-StateSPR.pdf

See discussions stats and author profiles for this publication at Self pierce riveting for sheet materials state of the art J Mater Process Technol 199 1 3 27 36 Article in Journal of Materials Processing Technology April 2008 DOI 10 1016 j jmatprotec 2007 10 071 CITATIONS 83 READS 654 3 authors including Xiaocong He Kunming University of Science and Technology 119 PUBLICATIONS 826 CITATIONS SEE PROFILE All content following this page was uploaded by Xiaocong He on 10 April 2014 The user has requested enhancement of the downloaded file All in text references underlined in blue are added to the original document and are linked to publications on ResearchGate letting you access and read them immediately journal of materials processing technology 1 9 9 2 0 0 8 27 36 journal homepage Review Self pierce riveting for sheet materials State of the art Xiaocong He Ian Pearson Ken Young Warwick Manufacturing Group International Manufacturing Centre University of Warwick Coventry CV4 7AL UK a r t i c l ei n f o Article history Received 12 April 2007 Received in revised form 8 October 2007 Accepted 24 October 2007 Keywords Self pierce riveting Sheet material Joint formation Process monitoring Mechanical properties Finite element simulation a b s t r a c t Self pierce riveting SPR is a high speed mechanical fastening technique for point joining of sheet materials It is used heavily in the automotive sector due to the growing use of alternativematerialssuchasaluminiumandmagnesiumalloysandthediffi cultyinwelding these Published works relating to SPR is reviewed in this paper The mechanics of joint formation and the types of defects that may occur are introduced The main mechanical properties of SPR joints such as strength corrosion properties and free vibration properties are discussed The prediction of joint distortion when SPR is used to create structures and the cost effects of the technique are also introduced The objective of this paper is to review recent progress in SPR usage and to provide a basis for further research 2007 Elsevier B V All rights reserved Contents 1 Introduction 28 2 SPR processes 28 2 1 The mechanics of joint formation 28 2 2 Process monitoring 29 2 3 Joint failure mechanics 29 3 Mechanical properties 30 3 1 Static and fatigue behaviour of SPR joints 30 3 2 Vibration behaviour of SPR joints 31 3 3 Fretting wear in SPR joints 31 4 Finite element analysis of SPR joints 31 5 Assembly dimensional prediction for SPR panels 32 6 Cost effects of SPR technique 33 7 Outlook 33 8 Summary 34 References 34 Corresponding author Tel 44 2476150076 fax 44 2476573743 E mail address xiaocong he warwick ac uk X He 0924 0136 see front matter 2007 Elsevier B V All rights reserved doi 10 1016 j jmatprotec 2007 10 071 28journal of materials processing technology 1 9 9 2 0 0 8 27 36 1 Introduction Though the self pierce riveting SPR process was originated around half a century ago it is only in the last 20 years that the technology of the SPR has signifi cantly progressed Hill 1994 Pond 1972 Anon 1975 Gausden and Gunn 1976 Endo 2001 Due to the increasing demand for energy effi cient energy saving vehicles there is an increasing need to design lightweight structures and these invariably use lightweight materials which are diffi cult or impossible to weld This has produced a signifi cant increase in the use of SPR technology in engineering structures and components Edwards 1992 Patrick and Sharp 1992a b Heeren and Timmermann 2002 Takaki et al 2004 Budde and SchuzBeenken 1996 Moss and Mahendran 2002 2003 Additionally the SPR process is of great interest to other industrial sectors including the aerospace packaging and appliance industries Severalcarmanufacturersemploythistechniquetoassem ble aluminium automotive bodies for both space frame and monocoque body assemblies Hill 1994 Doo 1993 Patrick and Sharp 1993 Blacket 1995 Zeitzmann 1997 Kochan 1997 2000 Barnes and Pashby 2000 Mortimer 2001 Anon 1990 1997 LaPensee 2003 Mortimer 2004 2002 Numerousmount ing brackets are attached using the SPR technique battery mountings spare wheel supports and exhaust heat shields are just a few examples of mounting requirements that can be satisfi ed BFL 2007 Additionally there is considerable use of the self piercing riveted joints in homes and offi ces and this widespread use is due to ease of application time and cost savings together with high corrosion and fatigue resistance Compared to the more traditional methods of sheet mate rial joining the advantages offered by SPR include Blacket 1995 Barnes and Pashby 2000 1 joining a range of dissimilar materials and multiple mate rial stacks 2 no need for a pre drilled hole 3 fast cycle times 4 environment safely and friendliness 5 easy of automation and process monitoring 6 achievement of high strength and increased fatigue prop erties 7 low energy requirements 8 relatively low costs 9 no waste material produced 10 a water tight joint is formed As with any technology however SPR has some disadvan tages which include the following 1 access is required to both sides of the joint 2 inappropriate for brittle substrates 3 bulges and indents associated with the forming process may not be aesthetically acceptable 4 relatively high force required for the forming process Inaddition theinstallationofSPRsystemsismuchsimpler and renders less cost than a spot welding system There is no Fig 1 Schematic representation of the SPR process Voelkner 2000 need for air extraction systems since there are no dangerous fumes produced Carle and Blount 1999 2 SPR processes 2 1 The mechanics of joint formation Essentially the SPR process is a cold forming operation used to fasten two or more sheets of material by driving a semi tubular rivet see Fig 1 through the top sheet s piercing the bottom sheet but not perforating it and spreading the rivet skirt under the guidance of a suitable die As there is no requirement for pre drilled holes in the sheet materi als the SPR process eliminates the need for exact alignment between components and between components and rivet setting machinery As the process relies on a mechanical interlock rather than fusion it can be used on materials and combinations of materials Examples are heavily zinc coated organic coated or pre painted steels combinations of steel to aluminium alloys and some plastics to metals For steel joints can be made in sheet from about 0 5 to 3mm thick ness with a total joint thickness of up to about 6mm For lightweight alloys a total joint thickness of up to about 10mm can be riveted The rivets are made of high strength steel and have appropriate shapes and diameters for the fi nished joint Dies are made of die steel and again have shapes and dimensions suited to the production of the desired fi nal joint geometry The process involves only two distinct phases piercing and fl aring It can be described by the following four steps Hill 1994 Blacket 1995 Porcaro et al 2006a Atzeni et al 2005 Voelkner 2000 1 Clamping Therivetisforcedbyafl atpunchperpendicularly to the top sheet surface and presses the sheets against the die 2 Piercing The punch pushes the rivet through the top sheet and into the bottom sheet journal of materials processing technology 1 9 9 2 0 0 8 27 3629 3 Flaring The material of the lower sheet fl ows into the die and the rivet shank is fl ared thus forming a mechanical interlock between the substrates 4 Releasing The punch stops and retracts when it reaches the predetermined value of force or stroke 2 2 Process monitoring Methods of in process monitoring have been developed by universities and industrial companies where substantial amounts of research have provided a greater understanding of the process and the development of computer based process monitoringpackages Hill 1994 BuddeandLappe 1991 Budde et al 1992 Bokhari 1995 King et al 1995 King 1997 Taylor 1997 ETI 2002 Henrob Group 2007 The SPR process moni toring system usually comprises a PC with bespoke software andintelligentsignalconditioningandcommunicationshard ware and transducers The system records various process parameters inputspeed forceetc andequipmentconditions desired input speed or force etc For in process monitoring it is necessary to establish measurable parameters which will give an overall picture a reproduciblequalityprocessandforce displacementhasbeen establishedasacrediblemeansofquantifyingprocessquality By measuring force and displacement directly at the riveting mechanism it is possible to produce a characteristic curve relating to the joint formation through all of its phases Fig 2 shows a typical four step setting force displacement curve for the SPR process Hou et al 2004 Since the shape of the force displacement curve will alter with variations in the process parameters the curve in effect becomes a fi ngerprint for all fastenings produced under the same process conditions The fi ngerprint curve from an acceptablyformedjointcanbecomparedtoeveryjointformed under the same process conditions King 1997 and deliver 100 inspection as well as partial control of the fastening quality 2 3 Joint failure mechanics SPR joints display similar failure modes to all other mechani callyfastenedjoints Fiveseparatestaticmodesoffailurewere established by King 1997 who showed that the strength and fl exibility of SPR joints were dependent on the failure mode of the joint Westgate and Razmjoo 1999 found that steel and aluminium joints exhibited different failure modes On the same topic Fu and Mallick 2001 2003 emphasised that fracture of the pierced sheet was the only failure system to occur during fatigue testing Recent investigations Chen et al 2003 Han et al 2006a indicated that both rivet fracture andsheetmaterialfailurecanoccurduringfatiguetestingand this is infl uenced by fretting behaviour The effect of secondary bending an inherent feature of lap joint geometry on single lap SPR joints was examined using strain gauge measurements by Han 2003 and concluded that secondary bending contributed to the failure mechanism and led to a signifi cant reduction in the fatigue strength Razmjoo and Westgate 1999 carried out a study by using so called H section specimens to eliminate the effect of the secondary bending The results showed that the fatigue strength of H section specimens was much higher than the single lap SPR joints With any joining technique there is the potential for inher ent corrosion problems Surface irregularities or crevices will exacerbate the problem Crevice corrosion is a severe form of highly localised corrosion attack and results from the pres ence of an electrolyte in a crevice Galvanic corrosion occurs when dissimilar conductive materials are joined and the ingress of water forms an electrolytic cell In this type of corrosion the material is uniformly corroded as the anodic and cathodic regions moves and reverses from time to time Howard and Sunday 1983 presented extensive data compar ing the amount of corrosion in SPR joints to commonly used resistance spot weld joints and suggested that the amount of corrosion could be reduced signifi cantly by using a polyester coating or cadmium plating The same authors also found that the ultimate shear strength for both SPR joints and spot welded joints showed no signifi cant degradation after being subjected to a 90 day alternate immersion test Galvanic cor rosion can be avoided if the rivet is manufactured from the same material as sheets being joined Preliminary work has been made on aluminium self pierce rivets for use in the constructionofaluminiumvehicles Bazdresch 2001 Theriv ets were produced by sintering as this method readily allows Fig 2 A typical four step setting force displacement curve for a SPR process Hou et al 2004 30journal of materials processing technology 1 9 9 2 0 0 8 27 36 the use of different alloys or mixtures of alloys In addition production of the rivets can be made in house with control over the whole manufacturing process It also allows small batch production quantities required for the initial stage of the research 3 Mechanical properties 3 1 Static and fatigue behaviour of SPR joints As SPR is considered to be an alternative to spot welding most research studies have focused on comparisons of the mechan ical behaviour of joints manufactured by these techniques Research in this area has shown that self pierce riveting gives joints of comparable static strength and superior fatigue behaviour to spot welding whilst also producing promising results in peel and shear testing Krause and Cherenkoff 1995 Riches et al 1995 Miller et al 1998 Stegemann et al 1998 Sun et al 2004 Sun and Khaleel 2005 Lennon et al 1999 have carried out shear tests on four types of mechanical connections these are self pierce riv eting press joining pop riveting and self tapping screws with sheet thicknesses 1 0 1 2 1 6 2 0mm Fig 3 shows that self pierce riveting produces a high peak load a high initial stiffness and high ductility compared to the other processes A number of authors have shown that the static strength of SPR joints is some degree lower than that of resistance spot welded RSW joints Bonde and Grange Jansson 1996 Olivier 2000 Boothetal 2000 Boothetal 2000 reportedthat for steel to steel joints the RSW joints exhibited failure loads morethan25 higherthanthoseforcorrespondingSPRjoints However when testing aluminium to aluminium joints in lap shearandTpeelconfi gurations noclearpatternwasobserved Booth et al 2000 For joints made with equal thickness sub strates of 3mm the strength of RSW joints was 10 20 higher than that of SPR joints For joints made with equal thickness substrates of 1 2mm thick and for joints with unequal thick ness substrates of 1 2mm and 3 0mm the SPR joints were approximately 10 20 stronger than the RSW joints Fig 3 Average load displacement paths of connections in 2 0 mm thick steel Lennon et al 1999 Fig 4 Fatigue behaviour comparison of spot weld clinch and SPR joints Cai et al 2005 Although the static strength of SPR joints is probably lower than that of spot welded joints it is generally believed that a satisfactory static strength could be achieved for SPR joints through suitable design of rivet and die Westgate and Razmjoo 1999 Riches et al 1995 ThefatiguestrengthoftheSPRjointshasbeeninvestigated by a number of authors for a number of materials favoured by the automotive industry All agree that the fatigue strength of SPR joints is superior to that of the spot welded joints Henrob Group 2007 Fu and Mallick 2001 2003 Razmjoo and Westgate 1999 Krause and Cherenkoff 1995 Bonde and Grange Jansson 1996 Booth et al 2000 Cai et al 2005 Hahn et al 1999 Sunday 1983 Bonde 1995 Litherland 1998 Tileli etal 1999 LiandFatemi 2006 Agrawaletal 2003 Fig 4com pares the fatigue behaviour of different joining techniques MizukoshiandOkada 1997 performedfatiguetestsonSPR joints clinched joints and spot welded joints for some alu minium automotive body sheet materials such as GC45 O GC55 O and SG112 T4 The SPR joints were made by using 5mm long steel rivet which were zinc or tin coated They compared joints by what they termed Fatigue Ratio defi ned as fatigue strength tensile strength The results show that SPR joints obtained higher fatigue strengths and generated fatigue ratios around 0 4 twice those of RSW joints The results also showed that though fatigue strengths of SPR joints decreased by about 30 after exposure to salt spray for 2000hours but were still equal to those of spot welded joints and this was regardless of base materials Researchers attribute these results to the facts that in spot welded joints the metal around the joint has been softened by the welding heat HAZ but in SPR joints the substrate adjacent to the rivet has been work hardened Efforts have also been focused on enhancing the fatigue life of SPR joints through process optimisation Jin and Mallick 2002 found that ring coining improved the fatigue life of SPR joints in aluminium alloys and the degree of improvement may be dependent on the coining condition and the sheet thickness combination A new method combining hydro forming and SPR was proposed by Neugebauer et al 2005 In contrast to the standard method the riveting process is achieved without a solid die instead high pressure fl uid acts as the die during joining The advantages of the Hydro Self journal of materials processing technology 1 9 9 2 0 0 8 27 3631 Pierce Riveting processes are the reduction of the number of processing steps and new design possibilities are feasible as joining in complex hydroformed units becomes possible also it allows SPR to be used in inaccessible places Neugebauer et al 2005 Hanetal 2006b reportedtheinfl uenceofsheetpre straining on the static and fatigue behaviour of self piercing rivetedaluminiumalloysheet Iyeretal 2005 foundthatboth the fatigue and static strength of double rivet SPR joints to be strongly dependent on the orientation combination of the rivets Hahnetal 1999 havecarriedoutfatigueperformancesofa combination of SPR and adhesive bonding in 6016 aluminium alloy with various surface pre treatments and coatings Their studyshowedthatthecombinationproducedamuchstronger joint than the rivets themselves in both static and fatigue test ing Some other researchers Olivier 1999 Madasamy et al 2001 2002 Weber 2004 Hahn and Wibbeke 2005 Anon 2005 Whitworth 2006 also showed additional benefi ts from hybrid SPR joints such as 1 continuous leak tight joints 2 higher strength joints 3 increased joint stiffness 4 improved peel and impact resistance because crack growth away from the joint is arrested by the adhesive bond In addition it should be mentioned that neglecting hid den factors such as secondary bending etc as indicated by Razmjoo and Westgate 1999 may result in the joint being under strength 3 2 Vibration behaviour of SPR joints In the design of mechanical structures which incorporate jointed components for minimum vibration response a spe cifi c knowledge of the damping capacity of t