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

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Presentation on theme: "Fundamentals of the Lost Foam Casting Process by Mark Ainsworth Operations Development Manager – Scaw Metals Group."— 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 Overview Process Attributes Process Attributes Process Issues Process Issues Process Summary & Conclusions Process Summary & Conclusions

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

4 Main Steps in the Process “White Side” “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 “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 Manufacture Pattern Removal Pattern Removal “Replicast” Process “Replicast” Process

8 Main Advantages of the Process Tighter Dimensional Tolerances Tighter Dimensional Tolerances Dimension (mm)Tolerance (+/-) < 25 mm0.17 mm 25 – 80 mm0.25 mm 80 – 125 mm0.30 mm 125 – 175 mm0.43 mm 175 – 250 mm0.003 per mm > 250 mm0.002 per mm Rough Guide < 175 mm0.50 mm > 175 mm0.80 mm

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

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

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

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

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

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

15 Critical Issues with the Process Bead Size & Fusion Bead Size & Fusion A Cold Tool Surface or a Short Steam Step Produces “Underfusion”. A Cold Tool Surface or a Short Steam Step Produces “Underfusion”. - rough, beady surface, low strength - rough, beady surface, low strength Extended Steam Exposure or Inadequate Cooling Produces “Overfusion”. Extended Steam Exposure or Inadequate Cooling Produces “Overfusion”. - wavy surface, high density

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

17 Critical Issues with the Process Glue Lines Glue Lines Energy of Pattern Degradation Estimated to be 900 kJ/kg of foam. 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. Hot Melt Glue Has a Density Approximately 40 times that of the Pattern.

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

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

20 Critical Issues with the Process Casting Speed & Pattern Entrapment 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 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 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 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 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 Casting Speed & Pattern Entrapment Pore-type Defect - Found on all fracture surfaces - Size variation between 400 and 1500 µm 1500 µm Film-type Defect - Found only where non-planar metal fronts were observed fronts were observed - Size variation between 1 and 4.5 mm

26 Critical Issues with the Process Casting Speed & Pattern Entrapment 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 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 Emissions & Sand Residues Residue Build-up in the Moulding Sand Residue Build-up in the Moulding Sand Hazardous Airborne Pollutants (HAPS) Hazardous Airborne Pollutants (HAPS) - Lost Foam = 1.02 lbs/ton of metal - Furan = 1.08 lbs/ton of metal - Furan = 1.08 lbs/ton of metal - Greensand= 0.64 lbs/ton of metal MEL (styrene) MEL (styrene) - 100 ppm (8 hrs) - 100 ppm (8 hrs) - 250 ppm (15 min)

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

30 Process Summary & Conclusions Some Useful Advantages Some Useful Advantages Practical Casting Size Range & Output Limited Practical Casting Size Range & Output Limited Large Range of Process Variables Large Range of Process Variables Gating System Flow Control not Possible Gating System Flow Control not Possible Filling Speed an Order of Magnitude TOO Low Filling Speed an Order of Magnitude TOO Low Unsuitable for Castings in Highly Stressed Operational Fields Unsuitable for Castings in Highly Stressed Operational Fields

31 Handtmann scrap levels ≈ 10% Handtmann scrap levels ≈ 10% BMW reverting to gravity and pressure die casting for aluminium heads and blocks. BMW reverting to gravity and pressure die casting for aluminium heads and blocks. Honda retaining die casting processes for their aluminium components. 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.” “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

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


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