Study Of Lapping Mechanism In Super Precision Finishing Of Hard Disk Recording Heads With Multiplex Surface

The material of the substrate of GMR(giant Magnetic resistance) magnetic recording head for hard disk is A1TiC,while that of the read/write part is metal or alloy.Moreover,the read/write part consists of many thin layers of film,and the thinnest layer of it is only 1 nm or so.Besides,the structure of the GMR recording head is very complicated.The surface quality of recording head,such as surface roughness,pole tip recession(PTR)etc,are the main factors that hinder the improvement of the storage areal density of the head.Up to now,the technology of precision finishing of recording heads for hard disk was controlled by several foreign companies,and the open literature about the technology is very rare.To master the lapping technology and make technical innovations,it is important to study and understand the lapping mechanism.Therefore,the forming and controlling process of roughness and PTR of the heads' surface was studied in this research.The main study process and results are list as follow.1.The experimental apparatus for lapping of GMR recording heads was build up.The relative movement of the recording heads and the lap in lapping process was investigated.The optimizing relative track of the heads to the lap was achieved with simulating methods.The relation of the angle velocity of the recording heads and the lap is supposed to as follow:ω₁-ω₂≠0.1nω₁ n=0,1,2……,Otherwise,a super smooth surface can't be achieved for the track of the abrasive will be repeated or singularity.Besides,the relations between performances of material even removal of the recording heads' surface and the rotate speed ratio of recording heads and lap was investigated.Furthermore, the effect of the rotate speed ratio of recording heads and lap on the performing parameters was investigated.2.The workpiece and the lap is a friction pair in the lapping process. According to the theory of tribology,the contact relation between the workpiece and the lap was researched.Furthermore,the distribution of the field the slurry fluid and the effect of it on the contact stress field of 'wokpiece-lap' was reaserached.Besides,the motion law of abrasive and the mechanism of abrasive embeded in the lap was reaserached.It is found that the rotate speed ratio of the workpiece and the lap effect the variety of the speed field of the interface of the workpiece and the lap.While the speed filed of the interface effect variety of thickness of the slurry film and carring capacity of the asperities.The abrasive will be embedded in the lap when the earring capacity is changed frequently.3.The effect of the contact pressure,the lap profile and the size of the abrasive of the slurry on the material removal rate is investigated.On account of the monocrystalline used in the lapping process,the statistic material removal mode for rhombus abrasive was established,and the result accord with the experiment.4.The material removal process of nanogrinding and the forming process of sub-nanometer smooth surface were investigated.According to theory of contact mechanics,a type of 'sphere-cavity' harmonious contact was formed between the plate and the diamond abrasive embede in the plate,which is different from the general hertz contact.A 'sphere-cavity' harmonious contact mode was established.At first,the abrasive recessed in the cavity in elastically way,as the increased of the contact pressure,the abrasive recessed in the cavity in plastically way gradually,the material removal ability is determined by the critical value of the transition.It is demonstrated that the removal of the uncontinuous asperities is the main removal way in nanogrinding,while in the free abrasive lapping and grinding,the material is removed in a layer. 5.The mechanism of the pole tip recession was investigated.The PTR formed in free abrasive lapping is related to the parameters of the plate profile, contact pressure,the size of the abrasive and the rotate spee of the plate.The PTR can be reduced when the suitable roughness of the plte,the density of the asperity of the plate and the curvature radius of the asperity is selective.The roughness of Rms is reduced to 0.26nm from 0.61nm and the PTR is reduced to 1.22nm from 10nm or so by used medial size nanometer diamond, meanwhile,the blemish and the nicks of the surface was eliminated.6.The lapping with ultrasonic is investigated.The ultrasonic was introduced into the free abrasive lapping process,smoother rocording heads' surface was achieved and the PTR was reduced obviously.The material removal rate of the substratd is increased from 10nm/m to 16nm/m.the macroscopical and microcosmic mechanism of the ultrasonicin the lapping was studied.7.The chemical action was introduced into the nanogriding process. Sub-nanometer PTR was achieved,meanwhile,the blemish occurred by materials transition was eliminated thoroughly.Especially,the pole tip and the GMR were not damaged.