A METHOD AND DEVICE FOR MACHINING A THROUGH BORE

Abstract: A method for machining a through bore (5) within a workpiece (W) and a device (10) for the implementation of the method. The method is suitable for finishing and semi-finishing machining operations of through bores and holes, in particular, tapping of internal threads, drilling, counter-boring, reaming, roll burnishing and piercing, etc. The method comprises imparting to the cutting tool (4) a linear motion accompanied by rotation thereof about the bore (5) axis and imparting to the tool auxiliary motion which is associated with the propelling thereof to an initial position after completing each stroke. Propelling of the tool is carried outside the bore (5) through a duct (14) between the bore (5) exit and entrance. Since friction associated with linear backward motion of the tool (4) through the bore (5) is avoided it is possible to reduce wear of the cutting tool (4) to improve tool life and to increase productivity of machining.

Description: A METHOD AND DEVICE FOR MACHINING A THROUGH BORE Field of the invention The present invention relates to the field of machining through-going bores within a workpiece by means of a cutting tool. More particularly, the present invention refers to serm-fmisr-ing and/or finishing machining operations in which a cutting tool performs an operative linear motion associated with the advancing thereof through the workpiece with simultaneous rotation of the tool about the bore axis. An example of such an operation is the threading of internal threads by virtue of a tap. It should be understood, however, that the present invention is not limited to the internal threading operation and can be also implemented in other machining operations such as drilling, counter-boring, reaming, internal roll burnishing, and piercing, etc. Background of the invention There are known various methods and devices suitable for the processing of through-going bores in which the cutting tool is brought into operative linear motion accompanied by rotation. One typical example of such a device is a nut tapping machine as disclosed, for example, in Soviet Authority Certificate No. 1114506 or in USA Patent No. 4299001. Such a machine usually comprises an elongated tap with a tap shank and a threaded screw cutting portion, a tap driving means for imparting rotary movement to the tap and a means for imparting relative reciprocating linear motion to the tap along the bore axis within the machined blank. By virtue of this motion, the tap, after completing the stroke, is reversed through the machined bore so as to be brought back into the initial position, ready for the new stroke. 2 The disadvantage of the known-in-the-art devices employing reciprocating linear motion is associated with the friction which takes place between the tool and the bore during the reverse motion. The above mentioned disadvantage is partly eliminated in a device for producing clear internal threads as described in Soviet Authority Certificate No. 1393555. In this device the reverse motion of the tap is eliminated by virtue of imparting auxiliary motion to the tap after completing each stroke outside the bore. The tap resides within a first rotating hollow spindle provided with internal thread for initiating linear motion of the tap by virtue of self winding. Also provided is a second rotating hollow spindle residing opposite to the first one and receiving the tap's forward end after it has passed the bore. The second spindle is also provided with internal thread to further advance the tap through the bore, also by virtue of self-winding. Both hollow spindles are in communication with a closed hydraulic system comprising a duct connecting between the bore's exit and entrance. A pressurized hydraulic medium is supplied to the duct under pulsating pressure and propels the tap after completing the stroke to its initial position, ready for the next cycle. It is mentioned that by virtue of this provision the cutting process is simplified, and it is possible to reduce the tap's length and to increase machining productivity. The above device even has definite advantages as compared to the traditional machining methods employing reciprocating motion; nevertheless, it is not free from serious drawbacks. Since in the prior art device the operative forward motion of the tap is effected by self winding thereof, the force capable of advancing the tap along the bore axis is limited. Therefore, the cutting forces which develop during maclrining might be insufficient for the machining of certain materials. The other disadvantage of the prior art device employing self winding for advancing the tap is associated with the fact that the pitch of tapped thread depends on the pitch of the spindle's thread. Therefore, if the variation of the pitch of tapped thread is required, the machining operation should be terminated so as to replace both hollow spindles. It can be readily appreciated that periodical termination of the machining operation makes the automation of such a process difficult and requires additional labor. An additional shortcoming of the prior art device is associated with the employing of a pulsating pressurized fluid for propelling the tap. In order to propel the tap through the duct, the hydraulic system supplying such a fluid should be capable of developing sufficient pressure. Therefore, it makes difficult, if not impossible, the implementation of such a device as a compact manual tool. Objects of the invention The object of the present invention is to provide for a new and improved method of machining through-going bores and a device for its implementation which will sufficiently reduce or overcome the above mentioned drawbacks of the prior art methods and devices. In particular, the main object of the present invention is to provide for a new and improved method for machining of through-going bores which is not limited by the pushing force advancing the tool along the bore and thus enabling reliable maclώiing of a wide range of workpiece materials. A further object of the present invention is to provide for a new and improved method of machining through-going bores which can be easily automated, does not require powerful hydraulic systems and can be easily implemented in a compact and simple device suitable both for manual and machine operation. Still a further object of the present invention is to provide for a new and improved method machining of through-going bores and a device for its implementation which operates continuously by virtue of easy evacuation of the cutting chip without its accumulation on the tool during machining. The above and other objects and advantages of the present invention can be achieved in accordance with the following combination of its essential features, referring to different embodiments thereof. These embodiments can be attributed to two independent groups, one of which refers to a method of machining, the other to disparate devices implementing this method. One of the embodiments refers to a method of machining a through-going bore within a workpiece by means of a cutting tool. The method comprises the following steps: 4 - imparting to said tool the operative linear motion associated with advancing said tool through the bore from the first position adjacent to the bore's entrance to the second position adjacent to the bore's exit, said operative linear motion being accompanied by the simultaneous rotation of the tool about the bore axis at a predetermined rotation rate - imparting to said tool of auxiliary motion associated with propelling said tool from said second position to said first position, said propelling being carried out through a duct connecting between the first and second positions, wherein said auxiliary motion is imparted by virtue of a fluid supplied to said duct under constant, non-oscillating pressure, said operative motion being imparted by virtue of a force applied to said tool so as to advance thereof along the bore. In accordance with a further preferred embodiment said force is applied to said tool by a pushing means capable of periodical advancing towards the tool so as to impart thereto said operative linear motion or retracting from said tool, so as to enable propelling said tool to said first position. In accordance with another preferred periodical advancing and retracting of said pushing means is carried out by a fluid supplied to said pushing means under pressure. As per still a further embodiment said fluid supplied to said duct is a mixture of compressed air and a coolant. In yet another preferred embodiment said mixture is supplied to said duct through said pushing means. As per still further preferred embodiment the pressure of said fluid capable of propelling said tool is not equal to the pressure of said fluid capable of advancing and retracting said pushing means. And according to another preferred embodiment said machining is a threading operation and said cutting tool is a tap suitable for cutting of the internal thread in said bore. According to one of the preferred embodiments referring to a device it comprises - a means for imparting to said tool the operative linear motion associated with advancing said tool through the bore from the first position adjacent to the bore's entrance to the second position adjacent to the bore's exit - a means for the rotation of said tool about the bore axis at a predetermined rotation rate substantially simultaneous with the operative linear motion 5 - a means for imparting to said tool the auxiliary motion associated with propelling said tool from said second position to said first position through a duct connecting between the first and second positions, wherein said means for imparting the operative linear motion is capable of applying a force to said tool so as to advance thereof along said bore. Said means for imparting the auxiliary motion comprises a source of pressurized fluid, said source being capable of supplying said fluid into said duct under constant, non-oscillating pressure. According to one of the preferred embodiments referring to a device, said means for imparting the operative linear motion comprises a pushing means and a source of pressurized fluid capable of periodically advancing said pushing means towards said tool or to retract thereof from said tool. In still a further preferred embodiment said pressurized fluid supplied into said duct is a mixture of compressed air and a coolant, said mixture being supplied under constant non-oscillating pressure of 1-2 atmospheres. In yet another preferred embodiment said pushing means comprises a pushing rod residing within a hydraulic cylinder connected to the source of pressurized fluid. As per additional preferred embodiment said pushing rod is formed as a tubular element connected to the source of said mixture. In a further preferred embodiment said source of pressurized fluid is capable of supplying to said hydraulic cylinder compressed air under pressure of at least 3 atmospheres. According to still a further preferred embodiment, said means for rotation of the tool about the bore axis comprises a motor and a hollow spindle member driven by said motor, the interior of said spindle member conforming the shape of said tool so as to enable imparting thereto rotation and operating linear motion. In another preferred embodiment of the device, it is mounted on a machine tool and said means for rotation of the tool about the bore axis is driven by a spindle of said machine tool. In yet another preferred embodiment said cutting tool is a tap suitable for cutting the internal thread into said through-going bore. The additional preferred embodiment of a device for machining a through-going bore within a workpiece comprises: The additional preferred embodiment of a device for machining a through-going bore within a workpiece comprises: - a table provided with at least one work station equipped with a hollow spindle carrying a cutting tool suitable for machining said bore, - a rotation means capable of rotating said spindle so as to impart to said tool rotation motion about the axis of the bore, - a means for revolving said table and bringing selected work station into position in which said spindle can be operatively coupled with said rotation means - a means for imparting to said tool an operative linear motion associated with advancing said tool through the bore from the first position adjacent to the bore's entrance to the second position adjacent to the bore's exit, and - a means for imparting to said tool the auxiliary motion associated with propelling said tool from said second position to said first position through a duct connecting between the first and second positions, wherein said means for imparting the operative linear motion is capable of applying a force to said tool so as to advance thereof along said bore. Said means for imparting the auxiliary motion comprises a source of pressurized fluid, said source being capable of supplying said fluid into said duct under constant, non-oscillating pressure. In an additional preferred embodiment of this device said table is equipped with work stations which carry cutting tools suitable for a variety of machining operations. The present invention in its various embodiments, referring both to a method and to disparate devices, has only been briefly summarized. For a better understanding of the present invention as well of its benefits and advantages, reference will now be made to the following description of the above embodiments taken in combination with accompanying drawings. Brief description of the drawings Fig.1 shows a side view of a device in accordance with the present invention. Fig.2 shows a top view of a device in accordance with the present invention. Fig.3a,b show, respectively, the pushing means in the forward-most and rear-most positions. Fig.4 presents a cross-section A-A of fig.1. Fig.5 presents an alternative embodiment of a device in accordance with the present invention including a revolving table equipped with several work stations. Figs.6,7 show two side views of a device in accordance with the present invention when it is coupled with a drilling machine. Detailed description of specific embodiments. With reference to fig.l there is shown an embodiment of a device 10 in accordance with the present invention, which comprises a housing 1 with a hollow spindle 2 residing therein, mounted with the possibility of rotation by virtue of bearings 3. The interior of the spindle conforms to the exterior of a cutting tool, so as to enable their joint rotation when the tool resides therein. The tool can pass the interior of the spindle so as to advance towards a workpiece W provided with a through-going bore 5 to be machined. The workpiece can be fed automatically from a chute (not shown) or by any other suitable feeding means. In the following description the advancing of the tool through the bore axis from the bore's entrance En to bore's exit Ex accompanied by the simultaneous rotation of the tool will be referred to as an operative linear motion. The result of this motion, in other words, the type of machining operation performed by the device can be different, depending on the particular cutting tool employed in the device. A further disclosure will refer to a threading operation which enables the cutting of an internal thread within the bore 5 made, for example, within a nut. For this purpose a cutting tool 4, which is a tap is used. The tap comprises a threaded screw portion provided with interposing flutes for the evacuation of chips generated during machining. With reference to fig.4 it can be seen that the cross-sectional configuration of the spindle's interior in general conforms to the cross-sectional configuration of the tap; a gap G is provided therebetween. By virtue of this gap linear motion of the tap is enabled through the spindle. The rotational moment is transferred to the tap through its flute areas FA. It should be understood, however, that the present invention is not limited by internal threading and can be equally employed for performing any other machining operation which employs the similar linear operative motion of a cutting tool. As an example of such a machining operation one can mention the increasing of the bore's diameter by a drill, reaming by a reamer, etc. Mounted on the housing is an electric motor 6 used for rotating the hollow spindle. The rotation moment is transferred from the motor by a driving wheel 7, a belt 8 and a driven wheel 9, rigidly coupled with the spindle by virtue of a screw 11. In contrast to the prior art tapping devices in which both the operative linear motion and the reverse motion of the tap takes place through the threaded bore, in the present invention the tap moves through the bore only during the operative linear motion. The tap is reversed to the initial position by virtue of a dedicated auxiliary motion taking place outside the threaded bore. For enabling this auxiliary motion the housing is provided with an elongated entrance portion 12 having a through-going opening 13 which communicates with the interior of the hollow spindle. Also provided is a hollow duct 14 connecting between the entrance portion and the exit of the threaded bore . The inner diameter of the duct and of the entrance portion slightly exceeds the outside diameter of the tap so as to enable its free passage through the duct and through the housing. The duct is connected with a source of pressurized fluid capable of propelling the tap through the duct. It can be readily appreciated that when the tap is about to leave the bore in the end of a stroke it enters the duct and from this point the tap is propelled through the duct by the pressurized fluid until it reaches the entrance portion of the housing, passes through it and returns to the initial position within the hollow spindle ready to begin a new stroke. In accordance with the present invention the advancing of the tap through the bore in the course of the operative linear motion is carried out by virtue of an external force applied to the rear portion of the tap. To apply this force a pushing rod 15 is provided. It is aligned and coaxial with the through-going opening 13 made in the housing The pushing rod is provided with a piston 16 and resides within a hydraulic cylinder 17 communicating with the source of pressurized fluid 18. The pressurized fluid, for example, compressed air, is supplied to the cylinder via a regulating valve 19 enabling changes in air pressure, and thus to control the force applied by the pushing rod to the tap. In practice the pressure of compressed air supplied to the cylinder is about 3 atmospheres. A control means 20, for example a double acting piston is provided, which enables connection of the source of pressurized fluid either to the forward or rear extremity of the cylinder, and coσespondingly, to retract the rod from the tap or to push it towards the tap. The pushing rod is formed as a tubular element, whose interior 21 is in communication with a source of pressurized fluid 22 capable of supplying thereof under constant non oscillating pressure. It can be readily appreciated that by virtue of the coaxial disposition of the pushing rod and through-going opening 13 the pressurized fluid passes the entrance portion of the housing, reaches the hollow spindle and is capable of propelling the tap via duct 14. As a suitable pressurized fluid one can use compressed air mixed with a coolant. For this purpose a source of coolant 23 can be installed within a line connecting the source of pressurized fluid 22 and the rod. In accordance with the present invention the source 22 should be capable of supplying the fluid to the duct during the machining cycle under constant non-oscillating pressure of 1-2 atmospheres. It should be understood, however, that if the machining cycle is paused, for example, for maintenance or for replacement of the workpiece, the source of pressure can be cut off and supply of the fluid to the pushing rod can be temporarily terminated. It should also be realized that the source of constant non-oscillating pressure of 1-2 atmospheres can be kept small, thus allowing to design the entire device as a compact tool suitable for manual operation. The entrance portion of the housing is formed with a port 24 for evacuation of chips generated during the machining operation. With reference to figs.3a,3b the operation of the threading device implementing the present invention will now be described. In fig.3a the situation is shown when compressed air is supplied from the source 18 to the rear extremity of the cylinder, therefore advancing the pushing rod to its forward position, which corresponds to the end of linear operative motion of the tap. The threading stroke is finished and the machined workpiece has left the working position so as to enable feeding of the unthreaded workpiece. The tap, after it has passed the bore, enters duct 14 and is propelled therefrom through the duct until it reaches the entrance portion of the housing. However, since the pushing rod is still in its forward position, the duct does not communicate with the through-going opening of the entrance portion. Therefore, the compressed air cannot bring the tap into its initial position within the hollow spindle until there is no workpiece in the working position. 10 The mixture of coolant and compressed air which is supplied to the pushing rod passes through the rod's interior, proceeds to the hollow spindle and exits therefrom outside. At the exit from the spindle the stream of pressurized mixture pushes forward the cutting chips which could have accumulated during the threading stroke. It is not shown specifically, but should be appreciated that the chip is followed by the tap and they are propelled together via the duct. When the chip reaches the entrance portion of the housing it can be evacuated therefrom via port 24 . By virtue of control means 20 the supply of compressed air from source 18 is now switched to the frontal extremity of the cylinder. This causes retracting of the pushing rod from the forward position to the rear position as shown in fig.3b. Simultaneously with retracting the pushing rod the new workpiece W is fed into the work position and is ready for threading. In the retracted position the pushing rod no longer blocks the through-going opening of the entrance portion 12 and therefore communicates with the duct. It can be readily appreciated that the stream of pressurized fluid circulating within the duct can now bring the tap into its initial position within the spindle so as to begin the operative linear motion associated with the new threading cycle. In fig.3 b one can see the tap pushed into the spindle by the mixture of compressed air and coolant supplied to the duct via interior 21 of the pushing rod from source 22. When the tap resides within the spindle it is brought into rotating motion and is ready for advancement towards the bore of the workpiece. By virtue of gap G between the spindle interior and the tap the stream of pressurized fluid flowing through the spindle's interior enables self-centering of the tap thus ensuring coaxial disposition of the tap with respect to the bore's axis. It can be readily appreciated that due to the self- centering of the cutting tool the accuracy of machining operation is improved. With reference to non-limiting example 1 it will be now described how the present invention was implemented for the internal threading of nuts. Example 1. The internal thread M8 with 7 mm depth was cut in nuts made of Aluminum- 12%Si alloy. The thread was cut by a tap made from high speed steel.. The constant non-oscillating pressure of 1.2 atmospheres was employed for propelling the tap through the duct. 11 The pressure of compressed air supplied to the hydraulic cylinder was 3 atmospheres. The rotational velocity of the spindle was 2000 rpm. The tap's tool life from re-sharpening to re-sharpening was 140000 nuts. The same operation was carried out in the traditional tapping machine employing reverse of the tap through the bore. The rotational velocity of the spindle was 680 rpm and the tap's tool life was 1400- 1500 nuts. From the above data one can clearly see that by virtue of the present invention it is possible to improve the efficiency of threading significantly and at the same time to increase the tool life. The explanation of this result lies in the fact that in the course of operative linear motion the tool is forced to advance along the bore by virtue of a dedicated pushing means. At the same time, since the auxiliary motion of the tool takes place outside the bore it is not accompanied by friction between the tool and the workpiece; thus, tool wear is significantly reduced. With reference to figs. 5 it will now be explained how the present invention can be implemented for effecting disparate machining operations. Fig.5 shows an embodiment of a device in accordance with the present invention provided with a worktable 25 formed as a turret carrying work stations 26,27,28,29 each of which is equipped with a hollow spindle 36,37,38,39 coupled with a pulley 46,47,48,49 similar to that described above in connection with a device provided with a sole work station. The worktable is provided with a revolving means (not shown) capable of revolving the table about its axis and to bring the selected work station to a position in which its hollow spindle can be operatively coupled with a hollow duct and with a means for imparting to the tool operative linear motion accompanied by simultaneous rotation (now shown). In fig.5 one can see the work station 28 brought to a position where its hollow spindle 38 receives rotation moment from pulley 48 driven by a belt 8. Each of the work stations can be provided with a disparate cutting tool so as to perform a variety of machining operations in a workpiece. Fig. 5 also shows a work station 26 equipped with a tap 56, work station 27 with a drill 57, work station 28 with a coarse drill 58 and work station 29 with a reamer 59. In the above described embodiments rotation of the hollow spindle imparting rotation motion to the cutting tool was effected by a dedicated autonomous rotation means, for

Claims: 12 example a motor. With reference to figs. 6,7 it will now be explained how instead of a dedicated rotation means one can use, for example, the drive of a machine tool. Fig. 6 schematically shows a working head 30 of a machine tool, for example, a drilling machine, provided with a spindle 31, a chuck 32 and a table 33 secured within a wig 34. The above described device for the machining of a through-going bore is mounted on the worktable in such a manner that the hydraulic cylinder 16 is held on the table by virtue of a bracket 35. The housing 1 of the device resides on the table and the hollow spindle 2 receives rotation moment via two meshing gears 40,41 from a shaft 42 fixed in the chuck. As in the previously described embodiments the cutting tool is propelled via duct 14 and is brought back into the initial position within the hollow spindle ready to begin a new stroke. It should be appreciated that the present invention is not limited to the above-described embodiments and that changes and modifications can be made by one ordinarily skilled in the art without deviation from the scope of the invention, as will be defined in the appended claims. For example, the hollow spindle can be rotated by an electric or a pneumatic motor, and the device can be mounted on any other machine tool and not only on a drilling machine. It should also be appreciated that the features disclosed in the foregoing description, and/or in the following claims, and/or in the accompanying examples, and/or in the accompanying drawings may, both separately and in any combination thereof, be material for realizing the present invention in diverse forms thereof. 13 I claim: 1. A method of machining a through-going bore within a workpiece by means of a cutting tool, said method comprising: - imparting to said tool the operative linear motion associated with advancing said tool through the bore from the first position adjacent to the bore's entrance to the second position adjacent to the bore's exit, said operative linear motion being accompanied by the simultaneous rotation of the tool about the bore axis at a predetermined rotation rate - imparting to said tool of auxiliary motion associated with propelling said tool from said second position to said first position, said propelling being carried out through a duct connecting between the first and second positions, characterized in that said auxiliary motion is imparted by virtue of a fluid supplied to said duct under constant, non-oscillating pressure said operative motion being imparted by virtue of a force applied to said tool so as to advance thereof along the bore. 2. The method as defined in claim 1, characterized in that said force is applied to said tool by a pushing means capable of periodical advancing towards the tool so as to impart thereto said operative linear motion or retracting from said tool, so as to allow propelling said tool to said first position. 3. The method as defined in claim 2, characterized in that periodical advancing and retracting of said pushing means is carried out by a fluid supplied to said pushing means under pressure. 4. The method as defined in claim 3, characterized in that said fluid supplied to said duct is a mixture of compressed air and a coolant . 5. The method as defined in claim 4 , characterized in that said mixture is supplied to said duct through said pushing means. 6. The method as defined in claim 3, characterized in that the pressure of said fluid capable of propelling said tool is not equal to the pressure of said fluid capable of advancing and retracting said pushing means. 7. The method as defined in claim 1, characterized in that said machining is a threading operation and said cutting tool is a tap suitable for cutting the internal thread in said bore. 14 8. A device for machining through-going bore within a workpiece by means of a cutting tool, said device comprising - a means for imparting to said tool the operative linear motion associated with advancing said tool through the bore from the first position adjacent to the bore's entrance to the second position adjacent to the bore's exit - a means for the rotation of said tool about the bore axis at a predetermined rotation rate substantially simultaneous with the operative linear motion - a means for imparting to said tool the auxiliary motion associated with propelling said tool from said second position to said first position through a duct connecting between the first and second positions, characterized in that said means for imparting the operative linear motion is capable of applying a force to said tool so as to advance thereof along said bore, Said means for imparting the auxiliary motion comprises a source of pressurized fluid, said source being capable of supplying said fluid into said duct under constant, non-oscillating pressure. 9. The device as defined in claim 8, characterized in that said means for imparting the operative linear motion comprises a pushing means and a source of pressurized fluid capable of periodically advancing said pushing means towards said tool or to retract thereof from said tool. 10. The device as defined in claim 9, characterized in that said pressurized fluid supplied into said duct is a mixture of compressed air and a coolant, said mixture beings supplied under constant non-oscillating pressure of 1-2 atm. 11. The device as defined in claim 9, characterized in that said pushing means comprises a pushing rod residing within a hydraulic cylinder connected to the source of pressurized fluid. 12. The device as defined in claim 10, characterized in that said pushing rod is formed as a tubular element connected to the source of said mixture. 13. The device as defined in claim 9, characterized in that said source of pressurized fluid is capable of supplying, to said hydraulic cylinder, compressed air under pressure of at least 3 atm. 14. The device as defined in claim 8, characterized in that said means for rotation of the tool about the bore axis comprises a motor and a hollow spindle member driven by

Inventors: KAGANOVICH MIRON, KAGANOVICH, MIRON
Applicants: FLYING TOOLS LTD, KAGANOVICH MIRON, FLYING TOOLS LTD., KAGANOVICH, MIRON
Application year: 1998
Main classification: B23B35
IPC codes: B23G9, B23Q5