Investigation On Head Disk Contact And Fretting Wear Simulation At The Dimple Gimbal Interface

The requirements of information storage density and safety increase with the increasingdevelopment of information technology. The gap between a slider and a disk is becomingsmaller and smaller in an ultra-high density disk. The current flying height is on the order of afew nanometers. The load, un-load, flying and searching performance of the slider will causethe un-stability of the head gimbal assembly, inducing a reciprocate micro-displacement at thedimple/gimbal interface. The reciprocate displacement is treated as fretting wear, whichaffects not only the dimple/gimbal interface but also the flying ability of the slider. In addition,contamination particles are more like to generate and cause serious contact at the head/diskinterface, which will damage the mechanical components disk surface, causing un-restoreddata lost. The head/disk contact is more likely to happen since the head/disk gap is only a fewnanometers if there is an impulsive force. The contact will accelerate the damage of thedimple/gimbal interface. If a hard disk drive is filled with helium instead of air, the dampingeffect is reduced due to helium density is far smaller than air. In this case, larger contact forceat the head/disk interface will be happen compare to air filled disks.Through the literature searching, little information is available about the contact of thedimple/gimbal interface induced by slider/disk contact, especially in helium environment.Therefore, a finite element suspension model, an air bearing model and a slider/disk contactmodel are combined to investigate the contact and friction forces at the dimple/gimbalinterface, especially when the slider and disk contact happens. The effect of dimple materialon the dynamic response of the dimple/gimbal contact is studied as well. The results showthat the contact and friction forces reach their maximum when the slider/disk contact happens.These maximum forces can be used for the fretting wear experiment and simulation as inputparameters.One of the newest technologies of hard disk drives is the helium-filled drives. Instead ofusing pure helium, the using of helium-air gas mixtures is proposed. The physical propertiesof the helium-air gas mixtures are first studied. The slider/disk contact model with surfaceroughness is implemented into the air bearing simulator. The slider dynamic flyingcharacteristic and the slider/disk contact performance in different helium-air gas mixtures areinvestigated. In this simulation, a new design air bearing surface was meshed and the finiteelement method is used to calculate the air bearing pressure and the flying height of each node.The effect of disk velocity on the slider/disk contact in a50%helium50%air gas mixture issimulated. The results show that the helium-air gas mixtures can provide enough damping when there is an external force applying on the slider. Thus, smaller contact force at theslider/disk interface is obtained.An experimental set-up for micro and nano-scale displacement was built. The frettingwear of the dimple and gimbal under different normal loads were carried out and the effect oflaser polishing on the fretting wear results is studied. Using the measurements from a load celland two Laser Doppler Velocimetries, friction-displacement loops and friction coefficient as afunction of the number of fretting wear cycles are obtained. The dimensions of wear scars ondimples were measured by scanning electron microscopy and the wear volume is calculated.The results show that normal load determines fretting wear regime, leading to differentsurface failures. The effect of laser polishing on the dimple/gimbal fretting wear can beneglected if the normal is small. However, if the normal load is bigger and the fretting weartime is longer, laser polished dimple can reduce the wear volume.The two-dimensional fretting wear model of the dimple and the gimbal was built. Thefriction coefficient and wear coefficient obtained from the experimental results areimplemented in this model. Local wear depth of each node is calculated using the modifiedArchard’s wear equation. An optimal fretting wear incremental cycle is determined and thesimulation time is greatly reduced. The model can be used to predict the wear profiles, thecontact pressure and the stress distribution of the dimple and the gimbal under differentnormal loads. The results show that the trends of the simulation are similar to theexperimental results. However, the relative error is big. In this case, the model can be used toqualitatively investigate the effect of geometric and material parameters on the dimple/gimbalfretting wear behavior due to the less calculation time.Based on the two-dimensional model, a three-dimensional model for the dimple and thegimbal fretting wear is built. A new local wear equation is deduced; a coordinates updatingmethod for the finite element model is suggested and an adapted fretting wear incrementalcycles is first proposed. Using these methods, it is possible to calculate the three-dimensionalfretting wear model on a normal computer. The model can accurately predict the wear profilesof the dimple and the gimbal. Comparing with the experimental results, the relative error isonly8.5%. Therefore, the simulation results can be a useful guidance for the dimple andgimbal design.