CN109590468B

CN109590468B - Control method of powder sticking on the surface of austenitic stainless steel components in laser direct additive manufacturing

Info

Publication number: CN109590468B
Application number: CN201811494574.3A
Authority: CN
Inventors: 张屹; 吴家柱; 陈寰宇; 赵鹏辉; 刘安丽; 韦海英
Original assignee: Hunan University
Current assignee: Hunan University
Priority date: 2018-12-07
Filing date: 2018-12-07
Publication date: 2021-07-23
Anticipated expiration: 2038-12-07
Also published as: CN109590468A

Abstract

The invention discloses a method for controlling powder sticking on the surface of austenitic stainless steel components by laser direct additive manufacturing. The influences of pulse frequency and duty cycle on the powder sticking on the surface of the sample are obtained respectively; the range of pulse frequency and duty cycle that can effectively suppress the surface sticking is determined according to the experimental data. The invention can effectively control the serious problem of powder sticking on the surface of austenitic stainless steel components by laser direct additive manufacturing; in addition, the invention does not need to add additional devices, and for some parts with low surface quality requirements, no post-processing process is required. Therefore, the method is simple and easy to implement and the manufacturing cost is low.

Description

Control method for manufacturing surface sticky powder of austenitic stainless steel component by laser direct additive manufacturing

Technical Field

The invention relates to advanced forming technologies such as metal laser direct additive manufacturing and laser cladding, can be applied to the fields of industrial manufacturing or repairing such as aerospace, automobiles, ships and energy sources, and particularly relates to a control method for the surface powder adhesion of an austenitic stainless steel component through laser direct additive manufacturing.

Background

The laser direct additive manufacturing technology belongs to the field of laser additive manufacturing, and is an advanced manufacturing technology with a good application prospect. The technology highly integrates the advanced concepts of laser cladding, layered manufacturing and digital manufacturing, and drives the rapid and direct manufacturing of the metal component by three-dimensional CAD data. Compared with the traditional material reducing process, the laser direct material increase manufacturing technology has the remarkable advantages of free forming, controllable structure performance, short manufacturing flow, short manufacturing period and the like. The laser direct additive manufacturing technology is favored and applied in the industrial fields of aerospace, automobile, medical treatment, mold manufacturing and the like because the laser direct additive manufacturing technology is suitable for the rapid direct manufacturing of metal, alloy, ceramic, metal matrix composite materials and the like.

In the laser direct additive manufacturing process, a laser beam firstly melts a substrate to form a molten pool, then the molten pool captures a part of powder particles synchronously conveyed by air force, and finally, after the laser beam leaves, the molten pool is rapidly solidified and coated on the substrate. In most cases, the distribution area of the powder beam on the substrate is larger than the area of the molten pool. Therefore, in the trailing edge and both side regions of the molten pool where the temperature is close to the solidification temperature, a part of the powder particles are adhered to the surface of the additive product because they have not been melted in time. According to the existing literature and a large number of experimental studies conducted by us, the surface dusting phenomenon is extremely serious when austenitic stainless steel components are formed by using a continuous laser-based direct additive manufacturing technology. This phenomenon greatly worsens the surface quality of stainless steel components, which in turn leads to failure to meet practical engineering requirements, while also limiting the wide application of laser direct additive manufacturing techniques to some extent. Of course, the existing additive and subtractive composite manufacturing technology can effectively solve the problem. But with a corresponding rise in time and manufacturing costs. In addition, the problem of powder adhesion of the closed cavity and the inner runner is a difficult problem which cannot be solved by subsequent material reduction manufacturing. Therefore, it is more important to research an effective method for controlling the powder adhesion on the surface of the austenitic stainless steel additive component.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a control method for powder adhesion on the surface of an austenitic stainless steel component through laser direct additive manufacturing aiming at the defects of the prior art, so that the powder adhesion degree of the austenitic stainless steel component through traditional continuous laser direct additive manufacturing is effectively reduced, the processing performance of the laser direct additive manufacturing technology is improved, and the manufacturing cost is reduced.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a control method for manufacturing powder adhered to the surface of an austenitic stainless steel component by laser direct additive manufacturing mainly comprises the following implementation processes: carrying out a quasi-continuous laser direct additive manufacturing test of austenitic stainless steel powder based on a single-factor method, and respectively obtaining the influence rule of pulse frequency and duty ratio on powder adhesion on the surface of a sample; according to experimental data, the pulse frequency for effectively inhibiting the surface from being adhered with the powder is determined to be 20-60 Hz, and the duty ratio is determined to be 20%.

The pulse frequency is 1/pulse period, and the duty ratio is pulse width × 100/pulse period.

The austenitic stainless steels include 304, 316, and 316L stainless steels.

The specific process for carrying out the quasi-continuous laser direct additive manufacturing test of the austenitic stainless steel powder comprises the following steps:

1) drying the selected austenitic stainless steel powder;

2) selecting proper inert gases as carrier gas and protective gas;

3) setting proper laser power, pulse waveform, laser spot size, scanning speed, powder feeding amount, lifting amount and carrier gas flow;

4) selecting pulse frequency and duty ratio as test factors, setting each test factor to be not less than four levels, and simultaneously keeping all process parameters in the step 8) constant; respectively carrying out single-factor tests of the influence of pulse frequency and duty ratio on surface powder adhesion;

5) according to the step 9), preparing the sample by adopting a laser direct additive manufacturing process, analyzing the powder adhesion amount on the surface of the sample, further obtaining the influence rule of the pulse frequency and the duty ratio on the powder adhesion amount respectively, and further determining the process parameter with the minimum powder adhesion amount on the surface of the sample.

Compared with the prior art, the invention has the beneficial effects that: the method can effectively control the problem of serious powder adhesion phenomenon on the surface when the austenitic stainless steel component is directly manufactured by the additive by laser; in addition, the invention does not need to add an additional device, and does not need to adopt a post-treatment process for parts with low surface quality requirements. Therefore, the method is simple and easy to implement and has low manufacturing cost.

Drawings

FIG. 1 is an output waveform of quasi-continuous laser power used in the present invention;

fig. 2 (a) - (d) are images of samples prepared at different duty cycles according to the present invention; (a) a duty cycle of 20%; (b) a duty cycle of 35%; (c) a 50% duty cycle; (d) a duty cycle of 65%;

fig. 3 (a) to (d) are images of samples prepared at different pulse frequencies; (a) a pulse frequency of 20 Hz; (b) a pulse frequency of 40 Hz; (c) a pulse frequency of 60 Hz; (d) a pulse frequency of 80 Hz.

Detailed Description

The present invention will be further described with reference to the following examples.

Example 1

The laser is made of YLS-5000-S4 type Yd of IPG photoelectric company: the laser output wavelength of the fiber laser is 1.07 mu m, and the fiber laser can output two modes of continuous laser and quasi-continuous laser. The quasi-continuous laser is output in a rectangular pulse wave (as shown in figure 1), the pulse frequency of the quasi-continuous laser is adjustable within 1-5000 Hz, and the duty ratio is adjustable within 0-100%. A coaxial powder feeding head with four nozzles was selected. The powder material is spherical 316L austenitic stainless steel prepared by a gas atomization process, and the particle size range of the powder material is 45-125 mu m. The substrate is a 316L stainless steel substrate with the thickness of 10 mm. The chemical composition of 316L stainless steel is shown in table 1. The carrier gas and the protective gas are high-purity argon with the purity of more than or equal to 99.999 percent. To improve powder flow, the powder was dried in a drying oven for more than 30 minutes prior to testing. During the test, the laser power is output in a rectangular waveform, and the laser power, the laser spot diameter, the scanning speed, the powder feeding amount, the lifting amount and the carrier gas flow are respectively set to be 900W, 1.32mm, 400mm/min, 11.63g/min, 0.13mm and 10 l/min. The sample piece adopts a single-pass multi-layer reciprocating printing strategy, the printing length is 40mm, and the number of printing layers is 80. The duty cycle and pulse frequency settings are shown in table 2.

TABLE 1316 chemical composition of stainless steel powder (% by mass)

TABLE 2 laser direct additive manufacturing test parameters

The test scheme is as follows: firstly, loading dried stainless steel powder, and operating a powder feeder without laser until four nozzles on a coaxial powder feeding head have no powder blocking phenomenon and output stable powder flow; then, a stainless steel substrate is placed, and the distance between the bottom end of the coaxial powder feeding head and the substrate is adjusted to be 14.5mm by taking the stainless steel substrate as a reference; thirdly, printing the sample pieces in sequence according to preset process parameters until the completion; and finally, observing and comparing the sample to obtain the influence rule of the pulse frequency and the duty ratio on the sticky powder, and determining the optimal range of the pulse frequency and the duty ratio according to the influence rule.

Results and conclusions: fig. 2 is an image of the sample corresponding to the pulse frequency of 20Hz and the duty ratio of 20% -65%, and it can be seen that the powder adhesion amount (e.g. black area in the figure) on the surface of the sample is increased significantly with the increase of the duty ratio, and the powder adhesion amount corresponding to the duty ratio of 20% is significantly less than the powder adhesion amount corresponding to the duty ratios of 50% and 65%. FIG. 3 is a sample image corresponding to a duty ratio of 20% and a pulse frequency of 20-80 Hz. As can be seen in the figure, when the pulse frequency is within the range of 20-60 Hz, the powder adhering amount on the surface of the sample piece is almost unchanged; when the pulse frequency was increased to 80Hz, the amount of the sticky powder was increased, but the increase was slight. The analysis can obtain that the influence of the duty ratio of the quasi-continuous laser on the sticky powder is very obvious, and the influence of the pulse frequency on the sticky powder is small, particularly within the pulse frequency of 20-60 Hz; the duty ratio is reduced, so that the powder sticking amount on the surface of the sample piece can be effectively inhibited.

Claims

1. A control method for direct laser additive manufacturing of powder on the surface of austenitic stainless steel components, characterized in that the main realization process of the method is: carrying out quasi-continuous laser direct additive manufacturing of austenitic stainless steel powder based on a single factor method Experiments were carried out to obtain the influence of pulse frequency and duty cycle on the powder sticking on the surface of the sample respectively; according to the experimental data, it was determined that the pulse frequency to effectively suppress the surface powder sticking was 20-60 Hz, and the duty cycle was 20%;

The specific process of conducting a quasi-continuous laser direct additive manufacturing test of austenitic stainless steel powder includes:

1) Dry the selected austenitic stainless steel powder;

2) Select appropriate inert gas as carrier gas and protective gas;

3) Set the appropriate laser power, pulse waveform, laser spot size, scanning speed, powder feeding amount, lifting amount and carrier gas flow;

4) Select the pulse frequency and duty cycle as the test factors, and set no less than four levels for each test factor, while keeping all the process parameters in step 3) constant; A single factor test of influence;

5) According to step 4), the laser direct additive manufacturing process is used to prepare the sample, and then the amount of sticky powder on the surface of the sample is analyzed, and then the influence of the pulse frequency and the duty cycle on the amount of sticky powder is obtained, and then the surface of the sample is determined. Process parameters with the least amount of sticky powder;

The quasi-continuous laser is output as a rectangular pulse wave;

Among them, the laser power, laser spot diameter, and scanning speed were set to 900W, 1.32mm, and 400mm/min, respectively.

2. The method for controlling powder sticking on the surface of austenitic stainless steel components manufactured by laser direct additive manufacturing according to claim 1, wherein the pulse frequency=1/pulse period, and the duty cycle=pulse width×100/pulse cycle.

3 . The method for controlling powder sticking on the surface of austenitic stainless steel components manufactured by laser direct additive manufacturing according to claim 1 , wherein the austenitic stainless steel is 304, 316 or 316L stainless steel. 4 .