-StateSPR.pdf

See discussions, stats, and author profiles for this publication at: /publication/222384675 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 ) 2736 journal homepage: /locate/jmatprotec 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 processes28 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 joints31 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.hewarwick.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 ) 2736 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 ) 273629 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 forcedisplacement curve for a SPR process (Hou et al., 2004). 30journal of materials processing technology 1 9 9 ( 2 0 0 8 ) 2736 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 1020% 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 1020% 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 ) 273631 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 s