and cause – effect matrix.
It is decided that the product damages can occur in any one of the two phases.
1. The first phase is the packaging for which packaging materials and packaging method are considered.
2. The second phase is the transportation for which handling equipments are analyzed.
DOE is conducted separately for each of the phases, and the results are discussed.
Process Map
Warehouse Truck Shopping Center Truck Customer
forklift attachment wet floor dropped product wet floor transporting withoutpressure package
nail stroke in shopwindow nailforklift attachment stroke to the door, pressure angel traffic accident traffic accident elevator, banister, etc.
hand vechile stroke
wood support stroke
type of board gutter Critical parameter
sytrophor density Process parameter
wet/dry board Noise
sytrophor thickness Instructions
distance betweenboard and product
number of producttrasported with forklift
Instructions
Cause and Effect Diagram
damage on the product
forklifts in the warehouse
packaging equipments
truck
attachment pressure
attachments angel
sytrophor density
sytrophor tickness
board type
nail in the truck
traffic accident
wet board due to the wet floor of truck
packaging method
with/ without wood support
distance between board and product
number and the wideness of the ribbon
shopping center warehouse
number product transported with forklift
hand vechile stroke
wood support stroke
dropped product
stroke in shopwindow
customer
transported witout package
srofe to the door
stroke to the elevator
stroke to the banister
Chi-Square test
Table-1: Chi-Square Test: front; two sides; non-damage vs. model
Expected counts are printed below observed countsFront Two side Non-damage Total
A 224106,90
8061,97
4545145586,13
45755
B 5645,20
1726,20
1927319274,60
19346
C 105131,34
5376,13
5605856008,53
56216
D 48149,56
10186,70
6386763779,74
64016
Total 433 251 184649 185333Chi-Sq =128,277 + 5,248 + 0,401 + 2,581 + 3,231 + 0,000 + 5,282 + 7,030 + 0,044 + 68,968 + 2,359 + 0,119 = 223,539DF = 6, P-Value = 0,000
It is clear that Model A has significantly higher number of damages on front than the other models. Model-D has significantly lower number of damages on front than the other models. This main difference between the packaging types of model A and D is the distance between the product and the board. The mentioned distance is larger in model-D than in model-A.
Cause-Effect Matrix
Rating of Importance to Customer10
1 2
Process Inputs Dam
age
on
the
Pro
duct
Total1 Sytrophor density 9 92 Sytrophor thickness 9 93 Board gutter type 8 84 Distance between product and board 8 85 Forklift attachment pressure 7 76 Number product transported with forklift 7 77 Forklift attachment pressure angel 6 68 Door, elevator, banister etc. stroke 6 69 Hand vehicle stroke 6 6
10 Wood support stroke 6 611 Forklift stroke 6 612 Transport without package 5 513 Stroke in shopwindow 5 514 Package without wood support 5 515 Truck nail 5 516 Dropped product 5 517 Truck wet floor 4 419 Wet/dry board 3 320 Ribbon number and wideness 2 224 Truck traffic accident 1 1
Total 113
Cause and Effect Matrix
DOE-1on the packaging materials and methods
The response is the area of the damage measured in mm2 by using caliper. Gage R&R study was conducted before DOE-1.
Factors Level (low) Level (high)
Sytrophor density SD1 SD2
Sytrophor thickness ST1 ST2
The distance between board and product
D1 D2
Board type Type-1 Type-2
Anova Table for DOE-1
Analysis of Variance for mm2 Source DF SS MS F P syt.dens 1 298,43 298,43 23,36 0,001 distance 1 120,78 120,78 9,45 0,011 board 1 30,25 30,25 2,37 0,152 distance*board 1 85,93 85,93 6,73 0,025 Error 11 140,55 12,78 Total 15 675,94
The residual analysis is performed, and it was seen that residuals were normal. The plot of residuals versus time shows that there is no any pattern. Also, there is no indication of inequality of the variances by the plot of residuals versus fitted values.
Main effects
syt.dens. distance
17
19
21
23
25
mm
2
Main Effects Plot - Data Means for mm2
Interaction effect
1 -1
1-1
25
20
15
board
distance
Me
an
Interaction Plot - Data Means for mm2
This interaction effect shows that response is robust for board type-2.
Pie chart
distance (121; 17,9%)
board ( 30; 4,5%)
syt.dens (298; 44,2%)
Error (141; 20,8%)
distance*boa ( 86; 12,7%)
Pie Chart of Source•The sytrophor density can explain the 44%,• the distance between board and the product can explain 18%, • the interaction between distance and board type can explain 13%,
of the damaged area.
DOE-2 on the set up values of forklift which is transportation equipment
Factors Level (low) Level (high)
Attachment pressure PR1 PR2
Attachment angel AG1 AG2
The number of product transported with forklift
TP1 TP2
The model of the product Model-1 Model-2
The response is the severity of the damage.
The response :
Severity
Defination
1 No damage
2 Little degree damage
3 Middle degree damage
4 Big degree damage
5 Very big damage
The attribute Gage R&R was made.
Anova for DOE-2
There is no any interaction. Attachment pressure and angel are affected on the damage severity.
Analysis of Variance for response Source DF SS MS F P pressure 1 3,1250 3,1250 5,95 0,059 angel 1 6,1250 6,1250 11,67 0,019 Error 5 2,6250 0,5250 Total 7 11,8750
Main Effects
angelpressure
3,1
2,7
2,3
1,9
1,5
resp
onse
Main Effects Plot - Data Means for response
Residual analysis
The residual analysis is performed, and it was seen that residuals were normal.
The plot of residuals versus time shows that there is no any pattern.
Also, there is no indication of inequality of the variances by the plot of residuals versus fitted values.
Pie Chart
pressure (3; 26,3%)Error (3; 22,1%)
angel (6; 51,6%)
Pie Chart of Source
The attachment pressure and angel are the significantly main effects with 26% and 52%, respectively
Results
By using the results from DOE-1 the packaging method and the material used were redesigned.
The values of attachment pressure and the attachment angel should be controlled periodically according to DOE-2.
These improvements were implemented, and a significant reduction was observed at the ratio of damaged product.
Further Research
Since these researches just in warehouse, it may be extended to other points of the process map, and the ratio of damaged product can be reduced.
Thank you.