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Fundamentals of the Lost Foam Casting Process

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Presentation on theme: "Fundamentals of the Lost Foam Casting Process"— Presentation transcript:

1 Fundamentals of the Lost Foam Casting Process
by Mark Ainsworth Operations Development Manager – Scaw Metals Group

2 Themes of the Presentation
Process Overview Process Attributes Process Issues Process Summary & Conclusions

3 Characterisation of the Process
No Mould Cavity Disposable Pattern Bondless Moulding Media Core Elimination

4 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

5 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

6 Overview of the Process

7 Derivatives of the Process
Pattern Manufacture Pattern Removal “Replicast” Process

8 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

9 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

10 Main Advantages of the Process
No Parting Lines No Stripping Taper Multiple Layers Possible Optimal Positioning of Downsprues and Risers No Fins No Mismatch

11 Main Advantages of the Process
Combination/Consolidation of Parts Glue Instead of Fasteners High Freedom of Design High Added Value Possibilities

12 Themes of the Presentation
Process Overview Process Attributes Process Issues Process Summary & Conclusions

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

14 Themes of the Presentation
Process Overview Process Attributes Process Issues Process Summary & Conclusions

15 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

16 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.

17 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.

18 Critical Issues with the Process
Pattern Density Under compaction Over compaction

19 Critical Issues with the Process
Coating Variation Permeability Conductivity Viscosity Wicking Capability Coating Penetration Between Foam Beads

20 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

21 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

22 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

23 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

24 Critical Issues with the Process
Casting Speed & Pattern Entrapment The Weibull modulus (m) suggests that plates filled by means of a planar front contain less defects.

25 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

26 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

27 Critical Issues with the Process
Casting Speed & Pattern Entrapment Planar metal front up to a filling velocity of about 15 mms-1

28 Critical Issues with the Process
Emissions & Sand Residues 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)

29 Themes of the Presentation
Process Overview Process Attributes Process Issues Process Summary & Conclusions

30 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

31 Process Summary & Conclusions
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.”

32 Process Summary & Conclusions
Low to Medium Volumes Highly Complex Parts (potentially joined) Low Stress Applications Weight between 1 – 100 kg (aluminium) A Niche Process for Niche Markets Requiring Very Tight Parameter Control


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