METHOD FOR FORMING HORIZONTAL OVERHANGING STRUCTURE WITHOUT VERTICAL SUPPORT IN SELECTIVE LASER MELTING

• US 20200130057A1
• Filed: 12/25/2019
• Published: 04/30/2020
• Est. Priority Date: 09/02/2019
• Status: Active Grant

• Current Assignee: Intelligent Manufacturing Institute of Hefei University of Technology
• Original Assignee: Intelligent Manufacturing Institute of Hefei University of Technology
• Inventors: Zhi, Xinlei, Yuan, Zijun, Chen, Xiangdong, Yan, Zhaohua
• Granted Patent: US 11,267,050 B2
• Time in Patent Office: Days
• CPC Class Codes: B22F 10/28 Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
• CPC Class Codes: B22F 10/36 of energy beam parameters
• CPC Class Codes: B22F 10/366 Scanning parameters, e.g. hatch distance or scanning strategy
• CPC Class Codes: B22F 10/385 Overhang structures
• CPC Class Codes: B22F 12/43 pulsed; frequency modulated
• CPC Class Codes: B22F 2301/35 Iron
• CPC Class Codes: B22F 2998/10 Processes characterised by the sequence of their steps
• CPC Class Codes: B33Y 10/00 Processes of additive manufacturing
• CPC Class Codes: B33Y 50/02 for controlling or regulating additive manufacturing processes
• CPC Class Codes: Y02P 10/25 Process efficiency

Abstract

A method for forming a horizontal overhanging structure without vertical support in selective laser melting, comprising: sequentially forming an initial layer, a repair layer and a conventional layer, wherein initial layer is printed by scanning at a speed set lower than the conventional speed using a laser spot in a defocused state, so that the Plateau-Rayleigh instability effect occurs in each track, to form an initial layer with a specific texture structure; repair layer is printed on upper surface of the initial layer by scanning at a speed set higher than conventional speed in a continuous-wave laser output mode using a laser spot in a focused state, and completes the transition from transition process parameter to conventional process parameters within the set number of processing layers; and conventional layer is printed on upper surface of repair layer using conventional process parameters, to form a horizontal overhanging structure without vertical support.

Claims

1. A method for forming a horizontal overhanging structure without vertical support in selective laser melting, comprising:

sequentially forming an initial layer, a repair layer and a conventional layer, wherein

the initial layer is printed by scanning at a speed set lower than the conventional speed using a laser spot in a defocused state, so that the Plateau-Rayleigh instability effect occurs in each track, to form an initial layer with a specific texture structure;

the specific texture structure refers to;

forming texture different from the scanning direction using the Plateau-Rayleigh instability effect which occurs in the track;

the repair layer is printed on the upper surface of the initial layer by scanning at a speed set higher than the conventional speed in a continuous-wave laser output mode using a laser spot in a focused state, and completes the transition from transition process parameters to conventional process parameters within the set number of processing layers; and

the conventional layer is printed on the upper surface of the repair layer using the conventional process parameters, to form a horizontal overhanging structure without vertical support.

2. The method for forming a horizontal overhanging structure without vertical support in selective laser melting according to claim 1, wherein

the process parameters of the initial layer are set into:

A₁=(1.4-1.7)A₃;

V₁=(10%-40%)V₃;

L₁=(1.3-1.6)L₃;

M₃<

M₁;

where;

A₁ represents the diameter of the A₃ represents the diameter of the scanning laser scanning laser spot of the initial spot of the conventional layer;

layer;

V₁ represents the scanning speed of V₃ represents the scanning speed of the the initial layer, conventional layer;

L₁ represents the scanning spacing L₃ represents the scanning spacing of the of the initial layer, conventional layer;

M₁ represents the linear energy M₃ represents the linear energy density of the density of the initial layer, conventional layer;

the number of the processing layer linear energy density=laser power/scanning of the initial layer is 1;

speed.

3. The method for forming a horizontal overhanging structure without vertical support in selective laser melting according to claim 2, wherein the repair layer is printed on the upper surface of the initial layer using the transition process parameters according to the following two phases:

first phase;

scanning at high speed in a continuous-wave laser output mode;

A₂₁=A₃;

V₂₁=(3-6)V₃;

L₃<

L₂₁<

L₁;

M₂₁=(50%-70%)M₃;

where;

A₂₁ represents the diameter of the V₂₁ represents the scanning speed in the scanning laser spot in the first phase;

first phase;

L₂₁ represents the scanning spacing in the M₂₁ represents the linear energy density in first phase;

the first phase;

the number of the processing layers in the first phase is 2-4, wherein the scanning direction of the first layer is along a non-zero included angle from the scanning direction of the initial layer, and the scanning directions of the subsequent layers are rotated 90°

layer by layer;

second phase;

setting other process parameters into conventional process parameters for selective laser melting except for the linear energy density and scanning spacing;

wherein the linear energy density and scanning spacing are set as follows;

from the line energy density M₂₁, the line energy density of each processing layer in the second phase is increased layer by layer, and from the scanning spacing L₂₁, the scanning spacing of each processing layer in the second phase is reduced layer by layer, so that the transition consistent with all process parameters of the conventional layer is completed within 10-20 processing layers.

4. The method for forming a horizontal overhanging structure without vertical support in selective laser melting according to claim 3, wherein for stainless-steel powder, printing to form a horizontal overhanging structure without vertical support according the following steps:

Step 1;

unidirectionally scanning using continuous-wave laser, wherein the laser power is 40 W, the laser spot diameter is 90-100 μ

m, the scanning speed is 0.1 m/s, the scanning spacing is 65 μ

m, the layer thickness is 30 μ

m, and the number of the processing layer is 1;

linear energy density M=400 J/m;

Step 2;

first phase;

unidirectionally scanning using continuous-wave laser, wherein the laser power is 300 W, the laser spot diameter is 60-70 μ

m, the scanning speed is 1.5 m/s, the scanning spacing is 60 μ

m, the layer thickness is 30 μ

m, and the number of the processing layers is 2-4;

linear energy density M₂₁=200 J/m;

second phase;

first, unidirectionally scanning using pulse laser with the duty ratio of 30%, and gradually increasing the average laser power between 80-90 W, wherein the laser spot diameter is 60-70 μ

m, the scanning speed is 0.3 m/s, the scanning spacing is 60 μ

m, the layer thickness is 30 μ

m, and the number of the processing layers is 5; and

then, keeping other parameters unchanged, and gradually increasing the average laser power between 90-100 W, wherein the scanning spacing is 50 μ

m, and the number of processing layers is 10;

Step 3;

unidirectionally scanning using pulse laser with the duty ratio of 30%, wherein the average laser power is 100 W, the laser spot diameter is 60-70 μ

m, the scanning speed is 0.3 m/s, the scanning spacing is 50 μ

m, and the layer thickness is 30 μ

m;

linear energy density M₃=333 J/m.