Rapid prototype injection molding
Disclosed is a method and apparatus for making a prototype injection molded part. An extruder of the type used for fused deposition modeling injects production thermoplastic material into a heated nonconductive plastic mold tool slowly at low pressure in an isothermic process. The mold tool may be built from a CAD drawing by fused deposition modeling or another rapid prototyping technique. Using the present invention, an injection molded prototype part can be made from a digital representation of the part within 24 hours by an engineer in an office environment.
1. A method for making a prototype plastic injection molded part, comprising the steps of:
providing a plastic mold tool defining a mold cavity;
injecting a liquified ribbon of plastic material into the mold cavity using an extrusion head at a pressure of less than 20 psi, until the material fills the cavity;
curing the plastic material in the mold cavity to form the prototype part.
2. The method of claim 1 , wherein the plastic mold tool is formed from an alkali-soluble modeling material.
3. The method of claim 1 and further comprising:
heating the mold tool to approximately the extrusion temperature, prior to the injecting step.
4. The method of claim 1 , further comprising building the plastic mold tool using a rapid prototyping technique based at least in part on computer data.
5. The method of claim 4 , wherein the plastic mold tool is built in a fused deposition modeling machine.
6. The method of claim 5 , wherein the building step and the injecting step are performed in the same fused deposition modeling machine.
7. The method of claim 1 , and further comprising the step of:
clamping the mold tool to a fixture with a clamping force of less than or equal to 10 tons, prior to the injecting step.
8. The method of claim 1 , wherein the injection step is an adiabatic process.
9. A method for making a prototype plastic injection molded part, comprising the steps of:
providing a plastic mold tool defining a mold cavity;
injecting a thermoplastic material into the mold cavity as a liquified ribbon of material using an extrusion head, at a pressure of less than 20 psi, so that the thermoplastic material fills the mold cavity; and
cooling the thermoplastic material in the mold cavity to form the prototype part.
10. The method of claim 9 and further comprising the step of:
building the mold tool using a rapid prototyping technique, based on computer file data representing a desired prototype part.
11. The method of claim 10 , wherein the mold tool is built in a fused deposition modeling machine.
12. The method of claim 11 , wherein the building step and the injecting step are performed in the same fused deposition modeling machine.
13. The method of claim 9 , wherein the injecting step is done in a fused deposition modeling machine.
14. The method of claim 9 , wherein the mold material is injected into the mold cavity using a melt extruder.
15. The method of claim 14 , wherein the melt extruder comprises a filament pump.
16. The method of claim 14 , wherein the melt extruder comprises a piston pump.
17. The method of claim 14 , and further comprising the steps of:
positioning a sprue in the mold tool such that a dispensing end of the sprue is directed into the mold cavity; and
attaching an inlet end of the sprue to a dispensing tip of the melt extruder;
wherein the thermoplastic material is injected from the melt extruder into the mold cavity via the sprue.
18. The method of claim 14 , wherein ultrasonic energy is induced in the extruder during the injecting step creating a thixotropic flow of thermoplastic.
19. The method of claim 9 and further comprising:
heating the mold tool to approximately the extrusion temperature, prior to the injecting step.
20. The method of claim 9 and further comprising:
coating surfaces of the mold cavity with a release agent, prior to the injecting step.
21. The method of claim 9 , and further comprising the step of:
monitoring pressure in the mold cavity during the injecting step and responsively adjusting the injection pressure.
22. The method of claim 9 , wherein the plastic mold tool is formed from an alkali-soluble modeling material.
23. The method of claim 9 , wherein the thermoplastic material comprises a curable material.
24. The method of claim 9 , wherein the curable material is selected from the group consisting of a photopolymer and a thermosetting material.
25. The method of claim 9 , and further comprising the step of:
clamping the mold tool to a fixture with a clamping force of less than or equal to 10 tons, prior to the injecting step.
26. The method of claim 9 , and further comprising the step of:
maintaining constant pressure on the mold tool during the cooling step to compensate for shrinkage of the prototype part and the mold tool.
27. The method of claim 9 , wherein the prototype part is cooled in the mold cavity to a temperature approximating room temperature.
28. The method of claim 9 , and further comprising the step of:
vapor smoothing surfaces of the mold tool prior to the injecting step.
29. The method of claim 9 , wherein the thermoplastic material is selected from a group consisting of ABS, polycarbonate, polystyrene, acrylics, amorphous polyamides, polyesters, polyphenylsulfone, polyphenylene ether, nylon, PEEK, PEAK, and blends thereof.
30. The method of claim 9 , wherein the plastic mold tool is formed from a thermoplastic material comprising at least 50 weight percent of a thermoplastic selected from the group consisting of polycarbonate, polystyrene, acrylics, amorphous polyamides, polyesters, polyphenylsulfone, polysulfone, polyphenylene ether, nylon, PEEK, PEAK, poly(2-ethyl-2-oxazoline), and blends thereof.
31. The method of claim 30 , wherein the thermoplastic forming the mold tool comprises a polyphenylsulfone-based resin.
32. The method of claim 30 , wherein the thermoplastic forming the mold tool comprises a polyphenylsulfone-based resin and the injected thermoplastic is ABS.
33. The method of claim 9 , wherein the injecting step is performed using a vacuum assist.
34. The method of claim 9 , wherein the injection step is an adiabatic process.
35. A method for making a prototype plastic injection molded part, comprising the steps of:
providing a plastic mold tool defining a mold cavity, the plastic mold tool being built with an additive process rapid prototyping machine;
injecting a polymer into the mold cavity using the additive process rapid prototyping machine at a pressure of less than 20 psi, until the material fills the cavity; and
solidifying the polymer in the mold cavity, thereby forming the molded prototype part.
36. The method of claim 35 , wherein the polymer comprises a photopolymer, and wherein solidifying the polymer comprises exposing the polymer to light.
37. The method of claim 35 , wherein the rapid prototyping machine comprises a fused deposition modeling machine.
38. The method of claim 35 , and further comprising vapor smoothing the plastic mold tool prior to the injecting step.
39. The method of claim 35 , and further comprising monitoring pressure in the mold cavity during the injecting step and responsively adjusting the injection pressure.
40. The method of claim 35 , wherein the injection step is an adiabatic process.
41. A method for making a prototype plastic injection molded part, comprising the steps of:
providing a plastic mold tool defining a mold cavity; providing a supply of two or more reactant materials which form a thermoset resin when reacted together;
mixing the reactant materials together;
injecting the reactant materials from an extruder into the mold cavity as a liquified ribbon of material, at a controlled pressure of less than 20 psi, so that the reactant materials fill the cavity;
heating the reactant materials in the mold cavity to form the molded prototype part; and
cooling the molded prototype part in the mold cavity.
42. The method of claim 41 , further comprising building the plastic mold tool using a rapid prototyping technique based at least in part on computer data.
43. The method of claim 42 , wherein the plastic mold tool is built in a fused deposition modeling machine.
44. The method of claim 41 , wherein the injection step is an adiabatic process.