JP5455156B2 - Manufacturing method of resin mold - Google Patents

Description

  The present invention relates to a method for manufacturing a resin molding die, and more particularly to a method for manufacturing a resin molding die made of Ni-Al-Cu age-hardening die steel used for injection molding of a large resin molded product.

  Resin-molding molds are widely used for injection molding of resin-molded products such as home appliances and OA equipment. In particular, in the case of injection molding of an exterior panel or casing that can be seen by the product user, if there are smooth unevenness, pinholes, etc. on the mold design surface, this is transferred to a resin molded product and the product is inferior. Accordingly, there is a demand for mold steels that are excellent in mirror finish.

For example, Patent Document 1 discloses Ni—Al—Cu age-hardening steel as a resin mold steel having excellent mirror surface workability. As one basic component composition of such steel, C: 0.05 to 0.18%, Si: 0.15 to 1.0%, Mn: 1.0 to 2.0%, Ni: 2.5 to 3 0.5%, Al: 0.5 to 1.5%, Cu: 0.7 to 1.7%, Mo: 0.1 to 0.4%, S: 0.015% or less. ing. In addition to suppressing the amount of S, the addition of predetermined amounts of Ni and Al prevents the “cloudy state” from being exhibited due to a loophole caused by the dropout of Al ₂ S _{3 in} the mirror surface finishing process, resulting in high mirror surface workability. Is disclosed.

  By the way, even if the mold steel itself has a high mirror surface workability, if it is not sufficiently forged at the stage of producing the mold steel, particularly at the forging stage, production unevenness will occur and the mirror surface workability will be greatly reduced. In particular, in the manufacture of a large resin molding die, the steel ingot is enlarged, so that problems such as insufficient power of the forging facility are also involved, and the mirror workability due to this manufacturing unevenness becomes a big problem.

  For example, in Patent Document 2, in a forging stage of a steel ingot made of austenitic stainless steel having high deformation resistance, in a large steel ingot, strain that becomes a driving force for recrystallization does not reach the inside of the steel ingot. It states that forging unevenness is generated. It also states that if a strain is repeatedly applied to give a large strain as a total, reheating must be repeated and the crystal grains become coarse.

  On the other hand, in this document, the steel ingot is heated to a high temperature of 1250 ° C. or higher and lower than the melting point, and the maximum strain (ε) per pass is 0.2 or higher until the steel ingot is lowered below the recrystallization start temperature. And after lowering to less than the recrystallization start temperature, the first forging process for forging so that the forging ratio is 2S or more, and again heating to a temperature of 1050 ° C. or more and 1150 ° C. or less, which is lower than the above-described temperature, A method of providing a forging process consisting of two stages, that is, a second forging process in which the maximum strain per pass is 0.2 or more and the forging ratio is 2S or more is disclosed. Since the deformation resistance can be lowered by increasing the heating temperature during forging, even a forging facility with less power can increase the maximum strain per pass and increase the forging ratio, thereby reliably destroying large cast structures. it can. Furthermore, in the second forging process after breaking the cast structure by dividing the forging process into two stages of the first forging process and the second forging process, grain growth is achieved by relatively lowering the heating temperature. It suppresses and gives a fine grain structure. That is, it is considered that forging unevenness in the cast structure and the crystal grain structure can be reduced, and the mirror workability can be improved.

Sho-60-67641 JP 2008-36698 A

  In recent years, as home appliances and OA devices are increased in size, there are many requests to use a glossy resin capable of producing a high-class feeling for exterior panels and housings. In such a resin molded product, the reflection of light on the surface is large, and the resin mold used for injection molding is required to have further improved mirror finish so that the surface undulation can be reduced more than before. On the other hand, since the steel ingot for such a resin molding die becomes large, it has become important in manufacturing to prevent forging unevenness that deteriorates the mirror surface workability as described above.

  The present invention has been made in view of such circumstances, and the object of the present invention is to manufacture a resin molding die made of Ni-Al-Cu age-hardening type steel used for molding a large resin product. It is a method, and it is providing the manufacturing method of the resin mold which was excellent in mirror surface property.

Method for producing a resin molding die made of Ni-Al-Cu-based age-hardening type steel according to the present invention includes a blooming forging step of blooming forging the billet was heated steel ingot to a temperature T _1, the blooming forging following step comprises a soaking step of holding and heating the billet to a temperature T _2, and the low temperature finish forging step of forging is heated to a temperature T ₃ of 1050 ° C. or less, and the soaking step and the low-temperature A hot gouging step of performing gouging at a temperature T ₄ that is 500 ° C. or higher and at least lower than the temperature T ₃ is further included between the finish forging step.

  According to this method, since gouging is performed hot, the time from the soaking process to the low-temperature forging process can be shortened, and the total amount of scale generated can be suppressed. Since the total amount of scale produced is small and the yield is good, the billet cross-sectional area in the soaking process can be minimized. Therefore, the soaking process can be efficiently performed so as to sufficiently eliminate segregation and enhance the specularity. Furthermore, in low temperature finish forging, hot gouging is used to perform low temperature forging with less scale, so there is no need to increase the forging ratio and peel off the scale by forging. As a result, it is possible to suppress the scale that is generated even during low-temperature forging. That is, by suppressing the scale, even with a low forging ratio, the rough surface of the billet surface layer can be suppressed, and a mold steel excellent in mirror surface workability can be obtained.

In the above-described invention, the billet has a thickness of 400 mm or less, and in the soaking step, when the billet is held at a temperature T ₂ (° C.) within a range of 1230 to 1280 ° C. for a time t (h),
(T ₂ +273) × (20 + logt) / 1000 ≧ 32
It is good also as a feature. According to this method, the segregation in the billet due to the soaking process can be further reduced, and the deterioration of the mirror surface workability due to the segregation can be further prevented. As described above, since the scale generated by the soaking process by hot gouging does not affect the low temperature forging process, the soaking process can be controlled according to the size of the billet. That is, it is possible to provide a large mold having excellent specularity used for molding a large resin product.

  In the above-described invention, in the low temperature finish forging step, forging may be performed by a forging ratio of 1.5S. According to such a method, forging time becomes long in low-temperature forging with a large deformation resistance, but the forging time is shortened by a low forging ratio. Give mold steel.

  The above-described invention may further include a solution treatment step in which the solution obtained by the low temperature finish forging step is subjected to solution treatment twice. According to this method, even if it is a low forging ratio, it can fully recrystallize and it can prevent the deterioration of the mirror surface workability resulting from the crystal grains being uneven and rough.

It is a figure which shows one component composition of steel used with the manufacturing method by this invention. It is a figure which shows the flow of the manufacturing method by this invention. It is a figure which shows the forge process by this invention. It is a figure which shows the manufacturing conditions and each measured value of the metal mold | die by this invention.

  The manufacturing method of the resin molding die which consists of Ni-Al-Cu age-hardening type steel by the Example of this invention is demonstrated in detail using FIG.

  FIG. 1 shows the component composition of Ni—Al—Cu age-hardening steel used in the forging test as an example. It should be noted that the steel component composition of the manufacturing method according to the present invention satisfies the general balance of hardness in the mold and machinability for processing into the mold, and the use of the mold. Can be selected to meet the specularity requirements determined by the target product being processed. In addition, a component composition that does not excessively increase deformation resistance can be selected in order to reduce forging unevenness in forging in the manufacturing process. That is, the steel as the object of the manufacturing method according to the present invention is preferably a Ni—Al—Cu age-hardening steel as shown in FIG. 1 and is similar to the above-described steel.

As shown in FIGS. 2 and 3, first, the steel ingot obtained by steelmaking is forged into pieces (S1). Forging forging, after heating to a temperature T ₁ in the temperature range from 1200 ° C. to 1280 ° C., which is a high temperature with low forging resistance, to leave a forging ratio to the final product in finish forging (S4) described later, A billet is obtained by forging at a predetermined training ratio.

The resulting billet by blooming forging, again, is heated to a predetermined temperature T ₂ in the range of from 1,230 to 1,280 ° C., as it is held for a predetermined time, the soaking heat treatment for homogenization by diffusion segregation component composition (S2).

In the soaking process, the soaking parameter S can be defined as the following equation, where the heating temperature is T (° C.) and the holding time is t (h).

S = (T + 273) × (20 + logt) / 1000 (Formula 1)

That is, the higher the heating temperature T and the longer the holding time t, the larger the soaking parameter S. The holding time t affects the value of the soaking parameter S on a log scale.

  Here, an experiment is conducted on the state of elimination of segregation of the soaking parameter S and the component composition. That is, soaking was performed by changing the soaking parameter S for a plurality of billets having a striped segregation pattern on the surface before the soaking process. And about each of the actual machine sample obtained through the process (S3-S6) mentioned later, hardness distribution was measured at 0.2 mm space | interval. Then, it was found that when the soaking parameter S ≧ 32.0, the variation in the hardness distribution becomes very small, and the striped segregation pattern disappears completely.

  From the above, it is preferable to perform soaking (S2) so that the soaking parameter S is 32 or more. According to this, it is possible to diffuse and homogenize a large billet having a thickness of up to about 400 mm as in Examples 1 and 2 to be described later up to a central portion where segregation tends to be particularly large. Note that the higher the heating temperature T, the lower the crystal grain size, and the longer the holding time t, the thicker the billet surface scale (black skin) and the lower the yield. The operating conditions are appropriately determined in consideration of such influence. As will be described later, the scale generated in the soaking process (S2) does not affect the low-temperature forging process (S4) because it passes through the hot gouging process (S3). That is, the elimination of segregation of the component composition by the soaking process (S2) can be controlled in accordance with the size of the billet and the like, and a large mold having excellent specularity used for molding a large resin product can be provided.

Hot gouging is performed on the billet in which the segregation of the component composition has been sufficiently eliminated by the soaking process (S2), in which the surface is ground by a grinder and the scale is removed before the temperature is greatly cooled (S3). Gouging is performed at a temperature T ₄ of 500 ° C. or higher. As a result, from the soaking process (S2) to the low-temperature forging process (S4), which will be described later, the process can be advanced in a shorter time and low-temperature forging can be performed with less scale.

Billet after removing the scale by gouging process again, the grain size of the rapidly lowered without temperature, for example, heated to a temperature T ₃ of 1050 ° C. or less, low temperature finish forging to shape close to the final product (S4). In such low temperature forging, since the scale is removed, there is no need to increase the forging ratio so that the scale is further peeled off. That is, forging at a relatively low temperature tends to increase the forging resistance, generally the forging speed is slow, and the forging time tends to be long. On the other hand, in this step, the forging ratio can be lowered, so that the forging time can be shortened, and as a result, the scale generated at the time of low-temperature forging can be suppressed. By suppressing the scale, forging unevenness, particularly rough surface of the billet surface layer, can be suppressed even at a low forging ratio, and a mold steel having excellent mirror surface workability can be obtained.

  The billet after low-temperature finish forging is subjected to a solution treatment as necessary (S5). In low-temperature forging, since the forging temperature is low and the forging ratio is low as described above, the shape and size of crystal grains are not uniform. In order to recrystallize such a “rough state” uniformly and sufficiently, it is preferable to perform the solution treatment at a temperature of about 850 ° C. a plurality of times, for example, twice. According to this, fine grains having a crystal grain size of about 6 to 7 are obtained, and a hardness of about 40 HRC can be obtained after the tempering heat treatment (S6) described later.

  The billet that has been subjected to the solution treatment (S5) is appropriately subjected to a tempering heat treatment (S6) such as an age hardening treatment, or a shape processing such as cutting or polishing (S7). This is well known and will not be described in detail.

  FIG. 4 shows the manufacturing conditions and measured values of two examples with different product dimensions manufactured by the above-described manufacturing method.

  In Example 1, the steel ingot was heated to 1200 ° C. and then forged in the partial forging step (S1), and a billet having a cross-sectional dimension of 270 × 850 mm was obtained. In the soaking process (S2), it was kept at 1280 ° C. for 30 hours. When the soaking parameter was calculated from Equation 1 above, it was 33.35. The hot gouging step (S3) was performed at 600 ° C. In the finish forging step (S4), after heating to 900 ° C. and holding for 6 hours, forging was performed to a cross-sectional dimension of 185 × 810 mm, that is, a forging ratio of about 1.5 (1.5S).

  In Example 2, in the partial forging step (S1), the steel ingot was heated to 1200 ° C. and then forged into pieces to obtain billets having a cross-sectional dimension of 260 × 1200 mm. In the soaking step (S2), the temperature was maintained at 1230 ° C. for 25 hours. When the soaking parameter was calculated from Equation 1 described above, it was 32.16. In the finish forging step (S4), the steel was heated to 900 ° C. and held for 10 hours, and then forged to a cross-sectional dimension of 180 × 1100 mm. That is, in the finish forging step (S4), forging was performed by a forging ratio of about 1.5 (1.5S).

  The billet after finishing forging obtained in Examples 1 and 2 was heated to 870 ° C. and held for 30 minutes, then quenched in water for the first solution treatment, and further heated to 870 ° C. and held for 30 minutes. Then, it was air-cooled and a second solution treatment was performed. Furthermore, in each billet after the solution treatment, tempering heat treatment was performed to obtain actual machine samples having a hardness of 40.0 HRC and 40.5 HRC.

  Using the cut material from the above-mentioned actual machine sample, the micro Vickers test for hardness, the Charpy test for impact value, the corrosion observation test for crystal grain size, and the appearance of the surface after mirror polishing were visually and optically observed.

First, impact values were good at 12.5 and 13.6 (J / cm ² ). The crystal grain size was 7.3 and 6.1 and was uniform throughout the test piece. The surface after mirror polishing was very homogeneous with no pinholes or orange peels (short-period swells), and no polishing irregularities such as scale-like patterns. As demonstrated, even when the hardness was measured at intervals of 0.2 mm, it was uniform with substantially the same hardness.

As mentioned above, the manufacturing method of the resin molding die which consists of a Ni-Al-Cu system age hardening type steel by a present Example is as follows. That is, a forging step (S1) in which the steel ingot is heated to a temperature T ₁ between 1200 ° C. and 1280 ° C. and then forged into billets (S1), and subsequently, the billet is heated to a temperature between 1230 and 1280 ° C. soaking step of holding heated to T ₂ (S2), the low-temperature finish forging step of forging a relatively small forging ratio of forging ratio 1.5S is heated to a temperature _{T 3} of 1050 ° C. or less and (S4), the And a hot gouging step (S3) for performing gouging at a temperature T ₄ that is 500 ° C. or higher and at least lower than the temperature T ₃ between the soaking step (S2) and the low temperature finish forging step (S4). . Then, solution treatment is performed twice, age hardening treatment (S6) is further performed, and processing (S7) is performed to obtain a mold.

Here, if the billet is 400 mm or less in thickness, if it is held at the temperature T ₂ (° C.) for the time t (h) in the soaking process (S2),
(T ₂ +273) × (20 + logt) / 1000 ≧ 32
To be processed.

  According to the above, the cross-sectional area of the billet in the soaking process can be reduced as much as possible, and the soaking process can be efficiently performed so as to improve the specularity by sufficiently eliminating the segregation. In addition, particularly in low-temperature finish forging, rough skin of the billet surface layer can be suppressed. That is, a mold having excellent specularity is provided.

  Up to this point, the representative embodiments according to the present invention and the modifications based thereon have been described, but the present invention is not necessarily limited thereto. It is needless to say that the method of the present invention can also be applied to the production of a mold made of the same kind of steel without being limited to the mold made of steel having the component composition of the above-described embodiments. That is, those skilled in the art will be able to find various alternative embodiments and modifications without departing from the scope of the appended claims.

Claims (4)

A method for producing a resin molding die made of Ni-Al-Cu age-hardening steel,
A forging process in which the steel ingot is heated to a temperature T ₁ and then forged into billets;
Following the blooming forging step, a soaking step of holding and heating the billet to a temperature T _2,
Anda low-temperature finish forging step of forging is heated to a temperature T ₃ of 1050 ° C. or less,
A resin molding die further comprising a hot gouging step in which gouging is performed at a temperature T ₄ which is 500 ° C. or higher and at least lower than the temperature T ₃ between the soaking step and the low temperature finish forging step. Manufacturing method. The billet has a thickness of 400 mm or less,
In the soaking step, when the billet is held at a temperature T ₂ (° C.) within a range of 1230 to 1280 ° C. for a time t (h),
(T ₂ +273) × (20 + logt) / 1000 ≧ 32
The method for producing a resin mold according to claim 1, wherein:   The method for producing a resin mold according to claim 1 or 2, wherein in the low temperature finish forging step, forging is performed by a forging ratio of 1.5S. The method for producing a resin mold according to claim 3, further comprising a solution treatment step of subjecting the finishing material obtained by the low temperature finish forging step to a solution treatment twice.

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