A low-cost, easy-to-machine, medium-strength titanium alloy parts rapid prototyping method

Abstract

This invention relates to the field of powder bed additive manufacturing technology, specifically a low-cost, easy-to-machine, medium-strength titanium alloy rapid prototyping method. The specific steps are as follows: S1, raw material metal powder preparation; S2, part blank printing; S3, part post-processing; S4, finishing. The inner surface layer of the blank is connected to the interior of the blank and is processed in a single pass. The outer surface layer is connected to the inner surface layer and is processed in at least two passes. A suitable energy density ensures near-complete compactness within the blank. The formation of unfused defects on the outer surface layer facilitates machining. Near-spherical pore defects on the inner surface layer prevent damage to the surface quality of the machined part due to crack propagation during cutting and also contribute to material removal during machining. A reasonable element ratio and low-temperature annealing ensure the mechanical properties of the material.

Description

Technical Field

[0001] This invention relates to the field of powder bed additive manufacturing technology, specifically a low-cost, easy-to-cut, medium-strength titanium alloy rapid prototyping method. Background Technology

[0002] Powder bed additive manufacturing technology is based on laser or electron beams sweeping and spreading powder layer by layer along a computer-preset path, causing the powder to melt and solidify, and accumulating layer by layer to form a part. It is especially suitable for the preparation of complex titanium alloy parts.

[0003] Currently, commonly used titanium alloy materials such as TC4(Ti-6Al-4V) and TA15(Ti-6.5Al-1Mo-1V-2Zr) have excellent comprehensive mechanical properties, with tensile strength reaching 800 MPa and elongation after fracture reaching 10%. However, they use a large number of alloying elements, and the prices of V and Zr are relatively high, resulting in a high total cost.

[0004] Powder bed additive manufacturing technology typically processes parts with a surface roughness of Ra 10–20 μm. Directly printed parts often do not meet usage requirements. It is necessary to set allowances during the forming process and then perform subsequent machining to obtain parts with the required dimensions.

[0005] Titanium alloys are more difficult to machine. The poor thermal conductivity of titanium alloys leads to high cutting temperatures, and the low elastic modulus results in a large contact area between the machined surface and the flank face, which in turn leads to more severe tool wear. Summary of the Invention

[0006] To address the aforementioned problems, this invention proposes a low-cost, easy-to-cut, medium-strength titanium alloy rapid prototyping method.

[0007] A low-cost, easy-to-machine, medium-strength titanium alloy part rapid prototyping method, the specific steps of which are as follows:

[0008] S1. Preparation of raw material metal powder:

[0009] S11. Metal powder is prepared by electrode induction melting gas atomization process using 50 mm diameter titanium alloy bars. The composition of the titanium alloy bars is compensated for element loss during the powder preparation process.

[0010] S12. First, evacuate the melting and atomization chambers to 1 Pa, then backfill with low-pressure argon gas.

[0011] S13. The melting process for the end face of the bar stock is 30-40 KW, the bar stock feed rate is 0.4-1 mm / s, the atomizing gas is argon, and the pressure is 2-7 MPa.

[0012] S14. The powder is sieved to select powders that meet the requirements of the laser selective melting process;

[0013] S15. The prepared powder contains 1.5-2.75% aluminum, 1-1.8% manganese, less than 0.045% oxygen, and contains Ti and unavoidable impurities.

[0014] S2. Printing of part blanks:

[0015] S21. Based on the part model, add 0.5 to 1 mm allowance to all dimensions (length, width, and height) and use laser selective melting process to print the blank.

[0016] S22. A blank is formed on a substrate, including the interior of the blank, the inner surface layer of the blank, and the outer surface layer of the blank.

[0017] S23. Set the internal parameters of the blank;

[0018] S24. The inner surface layer of the blank is connected to the interior of the blank. The inner surface layer 3 of the blank is a single pass. The outer surface layer of the blank is connected to the inner surface layer of the blank. The outer surface layer of the blank is no less than two passes.

[0019] S25. The inner surface of the blank is processed and formed by setting specific process parameters, and near-spherical pore defects are formed based on the keyhole effect.

[0020] S26. Process the outer surface layer of the blank and shape it by setting specific process parameters;

[0021] S27. The outer surface layer of the blank has a low energy density and a narrow molten pool width. The overlap between the molten pool at the outline and the internal formed area is insufficient, resulting in a lack of fusion defects.

[0022] S28. Incomplete fusion defects are formed on the outer surface of the blank, and the incomplete fusion defects have sharp corners;

[0023] S29. Near-spherical pore defects are formed on the inner surface of the blank;

[0024] S3. Part post-processing:

[0025] The blank and the substrate are subjected to overall heat treatment;

[0026] S4, Finishing:

[0027] The blank is separated from the substrate by wire cutting process, and the outer surface of the blank is machined to obtain a part whose dimensions meet the requirements of use.

[0028] In step S11, the composition of the master alloy bar is 1.75-3% aluminum, 1.2-2% manganese, less than 0.03% oxygen, and the balance is Ti and impurities.

[0029] In step S14, powder with a particle size of 15–53 μm is screened out. The powder yield in this particle size range reaches 30%, and the oxygen increment is less than 0.015%.

[0030] The parameters for step S23 are: laser power 150-200 W, scanning speed 800-1000 mm / s, and pass spacing 0.09-0.12 mm.

[0031] The inner surface processing technology of the blank in step S25 is as follows: laser power 90-120 W, scanning speed 200-400 mm / s, and pass spacing 0.09-0.12 mm.

[0032] The surface layer processing technology of the blank in step S26 is as follows: laser power 90-120 W, scanning speed 1000-1200 mm / s, and pass spacing 0.09-0.12 mm.

[0033] The temperature for heat treatment in step S3 is 500–600°C.

[0034] The beneficial effects of this invention are as follows: the inner surface layer of the blank is connected to the interior of the blank and is processed in a single pass; the outer surface layer of the blank is connected to the inner surface layer and is processed in at least two passes. Based on the appropriate energy density, the interior of the blank is nearly fully dense. The formation of unfused defects in the outer surface layer of the blank is beneficial for machining. The formation of near-spherical pore defects in the inner surface layer of the blank avoids damage to the surface quality of the machined part caused by the extension of cracks in the outer surface layer of the blank during the cutting process, and also helps to remove material during the machining process to a certain extent. Only a small amount of aluminum and manganese alloying elements are added, combined with a specific laser selective melting process and a low-temperature annealing process, so that the material obtains good mechanical properties, with tensile strength reaching above 850 MPa, yield strength reaching above 740 MPa, elongation after fracture reaching above 15%, and U-shaped specimen impact absorption energy reaching above 55 J. Attached Figure Description

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0036] Figure 1 This is a schematic cross-sectional view of the blank formed by the laser selective melting process of the present invention;

[0037] Figure 2 This is a schematic diagram of surface defects in the blank of the present invention;

[0038] Figure 3 This is a schematic diagram of the material microstructure after annealing treatment according to the present invention. Detailed Implementation

[0039] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below.

[0040] like Figures 1 to 3 As shown, a low-cost, easy-to-cut, medium-strength titanium alloy part rapid prototyping method is described, and its specific steps are as follows:

[0041] S1. Preparation of raw material metal powder:

[0042] S11. Metal powder is prepared by electrode induction melting gas atomization process using 50 mm diameter titanium alloy bars. The composition of the titanium alloy bars is compensated for element loss during the powder preparation process.

[0043] S12. First, evacuate the melting and atomization chambers to 1 Pa, then backfill with low-pressure argon gas.

[0044] S13. The melting process for the end face of the bar stock is 35 KW, the bar stock feed rate is 0.6 mm / s, the atomizing gas is argon, and the pressure is 3.5 MPa.

[0045] S14. The powder is sieved to select powders that meet the requirements of the laser selective melting process;

[0046] S15. The prepared powder contains 2.2% aluminum, 1.5% manganese, and 0.038% oxygen, with the amount of Ti and unavoidable impurities.

[0047] S2. Printing of part blanks:

[0048] S21. Based on the part model, add 0.5 to 1 mm allowance to all dimensions (length, width, and height) and use laser selective melting process to print the blank.

[0049] S22. A blank is formed on a substrate 1, including a blank interior 2, a blank inner surface layer 3 and a blank outer surface layer 4.

[0050] S23. Set the two parameters inside the blank, and ensure that the interior of the blank is nearly fully dense based on the set appropriate energy density.

[0051] S24. The inner surface layer 3 of the blank is connected to the interior 2 of the blank. The inner surface layer 3 of the blank is a single pass. The outer surface layer 4 of the blank is connected to the inner surface layer 3 of the blank. The outer surface layer 4 of the blank is no less than two passes.

[0052] S25. The inner surface layer 3 of the blank is processed. The inner surface layer of the blank has a high energy density. Specific process parameters are set to form a near-spherical porosity defect 5 based on the keyhole effect.

[0053] S26. Process the outer surface layer 4 of the blank by setting specific process parameters to form it;

[0054] S27. The outer surface layer 4 of the blank has a low energy density, a narrow molten pool width, and insufficient overlap between the molten pool at the outline and the internal formed area, resulting in an incomplete fusion defect 6.

[0055] S28. Incomplete fusion defect 6 is formed on the outer surface layer of the blank. The incomplete fusion defect has sharp corners, which are easy to form stress concentration after being subjected to force, and are easy to remove by machining.

[0056] S29. Near-spherical pore defects 5 are formed in the inner surface layer 3 of the blank, which avoids damage to the surface quality of the machined parts caused by the extension of cracks in the outer surface layer 4 of the blank during the cutting process, and to a certain extent helps to remove materials during the machining process.

[0057] S3. Part post-processing:

[0058] The blank and substrate 1 are subjected to overall heat treatment to maintain the fine α' structure formed during the selective laser melting process and to restore the dislocations, thereby improving the plasticity and toughness to a certain extent. The tensile strength of the material after treatment is 870 MPa, the yield strength is 750 MPa, the elongation after fracture is 16.5%, and the impact absorption energy of the U-shaped specimen is 58 J.

[0059] S4, Finishing:

[0060] The blank is separated from the substrate 1 by wire cutting process, and the outer surface 4 of the blank is machined to obtain a part whose dimensions meet the requirements of use.

[0061] In step S11, the master alloy rod composition is 2.5% aluminum, 1.6% manganese, and 0.026% oxygen, with the balance being Ti and impurities. The metal powder is prepared using an electrode induction melting gas atomization process. The oxygen content of the powder is 0.012% higher than that of the master alloy rod. Compared with traditional TC4(Ti-6Al-4V) and TA15(Ti-6.5Al-1Mo-1V-2Zr), the element content is lower, effectively controlling the cost.

[0062] The formation of near-spherical pore defects on the inner surface of the blank avoids damage to the surface quality of the machined parts caused by the extension of cracks on the outer surface of the blank during the cutting process, and also helps to remove material during the machining process to a certain extent. Only a small amount of aluminum and manganese alloying elements are added, combined with a specific laser selective melting process and a low-temperature annealing process, so that the material obtains good mechanical properties, with tensile strength reaching over 850 MPa, yield strength reaching over 740 MPa, elongation after fracture reaching over 15%, and U-shaped specimen impact absorption energy reaching over 55 J.

[0063] In step S14, powder with a particle size of 15–53 μm is screened out. The powder yield in this particle size range reaches 30%, and the oxygen increment is 0.012%.

[0064] The parameters for step S23 are: laser power 180 W, scanning speed 800 mm / s, and channel spacing 0.1 mm.

[0065] The processing technology for the inner surface layer 3 of the blank in step S25 is a laser power of 100 W, a scanning speed of 400 mm / s, and a pass spacing of 0.1 mm.

[0066] The processing technology for the outer surface layer 4 of the blank in step S26 is a laser power of 120 W, a scanning speed of 1200 mm / s, and a pass spacing of 0.11 mm.

[0067] The temperature for heat treatment in step S3 is 550°C.

[0068] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely prisms of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A low-cost, easy-to-cut, medium-strength titanium alloy rapid prototyping method, characterized in that: The specific steps are as follows: S1. Preparation of raw material metal powder: S11. Metal powder is prepared by electrode induction melting gas atomization process using 50 mm diameter titanium alloy bars. The composition of the titanium alloy bars is compensated for element loss during the powder preparation process. S12. First, evacuate the melting and atomization chambers to 1 Pa, then backfill with low-pressure argon gas. S13. The melting process for the end face of the bar stock is 30-40 KW, the bar stock feed rate is 0.4-1 mm / s, the atomizing gas is argon, and the pressure is 2-7 MPa. S14. The powder is sieved to select powders that meet the requirements of the laser selective melting process; S15. The prepared powder contains 1.5-2.75% aluminum, 1-1.8% manganese, less than 0.045% oxygen, and the balance is Ti and unavoidable impurities. S2. Printing of part blanks: S21. Based on the part model, add 0.5 to 1 mm to all dimensions (length, width, and height) and use laser selective melting process to print the blank. S22. A blank is formed on a substrate (1), including the interior (2) of the blank, the inner surface layer (3) of the blank, and the outer surface layer (4) of the blank. S23. Set the internal (2) parameters of the blank; S24. The inner surface layer (3) of the blank is connected to the interior (2) of the blank. The inner surface layer (3) of the blank is a single pass. The outer surface layer (4) of the blank is connected to the inner surface layer (3). The outer surface layer (4) of the blank is no less than two passes. S25. The inner surface layer (3) of the blank is processed and formed by setting specific process parameters, and a near-spherical porosity defect (5) is formed based on the keyhole effect. S26. Process the outer surface layer (4) of the blank and set specific process parameters to form it; The outer surface layer (4) of the blank has a low energy density and a narrow molten pool width. The overlap between the molten pool at the outline and the internal formed area is insufficient, resulting in an incomplete fusion defect (6). The incomplete fusion defect has sharp corners. S3. Part post-processing: The blank and the substrate (1) are subjected to overall heat treatment; S4, Finishing: The blank is separated from the substrate (1) by wire cutting process, and the outer surface layer (4) of the blank is machined to obtain a part whose size meets the requirements of use.

2. The method for rapid prototyping of low-cost, easy-to-cut, medium-strength titanium alloy parts according to claim 1, characterized in that: In step S11, the composition of the master alloy bar is 1.75-3% aluminum, 1.2-2% manganese, less than 0.03% oxygen, and the balance is Ti and impurities.

3. The method for rapid prototyping of low-cost, easy-to-cut, medium-strength titanium alloy parts according to claim 1, characterized in that: In step S14, powder with a particle size of 15–53 μm is screened out. The powder yield in this particle size range reaches 30%, and the oxygen increment is less than 0.015%.

4. The method for rapid prototyping of low-cost, easy-to-cut, medium-strength titanium alloy parts according to claim 1, characterized in that: The parameters for step S23 are: laser power 150-200 W, scanning speed 800-1000 mm / s, and pass spacing 0.09-0.12 mm.

5. The method for rapid prototyping of low-cost, easy-to-cut, medium-strength titanium alloy parts according to claim 1, characterized in that: The processing technology of the inner surface layer (3) of the blank in step S25 is as follows: laser power 90-120 W, scanning speed 200-400 mm / s, and pass spacing 0.09-0.12 mm.

6. The method for rapid prototyping of low-cost, easy-to-cut, medium-strength titanium alloy parts according to claim 1, characterized in that: The processing technology for the outer surface layer (4) of the blank in step S26 is a laser power of 90-120 W, a scanning speed of 1000-1200 mm / s, and a pass spacing of 0.09-0.12 mm.

7. The method for rapid prototyping of low-cost, easy-to-cut, medium-strength titanium alloy parts according to claim 1, characterized in that: The temperature for heat treatment in step S3 is 500–600°C.

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