mpc 5 2003
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Transcript of mpc 5 2003
Optimized Production Technology
Some production planning and control system focus on bottlenecks.
Bottlenecks are operations, machines that impede production because they have less capacity than upstream or downstream stages.
At bottlenecks operations, batches of product arrive faster than they can be completed
A bottleneck is defined as any resource whose capacity is less than the demand place upon it.
It is a constraints within a system that limits throughput
A bottleneck may be a machine, scarce or highly skilled labor or a specialized labor or a specialized tool
A non bottleneck is any resource whose capacity is greater than the demand place on it
A capacity constrained resource (CCR) is one whose utilization is close to capacity and can be a bottleneck if not scheduled carefully
• Increase capacity of constraint• Ensure that well trained people are
available to prevent constrain• Developing alternative routing,
processing procedure• Moving inspection to a position just
before the bottleneck. This restricts entry of defectives into bottleneck
• Scheduling less work at work centers supplying bottlenecks
TOC is that body of knowledge that deals with anything that limits an organization’s ability to achieve it goals
• Dr. Goldratt around 1980, founded that manufacturer were not doing good job in scheduling and in controlling their resource and inventory
• To solve this problem Goldratt developed a software that scheduled jobs through manufacturing processes taking into account limited facilities, machines, personnel, tools, material and any other constraint that would affect a firm’s ability to adhere to schedule
That is why sometimes OPT also called
Theory of Constraints To understand principles behind
OPT Goldratt described 9 principles based on production scheduling which are as follows
Do not balance capacity balance the flow
Each work center in a mfg. operation is subjected to different random occurrences for ex machine breakdown, raw material availability etc. This will lead to delay. Efforts should be made to create a smooth flow of material through the system for downstream market
• Use of nonbottleneck is determined by other constraints in the system
bottleneck non bottleneckCapacity = 100 unit/hr capacity=
200unit/hrOutput = 100 units/hr output =
100 unit/hr
1 2
Utilization and full employment of a resource are not same
NB B B NB
Capacity of box 4 is 250 units/hr however, it can only be utilized at the rate of 150 units/hr because of box 3. note that box 2 is bottleneck to box 1. but box 3 is principal bottleneck
1C= 400uO=400u
2c=300 uo=300u
3c=150uO=150u
4C=250uO=150u
An hour lost on a bottleneck is an hour lost on all the system
If a bottleneck can produce 130 units/hr then full system can produce that only, no matter whatever the capacity is at upstream and downstream
An hour saved on a non bottleneck source is just a mirage
Since capacity of the system is governed by bottleneck resource, saving time on a non-bottleneck source does nothing for the throughput in the whole system
Capacity= 200 units/hr capacity = 250 units/hrHour saved 0 hour saved 0.25
1 2
Bottlenecks govern both throughput and the accumulation of inventory
Capacity= 400 300 150 250Output= 400 300 150 150Production rate here is 150 unit/hr which is capacity
of bottleneck. As result inventory accumulates at a rate of 250 unit/hr
1 2 3 4
The size of transfer batch does not need to be equal to process batch
The transfer batch is the quantity of material transferred from one work center to another, where as the process batch or production lot, is that quantity of material produced between each machine set up
Lot sizes should be variable and not fixed
The lot sizes in OPT are a function of the schedule and thus should not be fixed over time or from operation to operation.
Schedules must be established by taking into account all system constraints
Identify the system constraint Decide how to utilize system
constraint Align every part of system to support
constraint even if this reduces the efficiency of non-constraint resources
Evaluate the system constraint If in the previous step the constraint
have been broken go back to step 1
According to Goldratt the goal of a firm is to make money.
If a firm makes only money than it will prosper
To adequately measure a firm’s performance three set of measurement are used.
(1) Financial measurement:-Net profit, Return On Investment, Cash
flow(2) Operational measurement:-Throughput (good sold), Inventory,
Operating expenses ( money that firm use to convert inventory into throughput)
(3) Productivity:-Productivity is measured in terms of
output per labor hour.
• All mfg. processes and flows can be simplified to four basic configuration show below:
If X is bottleneck and Y is non bottleneck (excess capacity)
There are so many means by which bottlenecks can be controlled, they are
DBR SchedulingTime componentsSaving timeAvoid changing a non bottleneck into
bottleneckQuality aspectsBatch sizingVAT analysis
There are two ways to find bottleneck in a system
One is capacity resource profile Other is knowledge, look and talk
• The instrument that can be used to control bottleneck/ control production are
• Drum, Buffer and Rope(1) Drum:- if the system contains bottleneck
the bottleneck is the best place for control. This control point is called drum because it strikes the beat to ensure the upstream operation do not over produce and build up excess WIP inventories.
If there is no bottleneck then best place to set drum is capacity constrained resource.
(2) Buffer:- Keep a buffer inventory in front of bottleneck make sure that it always has something to work on. Because it is a bottleneck so its output determines the throughput of the system
(3) Rope:- Communicate back upstream to A what D has produced so that A provides only that amount. This keeps inventory from building up. This communication is called rope
Following types of time make up production cycle time. If we identify them and measure them we can reduce bottlenecks.
(1)Set up time(2)Process time(3)Queue time(4)Waiting time(5)Idle timeFor a part waiting to go through
bottleneck queue time is greatest. For a non bottleneck waiting time is greatest
Always a bottleneck’s capacity is less than a market demand. There are number of ways we can save time of bottleneck for ex.
Better toolingHigher quality laborReducing set up time
When non bottleneck resources are scheduled with larger batch size, this action would create a bottleneck that we should avoid
The bottleneck does not have extra time so there should be quality control inspection just prior to bottleneck to ensure that the bottleneck work only on good parts
Also there should be assurance of quality downstream from bottleneck to maintain throughput
For bottleneck resource larger batch size is desirable because larger batch size reduces set up time so we can save time
For non bottleneck resource small batch size is desirable
• All manufacturing firms can be classified into one or a combination of three types designated as V, A & T.
• In a V plant to overcome problem of bottleneck batch size should be reduced
• In an A plant bottleneck problem can be overcome by reduced batch size as well as DBR scheduling
• In a T plant efficient human resource can be useful in reducing bottleneck
Production Supply chain (distribution) Finance and accounting (operating
expenses, investment) Project management ( critical chain
project management) Marketing and sales (sales process
engineering)
Increased throughput Increased productivity Reduction in WIP Better utilization of capacity
It may reduce efficiency of non bottlenecks
It is not part of main stream business Not as efficient as Operations
Research techniques Its an applied philosophy not pure Bottlenecks can always not be
improved because it may be due to intellectual property