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8/8/2019 Advances in Automation for Plastics Injection Moulding
A Rapra Review Report comprises three sections, as follows:
1. A commissioned expert review, discussing a key topic of current interest, and referring to the References andAbstracts section. Reference numbers in brackets refer to item numbers from the References and Abstractssection. Where it has been necessary for completeness to cite sources outside the scope of the Rapra Abstractsdatabase, these are listed at the end of the review, and cited in the text as a.1, a.2, etc.
2. A comprehensive References and Abstracts section, resulting from a search of the Rapra Abstracts database.The format of the abstracts is outlined in the sample record below.
3. An index to the References and Abstracts section, derived from the indexing terms which are added to theabstracts records on the database to aid retrieval.
Item 1
Macromolecules
33, No.6, 21st March 2000, p.2171-83EFFECT OF THERMAL HISTORY ON THE RHEOLOGICAL
BEHAVIOR OF THERMOPLASTIC POLYURETHANES
Pil Joong Yoon; Chang Dae HanAkron,University
The effect of thermal history on the rheological behaviour of ester- andether-based commercial thermoplastic PUs (Estane 5701, 5707 and 5714from B.F.Goodrich) was investigated. It was found that the injectionmoulding temp. used for specimen preparation had a marked effect on thevariations of dynamic storage and loss moduli of specimens with timeobserved during isothermal annealing. Analysis of FTIR spectra indicatedthat variations in hydrogen bonding with time during isothermal annealing
very much resembled variations of dynamic storage modulus with timeduring isothermal annealing. Isochronal dynamic temp. sweep experimentsindicated that the thermoplastic PUs exhibited a hysteresis effect in theheating and cooling processes. It was concluded that the microphaseseparation transition or order-disorder transition in thermoplastic PUs couldnot be determined from the isochronal dynamic temp. sweep experiment.The plots of log dynamic storage modulus versus log loss modulus variedwith temp. over the entire range of temps. (110-190C) investigated. 57 refs.
GOODRICH B.F.USA
Accession no.771897
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4. Integration of Automation Systems for Phase III and IV ...................................................................11
4.1 Expected Benefits of Phase III and IV ......................................................................................... 12
4.2 Actual Operating Results .............................................................................................................. 124.3 Requirements for Phase III and IV Integration ............................................................................ 13
4.4 Standards for Higher Levels of Integration .................................................................................. 14
4.5 Implementation of Phase III and IV Automation ......................................................................... 14
4.6 Equipment Differences for Phase IV Integration ......................................................................... 16
4.6.1 Plant Material Quick-Change Systems ............................................................................ 174.6.2 Press Material Quick-Change Systems ............................................................................ 174.6.3 Mould Quick-Change Systems......................................................................................... 174.6.4 Equipment Required to Unload the Mould ...................................................................... 17
4.6.5 Flexible Value-Added Systems ........................................................................................ 174.6.6 Parts Transport Systems ................................................................................................... 18
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The views and opinions expressed by authors in Rapra Review Reports do not necessarily reflect those of Rapra Technology Limited or the editor. The series is published on the basis that no responsibility or
liability of any nature shall attach to Rapra Technology Limited arising out of or in connection with anyutilisation in any form of any material contained therein.
4.6.7 Automated Stockyards and Automated Storage and Retrieval Systems .......................... 194.6.8 Logistics and Coordination .............................................................................................. 19
4.7 Design Criteria for Higher Levels of Automation ........................................................................ 20
5. Example Applications ............................................................................................................................ 21
5.1 Small Machines............................................................................................................................. 21
5.2 Cells that Extend Production Hours Without Labour ................................................................... 21
5.3 Automated Packaging with Manual Value-Added Operations..................................................... 21
5.4 Product or Contract Specific Cells ............................................................................................... 22
5.5 Group Technology ........................................................................................................................ 22
References from the Rapra Abstracts Database ........................................................................................ 27
Subject Index ................................................................................................................................................. 77
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1 Introduction
1.1 The Purpose of the Review
There are few complete technical sources of
information available for plastic injection mouldersto use relating to automation. However, there havebeen articles written on various components of thetechnology. This review has been compiled byresearching and analysing technical references, thenplacing them into a logical order. The overview is notan attempt to describe robot design theory andengineering, which can be found in engineeringpublications. It is intended to describe the basics of the technology and to explain how to put thetechnology to use.
1.2 How Automation is Defined
For the scope of the review, automation is defined asthose operations associated with handling the plasticparts after moulding. It includes operationscommencing when the mould opens and concluding atthe shipping dock. Operations such as the use of quickmould change devices are discussed only in a contextwhere they must be specified properly to integrate intothe overall automation strategy.
1.3 Why Automate?
Automation serves one main purpose: to generate costsavings. Most moulding facilities have made mouldingupstream processes, such as resin material handling,automatic. The injection moulding process itself ishighly automated. However, once the mould opens,many plants use direct and indirect labour to add value,to package, and to move parts. As so many moulders
have optimised the upstream processes, the post-moulding operations remain the biggest area for costsaving potential.
Additional savings can be generated depending onthe applications run in each cell. Converting a semi-automatic cycle to a fully automatic cycle canincrease production. More consistent cycles reduceprocess variability and increase the quality and yieldof good parts. The quality levels now demanded byend users cannot be produced with semi-automatic
operation of moulding machines, and 100% manualinspection to find defects is becoming too expensive.Mould damage is reduced by the robot monitoring
sensors that detect part removal from the mould.Controlled part handling reduces damage to parts.Reduced floor space and reduced work in processcan be substantial.
1.4 Other Forces Driving Automation
Original equipment manufacturers (OEMs) are askingmoulders to add more value to parts. They will have toadd value at costs competitive to low-wage countries.In addition, many moulders are being asked to lowercosts over the life of a moulding contract. Direct andindirect labour required to add value or transport partscould be eliminated through the use of automation.Capital that was previously used to add more mouldingcapacity is now being redirected to post-mouldingoperations and increasing utilisation of existingcapacity.
It will be difficult to make profits if a company is onlymoulding and shipping parts. Modern press controllershave made producing quality parts easier. Increasedprofits will depend on value-added operations and theefficiency of these operations as compared tocompetitors. Automation is the only way to compete.
Quality must be automatically checked and recorded
to achieve the quality levels now expected. Manualsystems are error prone in comparison to a programmedautomation system, which is more accurate and cancheck its work.
It may also be difficult to find personnel due to a labourshortage in many countries and jobs are sometimes lessthan desirable.
Moulders will need to use technology and automationto achieve quality and low-cost goals. The automation
will need to be flexible to adapt to shorter product lifecycles, shorter runs and quicker product introductions.
As moulders increasingly use automation, competitionfor new work will depend on the ability to competeand bid for jobs cost effectively. Being efficient andkeeping up with competitive levels of automation willmean survival in the future.
Automation will become critical to an OEMsperception of a moulder’s efficiency level. Advanced
levels of automation require greater sophistication fromthe moulder, which will help distinguish them andsecure new business.
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1.5 Phases of Automation
Robot implementation typically occurs in four phasesin moulding plants:
Phase I: Pick-and-Place. Robots are added to mouldingmachines to perform what is essentially a pick-and-placefunction. Parts are removed from the press and placedonto a downstream device such as a conveyor or table.The moulding cycle goes from semi-automatic to fullautomatic operation. Often no labour is saved, or oneoperator is shared between two presses saving one-half of an operator per machine. The production increases bya minimum of 15% due to the elimination of the operatorwho would normally interrupt the cycle to remove parts.
Phase II: Value-Added Production. Robots begin adding
slightly more value to parts with secondary operationssuch as decorating, palletising, degating or flexinghinges. Usually one-half to one operator is eliminated.
Phase III: Cell Manufacturing. The robots areperforming multiple operations beside the press to addas much value as the cycle will allow. A work cellconsists of two or more integrated devices that performmultiple, closely related operations next to the injection
moulding machine. Parts are processed, inspected, andpackaged for transport in the work cell. From one-half to two operators are eliminated based on how muchwork the cell can do.
Phase IV: Flexible Manufacturing System (FMS) (Figure
1). FMS can be defined in plastics moulding as a centralcomputer directing the automatic manufacturing of products, automatically transporting the products,automatically storing the products and automaticallyperforming changeovers. Short runs are easilyaccommodated. The moulding shop floor runs in a trulyautomatic (lights out) operation. Cells are retooled quicklyby reprogramming flexible elements. Minimum job-specific automation is used because the automation mustbe easily adaptable. Both direct and indirect labour issaved. Quality is automatically monitored and corrected.
Reference (296) details the use of FMS in Japan.
With the exception of small parts that can be shipped inbulk, this last phase remains elusive for moulders becauseof the degree of technology and investment required. In10 years, Phase IV will be common in large companies.Smaller moulders will need to automate up to Phase III,but may have difficulty automating further because of the large investment and engineering support required.
Figure 1
An example of a flexible manufacturing system
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2 Robots
At the centre of most moulding automation cells is arobot. Robots are multifunctional, reprogrammable,material-handling devices. The robot removes parts and
transfers them through a series of secondary operations.
Parts that can fall free from the machine undamagedand can be bulk-packaged without using any value-added operations, do not require robots.
2.1 History of Robots in Plastics Injection
Moulding
Several articles referenced below chronicle the advances
of robot technology for plastics injection moulding.
The traverse-type robots and sprue pickers that weredesigned specifically for plastics processing were firstused in the late 1960s and early 1970s. Japan, driven bylabour shortages, mould design, and requirements topick-and-place parts without many value-addedoperations, began using the technology extensively inthe 1970s. Early robots were pneumatic-type devicescontrolled by simple hard-wired electrical circuits.Sequence steps were initiated by timers or limit switchesat the end strokes of each axis. The robots were only
reprogrammable by activating selector switches orrewiring the controllers (272). The robots were usedprimarily to convert a semi-automatic cycle to a fullyautomatic cycle or to reduce damage caused by gravitypart ejection (298, 300). Early robot installations weresometimes less than successful, as the mouldingmachines, auxiliaries, materials or moulds they ran onwere not consistent or reliable (299). Programmablelogic controllers (PLCs) or microprocessors replacedhard-wired controllers in the late 1970s and early 1980s.Robots became commonplace in the United States andEurope replacing operators removing parts from the
moulding machine (300, 301).
Electric drives became more widely used in the late1970s and early 1980s. The long traverse axis was thefirst to be converted to electric drive due to the difficultyin obtaining and using very long pneumatic cylinders.The traverse axis also quickly benefited from electricdrives to multiposition parts outside the press. The firstelectric drives relied on limit switches and breaks forcontrol and positioning.
There is a rapid transformation going on presently inthe plastics industry to electric drives. The preferredmethod for axis drives uses servo motors for flexibility,
and the cost of the technology has lowered. Servomotors with encoders are very efficient, highlyrepeatable and capable of positioning anywhere alongthe physical axis limits.
With servo drives came considerably more advanced
controllers. The controllers initially used computernumerically controlled (CNC) languages, but thenconverted to robot languages that are easier to use.Some advanced controllers allow graphic programmingor programming by leading the robot through asequence and having the robot play it back in auto (a.1).
The moulding machine control technology evolved tosupport unmanned operation of a moulding cell. Processcontrollers could mould precisely and repeatedly, detectdefective parts, and signal the robot to separate them.This is a major step to unattended running. Mouldingmachine manufacturers also developed technology tochange moulds, to purge or change barrels and to restartproduction. The equipment costs were becomingeconomically feasible to deploy automation (290).Computer power, software and connectivity alsodeveloped during the mid-1980s to allow large-scaleintegration of unmanned cells and FMS. Auxiliarydevices such as material handling and water temperaturecontrol devices evolved to be precise and consistentenough to allow automation in the mid-1980s (288, 293).
By the mid- to late 1980s, all of the necessarytechnologies were developed, were economicallyfeasible, and were within view of many manufacturers.Plants with proprietary products had achieved highlevels of unmanned operation. Truly flexible,unmanned operation for custom moulders and short-run, just-in-time (JIT) moulders is now available.
2.2 Robots and Flexibility
A robot is used to transfer parts once moulded throughother operations. It is the main link to cellularmanufacturing.
The robot’s flexibility is based on the number and typeof axis motions, the size of the work envelope, the axis-drive method, the payload, the speed, theprogrammability, the ability to control and interlockto secondary machines or processes, and the ease of operation (235). The higher the level of specificationin each category, the greater the robot’s flexibility, andthe greater its potential to generate cost savings through
value-added work. However, the greater the flexibility,the greater the cost. Therefore, the robot’s configurationshould be optimised for its intended use (a.2).
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2.3 Robot Configurations
Robots in plastics processing usually consist of fourmain types. There are some configurations less usedthat are not outlined here.
2.3.1 Sprue Pickers
Three-axis, top-entry robots with two linear axes andone rotary axis are generally referred to as spruepickers (Figure 2). An arm enters the mould, removesthe runner, swings out over the safety door through90 degrees and re-extends the main arm to releasethe runner. Parts fall free under the mould. Sometimessprue pickers are equipped with end-of-arm tooling
and vacuum units to remove light parts with vacuumcups. Drive type is most commonly pneumatic withone linear axis, which is sometimes electric. Onelinear axis pulls the runner off the mould. The mainarm is also used to enter and exit the mould area. Therotary axis is used to pivot the main arm through 45to 90 degrees so that it can re-extend and release partsand runners past the side of the injection mouldingmachine. Sprue pickers are generally used to removerunners on machines of 500 tons and under.
2.3.2 Top-Entry, Traverse-Type Robots
Top-entry, traverse-type robots are the most commonrobots used to remove parts from injection mouldingmachines. Traverse-type robots have three linear axesand one rotary axis. Second arms are sometimes addedto remove runners from three-plate moulds, to stackmoulds or for secondary part manipulation. Up to twoadditional rotary axes may be added to the robot wristfor added flexibility. A vertical axis (main arm) is usedto remove parts from the mould area as well as to extendbeyond the outside of the press to place parts. Thetraverse axis is used to bring the main arm outside thepress. A kick axis or strip axis that runs parallel to theclamp axis of the moulding machine is used to removethe parts from the mould and runs in line with theinjection unit. The traverse axis is 90 degrees to the
injection unit on the moulding machine. Occasionally,the traverse axis is mounted in parallel to the injectionunit to allow part placement over the clamp end of themachine. This is useful for facilities with limited spacebetween machines. Drive types are pneumatic, electricor a combination of the two.
Top-entry, traverse robots have a large rectangular workenvelope and can perform a wide variety of value-addedwork. This includes assembly, boxing, and inspection.
Figure 2
A sprue picker
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2.3.3 Side-Entry, Linear-Drive Robots
Side-entry robots have one to three linear axes and arotary wrist axis. A side-entry robot mounts to thetop of the machine, the side of the machine or to apress-side table and enters the mould area from therear side. Two main types have been employed. Thefirst type is a very high-speed extractor designed toremove parts and feed them to secondary equipment.The work envelopes are usually restricted to thedistances and motions required for part removal. Thesecond type is designed for low ceiling clearanceapplications or those where restrictions will not allowthe parts to come out of the injection mouldingmachine (IMM) vertically. Drive types are pneumatic,electric or a combination of the two.
However, side-entry robots do have drawbacks. Theyrestrict access to the rear side of the machine and arein the way when not being used. They lack a longvertical arm, which limits their performance of secondary functions as they cannot reach into othermachines or containers.
2.3.4 Articulated Robots
Articulated robots are three- to six-axes, rotary-driven, jointed robots. Their advantage is the ability to
manipulate parts through a wide variety of positions.Difficult secondary operations can be performed. Forcomplex manipulations, the cell cost may beminimised with articulated robots because the robot’swrist can orient parts, as against building orientationfunctions into the downstream equipment (75). Manyusers feel articulated robots are most advantageouson large parts requiring complex manipulations andhave little benefit on smaller parts (87). Articulatedrobots are most often mounted beside the injectionmoulding machine, but sometimes on top of theplaten. Drive type is almost always electric and
usually servo motor.
There are disadvantages of articulated robots: theyare in the way when not being used, require a largework envelope, are slower to remove parts than linear-drive robots, require greater mould-open distances,and do not allow access or use of secondary machineswhen the robot is not in use (235). They also needextensive programming and expertise to operate thembecause their programming is designed for generalindustrial use and not specifically injection moulding.
The added support required for articulated robots cantake away savings generated, and therefore, they mustbe applied carefully.
2.3.5 Combination Cells
Sometimes, the best way to approach cell design is tocombine a linear-drive, extraction robot with anarticulated robot. The press cycle will have minimal
impact, and the cell can be flexible. The articulatedrobots can eliminate the requirement for fixedautomation that is application specific. References(38, 41, 83) outline the use of such cell design.
3 Advances in Drives and Controls
Drives and controls have advanced rapidly since robotswere first introduced. These advances have been
making robots more flexible, resulting in moreutilisation in moulding facilities.
3.1 Drives
Drives are chosen by considering the following factors:torque, speed range, size, positioning capability,repeatability, cleanliness, initial cost, operating costs(including energy and maintenance) and reliability.Repeatability is defined as the robot’s ability to return
precisely to a taught point. Repeatability is critical forautomation to perform its tasks reliably over a longperiod of time.
Drive methods for industrial robots consist of pneumatic, hydraulic, and electric. The application of hydraulics for robots used in plastics is almostnonexistent. Hydraulics are energy intensive. They canhave complications common to fluid systems: filtration,leakage and cooling. The forces required for robots inplastics are well under that of hydraulic systems.
3.1.1 Pneumatic Drives
Pneumatic drives are low cost, but can only positionaccurately and repeatedly at the end of strokes ormechanical stops. They are mostly used on applicationsrequiring pick-and-place operations without value-addedoperations. The setup of the robot must be donemechanically, making short runs difficult to accommodate.Pneumatic drives are familiar to shop floor personnel and
easy to maintain. Therefore, pneumatic drives are mostlyused in dedicated, long-running, pick-and-place operationsor entry-level applications.
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3.1.2 Electric Drives
Electric drives have the advantage of being able to stopanywhere along the axis of travel. Their costs are higherthan pneumatic.
Electric drives come in two main types:
The first type and the most flexible and repeatable isthe servo motor (Figure 3). A servo motor constantlymonitors its position and corrects it. The setup is allelectronic and adjusted through a teach pendant.
The second type is an induction motor with a feedbackdevice. The feedback device can be fixed on the axis(such as a switch) or be on the drive itself (such as anencoder). The motor usually does not correct itself once
it stops and often uses a break or locking mechanismto hold the axis position. The induction motor is nothighly repeatable, often varying by 1 mm, is moremechanically intensive, requires more energy tooperate, and is slower for the size motor that can beused. The setup of the robot must be done manuallyfor fixed-sensor robots and through a teach pendantfor motors with an integral feedback device.
3.1.3 Combination Drives
Some robots use a combination of pneumatic and electricdrives (Figure 4) to optimise cost. The pneumatic driveswill be on the axis that does not need multipositioning ordoes not require changing from one job to another. Electric
drives will be on the other axes. The most commoncombination drive is a servo motor on the traverse axis toallow for multiple part positioning outside the press.
3.2 Controls
The characteristics of the controller should fit theapplication. The design must be balanced incorporatingcost, operator interface, programmability, memory andexpandability. A pick-and-place or dedicated applicationwill not require the same level of sophistication as a
flexible value-added cell with servo drives.
3.2.1 Operator Interface
The operator interface must allow all functions withminimal training and time. The functions that will berequired are setup, troubleshooting, cycling and monitoring.
Figure 3
The servo feedback loop
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The use of graphics for operator interfaces isbecoming more widespread. A graphic interface(Figure 5) showing the robot and other main functionsgreatly reduces operator training, downtime and setuptime. Many controllers require knowledge of robotlanguages to operate safely without crashing.
Controllers have evolved to a stage where an engineeris no longer required to set up and operate the robot(131). Staff assigned to keep the moulding machinesin operation can handle the robot setup and operation.Technical staff that performs mould changes ormachine repair can create new programs.
Figure 4Combination drive robot
Figure 5
An example graphic operator interface
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3.2.2 Sequence Programmability
Sequence programmability is now very advanced.Teach pendants allow the robot to be programmed online. Off-line programming systems (Figure 6a and
6b) minimise cell downtime and accommodate
concurrent engineering or rapid product releases. Atypical off-line system allows up to 70% to 90% of theprogram to be developed off line and debugged on line(235). Some programming packages allow messagesto be written and displayed (Figure 7). The programmercan direct the operator to interact with the cell.
(a)
(b)
Figure 6
Example of off-line programming systems
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Figure 7
Example error message
3.2.3 Expandability
Controls for programmable robots are becoming moreexpandable. When hardware, software and operatingsystems comply with industry standards and are userexpandable, it is called open architecture. Openarchitecture is the desired configuration. Expandablecontrollers are used to control secondary devices or
machines in work cells, allowing more value to be addedto parts. Distributed control machines have processorsand input/output units at different places on the robot orwithin the cell (131). The advantages of distributedcontrol are the speed of processing programs and controlas well as reduced wiring on or between devices.
Distributed control also eliminates the requirement forduplicate control and software within a cell (235). Theoperator interface can be shared. When using onecontroller to control the cell, the setup flowsautomatically to each machine (292).
3.2.4 Communications and Controller
Integration
Communications from the robot to the IMM or to acentral computer are useful in Phase II and III and arerequired for Phase IV installations. Communicationsbetween the robot and moulding machine are used forquick program changing, clamp interlocks, starting andstopping and error logging. Communications between
the robot and a central computer are used for programchanging, remote monitoring, central administrationand status logging.
Communications to the moulding machine can gobeyond the information exchange above. In somecases, the robot controllers are integrated closely bydirect hook up to the moulding machine computer bus.This allows for fast, real time exchange of data suchas the clamp position. In other cases, additional
transducers are added to the press, but hooked up tothe robot controller (123, 131). The robot tracking of the clamp position allows it to move with the clampas it opens or closes. This feature is useful on largemachines with deep-draw parts. Cycle time is savedfor robot extraction.
4 Integration of Automation Systems
for Phase III and IV
Many companies have deployed Phase I and II systems.Small companies that do not have substantial financialand technical resources tend to automate up to Phase Ior II. However, Phase III and IV systems will berequired to compete with developing countries and low-wage competition when value is added. Many mouldershave difficulty reaching this level of automation dueto a lack of understanding, poor vision and planning,and lack of management commitment. Phase I and IIsystems can be retrofitted onto existing equipment with
little planning. Phase III and IV systems require arationalisation of the entire manufacturing operation,equipment and operational procedures. Machinepurchases and internal systems that are made for theshort term become barriers themselves to futureoptimisation. They can be incompatible with futurerequirements or tie up capital, and potential savingsare not realised.
Reduced product lifecycles and the quantity of productoptions have drastically reduced the amount of long-running moulding applications. The long-running jobsthat do exist are often produced with low inventory, just-in-time (JIT) requirements. Accordingly, post-mouldingautomation that is not dedicated to running one part forseveral years has to accommodate a wide variety of partgeometry and orientations. A high degree of flexibilityis required. Technology has evolved in the past few yearsto allow automated moulding in these conditions. Insome cases, it is still expensive or support-intensive torun. Some facilities that used fixed automation for oneproject have found automation equipment and itsdepreciation costs to be very burdensome and prohibitive
in adapting to other jobs. These facilities often fail orrequire large retooling costs that could have been avoidedwith more flexible automation.
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In the past, the absence of equipment from suppliersthat could operate and communicate seamlessly in ahighly automated facility was also a barrier. Moulderswere often faced with doing extensive research, makingmodifications and committing substantial resources tointegrating a facility. The resources required for this were
very specialised and expensive. An alternative is topurchase complete systems from highly developedsuppliers, but the cost may be high. Some conceptsdemonstrated by manufacturers are not economicallyfeasible and never make it from the trade shows intoplants. However, the evolution of computers has resultedin components that are now easier to integrate and morecost effective. The moulding industry’s use of computerintegration and communications has not kept pace withtechnology. However, industry standards are nowemerging to make the integration easier. Many suppliershave communications hardware, but do not havesufficient software tools to communicate to plant floorcomputer networks. Hopefully, certification processeswill emerge so that users will know that pieces will ‘plug-and-play’ and communicate with minimal effort.
All phases of automation are now economically feasible.The best approach to higher levels of automation maybe to specify equipment for the level of future integrationrequired in the next ten years. A project plan is then laidout to implement automation in phases. Sometimes whena moulding machine is replaced, the entire cell is
upgraded and integrated. Some manufacturers willimplement projects across a common press tonnagerange. Moulds within that tonnage are then standardisedfor quick-changeover systems. The experience fromprevious cells is used to design and integrate future cellsin a constant evolution process. Capital equipment andproject risk is minimised. Personnel in the facility havetime to adapt to new methods as well.
4.1 Expected Benefits of Phase III and IV
The amount of investment required for each employeeeliminated has been shown to increase for higherlevels of automation (256). Due to increased costs,more scrutiny is needed to identify applications, toproject manage them and to audit them to ensuresavings are delivered. However, studies have alsoshown that greater levels of investment have deliveredlinearly proportionately greater levels of savings. Thepoint of diminishing returns has not been reachedwithin the industry.
A European study showed a strong tendency forproductivity gains by flexible simplified organisations,not exclusively capital investment in automation (199).
Indicators that may show organisational flexibilitywould be the degree of implementation of JIT, statisticalprocess control (SPC), material resource planning(MRP), computer-aided design/manufacturing (CAD/ CAM), agile or lean manufacturing processes, andcontinuous improvement programmes.
As most companies are using purchased off-the-shelf technology, the competitive advantage depends on howthoroughly and efficiently the technology is deployedby the organisation. Many moulders added secondaryoperations after moulding for several years and maynot have assigned resources to optimise and organisethem into the best configuration. Non-value-addedoperations and poor layouts can smother the potentialprofitability of these operations.
A new perspective is required to implement automationand justify it. Many financial justifications are designedfor a short-term, one-time expenditure to solve amanufacturing problem. A different process is neededfor long-term, continuous, strategic manufacturingdecisions and justifications focused on efficientmanufacturing. The automation will have to be phasedin over a period of months or years. The justificationand purchasing process must allow measurement of productivity savings and expenses against a multiyearplan. Once plans are approved and implementationstarts, it is also essential to regularly audit the progress
of expenditures, utilisations and savings, and tocompare them against what had been planned. Thislevel of automation is a journey, not a one-timepurchase and installation.
It is common to find operations that may significantlyadd cost to the project, but contribute little to savings.Operations such as these are better eliminated,performed manually, or redesigned to be more costeffective. Compare the costs of options required forquick changeovers and justify them against the benefitsexpected.
Equipment required for unmanned flexiblemanufacturing systems can sometimes be twice theprice of standard machinery and must be justified withcareful analysis and implementation plans.
4.2 Actual Operating Results
Overall reduction in manufacturing costs of 20% iscommon and sometimes up to 40% has been achieved
from receipt of the resin to the finished productshipment (129). Press utilisation can go up as much as50% overall.
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Best-in-class machine/cell efficiency will averagearound 93% once debugged. Actual efficiency dependson the complexity of the cell and the amount of changeover required.
Many users gain the largest financial payback based on
the elimination of direct labour. Some applications, suchas quick cycles or large parts, are held up by the operatorsand more production can be obtained when automated.It is difficult to utilise 100% of labour beside themoulding machine. Utilisation of only 50 to 70% iscommon. Centralising the value-added operations orautomating them lowers lost labour (294).
The goal of several automation systems is to movebeyond direct labour savings to minimise or eliminateindirect labour. Labour required to change over systems,to monitor quality, to move materials to the machines,and to transport materials through the factory can beeliminated. Companies have found the only way toremove variability and to achieve zero-defect productionis to eliminate manual operations and automate theremaining ones. Operators are then in charge of monitoring the production, machinery and quality, andof making final shipments (41). When direct and indirectlabour is eliminated, there can be substantial savings inother support and administration departments due to thereduction in the management of personnel required.
Consistent cycles, consistent secondary operations, on-line measurement, segregation and control all contributeto the increase in quality. Automated measurement ismore accurate than human measurement systems. Theautomation systems used have integral quality checksof each operation to immediately detect errors, segregatethem and prevent scrapping of subsequent higher-valueproduction. The systems used prior to cell automationrequired a lot of work in process and errors that weredetected caused a lot of scrap.
Some companies automate initially to be able to offset
shorter mandated workweeks or to extend plantutilisation over weekends. The entire operationutilisation and efficiency goes up as fixed costs are spreadacross 20% more shipments when going from a five-day operation to a six-day operation. Weekend operationmay be done with little or no staff. The unmanned hoursuse less energy for human comfort and lighting.
Floor-space reductions due to less work in process,storage space and secondary operations can be up to20%. Floor space reduction is critical for costly real estateareas or cramped facilities where the cost of the
automation is much less than new facility space. Capitalexpenditure for more moulding machines and supportequipment is avoided. Automated vertical warehouses
can take up to one-quarter or one-half the area of conventional warehouses depending on their height.
Deliveries can be improved due to quick changeoversand shorter queue times in cell manufacturing.Scheduling complexities are greatly reduced and on-time
performance improves.
Short runs, low inventory, increased product variationsand shortened product lives propel the requirement.Quick changeovers are also required for rapid productlaunches. Rapid changeovers drive up the labour requiredto perform them if not automated, and hinder cellutilisation. The changeover time must be measured fromthe previous part to the first good new part. Systemsmust be designed and coordinated to be as automated aspossible with as many operations as possible changingover in parallel.
Automation that is implemented for quick changeoverscan increase press utilisation by at least 5% and as muchas 15 to 20%. Changeovers are quicker and require fewerpersonnel because they are done automatically. Quickchangeover systems allow companies to lower work-in-progress inventories. Some successful manufacturershave reported that the equipment investment equalledthe cost of the inventory reduction. In this case, it wasviewed that investment in equipment was preferable toinvestment in inventory. Certainly, the lower inventory
has a significant ongoing benefit after the equipment ispurchased. Automation of office functions, such as orderentry, quality control, and production control arenecessary to keep up with the speed of quick changeoversystems in the plant.
Worker satisfaction also escalates. A European studyfound that 50% of employees polled expressed that their
job became more interesting versus 13% who expressedthe job was more boring; 48% expressed the job waseasier versus 15% who expressed the job was harder.Only 1% lost jobs. This low number is probably due to
the fact that labour is in short supply and is difficult toretain in many plastics manufacturing environments.
4.3 Requirements for Phase III and IV
Integration
One of the most critical steps for higher levels of automation does not involve automation at all. Theorganisation, customers, parts, moulds and processes allhave to be rationalised and improved to accept greater
levels of automation. The improvements may start anytime and progress throughout the integration process (161,257). Moulders should discuss what production can be
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profitable and under what constraints, determine whatprocesses match the company’s competencies, determinewhat levels of efficiency will be required to reach theprofitability goals and determine the levels of quality andquality-tracability data required. Remaining processes willneed to be automated as much as possible and integratedinto the data-processing network. An automation missionstatement can then be written.
Next, the remaining processes from receipt of an orderuntil invoicing should be put into a flow chart. All nonvalue-added operations in the production flow path shouldbe eliminated, minimised or automated. Automating nonvalue-added operations is expensive and can make afacility noncompetitive and increase depreciation costs.
The company then needs to conduct a gap analysis to
determine how to get to the desired goals. The gap analysisshould include moulds and current production machinerycapabilities. Automation will not compensate for moulds,moulding machines or secondary equipment incapableof producing high levels of quality parts. A plan needs tobe implemented to improve tooling and machinery toachieve desired results. The improved tooling maintenancecosts and preventative maintenance (PM) programmecosts that are required to sustain high levels of qualityfrom processes should be factored into the justification.Each job or expected job should be analysed using actualdata, fitting it to the optimum machine and process
equipment, to produce parts with the lowest cost andhighest quality. From here, the plant layout, material flows,flexibility and changeover requirements can be defined.Finally, an investment schedule can be put together.
4.4 Standards for Higher Levels of Integration
The next step to higher levels of integration is bydeveloping standards. The moulding machines need sizestandardisation along with defined specifications and
options. Many plants will standardise on a small numberof different sizes of machines to reduce the number of variables and the variety of different support equipmentin the facility. Limiting machine size from three to fivesizes with at least three machines per size has workedwell for some facilities. Choosing one manufacturer, onecontroller or one communications interface is importantin order to use setups from one machine to the next. Ideally,the moulding machine will have a high degree of processcontrol and automatic adaptability to changing conditions.Machines should be able to start and stop automaticallyand communicate with other auxiliary machines.
The moulds will also need some standards set. Moulddimensions may need to be analysed and classified for
the tonnage of machine they will run in. The mould-to-press mechanical interface for quick-change systemsshould be fixed. Platen attachment methods need to bestandardised along with ejector, electrical, water,pneumatic, and hydraulic connections. Mould runnersystems must be extremely reliable as well. Hot runners
and sub-gated runners are easier to automate because theydo not require post-extraction processes to obtain gate-vestige quality. Automatic systems require greater mouldquality construction standards because there are no longeroperators present to inspect and correct mould problems.Preventative maintenance intervals must be set to maintainthe moulds’ consistent production of good parts.
Auxiliaries such as mould temperature controllers andresin material dryers should be tested, calibrated andcertified to be within specification before integration.Standardising auxiliaries will assist greatly in speeding
integration and maintaining quality. All devices shouldbe specified with communications for changeovers,process status and diagnostics.
For special machinery, standardise the components fromwhich the system will be assembled. The addedcomplexity of special machinery has a large support costif improperly coordinated. Programming, tooling,troubleshooting, spare parts and maintenancerequirements are operating expenses that need to becontrolled through standardisation and training. Try tochoose components that are flexible and reusable. Someprojects fail because the cost of ownership, retooling andsupport are excessive.
Since parts always need to be moved within a facility andto customers, part transport methods and containers mustbe standardised. Some users develop separate containersfor inside the facility and for shipment to customers. Otherusers have succeeded by using standardised, reusablecontainers for internal and external use. Containers needto be designed to be rigid and accurate. There are moreand more industry-wide container standards beingemployed and used in plants.
A computer network can be built to support the newsystems from door to door. The computer communicationsarchitecture, protocols and data collection/analysisrequirements need to be defined, and installed in levels tosupport future levels of integration.
4.5 Implementation of Phase III and IV
Automation
At this point, implementation of systems with solidproject management procedures can begin. The degreeof project management to get to Phase III and IV is very
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high compared to the lower phases. Many businessesdevelop informal methods of project management toobtain moulds, run jobs and manually add value. Theseinformal project-management methods are ineffectivein managing long-range automation strategies andassociated resources, communications and risks. This
applies in cross-functional projects like automation thatrequire understanding and assistance from alldepartments. Many projects have failed because of improper project-management techniques. Failures areblamed on individuals, when results actually rely ondirection from management. Formal projectmanagement procedures and reviews should beestablished to ensure success. Many resources exist fortraining and consulting in project management. Keyelements of project management are listed below.
• Assign a team leader in manufacturing whounderstands plant processes.
• State long-range objectives of the automationprogramme. Define at least five years and possiblyten years since the equipment life andimplementation will be approximately that long.
• Ensure all pertinent information is in writing, in oneplace and organised into a specification. Manyprojects that fail or have less than desired resultsare due to a lack of initial guidelines and planning.
• Define the project thoroughly with as manydisciplines as possible. At a minimum, eachstakeholder department should be involved. Earlysupplier involvement is critical if the entire processis to be suitable and cost effective to automate. Parts,moulds, factory layout, processes, materialshandling and QC requirements need to be workedout together. It is difficult and expensive to retrofithighly automated solutions to systems improperlydesigned or coordinated.
• Define performance measurements and milestonesso project status can be monitored and corrected asrequired.
• Develop a timeline and commit resources. Reviewthe plan regularly and more extensively at eachmilestone.
• Study the design of each major component carefullywith cross-functional teams. Try to define failuremodes and design them out or minimise their impact.For errors that may cause hold ups, define the desired
recovery methods to resume or maintain automaticoperation. Define the safety requirements of any newmachinery or process. Document all specifications
in writing. This step is extremely important toguarantee proper implementation and utilisation.
• Set up formal reviews and communication strategies,as all departments will need to be involved and keptadvised of the status. Communications must include
vendors and customers. Take corrective actionswhere required. Lack of team communications isone of the chief causes of project failures.
• Ensure the plan has sufficient training commitments.Ideally, training is performed just beforeimplementation of each milestone. Users report thattraining and retraining is critical to implementationand successful operation. Automation systems aremore complex and require new disciplines withinthe moulding facility. Multidisciplined employeesare important to keep a cell running with minimal
staff. Aim to identify competencies required for staff at each new level of integration. Develop trainingand verification systems supporting each level.
• Set installation and acceptance criteria carefully.Often, a large degree of coordination is requiredbetween departments to get all of the pieces runningand optimised. Confirm safety features and performfinal training before turning a system over toproduction. Installation planning must includesufficient preplanning to allow for productiondowntime and for scaling up the system through
optimisation and debugging. Plan for using extraresources for the first few weeks of implementationto get the cell running reliably and efficiently. Thereshould be a formal optimisation team in placeincluding key vendors. Redundant manual systemsor inventory build up may also need to be considered.
• Implement a PM procedure and monitor itseffectiveness. It is difficult with systems integrationto develop complete PM plans up front because of the customer nature of the systems and no pasthistory to rely on.
• Return and audit milestone installations after threeto six months running to ensure results are sustainedand no issues remain.
• A wise strategy is to implement in increasingcomplexity, after each phase is installed andcertified. Start off easily and debug processes andautomation strategies. Qualify each process step fordesired quality and consistency then integrate it. Alarge unqualified integration project will have toomuch downtime and associated frustration.
Integrating in steps uncovers barriers, which oncehandled, improves the operation and allows furtherintegration and continuous improvement (289).
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4.6 Equipment Differences for Phase IV
Integration
Phase IV is a much higher level of automation thanprevious phases and requires a high degree of integration and control. This phase goes beyond islandsof automation into a fully functional, highlycoordinated, quick changeover, lights out factory.
The key to implementing flexible manufacturingsystems is to buy flexible components. Flexiblecomponents are those that can be reconfigured easilyfor different parts, often by reprogramming thenrecalling setups. A minimum of mechanical changes isrequired to reuse or retool the equipment. Changeoversbetween runs must be done automatically and rapidly.Contract manufacturers, in particular, must use flexible
components or their main competitive advantage of quick reaction and adaptability is lost. Automation mustnot make an organisation slower or less adaptive.Flexible components cost more, but have a longer life,which lowers risks and allows the equipment to bedepreciated over longer time periods. The useful lifeof flexible systems is often two to four times that of inflexible dedicated components.
The main components requiring flexibility are:
• A plant material quick-change system to delivermaterial from the warehouse to the press.
• A press material, quick-change system.
• A mould quick-change system.
• A press par ts handling robot with a quickchangeover system.
• A value-added automation system with quick-change ability for different parts requiringdifferent tooling and software.
• A parts-transport system to deliver componentsto the cell and remove production. The systemwill link the cells to an automated stockyard orwarehouse. This portion of automationintegration links up the ‘islands’ of automationthat are stand-alone manufacturing cells(Figure 8).
Figure 8
Examples of Phase IV system
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• An automated stockyard or automated storageand retrieval system for work in process andfinished goods.
• A computer network to link all processes togetherand a central computer and software to control,monitor, change, and track data for the factory.
The degree of Phase IV development can be judged bythe amount and sophistication of the componentsimplemented.
4.6.1 Plant Material Quick-Change Systems
A plant material quick-change system must be designed
to deliver each different material to each different press.Systems may have to be designed to be self-cleaning toensure that no contamination occurs during changeover.The systems must be able to be sequenced from a centralcomputer and accommodate material, colorant and dryair if required. These systems are often quite differentfrom the ones presently installed in many facilities (258).The system sequence is purge the material lines andhoppers, confirm cleaning is complete and deliver newmaterials. The new moulding sequence can then begin.
4.6.2 Press Material Quick-Change Systems
Ideally, jobs can be scheduled in machines using thesame material. For many facilities, this is not possible.A moulding-machine material quick-change system isrequired and generally composed of systems to purgeand refeed the injection unit. Systems were developedin the 1980s to automatically change barrels, but theyproved to be not commercially viable.
Semi-automatic systems are still used because of the
complexities involved in performing changeovers andkeeping systems clean.
4.6.3 Mould Quick-Change Systems
A mould quick-change system may be composed of:
• A mould storage system.
• A mould t ranspor t system. Moulds can be
transported with overhead programmable cranes,automatic carts or semi-automatic carts.Programmable cranes require less floor space.
• A mould preheat and staging station.
• Mould loading systems to pull moulds out of thepress and load new moulds into the press.
• A mould clamping and location system. Thissystem must also have connectors for utilities.Quick connectors for hydraulics are required if core-pull sequences require them. Hot-runnersystems need to be quickly connected andintegrated to the press controller. Provisions maybe required to confirm the proper mould is in thepress and connected fully. Some companies haveeven used robots to change core and cavity setswithin the mould (287). Die positioning accuracyafter a mould change is important so a robot canautomatically change its end-of-arm tooling and
interface to the mould.
• On occasion, a mould cool-down station is requiredbefore storage.
Safety and interlocks of these systems must be wellthought out and controlled, as moulds are very heavyand expensive, and present considerable hazards if mishandled.
4.6.4 Equipment Required to Unload the Mould
For small parts or those that do not require secondaryoperations, conveyors or vacuum evacuation systemscan be used. For other parts, robots are required. A pressparts-handling robot with quick changeover capabilitylinks post-mould to pre-mould processes. The robotrequired at this point of integration must be highlyflexible, have computer communications, be capableof automatic programme changes, be capable of automatic tooling changes and have provisions to start,stop and pause automatically. Verification that the
correct end-of-arm tooling and robot sequencecorresponding to the current press set up are in use issometimes desirable to avoid errors.
4.6.5 Flexible Value-Added Systems
Flexible value-added systems that perform multiplesecondary operations or parts after extraction are themost elusive components to design.
Some manufacturers limit a cell’s value-added stepsbeside the moulding machine and then use automatedmaterial-handling devices to move production out of
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the cell. Value-added operations that are difficult toautomate or cannot be done within the moulding cycleare performed manually away from moulding. Linesfed automatically by conveyors or automated guidedvehicles (AGV) accomplish this. If the parts are placedinto standard containers and their position is
maintained, then value-added operations can beautomated in the future.
The difficulty in flexible value-added automation istrying to transport parts economically throughoperations, keeping their orientation and beingadaptable across a wide variety of different geometries.The most economical way to move parts through value-added operations is to use the part removal robot withmultipurpose or changeable end-of-arm tooling. Asecondary flexible robot can also be used to take parts
from the press robot and move them through operations.Beyond robots, several other devices are available butthese are less flexible or adaptable to transport partsthrough operations. Parts can be transported tosubsequent operations by means of conveyors, placedonto pallets, placed into trays or bins or placed ontorotary or linear indexers.
4.6.6 Parts Transport Systems
Conveyors can move the parts to a central location.
They can be inexpensive for some factory layouts.Conveyors can be belts, plastic-link chains oroverhead chain-driven systems. As a result of partslosing orientation in most applications, operators willbe required on the end of the system to reorient,inspect, add value and package parts. Similar partsmay be mishandled and placed into incorrectcontainers. The system does not lend itself well tofuture automation if parts are out of orientation oroverlapping. Parts liable to damage during transportdo not lend themselves to this type of automation.An exception to this would be the placing of partsonto fixtured pallets, transported on conveyors.Sensors to detect parts passing underneath otherrobots need to be installed to prevent parts frombeing placed on top of others and to avoid possiblerobot crashes. If robots can package beside eachmachine, then the conveyors can be used to transportcontainers in and out of the cells. Conveyors requirea lot of floor space and inhibit access to the mouldingcells unless they can be put overhead, in which casethey are difficult to service and clean, and parts maynot be easy to see. Conveyors to a central location
are best used for similar parts, large parts or easilydistinguishable parts that will not require or cannot justify the costs of added-value operations.
For small parts, some plants have used air conveyorsystems where the parts are transported in an air streamto a packaging room or machine. Parts are ejected intoa hopper that directs them into a tube and air stream.An air-vacuum transport system, hooked up to thehoppers under the machines, conveys the parts to boxes
located in another area of the facility. The vacuumtransport system must be sized to transport the largestexpected part size. A maximum part size of 30 mm iscommon. Parts must be those that can transport throughtubes without getting marked or damaged. Parts mustalso be able to be moved without tangling or causingblockages in the tubes. The system requires modestfloor space and labour.
Several automated plant concepts have evolved aroundcontainer filling cells (Figure 9). The containers can
be trays, bins or boxes with single or multiple layers(72). Large parts sometimes have rack systems that aretransported through the cells. The trays, bins, racks orboxes can be used internally, externally or both. Thebenefit of a container filling beside the press is that itallows unmanned operation and expandability forfuture off-line value-added automation. A benefit of placing parts into containers is that orientation can bemaintained. When automation of value-addedoperations occurs in the future, the system will readilyadapt. Machines exist to handle standard containers inand around the moulding cell. Multilevel shelves or
conveyors can be used to store production. Conveyorsthat destack and restack containers are common as well.The containers must be dimensionally accurate andhave features suitable for automation, such as beingrigid, stackable or collapsible, not easily damaged andeasy to clean. It is common to use inserts in thecontainers for parts requiring precise locations or thatmay be subject to damage in transport.
Once parts are in the containers, they can be removedat intervals by operators, conveyors, or loaded andunloaded by AGVs. The AGVs are self-propelled carts.
The drive is usually accomplished with electric motors.Electric-driven vehicles will require a rechargingstation for periodical charging during operation. Thevehicles are sized based on the maximum payload andsize of load to be accommodated. The top of the vehicleis usually designed to automatically load or unload thetype of container to be used in the particular facility.The vendor base for AGVs has been very volatilebecause of the large amount of research anddevelopment required and the varying marketconditions. Many factories have not advanced theirautomation to the point where an automatic vehicle cantake over; they also have not automated upstream ordo not have an automated warehousing linkage.
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AGV systems are expensive, but very flexible. They can
often be justified in one to two years in the rightapplication where the factory is reasonably organised.Indirect labour is saved along with reduced part damagethat may occur with manual systems (87). Unlike fixedconveyors, they can be reprogrammed and reconfiguredfor a wide variety of transport tasks. The systems makethe transition to automated storage and retrieval systemsseamlessly as all of the infrastructure and standards areput into place. Phase III or IV systems need carefulcoordination of containers and supplies to and from thecells and are inhibited by manual transport methods (72).Guidance systems are usually chemical paths paintedonto the floor, taped paths, or grid systems in which thevehicles navigate freely between points. Systems whichuse lasers for positioning are also in development. AGVsgive full access to the cells when not docked or whenmoving by them. AGVs are usually not installed until areasonable amount of cells are running efficiently. Beforethis point, manual or semi-manual methods are used.
4.6.7 Automated Stockyards and Automated
Storage and Retrieval Systems
Whether work in process or finished goods aretransported manually, by conveyors or by AGVs,
automatic storage and retrieval systems can be
employed. The simplest form consists of rollerconveyors, to which containers are off-loaded. Aseparate conveyor line is usually associated with onepart or moulding machine. Simple roller-conveyorsystems are frequently employed to store enough partsfor unattended shifts or weekend operation. Systemsthen increase in complexity enabling loading andunloading as well as computer tracking of containers.The most sophisticated systems are multilevel systemsthat use linear robots to pick and store containers andlater repick and deliver them to an outlet position whenrequired. These storage systems are mostly used whereland is at a premium or the cost to add floor space ismore than the storage system.
4.6.8 Logistics and Coordination
A very high degree of logistics and coordination isrequired for Phase IV implementation. Onlycomputers can keep up with the demands. If notproperly thought out, the personnel required tocoordinate the factory and run it efficiently in a small-
lot, quick-change environment will offset savings inother areas. It is critical to use local area networkarchitecture and ensure all major components in cells
Figure 9
Automated container filling
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are equipped to integrate to it. However, in case of asystem failure, production cells should be designedso as to be able to run without the computer network.It is common to have a local computer in each cellthat interfaces each machine within the cell to thecomputer network. Minimally, the system must
coordinate set up data for all of the cell equipmentwhen a new mould is run and verify that control pointsare met to begin production.
The central computer hooked up to the network willschedule production resources, handle changeovers,track and display status, gather quality information,perform quality analysis, display errors and schedulepreventative maintenance. The central computerdevelops schedules and sends them to each individualcell computer for execution (258). Status and error
display must be designed to get quick notification andreaction to problems. Often these systems are linkedto audible or visual alarm systems within the plant orto remote locations for off-hours.
4.7 Design Criteria for Higher Levels of
Automation
When implementing cells and FMS, system design iscritical. The following is a list of common design
considerations:
• The cell should have the ability to shut downautomatically if the run is complete or if there istrouble and no one responds. The cell must shutdown in an orderly way leaving all elements in asafe and known position. The status of the machinesshould be kept so the cell can be analysed andrestarted quickly. Irregular production may needto be isolated. Heating elements may need to bereset at a lower setting.
• Machines within a cell should be capable of uncoupled operation inside or outside of the cellin case of trouble. Thought must be given to howoperations can be performed manually if theautomation fails. Cell design may need to leaveroom for operators and for any movementsnecessary to allow manual intervention or havedecoupling abilities. Integrated machines mayrequire an automatic and manual control interface.Guarding that can be easily configured for manualoperation should be considered (37).
• Operator input or take away from a cell should notaffect its operation or safety. Feeding of
components into the system should be done withease while the machine is running.
• Buffers should be placed in front of operationsrequiring manual adjustment, cleaning or supplyreplenishment. According to a recent article, asmuch as 70% of cell downtime is operator induced(125). The buffer should be long enough to allowfor operator arrival and completion of the task.Some machines that are difficult to start up maybe required to keep in cycle and dischargeproduction for a short time while the cell isattended. The length of time the machine dischargesproduction should be limited so that excessive scrapmaterial costs are avoided. Cell design may requiremanual reintroduction of parts produced while amachine was down or from surplus capacity. It may
be required to take parts off line and reintroducethem downstream if a component fails. The rate of the downstream operations may need to be fasterthan the process to allow reintroduction of production while still on line.
• It is good practice to perform quality control foreach step immediately after or during the operationand to isolate bad parts once detected. It may bedifficult to track bad parts in a machine, and so thevalue added to them is wasted. The system shouldbe programmed to stop if a preset frequency of errors occurs at a station rather than stopping ateach error. Cells may need quality control of incoming material and process adaptation if thereis a likelihood that defects could occur, would behard to detect, or would cause interruption of thecell. Critical operations within a cell should allowfor quality control sampling without cellinterruption. The sampling can be programmed atintervals or triggered by an operator.
• Critical components can be serialised and the data
stored for traceability. This is common forcomponents where product liability may be aconcern.
• Consideration has to be given to productionbalancing, from multiple machines or for machineswhere cavities will be shut off. The part removalrobot or other devices can perform this function if equipped and programmed properly.
• One of the most important design considerations
is to specify flexible components to be adaptablefor families of related applications. Componentsshould be as modular as possible, to allow them to
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when there are no personnel on duty, the central computercalls a manager at home who can respond. Servo robots,on top of the moulding machines, fill trays with parts.Trays are automatically destacked, filled and restackedon a press-side, parts storage machine. When a stack iscompletely full, an AGV retrieves the stack and deliversa stack of empty trays. The AGV transports the trays toan elevator that brings the vehicle to the second floor.The AGV then delivers the stack to a roller conveyorstockyard. When the production in the trays is beingshipped or processed by operators for secondaryoperation such as assembly, quality control measurementor testing, an operator retrieves the stacks from thestockyard. The stockyard is sized to hold two to threedays of production for operation over a weekend.
5.4 Product or Contract Specific Cells
Some cells will have been designed for a specificproduct or a moulding contract of three to five years.For moulding contracts, it is important to chooseequipment that becomes adaptable after the contractterm. This avoids large depreciation costs during theproject and large retooling costs after the project.
A well thought out production cell in Germany illustratedthe maximum utilisation of a system. The goals of the
system were to provide maximum up time, toaccommodate short runs, eliminate work in progress,and to give maximum value-added operations by tryingto get the robot to work the entire moulding cycle (200).A servo-drive, traverse-type robot removes parts, checksdimensions, cuts off a sprue and loads the part onto arotary table. On the rotary table, the part is milled, hotstamped and presented again to the robot. The finishedpart is stacked into a magazine for storage. Beforestarting the next cycle, the robot picks up a bearing,checks its dimensions and inserts it into the mould. Thecell was designed so parts can be removed and fed back
in if a station goes down to keep production going. If manual attendance is required in the cell, the robot keepsrunning and loads parts into a buffer for up to 12 minutes.When the operator exits the work zone, the robot willautomatically begin to feed the cell again. Each stationcan be manually turned off outside the cell, and the othermachine stations will keep running.
5.5 Group Technology
Many cells have been designed around a group of partsrequiring similar operations, e.g., for in-mould decorating,insert moulding, and two-component moulding.
5.5.1 In-Mould Decorating
In-mould decorating has the advantages of theelimination of special downstream decoratingmachines, the elimination of scrap associated with on-line decorating, flexibility of using different labels andproducts, higher quality decorations on the parts andbetter environmental properties with integraldecorations (192). Systems are composed of magazinesfor labels, a label pick-and-place robot or device, anda vacuum or static electricity system to hold the labelin the mould. Typical products using in-moulddecorating are food containers, appliances, cell phonesor any other plastic parts requiring decorations.
5.5.2 Insert Moulding
Insert moulding has several advantages when automated.If inserting is done by an operator, the cycle variesconsiderably, quality cannot be maintained, scrap is highand mould damage occurs from misplaced inserts. Jobsrunning manually require close supervision, operatorrotation to prevent fatigue and strict control to remainprofitable. In view of these problems, many mouldershave realised that automation is the only way to makeparts profitable. Systems that are flexible are expensiveand need to be justified over long periods of time. Theexpense to tool each new job with insert moulding can
be prohibitive if done improperly.
Some manufacturers with long runs will use simplededicated transfer devices for insert loading. However,most manufactures use servo robots due to theirflexibility and accuracy. Servo robots can pick up insertsfrom manually fed shuttles, vibration part feeders orother magazines (Figure 10). Inserts are sometimesloaded into a mould fixture outside of the press, and thefixture is picked up by the robot and placed into themould. Sometimes inserts are handled on strips of tapeto simplify loading of delicate pieces or multiple inserts.
When strips are used, operators or a press can removethe parts from the strips after moulding. For high-volumesystems, inserts can be fed from a reel on the mould.The finished parts can be rolled up on another reel ordischarged in strips (297).
Common applications of insert moulding are threadedinserts for part assembly and moulded gaskets.
5.5.3 Two-Component Moulding
Two-component moulding is very popular. A commonconfiguration is to mould the first component in one
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Figure 10
Insert moulding operation
machine and unload it with a robot. The first robothands off to a second robot, which loads (as well asunloads) the second machine. Another configurationuses a robot to move parts from the first mould on atwo-injection unit machine to the second mould andto remove the finished part. Rotary platens used tomove moulds between the injection units on two-colour machines index to allow moulding of thesecond component. Then a robot unloads the finishedparts. Typical applications are soft-touch materials orlenses (73).
5.6 Quality Control Automation
Quality control operations are becoming one area of rapid advancement. The requirement for manualinspection holds many moulders back from automating.
Article (143) details the automation of quality controlmeasurement, recording, and traceability. The articleexplains the necessity of automated quality control forthe automotive industry, particularly with critical safetycomponents such as airbags. Airbag components are
automatically removed and fed to coded pallets. Thepallet identification is used to track the good and badparts for separation at the end of the system. Parts are
then degated, hot stamped, serial data applied on thepart, and a serialised bar code label is applied to theoutside. Bar codes are checked for readability. Partweights are taken and defects identified. All productiondata is stored for each assembly. Bad parts throughoutthe process are identified and separated by a robot atthe end of the process.
Vision systems with fibre optics (Figure 11), directlymounted to the robot's end-of-arm tooling (EOAT),have been used successfully. The robot checks the partsor inserts on the EOAT while transferring the partsbetween operations (218). Vision systems are also being
used to identify different parts on a line and to transferthat information to a robot that changes its programbased on the specific part requirements (292).
5.7 Thermoset Cells
Thermoset moulding has, in many cases, lackedautomation implementation. Part-extraction robots areused, but very little other work has been automated.The requirement to deflash parts and moulds, along
with difficulty in automating these operations, meantmanual systems were needed. A manufacturer hasreported that robots in their operation are used to
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prevent part damage, to demould parts requiringdifficult motions, to prevent tool damage, to degateparts, and to load parts onto jigs for further processingor cooling (295).
5.8 Examples of FMS
A Japanese automotive moulding facility was designedto automate the moulding of grilles, bumpers and
instrument panels. The mould changes, materialchanges, part extraction, part palletising, part transportfrom moulding to storage, and part transport fromstorage to post-process areas all run automatically. Partsare retrieved automatically and fed to an automaticpainting system. The facility has used an automaticcrane system to change moulds. Moulds are deliveredto two-position, mould-change tables located besidethe moulding machines. Moulds are preheated duringthe end of the run of the present mould. When the runis over, the mould in the machine is transported ontothe table. The table then indexes forward on rails andpositions the next mould. The mould is loaded into thepress. An automatic crane retrieves the completed
Figure 11
Vision system
mould after it cools down. Material is selected from astorage silo, sent to a dryer and then to the propermachine. Parts are removed with robots and palletisedonto press-side, conveyor systems. A central computerhooked to cell computers tracks production, sets upequipment and handles scheduling and logistics.Completed parts are automatically transported to amanual, value-adding area (258).
6 Future Developments
Developments are evolving rapidly in the field of automation. The increase in driving forces has changedthe mind-set of many moulders. Implementation of automation and its importance are becoming a majorpriority. The skills to project manage, install and operateautomation will continually evolve as moulders striveto compete. Moulders will be asked to project managethe entire cycle from part design to delivery logistics.
Projects will need to be completed more rapidly.Moulders should partner with suppliers to developrelationships for rapid launches.
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The rapid advance of computer power will meansmarter and more flexible machinery. The computerpower will be used for rapid changeovers, flexibilityand integration into plant-wide computer networks.Personal computers will become the most commoncontrollers for shop-floor machinery.
Control software will become more adaptive, detectingand correcting problems to keep machinery running.This will be important to increase the implementationof automated systems. These controls will be standardon moulding machines, robots, auxiliaries and othervalue-added machinery.
Servo technology is rapidly advancing. Servos will bethe dominant drive on robots and other machineryrequiring precise control, rapid changeover and
flexibility to adapt to changing conditions. Servos nowaccount for 60% or more of robot drives for plasticsand will continue to advance to levels of 80 to 90% inthe next five years.
The degree of quality, monitoring and documentationwill increase to support traceability and higher levelsof quality production and improvement. Measurement
and confirmation of each part will be important. Onlyautomation can achieve this without driving up the costof production through manual inspection.
Decreasing lot sizes and increasing product variabilitywill drive the requirement for flexible, quick-changeadaptive systems for implementation.
All of the above will influence moulders to implementadditional levels of automation. The trend will escalateover the next five years, and cell manufacturing (PhaseIII) will be common in five years, whereas less then10% of the moulders are at this level now. FMS willbe commonplace in ten years for moulders competingon a world basis.
Additional References
a.1 Evolution of Automation in Plastics InjectionMoulding by Yushin America, Inc.,www.yushin.com.
a.2 Injection Moulding, 1996, 4, 8, 84.
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