P O L Y TE C H N I C U N I V E R S I T Y O F T H E P H I L I P P I N E S
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CASE INTRODUCTION
In June 2000, the Weatherburn Aircraft Engine Company received an order for ten spare ring gears from Sierra Airlines !he ring gear "as the largest and the most e#pensive of the gears in the system "hich drives the propeller !he Weatherburn Company carried in stoc$ part %o &'()&, the gear blan$s from "hich the ring gears "ould be made !he gear blan$ "as a standard si*e used in many airlines !he number of teeth, ho"ever, "as non+standard When Sierra Airlines had bought the airplanes in "hich gears "ere used, its management had decided that flying reuirements peculiar to the airline necessitated a gear ratio slightly higher than the standard and Weatherburn had designed a special gear train accordingly %o other airlines used this ratio and Sierra "as on the point of converting its fleet of aircraft to -et operations .pon inuiry, the production manager of Weatherburn Company learned that the lot of ten ring gears "ould almost certainly last until Sierra/s current aircraft had been entirely replaced !he gear blan$s cost Weatherburn about (0 each to ma$e !he first step in the machining process "as hobbing Setup for the operation "as very e#pensive, costing about (00 but the direct cost of hobbing an e#tra gear "as negligible so long as the machine/s capacity of 2( gears at one time "as not e#ceeded After hobbing, each gear "as individually sub-ected to a series of drilling, grinding and finishing operations !he total cost of "hich "as 10 per gear In addition, there "as a setup cost of 2(0 associated "ith these operations !he machined gears "ere then heat treated at a cost of about '0 per gear after "hich they "ere sub-ected to
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P O L Y TE C H N I C U N I V E R S I T Y O F T H E P H I L I P P I N E S
a hardness test, the cost of "hich is negligible After hobbing and before the remaining operations, the gears "ere sub-ected to a '00 inspection In the past, an average of 3 of all hobbed gears failed to pass this inspection and had to be scrapped !he heat treating operation "as much more difficult to control !he test for hardness had rigid specifications and the Weatherburn Company had had considerable difficulty in meeting standards on this type of gear in the past4 only 50 of the gears had proved acceptable
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RESEARCHER4S POINT OF VIEW
III/
STATEMENT OF THE PROBLEM
!his case study "as conducted to ascertain the most favorable policy the Weatherburn Aircraft Engine Company should conduct in order for them to meet the order of ring gears of Sierra Airlines in a most cost+effective method Specifically, this study sought to ans"er the follo"ing uestions6 ' 7o" many gear blan$s are needed to deliver the order of he spare ring gears from Sierra Airlines8 2 What are the possible production costs of creating the ring gears for the order of Sierra Airlines to determine the most economical policy to be implemented8
IV/
AREAS OF CONSIDERATION
a/ St!en*t#s
+
Weatherburn Company already carries stoc$ part no &'()&, the gear blan$s from "hich the ring gears "ould be made
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P O L Y TE C H N I C U N I V E R S I T Y O F T H E P H I L I P P I N E S
+ +
Weatherburn Company sub-ects their products to '00 inspection !he direct cost of hobbing an e#tra ger "as negligible so long as the machine/s capacity of 2( gears at one time "as not e#ceeded
5/ Wea6nesses
+ + +
In the past, an average of 3 of all hobbed gears failed to pass the inspection and these are scrapped 9ifficulty encountered from heat treating operation and test for hardness :nly 50 of the gears had proved to be acceptable
$/ O''"!tuntes 7 !he lot of ten ring gears "ould almost certainly last until Sierra/s current 7
aircraft had been entirely replaced Weatherburn had designed a special gear train to meet the reuirements specific to Sierra/s
d/ T#!eats 7 %o other airlines used the specific ratio of gear peculiar to Sierra 7 Sierra "as on the point of converting its fleet of aircraft to -et operations V/
