assemblyengineering

THE NEXTASSEMBLY CHALLENGE

IN THE perpetual search for improvedproduct cost, smaller size and enhancedreliability, periodic and dramatic changesappear with astonishing regularitythroughout the electronics manufacturingindustry's process technologies. An impor-tant seminar structured around the need ofmanufacturers and design engineers to stayup to date with latest developments in thecritical area of 'high density electronicplacement and packaging' has beenarranged by the IProdE for April 25th.

Whilst the widely used, but still relativelyyouthful, surface mounting techniqueapproaches its golden years, new contendersare emerging. An advanced generation ofcomponents and assembly methods havebecome available, to offer yet higher levels ofintegration.

Traditionally, components, hybrids andfinal board assembly have each requiredseparate and distinct production methods. Inthe latest R&D brainchild, these individualoperations are merged, as new interconnectand packaging methods are combined tooffer considerable performance enhancing

opportunities and design challenges.Conventional board based technology is

now being applied within components toprovide single package custom circuits.Whilst silicon interconnect techniques arealready being used directly at final circuitassembly.

At the seminar, existing users of thistechnology together with process developersand suppliers, will be providing practicalinformation concerning a broad range ofdesign and production considerations, whilsta number of equipment suppliers will also beavailable with displays to answer implemen-tation questions individually.

New technologies to be covered in the halfday seminar at Loughborough University(Leics) include robotics, laser soldering,direct bonding, vision alignment and singlemodule circuits; to provide the professionalelectronics engineer with a valuable updateon leading edge assembly and packagingmethods.

For more information please contact theConference Department at Rochester House.Tel: 01-579 9411 ext 209.

MANUFACTURING ENGINEER MARCH 1990

SOUND SYSTEMS

Higher productivity andenhanced quality control areamong the benefits on offer fromthe latest generation of ultrasonicsystems.Bob Werrett, product manager ofKerry Ultrasonics Ltd, providesthe details.

Control and consistency viaan analogue controlledsystem with amplitudemonitoring

The basic principle of ultrasonicassembly involves the conversion ofhigh-frequency electrical energy tohigh-frequency mechanical energy in

the form of reciprocating longitudinal motion.When applied to a thermoplastic, this can generatefrictional heat at a plastic/plastic or plastic/metalinterface. The frictional heat causes localisedmelting of the plastic enabling the two componentsto be joined.

There are four basic methods of assemblyusing ultrasonics, namely welding, spot welding,staking and inserting. In ultrasonic welding, twoplastic components are joined via a speciallydesigned joint. Commonly, small 90° triangular-shaped ridges, or energy directors, are mouldedinto one of the mating surfaces. These energydirectors limit initial contact to a very small area,and focus the energy at the apex of the triangle togive rapid softening and subsequent flow of theplastic material.

Using spot welding, large thermoplasticcomponents and parts with awkwardly-positioned

joint surfaces, can be easily welded together viastrong structural welds at localised points. Thehorn used in spot welding has a specially designedtip. When it comes into contact with two sheets ofplastic, the ultrasonics cause the pilot of the tip topenetrate the top sheet and enter trie lower sheet toa depth of half the top sheet thickness. The moltenplastic which is displaced, is shaped by a radialcavity in the tip to form a ring of raised plasticaround the weld. Simultaneously, the moltenplastic displaced from the second sheet flows intothe preheated area and forms a permanentmolecular bond.

Ultrasonic staking is analogous to riveting. Itprovides an alternative to welding when either thetwo components are moulded from incompatiblematerials or when simple mechanical fixing of onepart to another is inadequate. A typical applicationof ultrasonic staking is the fixing of a pcb in aplastic enclosure. During this process, thecontrolled flow of molten plastic is used to retainanother component, often metal, in place. A hole inthis component receives a premoulded plastic

MANUFACTURING ENGINEER MARCH 1990

THERE ARE FOUR BASICTECHNIQUES OFULTRASONIC ASSEMBLY:WELDING: Two plasticcomponents are joined via atriangular energy directingjoint. Energy is focused atits apex, for rapid softeningand plastic flow.INSERTING: Frlctlonal heatgenerated at the insert/plastic Interface, causesthe plastic to meltencapsulating the insert.STAKING: Analogous toriveting, a hole in the topcomponent receives apremoulded plastic bosswhich melts to apredetermined shape.SPOT WELDING: The horntip penetrates both sheetsof plastic. Material fromthe lower sheet flows intothe preheated area, to forma permanent bond.

boss which melts, due to frictional heat createdduring the ultrasonic phase. A head is formed to ashape determined by the horn tip configuration.

In ultrasonic insertion, as the horn contacts athreaded metal insert, frictional heat is generatedwhere the insert interfaces with the speciallydesigned cavity in the plastic. The plastic meltsinto the knurls and flutes of the insert,encapsulating it and providing high torque andpull-out resistance values.

Ultrasonic assembly techniques provide weldjoints of high integrity and consistency at highproductivity rates. The need for expensiveadhesives and time consuming activities such asdrying and curing is eliminated. With negligiblerunning costs compared to standard adhesivetechniques, the assemblies produced are clean, •accurate and require no further processing.

The ultrasonic assembly process is particularlysuitable for automation. Maintaining the quality ofassembly, an automated system is capable ofcompleting a cycle in one or two seconds. Withhigher levels of productivity than are possible withadhesive techniques, ultrasonic assembly alsosignificantly reduces reject rates, particularly whensystems incorporate microprocessor control.

The ultrasonic assembly systemThe standard bench-mounted ultrasonic

assembly system, comprises a generator and aweld press containing a piezoelectric transducer.The generator supplies a high frequency electricaloutput of 20 kHz to the transducer, which convertsit into mechanical energy in the form of ultrasonic

vibration. This energy is transferred to a weldinterface by a sonotrode or acoustic horn.Generators are available with different poweroutputs to suit varying applications.

Basic systems are analogue-controlled, somefeaturing amplitude monitoring which gives adirect readout of welding power expressed as thevibratory amplitude. Two types of mechanism areavailable for triggering the onset of ultrasonicenergy. Force triggering compensates for vari-ances in component tolerances by allowing theultrasonic energy to be triggered only once theweld horn contacts the component to be welded.Alternatively, a pretrigger timer may be usedin certain applications, so that ultrasonicsare initiated prior to the horn contact-ing the component. Most standard systemswill also feature automatic frequency tuning,which uses a loop phase shift circuit andonly requires adjustment when a weld horn isreplaced.

For low-volume applications, or assemblingcomponents which are located in awkward orconfined situations, hand-held welding systemsare particularly suitable. These can be used in anyassembly application for welding, spot welding,staking or inserting, where a standard bench-mounted press is inappropriate. These systemscomprise standard ultrasonic assembly systemfeatures, the main difference being that the forceapplied to components is determined by thepressure exerted by the operator.

To improve weld quality, precision andproductivity, some systems incorporate a new

mechanical design of the vertical loaded assemblypress. In contrast to conventional systems withcylindrical sliding column presses, the newsystems have'a heavy section 'H' frame in castaluminium, and a counterbalanced press headwhich travels vertically. As a result, rigidity andmechanical precision are greatly increased. Inaddition, flexing of the structure during the criticalfraction of a second while components areclamped together under pressure and ultrasonicenergy is applied, is negligible. In this way,precise assembly at the component joint face isensured.

Microprocessor-controlled systemsRecently a new generation of assembly

systems has been introduced providing improvedprocess monitoring and control. Consequentlythere has been an improvement in quality of thefinished product, a reduction in reject rates, andsignificantly improved throughput.

These systems incorporate a microprocessorwhich not only enables the assembly process to bemonitored and controlled, but also provides areport on the process that has just occurred. Thereare three methods of assembly: welding by time,welding by energy-and welding by distance.Conventional systems weld by time with presetvalues for both weld and hold times. When thesystem is activated the horn descends and initiatesultrasonic vibration for a preset time. Once theweld time is completed, the preset hold timesensure pressure is maintained against theassembly allowing it to resolidify.

MANUFACTURING ENGINEER MARCH 1990

A custom designed andmicroprocessor-controlledsystem, using SKF flex-link

conveyors to serve 8ICLrotary workstations

With the introduction of microprocessor-controlthe assembly time is automatically adjusted tomeet the energy requirement; in other words,welding by energy occurs. Conditions at the weldinterface are continuously monitored, allowingenergy to be maintained at a constant levelregardless of line voltage fluctuations, materialinconsistencies, horn wear or irregularities inpart-to-part geometry. A predetermined energyvalue in Joules is consistently delivered to everyweld.

At the start of every assembly cycle the systemautomatically fires a 40 ms burst of ultrasonicenergy called a calibration pulse. This measureslosses within the system and accounts for themwhen calculating energy being delivered to theassembly. A piezoelectric load cell permits theultrasonics to be activated only once a pre-setcoupling force is met. In this way the timeassembly takes can be accurately measured.

The major benefit provided by a micro-processor-controlled system is the identification ofreject parts. As a part proceeds through theproduction process, the cost associated with itbeing found faulty steadily increases to amaximum once it is in the hands of the customer.With these systems, rejects may be detected at avery early stage. Limits can be set in either time orenergy mode and any component which exceedsthese limits is then counted as a reject. There arethree indications of the presence of a reject. Inaddition to an audible tone and a visible red LED, a24 volt dc supply can be used on automatedsystems to separate good parts from faulty ones at

the unloading station.Systems are also capable of reporting the

assembly process and its parameters. Informationsuch as assembly time, triggering force values,percentage of total rated power drawn and numberof rejects are all displayed on a' liquid crystaldisplay. Additionally, a printer may be incorporatedto provide a hard copy of power versus timecurves, and the set-up data for every weld.

In some instances a system may have to weldby distance, to ensure consistent finishedtolerance heights of an assembly. For theseapplications a linear encoder is incorporated. Forexample, if a threaded insert has to be positionedat a consistent depth, the linear encoder willautomatically terminate ultrasonic energy once ithas reached the preset depth. The position towhich the weld head is lowered can be set to within± 0.0002 inches.

Custom-designed assembly systemsFor each assembly application, the welding

horn and fixture are specially designed. For someapplications, it may also be necessary to employ aspecial-purpose system designed to meet specificrequirements. At its most basic level, this mayinvolve the addition of an indexing system toautomate the assembly process. By incorporatinga rotary table or linear indexing system, outputmay be increased dramatically. To suit otherapplications, automatic 'pick and place' orbowl-feeder systems may form an integral part ofthe automated production line.

Custom-design may however, be much more

specific than the above mentioned examples. Dustcontrol equipment manufacturers, DCE Limited,recently completed automation of its productionline by installing a special-purpose E-Seriesassembly system from Kerry.

This microprocessor-controlled system is usedin the production of filter bags which are used toremove dust from air in filtration units. Manufac-tured from polyester needled-felt, the filter ispresented to the assembly system in continuoustubular form and is held stationary throughout theultrasonic welding cycle by the custom-builtindexing station. Three consecutive welds areperformed across the width of the material by thewelding head, sealing it completely and formingthe bottom of the filter. The head slides horizontallyacross the product producing accurate andcontrolled sealing by use of the constant energymode.

SummaryA full range of ultrasonic systems now exists to

suit most thermoplastic assembly applications.With the recent introduction of microprocessor-control the assembly process may be preciselycontrolled, monitored and reported, ensuringconsistent results. In addition to the standardrange of systems, special-purpose machines areprovided, designed to conform to specificrequirements.

For more information on Kerry Ultrasonicscircle ME 96

MANUFACTURING ENGINEER MARCH 1990

A custom designed andmicroprocessor-controlledsystem, using SKF flex-link

conveyors to serve 8ICLrotary workstations

With the introduction of microprocessor-controlthe assembly time is automatically adjusted tomeet the energy requirement; in other words,welding by energy occurs. Conditions at the weldinterface are continuously monitored, allowingenergy to be maintained at a constant levelregardless of line voltage fluctuations, materialinconsistencies, horn wear or irregularities inpart-to-part geometry. A predetermined energyvalue in Joules is consistently delivered to everyweld.

At the start of every assembly cycle the systemautomatically fires a 40 ms burst of ultrasonicenergy called a calibration pulse. This measureslosses within the system and accounts for themwhen calculating energy being delivered to theassembly. A piezoelectric load cell permits theultrasonics to be activated only once a pre-setcoupling force is met. In this way the timeassembly takes can be accurately measured.

The major benefit provided by a micro-processor-controlled system is the identification ofreject parts. As a part proceeds through theproduction process, the cost associated with itbeing found faulty steadily increases to amaximum once it is in the hands of the customer.With these systems, rejects may be detected at avery early stage. Limits can be set in either time orenergy mode and any component which exceedsthese limits is then counted as a reject. There arethree indications of the presence of a reject. Inaddition to an audible tone and a visible red LED, a24 volt dc supply can be used on automatedsystems to separate good parts from faulty ones at

the unloading station.Systems are also capable of reporting the

assembly process and its parameters. Informationsuch as assembly time, triggering force values,percentage of total rated power drawn and numberof rejects are all displayed on a' liquid crystaldisplay. Additionally, a printer may be incorporatedto provide a hard copy of power versus timecurves, and the set-up data for every weld.

In some instances a system may have to weldby distance, to ensure consistent finishedtolerance heights of an assembly. For theseapplications a linear encoder is incorporated. Forexample, if a threaded insert has to be positionedat a consistent depth, the linear encoder willautomatically terminate ultrasonic energy once ithas reached the preset depth. The position towhich the weld head is lowered can be set to within± 0.0002 inches.

Custom-designed assembly systemsFor each assembly application, the welding

horn and fixture are specially designed. For someapplications, it may also be necessary to employ aspecial-purpose system designed to meet specificrequirements. At its most basic level, this mayinvolve the addition of an indexing system toautomate the assembly process. By incorporatinga rotary table or linear indexing system, outputmay be increased dramatically. To suit otherapplications, automatic 'pick and place' orbowl-feeder systems may form an integral part ofthe automated production line.

Custom-design may however, be much more

specific than the above mentioned examples. Dustcontrol equipment manufacturers, DCE Limited,recently completed automation of its productionline by installing a special-purpose E-Seriesassembly system from Kerry.

This microprocessor-controlled system is usedin the production of filter bags which are used toremove dust from air in filtration units. Manufac-tured from polyester needled-felt, the filter ispresented to the assembly system in continuoustubular form and is held stationary throughout theultrasonic welding cycle by the custom-builtindexing station. Three consecutive welds areperformed across the width of the material by thewelding head, sealing it completely and formingthe bottom of the filter. The head slides horizontallyacross the product producing accurate andcontrolled sealing by use of the constant energymode.

SummaryA full range of ultrasonic systems now exists to

suit most thermoplastic assembly applications.With the recent introduction of microprocessor-control the assembly process may be preciselycontrolled, monitored and reported, ensuringconsistent results. In addition to the standardrange of systems, special-purpose machines areprovided, designed to conform to specificrequirements.

For more information on Kerry Ultrasonicscircle ME 96

MANUFACTURING ENGINEER MARCH 1990

ASSEMBLY ENGINEERING—BUYER'S GUIDE

ALPHAAUTOMATION LTDPRINCE STREET,TONG STREET,BRADFORD.BD46HQ

TEL: 0274-685822FAX: 0274-651187

DESIGNERS AND MANUFACTURERSOF AUTOMATIC ASSEMBLYMACHINES

EITHER: ROTARY INDEXING OR INLINE FLEXIBLE TYPES.

ALSO SPECIAL PURPOSEMACHINERY OF VARIOUS TYPES.

Encircle ME166 on service form for further information

JOHN BROWNJohn BrownAutomation LtdTor ring ton Avenue,Coventry, CV49XQ,Tel: 0203 47 3748, Tlx: 312355, Fax: 474196Manufacturers and suppliers of flexibleautomation systems, robotic cells, auto-mated assembly machines and equipment.Consultancy services include logistics plan-ning, DFA and systems simulation. A widerange of standard equipment is used inMaterials Handling to integrate materialmovement in a factory. Small AutomatedSystems are engineered and built understrict budget control and Major Projectsuse the project management skills necessaryfor a turnkey approach.

Encircle ME167 on service form for further information

Davis (Decade) Ltd30 Spring Lane, Erdington, BirminghamB24 9BX, Tel: 021 377 6292, Fax: 021 3776645Manufacture a range of assembly loadmonitors to check that the load required toassemble components falls within pre-setlimits. Also systems to check positionalaccuracy and recording equipment to pro-vide permanent records of results.Encircle ME168 on service form for further information

EWAB Engineering LtdStafford Park 16, Telford, Shropshire TF33BB, Tel: 0952 290328EWAB Engineering design, build andinstall automated programmable flexibleflow conveyor systems for the transport-ation of parts for automatic or semi-automatic assembly or manufacture. Sys-tems can be supplied from simple expand-able buffer loop feed conveyors to fullyautomated conveyors for FAS, FMS, CIMetc.Encircle ME169 on service form for further information

©DEXIOHDexion Ltd HANDLING SYSTEMSAutomated Systems and Conveyor Divisions,Gainsborough, Lincolnshire DN21 iQE,Tel: 0427-810810, BT Gold Mailbox84,DXIoo3

A turnkey supplier of automated assembly,kitting and materials handling systems.Dexion can provide stand alone or systemsolutions which include robots, AGV's,vertical and horizontal carousels, stackercranes, man-rider cranes, package con-veyors, pallet conveyors, overhead con-veyors and free flow conveyors.Encircle ME170 on service form for further information

KUIKKA

FSRKARDTForkardtEngland LtdP.O. Box No. 29, Unit 6, Lodge CausewayTrad. Est., Fishponds, Bristol BS16 3JD,Tel: 0272-656356Full range of precision-made standardair-operated actuators, grippers andaccessories for simplified and safe work-place handling in almost any automation orrobotics application. Additionally sup-ported by a dualband palletised assemblyconveyor system.Encircle ME171 on service form for further information

INA AutomationDivision ofINA Bearing Co LtdCastle Vale Industrial Estate,West Midlands, B76 8AL, Tel: 021-3514047, Tlx: 334775,Fax: 021-351 7686The INA Automation Division of INABearing Co specialises in the design andmanufacture of vibratory and centrifugalfeeders, assembly machines, robotic andpick and place devices, index tables and acomplete spectrum of component handlingconveyors and elevators.Encircle ME172 on service form for further information

PJ Hare LtdWrington, Bristol BS18 7NL, Tel: 0934862608P J Hare Tooling Division specialise in theautomatic assembly of components requir-ing pressing, staking, riveting or forming.Turnkey projects, standalone machines andassembly machines for the automotive andaerospace industries incorporating full loadmonitoring, component sensing and fulldiagnostics and flexibility through the useof microprocessor controls.Encircle ME 173 on service form for further information

Martec EngineeringBouverie Mews, Bouverie Road, LondonN16 oAE, Tel: 01-809-4841Special purpose and automatic assemblymachinery designers and builders withextensive knowledge and experience over abroad spectrum of industry. Capable ofhandling all degrees of automation what-ever your needs justify. From initial feasibi-lity studies to on-stream manufacture.Modular or 'stand-alone' systems.Encircle ME174 on service form for further information

George KuikkaLimitedHill Farm Avenue, Leavesden, Watford,WD2 7BL, Tel: 0923 670611Kuikka design, manufacture and installflexible conveyor systems for automatedassembly and manufacture. Completeflowline and turnkey systems can behandled including pallet conveyors, robotsand ancillary equipment. Kuikka are alsoagents for Carryline and Lanco conveyorsystems, MHU and Pilo robots.Encircle ME175 on service form for further information

Southern Production SystemsUnit II, Fitzherbert Spur, Farlington,Portsmouth, Hants. PO6 iTT, Tel: 0705379424,Fax: 0705 377119Supply modules and complete turnkeyprojects based on the Bosch FMS concept.This system allows the build-up of com-plete assembly systems from manual orautomatic work stations and handling sys-tems to palletised transfer conveyors, usinga comprehensive range of extrusions andfixings as based construction.Encircle ME176 on service form for further information

VSI Automation Co Ltd7 Factory Road, Upton Industrial Estate,Upton, Pool, Dorset BH16 5SL, Tel: 0202624727, Telex: 418270, Fax: 0202 624727,Telex: 418270, Fax: 0202 624569Established over 20 years, specialises indesign and manufacture of both standardand special purpose automatic assemblyand parts feeding equipment, in additionoffering robots (pick and place units) within-line or radial movement. Modular build-up provides light machining, riveting,press-work, welding, application ofadhesives and marking as well as inspectionand assembly operations. Rotary indexingtables and linear conveyors using jig carry-ing pallets are available, allowing bothdedicated and flexible assembly equipmentto be produced.

Sister Company Automated ProductionLimited designs and manufactures automa-tic feed screwdrivers, ranging from hand-held units to complete multi-head systems.Also agents for 'Nejicco Automatic ScrewSupplier'.

No automation project is too.large orsmall and VSI Automation has unrivalledexperience in the field of hitherto labourintensive operations.Encircle ME 177 on service form for further information

Assembly Engineering News - BuyersGuideHaving successfully completed its first yearof publication in Manufacturing Engineerthis section appearing in the March, June,September and December issues hasbecome an established forum for relatedproducts and services. Your response tothese notices will help these enthusiasticsupporters. Entries are included at £8 persingle column centimetre with a 10%discount for bookings of four insertions.Encircle ME178 on service form for further information

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Encircle M E16 on service form for further information