fundamentals of the lost foam casting process by mark ainsworth operations development manager –...
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Fundamentalsof the
Lost Foam Casting Processby
Mark Ainsworth
Operations Development Manager – Scaw Metals Group
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Themes of the Presentation
Process Overview
Process Attributes
Process Issues
Process Summary & Conclusions
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Characterisation of the Process
No Mould Cavity
Disposable Pattern
Bondless Moulding Media
Core Elimination
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Main Steps in the Process “White Side”
Step 1
Filling Pre-Expander
Step 2
Pre-Expanding
Step 3
Patternmaking
Step 4
Pattern Assembly
Step 5
Cluster Assembly
Step 6
Coating
Step 7
Drying
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Main Steps in the Process “Black” Side
Step 1
Flask Positioning
Step 2
Cluster Location
Step 3
Sand Filling & Compaction
Step 4
Flask Transport
Step 5
Mould Casting
Step 6
Casting Cooling
Step 7
Casting Removal
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Overview of the Process
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Derivatives of the Process
Pattern Manufacture
Pattern Removal
“Replicast” Process
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Main Advantages of the Process Tighter Dimensional Tolerances
Dimension (mm) Tolerance (+/-)
< 25 mm 0.17 mm
25 – 80 mm 0.25 mm
80 – 125 mm 0.30 mm
125 – 175 mm 0.43 mm
175 – 250 mm 0.003 per mm
> 250 mm 0.002 per mm
Rough Guide < 175 mm 0.50 mm
> 175 mm 0.80 mm
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Main Advantages of the Process No Cores Are Required
Large Design Freedom Controllable Wall Thickness No Chaplets No Fins No Mismatch No Core Defects No Sand Mix Problems
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Main Advantages of the Process No Parting Lines
No Stripping Taper Multiple Layers Possible Optimal Positioning of Downsprues and Risers No Fins No Mismatch
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Main Advantages of the Process Combination/Consolidation of Parts
Glue Instead of Fasteners High Freedom of Design High Added Value Possibilities
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Themes of the Presentation
Process Overview
Process Attributes
Process Issues
Process Summary & Conclusions
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Attributes of the Process
Casting Alloys Size Range of Castings Cost of the Process Viable Manufacturing Quantities Casting Integrity Tooling Requirements
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Themes of the Presentation
Process Overview
Process Attributes
Process Issues
Process Summary & Conclusions
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Critical Issues with the Process Bead Size & Fusion
A Cold Tool Surface or a Short Steam Step Produces “Underfusion”.
- rough, beady surface, low strength
Extended Steam Exposure or Inadequate Cooling Produces “Overfusion”.- wavy surface, high density
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Critical Issues with the Process Dimensional Stability of the Pattern
Inadequate Cooling of the Tool Can Produce “Post Expansion”.
- soft, warm beads expand locally after ejection from the tooling.
- dimensional instability.
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Critical Issues with the Process Glue Lines
Energy of Pattern Degradation Estimated to be 900 kJ/kg of foam.
Hot Melt Glue Has a Density Approximately 40 times that of the Pattern.
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Critical Issues with the Process Pattern Density
Under compaction
Over compaction
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Critical Issues with the Process Coating Variation
Coating PenetrationBetween FoamBeads
Permeability Conductivity Viscosity Wicking Capability
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Critical Issues with the Process Casting Speed & Pattern Entrapment
Fill Pressure: 68.9 kPa
Unstable, discontinuous metal front which entraps degradation products before they can escape from the mould. Average fill rate = 24 mms-1
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Critical Issues with the Process Casting Speed & Pattern Entrapment
Fill Pressure: 68.9 kPa
Unstable, discontinuous metal front which entraps degradation products before they can escape from the mould. Average fill rate = 24 mms-1
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Critical Issues with the Process Casting Speed & Pattern Entrapment
Fill Pressure: 27.6 kPa
Cellular metal front with a slightly convex shape. Front profile exhibits small irregularities at approximately 5mm spacing. Average fill rate = 13 mms-1
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Critical Issues with the Process Casting Speed & Pattern Entrapment
Fill Pressure: 24.1 kPa
Stable, continuous metal front with very slightly concave shape. Average fill rate = 5 mms-1
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Critical Issues with the Process Casting Speed & Pattern Entrapment
Weibull Plot of UTS Results from Plates Cast at Different
Fill Pressures
m = 23,20
m = 10,67
-4,0
-3,0
-2,0
-1,0
0,0
1,0
2,0
18,2 18,4 18,6 18,8 19,0 19,2 19,4
ln o (MPa)
ln ln
(1/
S)
27.6 kPa Fill Pressure
24.1 kPa Fill Pressure
Linear (24.1 kPa FillPressure)Linear (27.6 kPa FillPressure)
The Weibull modulus (m) suggests that plates filled by means of a planar front contain less defects.
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Critical Issues with the Process Casting Speed & Pattern Entrapment
Pore-type Defect- Found on all fracture surfaces
- Size variation between 400 and 1500 µm
Film-type Defect- Found only where non-planar metal fronts were observed
- Size variation between 1 and 4.5 mm
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Critical Issues with the Process Casting Speed & Pattern Entrapment
Glass-sided Mould Containing Glucose Syrup
Mercury reservoir & displacement cylinder
Flow control valve
Secondary actuation cylinder
Compressed air inlet
Viscosities:
Mercury = 1.22 mPas
Glucose = 95 Pas
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Critical Issues with the Process Casting Speed & Pattern Entrapment
Planar metal front up to a filling velocity of about 15 mms-1
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Critical Issues with the Process Emissions & Sand Residues
Product Weight %
Hydrogen 0.03Methane 0.3Ethylene 0.5Ethane 0.04Propene 0.02Pentene and Hexane 0.01Benzene 2.1Toluene 4.5Xylene and Ethylbenzene 1.0Styrene 71.0Naphthanlene 0.8Carbon 0.3Dimers, Trimers and higher molecular weight compounds
15.0
Residue Build-up in the Moulding Sand
Hazardous Airborne Pollutants (HAPS)- Lost Foam = 1.02 lbs/ton of metal
- Furan = 1.08 lbs/ton of metal- Greensand = 0.64 lbs/ton of metal
MEL (styrene) - 100 ppm (8 hrs)
- 250 ppm (15 min)
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Themes of the Presentation
Process Overview
Process Attributes
Process Issues
Process Summary & Conclusions
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Process Summary & Conclusions Some Useful Advantages Practical Casting Size Range & Output
Limited Large Range of Process Variables Gating System Flow Control not Possible Filling Speed an Order of Magnitude TOO
Low Unsuitable for Castings in Highly Stressed
Operational Fields
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Handtmann scrap levels ≈ 10%
BMW reverting to gravity and pressure die casting for aluminium heads and blocks.
Honda retaining die casting processes for their aluminium components.
“Lost foam casting is on the decline at General Motors because the relatively low ultimate strength of aluminum cast in unbonded sand is not up to the high demand of current and future engine designs.”
Process Summary & Conclusions
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Process Summary & Conclusions Conclusions
Low to Medium Volumes Highly Complex Parts (potentially joined) Low Stress Applications Weight between 1 – 100 kg (aluminium)
A Niche Process for Niche MarketsRequiring Very Tight Parameter Control