JP6390096B2 - Anodized film generation method - Google Patents

Description

  The present invention relates to a method for producing an anodic oxide film in which a metal object to be treated is disposed in an electrolyte together with a cathode as an anode, and an oxidation treatment is performed on the surface of the object to be treated.

  As a conventional method for generating the anodic oxide film, a method is known in which a direct current is switched to output a pulse voltage, and positive voltage application and charge removal are periodically repeated (for example, Patent Document 1). Patent Document 1 describes that the processing speed can be increased by setting the positive voltage application time to 1 to 3 times the peak arrival time of the current waveform.

  Moreover, in the method of Patent Document 2, after applying a constant current for a predetermined time, before reaching the voltage at which the burn of the oxide film occurs, the control is switched to AC / DC superposition control to keep the voltage constant. High speed is realized.

JP 2009-228069 A JP 2009-235539 A

  The conventional anodic oxide film generation method achieves optimization when generating a film on the surface of an object to be processed that has a shaped appearance such as a piston, but a plurality of protrusions are formed on the outer surface. No consideration is given to workpieces with complex shapes. That is, in high-speed processing under a high current density as in Patent Document 1-2, current concentrates on the protrusions, Joule heat becomes excessive, and the oxide film tends to be burned, and the thickness of each part The balance may be uneven.

  In addition, the method of Patent Document 1 requires complicated control such as using positive and negative DC power supplies and inverter devices in order to control the cycle of positive voltage application and charge removal, which increases costs. I will invite you. Further, since the oxide film is not formed during the charge removal, the processing time is lost.

  Accordingly, an object of the present invention is to provide a method for producing an anodic oxide film that can achieve high-speed processing by a simple method on a workpiece having a complicated shape and can achieve a uniform film thickness.

The characteristic configuration of the method for producing an anodic oxide film according to the present invention is a metal workpiece having a cylindrical cylindrical portion and a protruding portion protruding from the cylindrical portion as an anode, and disposed in an electrolyte together with a cathode.
A first energization step of energizing and holding the first DC current between both electrodes so that the temperature difference between the portions of the surface of the workpiece is within a predetermined value set in advance; and from the first DC current At least one second energization step of energizing a second DC current having a large value between the two electrodes, wherein the first energization step increases the current value from the start of energization to the first DC current. And a first holding step for holding a current value with the first DC current, wherein the first DC current is set based on a temperature difference between the cylindrical portion to be oxidized and the protruding portion. It is in.

  According to this configuration, the anodizing treatment of the object to be processed is performed by a simple method in which constant current control is performed using only direct current. On the other hand, when a direct current is applied to an object to be processed having protrusions, the current concentrates on the protrusions and Joule heat is generated, and the temperature of the protrusions rapidly increases. As a result, burns occur in the oxide film, and the film thickness of the protrusion becomes larger than the film thickness of the cylindrical part, resulting in non-uniform film thickness. This is particularly noticeable at an early stage of the oxidation treatment.

  Therefore, in this configuration, a multi-stage energization process including a first energization process and one or more second energization processes is performed, and the energization is performed with a current value of the first DC current smaller than the second DC current. Decided to keep. For this reason, compared with the case where it raises to the value of a 2nd direct current at once, the surface roughness of a to-be-processed object is arranged in the initial stage of an oxidation process, and surface property is stabilized. In addition, by maintaining a small current value that avoids a rapid temperature rise of the protrusion in the initial stage for a predetermined time, the oxide film can be prevented from being burned, and the film thickness can be made uniform between the protrusion and the cylindrical portion. be able to. As a result, even if the current value is increased in the next second energization step in order to increase the oxidation treatment speed, the temperature of each part gradually rises due to the stabilized initial film of each part, and the film is entirely formed. A desired oxide film having a balanced thickness can be produced.

  Further, in this configuration, at the initial stage of the oxidation treatment, the temperature difference between the respective portions of the surface of the workpiece, that is, the temperature difference between the protruding portion and the cylindrical portion is set to a current value that is within a predetermined value set in advance. . For this reason, regardless of the surface area of the object to be processed and the complicated external shape, it is possible to avoid a rapid temperature rise of the protrusions. For example, it is desirable to apply a large current for high-speed processing, but the current concentrated on the protrusions also increases. That is, the value of the first direct current that should be increased as much as possible is set to an optimum value according to the temperature difference between the protrusion and the cylindrical portion. Therefore, a uniform oxide film can be reliably generated in the high-speed oxidation treatment.

  In another characteristic configuration, the second energization step includes a second ascending step of increasing the current value of the first DC current from the current value of the first DC current to a current value of the second DC current, and a second current holding step. The second holding step.

  If a stable alumite film is generated in the initial stage of the first energization process, then the temperature of each part rises uniformly even if the current value is continuously increased in the second energization process. As a result, with this configuration, the alumite film grows with the film thickness being uniform to some extent.

It is a figure explaining the anodizing apparatus based on this embodiment. It is an example of the to-be-processed object which has a complicated shape. It is a figure which shows the electricity supply process which concerns on 1st Example. It is explanatory drawing in which an oxide film grows on the surface of a to-be-processed object. It is a figure which shows the relationship between the raise temperature in a 1st Example and a comparative example, and an initial stage film thickness. It is a figure which shows the relationship between the electricity supply time which concerns on 1st Example, and temperature. It is a figure which shows the relationship between the electricity supply time which concerns on a comparative example, and temperature. It is a figure which shows the electricity supply process which concerns on 2nd Example.

  Hereinafter, embodiments of an anodizing treatment according to the present invention will be described with reference to the drawings. In the present embodiment, an example in which an alumite film is formed on the surface of an aluminum substrate will be described as an example of anodizing treatment. However, the present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the invention.

  As the aluminum substrate 1 (an example of an object to be processed), for example, an aluminum casting material such as die casting, an aluminum forging material, or the like can be used. As aluminum, pure aluminum, aluminum alloy, or the like can be applied. As the kind of the aluminum alloy, an alloy with one kind or plural kinds of copper, manganese, silicon, magnesium, zinc, nickel, tin, lead, titanium, chromium, dicuronium and the like can be considered. The base material to be anodized may be a metal such as titanium or tantalum other than aluminum, or an alloy of these with other metals.

  In the present embodiment, as shown in FIG. 2, the aluminum base material 1 that generates the anodized film includes cylindrical cylindrical portions P2 and P4 and protruding portions P1 and P3 that protrude from the cylindrical portions P2 and P4. It demonstrates as a complicated shape material which has. When forming an oxide film on the surface of such an aluminum substrate 1 having a complicated shape, the current tends to concentrate particularly on the protrusions P1 and P3, the oxide film may be burned, or the current value is unbalanced. Therefore, the film thickness between the portions P1 to P4 tends to be non-uniform. This is particularly noticeable under high-density current that generates an oxide film at high speed. Although details will be described later in this embodiment, the film thickness is made uniform in constant current control, which is a simple method, not pulse control or AC / DC superimposition control.

  As shown in FIG. 1, the anodizing apparatus used for generating the anodized film includes a DC power source 3, a cathode 4, and an electrolytic cell 5 having an electrolytic solution 51 inside. Moreover, the aluminum base material 1 is arrange | positioned in the electrolyte solution 51 with the cathode 4 as the anode 6, and an alumite film | membrane 2 is formed on the surface of the aluminum base material 1 by supplying a direct current between both electrodes. As the electrolytic solution 51, dilute sulfuric acid, oxalic acid, other organic acids, and the like are used, and lead, platinum, and the like are used for the cathode 4, but are not particularly limited.

  The electrolytic cell 5 is provided with temperature adjusting means (not shown) for adjusting the temperature of the electrolytic solution 51 in order to keep the temperature of the anodizing treatment constant. The treatment temperature is not particularly limited as long as the alumite film 2 does not dissolve and disappear, but is adjusted in the range of, for example, -5 ° C to 20 ° C.

  The electrolytic bath 5 is provided with a stirring means (not shown) for stirring the electrolytic solution 51 so as to suppress variations in the temperature of the electrolytic solution 51 so that the temperature difference of the electrolytic solution 51 does not affect the aluminum substrate 1. It is. As the agitation means, for example, the electrolytic solution 51 is circulated by a pump, or agitation by air publishing can be considered.

(Control method)
In the present embodiment, as shown in FIG. 3, the first direct current A1 determined according to the temperature difference between the cylindrical portions P2 and P4 of the aluminum substrate 1 and the protrusions P1 and P3 is between the two electrodes. First energization steps S1 and S2 for energizing and holding, and second energization steps S3 and S4 for energizing and holding the second DC current A2 having a value larger than the first DC current A1 between the two electrodes. . The first energization processes S1 and S2 include a first ascending process S1 that increases the first DC current A1 with a predetermined gradient, and a first holding process S2 that holds the first DC current A1. Similarly, in the second energization processes S3 and S4, a second ascending process S3 for increasing the first DC current A1 to the second DC current A2 with a predetermined gradient, and a second holding process S4 for holding with the second DC current A2. And have.

  In general, since the thickness of the alumite film 2 is determined by the integral value of the current value and the energization time, in order to increase the production efficiency of the aluminum base material 1 that has been subjected to the anodizing treatment, the processing speed is increased. Therefore, it is required to form a desired film thickness in a short time. On the other hand, when a large direct current is applied from the initial stage of the oxidation treatment as shown in the conventional example of FIG. 3, the alumite film 2 is burned or the film thickness balance is not uniform.

  Here, a general flow in which the alumite film 2 is generated on the surface of the aluminum base 1 will be described. Prior to the electrolytic treatment, the aluminum substrate 1 is subjected to roughing or surface polishing, but it is difficult to sufficiently smooth the surface, and minute irregularities are generated. When this aluminum substrate 1 is subjected to electrolytic treatment, aluminum is dissolved and a barrier layer, which is a conductive film, starts to be generated. Next, when the barrier layer grows to a certain thickness, fine pores are formed, and a porous layer (porous film) that is an aggregate of hexagonal columnar cells starts to be generated. Next, dissolution and generation of the coating simultaneously occur in the hole portion, the hole is lowered, and finally an alumite film 2 having a predetermined film thickness is generated in proportion to the integrated value of the current value and the processing time. The

  Next, a process in which the alumite film 2 grows on the surface of the aluminum substrate 1 when a direct current is applied with the current waveform of the present embodiment will be described with reference to FIG. At the time of starting energization (point (a) in FIG. 3), as shown in FIG. 4 (a), the surface of the aluminum substrate 1 has minute irregularities. Next, when the current value is gradually increased to the first direct current A1 (point (b) in FIG. 3), the alumite film 2 starts to be formed so as to fill the unevenness (FIG. 4 (b)). When the first direct current A1 is held for a predetermined time (point (c) in FIG. 3), as shown in FIG. 4 (c), an alumite film 2 having a uniform thickness is generated. If the current value is too large at the initial stage of the oxidation treatment, the temperatures of the protrusions P1 and P3 where the current tends to concentrate as in the comparative example shown in FIG. Furthermore, as shown in the comparative example of FIG. 5, the film thickness variation at the initial stage becomes large. Here, by reducing the current value, it is possible to form a film with a uniform film thickness so as to fill the unevenness without causing variations in the temperatures of the portions P1 to P4.

  Finally (point (d) in FIG. 3), as shown in FIG. 4 (d), an alumite film 2 having a predetermined film thickness in proportion to the integral value of the current value and the processing time is generated. It can be seen that the final film thickness is made uniform by making the film thickness uniform in the initial stage. In other words, if the stable anodized film 2 is generated at the initial stage, the present embodiment is focused on that the anodized film 2 between the portions P1 to P4 is uniformly generated even if the subsequent current value is increased. Then, the optimum first DC current A1 and first energization times T1 and T2 are set.

  The value of the first direct current A1 is set so that the temperature difference between the portions P1 to P4 of the aluminum base 1 is within a predetermined value set in advance. The first energization times T1 and T2 are set to times when the film thicknesses of the portions P1 to P4 are uniform according to the shape and surface area of the aluminum base 1.

(First embodiment)
The first embodiment will be described with reference to FIGS. 3 and 5-7. FIG. 3 shows current waveforms in the present example and the comparative example. FIG. 5 is a diagram showing the relationship between the temperature rise and the film thickness of each part P1 to P4 when the energization time of the first energization steps S1 and S2 is 20 seconds. 6-7 is a figure which shows the relationship between the electricity supply time and the temperature of each site | part P1-P4 in a present Example and a comparative example.

  In this example, the first current rising time T1 in the first rising step S1 was set to 5 to 10 seconds, and the first current holding time T2 in the first rising step S1 was set to 10 to 20 seconds. This is because the time during which the stable alumite film 2 is generated in the initial stage can be within the range of the first energization times T1 and T2 even if the shape and surface area of the aluminum base material 1 are changed. It is because it became clear. That is, the first energization times T1 and T2 are set as initial stage times when the thicknesses of the portions P1 to P4 are relatively smoothed.

  Further, it is preferable that the first current rise time T1 is set to be long so that the energization rises with a gentle gradient as the first DC current A1 increases. As described above, this is to prevent the anodized film 2 from being easily burned when the current value is suddenly increased.

  Furthermore, if a stable anodized film 2 is generated in the first energization steps S1 and S2, a rapid temperature rise is unlikely to occur thereafter, so the second current rise time T3 (for example, 0 to 10 seconds) What is necessary is just to provide suitably. The second current holding time T4 is a processing time necessary for generating a target film thickness in accordance with the shape and surface area of the aluminum substrate 1.

  When determining the value of the first direct current A1, as shown in FIG. 2, the temperatures of the cylindrical portions P2, P4 and the protrusions P1, P3 of the aluminum base material 1 actually oxidized are measured by the temperature sensors K1 to K1, respectively. Measure with K4. Specifically, when the current value of the DC power supply 3 is increased and the maximum value of the difference between the measured values of the temperature sensors K1 to K4 exceeds a predetermined value, the current value immediately before that is set to the first DC Set as current A1. In the present embodiment, as shown in FIG. 6, the value of the first direct current A1 is determined so that the temperature rises at the portions P1 to P4 of the aluminum base material 1 during the first energization times T1 and T2 are uniform. The temperature sensors K1 to K4 are not particularly limited, although thermocouples, thermistors, resistance temperature detectors, and the like are assumed.

  FIG. 7 shows a comparative example in which the first direct current A1 is not provided and the current value is increased from the initial stage. In this comparative example, the temperature difference between the portions P1 to P4 occurred at 7 to 8 ° C. at the maximum. In other words, current concentrates on the protrusions P1 and P3, Joule heat is generated, the temperature of the protrusions P1 and P3 rapidly increases, and the temperature decreases immediately after a minute (slight) burn is generated. .

  Furthermore, as shown in FIG. 5, the comparative example has a large variation in the film thicknesses of the respective portions P1 to P4 measured after the first energization times T1 and T2 have passed, as compared with the present example. As a result, the film thickness of the protrusions P1 and P3 becomes larger than the film thickness of the cylindrical parts P2 and P4, and the alumite film 2 is generated while the film thickness is not uniform. When verified with six aluminum base materials 1 for reference, in the comparative example, the final film thickness variation was as large as 2.7 to 4.0 μm with respect to the average film thickness of about 12 μm.

  On the other hand, in this embodiment, since the temperature difference between the parts P1 to P4 is set to the first direct current A1 at which the temperature difference is substantially zero, the film thickness variations of the parts P1 to P4 are small as shown in FIG. . Furthermore, even if it transfers to following 2nd electricity supply process S3, S4, the state from which the temperature difference between each site | part P1-P4 became substantially zero is maintained. That is, if the stable alumite film 2 is generated in the initial stage as described above, the temperatures of the portions P1 to P4 are uniformly increased even if the subsequent current value is increased. As a result, the alumite film 2 grows in a state where the film thickness becomes uniform to some extent. When verified with six aluminum substrates 1 as a reference, the final film thickness variation was 1.9 to 3.4 μm compared to the comparative example, while the average film thickness was about 12 μm. In this embodiment, the temperature difference between the portions P1 to P4 is set to be substantially zero, but there may be a temperature difference of 2 to 3 ° C.

(Second embodiment)
In the first embodiment, the second energization processes S3 and S4 are provided in one stage, but in this embodiment, the second energization process is provided in two stages (S3 to S4, S5 to S6) as shown in FIG. . For example, when the value of the second DC current A2 needs to be suddenly increased in order to perform high-speed processing, if the second DC current A2 is suddenly increased, a large load is applied to the stabilized alumite film 2, and the The occurrence of Therefore, by making the second energization process multistage as in the present embodiment, the temperature of each part P1 to P4 rises gently, and the temperature difference between each part P1 to P4 hardly occurs, and the anodized film 2 generation failure can be prevented.

  As shown in the first embodiment, if a stable alumite film 2 is generated in the first energization steps S1 and S2, there is no temperature difference between the portions P1 to P4 in the subsequent second energization steps S3 to S6. Is maintained. That is, if the value of the first DC current A1 and the first energization times T1 and T2 in the first energization steps S1 and S2 are optimized, the subsequent processing time and current value are formed on the aluminum base 1. What is necessary is just to set suitably according to the film thickness of the alumite film | membrane 2. FIG. Also in this embodiment, the final film thickness balance of the alumite film 2 can be made uniform.

[Other Embodiments]
(1) In the above-described embodiment, the second energization process is set to one stage or two stages, but the second energization process may be further subdivided, for example, to three stages.
(2) In the above-described embodiment, the first energization times T1 and T2 are set to the time when the film thicknesses of the respective parts P1 to P4 are uniform. For example, the film thicknesses of the respective parts P1 to P4 are a predetermined thickness. You may set to the time which becomes (for example, 1-2 micrometers). Further, the predetermined thickness may be set as a film thickness at which a stable alumite film 2 is generated, at a ratio to the final target film thickness.
(3) The method for generating an anodic oxide film in the present embodiment is intended for a workpiece having a complex shape having a plurality of protrusions and the like. However, the method may be applied to a workpiece having a shaped external appearance. Of course.

  The method for producing an anodized film of the present invention can be used as a method for producing an oxide film on the surface of an object to be processed at a high speed.

1 Aluminum substrate (object to be treated)
2 Anodized film (oxide film)
4 Cathode 6 Anode 51 Electrolyte A1 1st direct current A2 2nd direct current K1-K4 Temperature S1, S2 in each part 1st electricity supply process S3, S4 2nd electricity supply process T1, T2 1st electricity supply time

Claims (2)

A metal object having a cylindrical cylindrical portion and a protruding portion protruding from the cylindrical portion is used as an anode, and is disposed in the electrolyte together with the cathode.
A first energization step of energizing and holding the first direct current between both electrodes so that the temperature difference between the parts of the surface of the workpiece is within a predetermined value set in advance;
And at least one second energization step of energizing a second DC current having a value larger than the first DC current between the two electrodes,
The first energization step includes a first increase step of increasing a current value from the start of energization to the first DC current and a first holding step of maintaining a current value with the first DC current,
The first direct current is an anodized film generation method set based on a temperature difference between the cylindrical portion to be oxidized and the protrusion. The second energizing step includes a second ascending step for increasing the current value of the first DC current from the current value of the first DC current to a current value of the second DC current and a second holding step for holding the current value with the second DC current. The method for producing an anodized film according to claim 1 .