Frictional characteristic of micro structures for wooden pallets

Wooden pallets are widely used in the field of logistics.Their frictional characteristics directly determine the reliability of transport. Microstructuring is an effective method to enhance the friction coefficient between the wooden pallet and corrugated box. In this study, the micro-cutting method was used to manufacture the micro grooves and pillars efficiently. 12 different sizes of microstructure are designed and manufactured on pine wood which is commonly used for the wooden pallet. The experimental results show that sample with a thickness of the groove wall 100μm has a poor structural strength and not suitable for microstructure design. The test results show that, micropillars has larger friction coefficient than grooved surface. It can lead to a 57 percent increase in the friction coefficient (from 0.21 to 0.33). This study lays the foundation for the manufacture of microstructures on wood to improve the frictional characteristic

Characterisation of thrust performance of micro-nozzle machined by micro end-milling

Micro thruster is the power plant of mini-spacecraft. It enables the mini-spacecraft to realize orbit adjustment, station keeping and attitude controlling. Micro nozzle is one of key parts of the micro thruster. The surface roughness of its inner surface significantly influences the thrust performance of the thruster. In this paper, a residual surface model is developed for micro-nozzle obtained by micro machining using a ball end mill and a taper end mill. The residual surface model is then used to investigate the relationship between the surface quality and nozzle thrust performance in nozzle flow field. A thrust measuring apparatus is designed and manufactured to inspect the thrust performance of the machined micro nozzles. Both simulation and experiment results indicate that good machined surface quality is obtained with taper end mill. The nozzle machined with the taper end mill has better thrust performance than that with the ball end mill under the same inlet pressure

Hydrophobicity of pyramid structures fabricated by micro milling

Surgical site infection is the most common infection, which occurs after surgery in the part of the body where the surgery took place. Hydrophobic structure is an effective method to improve the anti-infection ability of surgical tools. The hydrophobic surface prepared by the conventional chemical coating method has poor durability. In this study, the micro-milling method was used to process the microstructure efficiently. 6 different sizes of microstructure is designed and manufactured on 7C27Mo2 which is commonly used for surgical tools. The capability of applying micro-milling for these structures is assessed. The optimal microstructure size is obtained. The experimental results show that the smooth surface of 7C27Mo2 is hydrophilic with contact angle of 64.1°. However, after micro-cutting, the hydrophilic surface can be converted into the hydrophobic surface, the contact angle contact angle nearly doubled (from 64.1° to 127.3°). This study lays the foundation for the manufacture of surgical tools with hydrophobicity and antibacterial properties

A real-time interpolator for parametric curves

Driven by the ever increasing need for the high-speed high-accuracy machining of freeform surfaces, the interpolators for parametric curves become highly desirable, as they can eliminate the feedrate and acceleration fluctuation due to the discontinuity in the first derivatives along the linear tool path. The interpolation for parametric curves is essentially an optimization problem, and it is extremely difficult to get the time-optimal solution. This paper presents a novel real-time interpolator for parametric curves (RTIPC), which provides a near time-optimal solution. It limits the machine dynamics (axial velocities, axial accelerations and jerk) and contour error through feedrate lookahead and acceleration lookahead operations, meanwhile, the feedrate is maintained as high as possible with minimum fluctuation. The lookahead length is dynamically adjusted to minimize the computation load. And the numerical integration error is considered during the lookahead calculation. Two typical parametric curves are selected for both numerical simulation and experimental validation, a cubic phase plate freeform surface is also machined. The numerical simulation is performed using the software (open access information is in the Acknowledgment section) that implements the proposed RTIPC, the results demonstrate the effectiveness of the RTIPC. The real-time performance of the RTIPC is tested on the in-house developed controller, which shows satisfactory efficiency. Finally, machining trials are carried out in comparison with the industrial standard linear interpolator and the state-of-the-art Position-Velocity-Time (PVT) interpolator, the results show the significant advantages of the RTIPC in coding, productivity and motion smoothness

Dynamics stiffness enhancement of fast tool servo by acceleration feedback

Fast Tool Servo (FTS) devices are widely used in manufacturing of micro features on large areas. Dynamic stiffness of such devices is usually poor due to their low inertia which cause profile errors. In this paper, a triple feedback scheme is proposed to enhance the dynamic stiffness by introducing acceleration feedback. Position and acceleration signals together with motor current were combined to estimate the cutting force. Then the force is compensated by the controller output. Frequency response tests showed supressed disturbance response around the cross over frequency. Further face turning experiments demonstrated that the new feedback scheme helped reducing the dynamic errors caused by sudden change of cutting forces

Material removal mode and friction behaviour of RB-SiC ceramics during scratching at elevated temperatures

Thermal assistance is considered a potentially effective approach to improve the machinability of hard and brittle materials. Understanding the material removal and friction behaviour influenced by deliberately introduced heat is crucial to obtain a high-quality machined surface. This paper aims to reveal the material removal and friction behaviours of RB-SiC ceramics scratched by a Vickers indenter at elevated temperatures. The material-removal mode, scratching hardness, critical depth of the ductile–brittle transition, scratching force, and friction are discussed under different penetration depths. The size effect of scratching hardness is used to assess the plastic deformation at elevated temperatures. A modified model is established to predict the critical depth at elevated temperatures by considering the changes in mechanical properties. The results reveal that the material deformation and adhesive behaviour enhanced the ductile-regime material removal and the coefficient of friction at elevated temperatures

Superhydrophobicity of micro-structured surfaces on zirconia by nanosecond pulsed laser

This paper presents a systematic approach to improve the hydrophobicity of microstructured surfaces. It includes a contact angle prediction model for microstructures obtained by nanosecond pulsed laser. Combining with the theoretical constraints for stable Cassie-Baxter state this approach can be used to optimize microstructures dimensions for maximising surface hydrophobicity. Laser machining experiments were conducted to evaluate the prediction model. It shows that the proposed systematic approach can accurately predict the contact angle and obtain microstructures dimensions for maximising surface hydrophobicity. The results also indicate that the contact angle increases with the decrease of pitch of the microstructures. Superhydrophobicity with maximum contact angle of 155.7° is obtained, for the first time, on a micro structured surface (P030) of Zirconia with a pitch of 30 μm machined under a laser power at 8W

Fabrication of hydrophobic structures by nanosecond pulse laser

In this paper, a feasibility study of manufacturing anti-bacteria surface on stainless steel 7C27Mo2 used for surgical tools by using nanosecond pulse laser is presented. The effect of laser power on the depth of groove was studied through laser cutting experiment. Micro-pillar arrays of different dimensions and spacing were generated by laser cutting. The wetting characteristics of micro-structured surfaces were assessed by using the static contact angle measurement approach. The measurement results show that the original hydrophilic stainless steel surface can be converted into a hydrophobic surface by using laser structuring as the contact angle can be doubled. This research shows that it is feasible to manufacture hydrophobic microstructures with a laser cutting process

A new grinding force model for micro grinding RB-SiC ceramic with grinding wheel topography as an input

The ability to predict grinding force for hard and brittle materials is important to optimize and control the grinding process. However, it is a difficult task to establish a comprehensive grinding force model that takes into account of brittle fracture, grinding conditions and random distribution of grinding wheel topography. Therefore, this study developed a new grinding force model for micro-grinding of RB-SiC ceramics. First, the grinding force components and grinding trajectory were analyzed based on the critical depth of rubbing, ploughing and brittle fracture. Afterwards, the corresponding individual grain force were established and the total grinding force was derived through incorporating the single grain force with dynamic cutting grains. Finally, a series of calibration and validation experiments were conducted to obtain the empirical coefficient and verify the accuracy of the model. It was found that ploughing and fracture were the dominate removal modes, which illustrate the force components decomposed is correct. Furthermore, the values predicted according to proposed model are consistent with the experimental data, with the average deviation of 6.793% and 8.926% for the normal and tangential force, respectively. This suggests that the proposed model is acceptable and can be used to simulate the grinding force for RB-SiC ceramics in practical

Fundamental understanding of the deformation mechanism and corresponding behavior of RB-SiC ceramics subjected to nano-scratch in ambient temperature

To get insight into nano-scale deformation behavior and material removal mechanism of RB-SiC ceramic, nanoscratch experiments were performed using a Berkovich indenter. Structure changes in chips and subsurface deformation were characterized by means of Raman spectroscopy. The result shows that the SiC phase underwent amorphization in ductile chips, while no amorphous feature can be observed in brittle chips and substrate within scratch groove. The following estimated stress surround the indenter reveals that amorphous deformation in ductile chips is governed by tangential stress (above 95 GPa), whereas the dislocations-based substrate deformation mechanism was dominated by normal stress. In the end, the effects of normal load and scratching velocity on the scratch behavior including scratch residual depth, elastic recovery and friction coefficient that related to RB-SiC ceramic deformation mechanism were also analyzed. With the increase of normal load, the deformation mechanism transfers from ductile to brittle fracture mode and cause the decrease of elastic recovery and the increase of residual depth and friction coefficient. Furthermore, the increased high density of dislocations as a result of the increased scratching velocity give rise to the increase of scratch hardness, which finally result in the increase of elastic recovery and decrease of residual depth and friction coefficients. This study contributes a new understanding of the brittle material deformation mechanism during a nano-scale scratching process