fundamentals of the lost foam casting process by mark ainsworth operations development manager –...

Fundamentalsof the

Lost Foam Casting Processby

Mark Ainsworth

Operations Development Manager – Scaw Metals Group

Themes of the Presentation

Process Overview

Process Attributes

Process Issues

Process Summary & Conclusions

Characterisation of the Process

No Mould Cavity

Disposable Pattern

Bondless Moulding Media

Core Elimination

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

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

Overview of the Process

Derivatives of the Process

Pattern Manufacture

Pattern Removal

“Replicast” Process

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

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

Main Advantages of the Process No Parting Lines

No Stripping Taper Multiple Layers Possible Optimal Positioning of Downsprues and Risers No Fins No Mismatch

Main Advantages of the Process Combination/Consolidation of Parts

Glue Instead of Fasteners High Freedom of Design High Added Value Possibilities


Process Overview

Process Attributes

Process Issues


Attributes of the Process

Casting Alloys Size Range of Castings Cost of the Process Viable Manufacturing Quantities Casting Integrity Tooling Requirements


Process Overview

Process Attributes

Process Issues


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

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.

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.

Critical Issues with the Process Pattern Density

Under compaction

Over compaction

Critical Issues with the Process Coating Variation

Coating PenetrationBetween FoamBeads

Permeability Conductivity Viscosity Wicking Capability

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



Cellular metal front with a slightly convex shape. Front profile exhibits small irregularities at approximately 5mm spacing. Average fill rate = 13 mms-1



Stable, continuous metal front with very slightly concave shape. Average fill rate = 5 mms-1


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.


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


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


Planar metal front up to a filling velocity of about 15 mms-1

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)


Process Overview

Process Attributes

Process Issues


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

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 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

fundamentals of the lost foam casting process by mark ainsworth operations development manager –...

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