A common problem in the aeronautical industry is the chatter vibration due to the lack of dynamic stiffness in the milling of thin walls and thin floors. The present work proposes a method for chatter avoidance in the milling of flexible thin floors with a bull nose end mill. It allows the calculation of the thickness previous to finish milling or the minimum dynamic stiffness that the floor must have to avoid the chatter vibration appearance. To obtain these values, the stability model algorithm has been inverted to estimate the thickness or the dynamic stiffness required in a floor to allow a stable milling. This methodology has been validated satisfactorily in several experimental tests.
The working conditions for the aircraft engines components demand a good response of their mechanical properties at high temperatures and aggressive environments. Those challenging conditions force the use of new materials like titanium (and nickel) based alloys, qualified as difficult-to-cut materials due to their low machinability. Among them, the Ti-6A1-4V is very widespread because of its high strength/weight ratio. On the other hand, a very demand task for aeronautical components is the hole making operation, being in most cases, the last performed operation. For this reason, drilling operation is strongly related to the quality and productivity since any machining error could damage the component in the final steps. Thus, drilling operation determines the minimum machining time which is reflected upon the cost per unit. This study focuses the attention on a relative new technique that could replace the conventional drilling resulting in a more added-value operation: ball helical milling (BHM). This new technique and a modified version (CBHM) were compared with a common drilling operation.
Free cutting steels, also referred to as free machining steels, include free cutting additives to improve tool life and machinability. Despite their wide applications in industry, scarce information is available to ensure reliable, safe, and productive cutting operations. This work presents a comparative study of the machinability of different free cutting steels to realize their real behavior and potential as alternatives to conventional steels. Three free cutting steels (SAE 12L14, 11L17, and 11L41), a resulfurized steel (SAE 1144), and a low-carbon steel (SAE 1010) were experimentally investigated employing turning tests. Key process parameters such as wear evolution, surface roughness, and material adhesion were analyzed. The results showed that low cutting speeds tend to improve tool life in free cutting steels, while this advantage disappears at high cutting speeds. Energy-dispersive X-ray spectroscopy analyses showed that chemical elements, such as Mn, S, and, especially Pb, play a significant role in self-lubrication at the cutting tool tip, thus reducing tool wear at low and medium cutting speeds. Besides, thermal simulations were done to verify the correspondence between material properties, machinability, and thermal field in the tool/chip interface.
Behavior of austenitic stainless steels is not well known and these materials are still considered as difficult to machining materials. Moreover, the continuous increment of cutting speeds and other cutting parameters derived from last technological advances in tool material makes it more difficult to understand the behavior of these materials in high performance machining. A mechanistic model is presented in this paper for cutting force prediction of austenitic stainless steels turned at very high cutting speeds (up to 750 m/min). The developed model allows the estimation of cutting forces in turning when the cutting action occurs on the side cutting edge and nose radius edge for general turning tools. A tool-part geometrical model is proposed and the cutting force coefficients have been calculated by means of characterization tests.
Manufacturing molds for plastic parts injection are a particular machining domain, where challenging materials, like AISI P20 steel, are forced to satisfy the highest surface quality requirements. Before mirror polishing, milling operation is a common and challenging task due to drilling and milling with the same tool. Thus, special cutting tools, like asymmetric indexable type, are often used. This tool presents two geometrically equal positive inserts -one placed horizontally and the other vertically -for the flexible machining of holes, cavities, floors, and walls. Rough-medium milling operations lead to a complicated relationship between cutting conditions and geometrical tool parameters, making it challenging to balance the tool life of both inserts. The novelty of this work is to propose a model for cutting force prediction with an asymmetric tool to explain the separated behavior of both inserts and determine a better compromise between cutting conditions and tool life. The experimental tests were done for model validation and then wear cutting tests for testing improved cutting conditions. The results predicted by the model proved that by changing the depth of cut from 0.3 mm to 0.8 mm, the wear in both inserts was more balanced, increasing chip volume up to 1.7 times.
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