DESC:TECHINCAL FIELD
[001] The present subject matter relates to, particularly, but not exclusively relates to machining operations.
BACKGROUND OF THE INVENTON
[002] Machining operations, such as grinding operation, milling operation or the like involves removing bits or chips of metals from a work piece to achieve a finished product. For example, during grinding operation, a grinding wheel makes contact with a rough surface of the work piece to smoothen the surface by removing metal bits that causes roughness of the surface. However, machining operations generate lots of heat and the generated heat, if not removed in a correct manner, can lead to inconsistent material removal rates, thereby causing poor finish of work piece. Further, inconsistent material removal rate can cause damages to the surface of the work piece, and excessive cutting tool wear thereby resulting in shortend tool life. Moreover, heat generated during machining operation can cause temperature of workpiece to increase, which leads to phase transformations in the material. Generally, phase transformations are often responsible for tensile residual stresses, reduced fatigue life, surface and subsurface cracks. As a result, accumulation of heat may also result in change in strength of the work-piece.

[003] In order to dissipate the heat generated during the machining operation, coolants are used. Coolants are the fluids that dissipates the heat from the machining operation and also provide lubrication between the surfaces of the work-piece and the cutting tool, such as a grinding wheel. Generally, the amount of heat dissipated from the coolant is governed by various factors such as coolant pressure, flow rate, temperature of the coolant and direction of the jet. Further, velocity of the coolant is controlled by the pressure of the coolant feed, while the rate of heat dissipated is goverened by the flow rate and the temperature of the coolant .

[004] Generally, in order to ensure that no above mentioned defects are not introduced in the work-piece, the heat is dissipated in a systematic way. Generally, in a grinding operation, an amount of coolant needed to remove the heat varies across different stages of the grinding operation. For example, an amount of coolant needed during the finishing operation is less than the amount of coolant needed during the roughing operation. Conventionally, in order to vary the feed rate of the coolant, the flow of the coolant is controlled by a plurality of valves where each valve feeds a fixed rate of cooling. Further, a combination of valves is operated to attain a predetermined rate of cooling. For example, the coolant is fed at a maximum rate during roughing operation on a work-piece, such as a crankshaft and the coolant is fed at a minimum rate during the finishing operations. Further, a reduction in the flow rate is achieved by the cutting operation of one or more valves to reduce the feed. However, a sudden drop in feed causes reduction in pressure near to the area of operation, thereby causing vibrations in the work piece. Further, such vibrations can disturb the position of the work piece. As a result, the work-piece may not be grounded properly, leading to a defective finished product. This also results in chatter marks generation at workpiece and increase in BNA (Barkhausen Noise Analysis) value. Further, vibrations can be reduced by retracting the cutting tool from the work piece, letting the vibrations settle, and engaging the cutting tool. However, retracting and engaging the cutting tool adds to the production time. Moreover, since the feed pump runs all the time while the valves are operated, the power consumed by the system is also wasted.

OBJECTS OF THE INVENTION
[005] An object of the present invention is to reduce the time required to perform the machining operation.
[006] Another object of the present invention to reduce the power required to perform the machning operation.
[007] Yet another object of the present invention is to elimate the imperfections occurred in product during the machining operation.
[008] Yet another object of the present invention is to reduce the noise and vibration occuring during the machining operation.
SUMMARY
[009] This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.
[0010] The present invention aims to alleviate the problems associated with the conventional coolant feeding system. The present subject matter is simple in design and prevents sudden change in feed rate thereby preventing imperfections in the final work piece.
[0011] In one implementation, an apparatus for machining a work piece is provided. The apparatus includes a work station to hold the work piece and a spindle head to mount and rotate cutting tool. The apparatus also includes a controller to control the operations, such as cutting speed, movement of the work piece, spindle head, feed of the coolant or the like. Further, the apparatus includes a coolant tank and a coolant pump. The coolant pump, in operation, feeds the coolant from the tank to the work station. The apparatus also includes a coolant feed controller that controls the operation of the coolant pump.
BRIEF DESCRIPTION OF DRAWINGS
[0012] Fig. 1 illustrates a grinding machine, in accordance with one implementation of the present subject matter.
[0013] Fig. 2 shows pump discharge curves, in accordance with one implementation of the present subject matter.
DETAILED DESCRIPTION
[0014] Fig. 1 illustrates an apparatus 10 for machining a work piece 12, in accordance one implementation of the present subject matter. The apparatus 10 can be, but not limited to, grinding machine, milling machine. In one example, the apparatus 10 can be a CNC based orbital grinding machine. Further, the apparatus 10 includes a workstation 14 to hold the work piece 12 in position. The workstation 14 can be a mount, platform, or the like. The apparatus 10 also includes a spindle head 16 to mount a cutting tool 18, such as a grinding wheel. Although a single spindle head 16 is shown, it may be understood that the apparatus 10 can have multiple spindle heads.

[0015] In one example, the apparatus 10 may include a cutting fluid tank 20 that stores cutting fluid or coolant which is fed to work piece by a coolant pump 22 to cool the work piece 12 during machining operation. In operation, the coolant pump 22 feeds the coolant at a predetermined flow rate. The apparatus 10 further includes a COOLANT FEED CONTROLLER 24 coupled to the coolant pump 22 to control the operation of the coolant pump 22. The manner by which the COOLANT FEED CONTROLLER operates would be explained in details in subsequent embodiments. The apparatus also includes a controller 26 coupled to the spindle head 16, and the COOLANT FEED CONTROLLER 24. In one example, the controller 26 can be a microprocessor used to store logics and instructions to perform the machining operation.

[0016] According to an aspect, the COOLANT FEED CONTROLLER 24 operates the coolant pump 22 to vary the amount of the coolant to be fed for the machining operation. In other words, the COOLANT FEED CONTROLLER 24 controls the coolant pump 22 to vary a feed rate of the coolant. Further, the COOLANT FEED CONTROLLER 24 may vary the flow rate of the coolant based on the step being performed during the machining operation. Moreover, the COOLANT FEED CONTROLLER 24 changes the feed rate of the coolant at a predetermined rate which is termed as acceleration/ deceleration rate. Exemplary operation characteristics of the coolant pump 22 are mentioned in the table 1 below.

Coolant flow
(%) Pressure
(bars) Frequency
(Hz) Motor Current
(Amps) Time
(sec)
100 8-10 50 17-18 330
70 4-6 35 11-12 110
30 1-2 16 6-7 160
Table 1: Operational characteristics of the coolant pump
[0017] For example, during the roughing operation, the coolant is fed at 100% of the predefined flow rate at 10 bars as shown in the table 1. During subsequent operation, such as the semi grinding operation, flow of the coolant is reduced to 70% of the predefined flow rate. Furthermore, during the finishing operation, the flow of the coolant is further reduced to 30% of the predefined flow rate. From this, it is clear that during the operation of the coolant 22, the COOLANT FEED CONTROLLER 24 changes the feed rate of the coolant by reducing the frequency fed to the coolant pump 22. As a result, a combination of COOLANT FEED CONTROLLER 24 and the coolant pump 22 does away the need of fixed flow rate valves. Moreover, the COOLANT FEED CONTROLLER 24 varies the current at a proportional rate. As a result, the coolant pump 22 reduces the feed rate at the proportional rate as opposed to sudden drop of feed rate in case of conventional systems. Therefore, no vibrations occur since back pressure is not created during a change in feed.

[0018] In addition, the COOLANT FEED CONTROLLER 24 can be configured to maintain an acceleration rate/ deceleration rate of the coolant pump 22. As shown in Fig. 2, the COOLANT FEED CONTROLLER 24 reduces the current flow to a pump to reduce speed, thus the flow also causes the pump discharge curve to shift down. Since, the COOLANT FEED CONTROLLER 24 does not operate the coolant pump 22 at full speed, energy needed to run the coolant pump 22 is reduced. Moreover, not running the coolant pump 22 at the maximum capacity also results in longer pump seal life, reduced impeller wear and less vibration in the coolant pump 22.

[0019] During operation, the work piece 12 is mounted on the work station 14. Thereafter, logic instructions are fed into the controller 26 and the controller 26 is set to initiate the machining operation. Thereafter, the controller 26 operates the spindle head 16 to run the grinding wheel against the work-piece . In response spindle head 16 sends feedback to the controller 26, as shown by dotted lines. Simultaneously, the controller 26 instructs the COOLANT FEED CONTROLLER 24 to run the coolant pump 22 to feed the coolant at the defined rate. As the operation proceeds and a change the coolant flow is needed, the COOLANT FEED CONTROLLER 24 changes the flow of the coolant at a proportional rate. Accordingly, the coolant pump 22 changes the feed rate of the coolant. Since the change in the feed rate is not abrupt, the work piece 12 does not deflect. As a result, the work piece 12 machined by the apparatus is free from machining imperfections or defects.

[0020] Technical Advancement and Economic Significance
a. The present invention reduces the cycle time by 8% as compared to conventional system as the cutting tool retraction is eliminated during maching operation changeover.
b. The present invention reduces possible causes for chatter marks and hence BNA Values reduced by 14%.
c. Due to present invention, the energy cost is reduced by 34%.

[0021] The above description of exemplary embodiments of the present invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the embodiments of the invention to the precise forms disclosed above. Although specific embodiments and examples are described herein for illustrative purposes and to allow others skilled in the art to comprehend their teachings, various equivalent modifications may be made without departing from the spirit and scope of the disclosure, as will be recognized by those skilled in the relevant art.
,CLAIMS:I/WE CLAIM:
1. An apparatus (10) for machining a work-piece in a plurality of steps, the apparatus (10) comprising:
a workstation (14) to hold a work-piece (12) ;
a controller (26) operably coupled to the spindle head (16) , and the coolant feed controller (24) to regulate machining of the workpiece;
a coolant pump (22) coupled to a tank to feed the coolant to the workstation (14) at variable feed rates, wherein an instaneous feed rate of the coolant is based on a step of machining operation; and
a coolant feed controller (24) operably coupled to the coolant pump (22) and a controller (26) , wherein the coolant feed controller (24) controls the coolant pump (22) to vary the flow rate of the coolant based on the step of the machining operation.
2. The apparatus (10) as claimed in claim 1 further comprises a spindle head (16) and a cutting tool (18) mounted thereon to:
perform the machining operation on the work-piece (14) ; and
provide feedback to the controller (26) based on the machining operation, wherein the feedback is indicative of a step amongst the plurality of steps of the machining operation.
3. The apparatus (10) as claimed in claim 2, wherein the controller (26) is to control a speed of the spindle.
4. The apparatus (10) as claimed in claim 1, wherein the coolant feed controller (24) is to change the feed rate at a predetermined rate.
5. The apparatus (10) as claimed in claim 1, wherein the coolant feed controller (24) is to vary on of electric current and a frequency of electric current that powers the coolant pump (22) .
6. A method of machining a workpiece (12) in a plurality of steps, the method comprising:
mounting the workpiece (12) on a workstation (14) ;
operating a cutting tool (18) mounted on a spindle head (16) to initiate the machining operation and feeding the coolant, using a coolant pump (22), to the workstation (14) and to the workpiece (12) at an initial flow rate;
recieving a feedback from the spindle head (16) , wherein the feedback is indicative of the step being performed;
determining the step of the machining operation being performed by using controller (24) based on a feedback from the spindle head (16) ; and
changing the feed rate of the coolant based on the determined step using coolant feed controller (24) .
7. The method as claimed in claim 6, wherein changing comprises varying one of electric current and a frequency of electric current that powers the coolant pump (22) .
8. The method as claimed in claim 6, wherein changing comprises varying the feed rate at a predetermined rate.
9. The method as claimed in claim 6, further comprises changing a speed of the cutting tool based on the determined step of the machining operation.