阅读说明：本技术 一种基于许用激光能量密度的增材制造工艺 (Material increase manufacturing process based on allowable laser energy density ) 是由 杨建春 李娜 赵坤 顾海 毛宁 姜杰 李彬 王铖 于 2020-12-18 设计创作，主要内容包括：本发明公开了一种基于许用激光能量密度的增材制造工艺,包括以下步骤：(1)根据材料的比热容C、密度ρ和温差变化ΔT确定材料加工的许用激光能量密度[E-1]；(2)确定材料的影响系数K；(3)根据许用激光能量密度[E-1]以及影响系数K,估算成形达到目标致密度所需的实际最低激光能量密度[E-(min)]；(4)根据成形设备的工作条件,在所需的实际最低激光能量密度[E-(min)]基础上设计选择性激光熔化成形实验。本发明大大减少了加工工艺试凑的次数,提高了材料成型的效率,降低了实验的成本,对SLM制品的研究具有重要的意义。(The invention discloses an additive manufacturing process based on allowable laser energy density, which comprises the following steps of: (1) according to the specific heat capacity of the material C Density, density ρ And change in temperature difference ΔT Determining allowable laser energy density [ E ] for material processing 1 ](ii) a (2) Determining the coefficient of influence of a material K (ii) a (3) According to allowable laser energy density [ E ] 1 ]And coefficient of influence K Estimating the actual minimum laser energy density [ E ] required to achieve the target density min ](ii) a (4) Depending on the working conditions of the forming equipment, the laser energy density is actually the lowest requiredDegree [ E ] min ]And designing a selective laser melting forming experiment on the basis. The invention greatly reduces the trial and error times of the processing technology, improves the material forming efficiency, reduces the experimental cost and has important significance for the research of SLM products.)

1. An additive manufacturing process based on allowable laser energy density, characterized by comprising the steps of:

(1) determining allowable laser energy density [ E ] of material processing according to specific heat capacity C, density rho and temperature difference change Delta T of the material₁]；

(2) Determining an influence coefficient K of the material;

(3) according to allowable laser energy density [ E ]₁]And the coefficient of influence K is also included,estimating the actual minimum laser energy density [ E ] required to shape to achieve the target density_min]；

(4) At the actual minimum required laser energy density [ E ] depending on the operating conditions of the forming apparatus_min]And designing a selective laser melting forming experiment on the basis.

2. The allowable laser energy density-based additive manufacturing process of claim 1, wherein: in the step (1), from the viewpoint of the specific heat capacity of the material, when the material is at the critical point of transition from the normal temperature state to the molten state, the allowable laser energy density theoretically required for the material is:

the formula (1) is simplified to obtain,

[E₁]＝C*ρ*ΔT (2)

wherein, [ E ]₁]The allowable laser energy density theoretically required for the material to be transformed from a normal temperature state to a molten state, C is the specific heat capacity, M is the mass of the material, Δ T is the temperature difference, and ρ is the density of the material.

3. The allowable laser energy density-based additive manufacturing process of claim 2, wherein: in the step (2), the specific process for determining the influence coefficient K of the material is as follows:

(2.1) determining the laser energy density [ E ] actually provided by the equipment according to the heat loss coefficient of the equipment₀]；

(2.2) determining the laser energy density [ Ereal ] of the material actually melted by the equipment according to the absorption and reflectivity of the material to the laser;

(2.3) determining the laser energy density [ Eyl ] required by the material to be completely transformed from the normal temperature state to the molten state;

(2.4) determining the influence coefficient K of the material according to the [ Emi ] ≧ [ E group ].

4. The allowable laser energy density-based additive manufacturing process of claim 3, wherein: in the step (2.1), if the heat loss coefficient of the device is k1, the laser energy density actually provided by the device is:

the formula (3) is simplified to obtain,

[E₀]＝(1-k₁)*E (4)

wherein, [ E ]₀]Laser energy density actually provided for equipment, E laser energy density theoretically provided for equipment, P laser power, V scanning speed, S scanning interval, D powder laying thickness and k₁Is the heat loss coefficient of the device.

5. The allowable laser energy density-based additive manufacturing process of claim 4, wherein: in the step (2.2), the laser absorption rate of the material itself is defined as k₂Then the laser energy density at which the device actually melts the material is:

the formula (5) is simplified to obtain,

[E_{fruit of Chinese wolfberry}]＝(1-k₁)*k₂*E (6)

Wherein, [ E ]_{Fruit of Chinese wolfberry}]Laser energy density, k, for the actual melting of material by the apparatus₂Is the absorption of laser light by the material itself.

6. The allowable laser energy density-based additive manufacturing process of claim 5, wherein: in the step (2.3), the laser energy density required for complete transition of the material from the normal temperature state to the molten state is:

[E_{base of}]＝k₃*C*ρ*ΔT (7)

Substituting the formula (2) into the formula (7) to obtain:

[E_{base of}]＝k₃*[E₁] (8)

Wherein, [ E ]_{Base of}]Laser energy density, k, required for complete transformation of material from ambient to molten state₃For magnification, C is the specific heat capacity, Δ T is the temperature difference, ρ is the density of the material, [ E ]₁]The allowable laser energy density theoretically required for the material to be transformed from a normal temperature state to a molten state.

7. The allowable laser energy density-based additive manufacturing process of claim 6, wherein: in the above step (2.4), according to [ E ]_{Fruit of Chinese wolfberry}]≥[E_{Base of}]And substituting the formula (6) and the formula (8) respectively to obtain:

(1-k₁)*k₂*E≥k₃*[E₁] (9)

the formula (9) is simplified to obtain:

is provided withThe influence coefficient K of the material is obtained by simplifying the formula (10):

where K is the coefficient of influence of the material and E is the theoretical laser energy density provided by the device, [ E₁]For changing the material from normal temperature to molten stateTheoretical required allowable laser energy density, k₁Is the heat loss coefficient of the apparatus, k₂Is the absorption of the material itself to the laser light, k₃Is a magnification factor.

8. The allowable laser energy density-based additive manufacturing process of claim 1, wherein: in the step (3), the actual minimum laser energy density required for forming to reach the target compactness is as follows:

[E_min]＝K*[E₁] (12)

wherein, [ E ]_min]K is the coefficient of influence of the material, [ E ] for the actual minimum laser energy density required to form to achieve the target density₁]The allowable laser energy density theoretically required for the material to be transformed from a normal temperature state to a molten state.

Technical Field

The invention relates to the technical field of additive manufacturing, in particular to an additive manufacturing process based on allowable laser energy density.

Background

Selective Laser Melting (SLM) is an important component of additive manufacturing technology, a type of additive manufacturing technology that has developed in recent years. Compared with other additive manufacturing technologies, the selective laser melting technology is more efficient and convenient, and has a wider development prospect. It can be made directly from single metal or mixed metal powder, and has good mechanical properties, good surface roughness, high density and high dimensional accuracy.

In recent years, many experts and scholars have devoted themselves to the study of SLM technology, and equipment and technology have advanced significantly. However, there are still some drawbacks and disadvantages: 1) most of the research only considers the influence of changing a single process parameter on the mechanical and physical properties of the SLM component, but does not consider the interaction between the material characteristics and the process parameters; 2) the laser energy required by the SLM forming process of different materials needs to be tested repeatedly, and the consumption of manpower and material resources is large. Therefore, the above problems need to be solved.

Disclosure of Invention

The invention aims to solve the technical problem of providing an additive manufacturing process based on allowable laser energy density, greatly reducing the trial and error times of the processing process, improving the material forming efficiency, reducing the experimental cost and having important significance for the research of SLM products.

In order to solve the technical problems, the invention adopts the following technical scheme: the invention discloses an additive manufacturing process based on allowable laser energy density, which is characterized by comprising the following steps of:

(1) determining allowable laser energy density [ E ] of material processing according to specific heat capacity C, density rho and temperature difference change Delta T of the material₁]；

(2) Determining an influence coefficient K of the material;

(3) according to allowable laser energy density [ E ]₁]And an influence coefficient K, estimating the actual minimum laser energy density [ E ] required for forming to reach the target density_min]；

(4) At the actual minimum required laser energy density [ E ] depending on the operating conditions of the forming apparatus_min]And designing a selective laser melting forming experiment on the basis.

Preferably, in the step (1), from the viewpoint of the specific heat capacity of the material, when the material is at a critical point of transition from a normal temperature state to a molten state, the allowable laser energy density theoretically required for the material is:

the formula (1) is simplified to obtain,

[E₁]＝C*ρ*△T (2)

wherein, [ E ]₁]The allowable laser energy density theoretically required for the material to be transformed from a normal temperature state to a molten state, C is the specific heat capacity, M is the mass of the material, Δ T is the temperature difference, and ρ is the density of the material.

Preferably, in the step (2), the specific process for determining the influence coefficient K of the material is as follows:

(2.1) determining the laser energy density [ E ] actually provided by the equipment according to the heat loss coefficient of the equipment₀]；

(2.2) determining the laser energy density [ E ] of the material actually melted by the equipment according to the absorption and reflectivity of the material to the laser_{Fruit of Chinese wolfberry}]；

(2.3) determination of the shape of the Material from Normal temperatureLaser energy density [ E ] required for complete transition of state to molten state_{Base of}]；

(2.4) according to [ E_{Fruit of Chinese wolfberry}]≥[E_{Base of}]And determining the influence coefficient K of the material.

Preferably, in the step (2.1), the heat loss coefficient of the equipment is set to k₁Then, the laser energy density actually provided by the apparatus is:

the formula (3) is simplified to obtain,

[E₀]＝(1-k₁)*E (4)

wherein, [ E ]₀]Laser energy density actually provided for equipment, E laser energy density theoretically provided for equipment, P laser power, V scanning speed, S scanning interval, D powder laying thickness and k₁Is the heat loss coefficient of the device.

Preferably, in the step (2.2), the laser absorption rate of the material itself is k₂Then the laser energy density at which the device actually melts the material is:

the formula (5) is simplified to obtain,

[E_{fruit of Chinese wolfberry}]＝(1-k₁)*k₂*E (6)

Wherein, [ E ]_{Fruit of Chinese wolfberry}]Laser energy density, k, for the actual melting of material by the apparatus₂Is the absorption of laser light by the material itself.

Preferably, in the step (2.3), the laser energy density required for complete transition of the material from the normal temperature state to the molten state is:

[E_{base of}]＝k₃*C*ρ*△T (7)

Substituting the formula (2) into the formula (7) to obtain:

[E_{base of}]＝k₃*[E₁] (8)

Wherein, [ E ]_{Base of}]Laser energy density, k, required for complete transformation of material from ambient to molten state₃For magnification, C is the specific heat capacity, Δ T is the temperature difference, ρ is the density of the material, [ E ]₁]The allowable laser energy density theoretically required for the material to be transformed from a normal temperature state to a molten state.

Preferably, in the above step (2.4), according to [ E ]_{Fruit of Chinese wolfberry}]≥[E_{Base of}]And substituting the formula (6) and the formula (8) respectively to obtain:

(1-k₁)*k₂*E≥k₃*[E₁] (9)

the formula (9) is simplified to obtain:

is provided withThe influence coefficient K of the material is obtained by simplifying the formula (10):

where K is the coefficient of influence of the material and E is the theoretical laser energy density provided by the device, [ E₁]Allowable laser energy density, k, theoretically required for the transition of a material from a normal temperature state to a molten state₁Is the heat loss coefficient of the apparatus, k₂Is the absorption of the material itself to the laser light, k₃Is a magnification factor.

Preferably, in the step (3), the actual lowest laser energy density required for forming to reach the target compactness is:

[E_min]＝K*[E₁] (12)

wherein, [ E ]_min]To achieve target compactness for formingThe actual minimum laser energy density required, K being the coefficient of influence of the material, [ E ]₁]The allowable laser energy density theoretically required for the material to be transformed from a normal temperature state to a molten state.

The invention has the beneficial effects that: the invention greatly reduces the trial and error times of the processing technology, improves the material forming efficiency, reduces the experimental cost and has important significance for the research of SLM products.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments are briefly described below, and it is obvious that the drawings in the following description are only some embodiments described in the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a fitting graph of laser energy density and compactness of 316L stainless steel in the invention.

FIG. 2 is a design drawing of a GH4169 nickel-based experimental forming process in the invention.

FIG. 3 is a fitting graph of laser energy density and compactness of GH4169 in the invention.

Detailed Description

The technical solution of the present invention will be clearly and completely described by the following detailed description.

The invention relates to an additive manufacturing process based on allowable laser energy density, which comprises the following steps of:

(1) determining allowable laser energy density [ E ] of material processing according to specific heat capacity C, density rho and temperature difference change Delta T of the material₁]；

In the above steps, when the material is at the critical point of transition from the normal temperature state to the molten state when analyzed from the specific heat capacity of the material, the allowable laser energy density theoretically required for the material is:

the formula (1) is simplified to obtain,

[E₁]＝C*ρ*△T (2)

wherein, [ E ]₁]The allowable laser energy density theoretically required for the material to be transformed from a normal temperature state to a molten state, C is the specific heat capacity, M is the mass of the material, Δ T is the temperature difference, and ρ is the density of the material.

(2) Determining an influence coefficient K of the material;

in the above steps, the specific process for determining the influence coefficient K of the material is as follows:

(2.1) determining the laser energy density [ E ] actually provided by the equipment according to the heat loss coefficient of the equipment₀]；

The energy density is generally the laser energy density theoretically provided by the SLM device, but considering that a certain heat loss coefficient exists in the SLM laser printing manufacturing process, the laser energy density actually provided by the device can be calculated after the actual situation is considered. Let the heat loss coefficient of the device be k₁Then, the laser energy density actually provided by the apparatus is:

the formula (3) is simplified to obtain,

[E₀]＝(1-k₁)*E (4)

wherein, [ E ]₀]Laser energy density actually provided for equipment, E laser energy density theoretically provided for equipment, P laser power, V scanning speed, S scanning interval, D powder laying thickness and k₁Is the heat loss coefficient of the device.

(2.2) determining the laser energy density [ E ] of the material actually melted by the equipment according to the absorption and reflectivity of the material to the laser_{Fruit of Chinese wolfberry}]；

From the analysis of the characteristics of the material, the absorption and the reflectivity of the laser exist in the material, and after the factors are considered, the practical material of the device can be calculatedThe energy density of the laser of the melting. Let the absorption rate of the material itself to laser light be k₂Then the laser energy density at which the device actually melts the material is:

the formula (5) is simplified to obtain,

[E_{fruit of Chinese wolfberry}]＝(1-k₁)*k₂*E (6)

Wherein, [ E ]_{Fruit of Chinese wolfberry}]Laser energy density, k, for the actual melting of material by the apparatus₂Is the absorption of laser light by the material itself.

(2.3) determination of laser energy Density [ E ] required for complete transition of Material from ambient to molten State_{Base of}]；

When the material is at the critical point from room temperature to the molten state, the required energy cannot completely melt the material, and the material is still in a state of coexisting solid and liquid, so that if the material is completely in the molten state, the material must be multiplied by a magnification k₃Therefore, the laser energy density required for complete transition of the material from the normal temperature state to the molten state is:

[E_{base of}]＝k₃*C*ρ*△T (7)

Substituting the formula (2) into the formula (7) to obtain:

[E_{base of}]＝k₃*[E₁] (8)

Wherein, [ E ]_{Base of}]Laser energy density, k, required for complete transformation of material from ambient to molten state₃For magnification, C is the specific heat capacity, Δ T is the temperature difference, ρ is the density of the material, [ E ]₁]The allowable laser energy density theoretically required for the material to be transformed from a normal temperature state to a molten state.

(2.4) according to [ E_{Fruit of Chinese wolfberry}]≥[E_{Base of}]Determining the influence coefficient K of the material;

in [ E ]_{Base of}]And E_{Fruit of Chinese wolfberry}]In the relationship of [ E ]_{Fruit of Chinese wolfberry}]The energy supplied should be greater than [ E_{Base of}]The energy of the energy transfer device is used for enabling the material to be continuously transferred with the surrounding material after being completely melted; so that the two relation is [ E ]_{Fruit of Chinese wolfberry}]≥[E_{Base of}]And then substituting the formula (6) and the formula (8) respectively to obtain:

(1-k₁)*k₂*E≥k₃*[E₁] (9)

the formula (9) is simplified to obtain:

is provided withThe influence coefficient K of the material is obtained by simplifying the formula (10):

where K is the coefficient of influence of the material and E is the theoretical laser energy density provided by the device, [ E₁]Allowable laser energy density, k, theoretically required for the transition of a material from a normal temperature state to a molten state₁Is the heat loss coefficient of the apparatus, k₂Is the absorption of the material itself to the laser light, k₃Is a magnification factor.

(3) According to allowable laser energy density [ E ]₁]And an influence coefficient K, estimating the actual minimum laser energy density [ E ] required for forming to reach the target density_min]；

In the above steps, the actual minimum laser energy density required for forming to reach the target density is:

[E_min]＝K*[E₁] (12)

wherein, [ E ]_min]K is the coefficient of influence of the material, [ E ] for the actual minimum laser energy density required to form to achieve the target density₁]The allowable laser energy density theoretically required for the material to be transformed from a normal temperature state to a molten state.

(4) At the actual minimum required laser energy density [ E ] depending on the operating conditions of the forming apparatus_min]And designing a selective laser melting forming experiment on the basis.

The invention determines the range of the influence coefficient K value by an experimental method, further determines the actual lowest laser energy density required by forming to reach the target density, and is used for guiding the forming process of different materials.

The invention is demonstrated below by means of a set of examples:

500-mesh spherical 316L stainless steel powder is adopted, and the composition components are shown in Table 1; wherein the particle size distribution (wt.%) is: <15 μm (50%), <30 μm (90%) and an average particle size of 17.11 μm.

TABLE 1316L stainless Steel powder composition Table (%)

The performance parameters of the 316L stainless steel powder are shown in table 2:

TABLE 2316L stainless steel Performance parameter Table

The size of the experimental molded test block is 1cm multiplied by 0.5 cm. The experimental forming process parameters of 316L stainless steel using the orthogonal experimental method are shown in table 3:

watch 3316L stainless steel forming process parameter table

In the final experiment, the density is taken as a standard for testing the quality of SLM forming, so that the density of 16 formed test pieces is measured as shown in Table 4:

TABLE 4316L FORMING CONDITIONS TABLE

As can be seen from table 4, the compacts formed by the above laser energy densities have densities of 90% or more, and the sample specimens having compacts having densities of 95% or more are 2, 3, 4, 5, 6, 11, 12, 13, 14, and 15, according to the allowable energy density of 95% or more defined. The formed part has higher density and good qualification rate. Wherein, the allowable laser energy density of 95% density is an SLM forming process technical index corresponding to the relative density which is artificially made, and means the laser energy density required by processing and manufacturing when the ratio of the SLM forming member density to the printing powder base material density is 95%. At the moment, the physical and mechanical properties of the member are similar to those of the base material, and the actual engineering application can be met. The allowable laser energy density of 95% densification is the minimum standard that is determined artificially to ensure the formation of SLM members, but is not the only standard. Due to different materials and application environments, the relative compactness corresponding to the lowest allowable energy density may be different, and the relative value may be reduced or increased, and is not necessarily limited to the standard of 95%.

In order to conveniently see the relationship between the laser energy density and the density, the data is subjected to fitting operation through origin operation software, an image between the laser energy density and the density and a fitting relational expression are made, and the result is shown in fig. 1;

equation obtained by origin image digital tool fitting:

y＝66.09+0.4375*X-0.00174*X²

calculated, when 95% density is reached, the laser energy density is:

X₁＝92.49J/mm³

X₂＝179.63J/mm³

after observing the fit chart, X should be discarded₂The actual lowest laser energy density at final 95% densification is therefore:

[E_min]＝92.49J/mm³

when the specific heat capacity is viewed, the parameter of the material is substituted into the formula (2), and the allowable laser energy density theoretically required by the material from the normal temperature state to the molten state is obtained as follows:

[E₁]＝C*ρ*△T＝0.502*7.98*1348＝5.4J/mm³

will [ E ]_min]＝92.49J/mm³And [ E₁]＝5.4J/mm³Respectively substituted into the formula (12) to obtain the influence coefficient of the material

The influence coefficient K obtained by the above experiment>17.13, GH4169 alloy powder Molding experiment was conducted, and the laser energy density at 95% densification was estimated to be [ E ]_min]＝K*[E₁]＝18*4.66＝83.88J/mm³。

This data is now demonstrated. GH4169 alloy powder (foreign brand Inconel718 alloy, particle size of 35-45 μm, spherical shape) was used, and the composition thereof is shown in Table 5:

TABLE 5 GH4169 alloy powder composition table (%)

The performance parameters of the GH4169 alloy powder are shown in Table 6:

TABLE 6 GH4169 alloy powder Property parameter Table

The size of the experimental molded test block is 10mm multiplied by 7mm multiplied by 10 mm. Experimental GH4169 forming process parameters using orthogonal experiments are shown in table 7:

TABLE 7 GH4169 Table of forming process parameters

According to the experimental scheme, 16 test pieces of 1cm × 1cm × 0.5cm are finally formed in the experiment, and the overall forming condition is shown in fig. 2.

In the final experiment, the density is taken as a standard for testing the quality of SLM forming, and the density of 16 formed test pieces is measured as shown in Table 8:

TABLE 8 GH4169 Molding cases Table

As can be seen from table 8, the formed parts formed by the laser energy density in the table have a density of 90% or more, and the sample samples of the formed parts having a density of 95% or more are 2, 3, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16 according to the allowable energy density of 95% density defined, and the formed parts have a high pass rate of formed density.

From the perspective of specific heat capacity, substituting the parameters of the material into formula (2) to obtain the theoretically required allowable laser energy density of the material from the normal temperature state to the molten state as follows:

[E₁]＝C*ρ*△T＝435*8300*1293＝4.66J/mm³

data fitting operation is carried out on the data through origin software, so as to obtain an image between the laser energy density and the density and a fitting relational expression, and the result is shown in fig. 3.

Equation obtained by origin image digital tool fitting:

y＝83.63+0.19*X-0.000644*X²

calculated, when 95% density is reached, the laser energy density is:

X₁＝83.22J/mm³

X₂＝213.65J/mm³

after observing the fit chart, X should be discarded₂The actual lowest laser energy density at final 95% densification is therefore:

[E_min]＝83.22J/mm³

and the estimated result 83.88J/mm³In close proximity, the present invention is demonstrated.

The invention has the beneficial effects that: the invention greatly reduces the trial and error times of the processing technology, improves the material forming efficiency, reduces the experimental cost and has important significance for the research of SLM products.

The above-mentioned embodiments are merely descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention, and various modifications and improvements made to the technical solutions of the present invention by those skilled in the art should fall into the protection scope of the present invention without departing from the design concept of the present invention, and the technical contents of the present invention as claimed are all described in the technical claims.