OPTIMIZATION OF BELLOWS AND TUBES CUTTING BY DISC KNIFE TO ACHIEVE THE MINIMUM BURR SIZE

The paper solves the determination of the optimal size of the shear gap when dividing components with a circular cross section (hydroformed metal bellows and tubes) with a disc knife to achieve the smallest burr size on the divided surfaces. The analyzes were performed on bellows with an outer diameter of 15 mm and a wall thickness of 0.4 mm. During the experiments, the size of the shear gap between the inner disc knife and the outer knife was changed, and the pressing force of the inner disc knife was changed. The experiments were carried out using a cutting tool after 20,000 cuts and after 120,000 cuts. The optimal size of the cutting gap was determined, allowing the minimum size of the burr to be achieved, thus reducing the time to remove it by brushing or tumbling in the subsequent operation. The mentioned procedure can be applied to analogous cases of division.

Tool Feed and Burr Size Influence on Wettability of Ti6Al4V Micro End-Milled

Surface texturing, using micro-milling, has promising applications in the industry of medical implants, since it can assist cell adhesion and thus improve osseointegration. Ti6Al4V alloy is used as implant material due to its excellent biocompatibility and high mechanical strength. However, those mechanical properties reduce machinability creating some challenges for micro-milling. The way to initially assess cell adhesion is using surface wettability, usually conducted with water. At the present work, micro-channels were machined in Ti6Al4V by micro end-milling with 500 µm width per 50 µm depth with 1000 µm distant from each other. The effect of feed per tooth (fz) on wettability was analysed and some interesting relations with burrs formed on channel walls were obtained. Values of feed per tooth were 3, 6, 12 and 15 µm. Wettability results showed that slotted surface is more hydrophilic on channel direction, with contact angles around 30° to 43°. In contrast, on the perpendicular direction the surface tends to be hydrophobic with contact angles between 75° and 146°. In addition, contact angle increases (hydrophobic tendency) as feed per tooth increases (along with roughness), even on channel direction. The presence of burrs also tends to disturb wettability results. Therefore, surface wettability depends on channel direction, burr size and tool feed per tooth, as well.

Optimum combination of machining parameters during drilling of Aluminium 7075 alloys using Grey based Taguchi approach

From ancient days to till today manufacturing industries, especially making of holes on the parts during drilling process for precision assembling of parts facing problems with burr formation. Drilling operation is one of the finishing operation in the production cycle, removing of burrs during drilling process is a time consuming and non-value added process to the manufacturing sector. So reducing the size of burrs is the main aim of the present study. In the present work, optimization of burr size is considered during drilling of aluminium 7075 alloy. From Grey relational grades of responses selected optimal combination of parameters to attain multiple performance characteristics of responses with a corresponding higher grey relational grade. For identifying the most significant input parameters that influence the output responses ANOVA is conducted. Finally, observations reveals that feed rate, point and clearance angles are the most influential factors on burr size and also experimental results divulge that the lower the thrust force causes to decrease the burr height. The proposed approach is helpful to the budding entrepreneurs in the related areas to select optimal combination of drilling parameters to attain multiple performance characteristics of responses especially in burr size to prevent the post finishing operations.

White Thrombosis on Optical Coherence Tomography after Rotational Atherectomy of Severely Coronary Calcified Lesions

Background: Rotational atherectomy (RA) has improved percutaneous treatment of severe coronary calcified lesions, but the "no-reflow" phenomenon remains a serious complication. Platelet activation by RA may contribute to the no-reflow, we use optical coherence tomography (OCT) to test the effect of RA on white thrombosis that could confirm platelet activation indirectly. Methods: We analyzed 53 consecutive patients with coronary angiographic severe calcified lesions. All the patients were examined by OCT. Twenty patients received RA and OCT imaging performed before and after RA and after stent implantation. The remaining patients were as a control group and OCT imaging performed before balloon dilatation and after stent implantation. Results: The patients were older and higher incidence of Diabetes mellitus in the RA group. In the RA group, the mean burr size was 1.48±0.14mm. The mean rotation speed was 152,300±4,200rpm. The mean number of rotations per patient was 5.3±2.1 times and the mean ablation time per RA was 11.3±3.2 seconds. In the control group, there was no thrombogenesis during the procedure, but in the RA group, all the target vessels had only white thrombosis on OCT after RA. The average number of white thrombus per lesion after RA was 7.23±4.4, and the average length of every white thrombus was 0.51±0.33mm. In Pearson Correlation Analysis, Thrombotic load was related with burr size (r=0.575, P=0.040) and rotation number (r=0.599, P=0.031).Conclusions: White thrombosis during RA is proved by OCT in vivo. Treating calcified lesions with RA may enhance thrombogenesis. These data suggest using a proper therapy to avoid no-reflow during RA.

Drilling Burr Minimization by Changing Drill Geometry

This article presents an attempt to solve the problem of the formation of burrs and drilling caps in the process of drilling in difficult-to-cut materials, specifically in the titanium alloy Ti-6Al-4V. In order to eliminate these phenomena, a chamfer of specific length and angle was made on FANAR drill’s margin. Taguchi and ANOVA methods were used to plan and analyze the experiment aimed at determining the optimal geometry of the modified drill. Chamfer with a length of 2 mm and an angle of 10° was selected. In the next stage of research, the values of cutting forces and burr heights obtained during drilling with the original and modified drill were compared for three different feed rate values. It turned out that the introduced changes significantly reduced both the axial cutting force (22–23%) and the height of burrs (10–22%) and caused the complete elimination of the presence of drilling caps. Additionally, a positive correlation between the cutting force and the burr size was found.

Platelet Aggregation on Optical Coherence Tomography after Rotational Atherectomy of Severely Coronary Calcified Lesions

Background Rotational atherectomy (RA) has improved percutaneous treatment of severe coronary calcified lesions, but the "no-reflow" phenomenon remains a serious complication. Platelet activation by RA may contribute to the no-reflow, we use OCT to test the effect of RA on platelet aggregation. Methods We analyzed 20 consecutive patients with severe coronary calcified lesions by OCT imaging performed before and after RA and after stent implantation. Results Mean burr size was 1.48 ± 0.14. Mean rotation speed was 152,300 ± 4,200 rpm. Mean number of rotations per patient was 5.3 ± 2.1 times and mean ablation time per RA was 11.3 ± 3.2 seconds. All the target vessels had platelet aggregation on OCT after RA. The average number of white thrombus per lesion after RA was 7.23 ± 4.4, and the average length of every white thrombus was 0.51 ± 0.33 mm. In Pearson Correlation Analysis, platelet aggregation load was related with burr size (r = 0.575, P = 0.040) and rotation number (r = 0.599, P = 0.031). Conclusions Platelet aggregation during RA is proved by OCT in vivo. The bigger burr size, higher number of ablation times, maybe together with higher rotation speed can influence the platelet aggregation load. These data suggest a proper RA strategy to avoid no-reflow during RA.

Investigation on laser-induced oxidation assisted micro-milling of Inconel 718

Poor surface quality and rapid tool wear are the main problems in micro-cutting of Inconel 718. In this study, a novel hybrid machining method named laser-induced oxidation assisted micro-milling is proposed to solve the aforementioned problems. A loose oxide layer and a relatively flat sublayer are formed on the material after laser irradiation. Under optimized laser parameters with a scanning speed of 1 mm/s and an average laser power of 4.5 W, the thicknesses of the oxide layer and the sublayer are 24 and 18 μm, respectively. The influence of cutting parameters on milling force, surface roughness, surface quality, and top burr size is studied in detail. Cutting force and thrust force in the proposed hybrid machining process are lower than those in the conventional micro-milling. Results show that for the investigated range of parameters, the optimal feed per tooth and depth of cut in the hybrid process are 3 μm/z and 3 μm, respectively. When using the optimal parameters, the surface roughness of the machined slot bottom is 108.5 nm. The top burr size on the up-milling side and the down-milling side is 26.8 and 36.2 μm, respectively. In addition, the tool wear mechanism is coating delamination in hybrid process, whereas chipping, coating delamination, tool nose breakage, and adhesion are the main tool wear mechanism in the conventional micro-milling. For the same amount of material removal, the proposed hybrid process can decrease the tool wear and enhance the service life of the micro-end mill as compared to conventional micro-milling.