Shrinkage Porosity Prediction Using Casting Simulation Amit V. Sata

117 Pages·2010·8.13 MB·English

Shrinkage Porosity Prediction Using
Casting Simulation

M. Tech. Dissertation

submitted in partial fulfilment of the requirements
for the degree of

Master of Technology
(Manufacturing Engineering)

by
Amit V. Sata
(08310301)

Guide
Dr. B. Ravi

Department of Mechanical Engineering
INDIAN INSTITUTE OF TECHNOLOGY BOMBAY
2010
Dissertation Approval Certificate

This is to certify that Mr. Amit V. Sata (08310301) has satisfactorily completed his
dissertation titled “Shrinkage Porosity Prediction using Casting Simulation” as a part
of partial fulfillment of the requirements for the award of the degree of Master of
Technology in Mechanical Engineering with a specialization in Manufacturing
Technology at Indian Institute of Technology Bombay.

Chairman External Examiner

Internal Examiner Guide

Date:
Mechanical Engineering Department,
IIT Bombay - Mumbai
Declaration of Academic Integrity

“I declare that this written submission represents my ideas in my own words and where
others' ideas or words have been included, I have adequately cited and referenced the
original sources. I also declare that I have adhered to all principles of academic honesty
and integrity and have not misrepresented or fabricated or falsified any
idea/data/fact/source in my submission. I understand that any violation of the above will
be cause for disciplinary action as per the rules of regulations of the Institute”

Date: Signature
Place: Name: Amit V. Sata
Abstract 

Shrinkage porosity is one of the most common defects in castings. Various existing
techniques of shrinkage porosity prediction like modulus and equi-solidification time and
criterion function have been reviewed. Various criteria functions including Niyama
criterion, dimensionless Niyama criterion, Lee et al. criterion and Franco criterion for
prediction of shrinkage porosity have been studied in this work.

From literature, L shape casting has been analyzed for predicting location of shrinkage
porosity using solidification simulation. Simulation result is comparable with available
experimental result. Threshold values of Lee et al., Davis, Franco and Bishop criterion for
cast steel have been established by comparing results with Niyama criterion.

Benchmark casting, a combination of three T-Junction, has been cast and analyzed to
understand dependency of shrinkage defect size on geometric parameters and thermal
parameters. The experiments were carried out for Ductile iron (500/7), plain carbon steel
(1005 steel) and stainless steel (SS 410). These experimental data are used to set limiting
temperature gradient values in AutoCAST®. Further, simulation experiments were carried
out by varying thickness ratio from 0.25 to 1.5. The result of experiments and simulations
are used as input to regression analysis to evolve a set of empirical equations to predict
shrinkage porosity defect size in T junction considering the effect of geometric parameter
alongwith thermal parameters. Further, an empirical model of SS 410 is validated by
casting of T junction which is having thickness ratio and length ratio of 1.75 and 5
respectively. The predicted size of shrinakge defect is approximately matching with
observed size of defect.

Keywords: Shrinkage porosity, Casting simulation, Criterion function, Plain carbon steel,
Stainless steel, SG Iron, LM 6 (Al Alloy).

i
Table of Contents

Abstract i
Table of Contents ii
List of Figures iv
List of Tables vi
Nomenclatures viii

1 INTRODUCTION 1
1.1 Porosity in Metal Casting 1
1.2 Need of Defect Prediction 3
1.3 Organization of Report 3

2 LITERATURE REVIEW 4
2.1 Classification and Formation of Porosity 4
2.2 Factors Affecting Shrinkage Porosity 8
2.3 Modeling of shrinkage porosity 10
2.4 Casting Solidification Simulation 12
2.4.1. Finite element method 15
2.4.2. Vector element method 16
2.5 Shrinkage Porosity Prediction 17
2.5.1. Modulus and equi-solidification time method 17
2.5.2.Criterion function method 19
2.6 Summary 31

3 PROBLEM DEFINITION 34
3.1 Motivation 34
3.2 Goal, Scope and Objectives 35
3.3 Approach to Project 35

4 SHRINAKGE DEFECT LOCATION 37
4.1 Approach to Predict Location of Shrinkage Porosity 37
4.1.1. Solidification simulation using FEM 38
4.1.2. Solidification simulation using VEM 44
4.2 Summary 46

ii
5 SHRINAKGE DEFECT SIZE PREDICTION 47
5.1 Benchmark shape 47
5.2 Solidification Simulation of Benchmark Shape 49
5.2.1 Solidification simulation : Ductile iron 51
5.2.2 Solidification simulation : Plain carbon steel 53
5.2.3 Solidification simulation : Stainless steel 55
5.3 Casting Experiements and Results 57
5.3.1 Ductile iron 57
5.3.2 Plain carbon steel 63
5.3.3 Stainless steel 67
5.4 Empirical Model Development 71
5.4.1 Approach 71
5.4.2 Ductile iron 76
5.4.3 Plain carbon steel 79
5.4.4 Stainless steel 82
5.5 Summary 87

6 SUMMARY AND FUTURE WORK 89
8.1 Summary 89
8.2 Future work 91

Annexure I : Comparison of Casting Simulation Software 93
Annexure II : Data for Regression Analysis – Ductile iron 95
Annexure III : Data for Regression Analysis - Plain Carbon Steel (AISI 1005) 97
Annexure IV : Data for Regression Analysis – SS 410 99

References 101
Acknowledgement 105

iii
List of Figures

Figure Description Page
1.1 Porosity in Casting 2

2.1 Solidification of a bar casting 6

2.2 Representation of the origin of porosity as section thickness is increased. 8

2.3 Shrinkage prediction by modulus method 18
2.4 Shrinkage porosity prediction by equisolidification Method 19
2.5 Comparison of Gradient and equisolidification time method 20

2.6 The relation between the experimentally determined G and t 21
f

2.7 The relation between the experimentally determined critical Niyama
criterion and the calculated t 22
f

2.8 Schematic of a 1-D mushy zone solidifying with constant temperature
gradient, G and isotherm velocity, R 24

2.9 (a) Relation of thermal gradient and porosity content 29
(b) Relation of solidus velocity and porosity content 29

2.10 (a) Porosity content as a function of solidification time. 29
(b) Prediction of porosity by feeding efficiency parameter. 29

4.1 Approach to locate shrinkage porosity 40
4.2 Geometric parameters of L shape casting 42
4.3 Modelling and meshing: cast steel L shape casting 42

4.4 Solidification simulation of L junction using FEM 43

4.5 Solidification simulation using VEM 45
5.1 Benchmark shape 48
5.2 3D model of Benchmark Shape 49
5.3 Temperature dependent (a) Specific heat (b) Density : Ductile iron 51
5.4 Solidification simulation using FEM and VEM: Ductile iron 52

5.5 Temperature dependent (a) Thermal conductivity (b) Specific heat (c) 53
Density: Plain carbon steel

iv
Figure Description Page

5.6 Solidification simulation using FEM and VEM: Plain carbon steel 54

5.7 Temperature dependent (a) Thermal conductivity (b) Specific heat (c) 55
Density: Stainless steel

5.8 Solidification simulation using FEM and VEM: Stainless steel 56

5.9 Wooden Patterns for Casting 58
5.10 Layout, runner, gating and cavity of casting – Ductile iron 59
5.11 Setup of casting – Ductile iron 60
5.12 Benchmark casting – Ductile iron 60
5.13 Porosity in benchmark casting – Ductile iron 62
5.14 Layout, runner, gating and cavity of casting – Plain carbon steel 64
5.15 Setup of casting – Plain carbon steel 64
5.16 Benchmark casting – Plain carbon steel 65
5.17 Porosity in benchmark casting – Plain carbon steel 66
5.18 Layout, runner, gating and cavity of casting – Stainless steel 68
5.19 Setup of casting – Stainless steel 68
5.20 Benchmark casting – Stainless steel 69
5.21 Porosity in benchmark casting – Stainless steel 70
5.22 Maximum gradient 73
5.23 Adjustment of percent limiting value of gradient in AutoCAST® 73
5.24 Relationship between thickness ratio (R ) and limiting value of gradient
1
(G) for Junction 1, 2 and 3 – Ductile iron 77

5.25 Relationship between thickness ratio (R ) and limiting value of gradient
1
(G) for Junction 1, 2 and 3 - Plain Carbon Steel 80

5.26 Relationship between thickness ratio (R ) and limiting value of gradient
1
(G) for Junction 1, Junction 2 and Junction 3 – SS 410 83

5.27 T junction casting for validation – SS 410 85

5.28 Feed path : validation casting 86
5.29 Hotspot: Validation casting 86

v
List of Tables
Table Description Page
2.1 Categories of approach on the basis of literature 13

2.2 Proposed and calculated critical values of several solidification parameters
for centreline porosity prediction 21

2.3 Thermal parameters based criteria for porosity prediction 32
4.1 Nomenclature for L junction 41
4.2 Properties of Cast steel and sand mould 41
4.3 Input parameters for Cast steel 42
4.4 Comparison of various Criteria for case I 44
5.1 Variations in benchmark shape 48
5.2 Input parameters for solidification simulation using FEM 50
5.3 Chemical Composition: Ductile iron 59
5.4 Experimental details: Ductile iron 59
5.5 Surface sink and Shrinkage porosity distribution - Ductile iron 61
5.6 Chemical Composition: Plain carbon steel 63
5.7 Experimental details: Plain carbon steel 64
5.8 Porosity distribution - Plain carbon steel 67
5.9 Chemical Composition: Stainless steel 67
5.10 Experimental details: Stainless steel 68
5.11 Porosity distribution - Stainless steel 71
5.12 Limiting value of gradient for junction 1, 2 and 3 – Ductile iron 76
5.13 Regression Statistics – Ductile iron 78
5.14 Regression analysis – Ductile iron 79
5.15 Limiting value of gradient for junction 1, 2 and 3 - Plain carbon steel 80
5.16 Regression Statistics – Plain carbon steel 81
5.17 Regression analysis – Plain carbon steel 81
5.18 Limiting value of gradient for junction 1, 2 and 3 - Stainless steel 82
vi
Table Description Page
5.19 Regression Statistics – Stainless steel 84
5.20 Regression analysis – Stainless steel 84
5.21 Co efficient of empirical model 88
6.1 Threshold Value of Various Criterion Function 90

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