Towards the Determination of Machining Allowances and Surface Roughness of 3D-Printed Parts Subjected to Abrasive Flow Machining

Abrasive flow machining (AFM) is considered as one of the best-suited techniques for surface finishing of laser powder bed fused (LPBF) parts. In order to determine the AFM-related allowances to be applied during the design of LPBF parts, a numerical tool allowing to predict the material removal and the surface roughness of these parts as a function of the AFM conditions is developed. This numerical tool is based on the use of a simplified viscoelastic non-Newtonian medium flow model and calibrated using specially designed artifacts containing four planar surfaces with different surface roughnesses to account for the build orientation dependence of the surface finish of LPBF parts. The model calibration allows the determination of the abrasive medium-polished part slip coefficient, the fluid relaxation time and the abrading (Preston) coefficient, as well as of the surface roughness evolution as a function of the material removal. For model validation, LPBF parts printed from the same material as the calibration artifacts, but having a relatively complex tubular geometry, were polished using the same abrasive medium. The average discrepancy between the calculated and experimental material removal and surface roughness values did not exceed 25%, which is deemed acceptable for real-case applications. A practical application of the numerical tool developed was demonstrated using the predicted AFM allowances for the generation of a compensated computer-aided design (CAD) model of the part to be printed.

INTERACTION OF THE ABRASIVE MEDIUM WITH THE TREATED SURFACE AND THE PROCESS OF METAL REMOVAL DURING VIBRATION TREATMENT IN THE PRESENCE OF A CHEMICALLY ACTIVE SOLUTION

Interaction of working medium granules with the processed surface of the part is considered. It is noted that the processing methods are characterized by the dynamic interaction of the abrasive medium with the processed surface. It is indicated that during vibration treatment there is an impact contact of the abrasive granule with the surface of the part, which leads to the formation of characteristic traces during the formation of the surface relief. The types of impact of abrasive grains of working medium granules on the surface of the processed part are identified. It is indicated that the effect of abrasive grains depends on the geometric parameters of the tops of the grains and the working contour of the granule as a whole. The alternation of the operation of abrasive grains in the connection with the nature of the motion of the granule over the surface of the part is shown. The interaction of surfaces of bodies during vibration treatment is considered. The distinctive features of the vibration treatment method from other analogs are indicated. The conditions for the formation of the surface layer of the part during vibration processing are given. The analysis of the mechanical-physicochemical model of the micro-cutting process in the presence of a chemically active solution is carried out and a comparison of the intensity of technologies for vibration treatment of steel parts is given.

Analysis of Wear-Resistant Materials of Mixer - Pneumosuperchargers Blades Operating under Conditions of Abrasive Wear

We conducted comparative tests of the wear resistance of metals operating under abrasive conditions. Samples were cut from the working parts of mixer-pneumosuperchargers. The chemical composition and mechanical properties were determined. To compare samples under abrasive wear conditions, we designed and assembled a carousel installation. The principle of its operation is based on mixing the abrasive medium by the samples being studied with a given speed. Wear resistance was evaluated by weight loss by samples after several test cycles. To determine changes in the structure of the metal during abrasive wear, metallographic studies of the samples were carried out before and after the tests. It is shown that the best complex of service and mechanical properties is possessed by 110G13L steel.

MECHANICAL PROPERTIES OF HEAT-STRENGTHENED STEEL 65G SURFACE-REINFORCED WITH HARD-ALLOY SURFACING

Increasing the service life of soil-cultivating equipment parts by the use of surfacing reinforcement of working surfaces has found a fairly wide application. However, the studies carried out on this problem were focused on parts, the metal of which had not been subjected to preliminary heat hardening. Meanwhile, in recent years, the components of the working tools of agricultural implements are almost completely hardened by heat treatment. This is especially true for imported products. Information on the reinforcement of parts that have undergone this kind of processing is extremely scarce, and sometimes contradictory. Therefore, the research task was to study the properties of heat-strengthened steel 65G after its surface reinforcement. During the experiments, as the base metal, use was made of spring sheets made of 65G steel with a hardness of about 45 HRC. T-590 electrodes were used as the surfacing material, intended for surfacing of parts operated in an abrasive environment. The reliability of the results obtained was guaranteed by a large number of measurements. Mechanical properties were evaluated by HRC hardness. As a result of experiments, it was found that the hardness value of 44…47 HRC for leaf springs taken out of service makes them suitable for use as repair materials. When surfacing one roller, the initial hardness of the base metal remains at the same level; surfacing two rollers leads to a decrease in HRC by 9 units. Three zones are distinguished in the area between the rollers. The use of reinforcing rollers on the surface of heat-treated steel 65G increases its service properties due to their high hardness, a decreased contact path of the abrasive particle with the working surface and forms a “fl uidized” layer of a moving abrasive medium between the rollers.

An Industrial Methodology for Erosion Analysis of FCC Expander Blades

Fluid Catalytic Cracking (FCC) is a process for the conversion of heavy stocks recovered from different refinery operations into high-octane gasoline, light fuel oils and olefin rich light gases. Zeolite particles are used as catalyst in the process to facilitate the cracking of long hydro-carbon molecules. Because of the contact between catalyst and feedstock, coke deposits on the catalyst active surface reducing its activity, air is used to remove it from the catalyst, in the regenerator. The coke burning produces a hot flow of flue gas with a valuable energy content (700°C – 3bar) that can be recovered using a Hot Gas Expander HGE before releasing the exhausts in the atmosphere. The flue gas is carrying a certain amount of catalyst so the expander hot parts (mainly blades but also the stator vanes) are constantly exposed to an abrasive medium that may compromise the reliability of the asset. Understanding how the solid particle erosion works is one of the challenges that HGEs designer shall deal with. To this purpose, a numerical approach was developed to account for some of the factors that are known to play a major role in erosion phenomena: particle velocity, angle of impact, composition and particle size, as well as the mechanical properties of the target surface at the operating temperature. The methodology was then applied to a cascade blade for which erosion data collected in a stationary erosion test rig are available. The comparison between numerical and experimental data showed a good agreement therefore providing confidence on the proposed methodology. Finally, the numerical procedure has been applied to a real case to show the effect of the different catalyst load on the life of the blades.

Finishing of Tubes using Bonded Magnetic Abrasive Powder in an Abrasive Medium

Magnetic abrasive flow finishing (MAFF) is an unconventional process capable of producing fine finishing with machining forces controlled by a magnetic field. This process can be utilized for hard to achieve inner surfaces through the activity of extrusion pressure, combined with abrasion activity of a magnetic abrasive powder (MAP) in a polymeric medium. MAP is the key component in securing systematic removal of material and a decent surface finish in MAFF. The research background disclosed various methods such as sintering, adhesive based, mechanical alloying, plasma based, chemical, etc. for the production of bonded MAP. This investigation proposes bonded MAP produced by mechanical alloying followed by heat treatment. The experiments have been conducted on aluminum tubes to investigate the influence of different parameters like magnetic field density, extrusion pressure and number of working cycles. The bonded magnetic abrasive powder used in MAFF is very effective to finish tubes’ inner surfaces and finishing is significantly improved after processing.

Theoretical and experimental researches of deburring process by loose abrasives

The results of vibro-abrasive treatment of radio electronic equipment parts in free abrasive medium are presented. The principle model of burr formed on workpieces as result of mechanical treatment is obtained. The mechanism of contact interaction of processing medium particles with the treated surface is analyzed. The mechanism is used as the basis for the development of probability-theoretical model of deburring. Complex of researches of technological factors effect on the duration of vibration treatment is carried out.