Table of Content

25 December 2015, Volume 3 Issue 4

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Articles

Single point and asymmetric incremental forming

J. Jeswiet, D. Adams, M. Doolan, T. McAnulty, P. Gupta

2015, 3(4):  253-262.  doi:10.1007/s40436-015-0126-1

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This paper presents an update on single point incremental forming (SPIF) of sheet metal since 2005. It includes a description of the process with new information on the maximum forming angle, Φ_max, for 5052-H32. An indepth example of the successful design and production of parts is given for industry. This includes discussion on production times and surface roughness with details thatwill help designers. A general design guide for users of SPIF is provided. It is based upon experience gained in the last decade. In general,materials show a trend of decreasing formabilitywith increasing initial thickness. It is shown that for thicker sheet metal, it is recommended using large spherical tools (12.7 mm or larger), or a large flat-ended tool. The flat-ended tool provides the best combination of good formability and very low surface roughness. For aluminum, galvanized steel and stainless steel, it is recommended using a flat-ended tool. Advances in multi-pass techniques and information on successful and useful numerical models which predict forming behaviour are included. Finally, there is a discussion on future work needed in SPIF.

Micro ball-end milling of freeform titanium parts

Ali Mamedov, Ismail Lazoglu

2015, 3(4):  263-268.  doi:10.1007/s40436-015-0123-4

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Micro machining has growing number of applications in various industries such as biomedical, automotive, aerospace, micro-sensor, micro-actuator and jewelry industries. Small-sized freeform titanium parts are frequently needed in the biomedical applications, especially in the implantations such as mini-blood pumps and mini left-ventricular assist devices, finger joint replacements and small bone implants. Most of the small-sized titanium parts with freeform geometries are machined using micro ball-end milling before polishing and other surface treatments. Decreasing the cycle time of the machining parts is important for the productivity. In order to reduce the cycle time of the roughing process in the micro ball-end milling, this paper investigates the implementation of a previously developed force-based feedrate scheduling (FFS) technique on micro milling of freeform titanium parts. After briefly introducing the instantaneous micro milling forces in micro ball-end milling of titanium parts with freeform surfaces, the FFS technique is implemented in the rough machining of a freeform titanium surface to demonstrate the cycle time reduction potentials via virtual micro milling simulations.

Dual phase titanium alloy hot forging process design: experiments and numerical modeling

A. Ducato, G. Buffa, L. Fratini, R. Shivpuri

2015, 3(4):  269-281.  doi:10.1007/s40436-015-0127-0

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Titanium alloys are considered desirable materials when both good mechanical properties and weight reduction are required at the same time. This class of materials is widely used in those fields (aeronautics, aerospace) in which common steels and light-weight materials, e.g., aluminum alloys, are not able to satisfy all operative service conditions. During the last decade, forging of titanium alloys has attracted greater attention from both industrial and scientific/academic researchers because of their potential in providing a near net shaped part with minimal need for machining. In this paper, a numerical model of the forging sequences for a Ti-6Al-4V titanium alloy aerospace component is presented. The model was tested and validated against experimental forgings. The model is then applied to predict loads final microstructure and defects of an aeronautical component. In addition to metal flow and die stresses, microstructural transformations (α and β phases) are considered for the determination of proper process parameters. It is found that transformation from α/β to b phase during forging and reverse transformations in post-forge cooling needs to be considered in the computational model for reasonable prediction of forging loads and product properties.

An experimental study on grinding of Zr-based bulk metallic glass

Mustafa Bakkal, Erdinç Serbest, İlker Karipçin, Ali T. Kuzu, Umut Karagüzel, Bora Derin

2015, 3(4):  282-291.  doi:10.1007/s40436-015-0121-6

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There are limited studies in the literature about machinability of bulk metallic glass (BMG). As a novel and promising structural material, BMG material machining characteristics need to be verified before its utilization. In this paper, the effects of cutting speed, feed rate, depth of cut, abrasive particle size/type on the BMG grinding in dry conditions were experimentally investigated. The experimental evaluations were carried out using cubic boron nitride (CBN) and Al₂O₃ cup wheel grinding tools. The parameters were evaluated along with the results of cutting force, temperature and surface roughness measurements, X-ray, scanning electron microscope (SEM) and surface roughness analyse. The results demonstrated that the grinding forces reduced with the increasing cutting speed as specific grinding energy increased. The effect of feed rate was opposite to the cutting speed effect, and increasing feed rate caused higher grinding forces and substantially lower specific energy. Some voids like cracks parallel to the grinding direction were observed at the edge of the grinding tracks. The present investigations on ground surface and grinding chips morphologies showed that material removal and surface formation of the BMG were mainly due to the ductile chip formation and ploughing as well as brittle fracture of some particles from the edge of the tracks. The roughness values obtained with the CBN wheels were found to be acceptable for the grinding operation of the structural materials and were in the range of 0.34-0.58 lm. This study also demonstrates that conventional Al₂O₃ wheel is not suitable for grinding of the BMG in dry conditions.

Experimental investigation of tool wear and chip formation in cryogenic machining of titanium alloys

D. Biermann, H. Abrahams, M. Metzger

2015, 3(4):  292-299.  doi:10.1007/s40436-015-0122-5

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Titanium alloys are one of the most important design materials for the aircraft industry. The high strength-to-density-ratio and the compatibility with carbon fibre reinforced plastic are the reasons for a raising application in this field. The outstanding properties lead to challenging machining processes. High strength and low heat conductivity affect high mechanical and thermal loads for the cutting edge. Thus, the machining process is characterized by a rapid development of tool wear even at low cutting parameter. To reach a sufficient productivity it is necessary to dissipate the resulting heat from the cutting edge by a coolant. Therefore the cryogenic machining of two different titanium alloys is investigated in this work. The results point out the different behavior of the machining processes under cryogenic conditions because of the reduced thermal load for the cutting tool. According to this investigation, the cryogenic cooling with CO₂ enables an increase of the tool life in comparison to emulsion based cooling principles when machining the α+β-titanium alloy Ti-6Al-4V. The machining process of the high strength titanium alloy Ti-6Al-2Sn-4Zr-6Mo requires an additional lubrication realized by a minimum quantity lubrication (MQL) with oil. This combined cooling leads to a smoother chip underside and to slender shear bands between the different chip segments.

Tool geometry based prediction of critical thrust force while drilling carbon fiber reinforced polymers

Y. Karpat, O. Bahtiyar

2015, 3(4):  300-308.  doi:10.1007/s40436-015-0129-y

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Carbon fiber reinforced polymers (CFRPs) are known to be difficult to cut due to the abrasive nature of carbon fibers and the low thermal conductivity of the polymer matrix. Polycrystalline diamond (PCD) drills are commonly employed in CFRP drilling to satisfy hole quality conditions with an acceptable tool life. Drill geometry is known to be influential on the hole quality and productivity of the process. Considering the variety of CFRP laminates and available PCD drills on the market, selecting the suitable drill design and process parameters for the CFRP material being machined is usually performed through trial and error. In this study, machining performances of four different PCD drills are investigated. A mechanistic model of drilling is used to reveal trade-offs in drill designs and it is shown that it can be used to select suitable feed rate for a given CFRP drilling process.

Finite element analysis of chip formation and residual stresses induced by sequential cutting in side milling with microns to submicron uncut chip thickness and finite cutting edge radius

Nejah Tounsi, Tahany El-Wardany

2015, 3(4):  309-322.  doi:10.1007/s40436-015-0128-z

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In this paper, the effect of four sequential cuts in side milling of Ti6Al4V on chip formation and residual stresses (RS) are investigated using finite element method (FEM). While the open literature is limited mainly to the studies of orthogonal sequential cutting with the constant uncut chip thickness greater than 0.01 mm, it is suggested herein to investigate not only the variable uncut chip thickness which characterises the down milling process, but also the uncut chip thickness in the sub-micron range using a finite cutting edge radius. For the resulting ductile machining regime, the characteristics of the chip morphology, the force profiles, the plastic deformation and temperature distributions have been analyzed. Furthermore, this study revealed that the RS should be extracted toward the area where the insert exits the workpiece in the FE simulation of the down-milling process. The simulation of a number of sequential cuts due to the consecutive engagements of the insert is required in order to capture the gradual accumulation of the RS before reaching an asymptotic convergence of the RS profile. The predicted RS are in reasonable agreement with the experimental results.

Analysis of hard turning process: thermal aspects

Varaprasad Bhemuni, Srinivasa Rao Chalamalasetti, Pavan Kumar Konchada, Venkata Vinay Pragada

2015, 3(4):  323-330.  doi:10.1007/s40436-015-0124-3

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In manufacturing sector, hard turning has emerged as a vital machining process for cutting hardened steels. Besides many advantages of hard turning operations, one has to implement to achieve close tolerances in terms of surface finish, high product quality, reduced machining time, low operating cost and environmental friendly characteristics. In the study, three dimensional (3D) computer aided engineering (CAE) based simulation of hard turning by using commercial software DEFORM 3D has been compared to the experimental results of stresses, temperatures and tool forces in machining of AISI D3 and AISI H13 steel using mixed ceramic inserts (CC6050). In the following analysis, orthogonal cutting models are proposed, considering several processing parameters such as cutting speed, feed and depth of cut. An exhaustive friction modelling at the tool-work interface is carried out. Work material flow around the cutting edge is carefully modelled with adaptive re-meshing simulation capability of DEFORM 3D. The process simulations are performed at constant feed rate (0.075 mm/r) and cutting speed (155 m/min), and analysis is focused on stresses, forces and temperatures generated during the process of machining. Close agreement is observed between the CAE simulation and experimental values.