VACUUM CASTING TRAINING GOALS • How to prepare a master model. • How to do a silicone mould for to vacuum casting. • How to use this tool (casting preparation) • Resins range review (practice).
VACUUM CASTING
CONCEPTION LINE DIGITAL
3 D MOCK-UP
DATAS
OR FIRST PART
DUPLICATION
CAD
SLA
Vacuum casting
3D digitization
SLS
RIM
LOM
Thermoplastic injection
CAD CAM
MODELS PREPARATION Keep in mind: The surface should be as smooth as possible
Models from stereolithography Apply only a varnish - Acrylic
- Urethane Finishing with light grained sand paper if necessary. *Check silicone compatibility of all materials prior to molding.
MODELS PREPARATION
Models from laser sintering:
Apply a sealer Never use polyester sealer
Sand the surface. Apply a varnish ( similar to SLA).
MODELS PREPARATION Models from 3D PRINTERS (like Z.CORP): • Reinforce the surface with PU resins like : •F 18 or F 23 ( mix of two different resins):
• Dip master model into the mixing and remove any excess. • Sand the surface and polish it.
• Finishing with varnish.
MODELS PREPARATION Parting lines
• Determine location of parting line part (number of mould pieces). • Put translucent or colored scotch tape along the parting lines.
• Close holes on the part. • Eventually, place inserts (copper, aluminium, steel or plastic).
MODELS PREPARATION
Injection port • Gate diameter depends on quantity being used • From 8 to 16 mm the diameter is correct
• Use a smooth round rod • Carefully choose right place for round rod
and risers (or vents) • Always use risers with 1 to 2 mm diameter • Multiple risers should be located to avoid bubbles.
• Don’t forget : We need vents even with vacuum
casting process.
MODELS PREPARATION Prepare the moulding frame
• Use melamine coated plywood fixed with screws or hot glue. • Dimensions : Add 20 mm (.79in.) around the part for a 200 mm (7.87in.)long part
Add 30 mm (1.18in.) around the part for a 300 mm (11.82in.) (100 mm is the maximum, more makes no sense) 3.94in.
MODELS SUSPENTION
Use the casting port and the risers to suspend the model into the box. This will keep models from rising to the surface of the liquid silicon. - Bond it very carefully - Mechanical attach part if possible.
MOULD CASTING
Calculate the amount of silicone • Frame internal dimensions X silicone density + 10 % waste = silicone quantity needed. • Choose the right container (5 times the silicone volume is needed). • Use appropriate mixing machine to blend products
SILICONE CASTING (with MK Machin)
• Apply a primary degassing for 20 to 30 minutes
• Use GO TO function to approach the full vacuum (step by step). • Use the LEAK key to make the bubbles burst
• Cast into the frame • Second degassing for 20 minutes • Come back slowly to atmospheric pressure.
MOULD CASTING
MOULD OPENING First step cutting • Make a pencil mark along the parting line (waves mark).
• Inject air pressure through the gate. • Start the first cutting aid of scalpel. • Cut in wave for better positioning of every pieces.
MOULD OPENING Second step cutting • Use mould openers
• Cut slowly from the tape to outside • Remove the model and tape traces. • Mould is ready for the first casting.
MOULD OPENING
VACUUM CASTING
• Preheat the mould at 70°C (160°F) before closing Place it open in an oven for a least 4 hours • Apply a release agent : silicone or wax
• Close the mould • Staple along the parting line for standard moulds • Reinforced tape + staples for large moulds
VACUUM CASTING • Place the preheated mould into the vacuum chamber • Use the lift to connect the funnel.
VACUUM CASTING • Calculate the quantity of resin • Weigh both components • place the lowest viscosity component in the smaller cup (upper) add extra material to allow for full fill of mold cavity (approx. 10 gr extra). • Place the second component in second cup • Check all items : Mould, material - mixing paddle - connections etc .. • Start the casting as mentioned for every resin
VACUUM CASTING
VACUUM CASTING
POST CASTING CYCLE
• Place the mould in a 70°C oven OPEN THE MOLD • Clean any excess resin from the mould
• Remove tape or staples • Introduce air pressure to mold cavity
• Open carefully with mould openers to avoid part distortions, let the mould cooling down few minutes.
VACUUM CASTING