CHAPTER 17: Operations Scheduling
Effective Production Control
Plan--->D=
evelop
production plans and schedules
Control-->=
;Monitor
Control-->= ;Revise as necessary to achieve conformance to plans and stay "on" schedu= le.
* An effecti=
ve
information system is essential to success. (Computerized Information systems =
can be
very helpful)
Schedulin=
g--developing and assigning specific dat=
es for
the start and/or completion of the necessary work tasks.
Controlli=
ng
production--collecting=
and
analyzing the data necessary to evaluate the progress on jobs relative to
plans, and initiating corrective measures as necessary.
Expeditin=
g--is the application of personal attent=
ion to
improve progress on specific jobs.
(A corrective measure)
Routing--specifying the flow through work stat=
ions
necessary to produce a product.
Job shop
variable
Batch Processing=
semi-variable
Repetitive
fixed
Scheduling i=
s a 2
stage process
1. Loading
2. Dispatching
Loading--assigns work to a work center but doe=
sn't
establish a sequence of jobs through that workcenter.
We use load =
reports
to determine what capacity is available for use.
Dispatchi=
ng--sequencing of the work through a work
station. (n--no. of jobs/1--n=
o.
machines) Which job first,
second,... &n=
bsp;
* Use some d=
ecision
rule to decide which of the n jobs at a machine goes first.
Select 1 of =
n jobs
then: select 1 of n-1 jobs
then: select 1 of n-2 jobs
Dispatchi=
ng
Rules:
1. Johnsons Rule (2 or =
3 work
centers)
2. FIFO
* =
3. SPT Shortest processing time
4. EDD Earliest Due Dat=
e
5. LAS Least Average Sl=
ack
Johnsons =
Rule
1. List processing time=
for
each job.
2. Select job with shor=
test
time at either W.C.
3. If 1st W.C. schedule=
ASAP
If 2nd W.C.
schedule ALAP
If tie:
diff. jobs:
=
1st station ASAP
2nd
station ALAP
same job: schedule arbitrarily
4. Remove job from list and continue.=
Job Shop Sche=
duling
is quite complex.
Often an order is received for a product we have never built. In such cases we must = first design the product, develop specifications, B.O.M., estimates of labor cost= s, material costs, lead times, etc. to come up with a bid. THESE ACTIVITIES MUST BE SCHEDULED ALSO. Therefore there is a L.= T. associated with work that must be done before production begins and there are costs associated with those activities.
Proposal from Customer
Design and Specifications
Estimating Procedure
Bid
Production
Delivery
* The success of a company depends on how well they ca= n do not one but all of these things.
A company may use:
a. BACKW= ARD scheduling
b. FORWA= RD scheduling
Production Control in Batch Processing.
MRP System is very helpful in this environment because= it is very helpful for planning and control.&nbs= p; It doesn't just schedule material orders and receipts=3D=3D>it can schedule production activities. Accurate info. is critical--must be timely also.
With scheduling done the focus shifts to Production= Activity Control 2 Major component= s
1. Input/Output Control=3D> = Balancing workloads and capacity at work centers to prevent starvation & Queues (W.I.P.)
2. Priority Control=3D> attempts to make sure that jobs worked on are the ones that are most needed.
OBJ.
1. Keep lead times predictable
2. Utilize capacity efficiently
3. Keep Queues to a minimum
Expediting (de-expediting): necessary because in a job shop th= ings don't always go as planned. (most of the time in the majority of job shops.= )
There would not be many problems if orders of material= s were received on time, the various work stations worked at a predictable rate all the time, nothing got scrapped, people were predictable, and capacity was adequate. This is generally n= ot the case and queues build up at some work stations and other work stations get starved. Constant monitoring = is necessary and problems must be uncovered and solutions developed =3D> Sh= op Floor Control
We attempt to assure that priorities are met and it is= a pretty much continuous job of expediting (making changes to hurry things al= ong) and de-expediting (halting or slowing the progress of a job--maybe because a delay has caused part of assembly needed to not be available when needed.)<= /p>
Priority systems such as the critical ratio.
CR =3D Due date - Today's date
divided by
Days required to complete j= ob
< 1 late =3D> maybe it gets 1st priority at W.S.=
The nature of production control and scheduling is som= ewhat different for different types of manufacturing.
Job Shop---Batch Processing---Repetitive
JOB SHOP
* most complex
* deals with everything from design to delivery
* major issues: bidding, scheduling, lead time, queues, bottlenecks
* keeping track of where everything is and at what sta= ge of completion is a major challenge
* Q control is useful here-- computer based tool to ma= ximize capacity use and minimize queues. O.P.T. can be useful.
BATCH PROCESSING
* Queues are a major issue--means that priority contro= l is very important. Bottlenecks also.<= /p>
* We would like to keep queues as small as possible so= that lead time is short and W.I.P. is low.
* MRP System can be helpful in this situation as can J= .I.T. and O.P.T.
REPETITIVE
* Least complex
* The efficient design of products and processes is critical.
* In system design engineers and management make decis= ions that influence system efficiency (Line Balancing). Balancing the flow is a major issu= e--the pace of the system influences level of output.
* Output level is adjusted by cutting back on, or decr= easing run time.
* MRP, JIT, OPT