The little book of Big Bolts This guide is iteded as a itroductio to the world of high torques. It gives a overview of the geeral treds i productio, poits to the key areas of process improvemet, presets the differet types of toolig ad fixtures, as well as what to thik of whe choosig tools.
CONTENT Geeral treds i assembly...1 How to improve the assembly process...4 Quality...4 Ergoomics...8 Productivity...10 Choosig assembly tools...12 Fixturig...14 What to cosider whe selectig tools...18
Geeral treds i assembly Whe lookig at maufacturig operatios i their most geeral sese, there exist several treds for how the idustry is buildig products ad takig them to the market. Some of these stad out i importace, ad will ifluece the look of the assembly operatios of tomorrow. We eed to produce faster, better ad cheaper! The umber of models per product has icreased sigificatly durig the last years ad product life cycles have become shorter, as a result of that more ad more compaies are ow cosolidatig their operatios ito specialized plats. I these plats, productio flexibility ad cycle rates are key, which i tur has several implicatios o productio methods: Use of platform cocepts meas faster time to market ad lower productio costs Higher lie speeds is oe of the aswers to the demad for icreased productio levels Better productio flexibility is eeded to respod to shorter product life cycles ad low extra capacity i productio 1
We eed to esure a appropriate quality! Maufacturers have uderstood that good quality will affect ot oly their costs but also their reveues. O top of that, badwill stemmig from quality cocers is ay compay s ightmare. Therefore, there is a strog drive towards elimiatig assembly related problems by reducig the possibilities for assembly errors, so called Error proofig. Icluded i this comes a eed to esure a appropriate clamp force i the joits that are tighteed. For example, the pump & valve idustry have products with critical seals o may differet models. 2
We wat to use the same maufacturig methods i all our plats! Maufacturers have uderstood that there are sigificat savigs to be made by usig the same assembly processes i plats maufacturig the same products. This has led to the creatio of master-member maufacturig setups, where oe factory is resposible for the process ad similar factories the copy methods ad equipmet at aother locatio. Although ot goig as far as relieveig their factories of the process owership, these compaies are exchagig best practices ad bechmarkig maufacturig methods to a larger extet tha before. We wat to esure the wellbeig of our operators! The eed to address health & safety related issues has icreased as compaies have uderstood the profoud beefits of havig a soud workig eviromet for their employees. Maufacturig compaies are cotiuig to strive to reduce potetial ad existig problems i operatios. Quick check: Are you subjected to demads for higher lie speeds or better quality output, ad will this have effect i how your assembly operatios will look like i the future? Do you see a drive towards commo processes i your assembly eviromet? Is operator wellbeig ad health & safety issues more of a cocer for you today tha it was 5 years ago? 3
How to improve the assembly process Improvemet areas for ay assembly process is of course heavily depedet o the uique assembly situatio. However, there are a umber of aspects that ca be doe o a process security ad toolig level that ca cotribute sigificatly to improvemets i assembly operatio. There are three differet corerstoes which all cotribute to the total cost reductios that ca be experieced by the ed user. Quality Ergoomics Productivity Quality Do it right the first time! The later a error is detected o the assembly lie, the more it costs to adjust. Fact! A maufacturer should always strive to correct ay assembly errors i the fastest possible way, whe they occur o the assembly lie. Statio 1 If a assembly error is committed ad detected here, the operator ca fix it by simply by retighteig the bolt. No damage is doe ad the additioal cost is the extra time to tighte ad perhaps the cost of a ew bolt. 4
Statio 2 If the error from Statio 1 is passed o to Statio 2, the additioal cost becomes higher. Now the operator perhaps eeds to dismatle the product to retighte the bolt or must walk over to Statio 1 to get compoets. Specially desigated rework areas are also commoally used. Ed statio If the error is ot corrected i Statio 2, it is hopefully detected i the Ed statio, where the quality check is beig made. If the error has reached this far, the cost of fixig it has goe up dramatically. The product eeds to be take aside for dismatlig ad rebuild ad if the product is made to order, there is a agry customer somewhere out there who will ot get his product o time. Customer detects error The worst possible sceario is that the error that was committed i Statio 1 goes udetected all the way to the customer ad that the product breaks dow durig operatios. Not oly will the maufacturer have large warraty costs because of this problem, but goodwill might be damaged. 5
How to elimiate assembly problems There are a few assembly problems that occur frequetly o productio lies globally. The problems o the lie or o a applicatio is oe importat factor to cosider whe determiig what tool type(s) to choose for assembly operatios. Delivered quality Lost Wrog quality Missig screws Stripped screws torqe Too early shut-of Bad Wrog repeatability forgotte Missed rework Problem Solutio Missig screws Screw coutig to esure all screws are accouted for Stripped screws Slower shut-off speed to prevet strip out Wrog torque Defied parameter sets with joit specific characteristics 6
Problem Solutio Wrog / forgotte parts Measurig rudow agles ad coutig screws esures correct type ad umber of compoets Bad repeatability Defied parameter sets with joit specific characteristics Missed rework Lie cotrol icorporates quality check poits to esure o faulty product is passed dow the lis Too early shut-off Operator guidace to otify of ay rudow problems Quick check: Who moitors the costs associated to warraty claims ad scrap frequecy today? What quality checks have you built ito your assembly process? Do these checks detect the most commo assembly problems? Do they esure that a faulty product is ot passed o dow the lie? Do you have a rework area today that takes care of products ot built to specificatio? Are all operators traied o how the various tools should be operated? 7
Ergoomics Soud ergoomics icrease productivity Ergoomics is playig a more importat role tha ever i assembly operatios. May compaies have ergoomic departmets or specialists who work closely together with their productio departmets. The importace of ergoomics is also stregtheed by the icreased media coverage o the issue ad trade practices adhered to o a global basis. It is clear that soud ergoomics icrease productivity. Happy ad safe employees are more productive. Furthermore, dowtime as well as labor absece related costs will go dow whe improvig ergoomics. For High Torque tools, this becomes eve more of a issue, as tools are ofte big ad heavy ad geerate high reactio force. Bad ergoomics Good ergoomics Whe workig to improve the ergoomic situatio i the high torque assembly eviromet, you always have to take a work statio perspective. The workstatio itself though, is quite complicated ad the selectio of power tool is oe importat parameter for workstatio desig. Iroically, the best power tool o the market will ot trasform a badly desiged workstatio ito a safe, comfortable work area for the operator Noise The lowest possible oise level should be aimed for. This cosists of reducig process oise, oise trasmitted by vibratio ad potetial aerodyamic oise. Example: Avoid usig a impact wrech i a hollow compartmet without ear protectio. 8
Vibratio All machies vibrate to some extet. By reducig vibratio levels ad process times, operator health problems ca be preveted. Example: Make sure to take frequet breaks whe ruig a highly vibratig tool durig log periods of time. Operator strai High torque tools are ofte heavy ad ca cause uatural strais for the operator. With the use of balacers ad torque arms, operator strais ca be miimized. Example: A big tool amouts to may kilos of weight whe carried aroud cotiuously durig a day. Always use a balacer. Workig posture Avoidig bad workig postures is of high importace. This ca be doe by reducig the load o the static muscles ad shorteig the duratio of each operatio, as well as providig the operator with the right workig techique. Example: Never use a tool durig log periods above shoulder level. Regardless of tool type, it is oly as good as the reactio device or fixture which it is used with Quick check: What ergoomic guidelies goverig workplace desig do you have today? Do these guidelies take the etire workplace ito accout; i.e. power tools, work orgaizatio, workplace, ad operator? Do you have ay health ad safety issues i work areas today? Are there ay had wrech operatios above 100 Nm? Are all applicatios with heavy tools ad or high torques fixtured ad supported? What costs does your factory associate to ijury ad work related health issues? 9
Productivity Productivity is about fidig a balace. Productivity should ot be cofused with tool speed, sice tool speed ad process speed are two completely differet thigs. Furthermore, productivity ca oly be maximized whe cosidered alogside quality. It is easy to build a lot of poor quality product. But it is equally easy to build low volumes of high quality products! There are two key areas to focus o whe tryig to icrease the productivity of assembly operatios: Decrease the umber of operatios, ad/or Icrease the speed of process. Decrease the umber of operatios By reducig the umber of operatios, cycle times ca be cut dramatically. This i may istaces have a higher impact o total cycle time tha choosig the tool with higher speed. Example: Covetioal method Statio 1 Tighte with hydraulic tool Preferred method Statio 2 Click Wrech to secure the joit has bee fasteed Statio 3 Pait marker to prove the joit has bee tighteed Statio 1 Safety / quality critical applicatio Tighte with electric tool Statio 1 Other applicatio Tighte with shut-off peumatic tool 10
Icrease the speed of process The cycle rate i a factory depeds partly o the speed of the assembly operatios. Other factors that cotribute are for example: overall product demad, feeder lie speeds, speed of pait, machiig or other o-assembly operatios, airlie istallatio pressure for peumatic tools etc. Whe lookig solely at assembly operatio speed, the fastest tool that does ot compromise error proofig level or ergoomics should always be selected. To maximize assembly operatio speed, the followig basic rule ca be applied: Step 1: Determie the level of Error Proofig Process speed Here you choose your error proofig requiremets as well as the desired accuracy of the tool for the job. The 5 steps to error proofig should be used as referece. Step 2: Determie the ergoomic demads of your istallatio Good ergoomics has a strog impact o overall productivity. A tool should always comply with regulatios ad stadards regardig oise ad vibratios. Usually compaies have specific ergoomic guidelies goverig the tool choice. Good ergoomics is good ecoomics! Step 3: Choose the fastest possible tool or rudow for the applicatio With Step 1 & 2 take ito cosideratio, the goal should be to maximize the rudow speed of the tool. Here umerous aspects must be cosidered: compoet materials, fasteer costraits, tool propulsio system etc. Quick check: Have you take ergoomics ad error proofig level ito accout whe tryig to maximize productivity? Which bottle eck operatios do you have today that are depedat o assembly tools? Are multiple assembly operatios performed i some statios ad if yes, is there a possibility to reduce the umber of these operatios? Do you use click wreches or pait markers? Are there eeds for quality checks ad for what reasos are there eeds? 11
Choosig assembly tools Today, there is scarcely ay discussio o techical issues relatig to tighteig that does ot also iclude process quality. However, everyoe uderstads process cotrol ad process quality slightly differetly. Atlas Copco has divided our products ito differet categories depedig o error proofig fuctioality. This defiitio provides a commo groud for discussio ad helps provide some log overdue clarity o the subject. The 5 steps to error proofig Step 1 Precise & pre-determied torque Operator Depedat Step 2 Screw coutig No re-hits Batch OK! Step 3 Agle moitorig => joit cotrol Calculated torque values Joit OK! Step 5 Cotrollers are etworked with factory productio Step 4 system Traceability Reject maagemet Tighteig data collectio Trasducerized Zero fault fasteig! tool Safety critical tighteig OK! Tool examples Torque OK! EP LTP RE - cotroller Tesor DS Tesor S Itegratio of the tighteig process ito the productio maagemet etwork 12
Selectio guide Every applicatio ad ideed customer have their ow specific requiremets whe it comes to tool selectio. Depedig o how critical the applicatio is, or the demads o access or lie speed all play a part i choosig the correct tools. Below is a simplified selectio process, accordig to process fuctioality levels, which highlights the key factors that differetiate the tools. Techology: Pulse Tool EP PT / PTS Peumatic Nutruer LMP / LTP DC Electric Nutruer Tesor DS DC Electric (trasducerised) Nutruer Tesor S Torque cotrol Shut-off Stall type / Shut-off DigiTork* Trasducer Documetatio -- -- Oly OK/NOK Yes Agle moitorig -- -- Yes (36 0 Steps) Yes Parameter sets -- --- 10 / 64 Up to 250 Networkig -- -- -- Yes Applicatios: Safety Critical No No No Yes Quality Critical No No Yes Yes Stadard Yes Yes Yes Yes Accuracy: +/- 15% +/- 10%** +/- 7,5%* +/-5%** Price level: 100% 200-400% 400 600% 600-1000% *Algorithm of motor curret, frequecy, voltage ad temperature.** Tested accordig to ISO 5393. These values should be see as a guidelie. 13
Tool fixturig Whe dealig with high torque applicatios, it is extremely importat to cosider the issue of torque reactio ad fixturig of the tools to be used. I all cases where a direct drive utruig system, such as peumatic shut-off, stall type or DC utruer are to be utilised o such a applicatio, particular cosideratio must be paid to both how the tool will be supported ad how the torque reactio will be dealt with. Below you fid a overview of the differet types of fixturig solutios for commo applicatios i the High Torque sector. There are differet categories of tool fixturig devices that all have their advatages ad disadvatages. The three that we will look at further are as follows: 1. Reactio Device: Reactio take through a additioal reactio device fitted oto the tool. 2. Support Fixture: Reactio take through a device or fixture oto which the tool is supported 3. Holdig System: Where a bolt or ut is held i positio whilst the other part is fasteed by the tool 14
1. Reactio device This method cosists of moutig a reactio bar oto the frot part of the tool. This will the rest agaist, or locate oto a associated compoet or fixture i the work area. The result is that whe the bolt is tighteed, the tool caot rotate or move i ay way. The most importat thig to cosider i this case is to esure that the area which the reactio bar is to react agaist is both stable ad caot move i ay way, especially A simple reactio bar with a dummy socket which ca locate over aother bolt head to take the torque reactio, for example i wheel assembly. bearig i mid that the reactio force will be equal to the torque beig applied to the fasteer. 2. Support Fixture This method of solvig the issue of torque reactio is differet from the above, i that rather tha mout a device o the tool, we istead ca mout the tool oto a additioal support device. This moutig device or fixture ca take may differet forms, commoly referred to by ames such as support arms, torque tubes, or articulated arms. Although all are differet i terms of how they are used, the pricipal i which they solve the issue is the same. A typical istallatio showig a articulated arm with a agle utruer mouted Bech or Floor Mouted Torque Arms These ca be simple bech mouted type whereby the tool is fixed i a arm, ad the tool carries out the tighteig operatio i a similar maer time after time. Alteratively if the arm has a kuckle or is floor mouted, this may give the flexibility for the tool to rotate about a poit to reach a variety of positios ear the workig area. 15
Torque Reactio Tubes Where a tool eeds to be suspeded i such a way that it must move alog a productio lie, or across a work cell area, it is ofte difficult to use a arm of ay descriptio. I the case of a excavator for example, the work area may be very large but you still wat both to take up torque reactio ad provide the ecessary flexibility i productio. A alterative method of istallig a tool is the to put it o a Torque Tube. This is i effect a metal tube which ca move i both the horizotal ad vertical plaes to give flexibility whilst at the same time absorbig the torque reactio through the tube itself. Articulated arms Articulated torque arms have may advatages, i that ot oly ca they take the torque reactio that is geerated but, they ca also take the etire weight of the tool. Furthermore, whe mouted o a overhead carrier or track, A typical istallatio showig a articulated arm with this gives the flexibility a agle utruer mouted to maoeuvre the tool parallel to a movig lie such as i a tractor maufacturig plat, or to several positios i a static build cell, such as i excavator assembly. As the tool is held by the arm the torque reactio geerated is take through the arm itself, whether it be mouted overhead, or fixed to the floor. 16
3. Holdig System Tromboe devices Below we ca see three typical examples of what is kow as tromboe reactio devices. You ca see how a reactio bar is mouted to the frot part of the tool, which i tur has a dummy socket or opeig o the other ed, holdig it i place while the utruer drives the bolt head (or vice versa). The reactio is take up by the reactio bar, as durig the tighteig process. The forces geerated o each side, work i the opposite directio to each other, ad hece cacel each other out. Examples of tromboe devices Straight utruer with Tromboe reactio device Agle utruer with Tromboe reactio device Pistol Peumatic Nutruer with Tromboe reactio device Separate Tromboe device ad agle tool 17
What to cosider whe selectig tools The selectio of the appropriate tool for a give applicatio is seldom straightforward ad i most cases there is o right tool, but several tools ca do the job. May differet factors must be cosidered whe choosig a tool, all of which have a ifluece o the fial decisio. Below we have listed the most crucial aspects that should be discussed before a tool ivestmet decisio is take. These are grouped accordig to the corerstoes Quality, Ergoomics & Productivity described i the chapter previously. Quality Who moitors the costs associated to warraty claims ad scrap frequecy today? What quality checks have you built ito your assembly process? Do these checks detect the most commo assembly problems? Do they esure that a faulty product is ot passed o dow the lie? Do you have a rework area today that takes care of products ot built to specificatio? Are all operators traied o how the various tools should be operated? Ergoomics What ergoomic guidelies goverig workplace desig do you have today? Do these guidelies take the etire workplace ito accout; i.e. power tools, work orgaizatio, workplace, ad operator? Do you have ay health ad safety issues i work areas today? Are there ay had wrech operatios above 100 Nm? Are all applicatios with heavy tools ad or high torques fixtured ad supported? What costs does your factory associate to ijury ad work related health issues? 18
Productivity Have you take ergoomics ad error proofig level ito accout whe tryig to maximize productivity? Which bottle eck operatios do you have today that are depedat o assembly tools? Are multiple assembly operatios performed i some statios ad if yes, is there a possibility to reduce the umber of these operatios? Do you use click wreches of pait markers? Are there eeds for quality checks ad for what reasos are there eeds? By selectig the correct tool for the applicatio, umerous cost savigs will be realized: Ergoomics beefits Low oise Low vibratio levels Superior tool cotrol No heavy straiig or liftig Quality Cost savigs with correct tools Ergoomics Productivity Productivity beefits Fewer operatios High process speed Less maiteace process Quality beefits Cosistet accuracy Traceable result Elimiatio of assembly problems Process cotrol 19
9833 1498 01 2004:2 More iformatio Atlas Copco has extesive experiece ad kow-how of assembly solutios i the High Torque segmet. We provide literature, courses, semiars ad audit services for our parters. If you wat to kow more, either order the followig iformatio, or cotact with your earest Atlas Copco resposible who ca provide specific iformatio i the areas of your iterest, e.g. Idustry best practices for assembly or High torques assembly culture, amog may others. Pocket guides Error proofed productio Statistical aalysis techique The art of ergoomics Tighteig techique Orderig umber 9833 1437 01 9833 8637 01 9833 8587 01 9833 8648 01