Flexible Manufacturing System

NPTEL : OPERATIONS MANAGEMENTDEPARTMENT OF MANAGEMENT STUDIES INDIAN INSTITUTE OF TECHNOLOGY DELHI Discussant Professor D.K.Banwet B.E. (Mech.),M.E. (Indl. Engg.),Ph.D. (Indl. Engg./ Production Operations Mgt.) [ IITD], FIE Group Chair (Operations & Supply Chain Management)Former HOD DMS , Dalmia Chair Professor Former Coordinators ASRP & Entrepreneurship Programme Email : dkbanwet@dms.iitd.ac.in1 Module 3 : Systems Design

Module 3.2Group Technology & Flexible Manufacturing Systems(Duration: 1 Hour)

Lecture 10GROUP TECHNOLOGYGROUP TECHNOLOGY IS A MANUFACTURING TECHNIQUE AND PHILOSOPHY TO INCREASE PRODUCTION EFFICIENCY BY EXPLOITING THE UNDERLYING SAMENESS OF COMPONENT SHAPE, DIMENSIONS, PROCESS ROUTE, ETC. Group Technology is the realization that many problems are similar, and that by grouping similar problems, a single solution can be found to a set of problems thus saving time and effort. Why Group Technology?

Average lot size decreasing Part variety increasing Increased variety of materials With diverse properties Requirements for closer tolerancesFLEXIBILITYPRODUCTION CAPACITYTRANSFERLINESPECIAL SYSTEMFLEXIBLEMANUFACTURINGSYSTEMMANUFACTURINGCellsSTD. AND GEN.MACHINERYVOLUMEHIGHVARIETYLOWHIGHHybrid LayoutCellular layoutsGroup machines into machining cellsFlexible manufacturing systemsAutomated machining & material handling systemsMixed-model assembly linesProduce variety of models on one line

7Hybrid Layout: Group Technology

Machine 1Machine 2Machine 3Machine 4Machine 5Materials inFinished goods outOne Worker, Multiple Machines714This slide presents Figure 10.3 for discussion.Group TechnologyDrillingDDDDGrindingGGGGGGMillingMMMMMMAssemblyAAAALathingReceiving and shipping LLLLLLLL(a) Jumbled flows in a job shop without GT cells814This sequence is based on Figure 10.5 and shows the basic job shop layout prior to the introduction of GT and builds automatically.Group Technology(b) Line flows in a job shop with three GT cells Cell 3LMGGCell 1Cell 2Assembly areaAALMDLLMShippingDReceivingG918This sequence shows how a shop using three GT cells improves the flows. This sequence builds automatically.Group LayoutAdvantages:By grouping products, higher machine utilization can result.Smoother flow lines & shorter travel distances are expected than for process layouts.Team atmosphere & job enlargement benefits often result.Has some of the benefits of product layouts & process layouts; it is a compromise b/w the two.Encourages consideration of general purpose eqpt. Group LayoutLimitations:General supervision required.Greater labour skills reqd. for team members to be skilled on all operations.Critically dependent on production control balancing the flows three individual cells.If slow is not balanced in each cell, buffers & WIP storage are reqd. in the cell to eliminate need for added material handling to 8 from the cell.Has some of disadvantages of product & process layouts(compromise between the two)Decreases opportunity to use special purpose equipment. Group Technology:Benefits1. Better human relations2. Improved operator expertise3. Less in-process inventory and material handling4. Faster production setup34Group Technology:Transition from Process Layout1. Grouping parts into families that follow a common sequence of steps2. Identifying dominant flow patterns of parts families as a basis for location or relocation of processes3. Physically grouping machines and processes into cells35Everyday Examples

1. Fast food chains2. Doctors, dentists and also manufacturing

A FAMILY OF PARTSProduction Family

Lack Of Common Database For Mfg., Design... Dont redesign the wheel Automated process planning Database to drive the automated factoryBenefits Of Group TechnologyReductions inThroughput timeSet-up timeOverdue orders

Production floor spaceRaw material stocksIn-process inventory

Capital expendituresTooling costsEngineering time and costs

New parts designNew shop drawingsTotal number of drawingsContdOther Benefits Of Group Technology

Easier to justify automation Standardization in design

Data retrieval

Easier, more standardized process plans

Increases in qualityGt affects most every operating and staff function. It is more than merely a technique, but a total Manufacturing philosophy.GTDESIGNENGINEERINGDATAPROCESSINGMAINTENANCETOOL ENGINEERINGESTIMATINGINDUSTRIALRELATIONSQUALITYCONTROLR & DCOSTACCOUNTINGSALESINVENTORYPLANNINGPURCHASINGASSEMBLYMANAGEMENTMFG.ENGINEERINGSHIPPING &RECEIVINGClustering Techniques: the Fundamental Issue in Cell DevelopmentWe cluster parts to build part familiesPart Families visit cellsPart Families share set-up ideas and equipment (Family Fixtures)Part Families follow the same (or similar) process routingThese are the ideas and activities that offer reported benefitsClustering Techniques: the Fundamental Issue in Cell DevelopmentWe cluster Machines to build cells:Cells lead to Flow MathematicsCells contain all equipment needed to produce a part familyCells allow development of Multi-functional workersCells hold work teams responsible for production and quality They Empower the workersEmpowered to set internal schedulesEmpowered to assign tasksEmpowered to train and rotate jobsEtc, etc, etcBuilding the CMS Facility

Before ClusteringAfter ClusteringClustering MethodsUsing Process Similarity methods:Create Machine Part MatricesCompute machine pairwise Similarity Coefficient comparisons:

Example:Part NumberMachine IDX123456A11B11C11D111E111Computing Similarity Coefficients:Total Number is: [(N-1)N]/2 = [(5-1)5]/2 = 10For 25 machines (typical number in a small Job Shop): 300 SijsHere they are:

Continuing:

Here, if the similarity coefficient is .33 consider clusteringThis criteria means clustering: A&D, A&B, B&DC & EDeclustering:A&C, A&E, B&C, B&E and C&D, D&E

Continuing:Examining our Matrix and our freshly clustered machine cells, we develop 2 part families:For the Cell A/D/B: Part Numbers 2, 3 & 5For the Cell C/E: Part Numbers 1, 4 & 6Care must be taken (in most cases) to assure that each cell has all the machines it needs sometimes a couple of families need a key machine In this case, the manager must decide to either replicate the common machine or share it between the cells creating a bottleneck and scheduling problem for each cellThis is typically one of the cost problems in CMS systemsSummarizing:Make Machine/Part MatrixCompute Similarity CoefficientsCluster Machines with positive ( .33) SijsDetermine Part Families for the clusters (cells)Decide if machine replication is cost effectiveRe-layout facility and Cross Train workforceStart counting your new found cashCourt customers to grow part families on Cell-by-Cell basisOther Clustering Methods:Rank order ClusteringThis method automates the cluster study by computing Binary weights from a machine part matrixIt orders parts and machine cells automatically by structuring and computing the matrix with binary weightsIt implies a computer algorithm for solving the clustering problemIt may not solve if machines are needed by more than one family forces intelligence in application and hand scanning after several ordering iterationsRank Order Clustering Method:For each row of the machine/part matrix (M/P/M) read the pattern of cell entries as a binary word. Rank the rows by decreasing binary value. Equal values stay in same order.Ask if newly ranked rows in the matrix are the same as previous order? Yes (STOP) No (continue)Re-form the M/P/M with rows in new descending order. Now rank the columns by decreasing binary word weight. Columns of equal weight are left where they areAre current column weights the same as current column order? Yes (STOP), No (continue)Re-form the matrix column order per rank order (highest to left) and return to #1.RANK ORDER CLUSTERING FOR CELL FORMATIONSTEP 1:

Parts1624823422221120Dec Low EquipmentRank MachinesIIIIIIIVV16A2411116 + 4 + 1 = 2118B231118 + 2 +1 = 1124C221118 + 2 + 1 = 1132D211116 + 4 = 20 41E201118 + 2 + 1 = 115Arrange rows as per rank of decimal row euipment.STEP 2:

IIIIIIIVV16A241118B23114C221112D211111E20111Dec. Col. Equivalent24724723Rank 1425332STEP 3:

IIIIIIIVVA111B11C111D111E111Cell formed A D 111 1111 1111I III BCDV II IV Lets try it with our earlier problem:Part NumberMachine IDX123456A11B11C11D111E111Step 1:Part NumbersD. EquivRankMachine ID123456B. Wt:252423222120A1123+21 = 105B1124+23 = 244C1125+22=362D11124+23+21 = 263E11125+22+20=371Step 2: Must Reorder!Step 3:Part NumberB. WT.123456Machine IDE24111C2311D22111B2111A2011D. Equiv24+23 = 2422+21= 622+21+20=724+23=2422+20=524=16Rank154263Step 4: Must ReorderBack at Step 1:Part NumberD. EqvRank146325B Wt:252423222120Machine IDE11125+24+ 23=561C1125+24= 482D11122+21+ 20 = 73B1122+21=64A1122+20=55Order stays the same: STOP!Great Cluster Result!Issues in Clustering:R/O clustering oscillations indicating need of machine replication (happens often!)Presence of Outliers and/or Voids in the finished clusters Outliers indicate the need of machine replicationVoids indicate skipped machines in a cellGenerally speaking, these clustering algorithms are designed to convert existing routes for facility re-organization They require a previous engineering study to be performed to develop a series of routers on a core sample of parts that represent most of the production in the shopReduction Of Mfg. Costs By Various Steps Of Group Technology Applications

Improvements in Engineering DesignMaterials Management & Purchasing BenefitsProduction Control BenefitsManufacturing Engineering BenefitsTooling & Setup BenefitsManagement BenefitsOverall Cost Reduction & Increased ProductivityNot All Cost Savings Are Immediate...0 6 12 18 24 36Time (months)Flexible Manufacturing Systems (FMS)What Will Be CoveredDefinitionHistory of FMSFMS equipmentTypes of FMSApplications of FMSFSM different approachesAdvantagesDisadvantageDevelopment of FMSNuts and BoltsHow FMS worksA real world exampleSummary

41This is the outline of the Power Point Presentation for FMS.DefinitionA Flexible Manufacturing System (FMS) is a production system consisting of a set of identical and/or complementary numerically controlled machine which are connected through an automated transportation system.Each process in FMS is controlled by a dedicated computer (FMS cell computer).42This definition is from the Russell and Taylor Ops. Mgmt. text used in this class.History of FMSAt the turn of the century FMS did not exist. There was not a big enough need for efficiency because the markets were national and there was no foreign competition. Manufacturers could tell the consumers what to buy. Henry Ford is quoted as saying people can order any color of car as long as it is black. This was the thinking of many big manufacturers of the time.

After the Second World War a new era in manufacturing was to come. The discovery of new materials and production techniques increased quality and productivity. The wars end opened foreign markets and new competition. Now the market focused on consumer and not the manufacturer. The first FMS was patent in 1965 by Theo Williamson who made numerically controlled equipment. Examples of numerically controlled equipment are like a CNC lathes or mills which is called varying types of FMS. In the 70s manufacturers could not stay to date with the ever-growing technological knowledge manufacturers competitors have, so FMS became mainstream in manufacturing.

In the 80s for the first time manufacturers had to take in consideration efficiency, quality, and flexibility to stay in business.

43System 24 could operate 24 hours a day and be controlled totally by computers. This system was built in England. From Ops. Mgmt. text book for this class.Equipment of FMS Primary equipmentWork centersUniversal machining centers (prismatic FMSs)Turning centers (rotational FMSs)Grinding machinesProcess centersWash machinesCoordinate measuring machinesRobotic work stationsManual workstations Equipment of FMS Secondary equipmentSupport stationsPallet/fixture load/unload stationsTool commissioning/setting areaSupport equipmentRobotsPallet/fixture/stillage storesPallet buffer stationsTools storesRaw material storesTransport system(AGVs,,robots)Transport units(pallets/stillages)

Typesof FMS

Sequential FMSRandom FMSDedicated FMSEngineered FMSModular FMS

Applications of FMSMetal-cutting machiningMetal formingAssemblyJoining-welding (arc , spot), glueingSurface treatmentInspectionTesting

Why do we need flexibility in manufacturing systems?Variety in products thus options for the consumersOptimizing the manufacturing cycle timeReduced production costsOvercoming internal changes like failure, breakdowns, limited sources, etc.External changes such as change in product design and production system.

Flexibility in Manufacturing System:?

Flexibility can be defined as collection of properties of a manufacturing system that support changes in production activities or capabilities (Carter,1986).

Ability of the manufacturing system to respond effectively to both internal and external changes by having built-in redundancy of versatile equipments.Various types of flexibility?

Machine flexibilityCapability of a machine to perform a variety of operations on a variety of part types and sizesRouting flexibilityAlternative machines, sequences or resources can be used for manufacturing a part for changes resulting from equipment breakdowns, tool breakages, controller failures, etc.Process flexibilityAbility to absorb changes in the product mix by performing similar operations, producing similar products or parts.Product flexibilityAbility to change over to a new set of products economically and quickly in response to marketsProduction flexibilityAbility to produce a range of products without adding capital equipmentExpansion flexibilityAbility to change a manufacturing system with a view to accommodating a changed product envelope

Volume-variety relationship

FMS different approaches

The capability of producing different parts without major retooling

A measure of how fast the company converts its process/es from making an old line of products to produce a new product

The ability to change a production schedule, to modify a part, or to handle multiple parts

Advantages of using FMSTo reduce set up and queue timesImprove efficiencyReduce time for product completionUtilize human workers betterImprove product routingProduce a variety of Items under one roofImprove product qualityServe a variety of vendors simultaneouslyProduce more product more quickly

Disadvantage of using FMS Limited ability to adapt to changes in product or product mix (ex:machines are of limited capacity and the tooling necessary for products, even of the same family, is not always feasible in a given FMS) Substantial pre-planning activity Expensive, costing millions of dollars Technological problems of exact component positioning and precise timing necessary to process a component Sophisticated manufacturing systems

Development of FMSSeveral actions must be decided on before you can have a have a FMS. These actions include.Selecting operations needed to make the product.Putting the operations in a logical order.Selecting equipment to make the product.Arranging the equipment for efficient use.Designing special devices to help build the product.Developing ways to control product quality.Testing the manufacturing system.

Illustration example of a FMS

Nuts and Bolts of FMSFMS Layouts

Progressive Layout:Best for producing a variety of parts

Closed Loop Layout:Parts can skip stations for flexibilityUsed for large part sizesBest for long process times

57Progressive Layout: All parts in the production process follow the same progression through the machining station. Closed Loop Layout: Arranged for the general order of processing for a larger variety of parts.

FMS Layouts ContinuedLadder Layout:Parts can be sent to any machine in any sequenceParts not limited to particular part families

Open Field Layout:Most complex FMS layoutIncludes several support stations

58Ladder Layout: Allows two machines to work on product at the same time. Open Field Layout: Enables material to move along the machine centers in any particular order necessary.Flexible AutomationAbility to adapt to engineering changes in parts

Increase in number of similar parts produced on the system

Ability to accommodate routing changes

Ability to rapidly change production set up59Flexible automation is used when the product mix requires a combination of different parts and products to be manufactured from the same system. Challenges with FMSDetermining if FMS the best production system for your company (economically and socially)

Possible expansion costs associated with implementing FMS

Day to day maintenance of FMS operations60These challenges must never be overlooked when deciding whether or not to implement a FMS system. In order to get the best possible results you must answer the these questions within your own firms.Flexible Manufacturing systemHow Does It Work ?Making FMS WorkBy implementing the components of robotics, manufacturing technology and computer integrated manufacturing in a correct order one can achieve a successful Flexible Manufacturing System62Every situation will differ. Sometimes you may be required to implement only robotics or manufacturing technology. These are only suggestions as to making a FMS work.

An outline for Mechanical Engineering CAD/CAM laboratory Integrated System

How does it work?

ROBOTSFirst 5 axis robot is in charge of picking and placing parts which are scanned by the barcode reader, and transfer them to the left side for machining or throw it to the conveyor for the other operations.This robot utilizes a vacuum gripper to pick the parts.Pneumatic Robot which contained a few reed sensors, used to set the limits for the pneumatic cylinder motion. This robot is using a general griper which can be close or open in each time. This robot just picks the parts which are detected by the Metal Detector sensor, placed before it.Hence, the duty of this robot is to pick the Metal-Coated parts, chosen by the sensor placed near it.Second Five axis robot which has the same specifications as the former one, used to pick the Non-Metal parts (which are detected by non-metal detector sensor on the big conveyor) from the flexible conveyor and place them into a rail way for the next defined operations.This robot placed on a special Nut and Screw system which is connected to a Motor using to turning the screw in case of moving the robot across the Big conveyor .

First robotsecond robot

pneumatic robotCOMPUTERS AND SOFTWARES

First Robot is controlled by a General PC, using a visual basic program to read the barcodes and also control the robots motion. For each part the program decide Where to be placed according to the parts barcodeThe second 5-axis robot is controlled by a PC using special software which is named Robotica.Generally, this software has a GIU (Graphical User Interface) which can be used for programming the robot remotely. After writing the program, by pressing the Run Button on the program screen, each line transferred to the robot using a general RS-232 cable. Also we have another PC which is used to monitor the Main PlC , placed in an anti dust cabin for safety.

CONVEYORSWe have 2 Conveyors, one general belt conveyor and one big flexible conveyor which are driven by two different Motors . The specifications of these two conveyors are as below:

11Cm97Cm

63Cm176CmPLCsWe have two different PLC devices :A Siemens S7-200 PLC with 5 inputs and 5 outputs , which is used as secondary plc device , just to transfer the fire signal to the second five axis robot.A Telemeqanic PLC with inputs and output , used as main PLC device for controlling the motors, conveyors, sensors and all other feedback signals.

Telemeqanic Micro TSX PLC SIEMENS S7-200 PLCREVIEWING THE SCENARIO

To run the system three parts are designed for three different operations. At the first cell the scenario is collaboration of the barcode reader and the first robot. After inserting the part in the input place , the small conveyor start switch pushed down and the small conveyor runs.After this the parts moves across the barcode reader for reading the parts barcode, after that the conveyor stopped when the part reached the optical sensor on the belt conveyor.

The Barcode reader Device 3 parts(1 Metal and 2 Non-metal with different barcodes)The non-metal parts continue their route until they reach the non-metal sensor, at this time, the sensor send a signal to the main PLC and the main PLC send the required signal to the robot and also to the screw motion control, so the screw starts turning and the robot get close to the part which is in the conveyor waiting to be caught by the robot. During this operation, the PC which is used to control the second robot must be run and ready to send the program to the robot.The robot catches the part and after that the signal from the non-metal sensor goes off, so the screw starts in reverse direction by receiving a signal from the main PLC , and the robot throws the parts into a special rail at the end of the rout.

Metal Detector SensorNon-Metal Detector SensorComputer integrated manufacturing and PLCIn todays manufacturing units several PLCs are used to switch on or off robots ,conveyer belts and other part of manufacturing systems. The advantages of PLC in automated systems made PLC one of the main component of any Manufacturing unit.

An example of a simple and modern manufacturing 12Host computerRawMaterialsAreaSwarfdisposalUniversal Machining CenterAGV transport system 1AGV transport system 2Universal Machining CenterHeadIndexingMachinesWashMachineCoordinateMeasuringMachineAssemblyCells1 & 2FinishMachineCellPiecepartBufferAreaFMS Example One Design + One Assembly Process = Multiple Models

When different models are designed to be assembled in the same sequence they can be built in the same plant.This maximizes efficiency and allows the company to respond quickly to changing customer

FMS ExampleThrough the use of reprogrammable tooling in the body shop, standardized equipment in the paint shop and common build sequence in final assembly, Ford can build multiple models on one or more platforms in one plant.

In the body shop, where the sheet metal comes together to form the vehicles body, flexibility means more than 80 percent of the tooling is not specific to one model. It can be reprogrammed to weld a car or a truck or a crossover of similar size.Body Shop

In the paint shop, flexibility means robotic applicators are programmed to cover various body styles as they move through the paint booth with equal precision. This results in minimizing waste and environmental impact while maximizing quality. Paint Shop

In the final assembly area, flexibility means the build sequence is the same among multiple models on one or more platforms allowing for efficient utilization of people and equipment.Final Assembly

FMS Example

Virtual VerificationVirtual manufacturing technology allows Ford to quickly add various models into an existing facility or to reconfigure an existing facility to produce a new model. In the virtual world, manufacturing engineers and plant operators evaluate tooling and product interfaces before costly installations are made on the plant floor. This method of collaboration improves launch quality and enables speed of execution.

Classification of the manufacturing system based on Volume-variety considerations:

Transfer Line (High-Volume, Low-Variety Production system, H-L)

Machines dedicated to manufacture of one or 2 product types. Nearly no flexibility Maximum utilization and high production volume Direct labor cost is minimal Low per unit cost

Stand Alone NC machines / Flexible Manufacturing module (Low-Volume High-Variety Production system, L-H)

Highest level of flexibility Low utilization and low production volume Very high per unit cost

Mid-Volume Mid-Variety Production systems, M-M

Manufacturing Cell Flexible manufacturing system Special Manufacturing SystemManufacturing Cell

Low to mid-volume, most of the parts are manufactured in batch mode Similar to an FMS, but no central control Most flexible in CIM category Lowest production rate in CIM systems

Flexible manufacturing system

Actual M-M manufacturing system. Automated material-handling system, NC machines (flexible machines), automated tools and pallet changer, auto-gauge systems, etc. Allows both sequential and random routing of a wide variety of parts. Higher production rate than manufacturing cell High degree of overlap between this and cell manufacturing system Higher flexibility than special manufacturing systems

Special Manufacturing System

Least flexible category of CIM system Multispindle heads and low-level controller High production rate and low per unit cost Main difference: - Fixed-path material-handling system links the machines together. - Sequence based dedicated machines.What is FMS?

an automated, mid-volume, mid-variety, central computer-controlled manufacturing system

Activities covered: machining, sheet metal working, welding, fabricating, assembly

Physical components:Potentially independent NC machine tools capable of performing multiple functions and having automated tool interchange capabilitiesAutomated material handling system to move parts between machine tools and fixturing stationsAll the components are hierarchically computer controlledEquipment such as coordinate measuring machines and part-washing devices

81Class work: ask students to do this example:

Answer: Figure 8.5

A FMS consists of:

Physical subsystem

-Workstations: NC machine tools, inspection equipment, part-washing devices, load & unload area.-Storage-retrieval systems-Material handling systems

Control subsystem -Control hardware-Control software

NC machine tools:The major building blocks of an FMS,determine the degree of flexibility,determine the capabilities.Machining centers with numerical control of movements in up to five axes. Spindle movement in x, y and z directions, rotation of table, and tilting of table.

Workholding and Tooling considerations Fixtures and pallets must be designed to minimize part-handling time Strategies required for storage/retrieval of different fixtures Integration with AS/RS and material handling system Machining centers are equipped with tool storage known as tool magazine.

Control systems in FMSWork-order processing and part control systemPart process planning module, part routing module, part setup module, etc.

Machine tool control systemDNC transmitter control module, NC editor, machine monitor and control module

Tool management and control systemTo control the processing of parts and enhance the flexibility to manufacturing variety of parts. Tool identification, tool setup, tool routing, tool replacement strategies are accomplished by the system

Traffic management control systemMaterial handling and storage control system coordinates part routing, fixtures, pallets and tool modulesQuality control management systemCapabilities include collection, storage, retrieval, and achieving of work-piece inspection data.

Maintenance control system (service control system)On-line help, alarms due to problems, etc.

Management control systemProvides the management status of output performance.

Interfacing of these subsystems with the central computerFMS Architecture An FMS is a complex network of equipment and processes that must be controlled via a computer or network of computers. System is usually divided into a task-based hierarchy. One of the standard hierarchies that have evolved is the National Institute of Standards and Technology (NIST) factory-control hierarchy. This hierarchy consists of five levels and is illustrated in Figures.

The system consists of physical machining equipment at the lowest level of the system.

Workstation equipment resides just above the process level and provides integration and interface functions for the equipment. Pallet fixtures and programming elements are part of the workstation. Provides both man-machine interface as well as machine-part interface. Off-line programming such as APT for NC or AML for a robot resides at the this level.

The cell is the unit in the hierarchy where interaction between machines becomes part of the system. Provides the interface between the machines and material-handling system. Responsible for sequencing and scheduling parts through the system .

At the shop level, integration of multiple cells occurs as well as the planning and management of inventory.

The facility level is the place in the hierarchy where the master production schedule is constructed and manufacturing resource planning is conducted. Ordering materials, planning inventories, and analyzing business plans are part of the activities that affect the production system.Operational Problems in FMSPart selection and tool managementFixture and pallet selectionMachine grouping and loading, considering part and tool assignments

Part Selection

Batching approach- Part types are partitioned into separate sets called batches. The selected part types in a particular batch are manufactured continuously until all the production requirements are completed. Then processing the next batch, removing all the tools, loading new tools for the new batch.

Flexible approach- When the production requirements of some part types are finished, space becomes available in the tool magazine. New part types may be introduced into the system for immediate and simultaneous processing if this input can help increase utilization of the system. This requires more frequent tool changes.Layout ConsiderationsLayout is one of the important design characteristics of FMS design.The layout of machines to process part families in an FMS is determined by the type of material handling equipment used.

Fixed Product LayoutLimitations:Personal & equipment movement is increased.May result in duplicate equipment.Requires greater skill for personnel.Requires general supervision.May result in increased space & greater WIP.Requires close control & coordination in scheduling production. Fixed Product LayoutAdvantages:Material movement is reduced.When a team approach is used, continuity of operations & responsibility results.Provides job enrichment opportunities.Provides & promotes pride & quality because an individual can complete the whole jobHighly flexible; can accommodate changes in product design, product mix, & production volume.Algorithm:Step 0: Calculate = 2 + 4Step 1: Calculate max {a, b}, then T2 is optimal. Calculate T2 and stop. Otherwise go to step 2.Step 2: If > max {a, b} and 2 a + b, then T2 is optimal. Calculate T2 and stop. Otherwise go to step 3.Step 3: If > max {a, b} and 2 > a + b, then T1 is optimal. Calculate T1 and stop.

Example: Determine the optimal cycle time and corresponding robot sequences in a two-machine robotic cell with the following data:Processing time of Machine M1=11.00 minProcessing time of Machine M2=09.00 minRobot gripper pickup= 0.16 minRobot gripper release time= 0.16 minRobot move time between the two machines= 0.24 minSolution: Step 0: = 2 + 4 = 2(0.16) + 4(0.24) = 1.28 minStep 1: max {a, b}1.28 max {11, 9}, i.e.1.28 < 11. Therefore, T2 is optimal.T2 = + max {, a, b}T2 = [4 + 4] + max {1.28, 11, 9} = [4(0.16) + 4(0.24)] + 11T2 = 1.6 + 11 = 12.6 minThe optimal cycle time is 12.6 min and the optimal robot is given by fig (b) as shown in the previous slide. FMS Scheduling and Control

Flexible manufacturing systems can differ significantly in complexity. Complexity is determined by:The number of machines and the number of parts resident in the system.The complexity of parts and control requirements of the specific equipment.

Example 1: The most simple FMS consists of a processing machine, a load/unload area, and a material handler (a one-machine system is the most simple FMS that can be constructed).

Operation of this system consists of loading the part/parts that move down a conveyor to the machine. Once the part is loaded onto the machine, the robot is retracted to a "safe position" and the machining begins.For a single part is to be processed in the system, a minimum number of switches and sensors required are: Parts on the conveyor all have to be oriented in the same way. Robot can pick up the part and deliver it to the NC machine in the same orientation. Proximity switch or micro-switch is required at the end of the conveyor to detect when a part is resident, and on the machine for the same purpose.

A simple programmable logic controller can easily control this system.

The logic for the system is as follows:

If a part is resident at the end of the conveyor (switch 1 is on) and no part is on the NC machine (switch 2 is off), then pick up the part on the conveyor and move it to the NC machine and retract the robot to a safe point (run robot program I). After the program is complete and switch 2 senses that the part is correctly positioned, start the NC machine (turn on relay M,). While the machine is running, a switch signal from the NC machine, switch #2, will be ON.

2. If switch 11 is off and switch # 2 is on (the NC machine has completed processing a part), take the part off the NC machine and move it to the output bin (run robot program 2).