Patent Publication Number: US-6981858-B2

Title: Mold interlock

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a continuation of U.S. patent application Ser. No. 09/900,392, filed Jul. 6, 2001, now U.S. Pat. No. 6,558,145, and claims priority under 35 U.S.C. §119(e) in U.S. Provisional Patent Application No. 60/216,274, filed Jul. 6, 2000, the entirety of both of which are incorporated by reference herein. 

   FIELD OF THE INVENTION 
   The present invention is directed to an apparatus for helping one mold half mate with another mold half, and more particularly to a mold interlock or locking device. 
   DESCRIPTION OF THE RELATED ART 
   Molds, such as those used in injection molding, typically include two mold halves that can each be equipped with a mold cavity used to make some part. During molding, relative movement between the mold halves bring the two halves together. A moldable material, such as a plastic, a resin, or the like, is injected into each cavity. After the moldable material has had a certain amount of time to set, the mold halves are separated and the molded part is ejected. 
   This process typically does not take very long. For example, in some molding application, the complete cycle time to make a molded component can be as little as a couple of seconds. 
   Molds are equipped with mold interlocks that help ensure accurate alignment and guidance of the mold halves during mold setup and later when they are repeatedly being brought together during operation. Such locks are also intended to help ensure guidance between mold cores and stripper inserts, when such mold components are used. 
   Typically, each mold has four such interlocks with an interlock located along each side of the mold. Each interlock includes a head, or male portion, that is attached to one mold half and a receptacle, or female portion, that is attached to the other mold half. When the mold halves come together, the head of each interlock is received in its respective receptacle helping to ensure accurate mating of the mold halves. 
   During mold setup, interlocks are attached to the mold halves at parting line and one mold half is brought into mating contact with the other mold half. When mated, the head of each interlock is received in its respective receptacle. Various components of the mold are thereafter adjusted to locate the mated mold halves relative to each other. This helps ensure smooth, fast and accurate operation of the mold during molding operation. 
   During molding operation, as the mold halves are brought together, the head of each interlock is received in the receptacle. The receptacle has one or more sidewalls that guide movement of the head as it enters and moves into the receptacle. As the head enters and moves into the receptacle it helps guide the mold halves together to ensure that that they accurately mate with each other. By helping to ensure accurate mating, mold interlocks help correct or compensate for slight misalignment between mold halves. This also helps ensure that mold cavities accurately overlie each other during molding and that the mold cavity shut-offs properly align. 
   One very common type of mold interlock is a side lock. A side lock has a head that extends outwardly from a horizontal mounting base that is of square or rectangular cross section. The head is defined by straight sidewalls that are typically generally perpendicular to the base. During operation, the head is received in a receptacle that is defined by a pair of straight sidewalls that are generally parallel to the straight sidewalls of the head. 
   Side locks are simple to use and install. They typically designed with an angular clearance of zero degrees and a dimensional clearance of between 0.0002 and 0.0004 inch between the head and the receptacle. They also allow for thermal expansion of the mold halves when properly installed. Zero clearance locking fitting typically is not required. 
   They are not without drawbacks. Their relatively narrow clearance means that they can bind if not opened in parallel, which can occur if there is some misalignment. These types of locks give little protection to smaller angle shut-offs, which can lead to shut-off misalignment or clashing. They usually need lubrication, which means that they cannot be used in certain medical and food component molding applications where lubricants typically cannot be used. Even when lubricated, metal to metal contact between the head and receptacle often result in excessive wear because any lubricant is often wiped during mold operation. 
   Another common type of lock is a rectangular tapered interlock. They are similar in construction to a side lock, except that its head is longer and its sidewalls tapered. While its sidewalls that define its head are straight, each sidewall has a taper angle of about 10° from perpendicular. Each sidewall of the receptacle in which the head is received is complementarily tapered. This type of lock is machined into both cavity mold halves at parting line and adjusted to zero clearance by grinding the overall height of the head. 
   This type of mold interlock is easy to install, provides a larger contact area, and accommodates greater mold misalignment than does a side lock. However, it too suffers from many of the drawbacks of side locks. For example, its tapered straight sidewall construction provides little protection to relatively small angle shut-offs. As a result, shut-off misalignment or clashing can undesirably occur. Lubrication can also be a problem. This can limit its use and lead to premature replacement due to excessive wear. 
   A still further type of mold interlock is a tapered round interlock. It has a head defined by a tapered, conical sidewall that is received in a complementary receptacle. Its application is limited because it does not accommodate thermal expansion and provide little protection for smaller angle shut-offs. 
   What is needed is a mold interlock that does not suffer from at least one or more of the aforementioned drawbacks. What is also needed is a mold interlock that is more economical to use. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a mold interlocking device that includes one portion that is attached to one mold half that has a head that is received in a pocket in a receptacle of another portion that is attached to the other mold half. In one preferred embodiment, the head has a sidewall with at least one channel in it for receiving an insert that facilitates insertion of the head into the pocket when one mold half is being brought toward the other mold half. In another preferred embodiment, the head includes a pair of spaced apart and generally parallel sidewalls that has a tapered section disposed between a straight section and a mounting base from which the head extends. The pocket is defined by sidewalls of complementary contour. In a still further preferred embodiment, the head includes a second tapered section that is located between its free end and the straight section. 
   In one preferred mold interlock embodiment, the head has a pair of spaced apart sidewalls that each have a plurality of channels therein. The head extends outwardly from the mounting base and the base is removably mounted to a mold half. An insert is received in each channel. Preferably, a portion of each insert extends outwardly beyond the sidewall in which it is disposed so that it can make contact with a sidewall of the pocket during insertion of the head into the pocket. In a preferred insert embodiment, each insert comprises a roller that is capable of rotation relative to the head. In one preferred roller embodiment, each roller comprises a needle bearing. In one preferred embodiment, each sidewall has three channels with a roller disposed in each channel. 
   Each channel is comprised of a pair of generally parallel lips that curl slightly around a roller received in the channel to retain the roller. Preferably, the channel and the lips are constructed such that at least about one-quarter of the roller surface is exposed. Each lip is constructed to provide a slight amount of clearance to facilitate rotation as well as to permit lubricant on a roller to pass between it and the roller. Additional clearance between the channel and the roller interiorly of the lip so as to provide a reservoir for lubricant. This reservoir helps lubricate and thereby increase the life of the roller. 
   The head includes a pair of spaced apart endwalls that bracket the sidewalls. Each channel preferably has an entrance in at least one of the sidewalls to permit insertion of a roller therein. A stop prevents withdrawal of the roller once it has been inserted. A preferred stop embodiment is a plate that is removably attached to the sidewall. If desired, the channel can extend through both endwalls and a pair of such stop plates can be used to retain rollers in their respective channels. 
   The channels are located in a straight section of each sidewall, which preferably are generally parallel to each other. Each sidewall preferably further includes an tapered section disposed between its straight section and the mounting base. The tapered section is outwardly tapered such that the head is wider adjacent the mounting base than adjacent its free end. When the head is inserted into the pocket, each tapered section preferably bears against a portion of a pocket sidewall to help ensure that a positive interlock is achieved. 
   The receptacle includes a pair of spaced apart upstanding arms that extend outwardly from a mounting base that mounts to a mold half. The receptacle includes a bottom wall and a pair of spaced apart and generally parallel sidewalls that are spaced apart so as to define a pocket therebetween that receives the head when one mold half is being brought toward the other mold half. The sidewalls are spaced apart so as to provide sufficient clearance for entry of the head while still accommodating some mold misalignment. In one preferred embodiment, the clearance between the head and pocket sidewall is at least 0.0005 inch to accommodate greater misalignment than a side lock. 
   In one preferred embodiment, each pocket sidewall has a tapered section adjacent the pocket mouth. Preferably, each tapered section tapers outwardly such that the width of the pocket adjacent its mouth is greater than the width of the pocket adjacent the bottom wall. Each tapered sidewall section of the receptacle bears against a corresponding tapered sidewall section of the head when the head is nearly completely inserted into the pocket to help correct misalignment. Preferably, when the head is inserted into the pocket, the tapered section of each head sidewall bears against a corresponding pocket sidewall such that there is zero clearance therebetween to help correct misalignment. 
   In a second mold interlock embodiment, the insert comprises a rectangular plate and each head sidewall preferably is equipped with only a single channel. To help prevent movement of the plate during mold operation, the lips of the channel converge slightly toward each other such that the channel is narrower on one end. The plate is of complementary construction such that it abuts against the lips during insertion and there is engagement between the lips and the plate that prevents lateral plate movement. 
   The plate is constructed so as to be replaceable, such as when wear warrants. In one preferred embodiment, the plate is intended to be sacrificial. In one preferred plate embodiment, the plate is comprised of a metal and includes spaced apart plugs embedded therein. Each plug preferably is comprised of a friction reducing material that can be a lubricant. For example, in one preferred plug embodiment, each plug is comprised of graphite. In another plate embodiment, the plate is comprised of a plurality of layers and can be of laminate construction. In one preferred plate embodiment, one of the layers comprises a friction reducing material that can be a lubricant. 
   In still another mold interlock embodiment, each head sidewall includes a second tapered section that is disposed between its free end and the straight sidewall section. The second tapered section is inwardly tapered such that the width of the head adjacent its free end is narrower than where the head sidewalls are straight. The second tapered section provides additional clearance that accommodates greater misalignment. 
   Objects, features and advantages of the invention include one or more of the following: to provide a mold interlock having improved wear resistance; to provide a mold interlock that tolerates mold misalignment while rapidly correcting the misalignment and providing protection to relatively small angle shut-offs; to provide a mold interlock that has replaceable wear surfaces for reduced operating costs; to provide a mold interlock that can be used in applications where liquid lubricants cannot be used; to provide a mold interlock that includes a reservoir for liquid lubricant that would ordinarily be wiped free of the interlock during mold operation; to provide a mold interlock that is particularly well suited for use in plastic injection molding applications; to provide a mold interlock that achieves one or more of the benefits of side locks, tapered rectangular interlocks and round interlocks without one or more of their disadvantages; to provide a mold interlock that accommodates greater misalignment while still achieving zero clearance when completely seated; and to provide a mold interlock that is of simple, durable, robust, tough and economical construction and which is simple to install and use. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred exemplary embodiments of the invention are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout and in which: 
       FIG. 1  is an exploded perspective view of a first preferred embodiment of a mold interlocking device of this invention; 
       FIG. 2  is an enlarged fragmentary cross sectional view of a part of the mold interlocking device of  FIG. 1  depicting a roller insert that facilitates mold interlocking and a channel in which the roller is received; 
       FIG. 3  is an end view of a mold with its two halves mated and the mold interlocking device in a closed position engaging one mold half; 
       FIG. 4  is a cross sectional view of the mold with its halves separated depicting a plurality of the mold interlocking devices; 
       FIG. 5  is a top view of a mold half equipped with four spaced apart interlocking devices preferably disposed along parting lines of the mold; 
       FIG. 6  is an exploded perspective view of a second preferred embodiment of an interlocking device; 
       FIG. 7  is an end view of a mold with its halves separated; 
       FIG. 8  is an enlarged side view of the mold interlocking device of  FIG. 6  that includes a locking apparatus; 
       FIG. 9  is a top view of a mold half equipped with four spaced apart mold interlocks of the type shown in  FIG. 6 ; 
       FIG. 10  is an enlarged perspective view of a head of a third preferred embodiment of a mold interlock; 
       FIG. 11  is an exploded perspective view of a fourth preferred embodiment of a mold interlock; 
       FIG. 12  is an exploded perspective view of a fifth preferred embodiment of a mold interlock; 
       FIG. 13  is a cross sectional view of the head of the mold interlock of  FIG. 12 ; 
       FIG. 14  is a cross sectional view of the receptacle of the mold interlock of  FIG. 12 ; 
       FIG. 15  is an enlarged cross sectional view of the insert of the mold interlock of  FIG. 12 ; 
       FIG. 16  is a side elevational view of the mold interlock of  FIG. 12 ; 
       FIG. 17  is an exploded perspective view of a sixth preferred embodiment of a mold interlock; 
       FIG. 18  is a cross sectional view of the head of the mold interlock of  FIG. 17 ; and 
       FIG. 19  is a cross sectional view of the insert of the mold interlock of  FIG. 18 . 
   

   DETAILED DESCRIPTION OF ONE OR MORE PREFERRED EMBODIMENTS 
     FIGS. 1–5  depicts a mold interlocking device  20  that includes a locking device  22  that is carried by one mold half  24  and which registers with a receptacle or receiver  26  that is carried by another mold half  28  during mold operation. The receiver  26  has a pocket  30  that receives at least a portion of device  22  when both mold halves are closed. 
   The locking device  22  has a base  32  that is generally cylindrical in the preferred embodiment shown in  FIGS. 1–5 . The base  32  includes some means for attaching the device  22  to one of the mold halves. For example, the base  32  has a pair of spaced apart bores  34 ,  36  that can each be threaded for receiving a threaded fastener, such as a bolt or screw. Referring to FIG.  4 , there is a pair of bolts  38 ,  40  that attach the device  22  to mold half. Preferably, the base  32  is disposed in a recess formed in the mold half to which it is attached. 
   The receiver  26  also includes some means for attaching it to another one of the mold halves. For example, as is shown in  FIG. 1 , the receiver  26  has a pair of spaced apart bores  42 ,  44  that can each be threaded. As is shown in  FIG. 4 , a pair of bolts  46 ,  48  are used to attach the receiver  26  to mold half. Preferably, the receiver  26  is disposed in a recess formed in the mold half to which it is attached. 
   The locking device  22  has a head  50  that is disposed in the pocket  30  of the receiver  26  when the mold halves  24 ,  28  are brought together. The head  50  has a generally rectangular cross sectional shape and includes a top wall  52 , a pair of end walls  54 ,  56 , and a pair of sidewalls  58 ,  60 . The sidewalls  58 ,  60  each have a tapered section  62 ,  64 , that tapers inwardly from adjacent the base  32  slightly toward each other toward the front wall  52 , such as is depicted more clearly in  FIG. 4 . As a result, the width of the tapered section  62 ,  64  of the head  50  is greater than the width of the head  50  adjacent its free end  52 . 
   As is shown more clearly in  FIG. 3 , each tapered section  62 ,  64  is disposed between the base  32  and a straight section  65 ,  67  in which inserts in the form of pins or rollers  68  are disposed. In one preferred embodiment, the straight sections  65 ,  67  are parallel and disposed parallel to a longitudinal axis  100  of the head  50 . 
   Where the head  50  has a tapered sidewall construction, it preferably also helps more accurately locate one mold half relative to the other mold half when the mold halves are closed. The tapered sidewall construction preferably also serves as a stop that helps limit movement of one mold half toward the other mold half when the mold is closed, such as during molding. In a preferred embodiment, each tapered section  62 ,  64  is disposed at an angle of between 7° and 10° relative to its corresponding straight sidewall section. In another preferred embodiment, each tapered section is disposed at an angle of between 7° and 10° relative to longitudinal axis  100 . 
   In another preferred embodiment, where additional clearance between the head  50  and receiver  36  during entry of the head  50  into the receiver  26  is desired, the head  50  can have a somewhat frustoconical cross sectional shape such that it is slightly narrower adjacent its free end. 
   At least one sidewall, preferably each sidewall  58 ,  60 , has a plurality of spaced apart grooves or channels  66  that preferably are parallel and disposed in its straight sidewall section. In the preferred embodiment depicted in  FIGS. 1–4 , each channel  66  preferably runs the full length or substantially the full transverse length of the sidewall, preferably from one end wall  56  to the other end wall  54 . Each channel  66  receives a pin or roller  68  that preferably has a generally cylindrical shape and can be tubular. 
   In the preferred embodiment depicted in  FIGS. 1–4 , each channel  66  preferably comprises an elongate raceway, preferably a bearing raceway. An example of one preferred roller  68  is a roller bearing, such as a roller bearing needle or tapered roller bearing that can be comprised of a metal, such as steel, or a non-metal material, such as a composite or a ceramic material. 
   Referring to  FIG. 2 , the cross sectional shape of each channel  66  preferably is generally complementary to that of the roller  68  that will be received in it. In a preferred channel embodiment, the channel  66  has a pair of arcuate sidewalls  70 ,  72  that form a mouth  74  through which the roller  68  is exposed. The rear of the channel also includes a flat  76  and each sidewall edge has a lip  78 ,  80  that narrows the clearance between it and the roller  68  received in the channel  66  from about 0.005 inches to virtually no clearance at all. In the preferred embodiment shown in  FIG. 4 , there is a clearance preferably of no more than 0.001 inches between each lip  78 ,  80  and the roller  68  and preferably there is no clearance between the flat  76  and the roller  68 . If desired, each lip  78 ,  80  can be rounded as shown in  FIG. 2 . The flat  76  helps maintain location of the roller  68  and can be comprised of a lubricant that gets distributed on the roller  68  during molding operation. 
   The channel configuration in  FIG. 2  is advantageous because it helps minimize friction, thereby extending the useful life of the head  50 . Where lubrication is used, the relatively small clearance between each lip  78  and roller  68  is sized to permit flow of lubricant into a reservoir  77  created by the larger clearance that is disposed interiorly. As indicated above, the preferred clearance between lip  78  and roller  68  is no more than 0.001 inch. Where equipped with a flat  76 , a second reservoir  79  is created. As a result of the creation of one or more reservoirs, lubrication placed on the head  50  or in the pocket  30  of the receiver  26  that ordinarily would be wiped away during operation, accumulates in at least one of the reservoirs  77 ,  79 . Rotation of the roller  68  along with the clearance between it and lip  78  permits a film of lubricant to coat at least part of the roller  68 , thereby reducing friction and wear. Lubricant also needs to be added less frequently because it is retained longer. Preferably, where lubricant is added, it is added no more frequently than every 25,000 cycles of the mold opening and closing. 
   Each channel  66  preferably is constructed so that it encompasses or encircles greater than 180° around a roller  68  received in the channel  66  so that the roller  68  is retained in the channel  66  and will not pass out the mouth  74 . Each channel  66  is also constructed so that a portion of the roller  68  extends outwardly beyond the sidewall  58  so that it, not the sidewall  58 , comes into contact with a portion of the receiver  26  when the mold halves  24 ,  28  are closed. In the preferred embodiment depicted in  FIG. 2 , the channel  66  encompasses or encircles as much as about 270° of the roller  68 . 
   As a result, preferably no more than about 90° of each roller  68  is exposed in a preferred channel construction. This arrangement also permits roller  68  contact with a sidewall surface of the receiver  26  during insertion without any other part of the head  50  contacting the receiver  26 . This helps ensure that contact between the head  50  and receiver  26  rotates at least one roller  68 , which reduces friction because roller rotation creates a dynamic friction condition instead of a static friction condition that normally results during operation of conventional mold interlocks. 
   Each channel  66  preferably extends to at least one of the endwalls  54 ,  56  such that there is an opening therein for permitting roller insertion. Once inserted, all of the rollers  68  are kept axially captive in its respective channel  66  by at least one end plate  82  that is removably attached to an end wall of the head  50  by a fastener, such as a screw, a bolt, or another type of fastener. In the preferred embodiment shown in  FIGS. 1–4 , there is a pair of such end plates  82 ,  84  each of which is attached by a screw  86 . 
   Each roller  68  can rotate relative to the rest of the locking device  22  to facilitate docking or seating of the head  50  of the locking device  22  with the receiver  26 . If desired, each roller  68  and/or each channel  66  can be lubricated to help reduce wear. If desired, each roller  68  and/or each channel  66  can be impregnated with lubricant, be made of a self-lubricating material and/or be made of a material that has a low coefficient of friction. In a preferred embodiment, liquid lubricant is added to the head  50  and/or the pocket  30  of the receiver  26  no more frequently than every 25,000 mold cycles. 
   The receiver  26  includes a base  88  from which a pair of arms  90 ,  92  extend, between which is disposed the locking device head-receiving pocket  30 . There preferably is a radiused portion  93 ,  95  between each arm  90 ,  92  and the base  88  to prevent cracking during operation. The pocket  30  is defined by a pair of opposed sidewalls  94 ,  96  and a bottom wall  98 . In the preferred embodiment depicted in  FIGS. 1 ,  3  and  4 , the sidewalls  94 ,  96  preferably are substantially parallel and the pocket  30  comprises a slot in which the head  50  is received when docked or seated. Preferably, the sidewalls  94 ,  96  are straight and generally parallel relative to a longitudinal axis  100  ( FIG. 4 ) of the locking device  50 . 
   In a preferred embodiment, a section  102 ,  104  of each sidewall  94 ,  96  can taper slightly outwardly away from each other, such as is depicted in  FIG. 4 , to help facilitate entry of the head  50  into the pocket  30 . Each tapered section  102 ,  104  preferably is tapered at an angle that avoids lockup of the head  50  during insertion. In a preferred embodiment each tapered section  102 ,  104  is tapered at an angle of between 7° and 10° relative to the straight section of its corresponding sidewall  94 ,  96 . In another preferred embodiment, each tapered section  102 ,  104  is tapered at an angle of between 7° and 10° relative to horizontal axis  100 . Preferably, the taper angle of each tapered sidewall section  102 ,  104  is substantially the same as the taper angle of each tapered sidewall section  62 ,  64  of the head  50 . As a result, the tapered sections  62 ,  64 ,  102 ,  104  bear against each other when the head  50  is completely seated in the pocket  30  to accommodate and preferably correct mold misalignment. When seated, there preferably is zero clearance between the mated tapered sections  62 ,  64 ,  102 ,  104  to correct misalignment. 
   The sidewalls  94 ,  96  preferably are spaced apart just enough so that the rollers  68  in the head  50  of the locking device  22  will contact them and ride them during docking. In a preferred embodiment, there is zero clearance on each side between the rollers  68  and the straight section of each sidewall  94 ,  96 . Rotation of the rollers  68  helps facilitate quick and easy closing of a mold while also helping to ensure that the one half  24  of the mold is more accurately located relative to the other half  28  of the mold. Rotation of the rollers  68  during registry of the head  50  with the receiver  26  helps reduce friction, decrease wear, and increase the life of the novel mold interlock. 
   Although the mold interlock  20  is shown in its seated position with a slight gap between the head  50  and bottom wall  98  ( FIG. 1 ) and a slight gap between the ends of arms  90 ,  92  and the top of the base  32  of the locking device  22 , the mold interlock  20  preferably is constructed such that when seated, there is abutment at least between the ends of arms  90 ,  92  and the top of base  32 . Such an arrangement preferably prevents the buildup of bending moments on the arms  90 ,  92 . If desired, the mold interlock  20  can also be constructed such that the end of the head  50  abuts against the bottom wall  98  of the pocket  30  of the receiver  26 . 
   Referring to  FIG. 4 , the base  32  of the locking device  22  is disposed in a pocket or bore in one half  24  of the mold and the receiver  26  is disposed in a pocket or bore in the other half  28  of the mold. The head  50  of the locking device  22  projects outwardly from the base  32  beyond the top surface  106  of the mold half in which it is mounted. In the preferred embodiment shown in  FIG. 4 , both the locking device  22  and the receiver  26  are attached by fasteners. 
     FIG. 5  illustrates a mold half  24  with a plurality of spaced apart mold interlocks  20 . In the exemplary mold shown in  FIG. 5 , there is a locking device  22  disposed along each side of the mold with at least one mold cavity  108  disposed between them. 
     FIGS. 6–9  illustrate a second preferred embodiment of a locking device  22   a . The locking device  22   a  shown in  FIG. 6  is similar to the locking device  22  shown in  FIG. 1  except that it need not be of cylindrical construction and it can accommodate a locking strap  110  that is used to keep the mold closed. Additionally, mounting of both the locking device  22   a  and the receiver  26   a  is accomplished using fasteners  112 ,  114  that are disposed generally perpendicular to the longitudinal axis  100  of the locking device head. Such a mounting arrangement permits both the receiver  26   a  and locking device  22   a  to be disposed in a pocket in a sidewall  116 ,  118  of the mold instead of in a top wall or top surface of the mold. An advantage of mold interlock device  22   a  is that it is configured to retrofit molds that previously used side locks. 
     FIG. 9  illustrates a mold half  24  with a plurality of spaced apart locking devices  22   a . In the exemplary portion of the mold shown in  FIG. 9 , there is a device  22   a  disposed along each side of the mold with at least one mold cavity  108  disposed between them. Preferably, each device  22   a  is disposed along a mold parting line. 
     FIGS. 10 and 11  illustrates the head  50   a  of another preferred embodiment of a locking device  22   b . The head  50   b  includes a removable sacrificial insert  120  that is carried by each sidewall. The insert  120  can be made of hardened steel, but preferably is made of a material having reduced friction characteristics. For example, the insert can be made of bronze plated soft steel, bronze plated hardened steel, or bronze. Where made of bronze plated soft steel, bronze plated hardened steel, or bronze, the mold interlocking device  22   b  need not be lubricated. 
   The insert  120  shown in  FIG. 11  differs from that shown in  FIG. 10  in that it slightly tapers and is received in a channel  122  defined by a pair of lips  124 ,  126  that also taper such that the channel  122  is complementary with the insert  120 . In a preferred embodiment, the taper of each lip  124 ,  126  of each channel  122  tapers inwardly about 2° such that one end  128  of the channel  122  is wider than the other end  130 . The sidewalls  132 ,  134  of the insert  120  shown in  FIG. 11  preferably also tapers at an angle of about 2° such that the insert  120  is wider at one end  136  than at the other end  138 . As a result, the insert  120  wedges into the channel  122  in which it is insert such that it preferably will not move during operation. 
     FIGS. 12–16  depict another preferred embodiment of a locking device  22   c . This device  22   c  is similar to the locking devices shown in  FIGS. 10 and 11  except that the insert  120  is equipped with spaced apart plugs  140  that reduce friction. In a preferred embodiment, the plugs  140  are embedded in an outer surface  142  of each insert  122 . Each plug  140  can be comprised of a solid lubricant such as graphite, carbon graphite matrix, polytetrafluoroethylene, or another type of solid lubricant. The use of such lubricant plugs  140  advantageously eliminate the use of liquid lubricant, which allows use in applications where no liquid lubricant can be used. 
     FIG. 13  depicts a sidewall configuration that facilitates registry of the head  50   b  with the receiver  26 . In addition to outwardly tapered sidewall sections  62 ,  64 , the sidewalls of the head  50   b  include second inwardly tapered sections  146 ,  148 . The inwardly tapered section  146 ,  148  reduces the width of the head  50   b  adjacent its free end to provide increased clearance between the head  50   b  and the receiver  26 . Increased clearance enables the interlock to accommodate greater misalignment between the mold halves. In a preferred embodiment, the angle of each tapered section  146 ,  148  is at least 15° relative to longitudinal axis  100  or the straight portion of its corresponding sidewall. Preferably, the taper angle is between 20° and 30° to rapidly take up misalignment as the head  50   b  is entering the pocket  30 . 
   Still referring to  FIG. 13 , the straight portion of each head sidewall is disposed between the outwardly tapered portion and the inwardly tapered portion. More specifically, the straight portion of each head sidewall comprises the outer surface  142  ( FIG. 12 ) of the insert  120 . Each inwardly tapered portion  146 ,  148  is disposed between the free end of the head  50   b  and the outer surface  142  of the insert  120 . Each outwardly tapered portion  62 ,  64  is disposed between the outer surface  142  of the insert  120  and the base  32 . 
   Referring to  FIG. 15 , the insert  120  has an outer surface  140  that preferably forms the straight portion of each head sidewall. The insert  120  also includes a rear wall  150  that preferably abuts part of the head  50   b  when the insert  120  is received in a channel  122 . The insert  120  includes a top wall  152  that is disposed at an angle of at least about 7° relative to a line perpendicular to the rear wall  150 . The angle of the top wall  152  is complementary with that of top lip  126  to retain the insert  120  in the channel  122 . The insert  120  further includes a bottom wall  154  that is also inclined at least about  70  relative to a line perpendicular to the rear wall  150 . The angle of the bottom wall  154  is complementary with that of bottom lip  126  to retain the insert  120  in the channel  122 . The insert  120  further includes a canted section  156  that forms part of the inwardly tapered section  146  or  148  when the insert  120  is received in a channel  122 . 
     FIGS. 17–19  illustrate another preferred embodiment of insert  120  that is comprised of a plurality of layers and which can be of laminate construction. As is shown in  FIG. 17 , the outer layer  158  is comprised of a material that facilitates registry of the head  50   b  with the receiver  26 . In one preferred embodiment, the outer layer  158  is comprised of a wear resistant material, such as a hardened steel, a tool steel, a high speed steel, or bronze. In another preferred embodiment, the outer layer  158  is comprised of a solid lubricant. In a still further preferred embodiment, the outer layer  158  comprises a coating that can be dipped, sprayed on, ion implanted, or drawn into the matrix of the underlying base  160 . The base  160  preferably is made of metal, such as a steel, but can be made of another material. 
   The interlocking apparatus  20  advantageously helps assure positive alignment between mold halves or between plate or individual cavities and cores. During operation, the head  50  moves toward the receiver  26  until it enters the pocket  30 . As it enters the pocket  30 , a portion of the head  50  typically contacts a portion of the receiver  26 . 
   Where the head  50  is equipped with roller inserts  68 , a roller  68  typically contacts the receiver  26 . When the roller  68  contacts the receiver  26 , it contacts a sidewall  94 ,  96  and preferably begins rotating. Rotation facilitates further movement of the head  50  into the receiver  26  as it reduces friction therebetween. The rounded exterior  68  of the contacting roller  68  also helps facilitate smooth registry and can accommodate some slight misalignment between mold halves. 
   As the head  50  travels farther into the pocket  30 , tapered head sidewall sections  62 ,  64  bear respectively against the tapered sidewall sections  104 ,  102  seating it in zero clearance and helping to accurately locate one mold half relative to the other mold half. Tapered sidewall section  102 ,  104  also serve to widen the mouth of the pocket  30  to help accommodate additional mold misalignment while also rapidly moving the mold halves toward alignment in a manner that protects smaller angle, e.g. 10 degrees or less, shut-offs. 
   Where the head  50  is equipped with plate inserts  120 , an exterior surface of one of the plates  156  or  142  preferably makes first contact with one of the sidewalls  94  or  96 . Tapered head section  146 ,  148  in combination with tapered section  102 ,  104  provide additional clearance to compensate for mold misalignment while rapidly reducing that clearance as the head  50  travels farther into the pocket  30 . As the head  50  travels farther into the pocket  30 , the inserts  120  on both sides are capable of making contact with sidewalls  94 ,  96 . As contact is made, the mold halves are brought further into alignment until tapered surfaces  62 ,  64  seat against tapered surfaces  102 ,  104  bringing the mold interlock into zero clearance alignment. 
   Each component of the interlocking apparatus can advantageously be economically produced using currently available production equipment, such as CNC mills, wire EDM machines, and CNC grinders and other types of machining and forming equipment. The head  50 , including in particular its insert-receiving channels, is machined using a wire EDM machine or a CNC grinder. 
   The roller arrangement advantageously allows for less required clearance at lower friction preferably without using a liquid lubricant (or much less liquid lubricant) as compared to a conventional interlocks. This is especially advantageous for medical molding and other high precision molding applications where grease or some other lubricant is not allowed. When properly installed in a mold, heated mold halves are permitted to expand independently while still being able to maintain a precise positive alignment relative to the centerline of the mold. The round base design shown in various drawing figures is advantageously self-centering around its own axis with a simplified round bore mold installation. The final lockup of the mold occurs with a tapered zero clearance lock, which helps keep the mold halves or cores from shifting due to internal mold pressure, such as from injected plastic or another molding material. 
   It is also to be understood that, although the foregoing description and drawings describe and illustrate in detail one or more preferred embodiments of the present invention, to those skilled in the art to which the present invention relates, the present disclosure will suggest many modifications and constructions as well as widely differing embodiments and applications without thereby departing from the spirit and scope of the invention.