METHOD AND APPARATUS OF MACHINING WITH IMPROVED CHIP CONTROL

Abstract: A nozzle apparatus (10) adapted for use with machine tools of different configuration, which perform different machining operations, comprises a nozzle body (26) having a nozzle insert (42) mounted within an outlet passageway (36) formed in the nozzle body at its intersection with a coaxial, larger diameter inlet passageway (28) connected to a source (34) of coolant. The nozzle insert and outlet passageway are constructed to induce the formation of shock waves within the coolant stream in the course of its passage through the interior of the nozzle body which increase the energy and velocity of the coolant stream so that it is effective to pierce the heat barrier developed at the interface between the cutting insert (18) and workpiece (14), and to assist in the breakage of chips (87) from the workpiece.

Description: METHOD AND APPARATUS OF MACHINING WITH IMPROVED CHIP CONTROL Field of the Invention This invention relates to metal working operations such as turning, milling, facing, thread¬ ing, boring and grooving, and, more particularly, to a method and apparatus for performing such metal working operations at high speeds with improved chip control. Background of the Invention Most machining operations are performed by a cutting tool which includes a tool holder and one or more cutting inserts each having a top surface termi¬ nating with one or more cutting edges. The tool holder is formed with a socket within which a cutting insert is clamped in place. The leading or cutting edge of an insert makes contact with the workpiece to remove material therefrom in the form of chips. A chip comprises a plurality of thin, generally rectan¬ gular-shaped sections of material which slide relative to one another along shear planes as they are sepa¬ rated by the insert from the workpiece. This shearing movement of the thin sections of material relative to one another in forming a chip generates a substantial amount of heat, which, when combined with the heat produced by engagement of the cutting edge of the insert with the workpiece, can amount to 1500°-2000°F, or higher. Among the causes of failure of the cutting inserts employed in prior art machining operations are abrasion between the cutting insert and workpiece, and a problem known as cratering. Cratering results from the intense heat developed in the formation of the chips and the frictional engagement of the chips with the cutting insert. As the material forming the chip is sheared from the workpiece, it moves along at least a portion of the exposed top surface of the insert. Due to such frictional engagement, and the intense heat generate in the formation of the chip, material along the top portion of the insert is removed forming "craters". If these craters become deep enough, the entire insert is subject to cracking arid failure along its cutting edge, and along the sides of the insert, upon contact with the workpiece. Cratering has become a particular problem in recent years due to the development and extensive use of hard alloy steels, high strength plastics and composite materials formed of high tensile strength fibers coated with a rigid matrix material such as epoxy. Prior attempts to avoid cratering and wear of the insert due to abrasion with the workpiece have provided only modest increases in tool life and machining efficiency. One approach has been to form inserts of high strength materials such as tungsten carbide. Although extremely hard, tungsten carbide inserts are brittle and are subject to chipping which can result in premature failure. To improve the lubricity ' of inserts, such materials as hardened or alloyed ceramics have been employed in the fabrication of cutting inserts. Additionally, a variety of low friction coatings have been developed for cutting inserts to reduce the friction between the cutting insert and workpiece. In addition to the improved materials and coatings used in the manufacture of cutting inserts, attempts have been made to increase tool life by reducing the temperature in the "cutting area", i.e., the cutting edge of the insert, the insert-workpiece interface and the area on the workpiece immediately upstream from the insert where material is being sheared to form chips. One method commonly employed to cool the cutting area is known as flood cooling which involves the spraying of a low pressure stream of coolant toward the insert and workpiece. Typically, a nozzle disposed several inches above the :ting tool and workpiece directs a low pressure stream of coolant toward the workpiece, tool holder, cutting insert and on top of the chips being produced. The primary problem with flood cooling is that it is ineffective in actually reaching the cutting area. The underside of the chip which makes contact with the exposed top surface of the cutting insert, the cutting edge of the insert and the area where material is sheared from the workpiece, are not cooled by a low pressure stream of coolant directed from above the tool holder and onto the top surface of the chips. This is because the heat in such cutting area is so intense, i.e., on the order 2000°F or higher, that a heat barrier is produced which vapor¬ izes the coolant well before it can flow near the cutting edge of the insert. Several attempts have been made to improve upon the flood cooling technique described above. For example, the discharge orifice of the nozzle carrying the coolant has been placed closer to the insert and workpiece, and/or fabricated as an integral portion of the tool holder, to eject the coolant more directly at the cutting area. See, for example, U.S. Patent Nos. 1,695,955; 3,323,195; and, 3,364,800. In addition to positioning the nozzle nearer to the insert, and workpiece, the stream of coolant has been ejected at higher pressures than typical flood cooling applica¬ tions in an effort to break through the heat barrier developed in the cutting area. See U.S. Patent No. 2,653,517. Other tool holders for various types of cutting operations incorporate coolant delivery passageways which direct the coolant flow across the exposed top surface of the insert toward the cutting edge in contact with the workpiece. In these designs, a separate conduit or nozzle for spraying the coolant toward the cutting area is eliminated making the cutting tool more compact. Examples of this type of design are shown in U.S. Patent Nos. 4,302,135; 4,072,438; 3,176,330; 3,002,140; 2,360,385; and, West German Patent No. 3,004,166. A common problem with apparatus of the type disclosed in the patents mentioned above is that coolant in the form of an oil-water or synthetic mixture, at ambient temperature, is directed onto the top surface of the insert toward the cutting area without sufficient velocity to pierce the heat barrier surrounding the cutting area. As a result, the coolant fails to reach the interface between the cutting insert and workpiece, and/or the area on the workpiece where the chips are being formed, before becoming vaporized. Under these circumstances, no heat is dissipated from the cutting area to prevent cratering. In addition, failure to remove heat from the cutting area creates a significant temperature differential between the cutting edge of the insert which remains hot, and the rear portion of the insert which is cooled by coolant, thus causing thermal failure of the insert. A failure to effectively reduce temperature in the cutting area results in a number of disadvan¬ tages and limitations in machining operations. As discussed above, high temperatures cause insert failure. This directly affects production speed in several ways. In order to reduce temperatures, the machine tools must be run at lower speeds, reduced depths of cut and reduced feed rates, each of which lowers productivity. If speeds are increased, the downtime of the machine tool increases because the inserts must be replaced more frequently. The less time the insert is in the cut, the lower the produc¬ tivity of a given machine tool. Overall productivity is therefore limited by the useful life and perfor¬ mance of the cutting inserts which have historically lagged far behind the operating speeds of machine tools. Another serious problem in present day machining operations involves the breakage and removal of chips from the area of the cutting insert, tool holder and the chucks associated with the machine tool which mount the workpiece and tool holder in place. If chips are formed in continuous lengths, they tend to wrap around the tool holder or chucks which can lead to tool failure or at least require a periodic interruption of the machining operation to clear the area of impacted or bundled chips. This is particu- larly disadvantageous in flexible manufacturing systems in which the entire machining operation is intended to be completely automated. If a worker must regularly clear impacted or bundled chips from the tool holders and/or chucks of such systems, their efficiency is drastically reduced. One attempt to solve the problem of removal and breakage of chips involves the formation of chip breaker grooves in cutting inserts. Chip breaker grooves extend inwardly from the exposed top surface of the insert, and are spaced from the cutting edge. The chip breaker groove engages chips as they are sheared by the cutting edge from the workpiece, and then turn or bend them upwardly from the exposed surface of the insert so that the chips tend to fracture. While acceptable performance has been achieved with some chip breaker groove designs in some applications, variables in machining operations such as differing materials ' , types of machines, depths of cut, feed rates, speeds and o^.her factors make it virtually impossible for one chip breaker groove design to be effective in all applications. This is evidenced by the multitude of chip breakers now available. Selection of a suitable cutting insert for a particular machining application, if one exists at all, is a difficult and continuing problem. In an effort to improve upon the chip control obtained with cutting inserts having chip breaker grooves, apparatus have been designed to control and break chips hydraulically, i.e., with a stream of coolant which is delivered to the cutting area at high speeds compared to flood cooling devices and other prior art systems. For example, my prior Patent No. 4,621,547 discloses a tool holder in which the clamp or cap which secures the insert to the tool holder is formed with a coolant delivery passageway for directing coolant at high speed toward the cutting edge of the insert. Coolant is accelerated within the clamp or cap and is preferably discharged at a speed of greater than about 250 feet per second in an effort to pierce the heat barrier developed in the cutting area and flow beneath the chips being formed from the workpiece. It has been found that the apparatus dis¬ closed in Patent No. 4,621,547 effectively breaks chips into relatively small lengths, but only under specific operating parameters and for certain types of materials. Specifically, where the discharge outlet of the coolant delivery passageway is maintained at a distance of about .040 inches to .440 inches from the cutting edge of the insert, and the feed rate is set in the range of about .004 to .025 inches, a coolant jet having a velocity of at least about 250 feet per second is effective to break chips into small lengths for some materials. A potential problem with this apparatus, however, is that the parameters within which the apparatus is effective cannot always be maintained for different types of machining opera- tions. In addition, the apparatus is relatively ineffective in machining harder materials at higher speeds and feed rates because of the elevated tempera¬ tures associated with such machining operations. This system has been improved in my U.S. Patent No. 4,829,859 which discloses a method of machining in which a high velocity, mixed phase coolant stream is directed toward the cutting edge of the insert and workpiece to lower the temperature of the cutting area and to break the material sheared from the workpiece into very small chips or particles. The "mixed phase" coolant stream comprises a combina¬ tion of a water-oil coolant, carbon dioxide gas and ice particles which is formed by intermixing a coolant stream with liquified carbon dioxide or similar fluid within an insert clamp prior to discharge into the cutting area. The heat produced by shearing material from the workpiece is transferred from the workpiece to the mixed phase coolant stream, thus converting the ice particles within the stream from solid to vapor phase. In the course of vaporization, the ice parti¬ cles undergo an explosive, volumetric expansion which produces a force capable of assisting in the shearing the material from the workpiece, and of breaking such sheared material into minute particles. It has been found that the method and apparatus disclosed in U.S. Patent No. 4,829,859 enables machining operations to proceed at much higher feed rates and speeds, and at greater depths of cut, while obtaining excellent chip control. But one potential limitation of this system is that liquified carbon dioxide or similar liquified gas is required to form the mixed phase coolant stream. Liquified gases are available commercially in tanks which must be stored on the premises of the machining facility before use, replaced at regular intervals during production and then stored for shipment back to the supplier after they are emptied. These handling and storage requirements can create problems, particularly for smaller machining facilities. In addition, a relatively large quantity of liquified gas is needed to perform the machining operation, especially on harder materials, and this can increase the expense of the machining operations. Summary of the Invention It is therefore among the objectives of this invention to provide a method and apparatus for machining which provides for excellent chip control, which permits machining operations to be run at high speed, which is easily adapted for machine tools of different configuration and which is relatively inexpensive to operate and maintain. These objectives are accomplished in a nozzle apparatus adapted for use with machine tools of different configuration, which perform different machining operations, comprising a nozzle body having a nozzle insert which is mounted within an outlet passageway formed in the nozzle body at its intersec- tion with a coaxial, larger diameter inlet passageway connected to a source of coolant, e.g., a water-oil mixture. The nozzle insert is constructed to acceler¬ ate the stream of coolant received from the inlet passageway, and to induce the formation of shock waves in the course of passage of the coolant stream through the interior of a nozzle body. These shock waves increase the energy and velocity of the coolant stream so that it is effective to pierce the heat barrier developed in the cutting area to reduce the tempera- ture thereat and to assist in the breakage of chips from the workpiece. In the presently preferred embodiment, a portion of the nozzle body of this invention is constructed in accordance with the teachings of my Patent No. 4,830,280, the disclosure of which is incorporated by reference in its entirety herein. The inlet passageway formed in the nozzle body is adapted to connect to a source of conventional water-oil coolant through a supply line and pump. The outlet passageway is formed with a smaller diameter than the inlet passageway, and is coaxial with and intersects the inlet passageway forming a shoulder at such intersection. A donut-shaped recess is formed in such shoulder, and this recess is concentrically disposed about the nozzle insert carried within the outlet passageway in the nozzle body. Preferably, the nozzle insert is formed with a throughbore having a radially inwardly tapering throat portion beginning at an angled inlet end of the throughbore, ' and a minimum diameter portion at approximately the midpoint of the throughbore. The throat portion and minimum diameter portion collectively form an the inlet section of the nozzle insert and are disclosed in Patent No. 4,830,280. As described below, the nozzle insert of this invention is modified to include a radially outwardly tapering outlet portion which extends from the midpoint of the throughbore to its outlet end. As described in detail in U.S. Patent No. 4,830,280, the inlet section of the nozzle insert is effective to accelerate the coolant from the inlet passageway in the nozzle body through the reduced diameter portion of the insert with minimal losses due to drag or turbulence. A portion of the coolant stream which flows into the inlet passageway of the nozzle body is made to enter the donut-shaped recess. This portion of the coolant stream is rotated within the recess in the same direction as the flow of coolant through the nozzle body. As the main body of the coolant stream moves through a transition area between the larger diameter inlet passageway and the smaller diameter outlet passageway, the rotating portion of the coolant within the recess impacts the outer boundary of the main body of coolant and func¬ tions to both guide and accelerate it into the inlet portion of the throughbore in the nozzle insert. The combined effect of the rotating coolant within the recess, and the radially inwardly tapering inlet portion of the throughbore, is to eliminate much of the turbulence and drag which can occur as the coolant stream moves from the larger diameter inlet passageway into the smaller diameter outlet passage- way. As a result, the coolant stream is efficiently accelerated from the inlet passageway to the outlet passageway, and its actual velocity at the reduced diameter portion of the throughbore in the nozzle insert more nearly approaches the theoretical velocity which would be obtained absent any losses due to drag or turbulence. Depending upon the flow rate and pump pressure at which the coolant stream is introduced into the nozzle body, it is believed that the coolant stream is accelerated to a velocity in the range of about 1000 to 1200 feet per second (fps) in the area of the reduced diameter portion or midpoint of the throughbore in the nozzle insert. It is theorized that such acceleration of the coolant stream produces a condition wherein a shock wave can be produced in the coolant stream in which at least some portion of the dissolved gases therein, i.e., nitrogen, oxygen, carbon dioxide, etc. , are caused to evolve or escape from the stream and form bubbles. An important aspect of this invention is that the formation of the shock wave within the coolant stream is induced and enhanced by the pro¬ vision of an expansion chamber defined by the radially outwardly tapering outlet portion of the throughbore in the nozzle insert, and a larger diameter discharge tube which is inserted within the outlet passageway of the nozzle body immediately downstream from the nozzle insert. This expansion chamber provides for volu¬ metric expansion of the coolant stream as the dissolved gases evolve or escape from solution, and thus allows the shock wave formed within the throughbore of the nozzle insert to propagate downstream. It has been found through experimenta- tion, that the wall in the nozzle insert formed by^ the radially outwardly tapering portion of the throughbore therein is preferably oriented at an included angle of about 8° with respect to the longitudinal axis of the throughbore to permit the coolant stream to expand radially outwardly to a sufficient extent to avoid undue damping or choking of the shock wave developed within the nozzle insert. The coolant stream including bubbles is transmitted from the expansion chamber downstream through the discharge tube of the nozzle body. Preferably, the discharge tube has a constant diameter from the nozzle insert to its discharge outlet where the outlet passageway in the nozzle body terminates. It is theorized that while gaseous bubbles are allowed to form immediately downstream from the reduced diameter section of the nozzle insert, i.e., within the expansion chamber, these bubbles will tend to dissolve back into the coolant stream in the course of movement through the remainder of the discharge tube. It is believed that this occurs because the discharge tube functions to confine further expansion of the bubbles soon after they are allowed to form, causing the bubbles to burst or collapse and re-enter the coolant stream. It is presently believed that a second shock wave is then formed in the coolant stream in the course of its passage through the outlet of the discharge tube into atmosphere. As the coolant stream is emitted from the discharge tube to atmosphere, the dissolved gases within the coolant stream are again allowed to escape and form bubbles. It is theorized that this produces a second shock wave within the coolant stream which accelerates it outwardly from the discharge outlet, and toward the cutting insert and workpiece being machined, at an increased velocity which may be in excess of 1200 fps. The energy and velocity of the coolant stream created by the second shock wave is utilized to assist in the machining operation, i.e., the coolant stream is directed onto the top surface of the insert toward its cutting edge and functions to both cool the cutting edge and workpiece, and to assist in the breakage of chips into relatively small lengths or particles as material is removed from the workpiece. Preferably, the coolant stream or jet emitted from the discharge outlet of the nozzle body is directed at an angle of about 20° upon the top surface of the insert and is oriented to cover the entire width of the chip being sheared from the workpiece. In some applications, particularly in connection with the machining of harder materials, it is desirable to provide at least some initial cooling of the workpiece in the area immediately above the cutting insert where material is about to be sheared from the workpiece. In one presently preferred embodiment, an air jet passageway is formed in the nozzle body having a discharge outlet which is oriented to direct pressurized air to this area on the workpiece. A source of pressurized air, i.e., shop air, is preferably directed into a manifold and then through a line connected to the air passageway within the nozzle body. In some instances, a small quantity of liquified gas, such as liquified nitrogen, is introduced into the manifold with the pressurized air to reduce the temperature of the pressurized air prior to introduction into the air passageway of the nozzle body. The operation of the manifold and the addition of liquified gas therein is controlled by a controller such as any commercially available personal computer or the like, which also controls the supply of coolant into the inlet passageway of the nozzle body. This invention therefore provides a number of advantages over prior methods of machining intended to increase speeds and feeds, and control the forma¬ tion of chips. No liquified gas or other cooling means are combined with the coolant stream as in Patent No. 4,829,859. This reduces costs, and the problems associated with storage of a large number of containers of liquified gas. The substantial energy and velocity produced in the coolant stream is obtained by promoting the formation of shock waves which result, in part, from the efficient transfer of the coolant stream from a larger diameter inlet passageway to a smaller diameter outlet passageway in the nozzle body with minimal turbulence and drag losses. High coolant stream velocity is therefore achieved by the efficiencies obtained with the struc¬ ture herein, which permits the use of a relatively small pump operating at relatively low flow rates. More expensive, higher pressure pumps are not required for many machining operations. Description of the Drawings The structure, operation and advantages of the presently preferred embodiment of this invention will become further apparent upon consideration of the following description taken in conjunction with the accompanying drawings, wherein: Fig. 1 is a partial isometric view, exag¬ gerated for purposes of illustration, showing a tool holder and cutting insert for performing a turning operation, including the apparatus of this invention; Fig. 2 is a cross sectional view taken generally along line 2-2 of Fig. 1; and Fig. 3 is an enlarged cross sectional view of a portion of the nozzle body illustrated in Fig. 2. Detailed Description of the Invention Referring now to Figs. 1 and 2, one present- ly preferred embodiment of the nozzle apparatus 10 of this invention is illustrated for use with a turning holder 12 performing a turning operation on a work¬ piece 14. The workpiece 14 is mounted in a chuck of a machine tool (not shown) which is adapted to rotate the workpiece 14 in the direction indicated in Fig. 1. While a turning holder 12 is illustrated in Fig. 1, it should be understood that the method and apparatus of this invention is applicable for use in other machin¬ ing operations such as milling, boring, cutting, grooving, threading, drilling and others, and the turning operation illustrated is shown solely for purposes of describing the present invention. The turning holder 12 comprises a support bar 16 formed with a seat adapted to receive a cutting insert 18 having an upper surface 20 terminating with a cutting edge 22. The cutting insert 18 is secured within the seat of the support bar 16 by a clamp 24 of conventional design. The nozzle apparatus 10 is mounted with respect to the upper surface 20 of insert 18 to direct a high energy, high velocity coolant stream towa„ the cutting edge 22 of insert 18 and the workpiece 14, as described in detail below. The nozzle . apparatus 10 is preferably carried on the turret of the machine tool (not shown) by mounting structure which is designed specifically for a partic¬ ular machine. Such mounting structure forms no part of this invention per se and is therefore ■ not described herein. In the presently preferred embodiment, the nozzle apparatus 10 comprises a nozzle body 26 formed with an inlet passageway 28 connected by a line 30 to a pump 32 which communicates with a supply of coolant 34. The pump 32 is connected to a controller 35 such as a personal computer, microprocessor or other closed loop controller, which, as described below, is opera¬ tive to control the flow of coolant into inlet pas- sageway 28. The term "coolant" as used herein is meant to refer to any one of a variety of commercially available liquid coolants employed in the machine tool industry which generally comprise a mixture of oil, water and other additives. The nozzle body 26 is also formed with an outlet passageway 36 which is coaxial with the inlet passageway 28. In the presently preferred embodiment, the outlet passageway 36 has a smaller diameter than the inlet passageway 28 forming a shoulder 38 where such passageways 28, 36 intersect. As shown in Figs. 2 and 3, the nozzle body 26 is formed with an annular, donut-shaped recess 40 at the shoulder 38 formed by the intersection of the inlet and outlet passageways 28, 36. Preferably, the recess 40 is formed with a generally U-shaped cross section, although it is contemplated that other cross sections could be employed for the purposes described below. In the presently preferred embodiment, the outlet passageway 36 of nozzle body 26 is formed with internal threads to mount a nozzle insert 42 and a discharge tube 44. The nozzle insert 42 has a cylin- drical-shaped, threaded outer surface 46 and an hourglass-shaped throughbore 48. The shape of the inlet portion of throughbore 48 is determined experi¬ mentally, and. in accordance with the teachings of my U.S. Patent No. 4,830,280, the disclosure of which is incorporated by reference in its entirety herein. Preferably, the inlet portion of throughbore 48 includes a rounded inlet end 52 which extends at least partially into the outlet passageway 28, and a throat portion 54 which tapers radially inwardly from the inlet end 52 to a minimum diameter designated D located at about the midpoint 56 of the throughbore 48. As explained in U.S. Patent No. 4,830,280, the exact configuration of this radially inwardly tapering throat portion 54 is determined empirically by experi- mentation, but it can generally be characterized as a smoothly tapering polynomial curve extending between the inlet end 52 of throughbore 48 and the diameter D at the. midpoint 56 of throughbore 48. This inlet portion of the throughbore 48 in the nozzle insert 42 thus forms a venturi, for purposes described below. It is estimated that the axial distance between the inlet 52 and midpoint 56 of throughbore 48 is approxi-. ately three times the diameter D of the throughbore 48 at midpoint 56. See Fig. 3. The discharge portion of the hourglass- shaped throughbore 48 of the nozzle insert 42, i.e., downstream from the midpoint 56, is characterized by a radially outwardly tapering discharge portion 58 extending from the midpoint 56 to the outlet end 60 of the nozzle insert 42. It has been determined experi¬ mentally that the wall of the throughbore 48 formed by this discharge portion 58 should be tapered at included angle « of about 8° measured between a line 62 extending parallel to the longitudinal axis of the throughbore 48, and a line 63 which extends from the midpoint 56 and is substantially coincident with such wall of throughbore 48 formed along the discharge portion 58. See Fig. 3. The axial distance of the discharge portion 58 measured between the midpoint 56 and the outlet end 60 of nozzle insert 42 is pref¬ erably on the order of about three times the minimum diameter D of the throughbore 48. The discharge tube 44 is threaded into the outlet passageway 36 of nozzle body 26 downstream from the nozzle insert 42 and has an end 47 which abuts the outlet end 60 of nozzle insert 42. Preferably, the discharge tube 44 is cylindrical in shape and has a constant diameter D-,. The diameter D„ of discharge tube 44 can be obtained with the following formula: D E D Q + 2(tan. 8 ' ) (l) As shown in Figs. 2 and 3, and the discharge tube 44 has a discharge end 64 located flush with the terminal end of the outlet passageway 36 which defines a discharge outlet 65. In the embodiment illustrated in the Figs. , the axial length of the discharge tube 44 is on the order of about twelve times the smallest diameter D of the throughbore 48 of nozzle insert 42. For some applications, as described below, it is advantageous to employ chilled air in connection with the machining operation performed with the nozzle apparatus 10 of this invention. For this purpose, the nozzle body 26 is formed with an air passageway 66 connected by a line 68 to a cooling manifold 70. See Figs. 1 and 2. This cooling manifold 70, in turn, is connected to a source of pressurized air 72, e.g., shop air, and a tank 74 of liquified gas such as liquified nitrogen. The controller 35 is operatively connected to the liquified gas tank 74 and manifold 70 to control their operation as described below. System Operation An initial objective in the operation of the nozzle apparatus 10 is to reduce turbulence and drag in the flow of the coolant stream to and through the inlet portion of the nozzle insert 42 in nozzle body 26 in order to assist in obtaining maximum energy and velocity of the coolant stream 78 which is ultimately ejected from the discharge outlet 65 of tube 44 toward the cutting insert 18 and workpiece 14. In this respect, the nozzle apparatus 10 of this invention employs the teachings of my U.S. Patent No. 4,830,280 to transmit coolant from the supply 34 through pump 32 and line 30 into the inlet passageway 28, and then through inlet portion of nozzle insert 42 within the nozzle body 26. In accordance with the teachings of Patent No. 4,830,280, a relatively low velocity stream of coolant 78, e.g., on the order of about 20 to 40 feet per second, is directed from pump 32 through line 30 into the inlet passageway 28 of the nozzle body 26. A portion 80 of this coolant stream 78 flows into the annular, U-shaped recess 40 which is concentric to the nozzle insert 42. It is believed that the coolant 80 entering the recess 40 is made to rotate in the direction of the arrow shown in Fig. 3, i.e., in the same direction as the flow of the main body of the coolant stream 78 through nozzle body 26. The portion 80 of the stream within recess 40 impacts the outer surface 82 of the coolant stream 78 and functions to guide and accelerate the main body of the coolant stream 78 into the smoothly angled, rounded inlet end 52 of the hourglass-shaped throughbore 48 in nozzle insert 42. The shape of the angled inlet end 52, and the radially inwardly tapering, throat portion 54 of throughbore 48, cooperate to smoothly receive the main body of the coolant stream 78 which lessens the turbulence in the transition area between the larger diameter inlet passageway 28 and the smaller diameter outlet passageway 36 in nozzle body 26. This produces minimal losses due to drag or turbulence and results in improved efficiency. Because the throat portion 54 of throughbore 48 tapers radially inwardly from the inlet 52 thereof, this inlet portion of the nozzle insert 42 functions as a venturi to substantially accelerate the velocity of the coolant stream 78 in the course of passage from the inlet passageway 28 of nozzle body 26 into the nozzle insert 42. For example, when employing a pump 32 rated at about 3000 psi operating pressure, at a flow rate of about one gallon per minute, it is believed that the velocity of the coolant stream 78 increases from about 20 to 40 feet per second within the inlet passageway 28 to a velocity on the order of about 1000 to 1200 feet per second at or about the midpoint 56 of throughbore 48 having the minimum diameter D . This substantial increase in velocity is achieved because of the rotating coolant 80 within the recess 40, and the configuration of the input portion of throughbore 48. Reference should be made to my U.S. Patent No. 4,830,820 for a more detailed discus¬ sion of same, and to obtain teachings on the design considerations for this structure based on desired pump pressure, flow rate and coolant velocity. It is believed that such an acceleration of the coolant stream 78 from the inlet passageway 28 into the nozzle insert 42 creates a condition wherein a shock wave can develop within the coolant stream 78 in which the dissolved gases within the water portion of the coolant stream, e.g., nitrogen, carbon dioxide, oxygen, etc. , leave or escape from solution and form bubbles 84. The formation of this shock wave, and the production of bubbles 84, is induced and enhanced by the configuration of the discharge portion 58 of throughbore 48 immediately downstream from the mid¬ point 56 of nozzle insert 42 having the minimum diameter Do. That is, it is believed that the radially outwardly tapering configuration of the discharge portion 58 of throughbore 48, in combination with the larger diameter discharge tube 44 immediately downstream therefrom, provides an expansion section or chamber 86 which allows for volumetric expansion of the coolant stream as the bubbles 84 are formed. It has been determined experimentally that where the dis¬ charge section 58 tapers radially outwardly from the midpoint 56 at an included angle α of about 8°, the air bubbles 84 are allowed to freely form within the coolant stream 78 which undergoes at least a limited volumetric expansion. As shown in Fig. 3, the coolant stream 78 including bubbles 84 contact the inner wall of tube 44 at a distance of about three times the diameter Do from the outlet end 60 of nozzle insert 42. Having induced the formation of bubbles 84 within the coolant stream 78 in the expansion chamber 86, it is believed that at least a portion of these bubbles 84 are forced back into solution as the coolant stream 78 continues moving through the dis¬ charge tube 44. While the diameter D„ of discharge tube 44 is sufficient to permit the initial formation of bubbles 84 as the coolant stream 78 moves from the midpoint 56 of throughbore 48 to the expansion area 86, further volumetric expansion of the coolant stream 78 is prevented as it continues toward the discharge outlet 65 of discharge tube 44. It is theorized that as the bubbles 84 try to expand further radially outwardly downstream from the expansion area 86, they are confined by the wall of discharge tube 44 which causes such bubbles 84 to burst or collapse and return into solution within the coolant stream 78. As a result, the coolant stream 78 has a lesser quantity of bubbles 84 by the time it reaches the discharge outlet 65 of discharge tube 44, than within the expansion area 86. See center portion of tube 44 in Fig. 3. It is theorized that the process of first allowing bubbles 84 to form in the coolant stream 78, and then forcing the bubbles 84 back into solution within the discharge tube 44, contributes to the formation of a second shock wave within the coolant stream 78 as it is emitted from the discharge outlet 65 of discharge tube 44 to atmosphere. As viewed in Figs. 2 and 3, when the coolant stream is exposed to atmosphere upon discharge from the tube 44, air bubbles 84 again are formed within the coolant stream 78 as at least some of the dissolved gases therein leave solution. This has the effect of greatly accelerating the velocity of the coolant stream 78, e.g., in excess of 1000 to 1200 fps, and increasing its energy, so that the coolant stream 78 can effec¬ tively break the chips 87 being sheared from workpiece 14 by the insert 18, and reduce the temperature in the cutting area, i.e., at the insert-workpiece interface and in the area 88 on the workpiece 14 where the chips 86 are being sheared. As shown in Fig. 3, the high velocity coolant stream including air bubbles 84 is directed at an angle Θ of about 20° with respect to the upper surface 20 of cutting insert 18, and is oriented such that the top portion 89 of the coolant stream 78 is aimed at the cutting edge 22 of insert 18 while the remaining portion of the coolant stream 78 flows along the upper surface 20 of insert 18. This has the effect of directing the coolant stream beneath the' chips 87 being sheared from the workpiece 14 to help break them into relatively small lengths or particles. Preferably, the distance at which the discharge outlet 65 is spaced from the insert 18 is sufficient so that the width of the coolant stream 78 covers the entire width of the chips 87 being formed. Such spacing can be obtained during operation of apparatus 10 by visual observation, but is typically on the order of about one inch or more. In some machining operations, particularly those performed on harder materials, a jet 92 of pressurized air is discharged from the air passageway 66 in nozzle body 26 onto the area 88 of the workpiece 14 immediately above the chips 87 being formed. As • mentioned above, the temperature of the air jet 92 may be reduced by combining a liquified gas such as nitrogen gas with the pressurized air in the cooling manifold 70. This reduced temperature air jet 92 is then directed through the air passageway 66 onto the area 88. Such reduction in the temperature of the workpiece 14 at area 88 assists in the breakage of chips 87 therefrom, which is particularly useful for harder materials. The introduction of liquified gas into the cooling manifold 70 is controlled by the controller 35 as desired. It is contemplated that for many types of materials, no liquified gas would be required. For harder materials, the liquified gas can be combined with the pressurized air as needed, e.g., in pulsed intervals, to reduce the temperature of the pressur¬ ized air jet 92 and thus reduce the temperature in the area 88 of the workpiece 14 to the extent desired. Additionally, the controller 35 is operative to control the flow of coolant entering the nozzle body 26 in accordance with the requirements of a particular application. For example, in the machining of harder materials, it may be necessary to increase the flow rate of coolant entering the nozzle body 26 and/or the operating pressure of pump 32, in order to obtain the optimum velocity of the coolant stream 78 ejected from the nozzle body 26. While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made. to adapt a particular situation or material to the teachings of the invention without departing from the scope thereof. For example, the nozzle body 26 is illus- trated in the Figs, as including a separate nozzle insert 42 and discharge tube 44. These items are provided in the preferred embodiment because they may be removed from the outlet passageway 36 in nozzle body 26, and replaced with other nozzle inserts 42 and/or discharge tubes 44 having different dimensions to accommodate varying operating parameters such as different pump sizes and different coolant flow rates which may be required for different types of materials or machining operations. It is contemplated, however, that the nozzle body 26 could be integrally formed with the structure provided by the separate nozzle insert 42 and discharge tube 44. Specifically, the discharge tube 44 could be eliminated and replaced by a constant diameter bore in nozzle body 26, and the hourglass-shaped throughbore 48 in the nozzle insert 42 could be machined directly into the nozzle body 26 using conventional machining techniques. A nozzle body 26 of this construction, therefore, is considered to be within the scope of this invention. Therefore, it is int?--ded that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims: 1. A method of machining, comprising: creating a first shock wave within a coolant stream in the course of directing the coolant stream through a reduced diameter area of a coolant passage- way formed in a nozzle body; creating a second shock wave within the coolant stream in the course of discharging the coolant stream from the outlet of the coolant passage¬ way to atmosphere, the coolant stream being accel- erated by said second shock wave and being directed at high velocity toward a cutting insert which is in engagement with a workpiece to perform a machining operation. 2. The method of claim 1 in which said step of creating a first shock wave comprises: accelerating the coolant stream through the reduced diameter area of the coolant passageway; and allowing dissolved gases contained within the coolant stream to escape and form bubbles within a larger diameter, expansion section of the coolant passageway located downstream from the reduced diameter area. 3. The method of claim 2 in which said step of creating a second shock wave, comprises: forcing at least a portion of the bubbles to dissolve within the coolant stream downstream from the expansion section of the nozzle body; and thereafter causing at least a portion of the dissolved gases within the coolant stream to escape and form bubbles in the course of discharging the coolant stream from the nozzle body to atmosphere so that the coolant stream containing bubbles is accel¬ erated at high velocity toward the cutting insert and workpiece. 4. The method of claim 1 further including the step of directing a jet of air toward a portion of the workpiece located immediately in advance of where the cutting insert contacts the workpiece to perform the machining operation. 5. The method of claim 4 in which said step of directing a jet of air comprises cooling the jet of air before it is directed toward the workpiece. 6. A method of machining, comprising: accelerating a coolant stream containing dissolved gases through a reduced diameter area of a coolant passageway formed in a nozzle body; transmitting the coolant stream from the reduced diameter area into a larger diameter expansion area of the coolant passageway in which at least a portion of the dissolved gases escape from the coolant stream to form bubbles; transmitting the coolant stream including gas bubbles downstream from the expansion area and forcing at least a portion of the gas bubbles to collapse and dissolve into the coolant stream; accelerating the coolant stream from the nozzle body into atmosphere and directing the coolant stream at high velocity toward a cutting insert and workpiece, at least a portion of the dissolved gases in the coolant stream escaping to form bubbles as the coolant stream is emitted from the nozzle body. 7. The method of claim 6 in which said step of accelerating and directing the coolant stream com¬ prises directing the coolant stream at an angle of about 20° relative to the top surface of the cutting insert. 8. Apparatus for ejecting a stream of coolant toward a cutting insert which is engageable with a workpiece to perform a machining operation, compris¬ ing: a nozzle body formed with a first passageway adapted to connect to a source of coolant, and a second passageway having an outlet end and an inlet end which intersects said first passageway; said second passageway being formed with an inlet section including a radially inwardly tapering throat portion which extends axially from said inlet end of said second passageway to a reduced diameter portion, and a radially outwardly tapering discharge portion which extends axially from said reduced diameter portion, said discharge portion communicating with a larger diameter expansion section formed along said second passageway downstream from said discharge portion; means for directing a stream of coolant from said first passageway into said inlet section of said second passageway, whereby said coolant stream is accelerated in the course of passage through said second passageway and is adapted to be discharged at high velocity from said outlet end of said second passageway toward the cutting insert and workpiece. 9. Apparatus for ejecting a stream of coolant toward a cutting insert which is engageable with a workpiece to perform a machining operation, compris¬ ing: a nozzle body formed with a first passageway adapted to connect to a source of coolant, and a second passageway having a discharge outlet and an inlet which intersects said first passageway; a nozzle insert carried at said inlet of said second passageway, said nozzle insert having an inlet end and an outlet end, said nozzle insert being formed with a throughbore having a reduced diameter portion, a radially inwardly tapering inlet portion extending from said inlet end of said nozzle insert in communication with said first passageway to said reduced diameter portion and a radially outwardly tapering discharge portion extending between said reduced diameter portion and said outlet end of said nozzle insert; said second passageway having a diameter downstream from said nozzle insert which is at least equal to the largest transverse dimension of said discharge portion of said nozzle insert; means for directing a stream of coolant from said first passageway into said throughbore of said nozzle insert in said second passageway, whereby said coolant stream is accelerated in the course of passage through. said nozzle insert and said second passageway and is adapted to be discharged at high velocity from said discharge outlet thereof toward the cutting insert and workpiece. 10. The apparatus of claim 9 in which said inlet end of said nozzle insert is rounded to smoothly receive the coolant stream from said inlet passageway in said nozzle body to reduce turbulence. 11. The apparatus of claim 9 in which the axial length of said radially inwardly tapering inlet portion of said throughbore of said nozzle insert is about three times the diameter of said reduced diameter portion of said throughbore. 12. The apparatus of claim 9 in which said radially outwardly tapering outlet portion of said throughbore defines a wall in said nozzle body which slopes outwardly from said reduced diameter portion of said throughbore at an included angle of about 8° . 13. The apparatus of claim 9 in which the axial length of said radially outwardly tapering outlet portion of said throughbore in said nozzle insert is about three times the diameter of said reduced diameter portion of said throughbore. 14. The apparatus of claim 9 in which a cylin¬ drical tube is mounted within said second passageway and extends between said outlet end of said nozzle insert and said discharge outlet of said second passageway, said cylindrical tube having a larger diameter than said outlet end of said throughbore in said nozzle insert. 15. Apparatus for ejecting a stream of coolant toward a cutting insert which is engageable with a workpiece to perform a machining operation, compris¬ ing: a nozzle body formed with a first passageway adapted to connect to a source of coolant, and a second passageway having a discharge outlet and an inlet which intersects said first passageway; a nozzle insert carried at said inlet of said second passageway, said nozzle insert having an inlet end and an outlet end, said nozzle insert being formed with a throughbore having a reduced diameter portion, a radially inwardly tapering inlet portion extending from said inlet end of said nozzle insert in communication with said first • passageway to said reduced diameter portion and a radially outwardly tapering discharge portion extending between said reduced diameter portion and said outlet end of said nozzle insert; said second passageway having a diameter downstream from said nozzle insert which is at least equal to the largest transverse dimension of said discharge portion of said nozzle insert; means for directing a stream of coolant from said first passageway into said throughbore of said nozzle insert in said second passageway, whereby said coolant stream is accelerated in the course of passage through said nozzle insert and said second passageway and is adapted to be discharged at high velocity from said discharge outlet; said nozzle body being formed with an air passageway adapted to be connected to a source of pressurized air, said air passageway having a dis¬ charge outlet located with respect to said discharge outlet of said second passageway so that upon posi¬ tioning said nozzle body relative to the cutting insert and workpiece, the coolant stream is ejected from said discharge outlet of said second passageway toward the top surface and cutting edge of the cutting insert, and a jet of air is ejected from said dis¬ charge outlet of said air passageway toward an area on the workpiece adjacent to from where the cutting insert contacts the workpiece. 16. Apparatus for ejecting a stream of coolant in the direction of a cutting insert which is engage¬ able with a workpiece to perform a machining opera¬ tion, comprising: a nozzle body formed with an inlet passage¬ way adapted to connect to a source of coolant and a coaxial outlet passageway having a discharge outlet and an inlet which intersects said inlet passageway, the diameter of said inlet passageway being greater than the diameter of said outlet passageway so that a shoulder is formed at said intersection thereof, said inlet passageway being adapted to receive a stream of coolant for discharge through said smaller diameter, outlet passageway; a nozzle insert carried at said inlet of said second passageway, said nozzle insert having an inlet end and an outlet end, said nozzle insert being formed with a throughbore having a reduced diameter portion, a radially inwardly tapering inlet portion extending from said inlet end of said nozzle insert in communication with said first passageway to said reduced diameter portion and a radially outwardly tapering discharge portion extending between said reduced diameter portion and said outlet end of said nozzle insert; a recess formed in said shoulder of said nozzle body, said recess receiving a first portion of said coolant stream entering said inlet passageway to form a rotating body of coolant therein which rotates in the direction of movement of the coolant stream through said nozzle body, said rotating body of coolant tangentially contacting a second portion of said coolant stream to smoothly guide and accelerate said second portion of said coolant stream from said inlet passageway into said radially inwardly tapering inlet portion of said throughbore in said nozzle insert; said coolant stream forming a first shock wave in the course of movement through said reduced diameter portion and said discharge portion of said throughbore in said nozzle insert wherein at least some of the dissolved gases within the coolant stream escape and form bubbles, said coolant stream there¬ after forming a second shock wave in the course of exiting said nozzle body through said discharge outlet of said second passageway which accelerates said coolant stream at high velocity for transmittal toward the cutting insert and workpiece. 17. Apparatus for ejecting a stream of coolant in the direction of a cutting insert which is engage¬ able with a workpiece to perform a machining opera¬ tion, comprising: a nozzle body formed with an inlet passage¬ way adapted to connect to a source of coolant and a coaxial outlet passageway having an outlet end and an inlet end which intersects said inlet passageway, the diameter of said inlet passageway being greater than the diameter of said outlet passageway so that a shoulder is formed at said intersection thereof, said inlet passageway being adapted to receive a stream of coolant for discharge through said smaller diameter, outlet passageway; said second passageway being formed with an inlet section including a radially inwardly tapering throat portion which extends axially from said inlet end of said second passageway to a reduced diameter portion, and a radially outwardly tapering discharge portion which extends axially from said reduced diameter portion, said discharge portion communicating with a larger diameter expansion section formed along said second passageway downstream from said discharge portion; a recess formed in said shoulder of said nozzle body, said recess receiving a first portion of said coolant stream entering said inlet passageway to for a rotating body of coolant therein which rotates in the direction of movement of the coolant stream through said nozzle body, said rotating body of coolant tangentially contacting a second portion of said coolant stream to smoothly guide and accelerate said second portion of said coolant stream from said inlet passageway into said radially inwardly tapering inlet portion of said outlet passageway; said stream forming a first shock wave in the course of movement through said reduced diameter portion and said radially outwardly tapering discharge portion of said outlet passageway wherein at least some of the dissolved gases within the coolant stream escape and form bubbles, said coolant stream there¬ after forming a second shock wave in the course of exiting said nozzle body through said discharge outlet of said second passageway which accelerates said coolant stream to a high velocity for transmittal toward the cutting insert and workpiece.

Inventors: YANKOFF GERALD K, YANKOFF, GERALD, K.
Applicants: PRODUCTIVITY XPERTS INC, PRODUCTIVITY XPERTS, INC.
Application year: 1991
Main classification: B23B27
IPC codes: B05B1, B05B17, B23B1, B23Q11