Stack mold having a melt homogenizing element

1. A method of improving melt flow in a stack injection molding apparatus comprising:

providing a first transfer nozzle having a first melt channel for receiving a melt stream from a melt source, said melt stream having a first temperature and viscosity distribution;

providing a second transfer nozzle having a second melt channel for receiving said melt stream from said first melt channel, wherein one of said first or second transfer nozzles includes a movable valve pin for controlling the flow of the melt stream between said first transfer nozzle and said second transfer nozzle;

providing a melt homogenizing element coupled to said valve pin for changing said melt stream from said first temperature and viscosity distribution to a second temperature and viscosity distribution, wherein said second temperature and viscosity distribution is more uniform than said first temperature and viscosity distribution; and

transferring the melt stream from the first transfer nozzle to the second transfer nozzle through the melt homogenizing element.

2. The method defined in claim 1 , wherein said melt homogenizing element mixes said melt stream to change said first temperature and viscosity distribution to said second temperature and viscosity distribution.

3. The method defined in claim 1 , wherein said melt homogenizing element rotates said melt stream to change said first temperature and viscosity distribution to said second temperature and viscosity distribution.

4. The method defined in claim 1 , wherein said first melt channel and said second melt channel are selectively in fluid communication with one another.

5. The method defined in claim 4 , wherein said first transfer nozzle and said second transfer nozzle are selectively separable from one another.

6. The method defined in claim 5 , wherein said melt homogenizing element is configured to reduce drooling of the melt stream when said first transfer nozzle and said second transfer nozzle are separated from one another.

7. An injection molding apparatus comprising:

a first melt transfer nozzle having a first melt transfer channel for receiving a melt stream of a moldable material under pressure;

a melt homogenizing element coupled to a valve pin and having a melt homogenizing channel for receiving the melt stream from the first melt transfer channel, wherein said melt homogenizing element resets a shear history of said melt stream;

a second melt transfer nozzle having a second melt transfer channel for selectively receiving said melt stream from said melt homogenizing channel, wherein the valve pin extends through one of said first and second melt transfer channels and has a diameter sized to restrict melt flow between said first melt transfer channel and said second melt transfer channel when in a closed position and allows melt to flow between said first melt transfer channel and said second melt transfer channel through said melt homogenizing element when in an open position;

a manifold having a manifold channel for receiving said melt stream from said second melt transfer channel and delivering said melt stream to a nozzle channel of a nozzle; and

a mold cavity receiving said melt stream from said nozzle, said nozzle channel communicating with said mold cavity through a mold gate.

8. The injection molding apparatus defined in claim 7 , wherein said melt homogenizing channel of said melt homogenizing element is generally helically shaped.

9. The injection molding apparatus defined in claim 7 , wherein said melt homogenizing element is integral with said valve pin and said valve pin is movable to selectively locate said melt homogenizing element across a portion of said first melt transfer channel and a portion of said second melt transfer channel simultaneously to allow melt to flow between said first melt transfer channel and said second melt transfer channel.

10. A stack mold injection molding apparatus comprising:

a first melt transfer nozzle having a first melt transfer channel for receiving a melt stream of a moldable material;

a second movable melt transfer nozzle having a second melt transfer channel in fluid communication with the first melt transfer channel;

a movable valve pin configured to control the melt stream from the first melt transfer nozzle to the second melt transfer nozzle;

a melt homogenizing element connected to said valve pin and disposed between the first melt transfer channel and the second melt transfer channel, wherein the melt homogenizing element redistributes melt in the melt stream such that the melt stream exiting the melt homogenizing element has a more uniform temperature and viscosity distribution than the melt stream entering the melt homogenizing element;

a manifold having a manifold channel for receiving the melt stream from the second melt transfer channel and delivering said melt stream to a plurality of nozzles;

a plurality of mold cavities for receiving said melt stream from said nozzles, said nozzles communicating with said mold cavities through a plurality of mold gates.

11. The stack mold injection molding apparatus defined in claim 10 , wherein the melt homogenizing element connected to the valve pin is located in the second movable melt transfer nozzle.

12. A stack injection molding apparatus comprising:

a machine nozzle configured to deliver a melt material to a sprue inlet;

a first transfer nozzle having a first melt channel in fluid communication with the sprue inlet;

a first movable valve pin disposed within the first melt channel, wherein the first movable valve pin is configured to control a flow of melt through the first melt channel;

a melt homogenizing element integral with said first moveable valve pin, wherein the melt homogenizing element is configured to redistribute the melt in the first melt channel such that the melt exiting the melt homogenizing element has a more uniform temperature profile than the melt entering the melt homogenizing element;

a second transfer nozzle having a second melt channel in fluid communication with the first melt channel, wherein the second transfer nozzle is mounted on a movable platen and is movably coupled to the first transfer nozzle;

a manifold having a manifold melt channel in fluid communication with the second melt channel; and

a nozzle having a nozzle melt channel in fluid communication with the manifold melt channel, wherein the nozzle is configured to deliver the melt to a mold cavity.

13. The stack injection molding apparatus defined in claim 12 , further including a movable valve pin disposed within the second melt channel, wherein the movable valve pin is configured to control a flow of melt through the second melt channel.

14. The stack injection molding apparatus defined in claim 12 , further including a second melt homogenizing element disposed within the second melt channel, wherein the second melt homogenizing element is configured to redistribute the melt in the second melt channel such that the melt exiting the second melt homogenizing element has a more uniform temperature profile than the melt entering the second melt homogenizing element.

15. The stack injection molding apparatus defined in claim 14 , wherein the second melt homogenizing element is integral with a second movable valve pin disposed within the second melt channel, wherein the second movable valve pin is configured to control a flow of melt through the second melt channel.

16. The stack injection molding apparatus defined in claim 12 , wherein the melt homogenizing element extends from the first melt channel to the second melt channel when the stack injection molding apparatus is in a melt delivery position.

17. A stack injection molding apparatus comprising:

a machine nozzle configured to deliver a melt material to a sprue inlet;

a first transfer nozzle having a first melt channel in fluid communication with the sprue inlet;

a second transfer nozzle having a second melt channel in fluid communication with the first melt channel, wherein the second transfer nozzle is mounted an a movable platen and is movably coupled to the first transfer nozzle;

a first movable valve pin disposed within the second melt channel, wherein the movable valve pin is configured to control a flow of melt through the second melt channel;

a melt homogenizing element disposed integral with said first movable valve pin, wherein the melt homogenizing element is configured to redistribute the melt in the second melt channel such that the melt exiting the melt homogenizing element has a more uniform temperature profile than the melt entering the melt homogenizing element;

a manifold having a manifold melt channel in fluid communication with the second melt channel; and

a nozzle having a nozzle melt channel in fluid communication with the manifold melt channel, wherein the nozzle is configured to deliver the melt to a mold cavity.

18. The stack injection molding apparatus defined in claim 17 , further including a second movable valve pin disposed within the first melt channel, wherein the second movable valve pin is configured to control a flow of melt through the first melt channel.

19. The stack injection molding apparatus defined in claim 17 , further including a second melt homogenizing element integral with a second movable valve pin disposed within the first melt channel, wherein the second melt homogenizing element is configured to redistribute the melt in the first melt channel such that the melt exiting the second melt homogenizing element has a more uniform temperature profile than the melt entering the second melt homogenizing element, and wherein the movable valve pin is configured to control a flow of melt through the first melt channel.

20. The stack injection molding apparatus defined in claim 17 , wherein the melt homogenizing element extends from the second melt channel to the first melt channel when the stack injection molding apparatus is in a melt delivery position.