Mechanism for making openings in plastic parts within a mold tool

An assembly disposed within a mold for forming openings in a plastic part includes a punch pin and a backing pin having faces disposed flush with a surface of a mold cavity. The backing pin is disposed opposite the punch pin. The punch pin is driven into the completed plastic part removing material to form an opening. The waste material is driven into a bore housing the backing pin. The backing pin recedes into the bore to accept the waste material. Upon ejection of the plastic part the waste material ejects from the mold cavity as the backing pin moves back to a position flush with the surface of the mold cavity.

BACKGROUND OF THE INVENTION

The invention relates to a mechanism for forming an opening in a plastic part within a mold tool before removal of the plastic part from the mold tool.

Typically, holes or openings are made in plastic parts by a core pin inserted into a cavity of the mold during the molding operation. Plastic injected into the mold will flow around the core pin forming the opening. After the plastic has solidified, the core pin is retracted from the inner cavity of the mold to allow the completed part to be removed from the mold tool.

This method of forming holes or openings is problematic for certain plastic materials and molding conditions. Plastic flowing around the core pin forms a knit line. The knit line is a term of art referring to a seam or inconsistency in the plastic part caused by two fronts of plastic failing to completely mix before the plastic solidifies. The molten plastic material flowing around the core pin forms two fronts. These fronts of plastic flow may begin to solidify before merging with each other on the opposite side of the core pin. This phenomenon creates knit lines that cause poor aesthetic appearance and weak points in the completed plastic part.

Another typical method of forming openings in plastic molded parts is byway of secondary boring or drilling operations. This is accomplished by removing the part from the mold and transporting the part to another workstation where the openings are machined into the plastic part. As appreciated, machining the opening or holes is an expensive and time-consuming process that increases the cost of the finished product.

Accordingly, it is desirable to develop an apparatus and method for forming opening within molded parts without additional machining process while minimizing formation of weak points within a molded part.

SUMMARY OF THE INVENTION

An embodiment of this invention is an assembly for forming openings in a plastic part before removal from a mold tool.

The mold tool includes upper and lower sections. A plastic part is formed by injection of molten plastic into a cavity formed between the upper and lower sections of the mold tool. A backing pin disposed in a bore of the mold includes a face positioned flush with a surface of the mold cavity. The backing pin is held in place against pressure of the plastic during molding by a holder pin actuated by a locking assembly. The locking assembly moves the holder pin between an unlocked position in which the backer pin may be pushed back into the bore and a locked position that prevents movement of the backing pin.

A cylinder actuates a punch pin driven into the plastic part forming the desired opening. Once the plastic part has solidified, the locking assembly moves to an unlocked position. The cylinder drives the punch pin into the plastic part forming the opening. The unlocked backing pin is free to slide back into the bore. As the punch pin drives through the plastic part, the material removed by the punch pin is driven back into the bore. The material remains in the bore. Once the opening is formed, the punch pin retracts out of the cavity. An ejection mechanism ejects the plastic part from the mold. The ejection mechanism pushes the backing pin outward to eject the waste material from the mold.

In another embodiment of this invention, a driving rod moved by an actuator actuates the backing pin. The backing pin slides within a keyway of the driving rod. The keyway is ramped up and back such that the backing pin slides into the bore and away from the surface of the cavity when the driving rod is moved downward. The actuator moves the driving rod relative to the mold, pulling the driving rod down, which in turn pulls the backing pin back within the bore and away from the surface of the mold cavity. The resulting opening accepts the waste material removed from the plastic part until ejected from the mold tool.

This invention provides an apparatus and method for forming openings within molded parts without forming knit lines and without additional machining processes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of this invention is an assembly10disposed in a mold tool12having upper and lower sections14,16. The upper and lower sections14,16cooperate to form a cavity20. The upper and lower sections14,16open and close with movement in a first pull direction perpendicular to the parting line. Plastic injected into the cavity20forms part18. The assembly10includes a backing pin22disposed in a bore30of mold12. The backing pin includes a face24positioned flush with a surface21of the mold cavity20. The backing pin22moves in a direction different than movement of the upper and lower sections14,16. Movement of the backing pin within the bore30is in a second direction different indicated by arrows B that is different than the first pull direction. The backing pin22moves within the bore30between locked and unlocked positions. A holder pin26locks the backing pin22in the locked position against pressure of the plastic during molding. A locking assembly28moves the holder pin26to lock or free the backing pin22. In the unlocked position, the backing pin22may be pushed back into the bore30. In the locked position, the face of the backing pin22remains flush with a surface of the cavity21.

A punch cylinder34actuates a punch pin32driven into the plastic part18. The punch pin32moves in a direction A that is different than the first pull direction. Preferably, the punch cylinder34operates pneumatically, however, it is within the contemplation of this invention the punch cylinder operate hydraulically. The punch pin32forms the desired opening or hole. The opening may be of any configuration required for the specific application such as a hole, slot, etc. It is within the contemplation of this invention that the opening may be of any configuration required by the specific application. Further, the shape of the punch pin32will correspond to the desired shape of the opening in the plastic part18.

Once the plastic part18has solidified, the locking assembly28retracts, unlocking the backing pin22. The punch cylinder34drives the punch pin32through the plastic part18, forming the opening. Because the locking assembly28is in an unlocked position, the backing pin22freely slides back into the bore30to accept material removed from the plastic part18. The material removed from the plastic part is driven back into the bore30and remains in the in the bore30. Once the opening is formed, the punch pin32retracts out of the cavity20. A part ejection mechanism36removes the plastic part18from the mold12. The part ejection mechanism36includes an ejection head38attached to an ejection rod40. The ejection head38moves in a direction D that is different than the first pull direction to eject the plastic part18.

Referring toFIG. 1, the plastic part18of this embodiment includes an under cut42. To eject the part18from the mold the ejector head38is driven upward and rearward by the ejector rod40. The backing pin22moves with the ejection head38and lines up with an ejection pin44. The ejection pin44pushes the backing pin22outward to eject the waste material from the mold10. Upon removal of the plastic part18, the ejection rod40retracts, pulling the ejection head38back to a molding position. Note that any ejection mechanism known to a worker in the art is within the contemplation of this invention. The specific configuration of the ejection mechanism is application specific and a worker skilled within the art would understand that modifications for specific parts are within the scope of this invention.

Referring toFIG. 2–6, another embodiment of the locking assembly48includes a backing pin46actuated by a driving rod48that moves the backing pin46between the locked and unlocked positions in the second direction indicated by arrows B. The backing pin46is slidably connected within a keyway50of the driving rod48. The keyway50is ramped up and back such that the backing pin46slides into the bore58and away from the surface of the cavity55when the driving rod48is moved downward in a direction indicated by arrows C.

Referring toFIG. 2, the backing rod46is attached to a movable plate52actuated by a cylinder54. The cylinder54moves the plate52downward in a direction D that is common with the first pull direction thereby pulling the driving rod48down, which in turn causes the backing pin46to be pulled back in the second direction B within the bore30and away from the surface of the mold cavity55.

In operation, the molten plastic material is injected into the mold cavity56and solidifies. During the molding process the backing pin46is held in place by the driving rod48and the punch pin32is retracted out of the mold cavity56. After the injected plastic has solidified into a completed part18, the cylinder54pulls the plate52and thereby the driving rod48downward in a direction D that is in this case common with the first pull direction of the upper and lower mold sections14,16. Downward motion of the driving rod48causes the backing pin46to ride upward within the keyway50. The upward movement of the backing pin46within the keyway50causes movement in the direction indicated by arrows B that retracts the backing pin46into the bore58. This provides space for waste material punched out of the plastic part18.

The punch pin32is then driven through the plastic part18by the punch cylinder34. The material punched out of the plastic part18is driven into the bore30. The punch pin32retracts from the mold cavity56allowing removal of the completed plastic part18. The driving rod48moves back to the locked position pushing the face24of the backing pin46flush with the surface of the mold cavity56.

The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.