MÉtodo de rectificado con variaciÓn de la presiÓn de refrigeracion

Abstract

The present invention relates to a grinding method with continuous variation of the cooling pressure, for the surface finish machining of a workpiece (1) by means of a grinding wheel (2) that rotates at a speed (Vs), contacting tangentially in a machining area (3) the workpiece (1) to be ground, which rotates at a speed (Nw), with approximation by means of a speed (Vf) of the grinding wheel (2) towards the workpiece (1) to be ground at and providing a jet (4) of liquid coolant in the machining area (3), which is sprayed by means of a pump (5) at a cooling pressure, using a pump (5) with variable pressure, to carry out the grinding process with a continuous and numerically-controlled variation of the cooling pressure, in combination with different factors of the grinding process.

Description

Technical field

[0001] The present invention relates to the grinding that is carried out to obtain high precision machining in the surface finish of workpieces, proposing a method of performing said grinding that is performed with continuous variation of the cooling pressure, with which it is possible to avoid possible disturbances generated by abrupt or stepwise variations in the cooling conditions during the machining process.State of the art

[0002] Grinding is a process that is performed as a finishing technology in the manufacture of machined workpieces, generally using a rotating grinding wheel that acts tangentially on the workpiece to be ground, also arranged in a rotating assembly, providing the contact area between the two with a cooling liquid to prevent the generation of an excessive temperature due to the machining action.

[0003] Under these conditions, the rotation speed of the workpiece being ground, the rotation speed of the grinding wheel and the approximation feed speed between the grinding wheel and the workpiece being ground must be taken into account during the grinding process.

[0004] Accordingly, there are different strategies to optimise the grinding process, generally based on varying the approximation feed speed between the grinding wheel and the workpiece being ground in a constant stepwise manner, while maintaining the rotation speed of the grinding wheel and the rotation speed of the workpiece being ground unchanged during successive stages of a grinding cycle, whereby the variation of the feed speed of the grinding wheel towards the workpiece being ground, according to the constant steps, causes abrupt jumps between the steps of said feed speed of the grinding wheel, resulting in process instabilities, such as vibrations, which cause an uneven finish on the surface of the workpiece being ground.

[0005] The stepwise variation of the workpiece speed and the cooling pressure (or other variables of the cooling conditions) is known, which, in addition to the stepwise variations of the feed speed, generates disturbances, small vibrations, which can lead to a poor workpiece finish.

[0006] To prevent this problem, patent DE102006015038 discloses a grinding method in which the rotation speed of the workpiece being ground varies according to a sinusoidal function, which partly minimises the occurrence of vibrations, but does not achieve a completely correct surface finish of the workpiece being ground. In addition, due to the stepwise variation of the rotation speed, disturbances are also generated which can lead to a poor workpiece finish.

[0007] Moreover, patent EP2610030, from the same applicant as the present invention, proposes a grinding method based on a continuous and combined variation of all the speeds involved in the grinding process, which prevents the phenomenon of regeneration of chatter, as well as preventing the regeneration of error patterns associated with constant forced vibration components and affecting in a continuous and controlled manner the thermo-mechanical behaviour of the start, thereby allowing less consumption and heat to be generated in a roughing step, thus improving the behaviour of the grinding process compared to methods with stepwise variation of the feed of the grinding wheel towards the workpiece being ground, since sudden changes in speed that cause disturbances during the grinding process are prevented.Object of the invention

[0008] The present invention proposes a grinding method for machining the surface finish of machined workpieces, wherein the cooling pressure is varied continuously and in a controlled manner by means of a numerical control of the grinding machine acting on a variable pressure pump. To establish the continuous variation of the cooling pressure, signals are used that ensure a progressive reduction of the cooling pressure, for example ramp, sinusoidal or logarithmic signals, throughout the grinding cycle.

[0009] In relation to this, the variation of the cooling pressure is performed as a function of the speed of the wheel and the thermo-mechanical load and / or the chip thickness of the machining according to the conditions of the feed speed of the grinding, the rotation speed of the workpiece being ground and the rotation speed of the grinding wheel, whether constant or variable throughout the grinding cycle, such that, having defined the variation of the cooling pressure throughout the grinding cycle, with its start and end values, and the form of the variation, a command is sent from a signal generation module to the variable pressure pump to vary the cooling pressure in a controlled manner for the duration of the grinding operation.

[0010] However, as the cooling pressure varies, the flow rate sent by the variable pressure pump for cooling varies, such that said variation in the coolant flow rate can be determined, for example, depending on a pressure-flow rate curve of the pump.

[0011] Furthermore, the variation of the cooling pressure can also be determined as a function of the limit temperature in the area where the workpiece to be ground is machined and as a function of the hydrodynamic factor in the contact area between the grinding wheel and the workpiece being ground.

[0012] In the method of the invention, in addition to the control of the cooling pressure, this control is also combined with the process parameters, that is, the feed rate of the machining, the rotation speed of the workpiece being ground and the rotation speed of the grinding wheel.

[0013] By controlling the cooling pressure and flow rate during the grinding cycle, surface quality, dimensional tolerances and integrity of the workpiece being ground are improved and a more sustainable process can be achieved by using the most suitable liquid coolant conditions at each point in the grinding cycle.

[0014] In addition, by applying a controlled progressive decrease of the cooling pressure, depending on the thermo-mechanical load of the process and / or the chip thickness of the grinding and the limit temperature of the area in which the grinding wheel is acting on the workpiece to be ground, disturbances and errors associated with staggered cooling pressure variations during the grinding cycle are minimised, and there is possibility of continuous and controlled adaptation of the cooling conditions to the thermo-mechanical conditions of the start-up process, while the strategy of reducing the cooling pressure of the grinding process reduces the consumption of the cooling pump and also reduces the generation of heat due to friction caused by the liquid coolant circulating at high pressure through the supply circuit, as well as the resulting consumption of the cooler required to cool said liquid coolant.

[0015] For all these reasons, the grinding method of the invention has very advantageous features for a suitable finish of the workpieces being ground, and therefore this method has a life of its own and is preferential with respect to conventional methods for the same function.Description of the Figures

[0016] Figure 1 represents a conventional diagram of the grinding process of a workpiece, in which the method of the invention is applicable. Figure 2 shows a graph of the variation of the cooling pressure during a grinding cycle according to the method of the invention. Figure 3 shows graphs of the feed speed of the grinding wheel towards the workpiece being ground, the rotation speed of the workpiece being ground and the rotation speed of the grinding wheel, in a grinding cycle according to the method of the invention. Detailed description of the invention

[0017] The subject matter of the invention relates to a grinding method for the surface finishing of a workpiece (1) by means of rough machining with a rotating grinding wheel (2) that acts on an area (3) of tangential contact on the workpiece (1) also arranged in a rotating assembly, the machining process being carried out with the provision of a jet (4) of liquid coolant that is sprayed onto the area (3) of contact between the grinding wheel (2) and the workpiece (1), as shown in figure 1.

[0018] In the grinding process, the jet (4) of liquid coolant is supplied at a pressure by a pump (5), while the workpiece (1) to be ground rotates with a speed (Nw) and the grinding wheel (2) rotates with a rotation speed (Vs), the grinding wheel (2) feeding towards the workpiece (1) with a linear speed (Vf).

[0019] Under these conditions, the method of the invention is based on performing the grinding process with a continuous variation of the pressure of the cooling jet (4), said variation being controlled by a numerical control of the grinding machine.

[0020] Continuously varying the pressure affects the pressure and flow rate, which results in a certain speed (Vc) (and flow rate) of the outlet jet through a cooling nozzle.

[0021] Accordingly, a variable pressure pump (5) is used to apply the jet (4) of liquid coolant and an optimal variation strategy of the cooling pressure is selected for the process by means of signals that ensure a progressive reduction of said cooling pressure during the grinding cycle, such as ramp, sinusoidal or logarithmic signals.

[0022] It should be noted that variable pressure pumps (5) are also known as variable frequency pumps (5), which are configured to vary the speed of the motor (for example, within a range of 10% to 100%).

[0023] The variation of the cooling pressure is also carried out as a function of the thermo-mechanical load of the process, and / or the chip thickness of the chip that the grinding wheel (2) removes from the workpiece (1), according to the conditions used of the feed speed (Vf) of the grinding wheel (2) towards the workpiece (1) being ground, the rotation speed (Nw) of the workpiece (1) and the rotation speed (Vs) of the grinding wheel (2), such that, once the variation of the cooling pressure during the grinding cycle has been defined with its start and end values, as well as the form of the variation, a command is sent from a signal generation module to the variable pressure pump (5) to vary the cooling pressure in a controlled manner for the duration of the grinding operation.

[0024] However, with the variation of the cooling pressure, there is, in turn, a variation of the flow rate sent by the variable pressure pump (5), for example, according to a pressure-flow rate curve.

[0025] Furthermore, the cooling pressure can also be varied according to the limit temperature of the area (3) in which the grinding wheel (2) acts on the workpiece (1) being ground, as well as according to the hydrodynamic effect factor that occurs in that area (3) of contact between the grinding wheel (2) and the workpiece (1) being ground.

[0026] Therefore, in addition to the control of the cooling pressure, in a progressive reduction variation as shown in figure 2, the grinding method also combines said control with the parameters involved in the grinding process, which are the feed speed (Vf) of the grinding wheel (2) towards the workpiece (1) being ground, the rotation speed (Nw) of the workpiece (1) and the rotation speed (Vs) of the grinding wheel (2), varying said parameters according to the curves shown in figure 3.

[0027] Thus, by controlling the cooling pressure and the flow rate of the cooling jet (4) during the grinding cycle, the surface quality, dimensional tolerances and integrity of the workpiece (1) being ground are improved and, in addition, more sustainable grinding processes can be achieved by using the most appropriate conditions of the liquid coolant.

Claims

1. A method of grinding with continuous variation of the cooling pressure, using a grinding wheel (2) rotating at a speed (Vs), acting in abrasion on an area (3) of tangential contact with a workpiece (1) to be ground that rotates at a speed (Nw), with spraying onto the area (3) of a jet (4) of cooling liquid that is supplied at a pressure by means of a pump (5), the grinding wheel (2) feeding towards the workpiece (1) at a linear speed (Vf), characterised in that the grinding process is carried out by continuously varying the pressure of the jet (4) of liquid coolant, regulating said variation by means of a numerical control of the grinding machine.

2. The grinding method with variation of the cooling pressure according to claim 1, characterised in that in order to regulate the variation of the cooling pressure, signals are used that guarantee a progressive reduction of said cooling pressure, such as ramp, sinusoidal or logarithmic signals.

3. The grinding method with variation of the cooling pressure according to claim 1, characterised in that the variation of the cooling pressure is regulated according to the thermo-mechanical load of the machining and / or the thickness of the chip removed by the action of the grinding wheel (2) on the workpiece (1) being ground, the rotation speed (Nw) of the workpiece (1) to be ground and the rotation speed (Vs) of the grinding wheel (2).

4. The grinding method with variation of the cooling pressure according to claim 1, characterised in that the variation of the cooling pressure is regulated according to the limit temperature of the area (3) in which the grinding wheel (2) contacts the workpiece (1) being ground and the hydrodynamic factor produced in said area (3) by the cooling.

5. The grinding method with variation of the cooling pressure according to claim 1, characterised in that the variation of the cooling pressure is combined with the feed speed (Vf) of the grinding wheel (2) towards the workpiece (1) being ground, the rotation speed (Nw) of the workpiece (1) being ground and the rotation speed (Vs) of the grinding wheel (2).

6. The grinding method with variation of the cooling pressure according to claim 1, characterised in that a variable pressure pump (5) is used to supply the jet (4) of cooling liquid.

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