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Operational Production Management - Coggle Diagram
Operational Production Management
Principles of PPC
Definitions
Production planning: defines action alternatives and goals for the production function
Production control tries to put the production plan into action
Hierarchical levels of PPC
Strategic production planning
Tactical production planning
Operative production planning
Results of PPC
Development of PPC systems
MRP I --> MRP II --> ERP --> ERP II (Internet based) --> APS
Lot sizing
Definition of production lot
A production lot is a certain quantity of product that is produced on a machine in a single production run without an interruption of the production process
Basic decision problem
Lot sizing aims on balancing the trade off between setup and inventory carrying cost by finding an optimal lot size that minimizes the sum of the both cost components --> lot sizing has to solve both a quantity and a scheduling problem
Two-stage lot sizing models
Open production: each completed unit is
immediately shipped to the next stage
Open push system (p>d)
Open pull system (d>p)
Closed production: the entire lot is shipped to
the next stage once it has been completed
Closed push system (p>d)
Closed pull system (d>p)
Equal-sized batch shipments
The lot size x is
split up into m batches
Push system (p>d)
Pull system (d>p_
Unequal-sized batch shipments
Push system: start with a small batch to minimise lead time
Pull system: start with a large batch --> batches of decreasing sizes
Multi-stage production system
combine push and pull system, open and closed system
determine a single optimal production lot size for the entire production system
The case of batch shipment in multi-stage production system
Lot sizing under constraints
Storage space restrictions
Use Lagrangean multipliers to calculate restricted lot sizes
Constrained production capacity
sum of setup and production times does not exceed the available total run time T
Use Lagrangean multipliers
Setup cost reduction
Simultaneously planning lot sizes
and lot sequences
Common cycle approach
: Production phases are repeated one after another in a cyclic fashion without any overlaps --> products have a common cycle
The case of batch shipments
Scheduling
Scheduling for a single machine
A branch and bound method
Scheduling for multi-machine
Methods that find an optimal solution
Johnson's method:
aims on minimising the makespan
The jobs are processed in the same sequence -->
Flow-shop problems
Lomnicki's method:
Aims on minimising the makespan of a flow shop problem
It is also a branch-and-bound method, but calculates a bound for each machine-job-combination, not only a single bound for each job
Heuristic methods
Priority rules
:
First come, first served
Shorted processing time
Earliest due date
Critical ratio
Shifting bottleneck heuristic for
job shop scheduling problems
n jobs must be processed on m machines
disjunctive graph
Generic algorithms
NEH, CDS
Other scheduling problems:
Minimizing the number of late jobs
Moore's algorithm
Lawler's algorithm
Introduction
The aim of scheduling is to determine a sequence for jobs that minimizes or maximizes the defined objectives
The role of graphs in scheduling: If graphs contain
short cycles
, then jobs block each other --> the graph is infeasible