Materials Handling: Materials Handling Chapter 11
Materials Handling: Materials Handling Material handling is an activity that uses the right method to provide the right amount of the right material at the right place, at the right time, in the right sequence, in the right position and at the right cost
Materials Handling (Cont): Materials Handling (Cont) Systems perspective
20-70% of product cost attributed to material handling
Materials Handling Principles: Materials Handling Principles
Materials Handling Principles (Cont): Materials Handling Principles (Cont)
Materials Handling Equation: Materials Handling Equation Material Handling Equation (see Fig 11.3)
Unit Load: Unit Load Unit load - number of items or bulk material arranged so they can be picked up and delivered as one load
Large or small?
If large, cost/unit handled decreases
But, depending upon
cost of unitizing, de-unitizing
Unit Load (Cont): Unit Load (Cont) space required for material handling
material handling carrier payload
work-in-process inventory costs
storage and return of empty pallets or containers used to hold the unit load
smaller unit load may be desired
Unit Load (Cont): Unit Load (Cont) Seven steps to design a unit load
Unit load concept applicable?
Select the unit load type
Identify most remote source of load
Determine farthest practicable destination for load
Unit Load (Cont): Unit Load (Cont) Establish unit load size
Determine unit load configuration
Determine how to build unit load
Material Handling Device Types: Material Handling Device Types Conveyors
Palletizers
Pallet Lifting Devices
Trucks
Robots
Material Handling Device Types (Cont): Material Handling Device Types (Cont) AGVs
Jibs, Cranes and Hoists
Warehouse MHSs
Conveyors: Conveyors Accumulation
Belt
Bucket
Can
Chain
Conveyors (Cont): Conveyors (Cont) Chute
Gravity
Pneumatic or vacuum
Power and free
Roller
Conveyors (Cont): Conveyors (Cont) Screw
Skid
Slat
Tow line
Trolley
Wheel
Palletizers: Palletizers
Pallet lifting devices: Pallet lifting devices
Trucks: Trucks Hand truck
Fork-lift truck
Pallet truck
Platform truck
Counterbalanced truck
Tractor-trailer truck
AGV
Robots: Robots Point-to-point
Contouring or continuous path
Walkthrough or teach
Lead through or teach pendant
Hydraulic
Servo-controlled
AGVs: AGVs
Hoists, Cranes and Jibs: Hoists, Cranes and Jibs
Warehouse MHSs: Warehouse MHSs Discussed in Chapter 12
MHSs in Action: MHSs in Action Europe Combined Terminals (ECT)
ECT - one of largest in world and largest in Europe
Goods shipped from and to Europe
Built on reclaimed land in the North Sea
Large and Small containers
MHSs in Action (Cont): MHSs in Action (Cont) Trucks wait to be off-loaded by straddle carrier
Carrier takes container to holding area
Shipped in approximately 2 days
Mobile gantry cranes on tracks deposit containers in forward area
MHSs in Action (Cont): MHSs in Action (Cont) Mobile gantry cranes hold containers in top four corners and deposit on waiting AGVs
Fleet of AGVs in forward area take containers to tower cranes
Tower cranes deposit load on ship bed
Procedure reversed for off-loading ship
AGVs: AGVs Classification of MHS
Synchronous systems
Asynchronous systems
Synchronous systems, e.g. conveyors, used in continuous processes or heavy traffic, discrete parts environments
AGVs (Cont): AGVs (Cont) Asynchronous systems, e.g., AGV, AS/RS, fork-lift trucks, monorails, cranes and hoists used in light traffic, discrete parts environments when material handling flexibility desired
Design and Control Problems in AGVSs: Design and Control Problems in AGVSs Material flow network
Location of pick-up/drop-off (P/D) points
Number and type of AGVs
AGV Assignments to material transfer requests
AGV routing and dispatching
Design and Control Problems in AGVSs (Cont): Design and Control Problems in AGVSs (Cont) Strategies for resolving route conflicts, so AGV throughput rate is maximized, and other costs (purchase, maintenance and operating costs of AGVs, computer control devices, and the material flow network, as well as inventory costs and production equipment idle costs incurred due to excessive material transfer and wait times), are minimized
MHD Selection and Assignment Model: MHD Selection and Assignment Model Minimizes operating and annualized investment costs of MHD
Variables and parameters
i part type index, i=1,2,...,p
j machine type index, j=1,2,...,m
l MHD type index, l=1,2,...,n
Li set of MHDs that can transport part i
H length of planning period
MHD Selection and Assignment Model (Cont): MHD Selection and Assignment Model (Cont) Di # of units of part type i to be produced
Kij set of machines to which part type i can be sent from machine j for next process
Mij set of machines from which part type i can be sent to machine j for next process
Ai set of machine types required for the first operation on part type I
Bi set of machine types required for last operation on part type I
MHD Selection and Assignment Model (Cont): MHD Selection and Assignment Model (Cont) Vl purchase cost of MHD Hl
Tijkl time required to move one unit of part type i from machine type j to k using MHD l
Cijkl unit transportation cost to move part type i from machine j to k using MHD l
Xijkl number of units of part type i to be transported from machine j to k using MHD l
Yl number of units of MHD type l selected
MHD Selection and Assignment Model (Cont): MHD Selection and Assignment Model (Cont)
MHD Selection and Assignment Model (Cont): MHD Selection and Assignment Model (Cont)
Example for MHS Selection and Assignment: Example for MHS Selection and Assignment Small manufacturing system
Processes two high volume parts P1 and P2- 50 and 60 units, respectively
Part P1 processed first on machine M1, and on machines M2 or M4 for second step and to machine M3 for final step
Example for MHS Selection and Assignment (Cont): Example for MHS Selection and Assignment (Cont) Of the 60 units of part P2, 30 are processed first on machine M1 and then on machine M2.
The remaining 30 units of part P2 are processed first on machine M3 and then sent to machine M2 for final processing
Example for MHS Selection and Assignment (Cont): Example for MHS Selection and Assignment (Cont) Two candidate MHDs - H1 and H2 with purchase costs of $100,000 and $140,000 available
Unit cost for transporting P1 and P2 on each of the MHDs as well as transportation times given
Example for MHS Selection and Assignment (Cont): Example for MHS Selection and Assignment (Cont) Assume there are 7150 seconds in the planning period
Each handling device is expected to make empty trips 30% of the time
Determine the required MHDs and assign departmental moves to them
Example for MHS Selection and Assignment (Cont): Example for MHS Selection and Assignment (Cont)
Example for MHS Selection and Assignment (Cont): Example for MHS Selection and Assignment (Cont)
Models for Conveyor Performance Analysis: Models for Conveyor Performance Analysis There are m stations which load or unload n carriers
Amount of material loaded on the jth carrier as it passes station i is fij
If material unloaded, assign a negative value to fij
Load/unload cycle is a period of length p
Models for Conveyor Performance Analysis (Cont): Models for Conveyor Performance Analysis (Cont) Construct a set Fi = {fi1, fi2, ..., fip} including load/unload activities carried out in p successive carriers
For eg., if add one load to one carrier at the first station, unload two from the next and let the third one go by without loading or unloading and repeat, cycle has a period of length 3
F1 = {1, -2, 0}
Models for Conveyor Performance Analysis (Cont): Models for Conveyor Performance Analysis (Cont) p need not be equal to n.
In a cycle, total material loaded must be equal to total unloaded
Models for Conveyor Performance Analysis (Cont): Models for Conveyor Performance Analysis (Cont)
Models for Conveyor Performance Analysis (Cont): Models for Conveyor Performance Analysis (Cont) One round completed when all m carriers have gone around the conveyor once
So, m/p load and unload cycles in the first round
Models for Conveyor Performance Analysis (Cont): Models for Conveyor Performance Analysis (Cont) If carrier j is in some position of the load/unload sequence (with respect to station i) during one round, it need not be in same position in subsequent rounds
Models for Conveyor Performance Analysis (Cont): Models for Conveyor Performance Analysis (Cont) It can be shown that if n mod p is not equal to 0, load picked up or dropped off will change from one round to the next, for the same carrier at the same station
Let Pijk be the load/unload sequence position of a carrier j, with respect to station i in round k
Models for Conveyor Performance Analysis (Cont): Models for Conveyor Performance Analysis (Cont) Given Pij1, Pijk can be determined using the following formula, for k=2, 3, ..., p
Pijk = [Pijk-1 + n mod p] mod p
After p rounds, the position sequence repeats itself
If Pijk=0, set Pijk=p
Models for Conveyor Performance Analysis-Example: Models for Conveyor Performance Analysis-Example
Models for Conveyor Performance Analysis-Example: Models for Conveyor Performance Analysis-Example Load/unload cycle length has a period 5
F1={2, 0, 0, 2, 3}; F2={-2, 0, 0, -1, -4}
Determine the conveyor capacity
Models for Conveyor Performance Analysis-Example: Models for Conveyor Performance Analysis-Example
Models for Conveyor Performance Analysis (Cont): Models for Conveyor Performance Analysis (Cont) Change conveyor capacity requirement in one of three ways
Change number of carriers n. Pijk will change resulting in different cumulative loads and hence, carrier capacity
Change load/unload sequence of one or more stations
Change the location of one or more stations