Toolholder matched with the internal jet cooling spindle for cryogenic coolant

Abstract

A toolholder matched with the internal jet cooling spindle for cryogenic coolant is mainly composed of a hollow toolholder body, a high-performance thermal insulation structure and a bidirectional sealing structure. They can guide the cryogenic coolant from the spindle to the internal cooling channel of cutting tool and realize the cryogenic thermal insulation and dynamic sealing. The high-performance thermal insulation structure inside the toolholder employs the material with a low thermal conductivity and a low linear expansion coefficient to restrain the low temperature impact of cryogenic coolant on the toolholder and spindle, to ensure the dimensional accuracy and assembly accuracy of the toolholder. The bidirectional sealing structure in the toolholder uses the ultra-low temperature resistant seal rings to prevent the cryogenic coolant from leaking towards the spindle and the cutting tool, to ensure the stability of the coolant transport.

Claims

1. A toolholder matched with an internal jet cooling spindle for cryogenic coolant, wherein the toolholder comprises: a hollow toolholder body, a high-performance thermal insulation structure and a bidirectional sealing structure; wherein the hollow toolholder body is of a hollow structure to provide a channel for cryogenic coolant transport; the high-performance thermal insulation structure is arranged inside the hollow structure of the hollow toolholder body to suppress diffusion of a cryogenic temperature field to the toolholder and the spindle; and the bidirectional sealing structure is seated in the hollow toolholder body to prevent a leakage of the cryogenic coolant towards the spindle and a cutting tool; an outer cone surface of the hollow toolholder body is a positioning surface connected with the spindle; an external thread on a front outer circle is used to install a locking nut for clamping the cutting tool; an inner cone surface on a front end is used to install a spring collet; the outer cone surface, the external thread and the inner cone surface are main working surfaces of the toolholder; the hollow toolholder body provides the channel for the cryogenic coolant transport as well as an installation space and positioning surface required by the high-performance thermal insulation and bidirectional sealing structures; an inner cavity bottom surface, an inner cavity surface, an inner hole, a tool escape, and an internal thread are cut in the hollow toolholder body; the internal thread is connected with the inner cone surface; the tool escape is located between the internal thread and the inner cavity surface; the inner cavity surface is a cylindrical surface which is located inside the outer cone surface; the inner cavity bottom surface is a bottom surface of the inner cavity surface which is located in an end direction of the hollow toolholder body; the inner hole is located in a thinnest end of the outer cone surface, and a shaft inside spindle extends into the hollow toolholder body through the inner hole to transmit the cryogenic coolant; and there are four flange-via holes on a horizontal flange surface of the hollow toolholder body, which are used to connect and fasten the spindle; wherein the horizontal flange surface is located between the outer cone surface and the external thread; the high-performance thermal insulation structure includes, in order, a thermal insulation sleeve, a compression sleeve and a locking sleeve; the thermal insulation sleeve is located inside the inner cavity surface, which is the main structure to isolate the cryogenic coolant from the hollow toolholder body; the compression sleeve is installed in the inner thread to provide a compression force for the thermal insulation sleeve and an installation groove for an outer seal ring; and the locking sleeve is also installed in the inner thread, which is used to press out the outer seal ring and fasten the compression sleeve; and the bidirectional sealing structure includes an inner seal ring and the outer seal ring which are ultra-low temperature resistant; and the inner seal ring and the outer seal ring are located inside the hollow toolholder body to prevent the cryogenic coolant from leaking towards the spindle and the cutting tool; wherein, while assembling the toolholder, first the inner seal ring is pushed into the hollow toolholder body along the inner cavity surface while a sealing surface is toward the outside, meanwhile an opposite side of the inner seal ring is in contact with the inner cavity bottom surface; the thermal insulation sleeve is installed into the hollow toolholder body along the inner cavity surface, there is an interference fit between the thermal insulation sleeve and the hollow toolholder body until it is pressed against the inner seal ring, meanwhile the tool positioning plane on the thermal insulation sleeve is kept toward the outside; then two auxiliary holes I on the compression sleeve are clamped with a tooling to screw the compression sleeve along the internal thread until the compression sleeve is pressed against the thermal insulation sleeve; then the outer seal ring is installed into the installation groove of the compression sleeve while its sealing surface is oriented inward, and the two auxiliary holes II are clamped with the tooling so that the locking sleeve is screwed along the internal thread to press out the outer seal ring; finally, the inner seal ring, the thermal insulation sleeve, the compression sleeve, and the outer seal ring are pressed out; meanwhile, the locking function is realized by the compression sleeve and the locking sleeve, and construction of the toolholder assembly has been accomplished; wherein, while installing the cutting tool, first the spring collet is installed into the locking nut, and an end face of the spring collet and the locking nut is superposed; the locking nut along with the spring collet is screwed on the hollow toolholder body along the external thread; then, an internal cooling tool is inserted into the spring collet until its end face is pressed against the tool positioning plane of the thermal insulation sleeve, meanwhile the outer surface of the internal cooling tool and the inner surface of the outer seal ring have an interference fit; finally, the locking nut is tightened using a wrench, and installation of the cutting tool has been accomplished; and during processing, the outer cone surface of the hollow toolholder body which has been assembled and installed with the tool is installed into a cone hole of the spindle; the shaft is inserted into the toolholder body through the inner hole and forms an interference fit with the inner seal ring; a gap is retained between a shaft end face and the thermal insulation sleeve inner end face; four bolts are screwed into four spindle threaded holes through the four flange-via holes, and a torque wrench is used to tighten the four bolts with a certain value of torque; thus, the outer cone surface of the hollow toolholder body and the cone surface of the spindle are closely matched to realize the installation and position of the toolholder; while the cryogenic coolant delivery system is started, the cryogenic coolant is jetted to a nose of a blade of the cutting tool through a shaft inner channel, a toolholder inner channel and a tool inner channel.

2. The toolholder matched with the internal jet cooling spindle for cryogenic coolant according to claim 1, wherein the hollow toolholder body and the spindle are connected and fastened by the flange surface.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is the schematic diagram of the toolholder body 1.1.

(2) FIG. 2 is the schematic diagram of the toolholder assembly.

(3) FIG. 3 is the schematic diagram of the installation of toolholder and spindle.

(4) FIG. 4 is the schematic diagram of the temperature measurement of cone surface of the toolholder.

(5) FIG. 5 is the temperature curve of the cone surface of toolholder.

(6) In Figure: 1.1—toolholder body; 1.2—inner seal ring; 1.3—thermal insulation sleeve; 1.4—compression sleeve; 1.5—outer seal ring; 1.6—locking sleeve; 1.7—flange-via hole; 1.8—spring collet; 1.9—locking nut; 1.10—bolt; 1.a—inner cavity bottom surface; 1.b—internal thread; 1.c—external thread; 1.d—auxiliary hole I; 1.e—auxiliary hole II; 1.f—thermal insulation sleeve inner end face; 1.g—tool positioning plane; 1.h—inner cone surface; 1.i—outer cone surface; 1.j—inner cavity surface; 1.k—end face; 1.m—tool escape; 1.n—inner hole; 2.1—spindle; 2.2—spindle threaded holes; 2.3—shaft; 2.4—internal cooling tool; 2.5—blade; 2.a—shaft end face; 3.1—shaft inner channel; 3.2—toolholder inner channel; 3.3—tool inner channel; 4.1—temperature sensor.

DETAILED DESCRIPTION

(7) The specific embodiments of the present invention will be described in detail below with reference to the drawings and technical solutions:

(8) In the embodiment, the cryogenic coolant is liquid nitrogen, and the material of thermal insulation sleeve 1.3, compression sleeve 1.4 and locking sleeve 1.6 are all modified polyimide with thermal conductivity less than 0.15 W/(m.Math.K). The wall thickness of thermal insulation sleeve 1.3 is 8 mm. The inner seal ring 1.2 and outer seal ring 1.5 are lip seals, and their materials are carburized polytetrafluoroethylene. The working temperature for seals ranges from −200 to 260° C., the maximum pressure is 3 MPa. The type of toolholder body 1.1 is BT40, the accuracy of cone is AT3 and its hardness is more than HRC55. The type of spring collet 1.8 is ER32, and its inner diameter is Φ13-14. The shaft 2.3 is of vacuum insulation structure. The outer diameter of the internal cooling tool 2.4 is 14 mm. The measurement range of temperature sensor 4.1 is −200-100° C.

(9) The assembly and installation process of the toolholder is as follows. As shown in FIGS. 1, 2 and 3, step one, the sealing surface of the inner seal ring 1.2 and the tool positioning plane 1.g of the thermal insulation sleeve 1.3 are kept outward. And then the inner seal ring 1.2 and the thermal insulation sleeve 1.3 are orderly pushed into the toolholder body 1.1 along the inner cavity surface 1.j in the way of interference fit, until the inner seal ring 1.2 is pressed against the inner cavity bottom surface 1.a meanwhile the thermal insulation sleeve 1.3 is pressed against the inner seal ring 1.2. The two auxiliary holes I 1.d on the compression sleeve 1.4 are clamped with a tooling to screw the compression sleeve 1.4 along the internal thread 1.b until it is pressed against the thermal insulation sleeve 1.3. The outer seal ring 1.5 is installed into the groove of the compression sleeve 1.4 while its sealing surface is inward. The two auxiliary holes II 1.e are clamped with the tooling to screw the locking sleeve 1.6 along the internal thread 1.b and press out the outer seal ring 1.5.

(10) Step two, the spring collet 1.8 is installed into the locking nut 1.9 meanwhile the end face 1.k is ensured coincident. Then, the locking nut 1.9 with the spring collet 1.8 is screwed on the toolholder body 1.1 along the external thread 1.c. The internal cooling tool 2.4 is inserted into the spring collet 1.8 until its end face is pressed against the tool positioning plane 1.g of the thermal insulation sleeve 1.3, also, the outer surface of the internal cooling tool 2.4 and the inner surface of the outer seal ring 1.5 have an interference fit. Finally, the locking nut 1.9 is tightened using a wrench.

(11) Step three, the outer cone surface 1.i of the toolholder body 1.1 is installed into the cone hole of the spindle 2.1. The shaft 2.3 is inserted into the toolholder body 1.1 through the inner hole 1.n to form an interference fit with the inner seal ring 1.2. The shaft end face 2.a and the thermal insulation sleeve inner end face 1.f keep a gap of 1 mm. The four bolts 1.10 are screwed into the four spindle threaded holes 2.2 through the four flange-via holes 1.7. A torque wrench is used to tighten the four bolts 1.10 with a torque of 10 N.Math.m, so that the outer cone surface 1.i of the toolholder body 1.1 is fitted closely with the cone surface of the spindle 2.1.

(12) Step four, the liquid nitrogen convey system is started, and then liquid nitrogen is jetted to the nose of blade 2.5 through the shaft inner channel 3.1, the toolholder inner channel 3.2 and the tool inner channel 3.3 in turn. At the moment, the machining can be started. The machining is stopped every 5 minutes and the toolholder is removed, and then the temperature of the outer cone surface 1.i is measured by the temperature sensor 4.1. The measurement process and results are shown in FIG. 4 and FIG. 5, respectively. The results show that the surface temperature of the toolholder is about 8° C. and no frost is found.

(13) The invention effectively eliminates the ultra-low temperature impact of cryogenic coolant on the toolholder through the thermal insulation and sealing structure, to ensure the accuracy of the toolholder and the stability of liquid nitrogen transport. The toolholder accomplishes the connection between the internal jet cooling spindle and the internal cooling tool, to assist the special cryogenic cooling machine tool to implement cryogenic machining under the internal jet cooling mode of cryogenic coolant. For the toolholder, the integral structure is simple, the integration is good, as well as the operation is safe and reliable.