# 基于瞬态有限元分析的薄壁结构扫描路径优化Scanning Path Optimization of Thin-Walled Structures Based on Transient Finite Element Analysis

DOI: 10.12677/MET.2019.82013, PDF, HTML, XML, 下载: 416  浏览: 1,100  科研立项经费支持

Abstract: Selective laser melting (selective laser melting, SLM) is a complex process, which involves the process of metal solid-liquid conversion, heat conduction, heat radiation, and so on. The warping deformation of molded parts has always been the main reason for influencing the forming precision of parts and restricting the development of SLM technology. Because of fast heating and heat dissipation of thin-walled parts, the distribution of temperature field is very uneven, which is more prone to warping deformation. In order to ensure the normal process of SLM and improve the forming precision of thin-walled parts, the distribution of temperature field must be controlled effectively. In this paper, based on the APDL language in ANSYS software, the transient finite element analysis of temperature field, stress field and warping deformation of the simple thin-walled structure in SLM processing was performed. The thin-walled structure model was es-tablished. The temperature field and stress field of multi-layer forming in six scanning modes were compared, and the warping deformation of thin-walled structures in different scanning modes was also compared. The relationship between temperature gradient, internal stress and warping deformation was investigated, and the mechanism affecting the forming precision of parts was analyzed from the whole forming process. According to the above, a kind of combination scanning forming method for thin-wall structure was proposed.

1. 引言

2. SLM过程瞬态有限元分析基本理论

SLM过程温度场的有限元分析属于非线性瞬态有限元分析和三维热传导问题，其瞬态温度场满足导热微分方程 [9] ：

$p{c}_{p}\frac{\partial T}{\partial t}=\frac{\partial }{\partial x}\left({K}_{q}\frac{\partial T}{\partial x}\right)+\frac{\partial }{\partial y}\left({K}_{q}\frac{\partial T}{\partial y}\right)+\frac{\partial }{\partial z}\left({K}_{q}\frac{\partial T}{\partial z}\right)+{H}_{r}$ (1)

SLM过程中残余应力的有限元分析主要用到的理论为热弹塑性理论，该理论是通过跟踪SLM成型过程中热循环的每一步热应变来计算应力和应变。在分析SLM成型过程中残余应力和翘曲变形的同时，可以详细的掌握其变化的一般规律，是在应力场分析中应用较多的一种分析理论 [10] 。

1) 在塑形区内，材料服从流动和强化准则；

2) 材料服从Von Mises屈服准则；

3) 力学性能和应力应变在很小的时间段内增量呈线性改变；

4) 温度应变和弹性与塑性应变紧密相关。

1) 屈服准则

$\stackrel{¯}{\sigma }=\frac{\sqrt{2}}{2}\sqrt{{\left({\sigma }_{1}-{\sigma }_{2}\right)}^{2}+{\left({\sigma }_{2}-{\sigma }_{3}\right)}^{2}+{\left({\sigma }_{3}-{\sigma }_{1}\right)}^{2}}$ (2)

2) 流动准则

${\left\{d\epsilon \right\}}_{p}=\zeta \frac{\partial \stackrel{¯}{\sigma }}{\partial \left\{\sigma \right\}}$ (3)

3) 硬化准则

3. 扫描成型方式与有限元模型的建立

Figure 1. Different scanning molding methods for thin-walled structures in SLM

SLM过程瞬态有限元分析的基本步骤主要包括材料属性的定义、有限元模型的建立、网格的划分、移动热源的加载和生死单元的处理等。本文分析所选用的材料为Q235B，建立了薄壁结构有限元分析模型，其网格划分示意图如下图2所示。

Figure 2. Schematic diagram of grid division of thin-walled structure

4. 温度场结果对比及分析

Figure 3. Distribution of temperature field in different scanning modes

5. 应力场结果对比及分析

Figure 4. Stress field distribution in different scanning modes

Figure 5. Maximum residual stress of different scanning modes

6. 翘曲变形结果对比及分析

Figure 6. Maximum warping deformation of different scanning modes

Figure 7. Deformation of different scanning modes along the X direction

Figure 8. Deformation of different scanning modes along the Y direction

Figure 9. Deformation of different scanning modes along the Z direction

Figure 10. Warping deformation of different scanning modes along different directions

7. 薄壁结构多层扫描成型方式的选择及优化

Figure 11. Layering combined scanning molding method

Figure 12. Stress field distribution of layering combined scanning molding method

Figure 13. Warping deformation of layering combined scanning molding method

Figure 14. Warping deformation of different scanning modes

8. 结论

1) 在不同扫描方式成型薄壁结构的过程中，分区扫描和光栅式扫描的散热效果较差，外螺旋扫描的散热效果较好，Z字形扫描在沿着Y方向的温度梯度较大，沿着Y方向容易形成较大的残余应力。六种扫描方式的最大残余应力最大值由大到小排序为：(a) Z字形扫描；(b) 分区扫描；(c) 光栅式扫描；(f) 轮廓偏移扫描；(d) 内螺旋扫描；(e) 外螺旋扫描。

2) 通过分析比较薄壁结构件在不同扫描方式下的翘曲变形量可得，轮廓偏移扫描和内螺旋扫描的翘曲变形量最小，而光栅式扫描和分区扫描的翘曲变形量较大。薄壁结构件沿着壁厚方向的变形是影响总的翘曲变形量的主要因素。

3) 通过分析六种扫描成型方式的温度场、应力场和其沿着不同方向的翘曲变形量，本文分析提出一种分层组合式扫描成型方式。通过分析得出，采用分层组合式扫描方式成型薄壁结构件，可减小翘曲变形量提高成型精度，相比已有的六种扫描方式，分层组合式扫描具有温度场和应力场较均匀，扫描成型精度高的特性。

2016年湖北省重大创新专项：面向潜艇泵喷推进器大型金属关键部件的微铸锻铣复合增材制造技术与装备(2017AAA003)。

“数字制造装备与技术”国家重点实验室开放课题(编号：DMETKF2017002)。

NOTES

*通讯作者。

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