Fundamentals of the Lost Foam Casting Process

1. Fundamentalsof theLost 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 Step 1 Filling Pre-Expander Step 2 Pre-Expanding Step 3 Patternmaking Step 4 Pattern Assembly Step 7 Drying Step 6 Coating Step 5 Cluster Assembly “White Side”

5. Step 1 Flask Positioning Step 2 Cluster Location Step 3 Sand Filling & Compaction Step 7 Casting Removal Step 6 Casting Cooling Step 5 Mould Casting Step 4 Flask Transport Main Steps in the Process “Black” Side

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

9. Main Advantages of the Process • Large Design Freedom • Controllable Wall Thickness • No Chaplets • No Fins • No Mismatch • No Core Defects • No Sand Mix Problems No Cores Are Required

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

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

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 • 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 Bead Size & Fusion

16. Critical Issues with the Process • Inadequate Cooling of the Tool Can Produce “Post Expansion”. • - soft, warm beads expand locally after • ejection from the tooling. • - dimensional instability. Dimensional Stability of the Pattern

17. Critical Issues with the Process • 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. Glue Lines

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

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

20. Critical Issues with the Process 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 Casting Speed & Pattern Entrapment

21. Critical Issues with the Process 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 Casting Speed & Pattern Entrapment

22. Critical Issues with the Process 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 Casting Speed & Pattern Entrapment

23. Critical Issues with the Process Fill Pressure: 24.1 kPa Stable, continuous metal front with very slightly concave shape. Average fill rate = 5 mms-1 Casting Speed & Pattern Entrapment

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

25. Critical Issues with the Process • 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 Casting Speed & Pattern Entrapment

26. Glass-sided Mould Containing Glucose Syrup Mercury reservoir & displacement cylinder Secondary actuation cylinder Compressed air inlet Flow control valve Critical Issues with the Process Viscosities: Mercury = 1.22 mPas Glucose = 95 Pas Casting Speed & Pattern Entrapment

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

28. Critical Issues with the Process • 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) Emissions & Sand Residues

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 • 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