A die, method and application for preparing optical aluminum alloy by equal-channel angular pressing severe plastic deformation

Abstract

The present invention belongs to the technical field of plastic forming of aluminum alloys, and discloses a mold base for preparing optical aluminum alloys by torsion extrusion large plastic deformation. A first discharge channel and a second discharge channel are formed on the base; a mandrel sleeve and a mandrel which are arranged in a supporting manner are disposed on the base. A forward mandrel and a reverse mandrel which are communicated with the first discharge channel and the second discharge channel are formed in the mandrel. The forward mandrel and the reverse mandrel include spiral cylindrical channels with equal diameters; an upper die is disposed on the tops of the mandrel sleeve and the mandrel; an extrusion rod seat assembly includes an extrusion rod seat, a first extrusion rod and a second extrusion rod which are disposed on the top of the upper die; first torsion extrusion channels and second torsion extrusion channels which are respectively communicated with the forward mandrel and the reverse mandrel are formed in the extrusion rod seat and the upper die. The first extrusion rod and the second extrusion rod move up and down correspondingly in the first torsion extrusion channel and the second torsion extrusion channel to extrude a blank to be processed. A preparation method and an application are also provided. In the above-mentioned mold, method and application, they have the characteristics of high efficiency, low cost and high precision.

Description

Technical Field

[0001] The present invention belongs to the technical field of plastic forming of aluminum alloys, and specifically relates to a die, a method and an application for preparing optical aluminum alloys by torsion extrusion large plastic deformation. Background Art

[0002] Optical aluminum alloy is a key material for preparing precision optical reflectors such as missile seekers, optoelectronic pods, spaceborne cameras, and automotive lidars. The higher the surface machining accuracy of the reflector, the more guaranteed the imaging quality of the optical instrument. To improve the machining accuracy of the optical reflector, it is required that the microstructure of the reflector material is ultra-fine and uniform.

[0003] The surface machining accuracy requirements for reflectors used in aerospace high-end equipment are extremely high, usually within 3 nm, and even within 1 nm. The Netherlands uses rapid solidification strip casting method and hot isostatic pressing to prepare optical microcrystalline aluminum materials, and the Ra value of the surface machining accuracy of the reflector has reached 1 nm, with a specification of Φ1000 mm. Imported Alcoa plates are often used for machining automotive reflectors, and the material consistency is good, but there are still problems such as many impurity phases causing low machining accuracy and unsatisfactory quality. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies and defects in the background art, and provide a die, a method and an application for preparing optical aluminum alloys by torsion extrusion large plastic deformation with high efficiency, low cost and high precision.

[0005] To solve the above technical problem, the technical solution proposed by the present invention is: A die for preparing optical aluminum alloys by torsion extrusion large plastic deformation, comprising:

[0006] A base, on which a first discharge channel and a second discharge channel are provided;

[0007] A matching core mold sleeve and a core mold, arranged on the base, and a forward core mold and a reverse core mold communicating with the first discharge channel and the second discharge channel are provided in the core mold. The forward core mold and the reverse core mold include spiral cylindrical channels with equal diameters, and the spiral directions of the forward core mold and the reverse core mold are opposite to cancel the lateral force;

[0008] An upper die, arranged on the top of the core mold sleeve and the core mold;

[0009] An extrusion rod seat assembly, comprising an extrusion rod seat, a first extrusion rod and a second extrusion rod arranged on the top of the upper die; the extrusion rod seat and the upper die are provided with a first torsion extrusion channel and a second torsion extrusion channel communicating with the forward core mold and the reverse core mold respectively, and the first extrusion rod and the second extrusion rod move up and down in the first torsion extrusion channel and the second torsion extrusion channel to extrude the workpiece to be processed.

[0010] In one embodiment, the base circle diameter of the spiral cylindrical channels of the forward core die and the reverse core die is 15 mm to 22 mm, the pitch is 110 mm to 140 mm, the helix angle is 18.6° to 24.5°, and the number of helix turns is 0.5 - 1.

[0011] In one embodiment, the spiral cylindrical channel includes a transition section connected to the upper and lower channels and an equal - helix section located between the two transition sections.

[0012] In one embodiment, the forward core die and the reverse core die are inverted conical, the shape of the core die sleeve is matched with the forward core die and the reverse core die, and the forward core die, the reverse core die and the core die sleeve are fixed by flat keys.

[0013] In one embodiment, there is a 1 - 2 mm gap between the forward core die and the reverse core die and the base, and the forward core die and the reverse core die are in contact with the upper die.

[0014] Based on the same inventive concept, a method for preparing optical aluminum alloy using the above - mentioned mold is provided, including:

[0015] First, place the billets into the first extrusion channel and the second extrusion channel respectively;

[0016] Press down the extrusion rod to cause the billets to undergo torsional extrusion deformation in the spiral channels of the core die, and take out the deformed billets from the outlets of the first discharge channel and the second discharge channel on the base;

[0017] Put the deformed billets back into the first extrusion channel and the second extrusion channel, and press down the extrusion rod again to cause the billets to undergo torsional extrusion deformation in the spiral channels of the core die. Repeat the operation of torsional extrusion deformation to obtain an optical aluminum alloy product with large plastic deformation by torsional extrusion. During the repeated operation process, the diameter of the billets remains unchanged.

[0018] In one embodiment, before loading the billets into the mold, first evenly apply a release agent on the surface of the billets and then heat them to a billet temperature of 250 ± 10°C, and at the same time heat the mold to a temperature of 250 ± 10°C; or

[0019] Before loading the billets into the mold, first evenly apply a release agent on the surface of the billets and then heat them to a billet temperature of 400 - 550°C, and at the same time heat the mold to a temperature of 400 - 550°C.

[0020] In one embodiment, before loading the billets into the mold, cool both the mold and the billets to the liquid nitrogen temperature, and repeat the operation of torsional extrusion deformation of one billet more than 6 times.

[0021] In one embodiment, when the extrusion rod presses down on the blank to be extruded and cannot provide a force on the current blank, the extrusion rod is removed, and a new blank is loaded into the first and second torsion extrusion channels. Then, the extrusion rod presses down to extrude the new blank, and the previous blank is extruded out of the mold by using the new blank.

[0022] Based on the same inventive concept, there is provided an application of a product obtained by the method for preparing an optical aluminum alloy as described above in an optical mirror.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: Compared with the multi-directional forging large plastic deformation method in the prior art, in the mold and method for preparing an optical aluminum alloy by torsion extrusion large plastic deformation provided by the present invention, by arranging a forward mandrel and a reverse mandrel in the core mold, a large plastic deformation aluminum alloy product is obtained by pressing down the extrusion rod in a spiral cylindrical channel with equal diameters. The production efficiency is high, the shape of the mirror blank is the same as that of the final mirror product, both are circular, the material utilization rate is high, the machining allowance is small, the blank is in a triaxial compressive stress state during forming, the cracking risk can be effectively reduced, and the yield rate is improved. At the same time, the implementation scheme is simple, the single strain reaches 2.0, large plastic deformation can be quickly realized, and the efficiency is high. Furthermore, in the mold and method of the present invention, different torsion extrusion forming schemes can be formulated according to the product quality requirements to improve efficiency and control costs. For optical aluminum alloys with general processing quality requirements, such as a processing quality level of 5 - 10 nm, warm torsion extrusion at 250 °C can be used, or hot torsion extrusion at 400 - 550 °C can be used, and the number of extrusion times can be 1 - 3 times; for optical aluminum alloys with higher processing quality requirements, such as a processing quality level of 2 - 5 nm, room temperature torsion extrusion or warm torsion extrusion at 200 - 250 °C can be used, and the number of torsion extrusion passes can be 3 - 6 times; by reducing the torsion extrusion forming temperature, although the energy consumption is higher, by increasing the number of torsion extrusion deformations, finer grains can be obtained, and the surface processing quality of the mirror blank can be improved; for optical aluminum alloys with ultra-high processing quality requirements, such as a processing quality level of 1 - 2 nm or less than 1 nm, cryogenic torsion extrusion can be used. Before extrusion forming, both the mold and the blank are cooled to the liquid nitrogen temperature, and the number of extrusion passes is greater than 6 times to prepare a nano-scale ultrafine grain structure, and the processing quality of the product can reach the sub-nano level. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 It is a schematic structural diagram of a mold for preparing an optical aluminum alloy by torsion extrusion large plastic deformation in one embodiment;

[0026] Figure 2 Schematic diagram of the partial structure of a die for preparing optical aluminum alloy by equal-channel angular pressing (ECAP), which is an embodiment

[0027] Figure 3 Schematic diagram of the die structure for preparing optical aluminum alloy by equal-channel angular pressing (ECAP), which is an embodiment

[0028] Figure 4 Schematic diagram of the equal-channel angular pressing (ECAP) channel parameters, which is an embodiment

[0029] Figure 5 Strain field distribution under different process parameter conditions, which is an embodiment

[0030] Figure 6 Schematic diagram of the deformation situation in one pass of Example 4 of the present application

[0031] Figure 7 Schematic diagram of the deformation situation in one pass of Comparative Example 1

[0032] Figure 8 Schematic diagram of the deformation situation in one pass of Comparative Example 2 Specific embodiments

[0033] For the convenience of understanding the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings of the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments

[0034] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention

[0035] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or can be prepared by existing methods

[0036] Please refer to Figure 1-8, A die for preparing optical aluminum alloy by equal-channel angular pressing (ECAP), from top to bottom, includes an extrusion rod seat assembly, an upper die 3, a sleeved core die sleeve 4 and a core die, and a bottom die 7. The extrusion rod seat assembly includes an extrusion rod seat 1 and an extrusion rod 2. The core die includes a forward core die 6 and a reverse core die 5. Specifically, the bottom die 7 is provided with a first discharge channel and a second discharge channel; the first discharge channel and the second discharge channel are respectively communicated with the forward core die 6 and the reverse core die 5. The forward core die 6 and the reverse core die 5 include spiral cylindrical channels with equal diameters, and the spiral directions of the forward core die 6 and the reverse core die 5 are opposite to offset the lateral force. The extrusion rod 2 includes a first extrusion rod and a second extrusion rod; the extrusion rod seat and the upper die are provided with a first ECAP channel and a second ECAP channel respectively communicated with the forward core die 6 and the reverse core die 5, and the first extrusion rod and the second extrusion rod move up and down in the first ECAP channel and the second ECAP channel respectively to extrude the workpiece to be processed.

[0037] Preferably, in one embodiment, the base circle diameter of the spiral cylindrical channels of the forward core die 6 and the reverse core die 5 is 15 mm to 22 mm, the pitch is 110 mm to 140 mm, the helix angle is 18.6° to 24.5°, and the number of spiral turns is 0.5 - 1. In the present invention, a large number of simulation optimizations are carried out on the spiral cylindrical channels by finite element simulation. Considering the experimental results comprehensively, within the above parameter range, more uniform and sufficient deformation can be obtained, while the forming load is small, the channel height is short, the die structure is more reasonable, and the implementation is convenient.

[0038] Preferably, the spiral cylindrical channel includes a transition section connected to the upper and lower channels and an equal-spiral section in the middle to achieve a smooth transition of the spiral channel. The feed inlet and the discharge outlet are on the same axis to obtain uniform deformation. Specifically refer to Figure 4 .

[0039] Preferably, in one embodiment, the forward core die 6 and the reverse core die 5 are fixed to the core die sleeve by a flat key 8 to prevent rotation along the axial direction.

[0040] Preferably, in one embodiment, the forward core die 6 and the reverse core die 5 are frustum-conical, and the shape of the core die sleeve 4 is matched with that of the forward core die 6 and the reverse core die 5 to play a fixing role during the forming process.

[0041] Preferably, in one embodiment, there is a gap of 1 - 2 mm between the forward core die 6 and the reverse core die 5 and the bottom die 7. During operation, the forward core die 6 and the reverse core die 5 are in contact with the upper die 3 to eliminate the gap at the joint surface of the core die and the upper die, and make the core die in a compressive stress state to improve the stress state of the die.

[0042] The mutually connected components in the extrusion rod seat assembly, the upper die 3, the sleeved core die sleeve 4 and the core die, and the bottom die 7 are connected by connecting bolts. The connection method is simple and the disassembly and assembly are convenient.

[0043] Based on the same inventive concept, a method for preparing optical aluminum alloy using the mold described above is provided, including:

[0044] S10. First, place the billets into the first swaging channel and the second swaging channel respectively.

[0045] Preferably, before placing the billets into the first swaging channel and the second swaging channel, first apply an oil-based lubricant to the first discharge channel, the second discharge channel, the first swaging channel, the second swaging channel, the forward mandrel 6, and the reverse mandrel 5. Preferably, apply a high-temperature grease to the surfaces of the forward mandrel 6 and the reverse mandrel 5 that cooperate with the mandrel sleeve 4. Then install the forward mandrel 6 and the reverse mandrel 5 into the mandrel sleeve 4, and then install them in sequence with the upper die 3 and the bottom die 7.

[0046] Specifically, during pressing, place the spacer on the top of the extrusion rod base 1, lower the punch in a non-pressure mode to contact the spacer, record the height of the press slider at this time, calculate the lower limit position of pressing, then remove the spacer, and raise the press to the upper limit position.

[0047] In one embodiment, before loading the billet into the mold, first apply a release agent evenly on the surface of the billet and then heat it until the temperature of the billet is 250 ± 10 °C, and at the same time heat the mold to a temperature of 250 ± 10 °C; or.

[0048] Before loading the billet into the mold, first apply a release agent evenly on the surface of the billet and then heat it until the temperature of the billet is 400 - 550 °C, and at the same time heat the mold to a temperature of 400 - 550 °C.

[0049] In one embodiment, before loading the billet into the mold, first cool both the mold and the billet to the liquid nitrogen temperature.

[0050] S20. Press down the extrusion rod 2 to cause the billets to undergo swaging deformation in the spiral channel of the mandrel, and take out the deformed billets from the outlets of the first discharge channel and the second discharge channel on the bottom die 7.

[0051] The extrusion rod 2 extrudes at a forging speed of 1 mm / s, is under-pressed by 2 mm at the calculated lower limit position, record the load data on the press display screen during forging, and slowly raise the press after pressing ends.

[0052] S30. Re-place the deformed billets into the first swaging channel and the second swaging channel, and press down the extrusion rod 2 again to cause the billets to undergo swaging deformation in the spiral channel of the mandrel. Repeat the operation of swaging deformation to obtain an optical aluminum alloy product with large swaging plastic deformation. During the repeated operation process, the diameter of the billets remains unchanged.

[0053] Preferably, in one embodiment, when the extrusion rod presses down on the blank and cannot provide a force on the current blank, the extrusion rod is removed, and a new blank is loaded into the first and second twisting channels. Then, the extrusion rod presses down on the new blank, and the previous blank is extruded from the die using the new blank.

[0054] That is to say, a complete extrusion operation process can complete the forming of 4 cylindrical aluminum alloy products.

[0055] Preferably, for different product requirements, the die and the blank are subjected to different temperature treatments before extrusion, specifically as follows: 1) For optical aluminum alloys with ordinary processing quality requirements, such as a processing quality level of 5 - 10 nm, warm twisting at 250 °C can be used, or hot twisting at 400 - 550 °C can be used, and the number of extrusion times can be 1 - 3 times;

[0056] 2) For optical aluminum alloys with higher processing quality requirements, such as a processing quality level of 2 - 5 nm, room temperature twisting can be used, or warm twisting at 200 - 250 °C can be used, and the number of twisting times can be 3 - 6 times; By reducing the twisting forming temperature and increasing the number of deformations, finer grains can be obtained, improving the surface processing quality of the mirror blank, but at the same time, the energy consumption is higher;

[0057] 3) For optical aluminum alloys with ultra - high processing quality requirements, such as a processing quality level of 1 - 2 nm or less than 1 nm, cryogenic twisting can be used. Before extrusion forming, both the die and the blank are cooled to the liquid nitrogen temperature, and the number of extrusion times is greater than 6 times to prepare a nano - scale ultrafine grain structure, and the processing quality of the product can reach the sub - nano level.

[0058] Preferably, after forming, the blank is subjected to solution and aging heat treatments to obtain the required optical mirror blank material.

[0059] In one embodiment, the product obtained by the method for preparing optical aluminum alloy as described above can be applied to an optical mirror.

[0060] Specifically, different parameters are set according to Table 1 below to obtain the strain performance results of the aluminum alloy product. Figure 5 For the strain field distribution of Examples 1 to 4, according to the results in Table 1, it can be seen that the result of Example 4 is the best, and the average strain and maximum strain of the obtained product are both larger. According to Figure 5 the results, the strain field distributions of the four examples are all very uniform. The average strain and maximum strain of Examples 1 to 3 are also within a relatively good range.

[0061] Table 1 Strain results of products obtained under different parameter conditions

[0062]

[0063] Comparative Example 1: Multi-directional forging: The single deformation amount is 40%, and one upsetting and one drawing is one pass. The deformation situation in one pass is as Figure 7 shown. The maximum strain is 2.72, the minimum strain is 0.85, and the average strain is 1.55. Multi-directional forging is often used for large plastic deformation in conventional hot forging. For example, the commonly used multi-directional forging process requires four upsetting and three drawing, with a long process flow and 12 compression deformations required. The present invention only needs one twist extrusion to achieve the deformation amount of four upsetting and three drawing in multi-directional forging.

[0064] Comparative Example 2: Deep cold multi-directional compression, the single deformation amount is 20%%, and one compression in each of the three orthogonal directions is one pass. The deformation situation in one pass is as Figure 8 shown. The maximum strain is 2.03, the minimum strain is 0.53, and the average strain is 0.96. Conventional deep cold multi-directional compression requires three passes, that is, 9 compressions. The effect obtained by the present invention only needs one twist extrusion deformation to exceed three passes of deep cold multi-directional compression.

[0065] Compared with the prior art, the beneficial effects of the present invention are as follows: Compared with the large plastic deformation method of multi-directional forging in the prior art, in the die and method for preparing optical aluminum alloy by twist extrusion large plastic deformation provided by the present invention, by arranging the forward core die 6 and the reverse core die 5 in the core die, and pressing down the extrusion rod 2 to obtain an aluminum alloy product with large plastic deformation in a spiral cylindrical channel with equal diameter, the production efficiency is high, the shape of the mirror blank is the same as that of the final mirror product, both are circular, the material utilization rate is high, the machining allowance is small, and the blank is in a triaxial compressive stress state during forming, which can effectively reduce the cracking risk and improve the finished product rate. At the same time, the implementation scheme is simple, the single strain reaches 2.0, and large plastic deformation can be quickly realized with high efficiency. Furthermore, in the die and method of the present invention, different twist extrusion forming schemes can be formulated according to the product quality requirements to improve efficiency and control costs. For optical aluminum with general processing quality requirements, such as a processing quality level of 5-10 nm, warm twist extrusion at 250 °C can be used, or hot twist extrusion at 400-550 °C can be used, and the extrusion times can be 1-3 times; for optical aluminum alloy with higher processing quality requirements, such as a processing quality level of 2-5 nm, room temperature twist extrusion or warm twist extrusion at 200-250 °C can be used, and the twist extrusion passes can be 3-6 times; by reducing the twist extrusion forming temperature, although the energy consumption is higher, but by increasing the twist extrusion deformation times, finer grains can be obtained, and the surface processing quality of the mirror blank can be improved; for optical aluminum alloy with ultra-high processing quality requirements, such as a processing quality level of 1-2 nm or less than 1 nm, cryogenic twist extrusion can be used. Before extrusion forming, both the die and the blank are cooled to the liquid nitrogen temperature, and the extrusion passes are more than 6 times to prepare a nano-scale ultrafine grain structure, and the product processing quality can reach the sub-nano level.

Claims

1. A mold for preparing optical aluminum alloy by equal-channel angular pressing, characterized in that Comprising: A base on which a first discharge channel and a second discharge channel are formed. A matching core mold sleeve and a core mold, which are arranged on the base. A co-rotating core mold and a counter-rotating core mold communicating with the first discharge channel and the second discharge channel are formed in the core mold. The co-rotating core mold and the counter-rotating core mold include spiral cylindrical channels with equal diameters, and the spiral directions of the co-rotating core mold and the counter-rotating core mold are opposite to cancel the lateral force. An upper mold, which is arranged on the top of the core mold sleeve and the core mold. An extrusion rod seat assembly, including an extrusion rod seat, a first extrusion rod and a second extrusion rod arranged on the top of the upper mold. The extrusion rod seat and the upper mold are provided with a first twisting extrusion channel and a second twisting extrusion channel respectively communicating with the co-rotating core mold and the counter-rotating core mold. The first extrusion rod and the second extrusion rod move up and down in the first twisting extrusion channel and the second twisting extrusion channel respectively to extrude the workpiece to be processed. The spiral cylindrical channel includes a transition section connected to the upper and lower channels and an equal spiral section located between the two transition sections.

2. The die for preparing optical aluminum alloy by twist extrusion severe plastic deformation according to claim 1, characterized in that The base circle diameters of the spiral cylindrical channels of the co-rotating core mold and the counter-rotating core mold are 15 mm to 22 mm, the pitch is 110 mm to 140 mm, the spiral angle is 18.6° to 24.5°, and the number of spiral turns is 0.5 - 1.

3. The die for preparing optical aluminum alloy by twist extrusion severe plastic deformation according to claim 1, characterized in that, The co-rotating core mold and the counter-rotating core mold are in an inverted conical shape. The shape of the core mold sleeve matches that of the co-rotating core mold and the counter-rotating core mold. The co-rotating core mold and the counter-rotating core mold are fixed to the core mold sleeve by flat keys.

4. The die for preparing optical aluminum alloy by twist extrusion severe plastic deformation according to claim 1, characterized in that, There is a 1 - 2 mm gap between the co-rotating core mold and the counter-rotating core mold and the base, and the co-rotating core mold and the counter-rotating core mold are in contact with the upper mold.

5. The method for preparing optical aluminum alloy by using the mold according to any one of claims 1-4, characterized in that, Comprising: First, place the workpieces into the first twisting extrusion channel and the second twisting extrusion channel respectively. Press down the extrusion rod to cause the workpieces to undergo twisting extrusion deformation in the spiral channels of the core mold, and take out the deformed workpieces from the outlets of the first discharge channel and the second discharge channel on the base. Put the deformed workpieces back into the first twisting extrusion channel and the second twisting extrusion channel, and press down the extrusion rod again to cause the workpieces to undergo twisting extrusion deformation in the spiral channels of the core mold. Repeat the operation of twisting extrusion deformation to obtain an optical aluminum alloy product with large plastic deformation by twisting extrusion. During the repeated operation process, the diameter of the workpiece remains unchanged.

6. The method for preparing an optical aluminum alloy according to claim 5, wherein Before loading the workpiece into the mold, first evenly apply a release agent on the surface of the workpiece and then heat it until the temperature of the workpiece is 250 ± 10 °C, and at the same time heat the mold to a temperature of 250 ± 10 °C; or Before loading the workpiece into the mold, first evenly apply a release agent on the surface of the workpiece and then heat it until the temperature of the workpiece is 400 - 550 °C, and at the same time heat the mold to a temperature of 400 - 550 °C.

7. The method for preparing an optical aluminum alloy according to claim 5, characterized in that, Before loading the workpiece into the mold, first cool the mold and the workpiece to the liquid nitrogen temperature, and repeat the operation of twisting extrusion deformation of one workpiece for more than 6 times.

8. The method for preparing an optical aluminum alloy according to claim 5, wherein When the extrusion rod presses down to extrude the workpiece and cannot provide a force on the current workpiece, take out the extrusion rod, load new workpieces into the first twisting extrusion channel and the second twisting extrusion channel, then press down the extrusion rod to extrude the new workpieces, and use the new workpieces to extrude the previous workpiece out of the mold.

9. Application of the product obtained by the method for preparing an optical aluminum alloy according to any one of claims 5 - 8 in an optical mirror.

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