Abstract:
A vacuum holding fixture for a thermoformed part carries a base attachment plate which is releasably coupled to the top wall of a vacuum support box having a vacuum passage sealed to a vacuum passage within the attachment plate and a vacuum chamber within the holding fixture. The attachment plate is precisely positioned and releasably locked to the vacuum box by a plurality of couplers each including a stud projecting downwardly from the attachment plate and received within a corresponding cylinder recessed within the vacuum box. Each cylinder has locking balls which releasably grip the corresponding stud in response to axial movement of a fluid actuated spring biased piston surrounding the cylinder.

Description:
BACKGROUND OF THE INVENTION 
     In the production of custom thermoformed articles or parts, such as parts produced by blow molding, vacuum molding, rotomolding, compression molding, resin transfer molding and reaction injection molding, it is usually necessary to perform one or more secondary operations on each part after it is formed. For example, the part may require peripheral trimming on a computer numerically controlled (CNC) router machine having a high speed router which is automatically moved around the base of the part to trim off an outwardly projecting flange. Commonly, each part is supported during the secondary trimming operation by a corresponding vacuum router fixture which receives the part and has small vacuum passages extending from an internal vacuum chamber within the fixture for positively holding the part firmly against the fixture. Each router fixture must be precisely positioned on the bed or table of the CNC router machine and then attached with clamps and/or bolts, after which the fixture is connected to a vacuum or suction line. These set up operations for the router fixture for each part require substantial time, and when it is necessary to perform trimming on a number of different thermoformed parts, several hours may be required for interchanging router fixtures and for precisely locating and positively securing or clamping each fixture to the router table. During this time period, the router machine is not operating, and the operator of the machine is not producing. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved quick change tooling system for a vacuum holding fixture which receives a thermoformed part in order to perform a secondary operation on the part, such as a peripheral trimming operation. The tooling system of the invention provides for quickly removing a vacuum holding fixture for a part from a machine which performs a secondary operation on the part and for quickly attaching another vacuum holding fixture for another part to the machine. As a result, down time of the machine and nonproductive time of the machine operator are minimized during set up for each fixture. The quick change tooling system of the invention further provides for quickly positioning each vacuum holding fixture on the machine and for positively locking the fixture to the base of the machine in a precise predetermined position, thus eliminating the use of hand tools, bolts, clamps and other fastening means. The tooling system also provides for quickly removing the vacuum holding fixture from the machine. 
     In accordance with one embodiment of the invention, an attachment plate is secured to the bottom surface of a vacuum holding fixture for a thermoformed part and has an opening which connects with a vacuum chamber within the fixture. The fixture is provided with an array of small vacuum passages connecting the internal vacuum chamber with the outer surfaces of the fixture. The attachment plate is adapted to seat on the top wall of a vacuum box which is connected by a line to a vacuum source. A resilient annular seal is mounted on the top wall of the vacuum box around a vacuum opening and forms an airtight seal between the vacuum opening in the attachment plate and the aligned vacuum opening within the top wall of the vacuum box. 
     A plurality or three air actuated locking couplers positively secure the fixture attachment plate to the vacuum box and precisely locate the vacuum fixture relative to the vacuum box which is secured to the bed or table of a machine. Preferably, each of the locking couplers includes a knob or stud projecting downwardly from the attachment plate and having an enlarged head portion which is received within a locking cylinder recessed within the top wall of the vacuum box. Each locking cylinder has circumferentially spaced balls for engaging the head portion of the corresponding coupler stud, and a spring loaded piston surrounds the balls and normally holds the balls in a locking position. The balls of all couplers retract to released positions in response to pressurized air simultaneously acting on the pistons of the couplers. 
     Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a quick change tooling system constructed in accordance with the invention for precisely positioning and positively and releasably locking a vacuum holding fixture for a thermoformed part to a supporting vacuum box; 
     FIG. 2 is a section taken through the attachment plate and vacuum holding box shown in FIG.  1  and showing the alignment between the attachment plate and the vacuum box in a released position with the vacuum holding fixture elevated above the vacuum box; 
     FIG. 3 is a fragmentary section taken generally on the line  3 — 3  of FIG.  2  and showing a locking coupler in its released position with the vacuum holding fixture elevated above the supporting vacuum box; and 
     FIG. 4 is a fragmentary section similar to FIG.  3  and showing a coupler when the tooling system is in its coupled and locked position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a vacuum holding fixture  10  for a thermoformed part (not shown) and which typically supports the part on the base or table of a CNC router machine. The fixture  10  conforms to the shape of the part which extends over the top wall and around the opposite side walls and opposite end walls of the fixture. Commonly, the part has a laterally outwardly projecting peripheral base flange which is removed or trimmed by a numerically controlled router machine having a router bit which traverses around the periphery of the part while the part is supported by the vacuum holding fixture  10 . Usually, the fixture  10  is cast of aluminum and defines an internal vacuum chamber (not shown) which is connected by small holes or passages to the outer surfaces of the fixture. When vacuum is introduced into the chamber of the fixture  10 , the part is held firmly against the outer surfaces of the fixture. 
     In accordance with the present invention, a quick change tooling system  12  includes an attachment plate  14  which is secured to the bottom surface of the vacuum holding fixture  10  by a series of bolts or screws (not shown) and defines a center vacuum opening or port  16  which connects with the vacuum chamber within the fixture. However, it is understood that the configuration of the vacuum holding fixture  10  is for purpose of illustration only and that the quick change tooling system of the invention may be used with other vacuum holding fixtures of different configurations. As illustrated in FIG. 2, the attachment plate  14  is adapted for mounting and seating on a vacuum box  20  which is shown in the form of a cast aluminum housing  22  having an inwardly projecting base flange  24  secured and sealed to a base closure plate  26  by peripherally spaced screws  27 . 
     The housing  22  has a top supporting wall  32  which has a center vacuum opening  33  positioned to be aligned with the vacuum opening  16  within the attachment plate  14 . A resilient O-ring  36  is recessed within an annular groove  37  within the top wall  32  of the vacuum box  20  and surrounds the vacuum  35  opening  33  to form a fluid-tight seal between vacuum box and the attachment plate  14 . An end wall of the vacuum box  20  has a vacuum port or opening  38  and receives a pipe coupling flange  41  which is secured by a set of screws  42 . 
     The flange  41  threadably connects with a vacuum pipe or line which extends from a vacuum source (not shown). 
     The attachment plate  14  and the fixture  10  are releasably coupled and locked to the vacuum box  20  by a plurality of locking couplers  55  preferably of the type manufactured and sold by Edward D. Segen &amp; Co., LLC of Shelton, Conn. and referred to in its catalog as a “Quick-Change Cylinder Lock”. 
     Each of the three couplings  55  includes a male portion in the form of a metal knob or stud  58  which is secured by a screw  59  (FIG. 3) to the attachment plate  14  and projects downwardly from the attachment plate. Each knob  58  has a tapered or frusto-conical base portion  62  integrally connected to a head portion  63  by a neck portion  66  of reduced diameter. 
     Each of the couplings  55  also includes a female portion in the form of a cup-shaped cylinder  68  (FIG. 3) having a tapered internal surface  69  which mates with the tapered surface  62  of the stud  58 . The cylinder  68  also has an outwardly projecting annular flange  72  which is received within a corresponding counterbore  74  within the top wall  32  of the vacuum box  20  and which is secured by peripherally spaced screws (not shown). Each of the coupler cylinders  68  also has an integral cup-shaped cylindrical portion  81  which defines a cavity for receiving the head portion  63  of the corresponding stud  58 , and a plurality of hardened steel locking balls  83  are retained within corresponding circumferentially spaced holes within the cylinder portion  81  for corresponding radial movement. 
     A cup-shaped piston  86  surrounds the portion  81  of the cylinder  68  and has a circumferentially extending internal groove or cavity  88  (FIG. 3) for receiving the balls  83  in their retracted positions when the piston  86  is in its released position (FIG.  3 ). A cylindrical cup-shaped housing  92  surrounds the piston  86  and has an upper end portion threadably connected to the cylinder  68 . The housing  92  confines and supports the piston  86  for axial movement between an upper released position (FIG. 3) with the balls  83  retracted and a lower locked position (FIG. 4) when the balls  83  are cammed radially inwardly to engage the head portion  63  and neck portion  66  of the stud  58 . A flat wire compression spring  96  normally urges the piston  86  downwardly to the locked position of the coupler  55  (FIG.  4 ). When it is desired to release each stud  58  from its cylinder  68 , pressurized fluid or air is introduced into a chamber  98  defined below the piston  86  and within the housing  92  to force the piston upwardly against the bias of the spring to the released position (FIG.  3 ). In this position, the balls  83  move radially outwardly into the cavity or groove  88 , allowing the stud  58  to be lifted and removed from its cylinder  68 . 
     In operation of the quick change tooling system  12 , the vacuum source to the vacuum box  20  is shut off, and pressurized air is simultaneously supplied to the chambers  98  of the locking couplers  55  so that the pistons  86  move upwardly allowing the locking balls  83  to shift to retracted and released positions, as shown in FIG.  3 . The vacuum holding fixture  10  with its attachment plate  14  may then be lifted from the vacuum box  20  and replaced by another vacuum holding fixture with its corresponding attachment plate  14 . After the next vacuum holding fixture and its attachment plate  14  are seated on the top wall  32  of the vacuum box  20 , the air pressure within the chambers  98  of the couplers  55  is released or exhausted, and the compression springs  96  move the pistons  86  downwardly to cam the balls  83  inwardly to their locking positions, as shown in FIG.  4 . When it is desired to replace one holding fixture with another holding fixture, the above steps for removing one fixture and replacing it with another fixture are repeated. 
     From the drawings and the above description, it is apparent that a quick change tooling system constructed in accordance with the invention, provides desirable features and advantages. For example, the tooling system provides for accurately and quickly positioning a vacuum holding fixture  10  on the bed or table of a CNC router and for positively and quickly locking the fixture to the bed or table. As a result, a change of fixtures or other tooling may be performed in only a few minutes so that down time of the router machine and the unproductive time of the machine operator are minimized. The quick change tooling system of the invention also eliminates the need for hand tools, bolts, clamps, shims and other such devices which are commonly used for precisely aligning and securing a router fixture on the table of a router machine. Moreover, as soon as the attachment plate  14  on the bottom of a fixture is seated on the top wall of the vacuum box  20 , a vacuum may be introduced into the vacuum box  20  and the vacuum holding fixture  10  simply by opening a valve in the vacuum line. 
     While the form of quick change tooling system or apparatus herein described constitute a preferred embodiment of the invention, it is to be understood that invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope and spirit of the invention as defined in the appended claims.