Additive manufacturing inner cavity composite polishing method

Abstract

The invention relates to a composite polishing method for an additive manufacturing inner cavity, and belongs to the technical field of additive manufacturing. The method specifically comprises the following steps that an inner cavity structure is pre-polished through a three-phase flow polishing medium; different chemical polishing solutions are prepared according to the material of the inner cavity structure; chemically polishing the pre-polished inner cavity structure through a chemical polishing solution; the inner cavity structure obtained after chemical polishing is cleaned and dried; the core problem of uneven polishing of the inner side, the outer side, the upper surface and the lower surface of a curve in a complex inner cavity in additive manufacturing is solved, and the final roughness difference lt is achieved; the method is far superior to gt of a traditional method; 30%; three-phase flow pre-polishing is adopted to improve the passing ability of subsequent media, the roughness difference is reduced in a targeted mode through chemical polishing, the overall polishing efficiency is improved by 2-3 times compared with a traditional method, and the over-polishing risk does not exist. The selected polishing medium is given according to the characteristics of different materials, the powder adhered to the surface of the inner cavity can be removed efficiently and uniformly by adopting the composite polishing method, and the surface roughness is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of additive manufacturing, and relates to an additive manufacturing inner cavity composite polishing method. BACKGROUND

[0002] The laser selective melting forming technology is an additive manufacturing technology based on powder bed powder laying and layer-by-layer stacking. The whole manufacturing of complex inner cavity structures such as inner flow channels and three-period minimum surfaces (TPMS) can be completed by using the technology. However, the preset powder technology of the laser selective melting forming technology causes some partially melted powders to be adhered to the surface of the formed part, and the layer-by-layer stacking manufacturing method causes the step effect to exist on the inclined surface, thereby increasing the surface roughness. The existing polishing and sandblasting methods are difficult to realize the polishing of the inner cavity structure. SUMMARY

[0003] The application solves the technical problem of overcoming the deficiencies of the prior art, proposing an additive manufacturing inner cavity composite polishing method, giving the selected polishing medium according to the characteristics of different materials, and removing the powders adhered to the inner cavity surface and reducing the surface roughness with high efficiency and high uniformity by using the composite polishing method.

[0004] The technical solution of the application is as follows:

[0005] The additive manufacturing inner cavity composite polishing method comprises the following steps:

[0006] The inner cavity structure is pre-polished by using a three-phase flow polishing medium;

[0007] Different chemical polishing liquids are configured according to the materials of the inner cavity structure;

[0008] The inner cavity structure pre-polished by the chemical polishing liquid is chemically polished;

[0009] The inner cavity structure chemically polished is cleaned and dried.

[0010] In the additive manufacturing inner cavity composite polishing method, the three-phase flow polishing medium is composed of compressed air, polishing particles and deionized water.

[0011] In the additive manufacturing inner cavity composite polishing method, the polishing particles comprise silicon carbide abrasive particles and a dispersing agent; and the dispersing agent comprises polyvinyl alcohol, sodium silicate and polystyrene.

[0012] In the additive manufacturing inner cavity composite polishing method, the pressure of the compressed air is 0.3-0.5 MPa.

[0013] In the additive manufacturing inner cavity composite polishing method, the weight proportions of the deionized water and the components of the polishing particles are as follows:

[0014] Deionized water 89.1%~94%, silicon carbide abrasive particles 2%~6%, dispersant 2.4%~3.3%; polyvinyl alcohol in the dispersant 0.7%~1%, sodium silicate 1.2%~1.5%, polystyrene 0.5%~0.8%.

[0015] In the additive manufacturing inner cavity composite polishing method, the inner cavity structure adopts titanium alloy, nickel-based superalloy, stainless steel or aluminum alloy material.

[0016] In the additive manufacturing inner cavity composite polishing method, when the inner cavity structure adopts titanium alloy material, the chemical polishing solution is 15-25% concentration ammonium persulfate aqueous solution;

[0017] When the inner cavity structure adopts nickel-based superalloy material, the chemical polishing solution is a solution mixed by 37% concentration hydrochloric acid, glycerol, 30% concentration hydrogen peroxide aqueous solution in a volume ratio of 1:1:1-2; when the inner cavity structure adopts stainless steel material, the chemical polishing solution is a solution mixed by 98% concentration sulfuric acid, 30% concentration hydrogen peroxide aqueous solution, deionized water in a volume ratio of 1:0.5-1:2;

[0018] When the inner cavity structure adopts aluminum alloy material, the chemical polishing solution is 10-20% mass fraction NaOH aqueous solution.

[0019] In the additive manufacturing inner cavity composite polishing method, the process parameters of chemical polishing are:

[0020] When the chemical polishing solution is heated to the set temperature, and the inner cavity structure after pre-polishing is subjected to chemical polishing, the chemical corrosion layer depth reaches 100-200 mu m, and the chemical polishing is ended.

[0021] In the additive manufacturing inner cavity composite polishing method, the inner cavity structure after chemical polishing is subjected to deionized water ultrasonic cleaning and vacuum drying.

[0022] In the additive manufacturing inner cavity composite polishing method, the turning deformation of the inner cavity structure is controlled to be less than 150 mu m, the surface roughness of the inner cavity structure is less than 1.6 mu m, and the roughness difference between the upper and lower surfaces and the inner and outer sides of the turning of the inner cavity structure is less than 15%.

[0023] The beneficial effects of the present application compared with the prior art are:

[0024] (1) The present application solves the core problem of uneven polishing of the inner and outer sides, upper and lower surfaces of the turning in the complex inner cavity of additive manufacturing through a two-stage composite polishing process, and the final roughness difference is less than 15%, which is much better than the traditional method (usually > 30%);

[0025] (2) The application adopts three-phase flow pre-polishing to improve the subsequent medium passability, and chemical polishing to reduce the roughness difference, so that the overall polishing efficiency is 2-3 times higher than that of the traditional method, and there is no over-polishing risk;

[0026] (3) The application realizes the use of polishing media according to different material properties, and the powder adhered to the inner cavity surface can be efficiently and uniformly removed and the surface roughness can be reduced by using a composite polishing method. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 A flow chart of additive manufacturing inner cavity composite polishing is provided for the application.

[0028] Figure 2 A comparison chart of inner cavity structure polishing before and after for stainless steel material is provided for the application.

[0029] Figure 3 A comparison chart of inner cavity structure polishing before and after for aluminum alloy material is provided for the application. DETAILED DESCRIPTION

[0030] The application will be further described below in combination with examples.

[0031] The application provides an additive manufacturing inner cavity composite polishing method, which is aimed at polishing the inner surface of complex inner cavity structures such as overall additive manufacturing flow channels and TPMS, and creatively proposes a three-phase flow pre-polishing + chemical polishing composite polishing method, and gives the selected polishing media according to different material properties. By using the composite polishing method, the powder adhered to the inner cavity surface can be efficiently and uniformly removed, and the surface roughness can be reduced.

[0032] The materials used for the complex inner cavity structures of additive manufacturing mainly include titanium alloy, nickel-based high-temperature alloy, austenitic stainless steel and aluminum alloy, which are four commonly used additive manufacturing materials.

[0033] The additive manufacturing inner cavity composite polishing method and the matching polishing media proposed by the application can realize efficient and uniform polishing of complex inner cavity structures such as large length-diameter ratio and TPMS by using a two-stage composite process of water-based three-phase flow pre-polishing + chemical polishing combined with special polishing media, while controlling the deformation of the turn to be less than 150 μm, the final surface roughness to be less than 1.6 μm, and the roughness difference between the upper and lower surfaces and the inner and outer sides of the turn to be less than 15%.

[0034] The additive manufacturing inner cavity composite polishing method, as described above, specifically includes the following steps: Figure 1

[0035] The three-phase flow polishing medium is used to pre-polish the inner cavity structure.

[0036] ​The three-phase flow polishing medium consists of compressed air, polishing particles, and deionized water. The polishing particles include silicon carbide abrasive grains and a dispersant; the dispersant includes polyvinyl alcohol, sodium silicate, and polystyrene.

[0037] In this invention, the pressure of the compressed air is 0.3-0.5 MPa. The weight percentages of the components—deionized water and polishing particles—are as follows:

[0038] The composition includes 89.1%–94% deionized water, 2%–6% silicon carbide abrasive particles, and 2.4%–3.3% dispersant; the dispersant contains 0.7%–1% polyvinyl alcohol, 1.2%–1.5% sodium silicate, and 0.5%–0.8% polystyrene.

[0039] Different chemical polishing solutions are formulated based on the material of the internal cavity structure.

[0040] The internal cavity structure is made of titanium alloy, nickel-based high-temperature alloy, stainless steel or aluminum alloy.

[0041] When the internal cavity structure is made of titanium alloy, the chemical polishing solution is a 15-25% concentration of ammonium persulfate aqueous solution.

[0042] When the inner cavity structure is made of nickel-based high-temperature alloy material, the chemical polishing solution is a mixture of 37% hydrochloric acid, glycerol, and 30% hydrogen peroxide aqueous solution in a volume ratio of 1:1:1-2; when the inner cavity structure is made of stainless steel material, the chemical polishing solution is a mixture of 98% sulfuric acid, 30% hydrogen peroxide aqueous solution, and deionized water in a volume ratio of 1:0.5-1:2.

[0043] When the internal cavity structure is made of aluminum alloy, the chemical polishing solution is a 10-20% NaOH aqueous solution.

[0044] The pre-polished internal cavity structure is chemically polished using a chemical polishing solution.

[0045] The process parameters for chemical polishing are:

[0046] When the chemical polishing slurry is heated to a set temperature and chemically polished on the pre-polished internal cavity structure, the chemical polishing is stopped when the depth of the chemical etching layer reaches 100-200μm.

[0047] The internal cavity structure after chemical polishing is cleaned and dried.

[0048] The internal cavity structure after chemical polishing is ultrasonically cleaned with deionized water and then vacuum dried.

[0049] The final result achieved is a controlled internal cavity structure with a turning deformation of less than 150 μm, a surface roughness of less than 1.6 μm, and a roughness difference of less than 15% between the upper and lower surfaces and the inner and outer sides of the turning area. Before and after polishing comparison images of the stainless steel and aluminum alloy internal cavity structures are shown below. Figure 2 , Figure 3 As shown.

[0050] This invention proposes a high-efficiency, high-uniformity composite polishing method and polishing medium combining three-phase flow pre-polishing and chemical polishing. It is primarily used for removing and polishing excess material from the surfaces of complex internal cavities such as large aspect ratio flow channels and TPMS in additive manufacturing, improving surface quality and reducing flow resistance. The two-stage composite polishing process proposed in this invention solves the core problem of uneven polishing on the inner and outer sides of bends and on the upper and lower surfaces in complex internal cavities of additive manufacturing, achieving a final roughness difference of <15%, far superior to traditional methods (typically >30%). The three-phase flow pre-polishing improves the flowability of the subsequent medium, while the chemical polishing specifically reduces roughness differences, resulting in an overall polishing efficiency 2-3 times higher than traditional methods, while avoiding the risk of over-polishing.

[0051] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A composite polishing method for additive manufacturing cavities, characterized in that: include: The internal cavity structure is pre-polished using a three-phase flow polishing medium; Different chemical polishing solutions are formulated according to the materials of the internal cavity structure; The pre-polished internal cavity structure is chemically polished using a chemical polishing solution; The internal cavity structure after chemical polishing is cleaned and dried.

2. The additive manufacturing cavity composite polishing method according to claim 1, characterized in that: The three-phase flow polishing medium consists of compressed air, polishing particles, and deionized water.

3. The additive manufacturing cavity composite polishing method according to claim 2, characterized in that: The polishing particles include silicon carbide abrasive particles and a dispersant; wherein the dispersant includes polyvinyl alcohol, sodium silicate and polystyrene.

4. The additive manufacturing cavity composite polishing method according to claim 2, characterized in that: The pressure of the compressed air is 0.3-0.5 MPa.

5. The additive manufacturing cavity composite polishing method according to claim 3, characterized in that: The weight percentages of the deionized water and polishing particles are as follows: The composition includes 89.1%–94% deionized water, 2%–6% silicon carbide abrasive particles, and 2.4%–3.3% dispersant; the dispersant contains 0.7%–1% polyvinyl alcohol, 1.2%–1.5% sodium silicate, and 0.5%–0.8% polystyrene.

6. The additive manufacturing cavity composite polishing method according to claim 1, characterized in that: The internal cavity structure is made of titanium alloy, nickel-based high-temperature alloy, stainless steel or aluminum alloy.

7. The additive manufacturing cavity composite polishing method according to claim 6, characterized in that: When the internal cavity structure is made of titanium alloy, the chemical polishing solution is a 15-25% concentration of ammonium persulfate aqueous solution; When the inner cavity structure is made of nickel-based high-temperature alloy material, the chemical polishing solution is a mixture of 37% hydrochloric acid, glycerol, and 30% hydrogen peroxide aqueous solution in a volume ratio of 1:1:1-2; when the inner cavity structure is made of stainless steel material, the chemical polishing solution is a mixture of 98% sulfuric acid, 30% hydrogen peroxide aqueous solution, and deionized water in a volume ratio of 1:0.5-1:

2. When the internal cavity structure is made of aluminum alloy, the chemical polishing solution is a 10-20% NaOH aqueous solution.

8. The additive manufacturing cavity composite polishing method according to claim 7, characterized in that: The process parameters for chemical polishing are: When the chemical polishing slurry is heated to a set temperature and chemically polished on the pre-polished internal cavity structure, the chemical polishing is stopped when the depth of the chemical etching layer reaches 100-200μm.

9. The additive manufacturing cavity composite polishing method according to claim 1, characterized in that: The internal cavity structure after chemical polishing is ultrasonically cleaned with deionized water and then vacuum dried.

10. The additive manufacturing cavity composite polishing method according to claim 1, characterized in that: The controllable internal cavity structure can achieve a turning deformation of less than 150 μm, a surface roughness of less than 1.6 μm, and a roughness difference of less than 15% between the upper and lower surfaces and the inner and outer sides of the turning section.

Images