Short-process nitriding method for improving surface performance of additive manufacturing conformal water-cooling mold

Abstract

A short-process nitriding method for improving the surface performance of an additive manufacturing conformal water-cooling mold relates to the field of additive manufacturing metal processing, and comprises the following steps: (1) additive manufacturing of a conformal water-cooling mold; and (2) low-temperature plasma nitriding and high-energy argon ion beam bombardment are alternately and repeatedly treated in the same equipment. According to the method, the additive manufacturing mold is directly put into the nitriding furnace, the strengthening and toughening of the surface and the core of the mold are synchronously realized by utilizing the synchronous heat effect of ion nitriding and the atomic layer etching effect of high-energy argon ion beam bombardment, and the surface heat treatment defect is avoided. According to the method, a short-process technology of direct nitriding of the additive manufacturing mold can replace a complex process technology of nitriding after solid solution-aging treatment of an existing additive manufacturing mold.

Description

Technical Field

[0001] The present invention relates to the field of additive manufacturing of metal processing, and particularly to a short-process nitriding method for improving the surface performance of additive manufacturing conformal water-cooled molds. Background Art

[0002] Laser additive manufacturing technology has the characteristics of high precision, high speed, high degree of freedom and intelligence, which can enhance the degree of freedom in the design and manufacture of special channels in conformal water-cooled molds, and is extremely suitable for preparing conformal water-cooled molds with complex spatial structures. At present, additive manufacturing conformal water-cooled molds prepared by selective laser melting technology have been industrialized.

[0003] Molds manufactured by laser additive manufacturing also need surface modification through nitriding treatment in actual applications, similar to traditional molds. However, the temperature of traditional nitriding treatment is usually above 500°C, and the furnace pressure is also several hundred pascals. Due to the heterogeneous structure generated by the rapid solidification characteristics of additive manufacturing molds, heat treatment defects such as pores, ablation tumors, and cracks are extremely likely to occur after traditional nitriding treatment. Therefore, additive manufacturing molds need to avoid or reduce the heterogeneous structure through solution-low temperature pre-aging treatment before nitriding, and even need low-temperature tempering treatment after nitriding, and the process is very complex.

[0004] At present, the research on short-process technologies for directly nitriding additive manufacturing molds is still in the theoretical research stage, and the research on avoiding heat treatment defects in additive manufacturing molds during short-process nitriding technology has not been publicly reported. Summary of the Invention

[0005] The purpose of the present invention is to provide a short-process nitriding method for improving the surface performance of additive manufacturing conformal water-cooled molds, so as to simplify the process flow and obtain a high-quality hardened surface.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solution: A short-process nitriding method for improving the surface performance of additive manufacturing conformal water-cooled molds, comprising the following steps:

[0007] (1) Using selective laser melting technology, preferably preparing conformal water-cooled molds with parameters.

[0008] Among them, the parameter range of the selective laser melting technology is: the laser power is 200-500W, the scanning speed is 700-1200mm / s, the thickness of the powder spreading layer is 20-60μm, and the scanning spacing is 90-130μm. The laser volume energy density is 40-120J / mm 3 ;

[0009] Furthermore, the relative density of the conformal water-cooled mold prepared by the selective laser melting technology exceeds 99.9% and the mechanical properties reach the level of standard forgings.

[0010] (2) Place the conformal water-cooled mold into a plasma nitriding furnace, and preferably alternate the low-temperature plasma nitriding process and the high-energy argon ion beam bombardment process with process parameters, and the number of times N of alternate repetition treatment ≥ 2.

[0011] Among them, the temperatures and pressures of the two processes are kept consistent to simplify the variables of the alternate composite treatment. The temperature is selected in the temperature range of low-temperature tempering of die steel so as to achieve the effect of die tempering while performing low-temperature nitriding; the pressure is much lower than that of traditional nitriding treatment to reduce the hollow cathode effect during nitriding and avoid defects such as ablation nodules and thermal cracking. After parameter optimization, the temperature range of the alternate composite treatment is 350 - 480 °C, and the pressure range is 50 - 100 Pa.

[0012] Preferably, the low-temperature plasma nitriding process uses a mixed gas composed of N2 and H2. Among them, N2 is used to generate N ions for workpiece nitriding strengthening; H2 is used to generate H ions, and the oxides generated on the workpiece surface are continuously removed through a reduction reaction to improve the workpiece quality. In addition, in this process, it is necessary to reduce the N2 atmosphere partial pressure and the electric field bias voltage to avoid the over-strong local hollow cathode effect and the formation of surface brittle nitrides. After parameter optimization, the volume ratio of N2 to H2 is 0.1 - 0.2, the bias voltage is 400 - 600 V, and the process duration is 20 - 40 minutes.

[0013] More preferably, the high-energy argon ion beam bombardment process uses a mixed gas composed of Ar and H2. Among them, Ar is used to generate Ar ions, and the ion bombardment is promoted through a high-voltage electric field to achieve the effect of atomic layer etching of the workpiece, further avoiding defects such as pores and ablation nodules, and at the same time promoting the decomposition of surface nitrides; H2 is used to generate H ions, and the oxides generated on the workpiece surface are continuously removed through a reduction reaction to improve the workpiece quality. After parameter optimization, the volume ratio of Ar to H2 is 1.0 - 1.5, the bias voltage is 1000 - 1200 V, and the process duration is 10 - 20 minutes.

[0014] In the above process, no bright layer is formed on the surface of the die workpiece after the treatment in step (2), and there are no heat treatment defects such as pores, ablation nodules, and cracking.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. The present invention adopts the short-process idea of directly placing the additive manufacturing mold into the nitriding furnace for nitriding, achieving the effect of synchronously performing nitriding and die back-tempering, and significantly reducing the process compared with the complex process of the existing additive manufacturing mold after solution-aging treatment and then nitriding.

[0017] 2. By combining low-temperature ion nitriding with high-energy argon ion beam bombardment, the present invention achieves the effect of short-process low-temperature nitriding while avoiding surface heat treatment defects. On the one hand, by using an ion nitriding method with low temperature, low atmosphere partial pressure, and low electric field voltage, the over-strong local hollow cathode effect and the formation of surface brittle nitrides are avoided. On the other hand, the atomic layer etching effect of high-energy argon ion beam bombardment is used to further avoid defects such as pores and ablation nodules. Finally, an additive manufacturing die without brittle nitride phase, without surface heat treatment defects, and with a significant strengthening effect is formed, achieving the effect of avoiding heat treatment defects in the short-process nitriding process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a process flow chart of the alternating combination of the high-energy argon ion beam bombardment process and the low-temperature plasma nitriding process in the present invention;

[0019] Figure 2 is a surface topography diagram of the nitrided layer structure on the surface of a martensitic die steel in Example 1;

[0020] Figure 3 is a surface topography diagram of the nitrided layer structure on the surface of a martensitic die steel in Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] For the convenience of those skilled in the art, the present invention will be further described below in conjunction with the embodiments and the drawings. The content mentioned in the embodiments does not limit the present invention.

[0022] Example 1

[0023] A short-process nitriding method for improving the surface performance of an additive manufacturing conformal cooling die includes the following steps:

[0024] (1) Using selective laser melting technology, a conformal cooling die is prepared according to the preferred parameter range, which can ensure that the relative density of the conformal cooling die exceeds 99.9% and the mechanical properties reach the level of standard forgings.

[0025] (2) The conformal cooling die is placed in a plasma nitriding furnace, and the high-energy argon ion beam bombardment process and the low-temperature plasma nitriding process are alternately carried out according to the Figure 1 process flow chart shown.

[0026] In this step, the number of times N of alternating repetition treatment is 2. The temperature is kept constant at 450 °C and the furnace pressure is kept constant at 80 Pa during the alternating combination treatment.

[0027] In this step, the low-temperature plasma nitriding process uses a mixed gas composed of N2 and H2. The volume ratio of N2 to H2 is 0.2, the bias voltage is 400V, and the process duration is 20 minutes. The high-energy argon ion beam bombardment process uses a mixed gas composed of Ar and H2. The volume ratio of Ar to H2 is 1.0, the electric field bias voltage is 1200V, and the process duration is 10 minutes.

[0028] Furthermore, after the treatment in step (2), no white bright layer is formed on the surface of the die workpiece, and there are no heat treatment defects such as pores, ablation tumors, and cracks, as Figure 2 shown. Through surface hardness testing, it is found that the surface hardness of the workpiece is 1170HV.

[0029] Example 2

[0030] A short-process nitriding method for improving the surface performance of additive manufacturing conformal water-cooled dies includes the following steps:

[0031] (1) Using selective laser melting technology, prepare a conformal water-cooled die according to the preferred parameter range, which can ensure that the relative density of the conformal water-cooled die exceeds 99.9% and the mechanical properties reach the level of standard forgings.

[0032] (2) Place the conformal water-cooled die in a plasma nitriding furnace and alternately perform the high-energy argon ion beam bombardment process and the low-temperature plasma nitriding process according to the Figure 1 process flow chart shown.

[0033] In this step, the number of alternating repetitions N = 2. The temperature is kept constant at 480°C and the furnace pressure is kept constant at 100Pa during the alternating composite treatment.

[0034] In this step, the low-temperature plasma nitriding process uses a mixed gas composed of N2 and H2. The volume ratio of N2 to H2 is 0.2, the bias voltage is 600V, and the process duration is 30 minutes. The high-energy argon ion beam bombardment process uses a mixed gas composed of Ar and H2. The volume ratio of Ar to H2 is 1.0, the electric field bias voltage is 1200V, and the process duration is 15 minutes.

[0035] Furthermore, after the treatment in step (3), no white bright layer is formed on the surface of the die workpiece, and there are no heat treatment defects such as pores, ablation tumors, and cracks. Through surface hardness testing, it is found that the surface hardness of the workpiece is 1155HV.

[0036] Comparative Example 1

[0037] A short-process nitriding method for improving the surface performance of additive manufacturing conformal water-cooled dies includes the following steps:

[0038] (1) Using selective laser melting technology, a conformal water-cooled mold is prepared according to the preferred parameter range, which can ensure that the relative density of the conformal water-cooled mold exceeds 99.9% and the mechanical properties reach the level of standard forgings.

[0039] (2) Place the conformal water-cooled mold in a plasma nitriding furnace and alternately perform the high-energy argon ion beam bombardment process and the low-temperature plasma nitriding process according to the process flow chart Figure 1 shown.

[0040] In this step, the number of alternating repetitions N = 2. The temperature during the alternating composite treatment is kept constant at 450 °C, and the furnace internal pressure is kept constant at 150 Pa.

[0041] In this step, the low-temperature plasma nitriding process uses a mixed gas composed of N2 and H2, the volume ratio of N2 and H2 is 0.8, the bias voltage is 600 V, and the process duration is 20 minutes. The high-energy argon ion beam bombardment process uses a mixed gas composed of Ar and H2, the volume ratio of Ar and H2 is 1.0, the electric field bias voltage is 1200 V, and the process duration is 0 minutes.

[0042] Furthermore, after the treatment in step (2), a bright white layer is formed on the surface of the mold workpiece, and there are heat treatment defects such as pores, ablation nodules, and cracks, as Figure 3 shown. Through surface hardness testing, it is found that the surface hardness of the workpiece is 833 HV.

[0043] Comparative Example 2

[0044] A short-process nitriding process for improving the surface performance of additively manufactured conformal water-cooled molds, comprising the following steps:

[0045] (1) Using selective laser melting technology, a conformal water-cooled mold is prepared according to the preferred parameter range, which can ensure that the relative density of the conformal water-cooled mold exceeds 99.9% and the mechanical properties reach the level of standard forgings.

[0046] (2) Place the conformal water-cooled mold in a plasma nitriding furnace and alternately perform the high-energy argon ion beam bombardment process and the low-temperature plasma nitriding process according to the process flow chart Figure 1 shown.

[0047] In this step, the number of alternating repetitions N = 2. The temperature during the alternating composite treatment is kept constant at 480 °C, and the furnace internal pressure is kept constant at 100 Pa.

[0048] In this step, the low-temperature plasma nitriding process uses a mixed gas composed of N2 and H2, the volume ratio of N2 and H2 is 0.8, the bias voltage is 400 V, and the process duration is 30 minutes. The high-energy argon ion beam bombardment process uses a mixed gas composed of Ar and H2, the volume ratio of Ar and H2 is 1.0, the electric field bias voltage is 1200 V, and the process duration is 15 minutes.

[0049] Furthermore, a bright white layer is formed on the surface of the die workpiece after being processed by step (3), but there are no heat treatment defects such as pores, ablation tumors, and cracks. Through surface hardness testing, it is found that the surface hardness of the workpiece is 977 HV.

[0050] Example 3-10

[0051] The difference between Example 3-10 and Example 1 lies only in the specific parameters involved, as shown in Table 1. Meanwhile, the surface topography characteristics and surface performance parameters of the additively manufactured conformal cooling die finally obtained in Example 3-10 are attached to Table 1.

[0052] Table 1 Process parameters, surface topography characteristics and surface performance parameters of each example and comparative example

[0053]

[0054]

[0055] In order to enable those of ordinary skill in the art to more conveniently understand the improvements of the present invention over the prior art, some drawings and descriptions of the present invention have been simplified, and the above embodiments are preferred implementation schemes of the present invention. In addition, the present invention can also be implemented in other ways. Any obvious replacement without departing from the concept of the technical solution of the present invention is within the protection scope of the present invention.

Claims

1. A short - process nitriding method for improving the surface performance of conformal cooling molds in additive manufacturing, characterized in that, It includes the following steps: (1) Prepare a conformal water-cooled mold by selective laser melting technology; (2) Place the conformal water-cooled mold in a plasma nitriding furnace and alternately repeat the treatment through a low-temperature plasma nitriding process and a high-energy argon ion beam bombardment process.

2. The short-process nitriding method for improving the surface performance of conformal cooling molds in additive manufacturing according to claim 1, wherein: In step (2), the low-temperature plasma nitriding process and the high-energy argon ion beam bombardment process are alternately repeated N times for treatment, where N≥2.

3. The short-process nitriding method for improving the surface performance of conformal water-cooled molds in additive manufacturing according to claim 1, characterized in that: In step (2), the temperatures and pressures of the low-temperature plasma nitriding process and the high-energy argon ion beam bombardment process are kept consistent. The temperature range is 350-480°C, and the pressure range is 50-100 Pa.

4. The short-process nitriding method for improving the surface performance of conformal water-cooled molds in additive manufacturing according to claim 1, characterized in that: In step (2), the low-temperature plasma nitriding process uses a mixed gas composed of N2 and H2, where the volume ratio of N2 to H2 is 0.1-0.2, the bias voltage is 400-600 V, and the process duration is 20-40 minutes.

5. The short-process nitriding method for improving the surface performance of conformal water-cooled molds in additive manufacturing according to claim 1, characterized in that: In step (2), the high-energy argon ion beam bombardment process uses a mixed gas composed of Ar and H2, where the volume ratio of Ar to H2 is 1.0-1.5, the bias voltage is 1000-1200 V, and the process duration is 10-20 minutes.

6. The short-process nitriding method for improving the surface performance of conformal water-cooled molds in additive manufacturing according to claim 1, characterized in that: In step (1), the selective laser melting technical parameters include: the laser power is 200 - 500 W, the scanning speed is 700 - 1200 mm / s, the thickness of the powder spreading layer is 20 - 60 μm, the scanning spacing is 90 - 130 μm, and the laser volume energy density is 40 - 120 J / mm 3 .

7. A conformal water-cooled mold with a high-quality hardened surface, characterized in that: It is made by using the short-process nitriding method for improving the surface performance of the additive manufacturing conformal water-cooled mold according to any one of claims 1-6.

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