Five steps to achieve zero fault fastening · tightening cycles have been processed correctly....

Error proofed production Five steps to achieve zero fault fastening

Error proofed production

The later an assembly defect is identified, the more it costs tocorrect. And the end result could be even higher costs and thetime-consuming problem of recalls. This has made errorproofing a critical factor in relation to all complex jointfastening.

Atlas Copco has defined five tightening process control stepstowards zero fault fastening. Which of these steps is suffici-ent in any given situation is a matter of individual decision.

With this five-stage classification we have tried to provide anaid for orientation. Of course, there are variations for everystep. But making the move from one step to the next isdistinctive in each case. The steps are thus designed to helpyou make decisions on what error proofing level is appropri-ate for you, and what safety requirements you have to meet.

Error proofed productionFive steps to achieve zero fault fastening

Contents

Chapter...........................................................................................................Page

1. Five steps to zero-fault fastening................................................................ 41.1 Functionality ......................................................................................... 14

2. Tool management and process auditing .................................................. 16

3. The new way of tightening........................................................................ 203.1 Zero fault production/error proofing..................................................... 213.2 Continuous process improvement......................................................... 233.3 Documentation for traceability...............................................................233.4 Efficient maintenance and monitoring ...................................................24

4. Machine capability of tightening tools:how accurate is exact torque .................................................................... 26

5. The three tightening tool condition classes inaccordance with VDI guideline 2862 ....................................................... 30

6. Error proofing cases .................................................................................. 316.1 Preventative maintenance system at Onan Cummins

Power Generation (Tool management) .............................................. 32

6.2 Ford Camaçari: Fast and accurate tool calibration

(Process auditing)............................................................................... 33

6.3 Valve fitting at Hoerbiger (step 2) ..................................................... 34

6.4 Cutting costs and improving quality at

Johnson Controls (step 3) .................................................................. 36

6.5 Wheel fitting for the Dutch Air Force (step 3) .................................. 37

6.6 Tightening tool approves seal tightness at

the same time (step 3) ........................................................................ 39

6.7 The new way of tightening – beer barrels (step 4) ............................ 40

6.8 Ford uses the new way of tightening on its engine lines (step 5) ..... 43

6.9 KISSQ: Zero defect assembly in the BMW Group (step 5).............. 46

E R R O R P R O O F E D P R O D U C T I O N 3

100% 10%1000%

1. Five steps to zero-fault production

Today, there is scarcely any discussion on technical issuesrelating to tightening that does not also include process quali-ty. However, everyone understands process control and pro-cess quality slightly differently. This is why this division intosteps helps provide some long overdue clarity.

When Henry Ford realized assembly line production, processquality was not taken into consideration. At that time increas-ing productivity was the main concern, thereby reducingproduction costs. Today, however, we want to enhancequality besides increasing productivity.

It is no accident that the automotive industry (see chapter 5:VDI 2862) has only three bolt classes: for safety-critical,function-critical and customer-critical joints. Each of these iscritical and therefore, some car manufacturers still differenti-ate between tightened joints that are documented (due to pro-duct liability, among other things) and other joints that arenot.

Process quality also reduces costs. Generally, it is true thatany defect becomes ten times more expensive to rectify forevery stage of production that passes before it is discovered.Not to mention the badwill that occurs if an assembly fault is discovered only once the product has made it out to thecustomer.

4 E R R O R P R O O F E D P R O D U C T I O N


Step 1. To assure a correct tightening torqueThe first step to zero fault production is obtained by usingan assembly tool that delivers a precise and predeterminedtorque. However, only the tightening torque is controlledat this first step, operators and work pieces are not yetinvolved in the monitoring process.

Good examples of tools to be used when taking the firststep are screwdrivers and nutrunners with clutches thatshut off the tool when a pre-set torque is reached.Another example is the shut-off type of hydraulic impulsetools.

At step 1, process quality isstill dependent on people andis based only on the "built-in"torque accuracy of the tighten-ing tool.


Step 2. To assure that all screws are tightenedOne of the most common causes of a faulty assembly is thefact that the operator simply forgets to tighten a screw ormakes a tightening, a so-called re-hit, on an already tightenedscrew. The remedy against this possible error is to use whatis known as an RE-controller. It monitors the tighteningcycle and identifies a proper shut-off of a tool. RE-control-lers are mainly used for pneumatic tools where a combina-tion of the air pressure at the tool and time are monitored.This can be done due to the fact that a pressure pulse occurs

Assembly station

Assembly Repair

Signal lightand alarm

Entrysignal

Clock Alert signal

OK signal

RE-Controller

RE-tool

At step 2 the operator is also"supervised" by the RE control-ler. No bolts are "forgotten"because the entire tighteningcycle is monitored. However, atthis stage, the only thing that iscertain is that the tighteningtool has switched off properly.What happened in the tight-ened joint itself is still notknown at this step.


in the tool at the moment of shut-off when the tool comes toa stop. But monitoring time is also necessary. A re-hit, forexample, would also cause a pressure pulse but this pulsethen comes immediately after the operator has pressed thetrigger. During a proper tightening a certain time elapsesbetween trigger pressing and shut-off.

The RE-controller is also used for counting the number ofcorrectly tightened screws. The RE-controller even providesa warning if the air pressure in the supply network fallsbelow the level at which the tightening accuracy is guaran-teed.

Step 3. To assure that the joint is correctWith steps 1 and 2 on the path to zero fault assembly the tooland the operator have been taken into consideration.However, the joint itself can also be a cause of the incorrecttightening. There can be several reasons for this. Missingparts like seals or washers will change the characteristics ofthe joint. The bolt quality can be wrong. A too low qualitybolt may lead to deformation of the screw into its plasticrange. This will also change the characteristics of the joint.Damaged threads or debris in the joint also leads to animproperly tightened joint. A tool would reach its shut-offtorque level long before the joint is properly tightened.

The way to detect these types of faulty joints is to monitorthe tightening angle during the tightening process. This is thethird step to zero fault assembly. Missing washers, faultythreads, debris in the joint, too short or wrong quality boltsmean that the tightening angle will be outside its tolerancerange.

At step 3, the tightening tool isno longer just an assemblytool, it is also a testing instru-ment. If the thread or hole isdefective, it activates a signaland tells the operator if awasher or seal is missing. Atthis step, the OK or NOT OKsignal is used to indicatewhether the tightened joint isin the green range.

It is necessary to use assembly tools with angle sensing func-tions to reach step three. The tool does not have to have aproper torque transducer built in. A good example is theTensor DS/DL tool. Its controller calculates the torque withan algorithm. This means that the tool cannot be used forsafety critical joints where reporting of a traceably calibratedtorque value is required. But the tool has an angle sensingfunction. Its controller can be programmed to give a toler-ance width within which the tightening angle has to lie inorder to obtain an OK signal. Faulty joints would lead to aNOT OK signal.

The Tensor DS/DL controller also has a screw countingfunction taking care of the requirements of step twodescribed earlier.


Angle

Speed

Torque

Final

Clampingangleacceptancewindow

Angle step 1acceptance window

Angle monitoring: The tighten-ing angle is supervised in thefirst and the second stage ofthe tightening to detect incor-rect joints.


Step 4. To assure that safety critical joints are tightened properlyA safety critical tightening is a tightening that, if it was notcorrectly performed, can result in a risk for the user of theend product. In the case of tightenings on a vehicle the drive-r’s and passenger’s personal safety being at risk. In order tolimit or avoid recalls it is essential for manufacturers toprove that critical fasteners are tightened correctly.

This proof requires advanced controlled industrial tools suchas the Tensor S/ST and QMX-series and tightening controlsystems such as the Power Focus 3000/3100 andPowerMACS. In combination these systems provide:

1. Torque control using a transducer that is traceablycalibrated.

2. The ability to store the torque results in the controller unit itself on a local level.

3. The ability to send the torque results to higher level systems, such as ToolsNet, for long term storage.

4. Continuous monitoring of the whole tightening process by using not only torque transducers and angle encodersbut also other parameters such as current limits.

5. The possibility to use Statistical Process Control to detect and correct deviations to the result even before a tightening outside of the limits is produced.

At step 4, all tightening data isalso documented and/or for-warded for the final documen-tation and can be called up atthe workstation at any time inorder to run error analyses, etc.

Fastening seatbelts is a typicalsafety critical application.


If there are indications that a recall is related to the fasteningprocess, it is easy to search the database, view the tighteningdata/trace and pinpoint vehicles with the suspected problem.

It is vital that the spindles are calibrated before delivery andthey must be recalibrated at regular intervals. The calibrationresults have to be stored for traceability. This is a service thatcan be provided by the Atlas Copco service organisation.

Power Focus 3000/3100 and PowerMACS controllers aredesigned to communicate via Ethernet, serial or Fieldbustechnology. If Ethernet is used it is possible to set up a cellfor a intra-controller communication with up to 20 control-lers in a very cost efficient and user-friendly way.

An assembly cell consists of one or several components withseveral joints that can be tightened by one tool using the pro-gramming alternatives in the controllers. To help the operatortighten the bolts in the correct order and to not forget anybolts the Power Focus units can be programmed so that anall-OK signal is sent when all joints in the cell have beenproperly tightened.

The Power Focus controllerscan link up to 20 mutuallysynchronized tightening toolsto one another in one assem-bly cell. One controller thenacts as a master and issues asignal to the line when alltightening cycles have beenprocessed correctly.

Sixteen con-rod bolts in an 8-cylinder Ford engine are tightened in foursteps in this station by this fully automatic multiple with the torque/anglecontrolled target values as 40 Nm and 90°.Assembly tools of the PowerMACS generation stand out due to theirspace-saving stand-alone control modules. These controllers have theirown assigned Ethernet IP addresses, which enables full synchronizationand real-time communication options for guaranteeing the process.

Zero-fault production does notmean that no mistakes aremade during assembly.However, it does mean that nofaults are allowed to leave theplant. And in the long run thisis achievable only at step 5 .


At step 5, the tightening tool isnot only an assembly devicebut also an information medi-um and integral component ofthe business system: it carriesout tests and informs the cen-tral management system as towhether the correct componentis being fitted. Furthermore itguides the operator where thebolt has to be tightened, auto-matically selects pre-program-med tightening parameters anddetermines which socket is tobe used, etc.

Step 5. To assure zero fault fasteningHaving reached step four in the advance to zero fault produc-tion still leaves room for mistakes. With step five two furtherelements are introduced for a fault-free production. One ele-ment is the introduction of part identification, the other isreject management. With step 5 the tool controllers are notonly networked – they are also connected to the factory net-work. Information about components is sent over the factorynetwork. By identifying the components that are to beassembled, relevant information is transferred to the toolcontroller via the network. This safeguards both that thecorrect component is being assembled and that correspondingtightening parameters are chosen.


Volkswagen's glass plant inDresden, Germany, is laid outfor 800 staff and 150 vehiclesa day. Almost half of the 55000 m2 production area overthree levels is floored usingwood from Canadian syca-more and smoked oak.Beneath this flooring are theelectric cables, which inducti-vely power all electric tighte-ning tools (exclusively BTVbattery-operated tools andTensor tools from AtlasCopco Tools and AssemblySystems).

Phaeton production is almostpurely manual work: automa-tion stands at 5%. There areonly three robots at the plant:for fitting the spare wheel,tightening of the wheels(with the aid of the automaticPowerMACS system) and forinserting and bonding in thefront and rear windscreens.

The glass plant in Dresden was the birthplace of the new way oftightening, with the first standard network solution for bolt assembly inaccordance with step 5.The tool carriers with battery-tools and Tensor S tools are poweredinductively via cables under the wooden flooring.


Despite all the functionality described above, cross threads,operator mistakes etc. can still occur. When a NOT OK sig-nal is sent it is not always the case that the tightening errorcan be corrected at the actual assembly station.This can be remedied by so called reject management. Viathe factory network information about the faulty joint is sentto the re-work part of the assembly line. When the compo-nent (motor, gearbox, whole car etc.) approaches the re-workstation of the assembly line it is automatically diverted to it.There the faulty joint is identified, corresponding tighteningparameters are set and the results are stored so that a releasedocument that shows that all bolts have been fastened accor-ding to specification and the correct components have beenused, can be made.

Factory OverviewToolsTalkWinTCInternetExplorer

ToolsNetServer DBStep 6

TCP/IPEthernet

Step 4aTightening data

Step 3TighteningSystem

Step 1Identification

Master

Slave

Step 3Tighteningsystem

Step 4bOK/NOK

ProductionControlSystem andQualitySystem

Step 5OK/NOK

PLCLine Control

NOKRe-work


1.1 Functionality

Torque control Torque setting via Torque setting viashut-off mechanism shut-off mechanism

Torque monitoring/controlTransducer redundancyAngle monitoring/controlJoint monitoring Monitoring of shut-off over timeTightening steps 1 1Yield point controlProcess time monitoring �Multiple parameter setsBatch count �Station monitoringTool alarmsTightening data collectionReject managementOperator feedback �Operator guidenceStatistical alarmsStatistical reportsRedundant tightening data collectionService indicator f (time, cycle)Service indicator f (usage)Network capability/InternetA: Safety-critical *) B: Function-critical *) C: Customer-critical *) � �Investment level 100 % 200%

Air-powered mechanicalscrewdriver or impulsetype screwdriver withautomatic shut-off

As for step 1, but withpressure-controlled andtime-controlled shut-off

Step 1 Step 2

* Joint classes in accordance with VDI guideline 2862 for the automotive industry.


”DigiTork”, algorithm Direct torque Direct torqueconsisting of motor measurement via measurement viacurrent, frequency, voltage transducer transducerand temperature� � �

Current monitoring Multiple transducers� �

In 36° steps � �2 8 Unlimited

�� 10 up to 250 Unlimited� � �

� ��

� �In station In station

� � �� Tensor ST� ��

� � �� 250–400% 600–1000% 600–1000 % per channel

Tensor DS/DL electricscrewdriver

Tensor S/ST elec-tric screwdriverwith Power Focus3000/31000

This highesterror proofingstep uses thetechnology ofstep 4. It inte-grates the tighteningprocess into thenetwork forproductionmanagementsystem andqualityassurancesystem.

Zero fault fasten-ing, network con-nected

Step 3 Step 4 Step 5

QMX spindles withmulti-channelPowerMACStightening system

Step 4

2. Tool management andprocess auditing

How often tools need to be torque audited is depending on alot of factors, for example the frequency of use and the typeof joint. Some companies does torque audits once a year,others do it hourly. The frequency is reliant on the companypolicy and the application. What is important is that the com-pany has a routine to check their tools so they have controlover their tightening process.

Without process auditing and tool management, let alone acorrectly set and/or calibrated tool, no process protection canbe achieved. This emerges at ISO audits and must be fulfilledby any company which holds ISO 9000 accreditation.

The demands can be found in quality standard ISO 9000,paragraph 4.11.2. This contains the following:

• There must be a QA system that reliably ensures that alltightening tools keep to the prescribed torques.

• There must be a calibration system for the tightening toolsand transducers in order to monitor the torque.

• There must be a system, which ensures that the tighteningprocesses remain within monitored limits.

• There must be a process auditing and tool managementsystem, which monitors the status of the tightening tool.

To meet the ISO 9000 requirements, each assembly operationhas to be equipped with the following:

• Torque transducers (in order to measure the torque at thetightening tool).

• Torque measuring instruments with the option of statisticalevaluation (in order to analyze the information acquiredusing the transducers).

• Test joints (to permit the simulation of tightened joints).• A process auditing and tool management system (to permit

the significant details of tools in operation to be followed).

However, as a rule process auditing and tool managementtakes place manually, even today in the IT age, with test cert-ificates completed by hand. Given that assembly systems aretoday networked, with details for each tightening tool – such

The Notebook-sized ACTA 3000forms the backbone of the QAmanagement system forassembly tools.



as machine capability (see chapter 4) this process should nolonger involve the use of pencils and notepads.

Moreover, manually entering the measurement and tool datagathered into databases is not only time-consuming, butabove all it is prone to errors. Furthermore, this kind of QAmanagement of all tightening tools in an assembly operationaccredited to an ISO standard is barely affordable. Computersolutions for process auditing, tool management and for guar-anteeing calibration intervals are therefore necessary.

ACTA torque testing formeasuring the applied torque.

Inline measurement transducerwith the ACTA 3000 for dynamictorque checking without inter-rupting work.

A database offering measurement and analysisfunctionsThe ACTA 3000 system is a QA package for paperless pro-cess auditing and tool management, which meets all thedemands of ISO 9000. It consists of a type of notebook devi-ce, a database and measuring instrument all in one, variousmeasurement sensors and test joints for measuring, recordingand analyzing the tightening process, and Atlas Copco PCsoftware for process auditing and tool management.However, the ACTA system does not have to be used forassembly tool calibration management; it can just as well beused to manage your quality assurance.

This solution offers PC-supported process auditing and toolmanagement which is compatible with other QA systemsand, even more besides: the ACTA 3000 is more or less adatabase that can also be used for measurement and analysis.In this way, the target parameters of a joint can be deter-mined, for example, and tool controller can be programmedusing it.

ToolsTalk ACTA, a PC software (for Windows operating sys-tems) takes care of the documentation and evaluation of thedata supplied by the ACTA. It is layout-compatible withother QA systems, supplies trend analyses and statistics andpermits Statistical Process Control (SPC).

The ToolsTalk ACTA database contains all data on the tight-ening tool and its supplier. It knows the life of the tool (pur-chase price, all maintenance, repairs, costs incurred, etc.)from commissioning to decommissioning. Of course, thedatabase also includes information on the location of the tool,the place where it is used and the tool conditions.

Torque limits can also be monitored using the ACTA. Aboveall, however, the database contains all measurement data everrecorded for each tool and supplies the documentation. Itensures that schedules are observed for preventive mainte-nance and calibration and automatically reminds the userwhen the next calibration is due. At the same time the ACTA3000 is also a measuring instrument and controls the mostdiverse functions. Thus it automatically recognizes the mea-surement transducer used in each case and sets itself automa-tically to that transducer (calibration filter data, etc.).

The ACTA3000 automaticallycommunicates with thecontroller for fast and securecalibration of the tool.



ACTA in-line transducer forsubsequent checking of thetorque.

In particular, it makes the measurement process very simpleand convenient. Even tightening curves can be recorded fortightening condition analysis.

The ACTA system can be used not only to test and set toolsbefore they are implemented in production, but it can also beused to dynamically monitor the tightening process duringassembly. Special torque limits are also used to check thatjoints are seated correctly.

Standard, plug-and-play net-work solutions and the newgeneration of tightening sys-tems make it possible to con-trol the tightening processremotely. Users monitor theprocess in real time on a laptopor PC via the Internet and carryout fault diagnosis or re-pro-gram tools as if they were actu-ally standing on the line.

3. The new way of tightening

Information is the key to making the right decisions at theright time. Simple access to reliable information is thereforeextremely important, especially in production facilities thatare expected to deliver large volumes of high qualityproducts at a high pace. The New Way of Tightening meansutilization of modern network technology to collect anddistribute tightening information in a structured way, withminimized manual work.

In factories aiming at zero fault production many differentproducts with corresponding software are used. If the tight-ening controllers are networked and integrated with theoverall production control system they can be coordinatedwith other products and processes to optimize the productionflow. The collected information can be refined and filteredby software applications to suit different purposes and users.Significant improvements can be achieved by visualizing theprocess and making information accessible to all personsinvolved.



Since there are big differences in how products are produced,all processes do not need to be on the same complexity level.However, as in the BMW-KISSQ case (Chapter 6.9) andmost other cases of high volume production, the features thatare described in this chapter can be beneficial.

Atlas Copco has defined the four success factors that shouldbe focused on to integrate quality in the fastening processand benefit from the possibilities that the new way oftightening offers:

3.1 Zero fault production/error proofingThe best way to satisfy customers is to deliver fault freeproducts. The customers expect products that work, in somecases it might even be dangerous if the product’s quality isnot secured. What is described as step 1, 2 and 3 in Chapter1, accurate tools, connected to systems that control that thecorrect number of tightenings are made on correct compo-nents, are the foundation for long term zero fault production.By using new technology it is now possible to implement thefeatures in step 4 and 5 at a reasonable cost.

Most fastening processes are more or less flexible, that is,several different operations are carried out in one station.The operators may need guidance to make sure that the rightoperations are executed in the correct order on the correctproduct. By using systems, such as Power Focus 3000/3100and PowerMACS, that provide guidance and automaticallychoose the correct settings, based on product identificationnumber, the number of faults can be minimized.


When something goes wrong in the fastening process it isimportant that it is rectified before that product leaves theplant. The sooner the fault is fixed the lower the cost. Thismeans that, if possible, the fault should be fixed in the sta-tion. If it is not possible to fix a problem in station the tight-ening system needs to communicate with the overall system.The overall system makes sure that the fault is fixed by send-ing the product to a re-work station that automatically getsthe right settings based on the product’s identification num-ber. When the fault is fixed the results are stored, linked tothe faulty results, so a release report can be made to showthat the product is 100% OK.

The figure above describes briefly the basic steps in a zerofault production process.

ProductionControlSystem

Build Data

ID

ResultsMonitoringNavigationProcess ImprovementMaintenance

Not OK

1. A product enters a station.The ID-number is read andsent to the production controlsystem. The controllers’ builddata are returned and settingsare automatically set to cor-respond with the product.

2. Tightenings are performedand the results are sent to thetightening database for docu-mentation and further distri-bution to PCs on the networkand the overall productioncontrol system.

3. The product moves forwardon the line. NOT OK results,which have not been correctedin station, are handled inrework stations. Correctedrework results are stored inthe tightening database.

4. A product leaves the line.A release report shows thatzero faults have been achievedand documented for traceabi-lity.

1.

3.

2.

4.

TighteningDatabase

OK

Build Data

ID

Results

OK2.


3.2 Continuous process improvementNo process is too good to be impro-ved. Structured work with continu-ous improvement is a must for allsuccessful industrial companies.

Statistical analysis of tighteningdata tells a lot about a process.By studying data from all tighten-ing controllers it is possible to seewhere the improvement resourcesshould be focused to be of most usefor the process productivity. Thequality of components and fine-tuning of new tightening strategiescan also be determined by usingstatistical reports and traces.

Visualization of the whole process at one central place helpsto avoid suboptimization. Access to all information from anyPC connected to the network makes it possible for all kind ofpersonnel to use the information that concerns their area ofresponsibility. By adding portal functionality that makes itpossible to access configuration and monitoring applicationsthe user-friendliness is increased even more.

3.3 Documentation for traceabilityFor safety critical applications traceability is a must andmore and more companies see the benefits of using it forquality critical applications too. Traceability makes itpossible to retrieve old data and show that a tightening wascorrectly made or find a few bad tightenings to make itpossible to avoid recalls of a larger number of products thannecessary. By using tools with transducers and angleencoders values for each tightening can be stored for futurereference. If tools for quality critical tightenings, withouttransducers, are connected to the database, OK or NOT OKresults can be stored.

Factory Overview is a programfor visualization, navigationand real time monitoring of alltightening processes on one ormore assembly lines.


To get complete traceability the product’s/component’s iden-tification number and the tool’s serial number should bestored together with the results. The tools must be calibratedregularly and the calibrations should be documented to makeit possible to verify that the tools that have been used gavethe correct values for each tightening. Another important fac-tor to achieved traceability is to make sure that no data islost. This can be done by using systems that store the resultslocally and have individual numbers on each result. If thenetwork connection goes down it is then possible for thecollection application such as ToolsNet 3000, to come backwhen the connection is back to collect the missing resultsinto the database.

3.4 Efficient maintenance and monitoring Correct maintenance at the correct time reduces the total lifecycle cost and improves the equipment’s precision. Maintenance can be planned based on time or the number oftightenings a tool has made. Software applications can helpmaintenance personal structure their work and give signalswhen it is time to service a tool. These signals can be sentvia network direct from the tightening controller or from themaintenance software. Atlas Copco’s newest electrical toolshave an intelligent service indicator that calculates the wearbased on several different parameters and gives a signalwhen it is time for service.

Signals about service and other types of events can be moni-tored in a centralized or decentralized way in real-time. AtlasCopco software Event Monitor provides this functionality.Filters can be used so that the right persons get the informa-tion of interest to them visually presented on their PC screen.By having access to all controllers and all related softwarefunctionality it is possible to react quickly to potentialproblems and work in a structured way with maintenance.

The new way of tightening:already implemented in thesevehicles.


Some exampels of vehicles that are assembled according to ”The new way of tightening”.


When calculating Cp, the toleranceinterval is related to the 6σ.

4. Capability

This chapter contains short information of statistics and howthis is used when checking tools and the production.

The accuracy of a tool tells us something about the perfor-mance, but this is not enough. The important aspect is howthe tool performs in an application, on the production line.So, somehow we have to relate the accuracy of the tool to theapplication. Every joint has a target value, but also sometolerance that is acceptable. By relating the mean and thestandard deviation to the target value and the tolerance limitsof an application we can tell how a tool is performing whereit really matters, in its application. This is possible thanks todifferent Capability Indices.

Cp The first, and most commonly used capability index, is calledCp. The formula for the Cp is:

Cp = Tolerance interval = HI – LO6σ 6σ

If you look at the formula, you can see that it simply relatesthe tolerance interval (HI-LO), to the process natural varia-tion! If we have a tool with a big spread, and an applicationwith very high demands (narrow tolerance limits), we get alow Cp value. Conversely, if we have a tool with very smallspread (small σ), but very wide tolerance limits, we get ahigh Cp. Of course this is what we want, because the smallerthe variation in relation to the tolerance limits, the lower therisk of tightenings outside the tolerances. The Cp require-ments vary. The most common is that Cp has to be greaterthan 1.33. This indicates that 6 times the standard deviationcovers no more than 75% of the tolerance interval.


When calculating Cpk also thetarget value is considered.

But is this enough for us to tell if the tool is good or bad for aspecific application? Do we need something more? Yes. TheCp does not consider whether the mean of the distribution isclose to the target value or not. This index does not guaranteethat the distribution lies in the middle of the tolerance inter-val. In the picture below you can see the same tool on thesame application, but before and after torque adjustment. Inboth cases we would have the same Cp. If we are off target,it is possible that the tightenings are outside one of the tole-rance limits, even if the scatter is small in relation to the tole-rance interval (high Cp). So we need something more thatalso relates the distribution to the target value.

CpkThe Cpk also relates the mean of the distribution to the targetvalue of the application. The way to do this is to divide thedistribution and the application into two different parts andmake one calculation for each side. The formula looks likethis:

Cpk = min [(HI – AVE) / 3σ , (AVE – LO) / 3σ]

First we relate the difference between the upper tolerancelimit and the average to half the natural variation (3σ). Thenwe make another calculation, relating the difference betweenthe average and the lower tolerance limit to 3σ. We now havetwo potentially different values, and the LOWER of the twois the Cpk. If you think this is difficult, just take a few minu-tes to think about this. If the average is higher than the targetvalue, then the difference between the upper tolerance limitand the average is smaller than the difference between theaverage and the lower tolerance limit. If this is the case, the

High Cp does not guarantee that we are close to the target value.


Process not capableChange tool oradjust for goodaccuracy.

Process capablebut average needsto be adjusted.

Not possible. Process capableand well adjusted.

Bad Cp Good

Bad

Cpk

Good

“upper calculation” will give us the Cpk, because we arecloser to the upper tolerance limit.

What happens to the Cpk if we are right on target? Well, inthis case we are as close to the upper tolerance limit as to thelower, and both calculations will give us the same result.

In this case, we can also see that the Cpk has the same valueas the Cp.

Now we have introduced the Cp and the Cpk. By stu-dying the formulas it is easy to see that Cp only rela-tes the tolerance interval to the process 6σ. Cpk alsoconsiders the target value. We want both Cp and Cpkto be higher than 1.33. If our average is right on tar-get, the Cp and Cpk are the same. The more off target

we are, the bigger the difference between Cp and Cpk.Obviously Cpk can never be higher than Cp.

When is a process capable?The question of “how good is capable?” has still not beendefinitively answered. Since Cp was first used, a Cp value of1.33 has become the most commonly acceptable criterion asa lower boundary. The Cpk requirements vary. The mostcommon is that Cpk has to be greater than 1.33. A processthat has a Cpk lower than 1.00 is never capable.

It is very important that you understand why we use both theCp and the Cpk. If we only use the Cp, we do not knowwhether we are on target or not. If we only use the Cpk, wecannot know whether a good or bad Cpk value is because ofthe centering of the process or because of the spread. So wehave to use both. Together they can give us a very good indi-cation of how well a specific tool is performing in a specificapplication. They are also the perfect way to compare diffe-rent tools.

Look at the following dartboards:

Dartboard 1:High Cp and low Cpk.Dartboard 2:Low Cp and low Cpk.Dartboard 3:High Cp and high Cpk

The relation between Cpand Cpk.


The first dartboard shows a poorly centered process, but witha low spread (high accuracy). In this case the Cp is high andthe Cpk low. On the second dartboard, the darts are spreadrandomly around the bull’s eye, but the spread is quite largerelated to the tolerances. Cp is probably not so good, but ifthe “mean value” is on target, the Cpk has the same value asthe Cp. The third dartboard shows a well centered process,with high accuracy. This means that both the Cp and Cpk arehigh; the process is capable.

An example: A joint should be tightened at 70 Nm ± 10 %. A tool is testedand we get an average of 71 Nm and a σ of 1.2 Nm.

Cp = (77-63) / 6*1.2 = 1.95Cpk = min [ (77-71) / (3*1.2) , (71-63) / (3*1.2) ] =

min [ 1.67, 2.22 ] = 1.67

Both the Cp and Cpk values are greater than 1.33 and theprocess is capable and does not need to be adjusted.

Machine capability indicesAs you now know, Cp and Cpk are process capability indi-ces. Everything that affects the process affects these indices.But if we take away all variation affecting the assembly pro-cess, except the variation in the tool itself, we get what arecalled Machine Capability indices. These must be measuredunder very controlled circumstances, preferably in a toolcrib. The tests should be carried out on the same joint and bythe same operator (or even better, by placing the tool in afixture in order to get rid of all the operator influence). Thecalculations are the same for Cm as for Cp, and the same forCmk as for Cpk.

So remember, Cp and Cpk determine whether the process iscapable. The Cm and Cmk determine whether the machine(tool) is capable.

What else is there to think about?When you analyze the capability of a tool, the sample size isof great importance in order to obtain reliable mean and stan-dard deviation calculations. A sample size of at least 25 tight-enings is strongly recommended.


5. The three tightening toolcondition classes in accordancewith VDI guideline 2862

There are many different joint standards defined by compani-es and organizations. Most of these standards are very similarto each other. One example of standard is the VDI guideline2862, “Use of tightening systems in the automotive industry”.It is a German standard that has been valid since 1 July 1999.This was compiled by the “Technical rules for the use of tigh-tening systems in the automotive industry” study group fromthe VDI “Production Technology” section.This guideline divides tightened joints for vehicle manufactureinto three risk classes:

Risk class A(“Direct or indirect danger to life and limb”) takes effect“when the failure of this bolt position is highly likely to leadto safety failure and/or to the destruction of the entire vehicleand thus direct or indirect danger to life and limb is indica-ted.” These kind of joints are also called “Safety criticaljoints”.

Risk class B(“Dropout”) is indicated “when the failure of the bolt positionwill lead to malfunction of the vehicle.”

Risk class C(“Annoyance for the customer”) then applies “when the failureof the bolt position would provoke annoyance among custo-mers.”

The minimum demands for each risk class can be achieved byfulfilling the solutions in the 5 steps to zero-fault production(Chapter 1) according to the table below.

Risk class Solutions as described in chapter 1

A Step 4 or higher

B Step 3 or higher

C Step 2 or higher


6. Error proofing cases

6.1 Onan Cummins PowerGeneration, USA.

6.2 Ford Camaçari, Brazil.

6.6 Daimler-Chrysler, Germany.6.5 Dutch Air Force, Netherlands.

6.7 InterBrew, Belgium.

6.3 Hoerbiger, Austria.

6.9 BMW Group, Germany.

6.4 Johnson Controls, USA.

6.8 Krause Maschinenfabrik,Germany.


6.1 Preventative maintenance system atOnan Cummins Power GenerationOnan Cummins Power Generation in Minneapolis USAmanufactures gas and diesel power generation equipment.In an effort to have control over their tools and tightening,Onan decided to set up a preventive maintenance systemconsisting of an ACTA 3000, ToolsTalk ACTA software andin-line transducers. Bruce LaMirande, responsible for Torqueand Fastening control, reports on the impact of their newQAT system from Atlas Copco.

“We have been using this system for two years. One majoradvantage is that we can now predict how long a tool willrun before further maintenance is required. Secondly, nowwe can check how the tools are being used and tell exactlywhen they are due for maintenance. Previously we threwaway tools when they broke down, which was very costlyand time consuming. Now we are using tools longer and realizing tremendous cost savings.

“We now have complete control of our tools and tightening.Previously, we sent tools out for maintenance and recalibra-tion and got them back some 3 - 4 days later. Now we need atmost 45 minutes to bring a tool in, repair it, do maintenanceand calibrate it before it is out running again. This means thatwe have both a more efficient and a faster system.

“Furthermore, by using ToolsTalk ACTA we now have justone software system that keeps calibration, maintenance etc.And the complete ACTA system helps us actively trouble-shoot tool problems before they occur. At every moment wecan tell how the tool is running and performing on theassembly line.”

Static torque check with ACTA3000 and MRTT at OnanCummins Power Generation.


6.2 Fast and accurate tool calibration atFord CamaçariMr. Ricardo Samori is an Industrial Engineer Supervisor atFord Camaçari in Brazil. He is responsible for the implemen-tation of a Quality Assurance Process in line with Ford’sstrict quality procedures. Ricardo says “We were looking fora level of Quality Assurance that would ensure purpose-designed customer satisfaction and a level of quality thatwould exceed our customer’s demands and expectations.”

This Ford facility opted for a total Atlas Copco solutionincluding: Tensor DS, ACTA 3000, IRTT torque transducers,the MRTT Torque Wrench and finally the dedicated softwa-re, ToolsTalk ACTA. One of the main tasks with this newsystem was to calibrate and update the Tensor DS systems in a fast and accurate way by using the ACTA 3000.

The ACTA 3000 connected to the Tensor unit, compares thecalibration torque in the DS with the values received fromthe transducer connected to the ACTA 3000. After the tight-ening is done, the ACTA 3000 calculates the new torquetuning value for the Tensor DS and sends it over to the unit.It also stores the value in the ACTA 3000 tool database. TheTensor DS is now updated and ready to be used again.

“The ACTA 3000 solution has empowered our ProcessAnalyses and created a straight communication channel toimprove our overall quality results. Furthermore, ACTA 3000makes it possible for us to guarantee the process results,especially when it comes to DS applications, by synchroniza-tion between the ACTA 3000 and the Tensor DS.”

The ACTA 3000 is used for toolcalibration directly on theassembly line.


“What we really appreciate is that the ACTA solution includ-ing the dedicated ToolsTalk ACTA software is so easy towork with. We save time, have total control over toolperformance criteria and maintenance and rule out datamanipulation. Thanks to the special features like SearchFilters, Tools List, and also the complete informationgenerated through the graphs, reports etc. we don’t needadditional software to complete the documentation audit.With the tools and the quality audit system from Atlas Copcowe now feel we have both the best tools and the best qualitycontrol system available” concludes Mr. Samori.

6.3 Valve fitting at HoerbigerHow do you get process control of two air tightening toolswithin budget limits when they have to tighten one hard andone soft joint reliably with precision of ±5 % and ±12 %.

Hoerbiger in Wiener Neustadt was faced with precisely thisquestion but did not want to pay 7000 euro including tool fora solution. The budget for the associated workstation hadalready been set for half that amount. In addition, jointsrequiring documentation, for which a controlled electric toolwould have been needed, were not required. Quality assur-ance demanded merely reliable process control and recogni-tion of incorrect tightening. In this case the solution was an“RE-Tightening controller” developed by Atlas Copco Toolsand Assembly Systems: a small electronic device that wasactually only designed to monitor a single tightening toolwas used for the first time at Hoerbiger to control two toolsplus operator.

This was necessary for the assembly of a control valve. Themain mounting bolt and cover had to be fitted. First, a boltwith a synthetic seal is tightened onto the mounting with aLUM screwdriver. The part is turned round and the cover istightened. After this, the operator puts the control valvesassembled in a four-stage cycle into a test station at theassembly point and loads the next four parts for assembly.

If the operator should by mistake go for the wrong tool, theoperator will notice this because the tightening adaptor willnot fit the mounting bolt that has to be assembled first.Confusion between tools is thus ruled out. In addition,

ProcessqualityStep 2

The RE-Tightening controllerobserves the number oftightenings.


between assembly cycles, that is when changing fromtightening mountings to tightening covers and vice versa, theoperator has to operate a program selector switch to switchthe RE-Tightening controller over to the appropriate tool ortightening program. At the same time, the selector switchalso controls the direction of the air supply so that air is sup-plied to the selected tool and the one used previously is cutoff or not under pressure.

This switch was the real trick in being able to monitor toolswith the tightening controller. A simple relay circuit pro-duced by Hoerbiger itself was used for the purpose. Thisgives the controller the time needed to set the appropriateparameters when changing over.

Otherwise, the RE-Controller operates in its normal mode:for double security, the tightening process is checked withsimultaneous pressure and time measurements and two sepa-rate pressure/time windows (see diagram). In this way aparticular (programmable) pressure value is assigned to theassembly time and to the dwell time at the point of discon-nection.

As a result, operator errors (finger taken off the trigger toosoon) are detected, as are any defects there may be in thecomponent or bolt since the head support is reached too soonor the bolt cannot be tightened fully home. In this way, thecontroller at Hoerbiger also discovers, for example, whetherthe seal under the main mounting bolt has been forgotten.

Above all the mains and flow pressures are checked since theproblem free operation of the disconnection coupling isdependent on these. If the working pressure is insufficient orincorrect tightening (NOT OK) occurs, the controller raisesvisual and audible alarms and cuts off the tool.

Besides the visual and audible OK and NOT OK checks onindividual connections, “Total OK” processing per individualcycle and overall cycle is also possible. Furthermore, usingTotal-OK and potential free signal inputs and outputs, down-stream assembly stages can also be positively controlled.

Since the RE-Controller recognizes when the programmednumber of connections per cycle have not been made (cycle

Torque

Time

Pressure 2

Pressure 1Rundown time Clamping

time

Pressure and time control

With the RE-Controller thistightening process is moni-tored with simultaneous pres-sure and time measurementsand two separate pressure/timewindows. This allows operatorerrors to be detected.


control), the signal raised in NOT OK cases is used to pre-vent the work piece going to the next stage until the cyclehas been completed and is OK. Conversely, the controllerwill not switch over to a new processing cycle if the workpiece is still missing. The controller is incidentally very easyto program and this can be done within minutes with a sepa-rate input device no bigger than a TV remote control.Separating the controller and programming device rule outunauthorized changes to the control parameters. The onlyprecondition for using this “low-cost” process control is adisconnectable tightening tool with an RE (RE = Reporting)signal output. They may equally well be compressed air toolsor DC tools from the Eliza range.

6.4 Cutting costs and improving quality at Johnson ControlsJohnson Controls is a major supplier of integrated seatingand interior systems for the automotive industry. At Lake-wood in Michigan, USA, the company produces headlinersfor large car manufacturers. Prevailing torque, differentscrew lengths, and varying joint types are typical challengesthe production engineers face when planning the assembly ofhandles, visors and other components to the interior roof.“This previously led to problems such as cross threads, mis-sing components and damaged parts,” states manufacturingengineer Phil Green.

Several Tensor DL screwdriver systems were introduced,allowing for integration to the line via PLC. JohnsonControls now has full line control and feedback. Sixconventional tools were replaced with only three Tensor DLsystems per station. These systems are set to tighten 16 Torxscrews at 1.6 Nm with a tolerance of ± 10% of target torque.

Phil Green explains that the new tools have improved qualitycontrol and taken away the need for final inspections. Theinvestment paid off in less than eight weeks by eliminatingassembly problems, cutting preventive maintenance servicecosts by 70%, and reducing downtime. “The ability tochange rundown speed and torque settings with the tool hasgiven me the flexibility we never had before,” he says.“Our experience to date has been excellent with the TensorDL and the performance and lack of downtime has justamazed me.”

The Tensor DL has improvedquality and taken away theneed for final inspection atJohnson Controls.



6.5 Wheel fitting for the Dutch Air force“Touch and go” as pilots have it forms a regular part of thetraining plan of the Royal Netherlands Air force 334Transport Squadron in Eindhoven in the Netherlands. “Ontheir training approaches our transport aircraft hit the run-way up to ten times an hour and then lift-off again immedi-ately” says Jake Verhoef. An officer of the U.S. Air force, he is responsible for maintenance and servicing at theEindhoven Air Base. This involves tire changes above allelse since many takeoffs and landings an hour like this aretorture for landing gear and tires. The team in the “TireWorkshop” (a combination of tire store, workshop and teststand) has its hands full keeping the squadron’s eleven trans-port aircraft “rolling”.

Yet their work used to be even harder. Previously, all wheelbolts were tightened with different impulse tools and thengiven a final tightening with a torque wrench. With torquesbetween 10 and 200 Nm, that was quite a strain on the arms.What is more, it took much longer than today when twotools known as “Tensor DS” are sufficient for the same workand make the final tightening unnecessary.

The base discovered the Tensor DS when the equipment fora new type of tire workshop was being planned. After theyhad almost decided to invest in a tightening system as usedin the car industry for particularly critical joints requiringdocumentation, “Atlas Copco demonstrated a new type oftightening tool that appeared almost tailor made for ourneeds”, recalls Willem Roelofsen, Adjutant of theMaintenance and Engineering Support Office.

It was less expensive but offered the same zero-fault securi-ty and versatility in the programming of different types oftightening job. Admittedly, it was not possible to record theresults of tightening using this solution but that was not cri-tical at all. What was more important was that it was possi-ble to cover the widest possible torque range without defectswith one tightening tool and while no longer having to dothe final tightening. It was also a relief that this was not aspecial solution requiring engineering input but a standardproduct.

To improve the process qualityof fitting tires to the aircraft ofits 334 Transport Squadron,the Dutch Air force now usesonly two tools for all types oftightening jobs. An angle anda pistol grip nutrunner fromthe Tensor DS Series. The tigh-tening control system onlyreleases the wheel when allthe bolts have been correctlytightened in three stages (mili-tary regulation).



Two tools for everythingToday, two tools are sufficient for fitting wheels to the fivetypes of aircraft stationed at Eindhoven – a Tensor ModelDS9 pistol grip driver (for 80 to 200 Nm) and a DS7 angletool (10 to 80 Nm) share the tightening jobs on the nose andmain wheels. As each one can store eight freely program-mable torque parameters, it also replaces 8 conventionaltools. This saves space and money. Using these two tools,the wheels of all transport aircraft are today fitted with atorque accuracy that could not be achieved with the formercompressed air tools. Above all, the DS tools offer high pro-cess-security since they monitor operator and work piecesimultaneously. Thus their control system only releases awheel when all the bolts have been tightened accurately andin the prescribed sequence. If the set torque is not achieved,perhaps because the thread is damaged, an LED on the toolshows red. If everything is OK, the green LED lights up.

Should a wheel bolt inadvertently be tightened twice, thetool control system detects this in exactly the same way as aforgotten bolt.

Consisting of two rim halves and a (tubeless) outer case andinflated to 7.5 bar, the aircraft tires must be tightened evenlyand reliably because they heat up seriously in the continuous“touch and go” maneuvers.

Three-stage tightening As a result, the twelve bolts on the nose wheel of a C-130-Hercules are not merely tightened using a set crossover pat-tern. The maintenance instructions also require that everyindividual joint be tightened in three stages. This evens outlocked-in stresses and avoids distortion of the rims. Thetightening torque required for each stage is set in the elec-tronic tool beforehand in programming mode and retrievedon a case by case basis way via a torque selector switch onthe Tensor DS tool.

Tire fitting on the main gear ofa KDC-10 tanker aircraft: theTensor DS pistol-grip nutrun-ner acknowledges every OKtightening operation with agreen LED signal (top at theend of the tool). If the red LEDlights, the operator mustchange the tool direction toreverse and re-tighten the boltafresh. If the tool then showsred again, the bolt is changed.


Officer Jake Verhoef is delighted:“In comparison with the previous air tools, bolt assembly istoday not only quieter and more vibration free but, in parti-cular, free of oil. Above all this Tensor tool meets all therequirements of the European Joint Aviation Regulations,which are based on the Federal Aviation Authority (FAA)rules. What is more, they came out cheaper than the tight-ening system we had previously budgeted for althoughobviously much more expensive than the time honored sock-et sets. But precision has risen so enormously and fittingtimes have fallen to such an extent that our investment willquickly pay for itself”, reckons Willem Roelofsen.

6.6 Tightening tool approves seal tightness at the same timeNormally, controlled tightening tools only consider whetherthe tightening parameters and tightening cycles have beencorrectly complied with. However, at Daimler-Chrysler’struck factory in Wörth am Rhein, electric tightening toolsalso check whether O-rings and clips have been properlyinstalled in the assembly of union bolts on valve blocks. Ifnot, the tightening tool raises the alarm and simply will notfunction.

This automatic checking of the complete assembly process isimplemented using Tensor-Electric tightening tools from theDS range which simply acquired different software for thecontrol electronics (DigiTork) and special adaptors for theoffset drive known as rotation distributors with pneumaticconnections. These have a sprocket that fits the bolts fromwhich a peg projects. Before every tightening operation, apneumatic interrogation lasting only 600 milliseconds ofwhether the O-ring and clips are present in the union bolttakes place via air-passages (Ø 2 and 3 mm) in the peg.

The indicator is a difference between impact and flow pres-sures of only 0.15 bar. Accordingly the control system firstchecks whether test air is actually getting to the rotation dis-tributor and whether the air passages are clear. The checkwhether the union bolt has all its components takes placeautomatically every time the start button on the handle of thetool is operated. The control system only releases the toolwhen the required pressure differential has been measuredand the test air turned off again.

The whole secret of the TensorDS nutrunner, which is hereused for reaction free tighten-ing down of the covers of thecanisters, is their servo-elec-tronics known as "DigiTork". Itrequires no external sensorsfor torque or angle but never-theless controls them – usingthe current, voltage, frequencyand temperature of the servo-motor as values.



If the bolt connection is OK, the whole cycle starts againfrom the beginning. On the other hand, if the bolt connec-tion is NOT OK, the tightening control system conveys thisto the operator visually. The flow pressure monitoring thenremains switched off. Only when the operator has disman-tled the parts and has confirmed this can a new cycle begin.

However, if there is no impact pressure, the O-Ring and/orclips have not been properly installed, a visual warning sig-nal is given and the tightening tool is not released. The op-erator must then rectify the fault and confirm that this hasbeen done to the control system. Only then can tighteningcontinue.

6.7 The new way of tightening – beer barrelsEven though they don’t look it, tap hole bungs in beer bar-rels are a difficult tightening job. When tightening the tap-ping lines, locked-in stresses arise through the rubber sealsand traditional tightening tools can not carry out a properclosure. This was what the Belgian InterBrew group and itsStella Artois brewery found when they had to convert 1.1million barrels to a standard closure system. Before that,each of Interbrew’s three Belgian sites had its own system.This entailed many empty trips between the sister breweriesin Brussels, Liège and Louvain since each one could onlyrefill its own barrels. After refitting with a standard closure,which Interbrew calls “MicroMatic”, the barrels could circu-late freely.

If O-Rings and clips are notproperly fitted, the tighteningtool raises the alarm and willnot start at all. To do this, theproduction team simply ac-quired the Tensor DS nutrunnerwith its DigiTork Control Unitand special adaptors for theangle nutrunner.

In Belgium, 1.1 million beerbarrels had to be re-equippedwith a standard closure sys-tem. In order to reduce thesevere locked-in stresses thatoccur in the process, operatorcontrolled high-tech tools fromthe Tensor S class were chosen.



Although this tightening operation was not safety critical andthus did not need to be documented, Interbrew chose thesame high-tech Tensor S Class tool as the car industry pre-scribes for safety critical bolts on airbags, steering and safetybelt anchorages. These controlled electric tools even have anown assigned Ethernet TCP/IP address.

Locked-in stresses from tightening arecompensated forBy doing this, hasn’t Interbrew bought itself a Lamborghinijust to do the shopping? Jan Van de Bergh refutes this firmly:“Our self-imposed quality standards demand one hundredpercent security for every barrel”. He is the team leader fromthe energy and fluids department at the Stella Artois breweryin Louvain. “In any case, it was the only way we could get agrip on the extreme locked-in stresses.” The MicroMatic tap-ping lines had to be tightened into the tops of the barrels, or“kegs”, with a torque of at least 70 but no more than 80 Nm.Not exactly a simple tightening job, since the joint behavesextremely soft because of the seal.

Team leader Jan Van de Berghwith the new MicroMatic barrelclosure. To the left of the pic-ture, the Power Focus unit. Thishas its own assigned EthernetTCP/IP address and can be cal-led up from anywhere, forexample to carry out a remoteanalysis of the tightening job,to make a program update orsimply to look at the tighteningresults for the day.


In order to keep within tolerance at all times, the tools areprogrammed for a target torque of 75 Nm. “Even withvariations of ±4 Nm, they always produce fault-free jointsthat way”, Van de Bergh declares. The tapping line is firstpre-tightened, then the tool stops for 50 milliseconds at a de-fined torque. This in order to compensate for locked-in stres-ses in the seals. After that it switches over to the final tight-ening of 75 Nm. If the tool control unit indicates “OK”, allis well.

Since, in this operation, the tightening control unit alsomonitors the angle of rotation, then faulty seals and damageto threads are detected before filling. With the old barrelclosures and without the current electric tools, these faultscould only be detected in a water-bath after filling: if airbubbles came out of the bolt connection, it had to be retight-ened somewhat and immersed again. If the barrel still wasnot gas-tight, the complete keg closure had to be exchanged.

Programming by laptopIt goes without saying that alternatives had been tried beforethe investments. However, the difference in cost comparedwith other compressed air or electrically based systems wasnot very great.

“We were surprised how simple programming and operationare and therefore we went for the solution with the mostfunctionality. From my laptop I can set the tightening para-meters for torque and angle at any time and call up extensivegraphics and tightening statistics”, says Van de Bergh. He isaware that far from all the functionality that the systemoffers is (yet) being utilized: “We run our six Tensor S tight-ening stations independently of one another, but we couldnetwork them at any time, through their assigned TCP/IP-addresses, so they can communicate with each other over anEthernet.”

So, at the moment, the Lamborghini is only being driven inbottom gear, but this could change. For the future, the teamleader envisages fitting every keg with a chip that wouldstore all the barrel data. “When a barrel comes back to thebrewery, we could carry out a goods inwards inspection withthe tightening system. This would bring up the dates of thelast filling and the last pressure test, torques, angles of rota-tion, etc. and direct the kegs accordingly within the brewe-

Jan Van de Bergh uploads cur-rent tightening data on his lap-top, with which he also pro-grammed the tools.


ry”, for example to the maintenance department if the regu-lar seal change has to be carried out or damage to a thread isdetected. “Only then could we get the most out of the com-munications capabilities of these tools”, speculates Van deBergh.

6.8 Ford uses the new way of tightening on itsengine linesFor its 6 and 8 cylinder engines, Ford has decided on the“new way of tightening” (chapter 3). This means tighteningsystems from the new Power generation: Power Focus andTensor tools for hand assembly stations and PowerMACStightening tools on automated stations.

Johann A. Krause Maschinenfabrik in Bremen builds all ofFord’s European lines as complete installations and acts asFord’s “continuous source” for planned new engine linesaround the world.

Dipl.-Ing. Detlev Kalter is in charge of tightening technolo-gy at Krause. Because he was inclined towards Atlas Copcoand the new way of tightening he had some persuading to doat Ford’s headquarters in Dearborn, USA. Ford had alreadyruled out Japanese tightening tool suppliers, and althoughAtlas Copco had better coverage of the market in Europeand the USA, Ford were still concerned that a shift frompneumatic to electric tools could involve risks associatedwith the new technology. From his long experience with

Cylinder head assembly: Twoten nutrunner machines arehere tightening down thecylinder head of a V8 engine.Tightening is controlled bytorque /angle of rotation(40 Nm, 180°) with a precisionof ±2,5 % over 6 sigma (i.e.Ford A10 classification).



Krause, Kalter objected to this: “Today, anyone can tightena bolt securely but the will and ability to provide holistic,worldwide collaboration is something few can offer.” Inaddition, he saw that the new Power generation tighteningsystems fulfilled many of the wishes that Krause had beenexpressing for years.

What was more, Ford required “commonality”, the stan-dardization of all equipment for the same task and one Fordplant in the USA had already decided on Atlas Copco’s newgeneration of tightening tools for a new gearbox line. Thisstrengthened Kalter’s case for the new Power Focus andPowerMACS generation of tightening tools.

“In the end, the deciding factors were the technology, theprice and the fact that Atlas Copco is present with serviceand training wherever there are Ford plants”, is how Kaltersums up the final decision to go for Power Focus andPowerMACS tightening tools as the “global solution”.

Space savingOn a tour of the assembly stations for a V8 line, Kalterpoints out the space saving wall-mounting of thePowerMACS stand-alone modules and the fact that theymake do with only one cable to the nutrunner “whereas oldmodel tightening tools had three”. Since no account need betaken of the tool equipment cabinets in the layout of thetightening stations it was possible to make them much smal-ler than appeared practical in the outline drawings for tender.The control systems are accommodated where they do notneed too much additional volume. Only the network hubs,mains safety devices and any additional mains filters re-quired need to be housed in the equipment cabinet on thestation. All this minimizes expensive container area.Dipl.-Ing. Detfel Kalter, in

charge of tighteningtechnology at Krause.


On the assembly station for the V8 sump (see picture above)the conversation turns to the operator interface of the newtightening system. This has an enhanced graphics functionfor programming and operator guidance via PowerMACSHMI Annunciator (photo-quality bitmap images monitoringin real-time tightening sequences). All stations on this lineare equipped with a control and display PC. The PC is notnecessary for the regular system, says Kalter. Programmingof the tool can be done equally well with a laptop. “But ifthe customer wants, a PC can be connected to thePowerMACS-System without problem.”

With its 6th generation of MACS automated tightening sys-tems (PowerMACS) within ten years, Atlas Copco is nowfor the first time breaking away from the convention ofalways having to build the control system into the equipmentcabinet. The new systems will cope with all tightening andmonitoring and methods that have been developed over thecourse of time. The software options also include faultmanagement (reject management), which Ford uses to re-duce re-working off the tightening station.

Sump tightening: all twelveM8 bolts on the sump aretightened simultaneously to20 Nm with torque/angle ofrotation control (60°) by thetwelve special tools. The PC tothe right of the picture waswanted by Ford in order to beable to interface with thetightening system right in thetightening station and to beable to use the graphics capa-bilities of the control systemsimultaneously on the spotinstead of only on a PCbelonging to the line controlsystem.


Internet access is becoming importantAn important thing for Ford was to be able to do program-ming and select spindles on the station at any time, to viewthe actual values and tightening curves and maintain statis-tics. “Visualization via Windows is an important argumentfor us”, stresses Kalter. The thing that is not yet provided inthe assembly line in question is the use of the TCP/IPaddresses of each tool to communicate with the systems viathe Internet. But a project for another customer is alreadyshowing how much this type of communication, whichforms a standard part of the new way of tightening, “willsoon become the deciding factor”, as Kalter puts it.

The new lines for Ford will keep Kalter busy for a while. Inthe autumn of 2001 he reckoned that the program would goon for six or eight years.

6.9 KISSQ: Zero defect assembly in the BMWGroupThey don’t talk about the zero-fault goal in the BMW Groupbut nonetheless, in tightening, they practice zero-fault pro-duction according to Step 5 (chapter 1). Every work elementand equally every bolt assembly is controlled, checked andrecorded by a plant and company quality management sys-tem. This is provided by the “Core manufacture integratedquality management system [Kernfertigung integrierendesteurerungssystem Qualität]”, known as KISSQ. This is thequality building block of the central KISSQ system whosegoal is to optimize working procedures and hence increaseproductivity and cost effectiveness. Since 1997, KISSQ isbeing introduced step-by-step at the BMW Group’s plants.

The KISSQ-System provides computer supported collectionof all quality data of every phase of production. From thebare shell to the final assembly and driving dynamics testingtogether with control of re-work. To do so it uses the auto-motive industry package of the standard Central AQ (QSYSstandard software). This is a quality management systemdeveloped by IBS AG. It allows collection, inspection, ana-lysis and documentation of all production quality informa-tion in a central database and is stored for every vehicleassembled, including the data on the tightening process.



Here too, the data communication process between tighten-ing tools and their control units (master and slave) and thetool control system and the management system (in this caseKISSQ) described on page 49 applies in principle. The tight-ening process starts only when the vehicle has been identifiedand the operator is guided through visual signals for OK andNOK, organization of the tightening sequence and settingsof parameters via socket selectors.

Everything is based on the plug-and-play IT of the new wayof tightening with Ethernet based ToolsNet server and thePower Focus 3000 tightening systems for hand assemblypoints and PowerMACS tightening tools.

The BMW Group also has two program building blocksfrom Atlas Copco (based on IBS solution) that are KISSQspecific and are known as ToolsIdent and ToolsControl.


ToolsIdent is the interface to the automatic vehicle identifi-cation. The barcode of the chassis number is not read in seri-ally with a hand scanner but is transmitted wirelessly i.e.mobile media (Station A in the diagram on page 49).

ToolsControl takes on a standardized interface function atproduction management level. It is also used as an interme-diate buffer to distribute target and actual data in communi-cation with KISSQ. The ToolsControl software tool canstore and handle up to 400 chassis numbers and vehicle datasets, which are communicated in advance by KISSQ via theline management system’s SPC in accordance with the pro-duction plan.

The tightening control system finds out what program jobs(parameter sets and number of bolts) are to be carried outand in what sequence via ToolsControl. ToolsControl alsohandles sending back the status evaluation (OK or NOT OK)of every tightening and job. In order to record the data, thetightening tool control system reports directly to theToolsNet Server.

Assembly at the BMW plant inDingolfing, Germany.


Defective bolts automatically appear in central re-workmanagement or on wireless terminals right on the assemblyline where they are immediately processed. A wireless instal-lation is incorporated at KISSQ level for mobile re-work onthe line.

The mobile terminals are also equipped with a barcode scan-ner for identifying the re-working operator and vehicle. Thepart for re-work is indicated. The results are acknowledgedand added to the history of the work on the vehicle. Onlywhen all re-work demanded by the KISSQ-System has beendone, is a final OK generated and the vehicle released.

The tightening tools communicate with the KISSQ quality managementsystem through an ordinary NT server.Example in the BMW Oxford plant in England.

KISSQ Server

Additional DataComm System

ProductionControl System

ToolsNet/Costa

TCP/IP Ethernet

Datalogic

Ident M

Moby E

ProductionControlSystem

SocketSelector

PF3000 Colorwith ToolsControlas Master

PF 3000 Compact as slavesIdenti-fication

Socketselector

PF 3000 Compacts

NT WorkstationwithToolsControl& ToolsIdent


Title Ordering No.

Air line distribution 9833 1266 01

Air motors 9833 9067 01

Drilling with hand-held machines 9833 8554 01

Error proofed production 9833 1437 01

Grinding 9833 8641 01

Percussive tools 9833 1003 01

Pulse tools 9833 1225 01

Riveting technique 9833 1124 01

Screwdriving 9833 1007 01

Statistical analysis technique 9833 8637 01

The art of ergonomics 9833 8587 01

Tightening technique 9833 8648 01

Vibrations in grinders 9833 9017 01

Atlas Copco Pocket Guides

www.atlascopco.com

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Date post:	18-Apr-2020
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Five steps to achieve zero fault fastening · tightening cycles have been processed correctly....

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