htManufac system desing

8/7/2019 htManufac system desing

1/13

ELSEVIER Int. J. Production Economics 42 (1995) 187-199product ioneconomics

An integrated manufacturing system design: an applied approachS. Dowlatshahi*

Information and Decision Sciences, College of Business Administration, The University of Texas at El Paso, El Paso,TX 79968-0544, USA

Received 30 January 1995; accepted 26 September 1995

AbstractThis paper details a real-life proposal that describes a design of self-contained, integrated manufacture and assem-bly for pipe valves. It presents a detailed and comprehensive analysis of part design, manufacturing operations, andmanufacturing system design. The part design is subjected to a set of DFM/DFA tests and it has been significantlyrevised and upgraded. These revisions or improvements provide for ease as well as economical manufacture and assem-bly operations. The paper explores and details the explicit information about the machining and assembly centers asit relates to the operations and equipment utilized. The components and technologies of the proposed manufacturingsystem design are explained and include: computer hierarchy, clamping fixture, transfer robot, packing robot, con-veyer system, AGV system, part tracking, incoming part packaging, buffer stocks, quality control centers, and safetyconsiderations. The proposal has been accepted for implementation. Subsequently, the manufacturing system imple-mentation is presented, a timetable for completion is provided, and future research directions are discussed. Finally,a conclusion and assessment is presented.

Keywords: Part design; Pipe valves; Integrated manufacture and assembly; DFM/DFA; Manufacturing operations;Robot

1. IntroductionThe design of integrated manufacturing systems

poses one of the greatest challenges for manufac-turing managers. Manufacturing activities areinherently interrelated in nature. The design ofmanufacturing systems should be based on aclear and consistent business and manufacturingstrategy of the firm and not on a purely technicaland engineering related function [l]. Productdesign, as the strategic embodiment of ones firm,

*Tel: 915 747-7759, fax: 915 747-5126, e-mail: [email protected].

should take the center stage of all the subsequentmanufacturing activities [2]. Manufacturing systemdesign in this paper considers the overall manu-facturing strategy of the firm as well as theproduct design.

1.1. The plan and objective of the paperThis paper details a proposal for an integrated,

self-contained manufacture and assembly facilityfor pipe valves in a Design For Manufacture/Design For Assembly (DFM/DFA) environment.This paper attempts to present a complete andeffective part/system design for a real-life problem

0925-5273/95/$09.50 0 1995 Elsevier Science B.V. All rights reservedSSDIO925-5273(95)00179-4


2/13

188 S. Dowlatshahillnt. J. Production Economics 42 /1995/187-199

facing a manufacturing enterprise and proposes anapplied approach to the design, manufacture, andassembly of pipe valves. This proposal is acceptedin its entirety. The manufacturing firm, in whichthis applied research was conducted, is in theinitial stage of product and system developmentand implementation.

This companys product design was roughlysketched. The manufacturing processes, in theirbroad terms, were contemplated. The objective ofthis paper is to evaluate and revise the existingpreliminary parts design and propose for imple-mentation a detailed and comprehensive manufac-turing system design. Every possible considerationwas given to the companys manufacturing strat-egy and business goals in devising the specifics ofthis proposal. The focus of this paper is to presentdetailed technical specifications with regard toproduct and system design. A simultaneous eco-nomic analysis was performed by another team,the result of which will be culminated in a laterreport, pending the initial evaluation and imple-mentation of some of the projects activities.

The presentation of materials in this paper fol-lows the normal progression of actual activities asthey took place in practice. The paper consists ofsix distinct yet interrelated sections. Section 1 pro-vides general information and a methodologicalfoundation for the paper. Section 2 addresses thepart design specifications for pipe valves and theproposed changes to the original design due toDFM/DFA considerations. Section 3 discusses themanufacturing operations and processes of fabri-cation, machining, and assembling for pipe valves.Section 4 explores the components and technolo-gies of the proposed self-contained manufacturingsystem. The implementation aspects of the manu-facturing system, along with a timetable for com-pletion/operations and future research directions,are presented in Section 5. Section 6 provides abrief conclusion and assessment.

1.2. The methodology of the paperThe foundation of this paper is based on sound

and effective manufacturing theories and prac-tices. The use of a concurrent engineering envi-ronment provides the appropriate framework for

the design of parts and a manufacturing system.Concurrent engineering, as it pertains to thispaper, attempts to coordinate design and manu-facturing activities. The methodology is based ontwo principles:(a) Design products that are easily manufac-turable and assemblable, require less materials andparts, are economically producible, require fewerprocesses and energy, have high reliability and areeasily maintainable

(b) A manufacturing process which is compati-ble and capable of meeting the specifications of theproduct. A manufacturing process in which fabri-cation and assembly concerns are properlyreflected in the product design stage

The conceptual framework for this paper is pre-sented in Fig. 1.The design of the pipe valve will be subjected todesign for manufacturability/assembly concerns.Manufacturing and design concerns are coordi-nated in advance of any actual production. Theproduct design also considers other manufacturingconsiderations which will be outlined in detail insubsequent sections of this paper. The methodol-ogy used here may also be used for other products,provided that the proper modifications are madefor each particular situation.

2. Part design specifications for pipe valvesPipe valves are manufactured in a range of seven

sizes with a 3312 inch inside diameter. Cast ironblanks are machined to the required specifications.

Designlorprocurability

Fig. 1. Product and manufacturing system design in concur-rent engineering.


3/13

S. Dowlatshahillnt. J. Production Economics 42 (1995) 187-199 189

They are then assembled into a finished productwith vendor-supplied parts. Fig. 2 represents theexisting part assembly drawing of a pipe valve.

Fig. 3 represents the existing plan for themachining and assembly operations of the pipevalves. This sequence is perceived to be the opti-mal procedure for the manufacture of the partsprior to the start of this study.

In Fig. 3, the face of the inlet half that mateswith the outlet half is machined first. Eight holesare then drilled, first with a center drill, thendrilled to size. The hole to accept the stud - whichholds the flow guide - is center drilled, drilled tosize, and then tapped. The part is repositioned andthe outside face of the inlet is machined. Eightholes are center drilled. then drilled to size. The

outlet rubber diaphragm inlet

stud copscrew nut

thread bolt hex nut

Fig. 2. Assembly drawing of a pipe valve.

part is then sent to a deburring operation toremove burrs on the machined surfaces. Next thecasting is sent through a cleaning process toremove chips and cutting oils. The center stud andthe flow guide are subsequently assembled to thecasting, and the cap nut screwed in place to holdthe flow guide.

The outside face of the outlet half is machined,eight holes are center drilled, then drilled to size.The part is repositioned, the face that mates withthe inlet half is machined, eight blind holes are cen-ter drilled, drilled to size, and then tapped to acceptthe attaching studs. The part is deburred andcleaned similar to the inlet half. The eight studs arescrewed in place and the diaphragm placed overthe studs.

The inlet and outlet halves are then broughttogether and attached using hex nuts. The part isthen packaged and made ready for shipping.

2.1. DFM/DFA considerationsDFM/DFA has received a great deal of atten-

tion under the general umbrella of concurrentengineering. Numerous studies have addressedtheories, application tools, and systems related tothe design, use, and implementation of DFM/DFAprograms. It is not the intention of this paper toprovide background information nor to discussrecent developments in DFMDFA areas. Among

Fig. 3. The existing machining and assembly operations.


4/13

190 S. Dowlatshahi/Int. J. Production Economics 42 (1995)187-1%

other highly relevant and useful publications,Dowlatshahi [3] provides definitions, applications,and some examples for DFM/DFA. Additionally,Dowlatshahi [4] provides specific factors for attri-butes such as: manufacturability, durability,maintainability, reliability, reproducibility, etc. asa part of the overall analysis of product design.Dowlatshahi [5] further argues that the greatestimpact and benefits are obtained by focusing anddirecting the manufacturability and assembly con-cerns at the early stages of the product/part design.In conforming with these requirements, an attemptis made to revise and upgrade the design of pipevalves by considering and incorporating design formanufacturing and assembly considerations in thedesign process.

(b) Ensure that the assembly has a suitable baseon which the assembly can be built [7].

(c) Design products so that the subassembly(assembly) does not have to be lifted or rotated [7].

It is highly inappropriate and unjustified toproceed with the development of pipe valve manu-facturing and assembly design without properconsideration given to DFM/DFA issues in thedesign phase. A set of design improvements -independent of one another ~ for the pipe valvesare proposed. Note that these modificationsare domain dependent (e.g. pipe valve) andmay not be generically applicable to other partdesigns.

2. According to the original design, the inlet andoutlet halves are assembled together by eight hexnuts. Another DFM/DFA suggestion is to avoiddesigns that require fasteners. Instead: (a) Designparts that can be snapped together. The inlet andoutlet halves can be snapped together instead ofbeing attached by a hex nut system, which is amore complex operation. (b) Design parts that canbe bonded with an adhesive. Adhesives are capa-ble of holding the inlet and outlet halves togetherin a useful fashion by surface attraction. Adhesivejoints are often less costly, more easily produced,and better able to resist fatigue and corrosion thanmechanical fasteners or welds.

In the case of the hex nut system, the casting hadto be rotated because the inlet and outlet halveshad already been mated and the vision system wasnot capable of detecting all of the attaching studs.The position information then had to be sent tothe robot and then the nuts had to be attached bythe robot. The vision system had to subsequentlyverify that the nuts were correctly assembled.

1. If the eight attaching studs were placed in theinlet half, most of the assembly could be performedon one half. This modification can make the assem-bly easier and less time consuming. The eightattaching studs and the flow guidance can beassembled at the same station. This can potentiallyreduce the cost and complexity of the manufac-turing operation. Additionally, this proposal mayresult in significant improvement in line balancingefficiency because of the inherent disparity offunctions that exist between the machining andassembly operations of inlet and outlet halves asillustrated in Fig. 3.

It is, therefore, proposed that an adhesivelybonded assembly be utilized for inlet and outlethalves. With this decision, the problem of detect-ing the positions of the studs is eliminated.Additionally, the results can be superior in termsof cost, quality, and ease of assembly when com-pared to a hex nut system. An experiment con-ducted with the adhesively bonded assembly forinlet and outlet halves proved that the hex nuts canbe eliminated with considerable ease and the newjoint assembly functioned properly. This designmodification is based on the following principles:

It is, therefore, proposed that the attaching studsbe placed in the inlet half and the entire assemblyoperations be performed on the inlet half. Thisaction is proposed to simplify and increase lineeffectiveness, and to reduce the cost of the assem-bly operations. This design modification is basedon the following principles:

(a) Avoid expensive and time consuming fasten-ing operations, such as screwing and soldering [7].

(b) Design for adhesive bonding joints shouldbe subjected to compressive, tensile, and shearforces, but not peeling or cleavage [8].

(c) The assembly should be designed so thata sufficiently large bonded area is obtained thuspreventing failures [9].

(a) Assembly should preferably be performed (d) The assembly should be designed withwithout flipovers [6]. these characteristics: thin bond lines are preferred;


5/13

S. Dow lat shahi llnt . J. Production Econom ics 42 (1995) 187-199 191

design for easy cleaning; smooth surfaces arepreferred; the width of the joint overlap is moreimportant than its length [lo].3. Since the necessity for eight hex nuts iseliminated due to the selection of an adhesivelybonded system, it is proposed that six ratherthan eight flow studs be used. This action canpotentially reduce the cost and improve the easeof assembly. This operation requires two lesscap nuts than the original design. The feed bowleroperation, to be explained later, can be consider-ably improved as well. There is certainly a lessfrequent need for the replenishment of the bowl.The reduction in the number of studs and cap nutsfrom eight to six (the feasible lower bound) willnot adversely affect the operation of the pipevalves. Several reliability tests on the new designwere performed and all yielded favorable results.This design modification is based on the followingprinciples:

(a) Minimize the number of parts in a product[ 7 1 .(b) The greatest influences on the selection of theassembly method are operational or economical[ill.4. A symmetrical assembly operation is pro-posed for feeding and assembling the inlet and out-let halves. This type of assembly, which can beperformed in more than one direction, reduces theneed for sensors to detect features and reduceshandling. This design modification is based onthe following principles:

(a) Parts should be symmetrical so that they maybe fed and assembled in more than one direction.Designing a symmetrical part reduces the need forsensors and reduces handling [12].

5. It is finally proposed that all of the threadbolts have the same diameter with a differentlength. The screws should all be the same size. Thedrill diameter should be slightly larger than thethread bolt diameter. This design modification isbased on the following principles:

(a) Design the part for easy fixturing and secureholding during machining operations [lo].

(b) Radii, unless critical for the parts function,should be large and conform to standard tool nose-radius specifications. The radius should often beleft to manufacturing preference [lo].

(c) Cut-to-length parts are inherently simple,and there is little that designers need to do totailor their designs to facilitate these operationsUOI-3. Manufacturing operations and processes

First a summary of machining and assemblyrequirements is presented. These requirements aredriven by the proposed parts design developed inSection 2.1. Then, the specifications of machiningand assembly operations are presented and dis-cussed.

The machining requirements for the valvesinclude:1. Facing of the flange coupling joints on bothhalves.2. Drilling of six holes around the face of the

flanges.3. Drilling and preparing for the flange halves.4. All internal surfaces of the valve are to be kept

as-cast.Assembly requirements include:1. Insertion of the threaded bolt which holds theflow guide.2. Attachment of a cap nut to hold the flow guidein place.3. Insertion of six studs to accept the rubberdiaphragm.

4. Attachment of two halves of the valve usingadhesive bonding.

3. I. Machining centerOne machining center will be used for each half

of the flow valve. Each center will have two four-axis machine tools, a deburring station, a cleaningtank, and a six degrees of freedom robot for eachmachining center. Fig. 4 represents the proposedlayout of a machining center.

Each component in the machining center isexplained as follows.3.1.1. Four-axis machine toolA four-axis machine tool (part translation inthe X, Y, 2 axes and a rotation about the vertical


6/13

192 S. Dowlatshahiilnt. J. Production Economics 42 (1995/187-199

0 Cleaning tankDeburr cl, Conveyer 1four axismachinetool-externalface

I6 DOF Robots

R

I 11 Pallet 1I 1r

Fig. 4. Proposed components and layout of a machiningcenter.

axis) will perform all the required machiningoperations on the part. This has been madepossible partially by the DFM/DFA revisionsincorporated in the initial pipe valve design.One machine tool will operate on the external faceof the casting while the other machine tool workson the internal face of the casting, thus increasingthe throughput of the system. The machine tooloperating on the internal face is the bottleneckmachine both in terms of time and cost. The loca-tion of this machine in the proposed layout allowsfor higher machine utilization time as well as moreefficient line balancing. The tool instructions canbe downloaded directly from the central computer.The tool instructions will, however, have the capa-bility of direct reprogramming to accommodatefor a central computer failure or special orders.Data as to machining times, downtime, tool break-age, and other system performance data will betransmitted to the central computer. The machinetool will have automatic tool change capability andenough tool storage to allow for all required toolsand replacements required for 20 h of operation.The machine tool will have torque-measuringcapabilities so as to detect a worn or broken tooland to replace it. The machine tool will have a cut-ting oil delivery and chip removal system capableof operating without attention for 20 h. Guards toprotect operating personnel from tool breakage,flying chips, and other safety hazards will berequired.

3.1.2. Six degree of freedom robotA six DOF robot will be used to tend the

machine tools, cleaning tank, and deburring sta-tion. The robot will require a servo control feed-back system which has a manufacturing accuracyand repeatability of f 0.005 inch and f0.010 inch,respectively. The payload capability of the robotexclusive of the end effector should be 50 lb.3.1.3. Deburring station

The deburring station will be a custom-designedsystem, capable of removing burrs around the out-side and in the inside of the machined casting.Two wheels will be required for the deburringoperation. The casting will be brought up underthe rotating wheel for the respective burr. Therobot will turn the casting 180 and repeat theaction. Fig. 5 represents the proposed deburringoperation.3.1.4. Cleaning tank

The cleaning tank will be a commercially avail-able system, capable of removing chips, dust, andmachining oils from the casting. The cleaning fluid,Freon TMS, will be connected to a central distil-lation and filtering unit. The system will have arefrigerated vapor recovery system to minimizefluid loss. The robot will tend the cleaning tank soas to minimize the exposure of operating person-nel to the cleaning solvents.

3.2. Assembly centersFor efficiency of operations, the assembly activ-

ities are divided into flow guide stud, diaphragmassembly, and adhesively bonded final assembly

Wheel for deburring Wheel for deburringexternal surface internal surfaceFig. 5. Wheels required for deburring operation.


7/13

S. Dowlatshahillnt. J. Production Economics 4.2 (1995) 187-199 193

operations. Each of these assembly operations isexplored in detail as follows.

the same actions as described previously. Once theflow guide has been placed over the stud, the gatewill open and the casting will exit the system.3.2.1. Flow guide stud and attaching studs

assembly system 3.2.3. Cap nut and adhesively bondedjnalThe operations used to assemble the flow guidestud and attaching studs to the casting will be sim-ilar and considered simultaneously. This is thedirect result of placing the attaching studs in theinlet half. By so doing, most of the assembly oper-ations can be performed on one half. This has beenaccomplished by the DFM/DFA revisions of theinitial design.

assembly system

The casting will enter the system via a conveyerand stop at a gate. A vision system will be used todetermine the position of the tapped holes toreceive the studs. The information from the visionsystem will then be forwarded to a SCARA typerobot that picks the studs from a pallet and screwsthe studs in place. A SCARA is chosen because ofits speed and the selective compliance feature. Thepallet system is chosen over a bowl feeder becauseit avoids jams preventing downtime. A special endeffector that has three fingers to hold the stud andan electric motor to quickly screw the studs intoplace will be required. A rotation detection systemon the end effector is necessary to determine whenthe stud has bottomed. The vision system verifiesthat the studs have been properly assembled. Ifnot, the system will notify the central computerthat no more work is to be done on the unit andit will be disposed of. If failures exceed a certainnumber, the computer will signal that the unitrequires attention. Once the stud has bottomed, thegate will rise and the casting will leave the systemvia the conveyer.

The casting will enter the inlet machining centerand will stop at a gate. A vision system will deter-mine the positions of the studs to which the capnuts are to be attached. The robot arm will bemounted with an off-the-shelf cap nut driver sys-tem. The robot will attach the cap nuts. This willrequire a feeder bowl. It is, however, felt that thetechnology is sufficiently advanced to allow thisoperation without excessive jams. To ensure this,the quality of the incoming nuts must be in therange of 100 defects per million cap nuts. Thefeeder bowl must be large enough to allow 2 h ofoperation between refills of the bowl. Once theappropriateness of the assembly has been verified,the casting will exit the system via the conveyer.

Bonds will be made by positioning a film ofliquid between inlet and outlet halves and immo-bilizing the assembly until the adhesive solidifies.Dry film will be a fast assembly operation whichrequires no particular skill. The operation is notmessy, but curing time will be slow [13]. For thisoperation the recommended adhesive type will beepoxy. The adhesively bonded joint (with all itspotential advantages) is a replacement for hex nutsas proposed by the DFM/DFA design revisions.

4. Components of the manufactur ing systemdesign

3.2.2. Flow guide and diaphragm assembly systemThe castings will enter the flow guide assembly

system via the conveyer and stop at a gate. A visionsystem will be used to determine the position ofthe flow guide stud. The position information willbe forwarded to the robot. A SCARA robot willbe used for the reasons previously cited. The robotwill pick a flow guide from a pallet and place itover the stud. The end effector will be a vacuumtype that forms an annular ring. The vision systemwill check the appropriateness of the assembly with

Now that the part design and respective manu-facturing operations are completed, attentionshould be focused on the development of a self-contained manufacturing system. In this section,various components of this system are identifiedand explained as follows:

4.1. Computer hierarchyAll manufacturing operations will be controlledby a centralized master computer. The centralized


8/13

194 S. Dow lat shahi lln~ . J. Production Economics 42 (1995)187-199

database is initially selected so that all the infor-mation on a manufacturing activity is located inone storage medium and access is provided to allindividuals who need to query the system forspecific information. It is, however, anticipatedthat the centralized system can be converted to adistributed system with LAN to provide lessvulnerability as well as make the manufacturingoperations less susceptible to computer failure.

The instructions will be downloaded from themaster computer to the machine tools, assemblyrobots, and transfer robots. These instructions willbe based on the data received from the bar codereader indicating the type and location of castingat a station. All machine tools and robots will havethe capability of on-site programming for specialsituations or when the central computer is down.Data will be transmitted to the master computerfrom the machine tools and assembly stations sothat system performance data can be maintained.If a part is determined to be defective, it will beidentified for removal at the packing operation.The terminal at the quality control center will beallowed to interact with the master computer sothat the quality control data can be transmitted tothe master computer. The master computer willsignal the operator if an out-of-control situation isobserved.

An engineering work station will be directly con-nected to the master computer so that if a designchange is made, it can be directly downloaded from

the engineering work station. Also, system perfor-mance data will be retrieved.

The master computer will be networked toterminals at shipping and receiving, ordering con-trol, and customer ordering so that it can deter-mine how many raw materials are needed forfuture orders, and how many materials are instock. It will automatically issue orders for mate-rials if the vendors are set up for such a procedure.This can potentially represent a savings in inven-tory costs.

The possibility of connecting the master com-puter to a corporate computer will be contem-plated if data concerning the system are needed atanother location. The proposed computer controlhierarchy is presented in Fig. 6.

In the manufacturing area, MAP standardswill be specified for all machine tools, robots, andvision systems. TOP standards will be specified forall office systems. The fundamental concept behindthe proposed computer hierarchy structure is thata complex control task cannot be effectively imple-mented with a single-level control mechanism.

4.2. Clumping jixtureThe clamping fixture will be designed so that it

can hold the entire range of diameters of castings.The flange of the casting rests upon three insertson the top surface of the fixture. The three points

AGVBarcode Assembly Vlslonreader -b-robot dC)*sysiem

Machine Robot Vision Quality1001


9/13

S. Dowlatshahilln t. J . Production Economies 42 (I99.3) 187-199

will locate the part upward and downward for themachining operations. The inserts will be madefrom carbide to insure long life. The fixture is thenclosed and the part is held from rotation by theclamping force. The clamping force will be sup-plied by a double acting air cylinder that opens andcloses on command from the robot when thecasting is in place. The carbide inserts will be highenough to insure clearance for the fixture duringmachining operations. The inserts should also beplaced at a position that is not under the throughholes drilled in the flange. The proposed clampingfixture for the machine tools is shown in Fig. 7.The clamping fixture is designed to allow forclearance during the loading and unloadingprocess.

4.3. Transfer robotA robot will be used to transfer the inlet half to

the outlet half. Separate vision systems will deter-mine the positions of inlet and outlet castings. Thedata will be transmitted to a rotating table underthe inlet casting so that the inlet has the properangular position before the robot picks it up. Theposition data will then be transmitted to the robot.The robot should be a six degree of freedom, servo-controlled feedback robot. Due to the heavy load,the robot must be a hydraulically actuated robotwith a payload of 50 lb excluding the end effector.The manufacturing accuracy and repeatability ofthe transfer robot must be L-O.005 and +O.OlO,respectively.The proposed end effector for the transfer robotsis shown in Fig. 8.

Carbideinsert Carbideinserts (2)I

Air cylinder

Fig. 7. Proposed components and layout of the clampingfixture.

J--i\ ange of195

3 self centeringfingers

casting hereFig. 8. Proposed end effector for the transfer robot.

The end effector will have three self centeringfingers that are driven by air pressure. The fingerswill slide in the tracks. The side to which air is sup-plied is controlled by an air valve. The fingers willbe constructed so as to allow the casting to beturned 180 about the horizontal axis and still ade-quately support the casting. The end effector wil1be designed to allow for clearance during the load-ing and unloading process.

4.4. Packing robotA robot will be used to transfer the completed

valve from the end of the line into the shippingcontainer. A vision system will determine the posi-tion of the valve and relay this information to therobot. The robot used should be a six degree offreedom, servo-controlled robot. Due to the heavyload used, the robot must be hydraulicallyactuated. The minimum payload must be 1OOlbexcluding the end effector. The manufacturingaccuracy and repeatability should be kO.005 and+ 0.010, respectively. At this point all the assem-blies that have been identified as defective areseparated from the non-defective parts. This willbe accomplished through a command from themaster computer.

4.5. Conveyer systemThe conveyer system will be a gravity roller con-veyer with certain segments powered to ensureproper part movement. The conveyer system will


10/13

196 S. Dowlutshah i,iInt. J . Production Economics 42 (199S)187-199

be modular so that future reconfigurations areeasily accomplished.

4.6. AGV systemAn AGV system is utilized to increase the

throughput, decrease the availability of unneededwork-in-process components and subassemblies,and to handle a large volume of parts and materi-als. Initially, two AGVs will be used and othersmay be added if the workload warrants it. The RFsignal will be employed to send control signalsfrom the master computer to the AGV. The AGVswill be capable of operating 10 h without recharg-ing and the recharging from completely dead tofully charged must be completed within 4 h. Thesystem must have a fail system so that if the bat-teries are approaching a discharged condition, theAGV can return to the charging center before run-ning out of power. The AGV is programmed sothat when it is idle, it will return to the chargingcenter.

4.7. Part tracking

Each station will be equipped with a laser barcode reader that reads a bar code placed on eachcasting. The bar code will serve to identify the kindof valve being worked on; thus, the instructionsrequired by the station will be keyed to the barcode. Data concerning each valve will be trans-mitted to the master computer. The data will thenbe archived so that long-term quality data can beassembled and part identification can be main-tained for future use in case of field failures.

4.8. Incoming part packagingThe incoming castings will be packaged in

40 inch square pallets, allowing nine of the 12 inchvalves per pallet and a larger number of the smallervalves per pallet. The inlet and outlet castings arepackaged separately. The pallet will be constructedso that a robot is able to pick the castings directlyfrom the pallet. The finished valves will be shipped

on the original pallet of the castings. Each castingwill have an attached identifying bar code capableof withstanding the cleaning process. The incom-ing studs, flow guides, and diaphragms will beplaced on the pallets so that the robots can havedirect and easy access to them. The pallets used forthese parts will have the same outside dimensionsas the casting pallets to ensure compatibility withthe AGV system.

4.9. BufSer stocksNo allowance for buffer stocks will be made

other than those inherent in the conveyers and pal-lets at the stations. Each station will have an alarmto indicate failure modes so that repairs can beinitiated quickly.

4.10. Quality control centerThis center will be provided so that an operator

may perform quality control audits of the line toverify proper operation of the various parts of thesystem and to inspect the parts that have beenidentified as defective by the inspection system. Thequality control center will be equipped with neces-sary inspection items, such as microscopes,micrometers, etc. A terminal connected to themaster computer will also be located in the qualitycontrol center so that the operators can load theinspection data into the master computer. A sys-tem kill switch is also located in the center. In theevent that an out-of-control situation exists, the linecan be stopped. Then adverse conditions can becorrected. The DFM/DFA part design revisions aremade at the parts design stage to substantiallyreduce downstream quality problems in the manu-facture and assembly operations of the valves.

4.11. Safety considerationsThe machine tools will have interlocking guards

to prevent operation when the guards are not prop-erly installed. The robots are surrounded by lightcurtains that will immediately stop the robot if thelight beam is broken. The pressure-sensitive mats


11/13

S. DowlatshahiJInt. J. Production Economics 42 (1995) 187-199 197

will detect the presence of personnel or objects inthe robots work envelope. The AGVs will have aphotoelectric detector to sense obstructions in thepathway and bumpers to stop the AGV beforecontact is made with an object. The conveyers willhave all pinch points guarded. The entire systemwill have signs indicating safety hazards. The areasthat require safety equipment, such as safetyglasses, will be clearly marked. Since no system canbe made fully safe, only those individuals trainedon the system will be allowed access to the area.

5. Manufacturing system implementationThe manufacturing system outlined thus far pro-

poses an assembly line where overall system pro-ductivity can be enhanced. The proposed floorplan is presented in Fig. 9.

The limiting factor of the system will be thetime spent machining, cleaning, and deburring theinlet half. The combined time for the proposedpart design is estimated to be 11.20 min/valve.Assuming an 80% availability and 20 h of opera-tion per day, with the remaining 4 h for mainte-nance, an output of 86 valves/day will be achieved.This result is approximately 23% more efficient

than the existing part design with the estimatedcombined time and output of 13.75 min/valve and70 valves/day, respectively.

5. I. Tim etable for com pletion/ operationsThe first phase of implementation will introduce

the four-axis machine tools. In this phase, limitedhand production of the valves will be run in orderto gain manufacturing experience. It is anticipatedthat the time required to receive the machine toolsand to make them operational for production isfour months.

During this time the assembly stations will bedesigned and constructed. It is anticipated that itwill take approximately nine months to completethe construction of the assembly stations. Duringthe debugging stage, the assembly stations will beoperated as islands of automation. This phaseshould last three months.

After the debugging stage, the entire line will beintegrated and automated. This phase will beintroduced gradually in an attempt to maintainproduction. The integration phase should takeapproximately nine months. Thus, the entireproject should take one year and nine months to

Bar Feeder

------mm-

! ! T----r-----1I !Row guide

;_____--____---------::~-L-,----------L-L--. AGVVS = Vision Syslem- - - = AGV Track I

chargestation

Fig. 9. Proposed floor plan, not drawn to scale.


12/13

198 S. Dowlatshahi!Int. J. Production Economies 42 (1995)187-199

complete. This proposal, in its entirety, has beenaccepted by the manufacturing firm.

The manufacturing operations and their respec-tive processing times are presented in Appendix A.Appendix B provides the items and their unitsneeded in the manufacturing operations.

5.2. Future research directionsUpon implementation of the system, and whenit becomes operational, complete technical and

economical analyses will need to be performed. Ananalysis and evaluation of design decisions must bemade in order to determine their benefits and short-comings. Specific issues such as line balancing andits utilization rate, overall system efficiency, pro-ductivity rate, system downtime and cost, systemavailability, etc. must be evaluated and determined.These evaluations and related analyses can beculminated in another research paper.

6. Conclusion and assessmentThis paper attempted to provide a complete

analysis of a manufacturing system design for pipevalves. The analyses included the part design, man-ufacturing processes, and the components andtechnologies of the manufacturing system. Thetimetable for completion/operations and systemprocessing times were presented as well.

The focus of this paper remained on the appli-cation of DFM/DFA considerations whereverappropriate. The part design was subjected to aseries of DFM/DFA tests. These tests were shapedand created a new pipe valve design which iseasier and more economical to manufacture andassemble. The effect and ramifications of thesechanges were also considered in the manufactur-ing system design wherever appropriate.

The proposed changes can potentially resultin an increase in overall system productivity andefficiency, improved systems throughput, andincreased line balancing efficiency. Additionally,the proposed system is flexible enough to accom-modate alternative pipe valve designs. It is, how-ever, important to note that the proposed systems

design, as effective as it is, is not the only viablesolution to the overall manufacturing systemdesign of pipe valves. Further economic and tech-nical studies and comparisons must be made tojustify and substantiate the effectiveness of thecurrent system and to suggest future improve-ments/alternatives.

Appendix AManufacturing operations and processing timeInlet half/manufacturing operation

Pick and load castingMill outside faceChange toolCenter drill six holesChange toolDrill six holes to sizeUnload casting, rotate 180 and load onsecond machineMill internal faceChange toolCenter drill six holesCenter drill flow guide stud holeChange toolDrill six holes to sizeDrill flow guide stud holes to sizeChange toolTap flow guide stud holeUnload casting and deburr inside surfaceof internal faceRotate 180Deburr inside surface of outside faceDeburr outside surface of outside faceRotate 180Deburr outside surface of internal faceClean castingLoad casting on conveyerAssemble flow guide studAssemble six studsAssemble flow guideAssemble cap nutOutlet half/manufacturing operation

Processingtime (min)

0.50 . 51.50.51.10.510.51.50.250.51.10.250.50.250.50.250.50.50.250.520.5

Processingtime (min)

Pick and load castingMill outside faceChange toolCenter drill six holesChange toolDrill six holes to size

0.510.51.50.51.1


13/13

S. Dowlatshahijlnt. J. Production Economics 42 (1995) 187-199 199

Appendix A. (continued) ReferencesUnload casting and rotate 180 andload on second machineMill internal faceChange toolCenter drill six holesChange toolDrill six holes to sizeChange toolTap six holesUnload casting and deburr inside ofinternal faceRotate 180Deburr inside surface of outside faceDeburr outside surface of outside faceRotate 180Deburr outside surface of internal faceClean castingLoad casting on conveyerAssemble diaphragmMate inlet and outlet halvesAdhesively bonding the halvesMove completed assembly to shippingcontainer

0.510.51.50.51.10.5210.250.50.50.250.520.510.540.5

VIPI[31

Hill, S., 1994. Manufacturing Strategy: Text & Cases, 2nded. Irwin, Homewood, IL, pp. 93-125.Whitney, D.E., 1988. Manufacturing by design. HarvardBus. Rev., July-August: 83-91.Dowlatshahi, S., 1994. A comparison of approaches toconcurrent engineering. Int. J. Adv. Manuf. Technol.,9: 106113.

[41

[51

WI

Dowlatshahi, S., 1994. A morphological approach toproduct design in a concurrent engineering environment.Int. J. Adv. Manuf. Technol., 9: 324332.Dowlatshahi, S., 1992. Product design in a concurrentengineering environment: An optimization approach. Int.J. Prod. Res., 30(8): 1803-1818.Sturges, R.S., 1989. A quantification of manual dexterity:The design for assembly calculator. J. Comput. IntegratedManuf.

[71181

Appendix BCapital budgeting items

191VOI[111(121

1131Item Units neededFour-axis machine tool 4Six DOF robot and controller 6Deburring station 2Cleaning system 1SCARA robot and controller 6Vision system 8AGV system 1Bar code reading system 1Conveyer 1

Boothroyd, G., Poli, C. and Murch, L.E., 1982. AutomaticAssembly. Marcel Dekker, New York.Kalpakjian, T., 1991. Manufacturing Processes forEngineering Materials, 2nd ed. Addison-Wesley, Reading,MA, pp. 787-790.Niebel, B.W. and Draper, A.B., 1974. Product Design andProcess Engineering. McGraw Hill, New York.Bralla, J.G. (editor-in-chief), 1986. Handbook of ProductDesign for Manufacturing. McGraw Hill, New York.Nevins, J.L. and Whitney, D.E., 1989. Concurrent Designof Products and Processes. McGraw Hill, New York.Laszcz, J.F., 1985. Product design for robotic and auto-mated assembly. Proc. Robots 8 Conf. Society ofManufacturing Engineers, Dearborn, MI, pp. 6-1-6-22.Schneberger, G.L., 1986. Adhesively bonded assemblies,in: J.G. Bralla (editor-in-chief), Handbook of ProductDesign for Manufacturing. McGraw-Hill, New York,pp. 7-61-7-77.

Documents

htManufac system desing