Burr formation

Helical milling is a hole-making process which can be applied to achieve a high quality finished boreholes in hardened steels. Due to the drilling process limitations, which are intensified when applied in hardened steels, the helical milling process can be applied on hole-making tasks in moulds and dies industry, since milling have been widely applied in moulds and dies machining to replace high-cost operations like grinding and electrical discharge machining. However, to succeed in achieving high-quality boreholes in hardened parts, which presents high added value due to previous operations, tool wear in the helical milling of hardened steels should be more investigated. In the present study dry helical milling tool life tests were conducted in AISI H13 hardened steel parts, varying the cutting velocity. The flank wear on frontal cutting edges was progressively measured through optical microscopy, and SEM/EDS was performed in frontal and peripheral worn cutting edges. The wear occurred progressively in the flank of the frontal cutting edges with adhesion and oxidation as main wear mechanisms. In the peripheral edges, it was observed coating loss, adhesion of workpiece material in the tool clearance surface, besides fracture in the tool nose flank with the highest cutting velocity. A nested ANOVA was performed to evaluate the burr height in the borehole exit. The tool life stage was statistically significant in the burr height.

The market for freeform and high quality microdies and moulds made of steel is predicted to experience a phenomenal growth in line with the demand for microsystems. However, micromachining of hardened steel is a challenge due to unpredictable tool life and likely differences in process mechanism compared to macro-scale machining. This paper presents an investigation of the size effect in micromilling of H13 hardened tool steel. In this case, the size effect in micromilling hardened tool steel was observed by studying the effect of the ratio of undeformed chip thickness to the cutting edge radius on process performance. The paper explores how this ratio drives the specific cutting force, surface finish and burr formation in micro-scale machining. In addition, the effect of different microend mill geometry on product quality was explored. The paper provides a valuable insight into optimum micro-scale machining conditions for obtaining the best surface finish and minimizing burr size.

ND YAG laser drilling of austenitic stainless-steel material is studied here. Taguchi method with grey relational analysis to determine the laser drilling parameters with consideration of multiple quality characteristics, is studied in this paper. The effort has been made to minimize the drilling defects, such as hole taper. In present research, A pulsed ND: YAG (Neodymium-doped Yttrium Aluminum Garnet) laser which creates high intensity infrared radiation at a wavelength of 1064 nm, with output powers ranging 600W used for laser drilling of austenitic stainless steel, a material which has performed well in laboratory tests as well as in various fields of engineering and industrial, is perceived. It has wide range of applications in various fields like industrial, medical, heat engines etc. Laser drilling input factors such as lamp current, pulse frequency, air pressure and pulse width. The dimensional accuracy and quality of holes are very important for some specific applications of holes. circularity of drilled hole at entry and exit, and taper are very important attributes which influence the quality of a drilled hole in laser drilling. Using the taguchi method an L27 orthogonal array has been used for this experiment. From the grey analysis, a grey relational grade is obtained and based on this value an optimum level of drilling parameters has been identified. The result of the confirmation experiments show that optimal laser drilling parameters can be determined successfully so as to perk up numerous quality characteristics through this approach.

Sake Sudhakar, Praveen Kumar, G Srinivas, S Ravishankar, D Chakradhar & Harish C Barshilia* aNanomaterials Research Laboratory, Surface Engineering Division, CSIR – National Aerospace Laboratories, Post Bag 1779, Bangalore 560 017, India bAircraft Prototype Manufacturing Facility, CSIR – National Aerospace Laboratories, Post Bag 1779, Bangalore 560 017, India cDepartment of Mechanical Engineering, National Institute of Technology, Surathkal 575 025, India

Micro-milling can be defined as milling with end mills smaller than 1 mm of diameter. The top-down approach from milling to micro-milling is often used to define cutting conditions. Unfortunately geometries either for the active part or the overall shape are quite different from conventional tools, leading to inexistent problems at the macro-scale, such as a larger cutting edge radius to uncut chip thickness ratio leading to ploughing effect. Moreover, micro-milling can be used on particular material such as shape memory alloys in biomedical domain which are difficult to machine. This study focuses on burr formation during shoulder milling for two biocompatible NiTi alloys: a martensitic NiTi (shape memory effect) and an austenitic one (pseudo-elasticity effect). Design of experiment is used to highlight the influence of various parameters (cutting parameters and material phases) on the burr formation in micro-milling NiTi alloys. Burrs were observed and measured using confocal, opt...

Micromachining techniques such as mechanical micro-drilling, electrical discharge machining (EDM) and laser beam machining (LBM) play an important role in the manufacturing of micro-devices used in mechanical, electronics, aerospace and medical applications. In this paper, an effort has been made to compare the performance of these micromachining techniques with regard to tool wear, burr formation and surface integrity. This is done by producing 20 micro-holes of approximately 800 μm diameter on a rectangular block (90×30×3 mm 3) of Nimonic 80A superalloy. TiAlN coated WC micro-drills, Cu electrodes and CO 2 laser beam are used to produce these holes in conventional micro-drilling, EDM and LBM, respectively. The quality of the drilled hole (diameter, surface roughness and micro-burr formation), tool diameter analysis, taper angle and material removal rate (MRR) are compared and reported. A comprehensive analysis is also carried out on overcut, which leads to hole inaccuracy. Results show that mechanical micro-drilling produces better results in the above mentioned characteristics in comparison to LBM and EDM techniques. The relatively better performance of mechanical micro-drilling is attributed to the usage of TiAlN coating on WC tool.

Machining experiments were conducted to evaluate the impact of cutting parameters on the hole quality and cutting forces in drilling Al2024-T3 aerospace alloy. Al2024-T3 specimen were drilled using Φ6-mm TiAlN-coated carbide twist drills under dry cutting conditions. The hole quality was inspected in terms of its surface roughness, burr and chip formations, hole size, circularity error and post-machining microhardness of the subsurface of the holes. An analysis of variance (ANOVA) was carried out to determine the percentage contribution of cutting parameters on cutting forces and the inspected hole quality parameters. A three-dimensional (3D) finite element (FE) model of drilling Al2024-T3 is developed using Abaqus/Explicit to predict thrust force and torque. The FE model was validated using experimental results and found to be in good agreement. The results of the study showed that the cutting parameters have a significant impact on cutting forces and inspected hole quality parameters. Drilling at feed rates of 100 and 300 mm/min and spindle speeds of 1000, 3000, and 6000 rpm are recommended for producing holes with smaller surface roughness, deviation from nominal hole size, circularity error and burrs.

The quality of machined components in the aerospace and automotive industries has become increasingly critical in the past years because of greater complexity of the workpieces, miniaturization, usage of new composite materials, and tighter tolerances. This trend has put continual pressure not only on improvements in machining operations, but also on the optimization of the cleanability of parts. The paper reviews recent work done in these areas at the University of California-Berkeley. This includes: Finite element modeling of burr formation in stacked drilling; development of drill geometries for burr minimization in curved-surface drilling; development of a enhanced drilling burr control chart; study of tool path planning in face-milling; and cleanability of components and cleanliness metrics.

The quality of machined components in the aerospace and automotive industries has become increasingly critical in the past years because of greater complexity of the workpieces, miniaturization, usage of new composite materials, and tighter tolerances. This trend has put continual pressure not only on improvements in machining operations, but also on the optimization of the cleanability of parts. The paper reviews recent work done in these areas at the University of California-Berkeley. This includes: Finite element modeling of burr formation in stacked drilling; development of drill geometries for burr minimization in curved-surface drilling; development of a enhanced drilling burr control chart; study of tool path planning in face-milling; and cleanability of components and cleanliness metrics.

Burr formation is very common phenomenon during various machining process such as drilling results into deterioration of quality of produced material and reduces the strength of the component. Therefore it is very important to reduce it to optimum level with the help of geometry and various other process parameters. The concentrated parameters in this project are its cutting speed, point angle of drill bit, the concentration of silicon carbide reinforcement and its feed rate. Various methods are available out of which the combination of "Response Surface Method" and "Taguchi Technique" is used to obtain the optimum limit to take burr formation to optimum level. However the most influencing parameters to responses are the point angle of drill bit, the feed rate and the percentage mixture of silicon carbide reinforcement material in the matrix say 30%. It can be concluded that higher the concentration of silicon carbide, enhancing the point angle and lowering down the feed rate resulted into optimum burr formation.

This article discuss the effects of heat treatment and lubrication modes on the machinability of A356 alloy (Al-Si-Mg), the alloy is studied as-received, with solution heat-treated alloy (SHT) as well as with solution heat-treated and then aged at 155 °C, 180 °C, and 220 °C. In the course of machinability evaluation, several criteria including cutting force, surface roughness, tool wears, and burr analysis (chip) were studied. The results and analysis in this work indicated that selected machinability criteria are important and necessary to effectively evaluate the machinability of A356 alloys. Machinability of both materials and tool was estimated in terms of cutting force, chip thickness ratio and burr formation, flank wear, and roughness. The effects of different cutting parameters (cutting speed and feed rate) and lubrication modes (dry, mist, and wet) on the machinability of A356 cast alloy were also examined. The influence of heat treatments on the burr formation and surface quality was clearly revealed by the experimental results. Experimental work revealed that cutting forces were influenced significantly by aging and cutting speed. However, the different aging at 155 °C, 180 °C, 220 °C and the cutting speed significantly affected the machinability of A356 cast alloy. The results obtained show that for better drilling performance in terms of surface quality occurs at high feed rate, dry drilling, and artificial aging at T6.

Helical milling is a hole-making process which can be applied to achieve a high quality finished boreholes in hardened steels. Due to the drilling process limitations, which are intensified when applied in hardened steels, the helical milling process can be applied on hole-making tasks in moulds and dies industry, since milling have been widely applied in moulds and dies machining to replace high-cost operations like grinding and electrical discharge machining. However, to succeed in achieving high-quality boreholes in hardened parts, which presents high added value due to previous operations, tool wear in the helical milling of hardened steels should be more investigated. In the present study dry helical milling tool life tests were conducted in AISI H13 hardened steel parts, varying the cutting velocity. The flank wear on frontal cutting edges was progressively measured through optical microscopy, and SEM/EDS was performed in frontal and peripheral worn cutting edges. The wear occurred progressively in the flank of the frontal cutting edges with adhesion and oxidation as main wear mechanisms. In the peripheral edges, it was observed coating loss, adhesion of workpiece material in the tool clearance surface, besides fracture in the tool nose flank with the highest cutting velocity. A nested ANOVA was performed to evaluate the burr height in the borehole exit. The tool life stage was statistically significant in the burr height.

We report the machining characteristics and machinability of a nickel based superalloy in this study. A micro-milling operation is loaded on Nimonic 75 using uncoated and TiAlN coated tungsten carbide micro-end mills. A full factorial design of experiments was devised to optimize the machining conditions to reduce the flank wear on the tool surface. The optimized machining conditions for uncoated micro-tools were found to be a cutting speed (v c) of 13 m/min and a feed rate (f z) of 6 mm/min. Following this, the tools were coated with TiAlN using a semi-industrial four-cathode reactive pulsed direct current unbalanced magnetron sputtering system. Further experiments were then performed using these optimized machining conditions using both uncoated and TiAlN coated micro-tools in order to ascertain the tool wear and surface integrity. The change in geometry of the machined slot was estimated based on the variation in tool radius of the micro-end mill with progression of the operation. A direct comparison was made between the results observed using both uncoated and TiAlN coated tungsten carbide to illustrate the effect of the nanocomposite TiAlN coating. It was seen that TiAlN coated micro-tools exhibited a superior performance as compared to the uncoated ones with respect to tool life and micro-burr formation.