Abstract:
An improved molding apparatus and method includes an adjustable mold component and a fixed mold component for molding precision articles; a bias force mechanism for applying a bias force to the adjustable mold component; and an adjustable mold component fine position adjustment mechanism operable exteriorly of the mold for applying a position adjustment force to the adjustable mold component to overcome the bias force and thereby adjust position of the adjustable mold component relative to a fixed mold component to reduce positional offset in a range of ±ten microns, or less, in at least one adjustment dimension. In one aspect, a plurality of bias force mechanisms and adjustment mechanisms provide positional adjustment in a plurality of adjustment dimensions. In another aspect, a feedback control loop responsive to optically sensed positional error automatically reduces positional offset.

Description:
FIELD OF THE INVENTION 
   The present invention relates to improved methods and apparatus for injection molding of articles having micron-range precision. 
   BACKGROUND OF THE INVENTION 
   The true position accuracy of mechanical features of a molded article is determined by accuracy of associated features of a mold used to produce the article. The true position accuracy of the mold features is, in turn, determined by the accuracy of fabrication of the mold components, the accumulation or stack-up of tolerances of the various components comprising the mold, the clearance gaps required to enable the mold to be assembled and disassembled, the clearance gaps required to enable moving parts of the mold to move freely, the accuracy with which the two halves of the mold are positioned relative to each other, the movement of the mold components that results from forces imparted to the mold during the molding process, the deformations of the mold resulting from forces imparted to the mold during the molding process, and changes that occur to mold components as a result of wear and tear over the useful service life of the mold. The tolerance limits to the true position accuracy of features of the molded article, which result from the sum of the foregoing factors, determine the suitability or ability of a particular molding process to produce a particular article capable of satisfying specified fit and function requirements. These limitations apply across the entire range of molding technology including injection molding, compression molding, transfer molding, ceramic molding, metal molding, sintering, or glass molding, for example. 
   There is a continuing need to produce molded parts with accuracy requirements exceeding the cumulative accuracy permitted by the limiting factors set forth above. As mold fabrication techniques have improved, the tolerances achievable via molding processes have accordingly improved, enabling manufacture of molded articles having accuracies previously not achievable. However, there are inherent limits to what can be achieved by improving the precision in execution of conventional molding techniques and with conventional mold tooling architectures. 
   Molded subassemblies are rapidly displacing subassemblies formed out of discrete components. For example, conventional optical subassemblies used in fiber optic transceivers typically have multiple structural elements including expensive discrete glass lens arrays. Requirements of individual component costs and manual assembly cause such subassemblies to be relatively very expensive, currently on the order of about $40.00 per completed subassembly. The assignee of the present invention has developed injection molding processes which enable production of one-piece molded polymeric optical components for use in fiber optic transceivers at much lower unit costs, currently on the order of about $4.00 per completed component. Precision molded optical subassemblies formed of optical grade thermoplastic polymers find practical use not only in fiber optic transceivers but also in fiber optic connectors, cameras in cell phones and the like, sensors in printers and scanners, and biomedical devices, for example. 
   A typical injection molding process includes steps of bringing two complementary mold halves holding die inserts with features defining an article to be molded into a close facing proximity, injecting e.g., a thermally plasticized polymer material as an amorphous mass into a molding volume or space between the die halves; applying sufficient pressure to the plasticized polymer to cause it to conform to the features of the molding volume defined by the die halves; allowing the material to cool in the mold to cause the material to resume a solid phase (“freeze”); moving the die halves apart; and, removing the molded article. The molding process cycle may then be repeated. Evidently, there are many tolerances associated with injection molding, particularly with regard to maintaining accuracy of alignment of the moving die half relative to the fixed die half. Mechanical alignment tolerances include three positional dimensions (x, y and z), as well as rotational and tilt dimensions. Mold tolerances are additionally affected by changes in temperatures and pressures associated with the molding process as well as mechanical clearances and wear, as noted above. 
   Molding machines typically include massive frames and guiding structures and features, as well as temperature and pressure control systems, in order to regulate, control and hopefully minimize molding process tolerances. Yet, as dimensional requirements for molded articles approach the micron range, the conventional techniques for controlling tolerances have proven inadequate. Control of molding dimensions to a tolerance of about ±one micron has heretofore proven illusive, if not practically impossible. Yet such tolerance is needed in order to provide molded optical components for plural-lens single-mode optical fiber applications, for example. 
   Various tolerances associated with thermoplastic injection molding may be understood by considering the molding environment.  FIG. 1  illustrates a conventional thermoplastic injection molding machine  10  that is fitted with a conventional mold. At a high level the molding machine  10  essentially includes a massive base or frame  12 , a fixed platen  14  directly secured to the base  12 , a fixed mold-half  16  secured to the fixed platen  14 , a moveable platen  18 , a moveable mold-half  20  secured to the moveable platen  18 , a platen actuator  22  secured to the base  12  for moving the moveable platen  18  toward and away from the fixed platen  14  along leader pins  24 , a hopper  26  for holding a supply of thermoplastic pellets, a plasticizer-injector  28  for plasticizing a quantity of thermoplastic pellets and for injecting a plastic-state amorphous mass via a conduit  30  through the fixed platen  14  and fixed mold-half  16  and into a molding volume  32  defined when the moveable mold-half  20  is forced to close against the fixed mold-half  16  by the actuator  22 . Force equivalent to 20 to 250 tons, more or less depending upon the molding machine, may be exerted by the actuator  22  against the moveable platen  18  and moveable mold-half  20  during the mold-closing operation.  FIG. 1  illustrates the molding machine in a mold-open position. Details such as heating/cooling supplies and conduits, automatic picker-gripper tooling for engaging and removing each molded article from the mold following molding, and mold machine controls, are not shown in  FIG. 1  but would be present in practical embodiments of automatic molding apparatus, as is well understood by those skilled in the art. 
     FIG. 2  illustrates a mold-half  20  for molding thermoplastic precision optical lens arrays in accordance with the prior art. This conventional mold-half  20  includes a number of alignment features and components. To begin with, the leader pins  24  guide the moveable mold-half  20  relative to the fixed mold-half  16  with a tolerance of ±75 microns due to lubricant thicknesses, etc. Zero-degree interlocks  34  engage complementary features of the fixed-mold half  16  and reduce relative positional tolerance between mold halves to about ±12 microns. A cavity block  40  is mounted to each mold half. According to current industry practice, locational precision of the cavity block  40  relative to the mold-half  20  is established by a precision fit with sufficient tolerances or gaps to enable insertion and removal of the block  40  from the mold-half cavity. 
   Cavity-block zero-degree interlock pins  42  register the cavity blocks together at mold closure with a tolerance of about ±12 microns. Angled taper locks  44  projecting from the moveable cavity block  40  mate with complementary angled recesses of the fixed cavity block (not shown in  FIG. 2 ) and reduce closure tolerance to about ±3 microns, establishing the smallest molding tolerance achievable with contemporary molding techniques of the prior art. A mold insert  46  defining structural features to be formed in the molded article is precisely fitted into an opening of the cavity block  40  and locked in place. The positional accuracy of the mold insert  46  relative to the cavity block  40  is limited by the precision of fit achievable in the particular molding operation. In the present example of a molded component with two precision optical lens surfaces, diamond-ground precision optical lens pins  48  are installed in the mold insert with a precision limited by the particular fit. 
   In order to form a precision optical lens molded article in accordance with conventional practice, the mold halves  16  and  20  are assembled and installed on the molding machine  10 . A test article is then molded and removed from the machine and carefully measured under a microscope, magnifying optical comparator, or other suitable tolerance measuring apparatus or device to determine dimensional errors and tolerances. Correction calculations are then carried out based on measured errors. At least one of the mold halves  16  and  20  is then removed from the machine, disassembled, dimensionally adjusted to reduce the measured errors in the test article and reassembled. Dimensional adjustments may be carried out by machining to remove mold material and/or plating or other deposition to build up mold material. The testing/adjustment process is repeated until an article is molded having acceptable dimensional/optical tolerances and qualities. Obviously, this mold setup procedure is very time consuming. Additionally, during a production run, molded articles are selected and manually checked to be sure that the molding process remains within tolerance. If articles are found to be out of tolerance, production is stopped and another setup procedure of the type described above is undertaken to correct the out-of-tolerance condition. Also, even though the mold halves  16  and  20  are regulated at precise temperatures and pressures during the molding process, control of molding tolerance at a ±one micron level of accuracy of the molded precision article has not been possible with contemporary techniques. 
   The prior art suggests several techniques for adjusting mold dimensions without requiring removal, disassembly, reassembly and reinstallation of a mold set. In U.S. Pat. No. 5,512,221 to Maus et al., entitled “Lens Thickness Adjustment Method and Apparatus in a Thermoplastic Injection Mold for Opthalmic Finished Spectacle Lenses” a wedge block operated by a manually rotated adjustment knob external to the mold provided a mold-half and mold cavity adjustment to change molded spectacle lens thickness without requiring disassembly of the mold. A slightly different approach using a worm gear mechanism in lieu of a wedge block to change molded spectacle lens thickness is described in U.S. Pat. No. 5,792,392 to Maus et al., entitled: “Lens Thickness Adjustment in Plastic Injection Mold”. These patents concerned controlling spectacle lens thicknesses in the millimeter range, as opposed to the micron range, and as described would not provide sufficiently accurate mold tolerance control to achieve tolerance control in the ±one micron range, due to mechanical tolerances and hysteresis associated with the mechanical components employed in the teachings of these patents to alter the mold thickness. 
   When thermoplastic material changes from a thermoplastic state to a solid state at the end of the molding process, the material typically shrinks slightly. A variety of techniques are known in the art to compensate for shrinkage. One approach is described in Japanese Published Patent Application 61-66623 published on May 4, 1986. This approach measures mold volume indirectly with a variable resistance sensor coupled between the fixed and moveable mold halves and automatically controls mold cavity dimension to achieve a predetermined article thickness. Again, this approach does not appear to describe a molding process having sufficient accuracy to achieve molding tolerance control in the ±one micron range. 
   Active alignment techniques are employed in the optical fiber splicing art in order to maximize light transmission at a fiber splice. In the active technique, light energy is launched into one fiber and its amplitude is measured through the other fiber. The fiber ends are automatically manipulated and spatially/axially adjusted in a manner to produce maximum transmission of light energy thereby denoting axial alignment of the ends. Then, the abutting fiber ends can be joined together by welding or bonding. While active alignment techniques have been employed in optical fiber splicing, they have not heretofore been applied to control mold alignment in a molding process for molding precision articles and components in order to achieve accuracy in the micron range. 
   A hitherto unsolved need has arisen to provide methods and apparatus enabling precision molding of thermoplastic optical articles having dimensional tolerances controlled to an approximate ±one micron range of accuracy. 
   SUMMARY OF THE INVENTION WITH OBJECTS 
   A general object of the present invention is to provide methods and apparatus for injection molding precision articles with micron-range molding accuracy in a manner overcoming limitations and drawbacks of the prior art. 
   Another object of the present invention is to provide methods and apparatus for sensing and correcting positional offset inaccuracies in precision molding of articles in a manner overcoming limitations and drawbacks of the prior art. 
   Another object of the present invention is provide methods and apparatus for injection molding precision articles defining plural spatially-offset features with micron-range molding accuracy in a manner overcoming limitations and drawbacks of the prior art. 
   In accordance with principles of the present invention an improved injection molding apparatus is provided for precision molding articles of thermoplastic material, for example. The molding apparatus typically includes a molding assembly having a moveable mold part and a fixed mold part, a force imparting mechanism for forcing the moveable mold part against the fixed mold part during a molding cycle and for thereafter retracting the moveable mold part from the fixed mold part, and an injection system for injecting thermoplastic material during the molding cycle into a precision molding cavity defined by adjacent faces of the moveable mold part and the fixed mold part of the molding assembly. The improvement includes an adjustable mold component and a fixed mold component, for molding the precision articles; a bias force mechanism for applying a bias force to the adjustable mold component; and an adjustable mold component fine position adjustment mechanism operable exteriorly of the mold for applying a position adjustment force to the adjustable mold component to overcome the bias force and thereby adjust position of the adjustable mold component relative to a fixed mold component to reduce positional offset in a range of ±ten microns, or less, in at least one adjustment dimension. In one preferred aspect, the improvement provides a plurality of bias force mechanisms and adjustment mechanisms enabling positional adjustment in a plurality of adjustment dimensions. Manual operation of the positional adjustment mechanism, and/or automatic adjustment of the positional adjustment in a feedback control loop, is provided. In this regard, one or more position sensors, such as optical position sensors, are provided to sense positional offsets of the adjustable mold component relative to the fixed mold component. Further, electromechanical actuators such as rotary or linear electric motors, piezoelectric actuators, bi-metal actuators, or other known electromechanical force providing elements, may be used to implement the position adjustment mechanism. A feedback control loop including a controller connected to the positional offset sensors and to the electromechanical fine position adjustment devices receives the offset information, determines and applies position correction values to the electromechanical fine position adjustment motors or devices in order to reduce sensed positional offset. The fine position adjustment mechanism may be manually operable, and in the form of a micrometer. The bias force may be provided by metal springs, other elastic or resilient elements or materials, or by a displaceable stop. 
   A method for improving positional accuracy of a moveable mold component relative to a fixed mold component of precision article molding apparatus, comprises steps of:
         a. sensing alignment of the moveable mold component relative to the fixed mold component to produce a positional offset value, and   b. positionally displacing one of the moveable and fixed mold components by applying a displacement force with an adjustment mechanism against a bias force of the molding apparatus without disassembly of the mold components to reduce the positional offset value in a range of 10 microns or less.       

   These and other objects, advantages, aspects and features of the present invention will be more fully understood and appreciated upon consideration of the detailed description of preferred embodiments presented in conjunction with the following drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the Drawings: 
       FIG. 1  is a highly diagrammatic view in side elevation of a molding machine having a two-part mold set for molding precision optical components and the like in accordance with the prior art. 
       FIG. 2  is a view in elevation of one-half of the  FIG. 1  mold set for molding precision optical components in accordance with the prior art. 
       FIG. 3  is a highly diagrammatic view in side elevation of a molding machine of the  FIG. 1  type having a two-part mold set for molding precision articles, components and the like in accordance with principles of the present invention. 
       FIG. 4  is a highly diagrammatic view in elevation of one-half of a mold set for molding precision articles as well as positional control devices and computer-based control elements in accordance with an automatic adjustment embodiment of the present invention. 
       FIG. 5  is a highly diagrammatic view in elevation of one-half of a mold set for molding precision articles wherein positional sensing and control devices enable adjustment of the mold insert in at least two lineal dimensions and one rotational dimension. 
       FIG. 6  is a highly diagrammatic view of a sensor of the type shown in the  FIG. 5  example wherein a photodetector matrix of one mold insert is illuminated by laser light from an optical fiber directed from the other mold insert. 
       FIG. 7  is a flow chart of steps followed in practicing method of the present invention. 
       FIG. 8  is a view in elevation of one-half of a mold set for molding precision optical components in accordance with a manual adjustment embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   With reference to  FIG. 3 , a molding machine  100  of the  FIG. 1  type has been improved for molding precision optical components and the like in accordance with principles of the present invention. In the  FIG. 3  embodiment  100  structural elements and features which remain essentially the same as described in connection with the molding machine  10  depicted in  FIG. 1  bear the same reference numerals, and the descriptions provided above apply to these structural elements as well. 
   The mold half  16  of the machine  10  has been replaced with an improved mold half  102  in the machine  100 . A mold block controller  104 , preferably a programmed digital controller of a type well understood by those skilled in the art of automatic machine tool control, receives information representing sensed position of the cavity blocks, automatically calculates positional offset correction values, and applies those values through a y-dimension electromechanical micro-actuator  106  and an x-dimension micro-actuator  108  to reposition at least one of the cavity blocks relative to the other, in order to reduce offset tolerance to the ±one micron range. Sensing of cavity block relative position may be carried out in a variety of ways and with a variety of known position sensing technologies. In the molding machine  100  shown in  FIG. 3  position sensing is carried out optically. An electro-optical transmitter  100  injects light, such as highly collimated laser light, into an optical fiber  112  which leads to an alignment office of the cavity block located in the fixed mold half  16 . A light beam  113  passes through the alignment orifice and is directed toward an alignment orifice  126  (see  FIG. 4 ) of the adjustable cavity block of the moveable mold half  102 . Therein, another optical fiber  114  receives a component of the light beam  113  and presents that component to an opto-electronic detector  116 . In accordance with known automatic fiber positioning techniques practiced in the optical fiber splicing art, the mold block controller  104  manipulates the position of the moveable cavity block with actuators  106  and  108  in the moving mold half  102  in order to bring about alignment of the cavity blocks by sensing maximized optical intensity at the opto-electronic detector  116 . 
   In the molding machine  100  of  FIG. 3 , the adjustable cavity block is shown to be included as part of the moveable mold half  102 . The adjustable cavity block could be provided in the fixed mold half  16  with equally satisfactory results. Importantly, in accordance with principles of the present invention, one cavity block of the pair thereof is adjustable positionally in the ±one micron range relative to the other one of the pair without requiring disassembly, dimensional adjustment and reassembly of a mold half. 
   Turning to  FIG. 4 , the improved mold half  102  is shown. Therein, a micro-positionable cavity block  120  holding die insert  46  is positioned within a cavity of the mold half  102  against resilient means or members. In the example of  FIG. 4 , compression springs  122  bias the cavity block  120  in the x-dimension, while compression springs  124  bias the cavity block  120  in the y-dimension. Actuator  108  applies an x-dimension precision displacement force to the cavity block  120  against the spring bias force provided by springs  122 , while actuator  106  applies a y-displacement precision displacement force to the cavity block against the spring bias force applied by springs  124 . 
   In the example presented in  FIG. 4 , two optical alignment orifices  126  and  128  are provided, preferably on opposite sides of the mold insert  46 . The alignment orifice  126  receives optical fiber  114  as previously explained. The other optical alignment orifice  128  receives an optical fiber  130  which leads to a second opto-electronic detector  132  providing light intensity information to the controller  104 . A second suitable light source directs a second light beam at the orifice  128  and fiber  130  from the mold block in the fixed mold half  16 . The second light source may be a separate electro-optic transmitter and fiber, or a second fiber  132  extending from a beam splitter of the electro-optic transmitter  110 , for example. 
   The molding machine  100  shown in  FIGS. 3 and 4  is capable of being operator programmed to operate automatically. In an automatic operational mode, when the mold is closed in a molding cycle, relative position of the mold blocks is sensed optically, and position is corrected, if necessary, before injection of amorphous plastic-phase material to be molded. 
   Alternatively, because of potential tolerances of the mold insert  46  within the mold block, it may be desirable to run a test cycle, measure the molded test article with a microscope or optical comparator  140 , and cause measured offsets or tolerances to be sent to the controller  104  via keyboard  136  manually, or automatically from the optical inspection station  140 . The controller  104  then determines positional corrections (e.g., by calculation, table look-up, or other known techniques) and applies the corrections to the actuators  106  and  108 , for example. A display  138  may be provided to display position correction values being applied to the actuators  106  and  108  and/or other information concerning operation of the mold  100 . 
   While the controller  104  has been described as dedicated to the correction of cavity block relative position in the ±one micron tolerance range, those skilled in the art will appreciate that the function of controller  104  may be a subset of functions of a mold machine digital controller and be implemented by software programming into an existing controller as modified to receive sensed position information and put out actuator control values to micro-actuators  106  and  108 , for example. Positional offset correction may be carried out as a single operational step or event, or it may be carried out as a series of incremental adjustments. The positional correction may be carried out in accordance with a correction algorithm designed for the particular molding apparatus and its components and tolerances, or it may be carried out heuristically by making molded test articles and developing correction tables based on manual or robotic-based automatic inspection and measurements of the molded test articles. 
   While two electromechanical actuators  106  and  108  have been illustrated, those skilled in the art realize that a single actuator, or three or more actuators, may be provided to achieve desired manipulation and positional correction of the moveable cavity block within one of the mold halves. In the example of  FIG. 5 , mold block  150  has four precision micro-actuators. Actuators  142  and  144  position a cavity block  152  generally in the y-dimension, while actuators  146  and  148  position cavity block  152  generally in the x-dimension. By separately controlling actuator pairs  142 - 144  and  146 - 148  a range of precision rotational displacement may be applied to the cavity block  152 . In order to support precision rotational displacement of cavity block  152  two multi-element photodetector matrix arrays  154  and  156  are provided.  FIG. 6  illustrates one array  154  having rows (labeled by letters) and columns (labeled by numbers) of separate photodetector elements. Photodetector matrix array  154  is electrically coupled to a photodetector interface circuit  158 , and photodetector matrix array  156  is electrically coupled to a photodetector interface circuit  160 . The circuits  158  and  160  translate electrical signals representing illumination energy into digital values indicative of the particular photodetector element(s) receiving optical energy from the optical fiber of the other cavity block. These digital values are then sent to the controller  104  for processing to determine correction values to be applied to the actuator pairs  142 - 144  and  146 - 148 . In the  FIG. 6  example, light energy from the fiber  112  is impinging at different energy levels on photodetector elements located at row B, columns  2  and  3 ; row C, columns  2  and  3 ; and row D, columns  2  and  3 . By measuring relative light energy amplitudes from multiple detector elements the molding system controller can command precision corrections over lineal and rotational adjustment ranges in the ±one micron range or better, depending upon the selected resolution of the detectors  154 ,  156  and actuator pairs  142 - 144  and  146 - 148 . The multi-element matrix detectors  154  and  156  provide an advantage over the single detector elements  126  and  128  in that detected peak optical amplitude at a particular element of an array may provide a more accurate mold block position measurement than a measurement based upon detected peak optical amplitude at a single photodetector. 
   The precision micro-actuator may apply linear or rotational force to the mold block. The actuator may correct for planar offset or rotation or tilt, as need be. The actuator may be a micro-step stepping motor rotating a finely threaded screw, a servo motor rotating a finely threaded screw, a piezo-electric device, a bi-metal thermal control device, a fluidic actuator (either hydraulic or pneumatic), a linear electric motor such as a solenoid or voice coil motor, a wedge-shaped or ramped sliding mechanism having a fixed part and a displaceable part, or any other known electromechanical device capable of applying a precise force over a very small dimension to reposition the cavity block in the micron range. 
   The resilience means for applying a positional bias force to the cavity block, illustrated as spring sets  122  and  124 , may be provided by any resilient or elastomeric component or material which is found suitable for the particular molding process or article to be formed. Leaf springs, coil springs, rubber springs, pneumatic compression springs, and the like may be employed to apply spring bias force to the positionable cavity block component. 
   Alternatively, a displaceable stop may be used in place of, or in conjunction with the bias spring  124  (and/or  122 ). In a preferred approach illustrated in  FIG. 4 , the bias spring  124  may be a coil spring seated in a cylindrical end well of a threaded shaft  125  having fine pitched threads mating with threads formed in the mold half  102 . The bias spring  124  provides a bias force against the cavity block  120  during the position adjustment step, as shown in  FIG. 4  at reference character A. Once the cavity block  120  is precisely positioned, the threaded shaft  125  is moved into fixed contact with the cavity block  120 , thereby locking it securely in position to obtain the desired molding tolerance during the molding operation, as shown in  FIG. 4  at reference character B. The threaded shaft  125  may be rotated by a step motor  123 , micrometer, or other suitable manual or computer-controlled mechanism. Some or all of the bias springs  122 ,  124  may include displaceable stop mechanisms as may be needed to lock the cavity block  120  in place. Alternatively, a displaceable stop which is structurally separate from the bias springs  122 ,  124  may be used to lock the cavity block  120  in place following the adjustment step (e.g., threaded shaft  210  in the  FIG. 8  embodiment). 
   The position sensing means, illustrated as optical fibers and associated transmitters and detectors or detector arrays in the preferred embodiments, may be provided in a number of ways. Focused light from an emitting optical device accurately affixed to a fixed (or moving) mold component may be directed to impinge on an optical pickup device accurately affixed to a moving (or fixed) mold component to provide positional alignment feedback information. An optical encoder array of a light source, reticle, micro-lined scale and photodetector array may be used as these components. The optical pickup device may be a single fiber, or a bundle of fibers, with each fiber leading to a separate photodetector element, or to a photodetector array. Light intensity or light position may be used to indicate relative offset of the mold block components. Any transmissive or reflective positional sensing technology having accuracy in the desired range may be employed to sense position of the adjustable cavity block component relative to the fixed cavity block component. 
   An automated measurement and adjustment method to enable a precision molding process in accordance with aspects of the present invention is outlined in the  FIG. 7  flow chart. Cavity blocks having suitable molding features or die inserts are installed in mold halves and the spring sets  122  and  124  are installed or otherwise brought into position against one cavity block  120  to provide positional bias force, at a step  170 . Assembled mold halves  102  and  16  are installed on the molding machine  100  at a step  172 . The molding machine is operated at a step  174  to provide a test article. The test article is measured at the inspection station  140  to measure positional inaccuracies in the test article and provide these inaccuracies to the controller  104  at a step  176 . If out-of-specification tolerances are determined to be present, at logical step  178 , the controller  104  determines positional corrections and applies the corrections automatically to actuators  106  and  108  at a process step  180 . Process flow returns to step  174  and a subsequent test article is made. When measurements at the inspection station  140  determine that desired positional accuracy has been achieved as determined at logical step  178 , the adjustment process ends, and production of precision molded articles may then commence at step  182  and continue as desired until production has been completed. 
   While the automatic measurement and adjustment process is always carried out at the beginning of a production run, it may be carried out continuously or at suitable intervals during molding operations, to be sure that molded articles remain precise throughout the production run. 
   Turning now to  FIG. 8 , a mold block half  200  is shown which enables manual adjustment of the cavity block  120 . In this example of the present invention, an x-dimension micrometer  202  having a calibrated adjustment knob external to the mold block half  150  enables manual rotation of a shaft  204  thereby providing a displacement force to the cavity block  120  in the x-dimension against spring bias force applied by springs  122 , for example. A y-dimension micrometer  206  having a calibrated adjustment knob external to the mold block half  150  enables manual rotation of a threaded shaft  208  thereby providing a displacement force to the cavity block  120  in the y-dimension against spring force applied by springs  124 , for example. A displaceable stop to lock the cavity block  120  in place following manual position adjustment may be provided by a threaded bolt  210 . The bolt  210  may be provided in the x-dimension, the y-dimension, or two bolts  210  may be provided to lock the cavity block  120  in both x and y dimensions. 
   In connection with the  FIG. 8  embodiment, optical position sensing may be employed via optical orifices  126  and  128  as described in connection with  FIGS. 3 and 4  above, or with mult-element photodetector matrix arrays  154  and  156  as described in connection with  FIGS. 5 and 6  above. Alternatively, manual tolerance measurements of molded test articles may be made, and cavity block adjustments manually entered at micrometers  202  and  204  to reduce tolerances to the ±one micron range. 
   Having thus described preferred embodiments of the invention, it will now be appreciated that the objects of the invention have been fully achieved, and it will be understood by those skilled in the art that many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. Therefore, the disclosures and descriptions herein are purely illustrative and are not intended to be in any sense limiting.