# IENG 471 Lecture 04 - Schedule Design

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```					IENG 471 - Lecture 04 - 2

Schedule Design:
The Sequel

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Agenda

 Assignments
 Schedule Design – Part 2:
 Estimating Equipment Needs (Equip. Frac.)
 Facilities Project Management Tools
 Questions & Issues

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Assignments
 Current Assignment:
 CH 2 (2.4 – 2.6)
 HW:        (HW 3)
 Product BOM
 Product Operation Process Chart
 Product Precedence Diagram

 Next Assignment:
 CH 3
 HW:        (HW 4) See Assignment Link
 CH 2: 13, 16, 17, 24, 38, 40, 41.

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Equipment Requirements
 Equipment Fractions are the number of
machines of one type required to produce
the required volume of product
 Some machines can be used to perform multiple
operations…
 So, if idle time on the machine exists, and there are
multiple products scheduled, then fewer total machines
may be required!
 Some machines may not be able to perform the
required operation(s) fast enough to reach the
required volume with only one machine…
 So, more copies of the machine may be required!

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Estimating Equipment Fractions
 The equipment fraction for each req’d machine is based on all
of the operations the machine will perform
 Good thing we got those Operations Process Charts!
 To find the number of machines of a type for the facility:
 The number of workstations for a shift (F) is:

SQ
F
where:           EHR
 S is the standard time to perform the operation, per unit
 Q is the quota of output units per shift
 E is the efficiency of production on the machine, expressed as a
percentage of the standard operation time
 H is the hours available for production on the machine during
the shift (or whatever unit of time matches parameter S)
 R is the availability (reliability*) of the machine, expressed as %
of the “up time” that the machine is available to work (%H)

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Reliability

 Reliability is a measure of how often a
system fails:
 How long (on average) you can run it until it
stops working right
 How do you know that it’s not working right?

 MTTF (Mean Time To Failure) or
 MTBF (Mean Time Between Failures)

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Maintainability

 Maintainability (serviceability) is a
measure of how long it takes to return
the system to proper operation:
 Sum of the times required to:
 diagnose the problem
 obtain repair parts / tools
 repair the failed components
 return the unit to operating conditions
 MTTR (Mean Time To Repair)
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Availability

 Availability is a function of Reliability
and Maintainability:

 It is the percentage of time that you can
count on using it for production

 % Availability =                    MTTF
MTTF + MTTR

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Equipment Fractions - continued
 Since the number of
Equip.     Integer
machines is an integer                      Op. No.
(from text p. 58)
Fraction   Ceiling
 The lower bound on the
number of machines                      0109         1.1        2
required is 4 – the sum of
the equipment fractions
0206         2.3        3
 The upper bound on the
number of machines
required is 6 – the sum of
0274         0.6        1
the ceiling values for each
operation…
Total
 But …                                              4         6
Req’d

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Equipment Fractions - continued
 We should adjust the required number of
machines to also account for:
 Number of shifts we will operate
 Amount of overtime anticipated
 Frequency of changeover (flexibility)
 Set-up times
 Maintainability…

 Therefore, the four machines estimate might
not really be feasible … it assumed that
everything was best case scenario!

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Ex: Injection Mold Rubber Feet
 Process for juicer is:
 Mold & trim feet – 2% scrap rate
 Transport trimmed feet to line – 1% scrap rate

 Assemble juicer – 0.5% scrap rate
 3 grams of rubber needed per foot

 Find the number of feet to be processed at each
workstation!
 Find the raw rubber needed for this process!
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Ex: Injection Mold Rubber Feet
 Shift is 8 hr, but reduced by two 15 min breaks, and 35 min
machine warm-up (to heat the mold and material).
 Production schedule requires 2450 sets of feet daily
 MTTF is 38 hours
 MTTR comprises 5 min to diagnose, 55 min to obtain spare
parts, 7 min to fix, 18 min to re-warm
 Run one shift per day
 Obtain one set of four feet per cycle
 Cycle time is 40 s (steady state)

 Find the equipment fraction for this process!

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Questions & Assignment

 What is the machine fraction if, instead:
 A Manufacturing Engineer suggests using a four unit
mold instead of a single unit mold?
 An Industrial Engineer suggests running three shifts,
eliminating daily warm-up time?
 An improved facility design reduces the time to get
spare parts to 2 min, and the re-warm time to 1 min?
 Assignment:
 HW 3
 CH 2: 13, 16, 17, 24, 38, 40, 41.

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