Effect of Square Texture on Tribological Properties of Nano-SiO2/POB-PTFE Composites

In order to study the seal design problem of piston rings in Stirling engine, on the basis of filling PTFE with Nano-SiO2 and POB and preparing the GCr15 contact surface with square texture by HM20-I laser marking machine, experiments were carried out on LSR-2M wear tester by indirect weighing and in-situ observation methods. Optical microscope (OM) and scanning electron microscope (SEM) were used to observe the evolution of Nano-SiO2/POB-PTFE composites’ transfer film on contact surface. The results showed that the square texture would shorten the running-in and transitionary periods of the composites’ tribological process, accelerate into the stationary period. The formation process of the composites’ transfer film on the square textured contact surface was also different from smooth contact surface. Although the square texture would increase wear rate, its ability to store wear debris is more conducive to the formation of reliable, uniform and continuous transfer film with a same friction direction. Obviously, reasonable design of surface texture can effectively improve the wear resistance of sealing parts made of filling modified PTFE composites, thus providing theoretical guidance for the seal design of Stirling engine piston ring.

Modification of Laser Marking Ability and Properties of Polypropylene Using Silica Waste as a Filler

Polypropylene (PP) belongs to the group of polymers characterized by low susceptibility to absorption of electromagnetic radiation in the infrared range (λ = 1064 nm). This research consisted of assessing the possibility of using silica waste from the metallurgic industry as an additive for PP laser marking. The modifier was introduced into the polymer matrix in the range from 1 to 10 wt%. The effects of laser radiation were assessed based on colorimetric tests and microscopic surface analysis. The mechanical properties of the composites were determined during the static tensile tests. The thermal properties were investigated via differential scanning calorimetry. It was found that the introduction of silica waste into polypropylene allows for the effective marking of sample surfaces with the use of a laser beam. The greatest contrast between the graphic symbol and the background was obtained for silica contents of 3 and 5 wt%, with the use of a low-speed laser head and a strong concentration of the laser beam. The application of silica caused an increase in the modulus of elasticity and the tensile strength of the composite samples. Increases in the crystallization temperature and the degree of crystallinity of the polymer matrix were also observed. It was found that silica waste can act as multifunctional additive for polypropylene.

A novel method for approximating local changes in the surface absorption for laser marking using 3D laser scanning

Laser marking is a non-contact technique, which achieves colouring by using a laser beam to increase surface oxidation. Controlling the amount of heat induced into the part is essential in ensuring the desired degree of oxidisation. However, the induced heat is not only dependent on the process parameters, but also on the surface absorption, which in turn is dependent on the material, laser wavelength, and surface quality, i.e., current degree of oxidation and contaminants as well as surface roughness. This paper proposes a method for correlating backscatter from a 3D laser scanner with the surface absorption of sheet metal parts. The purpose is to determine local changes in the surface absorption caused by surface oxidation and contamination. The method utilises a 3D laser scanner, which projects a laser line at the surface and measures the resulting backscatter at an angle. The proposed solution applies a bi-directional reflectance model to reduce the influence of varying scanning angles. The method’s sensitivity to variations in surface treatments is investigated and validated against backscatter spectroscopy measurements. The results show that the proposed method can identify changes in the absorption. However, these were, in some cases, more than 70% higher compared to spectroscopy measurements.

Fast and Effective Sample Preparation Technique for Backside Fault Isolation on GaN Packaged Devices

This paper describes a fast and effective sample preparation method to allow backside fault localization on GaN package devices. Backside analysis by Photon Emission Microscopy (PEM) is becoming preferable to frontside analysis when the die is covered by metal layers. This paper describes an optimized method for backside sample preparation on GaN package devices having a thick heavily doped p-type silicon substrate. The method combines mechanical and chemical deprocessing steps, resulting in a fast and effective sample preparation technique for PEM analysis. Additionally, the laser marking process parameters to facilitate orientation during the final physical failure analysis by Focused Ion Beam (FIB) are also shared.