Week 1 - 2 Flashcards
Machine
hardware that performs job (sometimes called tool)
Workstation
collection of one or more identical machines
Part
component that moves through workstations
Process
specific job or task adding value to a part
Processing time
time to takes to perform task on a machine (without waiting time)
Throughput TH
avg. quantity of parts produced per unit time
TH best
= w/Tπ (w <= Wπ)
= r (w > Wπ)
Cycle Time CT
avg. time between release of job at the beginning until it reaches inventory point at the end of routing
CT best
= Tπ (w <= Wπ)
= w/r (w > Wπ)
Science of Maufacturing
Science is essential: describes nature with simple but powerful model
-> Requiring descriptive model to explain nature in factory
Science offers
Basics
- Quantitative relationship
Intuition
- Tool for determining approaches to pursue
Synthesis
- Proving unified framework
Science for figure out root causes of βwasteβ
Descriptive Model
Define object with fundamental principles or general laws
Understanding relationship among Understanding relationship among inventory, cycle time, throughput, capacity, variability
Prescriptive model
Provides detailed methods for decision making
develop based on descriptive m, to design and control for objectives
Two essentials of Maf. System
- Demand
- Transformation
Variability
Demand and transformation is subject to variation
causing misalignment
-> essential to understand cause of variability and how to deal with it for an efficient system
Buffers
excess resource that corrects misalignment (absorbing variability)
Time: delay between demand and satisfaction
Capacity: extra transformation potential
Inventory Buffer
Extra material in transformation process or between it and demand process
-> storage / land cost
Time Buffer
a delay between a demand and satisfaction of it by the transformation
process
-> customer satisfacftion
Capacity Buffer
Extra transformation potential needed to satisfy irregular or unpredictable demand rates
-> investment cost
Efficient Frontier
Infeasible (under curve): Defined by the state of art technology
Inefficient: Better position is possible
Raw Material Inventory (RMI)
Stock point at the beginning of process
Finished Goods Inventory (FGI)
Stock point where end Item is held prior to shipping to the customer
Routing
Sequence of workstations passed through by a part
Customer order
A request from a customer for a part (Demand)
Work in Process (WIP or WIP inventory)
Inventory between the start and endpoints of a product routing
Jobs
A set of physical materials that traverses a routing together
Yield rate (or yield)
Amount of usable outputs over the total outputs
Setting objectives:
- Find out current position
2. consider customer relationship (time sensitivity)
Bottleneck rate π
Maximum throughput rate (Capacity) of the workstation having
highest long term utilization
A routing canβt accept parts more than bottleneck rate
Utilization
arrival rate / effective production rate
Portion of time a WS actually performs over the total available time
Raw process time ( ππ)
average time it takes a single job to traverse the empty line
Critical WIP (Wπ)
ππ = πππ
WIP level when a line with no variability achieves maximum
throughput (π) with minimum cycle time π
Littleβs Law
WIP = TH * CT
parts = (parts/hr) * hr
Worst Case Law
- Variability in processing time
CT worst = w*Tπ
TH worst = 1/Tπ
Practical Worst Case
Assumption:
- Single machine at workstation
- Balanced line
- Variability that all WIP configurations are equally likely
Practical Worst Case Law
E. processing time single machine
{1 + (w-1) / N } * t
E. proc. time (=CT) of production line:
CT = {1 + (w-1) / N } * Nt
= Tπ + (w-1) / r
E. Throughput:
TH = WIP/CT
= w*r / (Wπ + w-1)
