labor overloads

Computers ind. Engng Vol. 17, Nos I-4, pp. 453 458, 1989 Printed in Great Britain, All rights reserved

0360-8352/89 $3.00+0.00 Copyright ,© 1989 Pergamon Press plc

MRP DECISION SUPPORT TO RESOLVE PART SHORTAGES AND MACHINE/LABOR OVERLOADS

PHILIP S. CHONG,

PHD, CPIM

SCHOOL OF BUSINESS ADMINISTRATION DEPARTMENT OF MANAGEMENT CALIFORNIA STATE UNIVERSITY LONG BEACH, CA 90840

ABSTRACT Resolving part shortages and machine/labor overloads are c h a l l e n g i n g t h o u g h o f t e n n i g h t m a r i s h e x p e r i e n c e s faced by an MRP planner. Even though MRP systems have helped many companies to plan their material and capacity requirements, part shortages and machine/labor overloads are still commonplace in many companies today d u e to u n f o r s e e n c i r c u m s t a n c e s such as m a c h i n e b r e a k d o w n s , q u a l i t y problems, transportation delays and others. This paper will discuss how a planner could use the MRP system to help resolve part shortages and machine/labor overloads. INTRODUCTION Essentially, there are two basic approaches to solving the part shortage and machine/labor overloads. In the first approach, lead times are compressed to fill part shortages (expediting, special delivery, p r i o r i t y order, etc.) and m a c h i n e / l a b o r c a p a c i t i e s are e x t e n d e d to accomodate for overloads (overtime, second shift, subcontract, speeding up the machine, etc.) In the second approach, orders are rescheduled to a later delivery date in order to provide time to fill part shortages and to ease machine/labor overloads. The selection of either of the two approaches requires judgement on the part of the planner since it depends on the situation at hand. The planner has to negotiate and make d e c i s i o n s w i t h r e g a r d s to v e n d o r s (or p u r c h a s i n g ) , customers (or marketing/sales/distribution) and manufacturing in order to determine a plan of action that is acceptable to all parties. To effectively make these decisions, a planner will require useful and reliable information. Often times, the MRP system can indeed provide very helpful information to the planner. We will discuss the decision support an MRP system can provide the planner. The discusssion will be centered on and illustrated using MRP-DSS, a microcomputer based MRP system that was designed by the author [2],[3],[8]. Since the system has been implemented and used by several small manufacturing companies, illustrations are taken from these implementations where it is appropriate. MRP TABLES We will begin the discussion by using an example MRP table given by figure 0.1 for part C-II. A late bucket is used to capture all late orders irrespective of the degree of tardiness. The table shows that the reason for 437 units of late order and 120 units of immediate order is because of 600 units of late requirements and 120 units of immediate requirements and there are 803 units on hand. Also, of the 437 units of late orders, 197 units are 3 weeks late, 120 units are 2 weeks late, and 120 units are i week late. The table also shows the i00 units scheduled for receipt in week 2 will need expediting to have them in immediately. Notice that the on hand balance in week 08/11 is 400 units, which is less than the 500 units required for safety stock. The alternative to expediting is to reschedule orders that would be affected by the late order or receipt. The capability to perform "bottom up" replanning, that is, to trace the parts and finally to the sales orders that will be

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Proceedings of the 1lth Annual Conference on Computers & Industrial Engineering

a f f e c t e d by the late o r d e r or receipt, can be p r o v i d e d by the MRP system. H a v i n g a list of sales orders that are p o t e n t i a l c a n d i d a t e s for r e s c h e d u l e can be v e r y helpful to the planner. Each c a n d i d a t e will be reviewed. The i m p l i c a t i o n s of r e s c h e d u l e can be s t u d i e d b a s e d on their impact on the part shortages and machine/labor requirements. This i n v e s t i g a t i o n can be time consuming, but the r e s u l t s are o f t e n quite rewarding. PART NUMBER: C-11 LEAD TIME(WKS): ON H A N D : SAFETY S T O C K : ALLOCATED FOR: LATE RELEASES: # RECOM EXPEDITE: # RECOM DE-EXPED:

RD 220 16V 2.00 803.00 500.00 0.00 437.00 100.00 0.00

WEEK BEGINNING DATE TOTAL ORDERS SCHEDULED RECEIPT ON-HAND BALANCE NET REQUIREMENTS PLND ORDR RECPTS PLND ORDR RELEASE RECOMMEND *****LATE *****LATE *****LATE

EXPEDITE ORDER IN ORDER IN ORDER IN

-LATE 600.00 0.00 803.00 297.00 197,00 437.00

08/11 120.00 0.00 400.00 220.00 120.00 120.00

08/18 120.00 100.00 400.00 120.00 120,00 32.00

08/25 120.00 0.00 500.00 120.00 120,00 0,00

09/01 32.00 0.00 500.00 32.00 32,00 0.00

SCHEDULED RECEIPT IN WEEK 2 100 UNITS WEEK*** -2 ***ORDER QUANTITY** 197 WEEKW** -1 ***ORDER QUANTITY** 120 WEEK*** 0 ***ORDER QUANTITY** 120

FIGURE 0 . 1 :

MRP OUTPUT FOR PART NUMBER C-11.

In the next e x a m p l e g i v e n by figure 0.3, the M R P t a b l e for part Lii r e v e a l s e x p e d i t i n g and d e - e x p e d i t i n g recommendations. Of the i000 u n i t s of L-II due this week, 203 u n i t s s h o u l d be e x p e d i t e d to come in as soon as possible, and the rest of 797 u n i t s m a y be d e - e x p e d i t e d if d e s i r e d s i n c e t h e r e is no future r e q u i r e m e n t s for the part. O f t e n times, w h e n e v e r an o r d e r is expedited, some o t h e r o t h e r will have to be de-

expedited,

whether

it

is

formally

made now o r r u d e l y

pushed

aside

later.

De-expediting o r d e r s that are e ar l y can h e l p to r e m o v e some of the m a c h i n e and l a b o r o v e r l o a d s that o t h e r w i s e w o u l d o c c u r if only orders are e x p e d i t e d . PART NUMBER: L-11 LEAD TIME(WKS) : ON H A N D : SAFETY S T O C K : ALLOCATED FOR: LATE RELEASES: # RECOM EXPEDITE: # RECOM DE-EXPED:

59-77-002701 TORIOD @ 1000 15.00 897.00 500.00 0.00 0.00 203.00 797.00

WEEK BEGINNING DATE TOTAL ORDERS SCHEDULED RECEIPT ON-HAND BALANCE NET REQUIREMENTS PLND ORDR RECPTS PLHD ORDR RELEASE

-LATE 600.00 0.00 897.00 203.00 0.00 0.00

08/11 0.00 1000.00 297.00 0.00 0.00 0.00

08/18 0.00 0.00 1297.00 0.00 0.00 0.00

RECOMMEND EXPEDITE SCHEDULED RECEIPT IN WEEK 1 RECOMMEND DE-EXPEDITE SCHEDULED RECEIPT IN WEEK FIGURE 0 . 2 :

1

08/25 0.00 0.00 1297.00 0.00 0.00 0.00

09/01 0.00 0.00 1297.00 0.00 0.00 0.00

203 UNITS 797 UNITS

MRP TABLE FOR PART L-11.

THE USE OF A D E C I S I O N

SUPPORT

SUMMARY

ACTIONS

LIST

S i n c e the i n f o r m a t i o n g i v e n by an M R P t a b l e can be q u i t e extensive, and d i f f e r s in p r i o r i t y w i t h regards to a c t i o n s that need to be taken, the u s e of a s u m m a r y a c t i o n s list is a v e r y i m p o r t a n t d e c i s i o n support tool that can be b u i l t into an M R P system. For a typical m a n u f a c t u r i n g company, the n u m b e r of p a r t s can run in the thousands. The use of s u m m a r y a c t i o n s list can be a v e r y p o w e r f u l d e c i s i o n s u p p o r t tool to the p l a n n e r [13]. W h a t are the items of in a s u m m a r y a c t i o n s five c a t e g o r i e s of s u m m a r y a c t i o n s as follows:

list?

We

will

I. P a r t s r e q u i r i n g o r d e r r e l e a s e s this w e e k or earlier. 2. Parts w h o s e open shop or p u r c h a s e orders are p r o m i s e d this earlier. 3. Parts w h o s e sales orders are p r o m i s e d this w e e k or earlier.

describe

week

or

Chong: Resolving part shortages and machine/labor overloads

4. Parts w h o s e s c h e d u l e d r e c e i p t s are r e c o m m e n d e d 5. S t a t i o n s w i t h m a c h i n e / l a b o r overloads.

455

for reschedule.

i - PARTS R E O U I R I N G O R D E R R E L E A S E S THIS W E E K OR E A R L I E R This c a t e g o r y p r o v i d e s action r e c o m m e n d a t i o n s r e l a t i n g to planned o r d e r r e l e a s e s for both late orders as well as i m m e d i a t e orders. The o r d e r r e l e a s e s may be for a p u r c h a s e order or a shop order. Figure i.I shows a p r i n t o u t of the list for p u r c h a s e orders. The implication of this list is that new orders have to be placed. The e x a m p l e list as shown in figure l.l includes i n f o r m a t i o n such as quantities, prices, lead times and v e n d o r numbers - i n f o r m a t i o n w h i c h are r e q u i r e d in the c r e a t i o n of p u r c h a s e orders. P u r c h a s e orders are to be issued to vendors and shop orders are to be r e l e a s e d to the shop floor. C a t e g o r y 1 in c o m b i n a t i o n w i t h several of the other categories such as 2 and 4, and the MRP output table p r o v i d e the p l a n n e r a more c o m p l e t e p i c t u r e of the p a r t shortages. It is i m p o r t a n t t h e r e f o r e that the p l a n n e r a p p r o a c h e s the s u m m a r y actions list w i t h a m i n d set that is p r e p a r e d for p r o b l e m solving and investigation.

PURCHASE ORDERS TO BE RELEASED THIS WEEK: PART #

LD TM(DAYS) U/M

C-ll

COST $

QHT.REQ. VEH.CODE PART DESCRIPTION 0.060000 120.00 39/48 RD 220 16V

11

EA

F-Z0

5

GL

17.670000

7.30

R-45

5

EA

0.004000

120.00

FZGURE 1.1(a): CATEGORY RELEASED FOR IMMEDIATE WEEK.

1

11 SOLDER FLUX #2331 39 C/F 27K OHM I / 4 WATT ~ 5H

PURCHASE

ORDERS

TO

BE

PURCHASE ORDERS DUE FOR RELEASED LAST WEEK AND EARLIER: PART #

LD TM(DAYS) U/M

COST $

OHT.REO. VEH.CODE PART DESCRIPTION

A-13

21

EA

0.690000

693.00

C-11

11

EA

0.060000

537.00

C-19

11

EA

0.055000

499,00

C-21

11

EA

0.045000

712.00

C-75

72

EA

0.102000

200.00

C'87

72

EA

0.059000

200.00

H-09

16

EA

0.059375 1365.00

H-41

16

EA

0.110000

FIGURE 1 . 1 ( B ) : OPTION RELEASED THAT ARE LATE.

c

PARTS

I

WHOSE

OF

22.00

MODULE

SHOP

50 1-WAY PCB ~ 1000 39/48 RD 220 16V 39or48 PF .22 MFO 100 VOLT a 1000 39/48 PF .1MFD 100 VOLT ~ 2500 PAC/35 13 HFD lOOV NP PAC/35 4.4 MFD lOOV NP 20 HC SNI-1 16K g$950 8K ~$750 20 HC 8TW-6000 16

V

-

PURCHASE

O_RR P U R C H A S E

ORDERS

TO

ORDERS

BE

ARE

PROMISED

THIS

WEEK

O_RR

EARLIER

This c a t e g o r y p r o v i d e s r e m i n d e r s of open orders t h a t are due this w e e k or are a l r e a d y late. A c h e c k of open shop and p u r c h a s e orders s h o u l d reveal identical i n f o r m a t i o n and p e r h a p s p r o v i d e some additional i n f o r m a t i o n w h y these open orders are late. Figure 2.1 shows the list of open p u r c h a s e orders for this category. A g a i n this i n f o r m a t i o n should be s t u d i e d in c o n j u n c t i o n w i t h c a t e g o r i e s i, 4 and the M R P o u t p u t table. On b o t h p a r t i a l and c o m p l e t e receipt of the q u a n t i t i e s of the p u r c h a s e or shop orders, it is important to a d j u s t the o r d e r quantities and the stores on h a n d i n v e n t o r i e s accordingly. In the case of complete receipt, the o r d e r will be closed, and the date of r e c e i p t recorded.

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Proceedings of the I lth Annual Conference on Computers & Industrial Engineering

PURCHASE ORDERS DUE THIS WEEK: PART # L-11 P-08

DESCRIPTION 59-77-002701 TORIOD @ 1000 PLASTIC CASE # G700

ORDERS UNIT/M V/CODE 1000.00 EA 27 2000.00 EA 33

PURCHASE ORDERS DUE LAST WEEK AND EARLIER:

PART # A-12 B-06 B-07 B-13 G-06 1-08 1-09 1-38 J-D6 L-12 P-12 P-16 P-34 P-38 R-60 R'69

DESCRIPTION ORDERS SNI-35 PCD ADJ. @ 1000 1000.00 MASTER CARTON 4X4X4 RSC 200.00 MASTER CARTON 6X6X3 300.00 MASTER CARTON 9X8X4 RSC 250.00 # 4945-I" cut 4" @ 5RL = 1620pcs 1620.00 LABEL LLO @ A-SOO0 2500.00 LABEL LRO @ A-5000 2500.00 LABEL COIL 2 . 1 5 " @ 2000 2000.00 RCA MONO 2101J 2500.00 COIL SLUG # 4077235121 @ 50,00010000.00 BUBBLES 750' ROLL CUT EVERY 2 . 4 " 1.00 WASHER # 2 3 " x . 7 5 " @ 1000 1000.00 EL-CAST RESIN @ 45 tbs. per pail 675.00 N/S BLUE 42mm 1.65" 6mit @ 1300' 2600.00 C W RESISTOR 5 OHM 5 WATT @5000 5000.00 TRIMMER POT PTIOLH IK 2100.00

FIGURE 2.1: CATEGORY 2

3 -

PARTS

UNIT/M V/CODE EA 50 EA 28 EA 28 EA 28 EA ]2 EA 21 EA 21 EA 21 EA 12 EA 56 RL 28 EA 36 LB 26 FT 18 EA 40 EA 29

- OPEN PURCHASE ORDERS TO TRACK.

WHOSE

SALES

ORDERS

ARE

PROMISED

THIS

WEEK

O__RR E A R L I E R

This category provides reminders of customer sales orders that are due for delivery this week or are already late. A check of customer s a l e s o r d e r s s h o u l d p r o v i d e the p l a n n e r w i t h f u r t h e r i n f o r m a t i o n concerning the customers involved and the extent of the tardiness. Figure 3.1 s h o w s an e x a m p l e listing of s a l e s o r d e r parts. An investigation into the MRP output tables of the parts and components of those parts may also reveal additional insight of the tardiness. In many Just-In-Time (JIT) manufacturing [6],[11], the sales order is used as the production order in place of the shop order. The list in figure 3.1 then becomes the basis for the issue of production orders for the week. A storeroom transaction list for the sales order can be used for backflushing the component part inventories based on the bill of materials after the products are manufactured [4].

SALES ORDERS DUE THIS WEEK: PART # ANT'33 C 9 C 6 SNI-15 C 1.8 C 1.59 C .36 C .16 C .06 4TW-6000

DESCRIPTION MODEL ANT'33 COIL 9 mHy COIL 6 mHy MODEL SNI-15 COIL 1,8 mHy COIL 1.59 mHy COIL .36 mHy COIL .16 mHy COIL .06 mNy MODEL # 4TW-6000

ORDERS 407.00 40.00 60.00 1291.00 60,00 43.00 100.00 100.00 100.00 200.00

UNIT EA EA EA EA EA EA EA EA EA EA

SALES ORDERS DUE LAST WEEK AND EARLIER: PART # SNI-1 AC-IO0 AC'150 ALP-IO0 ANI-44 C 7.5 C 5.1 C 3.74 C 2.5 ENF-IO C .45 C .08 CSS-300 LP-IO0 FIGURE 3 . 1 :

DESCRIPTION MODEL SNI-1 MODEL AC-IO0 MODEL AC'150 MODEL ALP-IOO MODEL ANT'44 COIL 7 . 5 mHy COIL 5.1 mHy COIL 3.74 mHy COIL 2 . 5 mHy MODEL ENF-10 COIL .45 mHy COIL . 0 8 mHy MODEL CSS-300 MODEL LP-IO0

ORDERS UNIT/M 1275.00 EA 100.00 EA 20.00 EA 60.00 EA 500.00 EA 20.00 EA 59.00 EA 46.00 EA 100.00 EA 28.00 EA 120.00 EA 99.00 EA 600.00 EA 96.00 EA

CATEGORY 3 " SALES ORDERS TO TRACK.

Chong: Resolving part shortages and machine/labor overloads

4 - PARTS W H O S E S C H E D U L E D R E C E I P T S ARE R E C O M M E N D E D FOR R E S C H E D U L E If e v e r y t h i n g w o r k s to p l a n exactly, t h e n r e s c h e d u l e s will be c o m p l e t e l y u n n e c e s s a r y . A l t h o u g h m u c h has b e e n said and a c c o m p l i s h e d in JIT m a n u f a c t u r i n g [1],[6],[11], w h o s e p h i l o s o p h y is to p r o d u c e only to r e q u i r e m e n t s and e l i m i n a t e w a s t e s of all kinds i n c l u d i n g t a r d i n e s s and early timeliness, r e s c h e d u l e s a r e s t i l l r e q u i r e d d u e to u n f o r e s e e n circumstances such as machine breakdowns, quality problems, t r a n s p o r t a t i o n d e l a y s and others. R e s c h e d u l e s may involve expediting p a r t s that are late as well as d e - e x p e d i t i n g parts that are too early. R e f e r e n c e to the M R P table is e x t r e m e l y helpful in t h e s e cases, because b o t h e x p e d i t i n g and d e - e x p e d i t i n g actions s h o u l d be r e v i e w e d in the light of the overall p r o d u c t i o n r e q u i r e m e n t s of the company. Also the d e t a i l s of the e x p e d i t i n g and d e - e x p e d i t i n g actions such as the quantity to m o v e f r o m o n e t i m e p e r i o d to a n o t h e r can be more accurately determined. E x a m p l e s of these can be seen in e a r l i e r options such as t h o s e found in figures 0.i and 0.2.

PARTS RECOMMENDED TO EXPEDITE: PART # P-08 T-03 R-01 C-11 L-11 A-16 P-21 O-ENFIO 0-CSS300

DESCRIPTION PLASTIC CASE # G700 AUDIO TRANS 1:1 RED TAPE M/O .1 OHM 2 WATT @ 1000 RD 220 16V 59-77-002701TORIOD @ 1000 SNI-15 PCB 10:1 @ 1500 TUBE 1 3/6 PACKAGING FOR ENF-IO PACKAGING FOR CSS-300

UNITS TO EXPEDITE/RESCHED 425 5000 499 100 203 1291 400 28 144

PARTS RECOMMENDED TO DE-EXPEDITE: PART # W'76 W'80 B-07 P-38 P-08 R-60 W-69 W-71 W-72 R-01 U-03 V-13 J-06 L-11 R-69 U-02 G-06 FIGURE 4 . 1 :

DESCRIPTION UNITS TO DE'EXPED/RESCHED RED 7" WIRE 16 GUAGE 9922 BLUE 7" WIRE 16 GUAGE 5000 MASTER CARTON 6X6X3 300 N/S BLUE 42mm 1.65" 6miL @ 1300' 1401 PLASTIC CASE # G700 1575 C W RESISTOR 5 OHM 5 WATT @5000 5000 BLACK WIRE 5" 16 GAUGE 10000 ORANGE WIRE 5" 16 GAUGE 10000 YELLOW WIRE 5" 16 GAUGE 20000 M/O .1 OHM 2 WATT @ 1000 501 IC TLO74CN OP AMP 317 AGC-3A 838 RCA NONO 2101J 2500 59-77"002701 TORIOD @ 1000 797 TRIMMER POT PTIOLN 1K 2050 IC TLO72CP OP AMP 117 # 4945-1" cut 4" @ 5RL = 1620pcs 1620 OPTION 4 OF MODULE V " EXPEDITING AND DE'EXPEDITING OPEN ORDERS.

c S T A T I O N S W I T H M A C H I N E AND L A B O R O V E R L O A D S In b o t h the t r a d i t i o n a l job shop and JIT m a n u f a c t u r i n g , capacity o v e r l o a d s of a s t a t i o n (this may be a machine, a m a c h i n e group, an a s s e m b l y area or a U-line) in any of the w e e k s over the planning h o r i z o n , w i l l p r o v i d e t h e u s e r t h e w a r n i n g of i m p e n d i n g p r o b l e m s . R e s o l u t i o n of the o v e r l o a d p r o b l e m may include the w o r k i n g of overtime, t e m p o r a r y h i r i n g of workers, the a d d i t i o n of a second or third shift, the a d d i t i o n of machines, i n c r e a s i n g the speed of the m a c h i n e s if p o s s i b l e or r e s c h e d u l i n g of the o v e r l o a d s to w e e k s that h a v e underloads. The c a p a c i t y r e q u i r e m e n t s of late orders are often overlooked, and they h a v e to be t a k e n into account along w i t h o t h e r r e l e a s e d orders and p l a n n e d orders. The r e s o l u t i o n of o v e r l o a d u s i n g r e s c h e d u l e s of planned o r d e r s can be f a c i l i t a t e d if "pegging" [14], or just s i m p l y the tracing of the o v e r l o a d s to the p o t e n t i a l sales orders that will be affected. F i g u r e 8.1 shows the i m p l e m e n t a t i o n of this o p t i o n w i t h the facility to t r a c e the o v e r l o a d s to the end item orders.

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Proceedings of the 1lth Annual Conference on Computers & Industrial Engineering

REC# STATION #-DESCRIPTION

WEEK-BEGIN AVAIL-MHRS REQ-MHRS

1 000001 LABOR ASSEMBLY

-LATE

550.00

662.00

1 000001 LABOR ASSEMBLY

08/18

550.00

565.00

RESCHEDULE RECOMMENDATIONS FOR STATION: 000001 LABOR ASSEMBLY OVERLOAD IN WEEK OF : 0 8 / 1 8 THE FOLLOWING PARTS WILL BE AFFECTED: END PART ALP-85 WEEK BEGINNING: END PART C 9 WEEK BEGINNING: END PART C 6 WEEK BEGINNING: END PART C 1.8 WEEK BEGINNING: END PART C 1.59 WEEK BEGINNING: END PART C .36 WEEK BEGINNING: END PART C ,16 WEEK BEGINNING: END PART C .06 WEEK BEGINNING: END PART 4TW-6000 WEEK BEGINNING: SERVICE PART C .16B WEEK BEGINNING: END PART 8TW-6000 WEEK BEGINNING:

08/25 08118 08/18 08/18 08/18 08/18 08/18 08118 08/18 08/25 09/01

FIGURE 8.1: STATIONS OVERLOAD AND TRACING OF PARTS AFFECTED.

CONCLUSION MRP tables with materials schedules that require rush orders, late receipts and deliveries are presented to show the complexities faced by a planner who has to make decisions regarding order releases, order d e l i v e r i e s , e x p e d i t i n g and d e - e x p e d i t i n g of o p e n orders. A s u m m a r y actions list provides the decision support to planners of MRP systems. An example implementation of this approach on a microcomputer based MRP system is presented. This example implementation has been tested and used successfully by several small manufacturers over the last three years. The listings and s c r e e n d i s p l a y s are t a k e n from a real implementation at Pacific Accessory Corporation of Santa Ana, California [5],[9],[10], which has used the system for the past year or so. REFERENCES [i] A u t o m o t i v e I n d u s t r y A c t i o n Group, "The J a p a n e s e A p p r o a c h to Productivity Vol. 1-4, 1983. [2] Chong, P. S., "MRP-DSS Users Manual", copyright 1986. [3] Chong, P. S., "System Combines Manufacturing Resource Planning and Decision Support Approach," Industrial Engineering Journal, Oct. 1985, Vol.17, No.10. [4] Chong, P. S., "Designing an effective Inventory Control System", submitted to IIE Journal. [5] Chong, P. S., "Case S t u d i e s in M R P - D S S on the IBM PC and Compatibles", submitted to IIE Publications. [6] Hall, Robert, "Zero Inventories", Dow Jones-Irwin, 1983. [7] M R P - D S S s o f t w a r e , Advanced MicroPower Inc, P . O . B o x 8890-566, Fountain Valley, CA 92728 [8] Orlicky, J., "Materials Requirements Planning", McGraw Hill. [9] PAC - Pacific Accessory Corporation, 3016 A South Halladay, Santa Ana, CA 92705. [i0] PAC Catalog - Autosound Products for Maximum Performance. [Ii] Schonberger, R.J., "World Class Manufacturing", Free Press, 1986. [12] Taylor, D. L. "Backflushing MRP - Key to Streamlined JIT Materials Movement", Zero Inventories Seminar Proceedings, APICS, May 1984. [13] Turban, E., "Decision Support Systems (DSS): A New Frontier for Industrial Engineering," Computers and Industrial Engineering Journal, Vol.7, No.l, 1983. [14] V o l l m a n , T.E., B e r r y W.L. and W h y b a r k , O.C., "Manufacturing Planning and Control System", Richard D.Irwin, 1988, 2nd Edition.