WO2018228251A1 - 去除选区激光熔化成形零件内腔表面裂纹的方法 - Google Patents

去除选区激光熔化成形零件内腔表面裂纹的方法 Download PDF

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WO2018228251A1
WO2018228251A1 PCT/CN2018/090088 CN2018090088W WO2018228251A1 WO 2018228251 A1 WO2018228251 A1 WO 2018228251A1 CN 2018090088 W CN2018090088 W CN 2018090088W WO 2018228251 A1 WO2018228251 A1 WO 2018228251A1
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crack
cracks
isostatic pressing
hot isostatic
abrasive flow
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PCT/CN2018/090088
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English (en)
French (fr)
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侯慧鹏
张渝
雷力明
何艳丽
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中国航发商用航空发动机有限责任公司
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/20—Direct sintering or melting
    • B22F10/28—Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/60—Treatment of workpieces or articles after build-up
    • B22F10/64—Treatment of workpieces or articles after build-up by thermal means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/60—Treatment of workpieces or articles after build-up
    • B22F10/66—Treatment of workpieces or articles after build-up by mechanical means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/105—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/24—After-treatment of workpieces or articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/24—After-treatment of workpieces or articles
    • B22F2003/247—Removing material: carving, cleaning, grinding, hobbing, honing, lapping, polishing, milling, shaving, skiving, turning the surface
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/24—After-treatment of workpieces or articles
    • B22F2003/248—Thermal after-treatment
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • the present disclosure relates to the field of material processing technology, and more particularly to a method for removing cracks in the inner cavity surface of a selected portion of a laser melt-molded part.
  • Selective Laser Melting (SLM) technology is a typical additive manufacturing technology, which is predicted to be one of the key technologies that may trigger the "third industrial revolution.”
  • the main technical principles are: The three-dimensional digital model of the part to be processed is divided layer by layer and input into the selective laser melting forming device.
  • the substrate is fixed on the forming platform and leveled, and then a single layer is laid by a scraper or a powder roller, and the selected single layer powder is melted by one or more lasers to realize the selection from the point to The forming process of the line and the line to the surface, after which the forming platform is lowered to a certain height, the next layer of powder is laid and the selected area is melted and formed, and finally the surface-to-body forming process is realized, thereby obtaining the final part.
  • the selective laser melting technology has many advantages such as high material utilization rate, improved design freedom, high precision forming and good surface quality, and is especially suitable for high value-added industries such as aerospace.
  • the rapid solidification process is accompanied by extremely high temperature gradients, resulting in large residual stresses in the part.
  • the local residual stress exceeds the tensile strength, the part cracks and cracks. The stress is released to a certain extent.
  • the crack distribution range includes not only the inside of the part but also the part surface.
  • the following two methods are generally used to eliminate cracks: one is to use the hot isostatic pressing process to close the internal crack of the part; the other is to machine the machined surface by mechanical processing methods (such as turning, milling, etc.).
  • mechanical processing methods such as turning, milling, etc.
  • the use of mechanical processing methods has problems such as high processing position limitation and complicated process of complex structural parts.
  • the laser melting forming parts of the selection area usually have complex internal cavity structures, and the machining process is often difficult to play a role.
  • micro-cracks and open surface cracks in the parts can be eliminated by the hot isostatic pressing process and the conventional mechanical processing process, and the surface cracks of the inner cavity are difficult to remove.
  • the presence of surface cracks in the inner cavity can seriously damage the surface integrity of the laser-melted parts of the selection, which has a great influence on the service performance, life and reliability of the components.
  • statistics show that 90% of the failure of aerospace titanium alloy parts is related to fatigue performance, and surface cracks often act as a source of fatigue cracks, and the surface integrity of titanium alloys is improved by some processes. Improving fatigue performance plays a key role.
  • the technical problem to be solved by the present disclosure is to provide a method for removing cracks in the inner cavity surface of a laser-molded part of a selective area, which can remove surface cracks in the inner cavity of the laser-molded part of the selected area.
  • the present disclosure provides a method for removing cracks in the inner cavity surface of a selected portion laser-molded part, which includes:
  • Hot isostatic pressing treatment step performing hot isostatic pressing treatment on the laser-molded parts of the selected area
  • Abrasive flow processing step the abrasive flow processing of the selected portion of the laser melt-molded part after the hot isostatic pressing treatment.
  • the method further comprises a sectioning step between the hot isostatic pressing step and the abrasive stream processing step: performing a section analysis on the part after the completion of the hot isostatic pressing to obtain a crack depth of the inner cavity surface of the part Large value, based on the maximum value of the crack depth to determine the amount of material removal required to achieve the abrasive flow.
  • the model margin is increased, and the minimum value of the total model margin is greater than the maximum value of the crack depth.
  • the maximum value of the crack depth is obtained by detecting the roughness and the crack distribution at different positions on the surface of the cavity after the completion of the cutting.
  • the crack analysis comprises: performing multi-position cutting on the laser-molded parts of the selected area, and performing metallographic analysis and multi-batch repeated cutting analysis on the laser-molded parts of the selected area by using the vertical crack direction.
  • the abrasive flow processing step comprises: performing abrasive flow, performing abrasive removal, and detecting whether the grinding amount reaches an expected value, and if the measured grinding amount does not match the expected value, resetting the selected laser melting forming part. Model margin.
  • the method further includes the step of sampling the part: performing a section analysis on the part of the workpiece subjected to the abrasive flow treatment to determine whether there is a crack.
  • the method further includes a model pretreatment step, a blank processing step, and a heat treatment step, which are preceded by the hot isostatic pressing treatment step.
  • the present disclosure removes the surface crack of the inner cavity of the selective laser melting forming part by setting the abrasive flow step after the hot isostatic pressing step.
  • Abrasive flow is used for finishing, polishing and deburring parts, with good repeatability and high surface quality.
  • the original surface quality of the laser-molded parts in the selected area is good, and the abrasive flow process is used to eliminate the cracks in the internal cavity of the part and further improve the surface roughness.
  • the present disclosure is directed to internal cavity cracks that cannot be removed by mechanical processing or by manual sanding after hot isostatic pressing.
  • FIG. 1 is a flow chart of a method for removing surface cracks in a cavity of a selected portion of a laser melt-molded part according to the present disclosure
  • FIG. 2 is a flow chart showing the steps of the cutting analysis in the method for removing the surface crack of the inner cavity of the selected portion of the laser melting forming part;
  • FIG. 3 is a flow chart showing the steps of the abrasive flow processing in the method for removing the surface crack of the inner cavity of the selected portion of the laser melting forming part;
  • 4(a) and 4(b) are diagrams showing the internal crack distribution of the selective laser melting forming GH4169 alloy in the as-deposited state and the hot isostatic pressing state by using the present disclosure to remove the surface crack of the inner cavity of the selected portion laser-molded part;
  • Fig. 5(a) and Fig. 5(b) are diagrams showing the crack distribution of the inner surface after the hot isostatic pressing of the selective laser melting forming GH4169 alloy part by the method of the present invention for removing the surface crack of the inner cavity of the selected portion laser-molded part.
  • the method includes:
  • Hot isostatic pressing step 4 hot isostatic pressing treatment of the selected area laser-molded parts
  • Abrasive flow treatment step 6 The abrasive-flow processing of the selected laser-molded part after the hot isostatic pressing treatment.
  • the process steps of the laser selective melting of the part are generally: model processing; blank forming; stress relief annealing; desupporting; hot isostatic pressing.
  • the present disclosure differs from the conventional process in that the abrasive flow is performed for the finishing, polishing, deburring of the part by the abrasive flow processing step 6 after the hot isostatic pressing step 4. It has the characteristics of good repeatability and high surface quality. The original surface quality of the laser-molded parts of the selected area is better.
  • the abrasive flow process is used to eliminate the cracks in the inner cavity of the part, and the surface roughness of the inner cavity of the laser-molded part of the selected area is further improved.
  • the present disclosure is directed to the internal cavity crack which cannot be removed by mechanical processing or manual grinding after hot isostatic pressing, and the surface flow of the inner cavity of the part is eliminated by the abrasive flow method.
  • the method for removing surface cracks in the inner cavity of the selective laser melting forming part of the present disclosure further includes a cutting analysis step 5 between the hot isostatic pressing treatment step 4 and the abrasive flow processing step 6. : Performing a section analysis on the part after the completion of the hot isostatic pressing to obtain the maximum value of the crack depth of the inner cavity surface of the part, and determining the amount of material removal required for the abrasive flow according to the maximum value of the crack depth.
  • the present disclosure determines the amount of material removal required for the abrasive flow according to the maximum value of the crack depth of the inner cavity surface of the part, eliminates cracks in the inner cavity of the part and realizes on-demand use, avoids unnecessary waste, and saves cost.
  • the method for removing the surface crack of the inner cavity of the selective laser melting forming part of the present disclosure is specifically or preferably described below with reference to the flow shown in FIGS. 1 to 3 as follows:
  • Model preprocessing step 1 including the addition of model margin and support design, and slicing the three-dimensional model to obtain a process model;
  • Blank processing step 2 including introducing the process model file into the equipment, using the optimized selection laser melting forming process parameters for laser melting forming, part collection and cavity powder cleaning;
  • Heat treatment step 3 which also includes the wire cutting process required to separate the substrate from the part after the stress relief annealing of the part, and the support removal process.
  • Hot isostatic pressing step 4 serves to eliminate internal cracks in the part.
  • Section analysis processing step 5 performing a section analysis on the parts after the completion of the hot isostatic pressing, as shown in Fig. 2, specifically including a sectioning scheme 5.1 of the design part, the sectioning scheme should be able to display the complete inner
  • the cavity structure is in an optimal state; the cutting is performed 5.2, and the cutting is performed by a wire electric discharge machine or other process technology; the roughness detection 5.3 is used to detect the roughness of different positions on the surface of the cavity after the cutting is completed, which is a crack analysis and Detection provides basis; crack detection 5.4, using fluorescence infiltration detection, metallographic analysis or a combination of two processes to determine the distribution of surface cracks; crack analysis 5.5, focusing on areas with small roughness values, and changes in lumen cross-sectional area Area, using appropriate methods (such as further multi-position cutting of selected laser-molded parts, metallographic analysis of selected areas of laser-melted parts using vertical crack direction and multi-batch repeated section analysis) After comprehensive comparison, the maximum value of the crack depth is obtained. It should
  • the abrasive flow is performed; if the maximum value is larger than the model allowance of the laser-molded part of the selected area, repeating Step 1 model processing, adding a corresponding margin on the surface of the crack cavity.
  • the specific value of the residual position of the inner cavity is closely related to the structural characteristics of the inner cavity of the part, but the minimum value of the model residual after the increase should be greater than the maximum value of the crack depth obtained by the analysis to ensure the crack removal is achieved. The effect is close to 100%, improving the overall performance of the part.
  • Abrasive flow processing step 6, as shown in FIG. 3, specifically includes process parameter design 6.1, selecting different abrasive types, abrasive grain sizes, pressures, binder types, etc. according to different types of materials and different cross-sectional areas of the inner cavity; Design abrasive cleaning plan 6.2, it is necessary to pay special attention to the use of abrasive flow to remove the internal cavity surface crack, the use of appropriate process to clean the abrasive is the key link; abrasive flow implementation 6.3; abrasive removal 6.4; analysis and detection 6.5, using industrial CT Check if the grinding amount reaches the expected value. When the analysis and detection of the measured grinding amount does not match the expected value, repeat the step 1 model margin setting.
  • Part sampling step 7 mainly refers to the extraction of a certain number of parts in the mass production stage, repeated detection according to step 5, to check whether the purpose of removing the surface crack of the inner cavity is achieved.
  • Final inspection and acceptance step 8 the means available include, but are not limited to, metallographic analysis, X-ray detection, fluorescence detection, and the like.
  • the present invention proposes a method for eliminating surface cracks of a part by using an abrasive flow process on the basis of eliminating the internal crack of the part by the hot isostatic pressing process, and finally achieves the purpose of completely eliminating cracks in the part, compared with the current existing methods.
  • the crack elimination process can avoid the damage of the internal and surface cracks on the mechanical properties (including stretching, durability, fatigue, etc.), and plays an important role in improving the overall performance of the parts.
  • the dimensional accuracy and surface roughness of selected laser-molded parts are often difficult to meet the requirements of high-precision and complex structural parts.
  • the appropriate process control can greatly improve the roughness of the inner and outer surfaces, improve the dimensional accuracy, and meet the product requirements.
  • the product quality can be improved by eliminating surface cracks in the inner cavity of the part, which has important practical significance for promoting the engineering application of laser melting technology in aerospace and other fields.
  • Model pre-treatment of an internal pipe part with equal section using UG NX7.5 the part material is GH4169 alloy, pipe inner diameter Outer diameter There is a smooth transition with a bending radius of R6.0mm, and a R10.0mm causes two changes in the direction of the pipeline.
  • the total length of the pipeline is about 100mm.
  • the slice file is introduced into the selective laser melting forming apparatus to perform a blank forming process.
  • the forming process parameters were set to a layer thickness of 40 ⁇ m, a laser power of 200 W, a scanning speed of 900 mm/s, a laser spot diameter of 100 ⁇ m, and a scanning pitch of 110 ⁇ m.
  • a stress-relieving heat treatment was performed, and the heat treatment system was 1170 ⁇ 50° C./h, AC.
  • the parts are separated from the substrate by wire cutting, and the support is removed, and the internal crack distribution of the parts is observed as shown in Fig. 4(a).
  • the hot isostatic pressing process is 1170 ° C / 2 h, the pressure is 150 MPa, and the cooling rate is 3 K / min. After analysis, the internal crack removal effect is close to 100%, as shown in Figure 4(b). If the crack elimination effect is not satisfactory, the hot isostatic pressing process needs to be adjusted, and the above steps are repeated.
  • the maximum value of the crack depth is determined by the combination of fluorescence permeation detection and metallographic analysis.
  • Penetration testing using halogenated hydrocarbon solvents to clean the cut parts, fully remove the grease on the surface of the parts and other substances that may affect the penetration detection effect, to ensure that the parts are clean and dry.
  • the penetrant is applied by manual brushing to maintain the contact time of the penetrant for 15 min to 30 min.
  • a water temperature consistent with the ambient temperature a large amount of penetrant is removed from the surface of the part by pre-washing, an emulsifier is applied, and final cleaning is applied to apply the developer.
  • check under the black light to obtain the distribution of cracks on the surface of the part. Further metallographic analysis should be performed for the presence of crack equal positions.
  • the surface crack width in the observation region is 2 to 5 ⁇ m.
  • the maximum value of the crack depth can be determined by the entire cross-sectional observation to be about 30 ⁇ m, and the maximum value of the crack depth is positioned in consideration of a certain margin.
  • the cut surface hardness value was tested to be HRB94.

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Abstract

一种去除选区激光熔化成形零件内腔表面裂纹的方法，包括：热等静压处理步骤：对选区激光熔化成形零件进行热等静压处理；磨粒流处理步骤：对热等静压处理后的选区激光熔化成形零件进行磨粒流处理。上述去除选区激光熔化成形零件内腔表面裂纹的方法通过在热等静压步骤后设置磨粒流步骤，选区激光熔化成形零件原始表面质量较好，采用磨粒流工艺消除了零件内腔开口裂纹，提升零件的综合性能。

Description

去除选区激光熔化成形零件内腔表面裂纹的方法
本申请是以申请号201710445500.X，申请日2017年6月13日的中国申请为基础，要求其优先权，该中国申请的公开内容在此作为整体引入本申请中。
技术领域
本公开涉及材料加工处理技术领域，尤其涉及一种去除选区激光熔化成形零件内腔表面裂纹的方法。
背景技术
选区激光熔化(Selective Laser Melting，简称SLM)技术是一种典型的增材制造(Additive Manufacturing)技术，被预测为可能引发“第三次工业革命”的关键技术之一，其主要技术原理为：将待加工的零件三维数字模型进行逐层分割，输入到选区激光熔化成形设备中。首先将基板固定在成形平台上，并进行调平，之后利用刮板或粉辊进行单层铺粉，利用一束或多束激光对铺放好的单层粉末进行选区熔化，实现由点到线、由线到面的成形过程，之后成形平台下降一定高度，进行下一层铺粉及选区熔化成形，最终实现了由面到体的成形过程，由此获得最终零件。相比于传统工艺，选区激光熔化技术具有材料利用率高、提高设计自由度、成形高精度、表面质量好等多重优势，特别适合于航空航天等高附加值行业。
然而，由于选区激光熔化成形过程伴随着快速凝固过程，快速凝固过程伴随着极高温度梯度，导致了零件存在较大的残余应力，当局部残余应力超过抗拉强度时，零件出现裂纹，通过开裂使应力得到一定程度释放。通常，裂纹分布范围不仅包括零件内部，也包括了零件表面。
由于选区激光熔化成形零件存在裂纹，难以满足结构耐久性和损伤容限设计的要求，这一点在航空航天领域尤为显著。针对这一问题，目前通常采用以下两种办法消除裂纹：一是采用热等静压工艺使零件内部裂纹闭合；二是采用机械加工方法(如车削、铣削等)对可加工面进行机械加工。然而由于热等静压工艺固有的特点，仅能使零件内部裂纹闭合，起到消除内部裂纹的作用，而对于表面开口裂纹没有效果。而采用机械加工方法存在加工位置局限性高、对复杂结构零件工艺复杂等问题，特别是选区激光熔化成形零件通常具有复杂的内腔结构，机械加工工艺往往难以起到作用。
由此可见，通过热等静压工艺及传统机械加工工艺，可以消除零件内部微裂纹及开敞表面裂纹，而内腔的表面裂纹很难去除。内腔表面裂纹的存在会严重破坏选区激光熔化零件的表面完整性，对零部件的服役性能、寿命和可靠性有很大影响。如以钛合金构件为例，统计表明，90％的航空钛合金零件的失效与疲劳性能相关，而表面裂纹往往起到了疲劳裂纹源的作用，通过某些工艺提高钛合金的表面完整性，对于提升疲劳性能有关键作用。
发明内容
为克服以上技术缺陷，本公开解决的技术问题是提供一种去除选区激光熔化成形零件内腔表面裂纹的方法，能够去除选区激光熔化成形零件内腔的表面裂纹。
为解决上述技术问题，本公开提供了一种去除选区激光熔化成形零件内腔表面裂纹的方法，其包括：
热等静压处理步骤:对选区激光熔化成形零件进行热等静压处理；
磨粒流处理步骤:对热等静压处理后的选区激光熔化成形零件进行磨粒流处理。
进一步地，还包括热等静压处理步骤和磨粒流处理步骤之间的剖切分析步骤:对完成热等静压后的零件进行剖切分析，以获得零件内腔表面的裂纹深度的极大值，根据裂纹深度的极大值确定磨粒流需达到的材料去除量。
进一步地，若裂纹深度的极大值大于选区激光熔化成形零件的模型余量，增加模型余量，且总的模型余量的最小值大于裂纹深度的极大值。
进一步地，裂纹深度的极大值通过检测剖切完成后的内腔表面不同位置的粗糙度和裂纹分布并经过裂纹分析获得。
进一步地，裂纹分析包括：对选区激光熔化成形零件进行多位置剖切，对选区激光熔化成形零件利用垂直裂纹方向剖切后进行金相分析以及多批次重复剖切分析。
进一步地，磨粒流处理步骤包括：进行磨粒流、进行磨料去除以及检测磨削量是否达到预期值，若测得的磨削量与预期值不符合时，重新设置选区激光熔化成形零件的模型余量。
进一步地，还包括零件抽检步骤：对抽取预设数量的进行磨粒流处理后的零件进行剖切分析检测，判断是否存在裂纹。
进一步地，还包括依次进行的模型预处理步骤、毛坯加工步骤以及热处理步骤，热处理步骤位于热等静压处理步骤之前。
由此，基于上述技术方案，本公开去除选区激光熔化成形零件内腔表面裂纹的方法通过在热等静压步骤后设置磨粒流步骤。磨粒流用于零件的精加工、抛光、去毛刺，有着可重复性好，表面质量高的特点。选区激光熔化成形零件原始表面质量较好，采用磨粒流工艺消除了零件内腔开口裂纹，进一步提高表面粗糙度。本公开针对经过热等静压后无法通过机械加工或手工打磨消除的内腔裂纹。
附图说明
此处所说明的附图用来提供对本公开的进一步理解，构成本申请的一部分，本公开的示意性实施例及其说明仅用于解释本公开，并不构成对本公开的不当限定。在附图中：
图1为本公开去除选区激光熔化成形零件内腔表面裂纹的方法的流程图；
图2为本公开去除选区激光熔化成形零件内腔表面裂纹的方法中剖切分析步骤的流程图；
图3为本公开去除选区激光熔化成形零件内腔表面裂纹的方法中磨粒流处理步骤的流程图；
图4(a)和图4(b)分别为选区激光熔化成形GH4169合金利用本公开去除选区激光熔化成形零件内腔表面裂纹的方法在沉积态和热等静压态下的内部裂纹分布图；
图5(a)和图5(b)为选区激光熔化成形GH4169合金零件利用本公开去除选区激光熔化成形零件内腔表面裂纹的方法经过热等静压后的内表面裂纹分布图。
具体实施方式
下面通过附图和实施例，对本公开的技术方案做进一步的详细描述。
本公开的具体实施方式是为了便于对本公开的构思、所解决的技术问题、构成技术方案的技术特征和带来的技术效果有更进一步的说明。需要说明的是，对于这些实施方式的说明并不构成对本公开的限定。此外，下面所述的本公开的实施方式中涉及的技术特征只要彼此之间未构成冲突就可以相互组合。
在本公开去除选区激光熔化成形零件内腔表面裂纹的方法一个示意性的实施例中，如图1所示，该方法包括：
热等静压处理步骤4:对选区激光熔化成形零件进行热等静压处理；
磨粒流处理步骤6:对热等静压处理后的所述选区激光熔化成形零件进行磨粒流处理。
通常选区激光熔化成形零件的工艺步骤包括：模型处理；毛坯成形；去应力退火；去支撑；热等静压。在该示意性的实施例中，本公开与传统工艺路线不同的是，通过在热等静压处理步骤4后设置磨粒流处理步骤6，磨粒流用于零件的精加工、抛光、去毛刺，有着可重复性好，表面质量高的特点。选区激光熔化成形零件原始表面质量较好，采用磨粒流工艺消除了零件内腔开口裂纹，进一步提高选区激光熔化成形零件内腔表面粗糙度。本公开针对经过热等静压后无法通过机械加工或手工打磨消除的内腔裂纹，采用磨粒流方法消除零件内腔表面裂纹。
具体地或优选地，如图1所示，本公开去除选区激光熔化成形零件内腔表面裂纹的方法还包括热等静压处理步骤4和磨粒流处理步骤6之间的剖切分析步骤5:对完成热等静压后的零件进行剖切分析，以获得零件内腔表面的裂纹深度的极大值，根据裂纹深度的极大值确定磨粒流需达到的材料去除量。本公开根据零件内腔表面的裂纹深度的极大值来确定磨粒流需达到的材料去除量，消除了零件内腔开口裂纹且实现按需使用，避免不必要的浪费，节省成本。
下面结合图1～图3所示的流程来具体地或优选地说明本公开去除选区激光熔化成形零件内腔表面裂纹的方法如下：
(1)模型预处理步骤1，包含模型余量的添加和支撑设计，并将三维模型进行切片，获得工艺模型；
(2)毛坯加工步骤2，包括将工艺模型文件导入设备，采用优化的选区激光熔化成形工艺参数进行选区激光熔化成形、零件收取及内腔粉末清理等；
(3)热处理步骤3，同时包含了零件完成去应力退火后，将基板与零件分离所需线切割工序，以及支撑去除工序。
(4)热等静压处理步骤4，起消除零件内部裂纹的作用。
(5)剖切分析处理步骤5，对完成热等静压后的零件进行剖切分析，如图2所示，具体包括设计零件的剖切方案5.1，剖切方案应以能够展示完整的内腔结构为最佳状态；实施剖切5.2，利用电火花线切割机或其他工艺技术进行剖切；粗糙度检测5.3，检测剖切完成后的内腔表面不同位置的粗糙度，为裂纹分析与检测提供依据；裂纹检测5.4，利用荧光渗透检测、金相分析或者两种工艺相结合，确定表面裂纹的分布情况；裂纹分析5.5，重点针对粗糙度值较小的区域、以及内腔截面积突变区域，采用 恰当的方法(如进一步对选区激光熔化成形零件进行多位置剖切，对选区激光熔化成形零件利用垂直裂纹方向剖切后进行金相分析以及多批次重复剖切分析)分析裂纹深度，综合比较后得出裂纹深度的极大值。应注意的是，由于进行磨粒流时，原粗糙度较大的表面磨削量会大于粗糙度较小区域，因此在裂纹深度分析时，针对相对表面质量较好的区域应作分析重点。
根据确定的裂纹深度极大值，若裂纹深度的极大值小于选区激光熔化成形零件的模型余量，则进行磨粒流；若极大值大于选区激光熔化成形零件的模型余量，重复进行步骤1模型处理，在裂纹内腔表面增加相应的余量。需要注意的是，内腔不同位置余量的具体值，与零件内腔的结构特点密切相关，但增加后的模型余量最小值应大于分析所得的裂纹深度极大值，以保障裂纹去除达到效果趋近于100％，提升零件的综合性能。
(6)磨粒流处理步骤6，如图3所示，具体包括工艺参数设计6.1，根据材料种类不同、内腔截面积不同选择不同的磨料类型、磨料粒度、压力、粘结剂种类等；设计磨料清理方案6.2，需要特别注意的是，采用磨粒流去除内腔表面裂纹后，采用恰当的工艺清理磨料是关键环节；磨粒流实施6.3；磨料去除6.4；分析检测6.5，采用工业CT检测磨削量是否达到预期值，当分析检测测得的磨削量与预期值不符合时，需重复进行步骤1模型余量设置。
(7)零件抽检步骤7，主要指在实现量产阶段，抽取一定数量零件，重复按照步骤5进行检测，检查是否达到了去除内腔表面裂纹的目的。
(8)最终检验及验收步骤8，可采用的手段包括但不限于金相分析、X射线检测、荧光检测等。
本公开在热等静压处理消除零件内部裂纹的基础上，提出了利用磨粒流工艺消除零件表面裂纹的方法，最终达到完整地消除零件中的裂纹的目的，与目前现有工艺方法相比，具有以下优势：
(1)改善零件力学性能；
消除裂纹工序可以避免零件内部及表面裂纹对力学性能(包括拉伸、持久、疲劳等)的破坏作用，对提升零件的综合性能有重要作用。
(2)提高零件的批次稳定性；
选区激光熔化成形零件裂纹的存在会导致零件的批次性能数据的分散性大幅提高，即导致了零件使用寿命在较大范围内波动，难以准确预测零件的使用寿命。消除 裂纹工序可以使零件性能波动减小，提升批次稳定性。
(3)粗糙度、尺寸精度得到优化；
选区激光熔化成形零件的尺寸精度、表面粗糙度通常难以满足高精度复杂结构零件的使用要求。在消除裂纹的同时，通过恰当的工艺控制，可以大幅改善内外表面的粗糙度，提高尺寸精度，满足产品需求。
总而言之，通过消除零件内腔表面裂纹可以提升产品质量，对于推广选区激光熔化技术在航空航天等领域的工程化应用具有重要现实意义。
下面以去除选区激光熔化成形GH4169含等截面管路零件内表面裂纹为例来说明本公开方法如下：
(1)使用UG NX7.5对某个具有等截面内部管路零件进行模型预处理，零件材质为GH4169合金，管路内径
Figure PCTCN2018090088-appb-000001
外径
Figure PCTCN2018090088-appb-000002
有一处弯曲半径为R6.0mm的圆滑过渡，及一处R10.0mm导致管路方向发生两次变化，管路总长度约100mm。首先对零件外部确定的机械加工面添加1mm左右余量，并导出STL文件，采用Magics19.0进行支撑设计并输出切片文件。将切片文件导入到选区激光熔化成形设备中，进行毛坯成形过程。设置成形工艺参数为层厚40μm，激光功率200W，扫描速度900mm/s，激光光斑直径100μm，扫描间距110μm，完成毛坯成形后进行去应力热处理，热处理制度为1170±50℃/1h，AC。热处理完成后采用线切割将零件从基板分离，并将支撑去除，观察零件内部裂纹分布情况如图4(a)所示。
(2)使用真空热处理炉对完成支撑去除的零件进行热等静压，以达到消除内部裂纹的目的，选用热等静压工艺为1170℃/2h，压力为150MPa，冷却速度3K/min。经过分析，内部消除裂纹效果接近100％，如图4(b)所示。如消除裂纹效果不理想时，需调整热等静压工艺，重复进行以上步骤。
(3)采用电火花线切割或其他剖切方法对零件进行剖切。
(4)采用荧光渗透检测与金相分析相结合确定裂纹深度极大值。
渗透检测，采用卤代烃类溶剂清洗剖切后的零件，充分去除零件表面存在的油脂及其他可能影响渗透检测效果的物质，保证零件清洁干燥。在使用黑光灯对施加效果进行监控的前提下，采用手工刷涂的办法施加渗透剂，保持渗透剂接触时间15min～30min。采用与环境温度一致的水温，通过预水洗去除零件表面大量的渗透剂后，涂覆乳化剂，并进行最终清洗，施加显像剂。最后在黑光灯下检查，获得零件表面裂纹的分布情况。存在裂纹等额位置应进行进一步的金相分析。
金相分析，选择经过荧光渗透检发现的裂纹位置，以及选择一定数量具有代表性的表面区域，或者观察区域裂纹的分布情况。如图5(a)和5(b)所示，该观察区域内表面裂纹宽度2～5μm。本实例中，通过整个截面观察观察可确定裂纹深度极大值约30μm，考虑一定余量，将裂纹深度极大值定位。
测试剖切面硬度值为HRB94。
(5)重复进行步骤1模型预处理，将管路内径调整为
Figure PCTCN2018090088-appb-000003
后，重复步骤2～步骤4.
(6)进行磨粒流工艺流程。选择150目碳化硅磨料，设置压力10MPa。磨粒流连续进行30min时间后，采用工业CT检测管路直径的变化，确定是否需要继续进行磨粒流。当管路直径达到预设值
Figure PCTCN2018090088-appb-000004
后，过程停止。
在12MPa压力下，采用航空煤油进行清洗20min后，更换未使用过的洁净航空煤油冲洗5min，收集全部出油口，目视对比出油口和进油口处煤油洁净程度，直至两者接近一致。之后，进行真空烘干，并采用压缩空气从入口处吹3min，同时进行人工敲击，如发现管路出口处有颗粒被吹出，则继续重复进行洁净煤油冲洗-烘干-吹压缩空气，直至不再有颗粒物产生。
(7)进行X射线检验、剖切后荧光渗透检验、金相分析检测是否仍然存在表面裂纹，如不存在裂纹则固化工艺后，批量生产。但仍应执行批次抽检。
(8)完成零件最终检验及入库。
以上结合的实施例对于本公开的实施方式做出详细说明，但本公开不局限于所描述的实施方式。对于本领域的技术人员而言，在不脱离本公开的原理和实质精神的情况下对这些实施方式进行多种变化、修改、等效替换和变型仍落入在本公开的保护范围之内。

Claims (8)

  1. 一种去除选区激光熔化成形零件内腔表面裂纹的方法，其特征在于，包括：
    热等静压处理步骤:对选区激光熔化成形零件进行热等静压处理；以及
    磨粒流处理步骤:对热等静压处理后的所述选区激光熔化成形零件进行磨粒流处理。
  2. 根据权利要求1所述的去除选区激光熔化成形零件内腔表面裂纹的方法，其特征在于，还包括所述热等静压处理步骤和所述磨粒流处理步骤之间的剖切分析步骤:对完成热等静压后的零件进行剖切分析，以获得零件内腔表面的裂纹深度的极大值，根据所述裂纹深度的极大值确定磨粒流需达到的材料去除量。
  3. 根据权利要求2所述的去除选区激光熔化成形零件内腔表面裂纹的方法，其特征在于，若所述裂纹深度的极大值大于所述选区激光熔化成形零件的模型余量，增加所述模型余量，且总的所述模型余量的最小值大于所述裂纹深度的极大值。
  4. 根据权利要求2所述的去除选区激光熔化成形零件内腔表面裂纹的方法，其特征在于，所述裂纹深度的极大值通过检测剖切完成后的内腔表面不同位置的粗糙度和裂纹分布并经过裂纹分析获得。
  5. 根据权利要求4所述的去除选区激光熔化成形零件内腔表面裂纹的方法，其特征在于，所述裂纹分析包括：对所述选区激光熔化成形零件进行多位置剖切，对所述选区激光熔化成形零件利用垂直裂纹方向剖切后进行金相分析以及多批次剖切分析。
  6. 根据权利要求1所述的去除选区激光熔化成形零件内腔表面裂纹的方法，其特征在于，所述磨粒流处理步骤包括：进行磨粒流、进行磨料去除以及检测磨削量是否达到预期值，若测得的磨削量与预期值不符合时，重新设置所述选区激光熔化成形零件的模型余量。
  7. 根据权利要求1～6任一项所述的去除选区激光熔化成形零件内腔表面裂纹的方法，其特征在于，还包括零件抽检步骤：对抽取预设数量的进行磨粒流处理后的零件进行剖切分析检测，判断是否存在裂纹。
  8. 根据权利要求1～6任一项所述的去除选区激光熔化成形零件内腔表面裂纹的方法，其特征在于，还包括依次进行的模型预处理步骤、毛坯加工步骤以及热处理步骤，所述热处理步骤位于所述热等静压处理步骤之前。
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