CN111633208B

CN111633208B - Method for controlling printing forming quality by controlling powder fluidity

Info

Publication number: CN111633208B
Application number: CN202010376085.9A
Authority: CN
Inventors: 褚夫众; 侯娟; 张和; 张恺; 杨义; 黄爱军
Original assignee: University of Shanghai for Science and Technology
Current assignee: University of Shanghai for Science and Technology
Priority date: 2020-05-07
Filing date: 2020-05-07
Publication date: 2022-09-06
Anticipated expiration: 2040-05-07
Also published as: CN111633208A

Abstract

The invention provides a method for controlling the printing forming quality by controlling the powder fluidity, which sequentially dries a metal powder sample in a vacuum box; placing the dried metal powder in a rheometer device for operation; processing and analyzing the data through a computer to obtain a fluidity index; printing the metal powder by using selective laser melting printing equipment; and a step of carrying out density statistics on the printed sample by using a microscope and analysis software, and making range limitation on the fluidity parameters of the metal powder, so that a product with good forming quality can be effectively printed, and the process application range of evaluating the fluidity of the metal powder is widened.

Description

Method for controlling printing forming quality by controlling powder fluidity

Technical Field

The invention relates to the technical field of selective laser melting, in particular to a method for controlling the printing forming quality by controlling powder fluidity.

Background

In recent years, the industry has been rapidly developed, and as one of the technologies of Additive Manufacturing, the Selective Laser Melting (SLM) reduces the limitation on the size and shape of parts, and increases the Manufacturing capability of lightweight parts to a greater extent, and also reduces the waste of resources due to the recyclable powder, which leads to a great increase in the Manufacturing capability of parts. The selective laser melting technology is mainly applied to the fields of aerospace, medical treatment and automation. The aluminum alloy has light density and good elasticity, can realize light weight of parts, and is applied to the field of selective laser melting. The powder is used as a raw material of a selective laser melting technology, the flowability influences the powder laying quality during printing of parts, and if the flowability of the powder is poor, the uniformity of powder laying cannot be ensured, so that the quality of subsequent printed parts is poor. Therefore, the flowability is an important index for evaluating the powder, and the quality of the printing forming quality can be predicted.

The traditional powder fluidity evaluation methods mainly comprise methods such as a Hall flow meter, an angle of repose, a dispersion degree, a apparent density and the like. Each of these assessment methods has its own unique advantages, but also has limitations.

The hall-flow meter measures the loose density value of the powder using a 5mm funnel by expressing the flowability of the powder as the time required for 50g of metal powder to flow through a standard funnel. The angle of repose was observed by naturally depositing the metal powder, and observing the maximum angle formed between the slope and the powder in a static state. The powder has good flowability and the smaller the angle of repose. The disadvantage of both methods is that each test gives a single datum and flowability cannot be assessed for some powders that cannot be used with hall flow meters. The degree of dispersion refers to the degree of scattering of the powder when the powder falls from a certain height, and if the degree of splashing is too large, the powder spreading effect in the laser melting process of the selected area is affected. The method has the disadvantages that the data obtained by the test is relatively single, and for AlSi10Mg powder, the evaluation method is easy to cause experimental safety hazards. The loose density refers to the density of the alloy powder in a natural fill in a particular container.

The powder fluidity evaluation methods are all tested under different experimental environments, and experimental errors are easily caused, so that the judgment result is influenced.

At present, the highest printing quality of the selective laser melting technology can reach 99.5 percent or more, but the adopted method mostly adopts an experiment trial-and-error method to achieve the aim, so that the experiment cost and time cost are increased, and manpower and material resources are greatly lost.

Therefore, it is important to establish a method for controlling the quality of the selected laser melting printing by determining the flowability of the Al — Si powder.

Disclosure of Invention

The invention aims to provide a method for controlling the quality of printing formation by controlling powder flowability, which has wide application range and accurate quality control.

In order to achieve the above object, the present invention provides a method for controlling the quality of a print formation by controlling the flowability of a powder, comprising the following steps:

step 1: placing the metal powder sample in a vacuum box for drying;

step 2: placing the dried metal powder in a rheometer device for operation;

and step 3: processing and analyzing the data by a computer to obtain a fluidity index;

and 4, step 4: printing the metal powder by using selective laser melting printing equipment;

and 5: and carrying out density statistics on the printed sample by using a microscope and analysis software.

Preferably, the metal powder is an Al — Si-based metal powder.

Preferably, the fluidity indexes of the Al — Si-based metal powder are: the elementary flow energy is in the range of 180-201mJ, the specific flow energy is in the range of 2-3.2mJ/g, the apparent density is in the range of 1.41-1.6g/ml, the tap apparent density is in the range of 1.6-1.68g/ml, the inflation energy is in the range of 2-3mJ, the compressibility is in the range of 3-5% and the shear stress is in the range of 2.5-3.2 kPa.

Preferably, in step 1, the metal powder is dried in a vacuum oven for 8 hours under a vacuum atmosphere at a temperature of 80 ℃.

Preferably, in step 5, before density statistics is performed on the printed sample, a pretreatment process is performed on the printed sample, wherein the pretreatment process comprises the steps of grinding, polishing and cleaning the printed sample in sequence.

Preferably, the sanding is performed by using sand paper, and the polishing solvent is a 0.05 mu m solution of BUEHLER MasterPrepTM; the cleaning is carried out by adopting absolute ethyl alcohol.

Compared with the prior art, the invention has the advantages that: the control method of the invention has no strict limitation on the powder raw materials, has wide applicability and no special requirement on the material size, can repeatedly test experiments for many times, can effectively distinguish the quality of printing and forming quality for the powder materials with different fluidity, and can well predict the laser melting and printing and forming quality of a selected area, wherein in the fluidity parameters, the basic flow energy is 180 plus 201mJ, the specific flow energy is 2-3.2mJ/g, the apparent density is 1.41-1.6g/ml, the tap apparent density is 1.6-1.68g/ml, the inflation energy is 2-3mJ, the compressibility is 3-5%, and the shear stress is within the range of 2.5-3.2kPa, and can effectively print out a sample with better forming quality. The method greatly widens the application range of the process for evaluating the fluidity of the metal powder, and greatly saves the cost of experimental expenses and time cost.

Drawings

FIG. 1 is a schematic diagram of an experimental setup used for powder flowability test according to the present invention.

FIG. 2 is a Scanning Electron Microscope (SEM) morphology of three AlSi10Mg powders according to an embodiment of the present invention.

FIG. 3 is a diagram showing the flow analysis of three AlSi10Mg powders in the example of the present invention.

FIG. 4 is an optical microscopy analysis of three AlSi10Mg powder printed samples according to an embodiment of the present invention. .

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be further described below.

The specific embodiment and the advantageous effects of the present invention will be further explained by three AlSi10Mg powder materials, namely, the AlSi10Mg powder material used is a commercially available powder material having a particle size distribution in the range of 20 to 63 μm, the rheometer used is a commercially available rheometer, and the selective laser melting apparatus used is a commercially available apparatus. Other auxiliary experimental materials are commercially available.

As shown in fig. 1, a fluidity tester is used to detect the fluidity index of the metal powder; wherein, 1 is a computer, 2 is two data lines, and 3 is a fluidity tester.

Procedure for AlSi10Mg powder flowability assessment:

putting the three kinds of powder into a drying box to be dried for 8 hours in a vacuum atmosphere;

opening the rheometer equipment, and operating according to the instruction;

and after the data collection is finished, downloading, processing and analyzing the data by adopting a computer.

The method comprises the following steps of evaluating the printing forming quality of AlSi10Mg in the field of selective laser melting:

printing a sample of squares at 15 x 15 using AlSi10Mg powder;

polishing the sample to a mirror surface through the experimental steps of grinding, polishing and the like;

and carrying out density statistics on the printed sample through microscope equipment and data analysis software.

TABLE 1

Samples of the AlSi10Mg powder prepared in the examples were subjected to Scanning Electron Microscope (SEM) morphology analysis and flowability testing as well as density statistical analysis of the print forming quality.

Table 1 shows the chemical compositions of three AlSi10Mg powder samples, which meet the DINEN-1706 standard. Fig. 2 is a morphology diagram of three samples under a scanning electron microscope, and it can be seen from the diagram that the sphericity of the

samples

1 and 2 is better, the powder particles with irregular shapes and sizes are less, and the sample 2 has a little agglomerated powder. The sphericity of the powder of sample 3 is poor, a large amount of agglomeration occurs, the uniformity of the particle size is poor, the fluidity of the powder is affected, and the powder is easily spread unevenly.

Table 2 and fig. 3 are the rheological properties of the three samples obtained by the rheometer data acquisition. In the flowability test experiment, the powder to be tested was filled into a container by recording the torque applied as the rotating blade passes through the powder bed. Some parameters were obtained: basic kinetic energy is the energy required for the blades to rotate downward within a given powder volume. Specific flow energy is the energy required to measure the upward unconstrained movement of the blade. The aeration energy experiment is to introduce air into the bottom of the powder bed and calculate the aeration energy by measuring the decrease in energy. The degree of energy reduction depends on the physical properties of many powders, such as cohesion, morphology, density. Permeability is an indicator of how easily a material can transfer fluid (in this case air) through the powder volume. Compressibility of the powder is obtained while consolidation energy is obtained by compressing the sample with a vented piston under increased normal stress. The compression index is calculated by dividing the compressed density by the pre-treatment bulk density measured before compression begins. By rotation of the tablet press, the powder is subjected to a certain degree of shear stress during the experiment to determine whether the powder is susceptible to clogging or non-flow due to shear forces during flow. The rotating wall friction module consists of a container holding the powder sample and a wall friction head to generate vertical and rotational stress. The wall friction head moves down to the powder surface, and when the disc contacts the top of the powder, normal stress is generated, and the wall friction angle value is obtained.

The lower the data of basic flow energy, specific flow energy, wall friction angle, shear stress, compressibility, consolidation energy and aeration energy are, the better the powder flowability is, the less blocking and no flow are easy to occur, and the better the powder laying quality is.

It can be clearly seen from the radar plots that in the pre-treatment bulk density and tap bulk density values, sample 1 > sample 2 > sample 3, mainly because sample 1 is more spherical than the other two. Sample 3 > sample 2 > sample 1 among other parameters, such as values of basic flow energy, compressibility, gas filling energy, etc. Based on the analysis of various data, it can be seen that the fluidity of sample 1 is better than that of sample 2 than that of sample 3.

TABLE 2

Fig. 4 is a longitudinal section picture of three AlSi10Mg powder samples taken by an optical microscope after being printed by the same process parameters of the same selective laser melting device. It can be clearly seen from the figure that the sample 1 and the sample 2 have no obvious defects, the sample has high density, and the characteristic of a selective laser melting printing molten pool is obvious. However, in sample 3, there were many defects and large defects were formed, and the sample density was low. Wherein, three samples are obtained by data analysis software, and the density of the sample 1 is 99.947%. Sample 2 had a density of 99.866% and sample 3 had a density of 97.550%.

Therefore, the quality of the printing forming quality can be controlled and predicted by analyzing the powder flowability, and the method has important significance for printing samples, experimental planning and the like in the field of actually selected laser melting.

The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any way. Any person skilled in the art can make any equivalent substitutions or modifications on the technical solutions and technical contents disclosed in the present invention without departing from the scope of the technical solutions of the present invention, and still fall within the protection scope of the present invention without departing from the technical solutions of the present invention.

Claims

1. A method for controlling the quality of printing formation by controlling powder flow is characterized by comprising the following steps:

step 1: placing a metal powder sample in a vacuum box for drying;

step 2: placing the dried metal powder in a rheometer device for operation;

and 3, step 3: processing and analyzing the data through a computer to obtain a fluidity index;

and 4, step 4: printing the metal powder meeting the fluidity index by using selective laser melting printing equipment;

and 5: carrying out density statistics on the printed sample by using a microscope and analysis software;

the metal powder is Al-Si series metal powder; the fluidity indexes of the Al-Si series metal powder are as follows: the elementary flow energy is in the range of 180-201mJ, the specific flow energy is in the range of 2-3.2mJ/g, the apparent density is in the range of 1.41-1.6g/ml, the tap apparent density is in the range of 1.6-1.68g/ml, the inflation energy is in the range of 2-3mJ, the compressibility is in the range of 3-5% and the shear stress is in the range of 2.5-3.2 kPa.

2. The method for controlling the print forming quality by controlling the powder flowability according to claim 1, wherein in step 1, the metal powder is dried in a vacuum oven for 8 hours at a temperature of 80 ℃ under a vacuum atmosphere.

3. The method for controlling the quality of printing and forming by controlling the powder flowability according to claim 1, wherein in the step 5, before the density statistics is performed on the printing sample, the printing sample is subjected to a pretreatment process, and the pretreatment process comprises the steps of sequentially grinding, polishing and cleaning the printing sample.