APARATO DE USINAGEM CRIOGÊNICA COM NITROGÊNIO LÍQUIDO SOB CAVACO

Abstract

This invention, belonging to the field of engineering, consists of an apparatus for applying liquid nitrogen to the contact interface between a chip and a textured cutting tool. Comprising a modified tool holder and a textured cutting tool, this invention presents the innovative technique of cryogenic machining through the application of liquid nitrogen in contact regions inaccessible to any other cryogenic machining technique. The reduction of the contact area promoted by the application of textured cutting tools allows the chip-tool contact interface to be reached by liquid nitrogen through a modified micro-channel present in the textured region. The device possesses functional characteristics with a fundamentally innovative character, representing a significant advance over the current state of the art.Longer tool life, lower aggregate costs, shorter production time, and improved machining conditions for poorly machinable materials and metallic superalloys are cited as advantages associated with the present invention. The apparatus and its use are claimed.

Description

Cryogenic machining apparatus with liquid nitrogen under chip.

[001] The present invention, belonging to the field of engineering, consists of an apparatus for applying liquid nitrogen to the contact interface between a chip and a textured cutting tool. Consisting of a modified tool holder and a textured cutting tool, the present invention presents the innovative technique of cryogenic machining by applying liquid nitrogen to contact regions unreachable by any cryogenic machining technique. The reduction of the contact area promoted by the application of textured cutting tools allows the chip-tool contact interface to be reached by liquid nitrogen through a modified micro-channel present in the textured region. The device has functional characteristics with a fundamentally innovative aspect, representing a great advance for the current state of the art.

[002] Longer tool life, lower aggregate costs, shorter production time and better machining conditions for low-machinability materials and metal superalloys are cited as advantages associated with the techniques. STATE OF THE ART

[003] During the machining process, friction between the workpiece and the tool causes deterioration of the workpiece surface quality and energy loss, as well as wear on the cutting tool. Some studies have shown that machining accounts for approximately 31% of total energy consumption in developed countries, such as Europe and America; therefore, the energy expended due to friction is extremely important. Currently, the main method for reducing friction and wear on cutting tools is the use of cutting fluid, which can play a role in lubrication. However, the production, application, and disposal of cutting fluids cause significant pollution. Petition 870200158413, dated 12 / 17 / 2020, page 13 / 29 -2 / 9 seriously harming the environment and increasing production costs.

[004] The aeronautical and automotive industrial sectors, for example, encounter certain machining difficulties, since the materials they use have special characteristics that make machining with conventional lubrication difficult. Super duplex stainless steels and superalloys such as Inconel and Waspaloy are corrosion-resistant alloys with high mechanical strength, developed for applications with high levels of technical requirements. Given their qualities, the machinability of these alloys is very low, resulting in long production cycles and high tooling costs, even when using tools specifically designed to withstand the typical stresses of these materials.

[005] Thus, cryogenic machining based on the application of liquid nitrogen, for example, is applied in machining conditions of high-strength, low-machinability materials. However, liquid nitrogen application techniques are not effective in reaching the cutting interface between chip and tool in jet or spray applications.

[006] More recent studies indicate that surface modifications promoted at the cutting interface alter tribological conditions during machining. This modification is characterized by surface texturing, which aims to provide the cutting tool with micro or nano surfaces at the contact interfaces or in their vicinity. Results indicate that applying altered surfaces through texturing can improve the interaction between chip and tool, making it possible to achieve reductions in cutting forces, friction, machining temperatures, and increased tool life. These improvements are achieved through a reduction in the contact area, a larger heat exchange area, and the ability to store micrometric machining residues and lubricant. Furthermore, the application of Petition 870200158413, dated 12 / 17 / 2020, page 14 / 29 -3 / 9 lubricants in textured cutting tools favor capillary lubrication at the contact interface and promote hydrodynamic lubrication during machining.

[007] Thus, the present invention presents the innovative technique of applying cryogenic machining with textured tools equipped with micro-channels, which allow the application of liquid nitrogen under the chip. Searches carried out in the main patent databases aimed to verify the most recent patents concerning textured cutting tools and cryogenic machining. Patent BRPI0501328 presents a cryogenic machining application system by means of jets positioned in the vicinity of the chip formation region, being extended to any application of cryogenic fluid or manufacturing process, in a manner very similar to that found in patent AU1995033236. Another invention presented in patent WO2012107267 consists of a specific machining system for machining crankshafts, characterized by the presence of a tool holder carrying several machining inserts and nozzles for applying cryogenic jets.Indian patent 2177DEL2009 defends the technique of cryogenic jets for machining brass. The application of liquid nitrogen can be observed in patent PI20063059, where there is a closed system for the circulation of liquid nitrogen that cools the cutting tool without injecting the fluid into the machining environment. With a view to breaking the chip by means of a cryogenic jet, patent WO1996005008 presents the technique of applying a cryogenic jet from an orifice contained in a chip breaker insert in the cutting tool; this jet can be of any origin, but must meet the characteristic of reduced temperature.

[008] Techniques presented regarding textured tools can be seen in patents MX2016014284, IN201611016675, EP2580370, Petition 870200158413, dated 12 / 17 / 2020, page 15 / 29 The patents BRPI0501328, AU1995033236, WO2012107267, 2177DEL2009, PI20063059 and WO1996005008, which deal with traditional applications for textured cutting tools, do not provide any indication regarding cryogenic machining by applying liquid nitrogen. Similarly, the current state of the art represented by patents BRPI0501328, AU1995033236, WO2012107267, 2177DEL2009, PI20063059 and WO1996005008 makes no mention of textured cutting tools nor cutting tools provided with micro-channels at the contact interface, covering only conventional jetting or internal cooling techniques.

[009] In view of the foregoing, the invention presented is unique and innovative, providing a great advance in the current state of the art and allowing better machining conditions for materials with low machinability. ADVANTAGES OF THE INVENTION

[010] The proposed invention demonstrates several uses and important applications for users, of which the following are cited:

[011] It is presented in the form of a set between tool holder and textured cutting tool provided with micro channels for liquid nitrogen jet lubrication;

[012] Positioning the micro channel on the textured interface allows for the application of liquid nitrogen at the contact interface;

[013] Applying liquid nitrogen to the contact interface allows for a reduction in friction at the contact interface, due to the formation of a thin layer between the chip and the tool;

[014] With adequate pressure and flow, better chip breakage occurs;

[015] It provides the elimination of traditional cutting fluids and eliminates costs associated with their disposal; Petition 870200158413, dated 12 / 17 / 2020, page 16 / 29 -5 / 9

[016] Applying liquid nitrogen to a textured contact area via a micro-channel allows for a reduction in the amount of liquid nitrogen needed compared to other cryogenic applications with external jets; and

[017] Expands the machining capacity of steels such as superalloys and super duplex, reducing the manufacturing cost of demanding mechanical components. BRIEF DESCRIPTION OF THE FIGURES

[018] In order to have a better visualization of the characteristics of the invention, descriptions of the following figures are presented.

[019] Figure 1 shows the cutting tool (1) and its textured region (2). The liquid nitrogen supply micro-channel (3) is indicated in the cutting section AA.

[020] Figure 2 shows the tool holder (4) and indicates by means of cut BB the liquid nitrogen supply channel (5).

[021] Figure 3 shows the support element for the cutting tool (1) being presented by the name of shim (6), which, for the correct supply of liquid nitrogen at the cutting interface, is equipped with a micro channel (7), represented by the cut CC.

[022] The assembly of the set for application is shown in Figure 4, representing the textured cutting tool (1), the tool holder (4) and the shim (6).

[023] Figure 5 shows the average efforts obtained experimentally for the evaluated conditions.

[024] Figure 6 shows the comparison between the volume of material removed and the life of the cutting tools.

[025] The system is represented by the CTGPL 20x20 tool holder and the TPUN 160308 cutting tool, but it can be replaced by other tool holder geometries and textured tools that can meet the minimum application requirements. Petition 870200158413, dated 12 / 17 / 2020, page 17 / 29 -6 / 9 DETAILED DESCRIPTION OF THE INVENTION

[026] Prior to this, the cutting tool must have a textured region, exhibiting features such as micro or nano grooves, micro or nano holes, or any texturing geometry compatible with the machining process. The tool presented in the invention is made of tungsten carbide, but other tool materials compatible with the process may be used.

[027] In the textured region, a micro hole is preferably made, with a diameter that does not compromise physical integrity during machining, and can be made by any machining process that can meet the dimensional requirements of the project.

[028] Along with the change of cutting tool, a channel for the passage of liquid nitrogen is made in the tool holder, as well as a micro channel in the cutting tool shim.

[029] The assembly of the unit is carried out in such a way as to position the micro channels and promote the ideal flow of liquid nitrogen during machining.

[030] The flow of liquid nitrogen is promoted by a pumping system, piping and connections suitable for the fluid in question.

[031] Its innovative operation is characterized by the application of liquid nitrogen during machining at the contact interface between chip and tool, in which the textured surface allows the formation of micro pools of cryogenic fluid, assisting in the reduction of friction, forces, temperature and better chip breaking conditions.

[032] Controlled laboratory tests were carried out to verify the functionality of the present invention. The procedures and results found during the analyses are described below. Procedure for analyzing forces, coefficient of friction, and tool life. Petition 870200158413, dated 12 / 17 / 2020, page 18 / 29 -7 / 9

[033] The tests were performed on a ROMI brand CNC lathe, model Centur 30D, on which a Kistler brand three-coordinate dynamometer, model 9257BA, was mounted. The dynamometer signals are sent to the 5233 A1 control unit, where the signals were configured in Fx, Fy, and Fz according to the forces reached during machining. The coaxial outputs of the dynamometer control unit were connected to a National Instrument model NI-9207 analog data acquisition module, connected to the cDaq-9188 ethernet chassis, also from National Instrument, and read on a computer with Labview® analysis software at an acquisition frequency of 200 Hz.

[034] Cutting forces were measured in each test and represented by their average values ​​for each pass until the end of the tool life. The cutting force values ​​measured during the tests were applied to quantify the coefficient of friction between chip and tool, as proposed in Equations 1, 2 and 3: Fat = (Fxy + Fztana)cosa (1) Fn = (Fz - Fyy tan cr) cos a (2) μ = (3) where, Fat is the friction force, FN is the force in the direction normal to the rake face and Fxy = Fx / sin(90 - θ), α is the rake angle and θ is the tool positioning angle or lateral angle of the cutting edge. The lateral angle of the cutting edge is defined as the angle between the cutting edge and the lateral surface of the tool holder. In the given situation, the assembly between the cutting tool and the tool holder has θ = 1° and α = 6°. This relationship represents the value of the overall coefficient of friction, and cannot only indicate Petition 870200158413, dated 12 / 17 / 2020, page 19 / 29 -8 / 9o friction in a given region, which, as already presented, can originate from the flank surface, tip, or exit surface of the cutting tool.

[035] The ISO 3685 standard establishes that one of the criteria for the end of life of a cutting tool is a mean flank wear of 0.3 mm (VBB). During the tests, the wear was measured until it reached the limit value of 0.3 mm, or the operation was interrupted if a catastrophic failure occurred in the tool. The measurement was performed using data obtained from images taken with an optical microscope (Nikkon SMZ 800) coupled to a digital camera.

[036] The evaluated results were compared based on the application of turning with conventional lubrication and cooling and the present invention. The cutting parameters applied were fixed at a cutting speed of 100 m / min, a feed rate of 0.2 mm / rev, and a depth of cut of 1 mm. Next, we present the results in terms of tool life and cutting forces. Results regarding shear force and friction.

[037] Machining with the application of liquid nitrogen at the cutting interface, enabled by the present invention, has allowed for significant improvements in machining conditions. Figure 5 shows the average cutting forces obtained experimentally for the conventional condition and the condition presented in this invention. The reduction in forces of up to 35% was achieved thanks to the low temperatures of the nitrogen and the application region. Traditional techniques for applying liquid nitrogen in turning apply the fluid directly onto the chip, thus not reaching the necessary region. The application of liquid nitrogen under the chip, as enabled by the present invention, can drastically reduce fluid consumption, generating real possibilities for cryogenic machining of difficult-to-machine materials. The reduction in forces is a result of the drastic reduction in Petition 870200158413, dated 12 / 17 / 2020, page 20 / 29 -9 / 9 temperature. The reduction in adhesion resulting from the high temperatures reduced the friction from 0.62 to 0.55. Results of the cutting tool life analysis.

[038] Figure 6 shows the wear profile for conventional conditions and the condition applied in the present invention. The conventional tool reached the end of its life after removing approximately 150 cm3 of material, while the textured cutting tool equipped with the present invention removed approximately 217 cm3 of material, showing an increase of approximately 41% in the volume of material removed. Conventionally, cryogenic machining removes temperature globally; however, in the present invention, liquid nitrogen is applied to the contact interface, more specifically between the chip and the tool, a condition only permitted by the present invention. The rapid cooling of the cutting tool and the chip can prevent material exchange on an atomic scale (diffusion). Therefore, the cutting edge of the cutting tool can remain preserved for a longer time, thus removing a greater amount of material compared to the conventional condition.

[039] Finally, it is noted that the unique feature seen in this invention represents a major evolution for cryogenic machining processes, aiming at cost-effectiveness of the machining process with reduced machining times, reduced volume of liquid nitrogen applied and increased life of the cutting tools used.

Claims

1 - CRYOGENIC MACHINING APPARATUS WITH LIQUID NITROGEN UNDER CHIP, comprising a cutting tool (1), a tool holder (4) and means for directing cryogenic fluid to the tool-chip interface, characterized in that said cutting tool (1) has at least one textured region (2) integrated with at least one liquid nitrogen supply microchannel (3), said microchannel (3) being fed by a network of internal channels (5, 7) arranged concentrically in the tool holder (4) and in a shim (6), configured to establish a pressure gradient capable of forming a liquid nitrogen lubricating-cooling film at the contact interface defined by the textured region (2). 2 - APPARATUS, according to claim 1, characterized by comprising a high-precision pumping system connected to the network of channels (5, 7, 3), operating in a controlled flow regime for maintaining a hydrodynamic fluid film between the geometry of the textured region (2) and the lower surface of the chip during the material removal process. 3 - USE OF THE APPARATUS, as defined in claims 1 and 2, characterized by being applied in machining processes, where the morphologies of the textured region (2) allow, concomitantly with the manufacturing process, the supply of liquid nitrogen below the chip to optimize thermal conductivity in the cutting zone. 4 - USE, according to claim 3, characterized by being implemented in cutting tools manufactured from tungsten carbide with cobalt binder, high-speed steel (HSS), cubic boron nitride (CBN) or polycrystalline diamond (PCD), aiming at reducing thermal wear via integration of surface texturing with cryogenic under-chip cooling.

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