FABRICATION COST OF STEEL AND ALUMINIUM STRUCTURES

Transcription

1 EUROSTEEL, September -,, Naples, Italy FABRICATION COST OF STEEL AND ALUMINIUM STRUCTURES Károly Járma a, József Farkas b ab Unversty of Mskolc, H- Mskolc, Egyetemváros, Hungary a altjar@un-mskolc.hu, b altfar@un-mskolc.hu KEYWORDS: optmum desgn, cost calculaton, fabrcaton cost, weldng cost, cuttng cost ABSTRACT The man requrements of modern welded metal structures are the load-carryng capacty (safety), the ftness for producton, and economy. These requrements can be met by structural optmzaton: the economy s acheved by mnmzng a cost functon. The safety and ftness for producton are guaranteed by fulfllng the desgn and fabrcaton constrants. The paper descrbes the cost calculatons, whch are founded on materal costs and those fabrcaton costs, whch have drect effect on the szes, dmensons or shape of the structure. Mnmum mass and mnmum cost structures are usually dfferent. GENERAL The cost functon ncludes the cost of materal, assembly, weldng as well as surface preparaton, pantng and cuttng, edge grndng, formng the shell and s formulated accordng to the fabrcaton sequence. The paper descrbes the new cost calculatons of the dfferent technologes, consderng some newer technologes lke laser, plasma, waterjet, etc. These costs are the objectve functons n structural optmzaton. Other costs, lke amortzaton, nvestment, transportaton, mantenance are not consdered here. Sometmes we can predct the cost of desgn and nspecton, but usually they are proportonal to the weght of the structure. Cost and producton tme data come from dfferent companes from all over the world. When we compare the same desgn at dfferent countres, we should consder the dfferences between labour costs. It has the most mpact on the structure, f the technology s the same.. The cost of materals The cost functon of a real structure may nclude the cost of materal, assembly, the dfferent fabrcaton costs such as weldng, surface preparaton, pantng and cuttng, edge grndng, formng the geometry, etc. K M k M V, () For steel the specfc materal cost can be k M =.-. $/kg, for alumnum k M =.-. $/kg, for stanless steel k M =.-. $/kg, for glass fbre - $/m dependng on the thckness. K M [kg] s the fabrcaton cost, k M [$/kg] s the correspondng materal cost factor, V [mm ] s the volume of the structure, s the densty of the materal. For steel t s.8x - kg/mm, for alumnum.x - kg/mm, for stanless steel.8x - kg/mm, for glass fbre.x - kg/mm. If several dfferent materals are used, then t s possble to use dfferent materal cost factors smultaneously n Eq. ().. The fabrcaton cost K f = k f, () T where K f [$] s the fabrcaton cost, k f [$/mn] s the correspondng fabrcaton cost factor, T [mn] are producton tmes. It s assumed that the value of k f s constant for a gven manufacturer. If not, t s possble to apply dfferent fabrcaton cost factors smultaneously n Eq. ().

2 .. Fabrcaton tmes for weldng One of the man tmes of welded steel and alumnum structures are related to weldng as follows: preparaton, assembly, tackng, tme of weldng, changng the electrode, deslaggng and chppng. Calculaton of the tmes of preparaton, assembly and tackng The tmes of preparaton, assembly and tackng can be calculated wth an approxmaton formula as follows T w C dw V, () where C s a parameter dependng on the weldng technology (usually equal to ), dw s a dffculty factor, s the number of structural elements to be assembled. The dffculty factor expresses the complexty of the structure and t depends on the knd of structure (planar, spatal), the knd of members (flat, tubular). The range of values proposed s between - []. Calculaton of real weldng tme Real weldng tme can be calculated on the followng way T C a L, () w w w where a w s weld sze, L w s weld length, C s constant for dfferent weldng technologes. C contans not only the dfferences between weldng technologes but the tme dfferences between postonal (vertcal, overhead) and normal weldng n downhand poston as well. The equatons for dfferent weldng technologes can be found n the []. Calculaton of addtonal fabrcaton actons tme There are some addtonal fabrcaton actons to be consdered such as changng the electrode, deslaggng and chppng. The approxmaton of ths tme s as follows n Tw. Caw Lw. () Table Weldng tmes T w (mn/mm) n the functon of weld sze a w (mm) for longtudnal fllet welds, downhand poston Weldng a w [mm] Tw Ca Weldng technology a w w [mm] Tw Caw technology SMAW -.889a FCAW -.a w w SMAW HR -.9a FCAW-MC -.a w w GMAW-C -.9a SSFCAW ( ISW ) -.9a w w GMAW-M -.8a SAW -.9a w In s proportonal to T w. It s the % of t. The two tme elements are as follows: w n Tw Tw. CawLw. () The weldng tme for ½ V, V, K and X weldngs are very smlar for the dfferent technologes: SMAW = Shelded Metal Arc Weldng, SMAW HR = Shelded Metal Arc Weldng Hgh Recovery, GMAW-CO = Gas Metal Arc Weldng wth CO, GMAW-Mx = Gas Metal Arc Weldng wth Mxed Gas, FCAW = Flux Cored Arc Weldng, FCAW-MC = Metal Cored Arc Weldng, SSFCAW (ISW) = Self Shelded Flux Cored Arc Weldng, SAW = Submerged Arc Weldng.... Thermal and waterjet cuttng The other man cost s cuttng of the elements. The four most commonly used non-contact methods of metal cuttng are oxy-fuel gas, plasma, laser, and abrasve waterjet. These four processes are prmarly used to make precson external and nteror cuts on flat sheet and plate materal and tubes. Plate cuttng and edge grndng tmes

3 Oxy-fuel gas cuttng, usually wth acetylene gas, was once the only method of thermal cuttng. The oxy-fuel torch has a pre-heatng flame provdng a relatvely smooth and regular cut. Laser weldng The spectrum of laser weldng extends from heat conducton weldng to deep-penetraton weldng, a keyhole process n whch aspect ratos of up to : are attaned. Hgh power denstes permt a concentrated energy nput, achevng hgh weldng speeds as well as sgnfcantly reduced heat nfluence and dstorton. Compared wth arc weldng, t allows a much wder range of materals to be welded, and materal thcknesses of up to approxmately mm can be welded n one pass. One of the largest advantages that pulsed laser weldng offers s the mnmal amount of heat that s added durng processng. Ths makes laser weldng deal for thn sectons or products that requre weldng near electroncs or glass-to-metal seals. Low heat nput, combned wth an optcal (not electrcal) process, also means greater flexblty n toolng desgn and materals. The speed of laser weldng of steel plates can be seen on Fg. ab, the value of weldng speed [m/mn] and tme/unt length [mn/m] n the functon of plate thckness t [mm].. Laser weldng of steel Rank Eqn lny=a+bx^(.) r^=.999 DF Adj r^=.998 FtStdErr=.8 Fstat=8.8 a=-.988 b= Laser weldng of steel Rank Eqn 9 y^=a+bx^ r^=.99 DF Adj r^=.99 FtStdErr=. Fstat=.9 a=. b= Fg. a Laser weldng speed S [m/mn] n the functon offg. b Laser weldng tme/un length [mn/m] n the plate thckness t [mm] functon of plate thckness t [mm] S= /lnt=/(a+bt. ) [mm/mn] () a= b= where S s the weldng speed [mm/mn], T s tme [mn], t s thckness [mm]. Thermal and waterjet cuttng The four most commonly used non-contact methods of metal cuttng are oxy-fuel gas, plasma, laser, and abrasve waterjet. The frst three cuttng processes are thermal n nature, whle the waterjet method cuts by abrasve eroson. These four processes are prmarly used to make precson external and nteror cuts on flat sheet and plate materal. Plate cuttng and edge grndng tmes The cuttng and edge grndng can be made by dfferent technologes, lke Acetylene, Stablzed gasmx and Propane wth normal and hgh speed. Table Cuttng tme of plates, T CP (mn/mm) n the functon of weld sze a w (mm) for longtudnal fllet welds and T-, V-, / V butt welds Cuttng technology Thckness n TCP CCPt t [mm] Acetylene ( normal speed ) -..88t Acetylene ( hgh speed ) -..9t Stablzed gasmx ( normal speed ) -..9t Stablzed gasmx ( hgh speed ) t Propane ( normal speed ) -..9t Propane ( hgh speed ) -..t

4 The cuttng cost functon can be formulated usng n the functon of the thckness (t [mm]) and cuttng length (L c [mm]). Parameters are gven n []: n T CP CCPt Lc, (8) where t the thckness n [mm], L c s the cuttng length n [mm]. The value of n comes from curve fttng calculatons. The thermal processes and the oxy-fuel gas process n partcular share two dsadvantages. Frst, heat changes the structure of metal n a "heat-affected zones" adjacent to the cut. Ths may degrade some metallurgcal qualtes at the cut's edge, requrng pre-treatment or trmmng. Secondly, tolerances may be less accurate than a machned cut, except for laser cuttng. Laser cuttng of steel (Fg. ) and alumnum (Fg. ) 9 Steel sheet cuttng by laser Rank Eqn lny=a+bx^(.)lnx r^=.999 DF Adj r^= FtStdErr=.8 Fstat=.99 a=.988 b=-. 9 Laser cuttng of alumnum Rank 8 Eqn y=a+b/x^ r^=.9999 DF Adj r^= FtStdErr=.8 Fstat=8 a= b= Fg.. Steel sheet cuttng speed by laser [m/mn] Fg.. Alumnum sheet cuttng speed by laser [m/mn] Laser cuttng allows metals and some non metallc materals to be cut wth extreme precson f requred. At laser cuttng process, a beam of hgh-densty lght energy s focused through a tny hole of the nozzle. When ths beam strkes the surface of the work pece, the materal of the work pece s cut mmedately. Lasers work best on materals such as carbon and stanless steels. Metals such as alumnum and copper alloys are more dffcult to cut by laser due to ther ablty to reflect the laser lght as well as absorb and conduct heat. Water cuttng of carbon steel Rank Eqn 9 y^(-)=a+b/x r^=.999 DF Adj r^=.9998 FtStdErr=.8 Fstat=9. a=-.98 b=.89 Waterjet cuttng of stanless steel Rank Eqn y^(.)=a+bx^(.) r^=.999 DF Adj r^=.999 FtStdErr=.8 Fstat=9.9 a=-.9 b=.9 Fg.. Waterjet cuttng of steel sheet cuttng [mn/m] Fg.. Waterjet cuttng of stanless steel sheet cuttng [mn/m] Laser cuttng of steel sheets S=/lnT=/(a+bt. lnt) [mn/mm] a= b= -.9 Laser cuttng of alumnum sheets S= /T=/(a+b/t )[mn/mm] (9) a= b= 9.99 Waterjet cuttng of steel (Fg. ) and stanless steel (Fg. ) A water jet cutter s capable of cuttng a wde varety of materals usng a very hgh-pressure jet of water, or a mxture of water and an abrasve substance. Waterjet cuttng, carbon steel bar Waterjet cuttng stanless steel pressure bar S= /T=a+b/t [m/mn] S=/T. =/(a+bt. )[m/mn] () a= -.9 b=.89 a= -.9 b=.98

5 Plasma cuttng of steel (Fg. ) and stanless steel (Fg. 8) Plasma cuttng uses an extremely hgh temperature, hgh velocty stream of onzed gas to cut the metal. Plasma temperatures range from about ºC to 8, ºC. Dependng upon the materal to be plasma cut, the gases used nclude: standard compressed shop ar, oxygen, argon and hydrogen, or ntrogen and hydrogen. Gas sheldng s accomplshed wth ar, water, or carbon doxde. Plasma cuttng of stanless steel Rank Eqn 9 y^(-)=a+b/x r^=.99 DF Adj r^=.999 FtStdErr=.89 Fstat=8.88 a=-.89 b=.8 Plasma cuttng of alumnum Rank Eqn lny=a+blnx/x r^=.98 DF Adj r^=.9 FtStdErr=. Fstat=9.9 a=.8 b= Fg. Plasma cuttng of stanless steel [mn/m] Fg. 8 Plasma cuttng of alumnum [mn/m] Plasma cuttng requres a torch, a power supply, and an arc-startng crcut. Ths plot arc leaves the torch tp as a plasma jet and becomes the path for the man plasma arc. The man arc forms, when the plot arc contacts the metal s surface. The plot arc then shuts off, and the cuttng torch begns operaton. Plasma cuttng of stanless steel S=/T=a+b/t [m/mn] a= b=.889 Plasma cuttng of alumnum S=/lnT=/(a+b/t. ) [m/mn] () a=.98 b= Tme for flattenng plates TFP df ae bet A p aet, () where a e =9.x - mn/mm, b e =.x - mn/mm, df s the dffculty parameter ( df =, or ). The dffculty parameter depends on the form of the plate... Surface preparaton tme The surface preparaton means the surface cleanng, sand sprayng, etc. The surface cleanng tme can be defned n the functon of the surface area (A s [mm ]) as follows: TSP dsasp As, () where a sp = x - mn/mm, ds s a dffculty parameter... Pantng tme The pantng means makng the ground- and the topcoat. The pantng tme can be gven n the functon of the surface area (A s [mm ]) as follows: TP dp( agc atc ) As, () where a gc = x - mn/mm, a tc =.x - mn/mm, dp s a dffculty factor, dp =, or for horzontal, vertcal or overhead pantng. For complcated structures we use k P = x.x - $/mm.... Tmes of hand cuttng and machne grndng of strut ends At tubular structures a man part of the total cost s the cost of hand cuttng and machne grndng of strut ends. We use the followng formula []:. d KCG($), () ( t ). sn

6 where mm/mn s the cuttng speed,. s the effcency factor, d and t are n mm, : φ s the nclnaton angle of a dagonal brace.... Cost of ntumescent pantng Intumescent pantngs are gettng more and more popular, because they look attractve, does not have a bad effect on slm steel structure vew, but the pantng s relatvely expensve [] K p = (k p +k p ) A p, () where the specfc pantng cost k p = $/m, means the normal pantng n two layers (ground and top coat). The addtonal ntumescent pantng cost depends on ts thckness. The thckness s proportonal to the protecton tme. The cost s k p = $/m, for R, half hour, or k p = $/m for R, one hour protecton. A p s the full covered surface.. Total cost functon The total cost functon can be formulated by addng the prevous cost functons together (dependng on the structure some can be zero). K k f K p V T w Tw Tw TFP TSP TP TCG () km km km Takng k m =.-. $/kg, k f = - $/mn. The k f /k m rato vares between - kg/mn. If k f /k m =, then we get the mass mnmum. If k f /k m =. t means a very hgh labour cost (Japan, USA), k f /k m =. and. means a West European labour cost, k f /k m =. means the labour cost of developng countres. Even f the producton rate s smlar for these cases, the dfference between costs due to the dfferent labour costs s sgnfcant. CONCLUSION In ths paper the cost calculaton of dfferent weldng, cuttng, pantng, etc. technologes have been descrbed. These cost calculatons are founded on materal costs and those fabrcaton costs, whch have drect effect on the szes, dmensons or shape of the structure. The calculated tmes for dfferent newer technologes lke laser, plasma, waterjet, etc. have been ncluded also. These costs are the objectve functons n structural optmzaton. Cost and producton tme data come from dfferent companes from all over the world. When we compare the same desgn at dfferent countres, we should consder the dfferences between labour costs. It has the greatest mpact on the structure szes, when the technology s the same. ACKNOWLEDGMENT The research was supported by the TÁMOP...A/---- prorty project enttled Natonal Excellence Program - Development and operaton of domestc personnel support system for students and researchers, mplemented wthn the framework of a convergence program, supported by the European Unon, co-fnanced by the European Socal Fund. The research was supported also by the Hungaran Scentfc Research Fund OTKA T 98 projects and was partally carred out n the framework of the Center of Excellence of Innovatve Engneerng Desgn and Technologes at the Unversty of Mskolc. REFERENCES [] Farkas J., Járma K. (99) Analyss and Optmum Desgn of Metal Structures. Balkema Publshers, Rotterdam, Brookfeld, p. ISBN 9 9 [] Farkas J., Járma K. () Economc desgn of metal structures, Mllpress Scence Publsher, Rotterdam, p. ISBN 9 99 [] Farkas J., Járma K. (8): Desgn and optmzaton of metal structures, Horwood Publshers, Chchester, UK, 8: 8. ISBN: [] Farkas J., Járma K. () Optmum desgn of steel structures. Hedelberg, etc. Sprnger.. 88 p. ISBN