Plastic injection mold assembly and method of molding threaded plastic parts

Abstract

A plastic injection mold assembly is disclosed in which an electric servo motor very precisely controls rotational speeds and amounts of torque applied to cores which extend into the mold cavities as the cores are withdrawn from plastic components being molded and simultaneously directs the linear distances which the cores travel during such withdrawal. A method of accomplishing the molding of plastic components in this manner is also disclosed.

I claim:  
     
         1 . A mold assembly comprising 
 an injection mold having    a molding chamber for receiving and forming a predetermined amount of flowing molding material during a molding cycle, and 
 a channel in the mold leading to the molding chamber,  
   a core member disposed in and rotatably and longitudinally moveable along the channel, and including 
 a threaded molding segment adjacent one end for forming the molding material in the chamber during the molding cycle, and  
 a drive segment having 
 a core rotary movement member and  
 a core linear movement member connected to the core rotary movement member, and  
 
   an electrically powered drive member connected to the core rotary movement member for simultaneously moving the core rotary movement member and the core linear movement member and positioning the molding segment adjacent the end of the core member in or out of the molding chamber.    
     
     
         2 . The mold assembly of  claim 1  in which the drive member is a worm gear and the core rotary movement member is a worm wheel engaged on the worm gear.  
     
     
         3 . The mold assembly of  claim 1  which includes an electric servo motor connected to the drive member.  
     
     
         4 . The mold assembly of  claim 1  in which the drive member is powered by a programmable electric servo motor.  
     
     
         5 . The mold assembly of  claim 1  in which the core member is a cylindrically shaped bar having the molding segment adjacent one end and the drive segment adjacent a second end and a longitudinal axis extending through the bar from end to end.  
     
     
         6 . The mold assembly of  claim 1  in which the molding segment of the core member includes a threaded area on the outside of the core member for forming internal threads on the inside of a component being molded in the molding chamber.  
     
     
         7 . The mold assembly of  claim 1  in which the molding segment of the core member includes a threaded surface area inside the one end of the core member for forming external threads on the outside of a component being molded in the molding chamber.  
     
     
         8 . The mold assembly of  claim 4  in which the core is rotated and moved longitudinally at different speeds and at different torque levels by a program applied to the motor while the molding segment of the core member is being moved out of the molded plastic component in the molding chamber.  
     
     
         9 . The mold assembly of  claim 1  in which the core linear movement member includes an externally threaded element on the outer surface of the core containing threads arranged substantially normal to a longitudinal axis in the core and engageable by a complementary threaded element affixed to the mold and arranged about the drive segment to intersect the externally threaded element of the core linear movement member.  
     
     
         10 . The mold assembly of  claim 1  in which the core rotary movement member is a disk shaped element disposed around the core member in a plane substantially normal to a longitudinal axis of the core and the core linear movement member is engaged to the disk shaped element through a centrally located aperture in the disk shaped element  
     
     
         11 . The mold assembly of  claim 1  in which the core linear movement member includes a projection extending radially from the core member slideably engaged upon walls of a central opening in the core rotary movement member to receive pressure from the core rotary movement member and rotate the core member about a longitudinal axis of the core member while simultaneously sliding the core member along the walls of the central opening in the core rotary movement member in a direction substantially normal to the direction of the pressure from the core rotary movement member.  
     
     
         12 . The mold assembly of  claim 11  in which the projection on the core linear movement member is a spline disposed on the outside of the core member and extending in a direction of the longitudinal axis of the core member.  
     
     
         13 . A method of molding a component from a flowing plastic material comprising the steps of 
 providing a molding chamber in an injection mold having a predetermined configuration of the outer form of the component,    providing a core member having a molding segment adjacent one end of the core member disposed in the molding chamber,    filling the molding chamber around the molding segment of the core member with the flowing molding material    cooling the molding material in the molding chamber until the material is firm enough to retain a shape matching the shape of the molding chamber and the molding segment of the core,    applying rotational power to the core from an electric servo motor, simultaneously rotating and longitudinally moving the core member until the molding segment adjacent one end of the core member is separated from the component, and    ejecting the component from the molding chamber.    
     
     
         14 . The method of  claim 13  in which the rotational power applied to the core is supplied from an electric servo motor programmed to vary the speed and torque of the core member rotation.