G. Urbikain

HOLE MAKING USING BALL HELICAL MILLING ON TITANIUM ALLOYS

In this article, results of helical ball milling for hole making on Ti-6Al-4V alloy are presented and compared with drilling. Two different machining strategies were tested with a ball end mill. In the first strategy only a helical milling path was used to achieve the nominal diameter. The second strategy has two stages; first, helical milling considering a diameter 50 µm below the nominal, and second, the tool flank of the ball end mill were used to remove the stock left with a single contouring operation. Experimental tests were performed taking into account the process time, final quality of holes, hole diameter, roughness and burr formation at tool entrance and exit. With helical milling two advantages were concluded: the process is versatile because one tool is suitable for a range of diameters and negligible burrs are produced. However hardness in the zones close to hole internal surfaces machined with the ball end mill tool decreases with respect to twist drilling. The information obtained from this research work defines suitable cutting parameters for the helical milling process in the titanium alloy Ti-6Al-4V with ball end mills.

Combination of friction drilling and form tapping processes on dissimilar materials for making nutless joints

In this article, a new method for the rapid and economical production of ‘nutless’ bolted joins is presented, using a combination of two hole-making techniques, namely, form drilling and form tapping. The combined method achieves a quick way for the production of threaded holes on couples of dissimilar metal alloys, as it is the case of steels and aluminium alloys. After the simultaneous form drilling on the aluminium–steel pairs and followed by form tapping, a fastener can be introduced and screwed for achieving a tight bolted joint, without any necessity of nut. However, form drilling and threading are performed consecutively in the same machine tool, reducing the whole process time. The process parameters were studied for reducing the gap between surfaces and producing a good cup for making the posterior threading. Then, mechanical testing of several test pieces resulted in a similar behaviour than traditional bolted joints. Finally, corrosion tests were performed for a better understanding of the joint manufactured. In this way, savings in time and money are derived from the application of the approach. Target markets for the new approach are the light boilermaking industry in order to eliminate either welding beads or classical bolted joints using nuts.

Definition of Cutting Conditions for Thin-to-Thin Milling of Aerospace Low Rigidity Parts

The main drawback of the high speed milling of monolithic parts for the aerospace industry is the high buy-to-fly ratio that leads to a huge material waste. This problem is caused by the need to stiffen the part during the machining in order to avoid chatter, excessive vibration and residual stresses. The present work proposes a methodology for the milling of compliant parts based on the selection of cutting conditions free of chatter. First, the modal parameters of the part in the most problematic stages of the machining are calculated by means of the finite elements method. Secondly, a three-dimensional stability model is used in each stage to calculate a three-dimensional stability lobes diagram dependent on the tool position along the whole tool path. Given the fact that the depth of cut is defined by the bulk of material, the three-dimensional stability diagram can be reduced to a two-dimensional one, which relates tool position during the machining and spindle speed, and indicates how to change the spindle speed in order to avoid the unstable areas. What is more, the proposed methodology can also be used to dimension the bulk of material, select the proper tool or improve the fixturing of the part. Finally, the methodology is validated experimentally on a test part.Copyright

Modelling of surface roughness in inclined milling operations with circle-segment end mills

Abstract There is currently a lack of knowledge in the manufacturing of high complexity aerospace components. Impellers or blade-integrated disks (blisks) are expensive, and manufacturers tend to prefer reliability over productivity. Thus, manufacturing times are higher than they should be. These challenging parts need to be machined using new advanced tools for several reasons, such as requirement of 1) special and complex tool paths, 2) smoother cutting forces, and 3) good accessibility. Circle-segment or oval-form cutters have recently demonstrated their usefulness and adaptability in the machining of profile and free-form surface operations, and are becoming a solution for a wide range of applications and materials. However, machinists who use them know very little about such tools. In fact, there has been a lack of real-world modelling applications. This paper proposes for the first time a geometrical model that allows the prediction of the surface topography in flank-milling operations using circle-segment end mills. This time-domain model includes the most important mechanical and kinematical parameters during cutting: the tool geometry, feed rate, radial immersion, and tool runout. Tool orientation angles commonly used in 5-axis operations are also included. The developed model was positively verified against experimentally measured values in a milled wall made of aluminium Al7075T. This knowledge-based tool is useful for manufacturing companies and suppliers interested in optimizing and controlling their production parameters.

Combination of simulated annealing and pseudo spectral methods for the optimum removal rate in turning operations of nickel-based alloys

Abstract In this paper, an approach that combines simulated annealing technique (SA) with the Chebyshev collocation method (CCM) or with the Enhanced Multistage Homotopy Perturbation (EMHPM) is established. Then, these two new approaches are applied to find optimal cutting conditions in turning operations of nickel-based superalloy (Inconel 718©) by using SNMG and VBMT tool-inserts. To validate the proposed approaches in terms of material removal rate and stability, a series of turning cutting tests were carried out. Numerical results show that when the CCM is combined with SA technique, the optimum stable cutting conditions such as the axial depth of cut and the spindle speed, were estimated 100 times faster than from the CCM. Furthermore, experimental data and numerical results confirmed that the productivity by using a tool-SNMG insert is 19% higher than when using VBMT tool-insert, which is mainly due to the tool stability dynamic response.

Training and learning of specialized engineers by means of a new advanced software

The Group of High Performance Manufacturing of the University of the Basque Country (UPV/EHU) conducts training of specialized industrial engineers, providing specific courses of Advanced Manufacturing together with student participation in innovative projects. Arising from the research activities of the High Speed Machining (HSM) division, a new software with key utilities is presented as a personal approach of the authors to address vibrations and other problems in distinct machining systems. The tool begins to be used during computer‐based practice sessions as well as during practical sessions at the mechanical workshop. It is capable of generating predictive results and extracting direct information from real data. Following the objectives of the instructional strategy, a more than favorable perception was found from the surveys and examination passing rates. This evolving application is conceived of as an introductory learning and training tool for vibration analysis for future manufacturing engineers to reduce the gap between the theoretical and practical sides of the subject.

Effect of centrifugal forces on dimensional error of bored shapes

Boring operations of deep holes with a slender boring bar are often hindered by the precision because of their low static stiffness and high deformations. Because of that, it is not possible to remove much larger depths of cuts than the nose radius of the tool, unlike the case of turning and face milling operations, and consequently, the relationship between the cutting force distribution, tool geometry, feed rate and depth of cut becomes non-linear and complex. This problem gets worse when working with a rotating boring head where apart from the cutting forces and the variation of the inclination angle because of shape boring, the bar and head are affected by de centrifugal forces. The centrifugal forces, and therefore the centrifugal deflection, will vary as a function of the rotating speed, boring bar mass distribution and variable radial position of the bar in shape boring. Taking in to account all this effects, a load and deformation model was created. This model has been experimentally validated to ...

Force and Deformation Model for Error Correction in Boring Operations

Boring operations of deep holes with a slender boring bar are often hindered by the precision because of their low static stiffness and high deformations. Because of that, it is not possible to remove much larger depths of cuts than the nose radius of the tool, unlike the case of turning and face milling operations, and consequently, the relationship between the cutting force distribution, tool geometry, feed rate and depth of cut becomes non-linear and complex. This problem gets worse when working with a rotating boring head where apart from the cutting forces and the variation of the inclination angle because of shape boring, the bar and head are affected by de centrifugal forces. The centrifugal forces, and therefore the centrifugal deflection, will vary as a function of the rotating speed, boring bar mass distribution and variable radial position of the bar in shape boring. Taking in to account all this effects, a load and deformation model was created. This model has been experimentally validated to use as a corrector factor of the radial position of the U axis in the boring head.