Improvement of Boss Tower for Single Ball Swaging in Hard Disk Drive

Transcription

1 Intenational Jounal of Scientific and Reseach Pulications, Volume, Issue 11, Noveme 01 1 ISSN Impovement of Boss Towe fo Single Ball Swaging in Had Disk Dive Joompondej Bamungwongtaee *, Mongkol Mongkolwongojn ** * College of Data Stoage Innovation, King Mongkut s Institute of Technology Ladkaang, Thailand ** Mechanical Engineeing Depatment, King Mongkut s Institute of Technology Ladkaang, Thailand Astact- Ball swaging is a mateial pocess used to assemle a oss towe and an am apetue. A swage all is inseted into the oss towe to swage and couple two components. The swage all has a lage diamete than an inne diamete of the oss towe, applies a compession foce to the inne suface of the oss towe to hold oth components togethe with adequate holding foce and without damaging the oss towe. This study poposes a new design of the oss towe y elief ing width optimization. It educes the am tip defomation while avoiding HSA esonance and allows simila swaging quality y using single all. The 3-D FE method was used fo analysis. The esult analysis and expeiment show oss towe defomation vey simila. Although the vaiation of CTQ has een deceased, cleanliness has een impoved. Moeove, non-cicula am apetue is ale to educe swage effect. Index Tems- Ball Swaging, Finite Element, Head Stack Assemly, Space Key, Boss Towe I I. INTRODUCTION n the had disk dive (HDD) manufactuing pocess, all swaging has long een a common pocess. The pocess assemles the Head Gimal Assemly (HGA) ase plates with actuato am called the head stack assemly (HSA). A ase plate includes a flange having a top suface and an opposing second suface; and a oss towe having a swage hole and extending fom an aea whee the oss towe meets the top suface of the flange to an end suface of the oss towe. The ase plate is a component of a swage coupling assemly that is coupled to a component having an am apetue as shown in Figue 1. The Figue shows the configuation of the oss towe and the figue 3 shows seveal types of the oss towe pofile which consist of asic components. Duing the swaging pocess, the all is inseted though the oss towe to swage couple the oss towe to the am apetue that clamped y swage keys. The swage all applies a compession foce to the inne suface of the oss towe, theefoe the oss towe expands to hold the second component to the fist component with adequate holding foce and without damaging the oss towe. The ase plate and am tip defomation cause an effect to many Citical To Quality paametes (CTQ). () Figue 1: Components of a ase plate and () the Head Stack Assemly fo swaging pocess

2 Intenational Jounal of Scientific and Reseach Pulications, Volume, Issue 11, Noveme 01 ISSN Figue : Configuation of the Boss Towe A = Boss ID, B = Boss OD, C = Backoe Dia., D = Boss Height, E = Relief Ring, F = Top Tansition Angles, G = Bottom Tansition Angles, H = Back Angles and I = Backoe chamfe Figue 3: Boss Towe pofiles At pesent, the had disk dive (HDD) capacity is dynamically inceased while its size ecomes slimme and the ead-wite head was tightened to move on the media. To educe the swage effect of the new am pad and head gimal designed, all the configuation of the oss towe can e studied to educe deviation afte swaging pocess. The high defomation has occued whilst the all was passing though the oss towe as simply shown in Figue 4. The swaging pocess esults in elastic-plastic defomation of oss towe and actuato am hole. This defomation can cause distuance in desied sping chaacteistic of the suspension on the actuato am, known as the gamload changes fom its design value, and change to desied toque out. Since gamload and toque out ae the citical paametes affecting the slide flight height and op-shock pefomance of had disk dives, investigating the swaging pocess that induced ase plate and am defomation, HSA popety and toque out change ae of main focus. Howeve, it is necessay to claify the dimension of the oss towe pofile to educe swage effect and fo single all swaging. The fist study, Wadhwa [1] analysed the all swaging pocess using an axially symmetic model, and Kittipong [] numeically veified the defomation of the entie am and HGA ut the accuacy of the simulation has yet to e veified though expeimentation. Aoki and Auga [3] analysis using a thee-dimension finite element was ased on a symmetical model fo an actuato inne am and two attached ase plates. These studies povide a ette undestanding of the ase plate defomation. In Jian Yang [4] s analysis using a thee-dimension finite element to study gam load changes, helps to undestand the elationship etween defomation and gam load changes. Some ecommendations on having a space key to educe swage effect and esonance analysis y thee dimensional finite element analysis model wee given [5-8]. Athena Jiao et al. [9] found that the all size intoducing a 15% defomation is pefeed fo esonance pefomance. The aim of this eseach is to study the effects of the oss towe paametes and to optimize the use of single all swaging pocess. The cuent oss towe will e developed to e used fo a single all in swaging pocess. The swaging pocess is investigated y pefoming explicit dynamic finite element analysis (FEA) using a commecial pogam ANSYS/LS-Dyna [10]. Initial study is on an am coupon and validation then move into expeiment with ten ase plates and six ams in the assemly as a pototype in actual pocess. The clamping foce in a single all swaging pocess is consideed constant; its velocity emains constant in the top-to-ottom diection. II. GOVERNING EQUATION The Figue 4 shows the diagam of the swaging stuctue. Inheently, the swaging pocess is a sophisticated polem of metal tansfomation involving thee ojects which includes ase plate, am and swage all that ae diffeent in shape and mateial popeties. Thus, the complete model fo the swaging pocess would e extemely complicated and will e affected y a nume of paametes. Many factos ae involved which all contiute to the shift of the HSA chaacteistics. In this pape, the focus is on how to use a oneall to assemle HSA while maintaining the HSA chaacteistics. Many paametes elatively wee vaied.

3 Intenational Jounal of Scientific and Reseach Pulications, Volume, Issue 11, Noveme 01 3 ISSN () Figue 4: Swaging schematic () Am apetue model as thick cylindes The govening equation of swaging pocess can e witten in equation 0 (1) and d 4 d 3 1 d 1 d 0 () d 4 d 3 d 3 d Whee and ae adial and cicumfeential stesses espectively and is the Aiy's stess function is in the fom log (3) To simplify the theoetical model and make it is easonale, the defomation occuing in the swaging pocess is consideed as thick cylinde as shown in Figue 4(). In asence of ody foce fo this axisymmetic, Lame fomula can e used hee to calculate the stess geneated at diffeent locations [9]. pa P ( p P) a 1 (4) a a pa P ( p P) a 1 (5) a a The displacement can e deived using the fomula elow. 1 (1 )( pa P ) (1 ) a ( p P) u (6) E a a With Tesca ules applied [9], then futhe elationship can e deived, mateial will egin to yield when max, the maximum shea stess, is equal to y the yield stess. Since and ae pincipal stesses, yielding will egin when (7) max y Now define a adius p so that egion a p is in the plastic egion and p is in the elastic egion then otain p log p ; a (8) y p p The all size will affect the inne pessue applied to the oss towe and then futhe engage to an am hole. The elationship etween all size and the inne pessue foce is as well as the degee of plastic defomation of ase plate and oss towe. In the actual swaging pocess, the ase plate's oss towe is moe complicated than in the simulation. Thus, the finite element analysis will e used to study fo the single all swaging to appoach this ehaviou. III. SWAGING NUMERICAL MODEL The finite element simulation of a single all swaging pocess was pefomed with the commecial softwae package. The explicit dynamics simulation, the equiliium equations in dynamic analysis can e witten in the fom ( i) ( i) ( i) M u F I (9) whee [M] is mass matix, F is the vecto of extenally applied load and I is the vecto of inetia foces. The mathematically equiliium elation is a system of linea diffeential equations of second ode. The solution can e otained y finite diffeence expession to appoximate the acceleations and velocities in tems of displacement which can e witten as

4 Intenational Jounal of Scientific and Reseach Pulications, Volume, Issue 11, Noveme 01 4 ISSN ( i) 1 ( i 1) ( i) ( i 1) u u u u (10) t The eo of calculation depends on stale incement of time as the elation is shown elow L t min c (11) stale c whee L c is limited element edge length and c is velocity of longitudinal wave fo an element is in the fom c (1) and µ is Lame' constants can e witten in tems of young's modulus and passion atio as follows E ( 1)(1 ) E (1 ) The stale time expession mentioned fo only one element in pactically the LS-DYNA solve automatically calculates the minimum time step fo each element ased on its chaacteistic length and density. The smallest of these element time steps is called the citical time step. The actual time step used duing solution is the poduct of the cuent citical time step and a staility facto (usually 0.90). As elements distot duing the analysis, thei time steps ae ecalculated. Howeve, an element s time step is calculated ased on its mateial popeties (E,,) and chaacteistic length. The equation can e eaanged to find the equied density of each element fo a desied time step size. By adding the coesponding mass to these elements, the solution time will e educed. This pocedue is known as mass scaling and not ecommended. In this pape, mass was not added to speed up un. A thee-dimensional (3-D) and a coss-sectional view of the finite element (FE) model used fo swaging pocess of actuato ams ae shown in Figue 5 and 6. (13) (14) Figue 5: Fou ase plate and thee ams in the assemly fo swaging simulation Figue 6: Coss-sectional view of fou ase plates and thee ams in the assemly fo swaging simulation The swage toque out afte the all is diven though the oss towe the ase plate and attached suspension was secuely fastened to the actuato am pad. The equation of swage toque can e deived fom T F (15) Whee F N (16) And now sustitution eq. (16) into eq. (15) got L T P d (17) 0 N e Simplify the eq. (17) otain

5 Intenational Jounal of Scientific and Reseach Pulications, Volume, Issue 11, Noveme 01 5 ISSN D T PA (18) N e whee T is HGA toque out, is coefficient of fiction, P is contact pessue, D is a diamete of swage hole, and N e is the nume of engaged element. Pactically, an aveage pessue and contact aea sustitution in (18) to otain HGA toque out. Howeve, cuent pocess has standad swage and mico-swage; the swage toque out elation of oth can stat fom (15). Fo standad swaging, T F (19) s s s Whee F then s s s T (0) s s s Solving fo µ T s (1) s As fo mico-swage stat fom eq. (15) Solving fo µ Fom Eq. (1) and (3) otain Thus T F () ms ms ms T ms (3) ms T T s ms (4) s ms T s T (5) s ms ms Equation (5) is theoetical mico-swage flange effect compaison whee T s is standad HGA toque out, T ms is mico-swage HGA toque out, s is adius of standad swage, ms is adius of mico-swage. In this analysis, a nonlinea explicit dynamics analysis is pefomed. The swaged pat of the ase plate undegoes plastic defomation. Nonlinea mateial popeties ae consideed. To save time consumption, the model is pesented with thee actuato am tip, fou ase plates with pat of hinges, fou swage keys, and one swage all. The inne space key was sepaated to two pat of assemly fo specific analysis, as shown in Figue 6. As fo the expeiment, six ams with ten heades ae used. IV. BOUNDARY CONDITIONS AND CONTACT SURFACES Duing the swaging pocess, the constant clamping foce at the oute key pats duing swaging is constant and the ams ae sepaated fom each othe y the space keys. In the FE model, the clamping pessue is applied as foces via foce load cuve. In othe wods, the swage keys, which ae employed to simulate the clamping ounday at the am contact condition, ae patial modelled as igid odies and does not include space key s tail while the othe components including actuato am tip, ase plates and hinges ae defomale pats. The simulation uses the same load cuve fo all speed fo each heads and swage all; and is foced to move in Z diection only accoding to its load cuve. The oss towe of the ase plate is plastically defomed and joined to the am. The contact suface etween the all and swaging oss, etween the ase plate and the am, and the one etween swaging oss and the clamp ae taken into account in analysing the oss am foce. The fiction coefficients fo each contact suface ae divided into two goups, contact suface of assemly and pat-to-pat contact. The ase plate, hinge and the suspension ae made of stainless steel while the am is made of aluminum. The swaging all is made of stainless steel with hadened coating. Thus, the all is simulated as a igid ody. The mateial models defined in the analysis ae ilinea isotopic mateial and i-linea kinematics hadening. The popeties of the mateials used in the simulation ae listed in Tale 1. The inteesting aea will e defined as component name to ecall in post pocesso. All the elements used in the analysis ae eight-nodes ick elements. To futhe educe the computing time, the model consists of oth igid odies and defomale odies. The actuato am hole and the ase plate s oss towe ae pepaed and that the fine meshes ae only equied in the vicinity of the contact aeas and the elements ae coase in the aeas fathe away.

6 Intenational Jounal of Scientific and Reseach Pulications, Volume, Issue 11, Noveme 01 6 ISSN Tale 1: Mateial popeties fo finite element analysis Mateial Popeties Type of Mateials Stainless steel Aluminum Elastic modulus, E (MPa) 190,000 71,016 Yield stess, Y (MPa) Poisson atio Mass density (kg/m 3 ) 7,889,700 V. FINITE ELEMENT MODEL VALIDATION The oss towe and am tip defomation esults fom FEA simulations fo inne and oute ams ae evaluated fom the displacements value that measued fom specific nodes compaed to the efeence plane. Fo all simulated cases, the esults have tendency to value fom expeimental data with stictly contol the incoming pat. Howeve, the focus is on the effect of the oss towe to maintain the HSA chaacteistics with single all which accompany with cost saving, thee ae some offset that must e contolled. These diffeences could e fom some othe effects that wee not consideed in the pesent analysis fo sample swage shuttle. The illustation of oss towe defomation fom swaging pocess is shown in Figue 7 and 8. Figue 7: DN Facing head () UP Facing head compaison oss towe X-section defomation and Veeco scan () () (c) Figue 8: Head #3 () Head #1 and (c) Head #0 compaison oss towe X-section defomation

7 Intenational Jounal of Scientific and Reseach Pulications, Volume, Issue 11, Noveme 01 7 ISSN VI. RESULTS AND DISCUSSIONS In this study, the ehavios and chaacteistics of the ase plate's oss towe pofile afte a completed swaging pocess ae studied. Tale shows compaison etween simulation and expeimental esults. This pape pesented the esults of sceening paametes on pocess optimization of key paametes fo single all swaging. The optimal paamete setting yield the optimum pefomance with thee paametes afte seeening fom nineteen paametes. In this case, these paametes ae main effect of the paamete vaiation. The main paametes that affected HSA chaacteistics ae the ase plate elief ing width oth DN and UP Ta as shown in Figue 9. Tale : Simulation and expeimental esults Paametes Tip Height (inch) Tip Pitch (degee) FEA esult Actual data FEA esult Actual data Head 0 Oute am Head 1 Inne am Head Inne am Head 3 Oute am Figue 9: Main effect plot fo DN Ta, Tip_Ht () UP Ta, Tip_Ht Afte the effects of thee paametes i.e oss height, elief width and elief depth wee sceened fom nineteen paametes, the esult fom the simulation will e used fo optimal facto setting. The optimum paamete is shown in the Figue 10. The othe two paametes wee fixed at the same condition to find the pope elief ing width. Oviously fom expeiment, lage elief ing width povides toque out a it highe oth two tas fo oute am and compaale with the middle am. UP ta should e small elief ing width. On the othe hand, DN ta should e lage. () Figue 10: Optimization UP Ta () DN Ta

8 Intenational Jounal of Scientific and Reseach Pulications, Volume, Issue 11, Noveme 01 8 ISSN Fom this analysis, it leads to new design of the oss towe y elief ing width optimization. A elief ing is not identical width which distance A is moe than that B as shown in Figue 11. Figue 1 shows coss section of the optimal elief ing width. Moeove, this design is ale to avoid HSA esonance (Nyquist fequency of using 56 sevo sectos) simila to using loctite HGA to am. The expeimental esults eveal that the fequency shifted fom 11kHz to 1kHz. The actual pat of HGA toque out, actual coss section, the actual HSA fo ten heades ae studied and tested and those esults eveal that am tip defomation is educed as shown in Figue 13. The HSA ten heade with single all swaging was tested the esonance of FRF, the esult ae acceptale and shift the 11.5kHz to lowe fequency to avoid esonance. Also found that the single all swaging pocess fo ten heades appoach to KPIV chat model. The effects of swage shuttle, space key land on swaging pocess will e used as STX DFM. Figue 11: Optimal elief ing width A B B A B Coss Section A Coss Section Figue 1: Coss section of the optimal elief ing width () Figue 13: Relief ing width Optimized cause less defomation oth TAB UP and DN () Non-Optimized

9 Intenational Jounal of Scientific and Reseach Pulications, Volume, Issue 11, Noveme 01 9 ISSN VII. CONCLUSION In this pape, the ehavios and chaacteistics of the ase plate's oss towe pofile wee studied. The analysis eveals that the elief ing width should e a main focus when using single all in swaging pocess. The analysis leads to a new design of the oss towe y comination of optimal elief ing width togethe. Figue 11 illustates a schematic diagam of a peimete of elief ing. In paticula, Figue 1 and 13 illustate how the peimete vaies fom a minimum compession foce to a maximum compession foce. The expeimental esult also shows that the am thickness is not elated to HGA toque out. Still, the impact to am tip defomation leads to esonance fequency. The new design of oss towe is ale to apply with thin am fo eduction of the am tip defomation. Fom analysis, the elief ing depth excessive esults in flange effect. A small top tansition angle can educe the oss towe defomation. The vey low ottom tansition angle esults in swage push out defect. The ackoe diamete is used fo oss towe hinging. Although elief ing is mainly a potential impact to HSA quality, fo a single all swaging, not only elief ing is impoved, in actual pocess some paametes also ae slightly adjusted to keep HSA chaacteistics CTQ and swage push out is deceased; thus a contact angle is ecommended. Back oe chamfe is equied to educe suspension weight, ight angle can e ignoed fo ack oe. When e-wok is consideed, thee is no impact to the installed head due the same all size is used and just passed though. Howeve, HSA lowe heade has lowe impact to HSA chaacteistics ecause long distance has moe chance to face swage damage if all speed is inceased. The dimension of space key land should e contolled to ensue that othe defect will not occued duing swaging pocess. Fom eq. 5, with STX oss towe the standad swage has HGA toque out appoximately two times of mico-swage. ACKNOWLEDGMENT This study is suppoted y Coopeate Poject etween National Electonics and Compute Technology Cente (NECTEC) and Seagate Technology (Thailand) via Industy/Univesity Coopeative Reseach Cente (I/UCRC) in HDD Component, King Mongkut s Institute of Technology Ladkaang. REFERENCES [1] S.K. Wadhwa, Mateial Compatiility and Some Undestanding of the Ball Swaging Pocess, IEEE Tansactions on Magnetics, Vol. 3, No. 3, 1996, pp [] E. Kittipong, C. Suachate, K. Thoatsanope, Effects of Swaging Pocess Paametes on Specimen Defomation, Eighth Asian Symposium on Visualization, Chiangmai, Thailand, 005, pp [3] K. Aoki and K. Auga, Numeical Ball Swaging Analysis of Head Am fo Had Disk Dives, Micosyst. Technol, Vol. 13, 007, pp [4] L. Chen-Chi, Y. Jian, and Ti. Shaha, Finite Element Simulation of Ball Swaging Pocess of Jointing HGA With Actuato Am and Gam Load Calculation, ASME Infomation Stoage and Pocessing Systems Confeence Santa Claa, CA. [5] B. Joompon, Effect of the Space Key on Swage Push out, Intenational Confeence of Business and Industial Reseach, Bangkok, Thailand, Mach 010.Bangkok, Thailand. [6] B. Joompon, Effect of the Space Key to HAS, 3 d Intenational Confeence on Data Stoage Technology, Bangkok, Thailand, 010, pp [7] B. Joompon, Study of Oute Key to Reduce Oute Am Swage Effect, Joint Intenational Confeence On Infomation & Communication Technology Electonic and Electical Engineeing, Luangpaang, Lao PRD, 010, pp [8] B. Joomponladej, A Development of modeling fo Resonance Analysis, 4 th Intenational Confeence on Data Stoage Technology, Bangkok, Thailand, 011, pp [9] A. Jiao, Z. Liu, L. Pan, M. Ying, Swaging Foce Contol in Dive Resonance Response, IEEE Tans. Magnetic Recoding Confeence, Singapoe, 009, pp. BS04 [10] Livemoe Softwae Technol. Cop. LS-Dyna Theoy Manual, Livemoe, CA, 006. AUTHORS Fist Autho Joompondej Bamungwongtaee, M.Eng, King Mongkut s Institute of Technology Ladkaang, joompondej.amungwongtaee@seagate.com. Second Autho Mongkol Mongkolwongojn, Ph.D (Mechanical Engineeing), King Mongkut s Institute of Technology Ladkaang, kmmongko@kmitl.ac.th Coespondence Autho Pattaaweein Woaatsoonton, oaw50@hotmail.com, jome@hotmail.com, (66)