Laser Bump Research Articles

Effect of laser bump texture combination characteristics on friction-wear properties of roll surface

PurposeThe purpose of this paper is to find the influence of surface bump texture combination characteristics on friction-wear properties so as to provide a basis for the selection of the bump texture combination scheme on the surface of the roll.Design/methodology/approachIn this paper, six groups of different bump texture combination characteristics and their processing methods are introduced, of which three groups are regular distribution with different spacing and three groups are random distribution with different spacing. Then the effect of bump textures with different spacing, regular and random distribution on friction-wear properties was studied by ring block friction-wear experiments.FindingsThe results show that the friction coefficient of random distribution texture surface is lower than that of regular texture surface under the same spacing condition. In the regular distribution, the friction coefficient decreases with the increase of texture spacing. In the random distribution, the friction coefficient increases at first and then decreases with the increase of texture spacing. In addition, the wear resistance of textured surface is significantly higher than that of smooth surface because of the higher microhardness of the textured area. The attenuation ratio of textured surface roughness decreases with the increase of the distance between adjacent textures.Originality/valueAt present, the research on roller surface friction-wear is mainly based on the change of the overall surface roughness. However, there are few reports on the influence of the combination characteristics of laser bump texture on friction-wear from the microscopic scale.

Research on the influence of laser molten pool flow and evaporation on the bump texture forming of aluminum plate surface

At present, the research of laser texture mainly focuses on the machining quality and its properties, but the forming mechanism of laser bump texture surfaces is relatively less studied. In this paper, a long pulse laser ablation model was established based on the laser molten pool flow and evaporation phenomena by numerical simulation. And the evolution mechanism of bump texture morphology on metal surface during laser irradiation time was studied. The results show that the bump texture morphology shows edge protrusions and central depressions, and in the cooling stage, under the action of surface tension, the concave and convex height will show a rebound phenomenon. At the same time, the influence of laser parameters on the morphology of laser bump texture was studied by experiments. By comparing the numerical simulation with the experimental results, it can be found that when the laser irradiation time is equal to 0.5 ms, the morphology obtained by numerical simulation is close to the experimental results. In addition, the differences of pressure field and velocity of vaporized metal gas at different time and under different laser power are compared. Finally, the plasma on the surface of aluminum during laser machining captured by a high-speed camera indirectly indicates that the evaporated metal gas ionizes and forms a stable plasma layer floating above the target material.

Analysis of magnetohydrodynamic partial slip laser bump texture slider and journal bearing

A model of magnetohydrodynamic partial slip laser texture bearing (slider and journal) is developed. The influence of laser bump texture and slip laser texture partial configuration on the magnetohydrodynamic performance analysis of bearing is presented. An electrically conducting fluid is confined to bearing surfaces under uniform magnetic field perpendicular to slider bearing and inclined to the line of maximum film thickness to journal bearing. A one-dimensional analysis based on the narrow groove theory is considered to evaluate the nondimensional pressure distribution in bearing. Results of the nondimensional load capacity and coefficient of friction of magnetohydrodynamic partial laser bump texture and partial slip laser texture bearing configurations are analyzed. Partial slip configuration under MHD lubrication without laser bump texture brings in the performance improvement.

Watt-level passively <i>Q</i>-switched mode-locked Tm: LuAG laser with graphene oxide saturable absorber

A watt-level passive Q-switched mode-locked operation in Tm: LuAG all-solid-state laser is realized for the first time by using graphene oxide (GO) saturable absorber as a mode-locked starting element. The laser is pumped by a wavelength tunable Ti: sapphire laser operating at 794.2 nm. In this experiment, the maximum continuous-wave (CW) output power of 1440 mW, 2030 mW and 2610 mW are obtained by 1.5%, 3% and 5% output coupled (OC) mirrors respectively, in which the corresponding slope efficiencies are 22.3%, 32.6% and 40.6%, respectively. When the GO is inserted into the cavity, the laser bump threshold is further increased due to more intracavity loss. With a 1.5% OC mirror, the absorbed pump threshold is as low as 325 mW, the maximum output power is 787 mW, and the corresponding slope efficiency is 12.5%. With a 3% OC mirror, the absorbed bump threshold is 351 mW, the maximum output power is 1740 mW, and corresponding slope efficiency is 30.3%. With a 5% OC mirror, the QML operation is not realized due to the increase of intracavity loss. Although the laser pump threshold power of 3% OC mirror differs from that of 1.5% OC mirror by 26 mW, the output power is more than twice higher than that of 1.5% OC mirror. For these reasons, we use a 3% OC mirror in our experiment. In this case, a stable QML operation with a threshold of 3420 mW is obtained. When the pump power reaches 8.1 W, the corresponding maximum output power is 1740 mW, the central wavelength is 2023 nm, the repetition frequency is 104.2 MHz, the maximum single pulse energy is 16.7 nJ, and the modulation depth is close to 100%. According to the symmetrical shape of the mode locked pulse and considering the definition of rise time, we can assume that the duration of the pulse is approximately 1.25 times the pulse rise time. So the width of the mode locked pulse is estimated at about 923.8 ps. The results show that the GO is a promising high power saturable absorber in 2 μm wavelength for the QML solid-state laser. In the next stage, we will increase the pump power, optimize the quality of the GO material, and compensate for the dispersion in the cavity. It is expected to achieve a CW mode-locked operation and femtosecond pulse output.

Ultra-fast Movies Resolve Ultra-short Pulse Laser Ablation and Bump Formation on Thin Molybdenum Films

Abstract For the monolithic serial interconnection of CIS thin film solar cells, 470 nm molybdenum films on glass substrates must be separated galvanically. The single pulse ablation with a 660 fs laser at a wavelength of 1053 nm is investigated in a fluence regime from 0.5 to 5.0 J/cm 2 . At fluences above 2.0 J/cm 2 bump and jet formation can be observed that could be used for creating microstructures. For the investigation of the underlying mechanisms of the laser ablation process itself as well as of the bump or jet formation, pump probe microscopy is utilized to resolve the transient ablation behavior.

Laser Zone Texture Design for Padded Slider on Magnetic Storage Media

This study investigates the tribology performance of padded sliders on different designs of laser zone texture in comparison with that of conventional slider. A one-sided change in the laser bump parameter will not satisfy tribological requirements. Optimization of stiction and micro-wear should be an important consideration in LZT design and padded slider design. It is found that the padded slider design combined with an optimized laser zone texture exhibits lower stiction during CSS testing than a conventional slider for the same laser texture design. With the use of a padded slider, media can be designed with lower laser bump height, hence lower glide height, while maintaining excellent tribology performance. Of particular interest was stiction caused laser bump crashes that occurred in a hot/wet environment. On the other hand, increasing pad numbers is also another feasible way to solve these issues

A novel textured design for hard disk tribology improvement

A novel textured design with characteristics of low glide avalanche, low stiction and long wear durability has been studied. The novel textured design contains a normal laser process and mechanical texture process. The first step was to create the conventional crater circular laser bump, the second step was to modify the bump shape using different sizes of texture slurry. The mechanical texture consists of three-stage process from grinding bump rim to flatting bump rim. This novel bump design has large volume and small curvature of bump rim to minimize the level of impact between head and disk. The new design also has high roughness of bump rims to reduce the contact area of interface, and the grooves of the texture line on the bump rim providing paths to improve the reflow of lube. We have shown that the new design has the lower stiction, longer wear durability, less lube degradation and carbon overcoat wear, less probability of tipping occurrence and lower glide avalanche than that of the conventional design.

A novel laser bump design for low glide/low stiction disk

The effects of different geometry of the laser bump in contact start/stop (CSS) and glide avalanche performance were investigated. Traditionally, a lower laser bump height can reduce the glide avalanche, but if the height is lower than a specific value there will appear a “stiction barrier‘’. In order to overcome this barrier, a novel design of obtaining cavities on the disk is proposed. In this design, changing the depth and relative position of the laser bump can obtain a lower stiction and glide avalanche. The effects of lubricant film thickness and environmental temperature/humidity were also observed.

Study of media design on acoustic emission and take-off velocity by using the Taguchi method

This paper presents the results obtained from the optimization of disk design parameters to achieve the less acoustic emission (AE) signal and take-off velocity (TOV), and the steady and less stiction performance by using Taguchi experimental design with a four-factor three-level (L9) orthogonal array. The factors considered were laser bump height (BH), bump spacing (BS), overcoat type, and lubricant thickness. BH is the most significant factor and its percentage contribution is 86% on AE signal and 72% on TOV, respectively. The lower AE signal was obtained from the higher BH, lower BS, and lower lubricant thickness, over the design range. On the other hand, the lower TOV was obtained from the lower BH and lower BS. Overcoat type is not a significant factor to affect the AE signal and TOV.

Calibration of sub-10-nm flying height using the bump response

This paper presents a study on the calibration of sub-10-nm fly height of slider by detecting slider response to laser bump with known height. The PZT sensor signal was applied to identify the slider air bearing resonance and slider body resonance. By comparing the signals from these two sources, improper measurement results due to the uncertainty of slider-bump response process can be eliminated. The time-frequency analysis of laser Doppler vibrometer measured slider bump responses also correlates the results.

Resonance phenomenon and its effects of laser texture disk

To achieve lower flying height for high areal recording density, the laser zone texturing of the disk needs to be designed to reduce glide height. One problem of the laser bump design is that the regular laser bump pattern often produces glide resonance phenomenon, which leads to failure of the glide height test. However, it was found in this study that glide resonance is an intrinsic problem of the glide head used and resonance phenomenon depends on the type of the head slider, that is, the natural frequency of the slider body. Therefore, higher glide height or glide failure caused by glide resonance does not lead to head/media interface problem in the real drive operating conditions in which the data head is used. Pseudo- random bump pattern greatly reduces the glide resonance. Smaller bump pitch will also help to reduce the glide resonance. However, as bump spacing becomes smaller, glide height will be increased due to increased air pressure developed around the bumps. Lowering bump height is the most effect way to reduce glide avalanche.

Failure analysis of laser-textured surfaces

Friction/stiction behaviour of ultrahigh-density magnetic disk drives can be controlled by controlling the size and shape of the laser bumps. Tribological behaviour of laser-textured disk surfaces depends on the size and shape of the laser bumps, bump density and operating conditions. In this study, theoretical and experimental analyses have been carried out on nine different laser-textured disk surfaces. Stiction and friction experiments have been carried out on sombrero, V-type and W-type laser-textured disks and these results are compared with theoretical results. A good correlation is obtained between experimental and theoretical results. The effect of laser bump uniformity on critical number of bumps required to prevent plastic deformation and stiction has also been studied.

Studies of failure mechanisms for head-disc interface using in situ instrumentation

The failure mechanism for a head-disc interface has been studied using in situ multi-instrumentation. Combined with ex situ atomic force microscopy observations, the sequence of events for the failure of a head-disc interface is proposed as depletion of the lubricant on laser bumps, uniform wear of the carbon coating on laser bumps, failure of the carbon coating on laser bumps and abrasive wear of the underlying substrate.

Stiction and Deformation Analysis of Laser Textured Media with Crater-Shaped Laser Bumps

A model is developed for the stiction and deformation of laser textured disks with crater-shaped laser bumps. Stiction and laser bump deformation are investigated as a function of laser bump and head/disk design parameters. In addition, a Monte Carlo analysis is performed to numerically study the dependence of the stiction force on laser bump and head/disk, design parameters. The results from the model are in very good agreement with experimental data. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in Orlando, Florida, October 11–13, 1999

Bump characterization with MR/GMR head as transducer

With a magneto-resistive (MR) head as transducer, this paper report a method and experimental results of fast in-situ characterization of laser textured bumps over disk surface. The thermally induced change of the resistance of MR head is used to conduct fast analysis of the uniformity of bump width, bump pitch interval, and bump height in the laser textured landing zone of a magnetic disk. Two modes of the tester setup are discussed. One mode is for the fast detection of the above mentioned uniformity within one disk revolution. Another mode is for mapping the selected bumps or all the bumps in a selected sector or a sub-zone of the textured landing zone. The setup can be used in both on-line and off-line analysis of the laser bump uniformity in media manufacturing process.

Investigation of head-disc dynamics with laser pattern simulated disc microwaviness

As the fly height requirement for ultrahigh density magnetic recording becomes more stringent, the control of head media spacing (HMS) modulation becomes extremely critical not only for the reliability of the head-disc interface but also for magnetic read/write performance. Disc topographical features with lateral dimensions ranging from 10% to 80% of the slider length are known as and these features can have a profound influence on HMS modulation. In this work, we demonstrate that disc microwaviness can be simulated by laser texture patterns. The controllability of such simulated microwaviness, in terms of frequency, amplitude and aspect ratio, makes this technique particularly powerful to gain fundamental understanding of the effect of disc microwaviness on the HMS modulation. It was found that when the laser pattern frequency intercepts the air bearing frequency, the resulting resonance induces severe HMS modulation. The response is a linear function of head-disc spacing, and the effect of spacing modulation becomes much more pronounced at higher laser bump heights.

Plasticity Index for Contact Between a Head and a Disk With Crater-Shaped Laser Bumps

A plasticity index formula for the contact between a flat plane and crater-shaped laser bumps is derived based on contact analysis of a circular cylinder in contact with a flat plane. The plasticity index for “cylinder-on-plane” contacts differs by a scale factor from that for “sphere-on-plane” contacts while the criterion for the deformation mode is the same for both types of contacts. For a wide range of typical head/disk interface conditions, the plasticity index for “cylinder-on-plane” contacts is found to be smaller than that of “sphere-on-plane contacts.” [S0742-4787(00)03501-3]

Experimental investigation of AE and friction signals related to the durability of head/disk interface

The durability of a hard disk drive is one of the most critical issues that must be optimized for best performance. Especially as the flying height of the head slider of a hard disk drive decreases over the years, the concern for surface damage and head contamination continues to grow. In this paper the characteristics of AE and friction signals for various operating conditions using CSS and drag tests were investigated from the durability point of view. Also, the wear characteristics of the laser bumps on a magnetic disk were compared between the CSS and drag tests. The general shapes of the AE and friction signals during a single CSS test were quite similar even under less than ideal operating conditions. However, it was found that the AE signal was more sensitive than the friction signal in assessing the damage of the slider/disk interface. Finally, a correlation was established between the CSS and drag testing methods with respect to the laser bump wear. This outcome suggests that the drag test may be used to accelerate the surface damage effect of head/disk system.

Effect of peak radius on design of W-type donut shaped laser textured surfaces

Friction/stiction behavior of ultra high density magnetic disk drives can be controlled by controlling the size and shape of the laser bumps using a laser texturing tool. Different laser bump parameters like rim radius, rim height, peak radius and number of bumps (under the slider) play an important role in the design of laser textured disk surfaces. In the present study, an algorithm is developed for generation of W-type laser bumps on the computer. W-type laser surfaces with a Gaussian height distribution have been generated and contact analyses of these surfaces have been carried out. Design curves have been generated to calculate critical number of asperities required to minimize wear and stiction. Effect of the coefficient of friction on the number of bumps has also been studied.

Contact analysis of laser textured disks in magnetic head–disk interface

Friction and wear behavior of a laser textured disk surface in contact with a magnetic head slider depends on the shape and size of the laser bumps, number of bumps, and mechanical properties of the disk and slider surfaces. In this study, analytical expressions for the height distributions of sombrero- and donut-shaped laser bumps, commonly used in the disk applications, have been developed. These expressions are used to generate the bumps on the computer. Contact analyses of these surfaces are carried out using analytical and numerical methods. Expressions for calculation of meniscus forces for spherical bumps and cylindrical rims are derived. An analytical method is developed to calculate meniscus forces, contact area and optimum number of bumps of a constant height, as a function of bump size and shape to minimize plastic deformation and stiction. A generalized numerical model, developed earlier for random surfaces, is used for contact analysis of bumps with a height distribution. Design curves are generated to estimate optimum number of bumps for a given height distribution, as a function of yield stress of the disk surface. Contact areas (pressure) and meniscus forces of the two bump geometries for a given rim radius and bump height are compared. It is observed that at a given yield stress, donut-shaped bumps result in lower contact area and meniscus force compared to sombrero-shaped bumps.