Claims
- 1. A method for heating at least a portion of mold surface by:
passing a substantially high frequency alternating electric current through a portion of said mold half and then to a portion of the other mold half thereby heating selective surface areas of the mold by said proximity effect to a predetermined temperature whereby elevated temperature of the inner surface of the mold can yield one or more following advantages in molding an article: improved weldline strength, smooth surfaces, replication of microfeatures, low birefringence, increasing flow length, low residual stresses, controlled crystallinity, resin rich surfaces, reduced cycle time, glossy surfaces in formed or microcellular formed articles.
- 2. The method of claim 1 wherein said heating is followed by cooling at least a portion of mold by:
passing a cooling medium to a portion of said mold
- 3. The method of claim 2 wherein said cooling is accomplished rapidly by:
passing a cooling medium through a micro channel network that is located on the order of one millimeter below the inner surface of the molds whereby a rapid cooling reduces the cooling time of the molding cycle time.
- 4. The method of claim 2 wherein the cooling medium is displaced before the heating cycle begins,
- 5. The method of claim 4 wherein the cooling medium is displaced by the pressure gradient of a gas.
- 6. The method of claim 1 wherein the substantially high frequency alternating electric current is between 50 Hz to 100 MHz.
- 7. The method of claim 1 wherein said heating is applied for molding an article using a mold having a pair of mold halves to be mated to define a cavity therebetween, comprising the steps of:
a) closing said pairs of mold halves b) heating at least a portion of the mold surface by said proximity heating c) injecting molten material or placing malleable material into the mold cavity d) cooling the mold, opening the mold, and removing a molded article.
- 8. The method of claim 7 wherein said heating is done before closing said pairs of mold halves, comprising the steps of:
a) closing said pairs of mold halves with a narrow gap between said pairs of the mold b) heating at least a portion of the mold surface by said proximity heating c) closing said pairs of mold halves d) injecting molten material or placing malleable material into the mold cavity e) cooling the mold, opening the mold, and removing a molded article.
- 9. Method of claim 8 wherein steps c) and d) are carried out simultaneously to accomplish injection and compression (coining) operation.
- 10. An apparatus of mold for molding objects, comprising:
a) means for providing insulation layers that electrically isolates said portion of mold halves from the rest of the machine and allowing the magnetic flux generated by said current to pass through said insulation layers b) means for providing electrical connections from a high frequency power supply to said portion of mold half and then to a portion of the other mold half and back to the high frequency power supply.
- 11. The mold of claim 10 wherein said portion of the mold is made of materials with a selective magnetic permeability to achieve a selective said skin layer thickness.
- 12. The mold of claim 10 wherein said portion of the mold is placed in juxtaposition with magnetic materials such as magnetic core to confine the skin thickness.
- 13. The mold of claim 10 wherein said portion of the mold has thermal insulation whereby said thermal insulation provides energy efficiency in heating said portion of mold surface.
- 14. The mold of claim 13 wherein said thermal insulation is comprised of any combination of metal oxide layer, polymeric materials, or porous materials.
- 15. The mold of claim 14 wherein said metal oxide layer is Zirconium Oxide.
- 16. The mold of claim 13 wherein said thermal insulation consist of air gap and ribs to support the mechanical load and minimize the deflection between the ribs.
- 17. The mold of claim 10 wherein the cooling channel is placed within said mold.
- 18. The mold of claim 17 wherein the cooling channels are located near the back of the surfaces of said mold whereby said cooling channels conforming to the cavity aids uniform cooling.
- 19. The mold of claim 18 wherein the size of cooling channel gap, the ribs between the channels, and the thickness of the mold surface are between 0.05 mm to 20 mm.
- 20. The mold of claim 10 wherein a parasitic induction coil is attached for the purpose of increasing the inductance.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] Research leading to the invention disclosed and claimed herein was supported in part by the National Science Foundation, NSF Grant No. DMI-9713519. The U.S. Government may have certain rights to the invention.