Q&A

C3P Cast Designer縮孔體積量測

Cast Designer 鑄造模流分析結果中,其中一項是縮孔縮松分析。

透過分析結果,可以幫助判斷鑄件縮孔產生位置,還可透過工具輔助量測縮孔體積。

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FEM與CFD求解器差異

C3P Cast Designer 鑄造模流分析軟體-流動氣孔模擬

FEM:Finite ElementMethod,有限元技術,擅長於多物理場耦合,流動+溫度+應力。

CFD:Computational FluidDynamics,計算流體力學,擅長於模擬自由表面的流動,處理紊流、飛濺、大自由液面,考慮液體表面張力。

經常聽到大家在討論FEM與CFD的差異性,下方轉錄了Quora討論的內容提供大家參考。

對於C3P Software來說,Cast Designer一開始是以FEM作為主要求解器,提供凝固最佳分析結果搭配基本的流動分析,在大部分的產品上都有很好的準確性。

2016年開始,C3P Sofeware Cast Designer將有限元FEM與流體力學CFD完美地結合、同時提供雙求解器。

2017起許多使用者陸續導入於設計流程,利用CFD求解器獲得更準確的流動結果,精確地模擬出金屬充型過程中氣泡的產生和流動路徑,提供氣孔缺陷的預測帶來更準確的工程判斷。

C3P Cast Designer 鑄造模流分析軟體-流動氣孔模擬

轉錄 https://www.quora.com/What-is-the-difference-between-FEA-and-CFD

What is the difference between FEA and CFD?

“Most physical phenomenon – be it structural behavior or fluid flow can be described in terms of Partial Differential Equations (PDEs). There are closed-form analytical solutions to these PDEs for simple boundary conditions.

However, in the case of a general boundary conditions, it is not possible to obtain analytical solutions. Atleast this is the case with our today’s knowhow. Alternatively numerical methods are used to solve these equations. Some of the commonly used numerical methods / techniques include

  • Finite element method (FEM)
  • Boundary element method (BEM)
  • Discrete element method (DEM)
  • Finite volume method (FVM)
  • Finite difference method (FDM)

The first two are more commonly used in structural-related problems; the third for problems that involve particulate behavior; the last two are commonly used in fluid-flow related problems.

Finite Element Method as generally known is what can be actually called a Bubnov-Galerkin approach / method. This is suitable for solving only certain types of PDEs and not everything. For example: Fluid-flow problems are described by Navier-Stokes equations. Due to the presence of advection-convection terms (or first order terms) in this problem, FEM does not perform well in certain conditions. This is the primary reason FEM is not that widely used for fluid-flow problems.

Lately, there have been alternative technique called “Petrov-Galerkin Approach” or even “Petrov Discontinuous Galerkin Methods” that have shown promise towards using the idea of FEM in fluid-flow as well.

Computational Fluid Dynamics (CFD) would related to computational techniques that can be used to solve fluid-flow problems. Here generally FDM or FVM are more commonly used to solve the Navier-Stokes equations due to the above described issue.”

冷卻水管分析設定

水管冷卻計算三步驟:

1. 流道分析,完成充填平衡、排除氧化渣缺陷,找出熱傳不均勻導致的縮孔位置。

2. 虛擬模恆定溫度帶入冷卻水管計算,確認顯著熱節區域的改善幅度。
以壓鑄來說,只有顯著的熱節區域,才有機會通過佈置冷卻水管得到徹底消除,因為熱量就是集中在這個位置,冷卻水管的埋設也不能立竿見影的有效。畢竟模具有熱平滑效應,加冷卻水管類似於“隔靴搔癢”。
而且冷卻水管不能佈置得太靠近模具表面,否則會有裂紋滲漏。

3. 真實模具網格計算,存在兩種情況:
A,起始溫度均勻分佈,計算分析後依照熱傳各區不同,影響鑄件凝固變化。
B,起始溫度非均勻分佈,帶入循環計算後的模具溫度場,更符合實際生產結果。因為達
到穩態模溫後,高溫區域和低溫區域的溫差可能有100多度。

無論是虛擬模或真實模具的分析,都可以幫助模具設計找到改善方向,冷卻水路多少能讓熱平衡更好一些,即使解決不了顯著的宏觀縮孔,但是對於微觀縮鬆和組織緻密性是有一定幫助的。

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