Abstract:
A strain gauge nozzle adapter that may be placed between a barrel end cap and a nozzle body of an injection molding system, the strain gauge nozzle adapter having a strain gauge pin that measures strain within the strain gauge nozzle adapter for use in approximating conditions within an injection molding system, such as pressure or the location of a melt flow front. The strain gauge nozzle adapter may include a plurality of strain gauge pins. An alternative material insert in the strain gauge nozzle adapter may surround a strain gauge pin to amplify meaningful measurements obtained by the strain gauge pin so that noise measurements do not compromise the accuracy of approximation of conditions within a mold.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is the non-provisional, which claims the benefit of the filing date under 35 USC §119(e), of U.S. Provisional Application No. 62/356,638, filed on Jun. 30, 2016, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    This application relates generally to injection molding and, more specifically, to an upstream strain gauge nozzle adapter for use in an injection molding process to amplify and sense a condition, such as strain, experienced by the nozzle over the course of the injection molding process, the sensed condition then usable to approximate other conditions, such as pressure or melt flow front position, within a downstream injection mold cavity for purposes of determining whether adjustments should be made to the injection molding process. 
       BACKGROUND 
       [0003]    During injection molding, thermoplastic pellets are fed by a hopper into a heated barrel and driven to the end of the heated barrel by a reciprocating screw. The thermoplastic pellets melt into a molten thermoplastic material, and shots of thermoplastic material are extruded through a nozzle. The molten thermoplastic material then flows through runners to the gate of a mold. After entering the gate, the molten thermoplastic material fills a mold cavity formed between two or more sides of the mold. 
         [0004]    The pressure within the mold cavity is an important vector, as insufficient pressure may result in improperly formed parts while excessive pressure may result in damage to the mold. The pressure at the melt flow front provides information relevant to the injection molding process overall by, for example, enabling calculation of how fast a mold cavity is filling and how long cooling of the molded part within the cavity is likely to take. Some injection molding processes aim to have the melt flow front follow a particular pressure pattern over time in order to optimize the injection molding process. For example, some injection molding processes maintain a pressure balance between the air pressure in the cavity, which changes based on the mold cavity geometry as the molten thermoplastic material moves into the cavity of the mold, and the pressure at the melt flow front, in order to produce a final product that is fully relieved of internal stresses that would otherwise undesirably lead to shrink, sink and warpage. For such injection molding systems, determining the real-time pressure at the melt flow front is important in order to determine whether the desired pressure/time curve is properly being followed and, if deviations from the pressure/time curve are identified, to make adjustments to correct the pressure of the melt flow front. 
         [0005]    One particular motivation to monitor flow front position and/or control internal pressure at certain times during the short duration of filling of a mold cavity is to account for flow filling challenges. The term “flow filling challenge” is defined as a region of a part of a mold that forms a feature of a part to be molded which is particularly susceptible to any one or more of a number of problems that complicate the molding of the part or render the molded part more likely to suffer from one or more defects or reduced mechanical properties, such as short-fills, warp, sinks, brittleness, flash, voids, non-fills, weakness (e.g., low tensile, torsional, and/or hoop strength), high stress concentrations, low modulus, reduced resistance to chemical exposure, premature fatigue, non-uniform shrinkage, and discontinuities in color, surface texture, opacity, translucency, or transparency. Non-exhaustive examples of flow filling challenges are: Locations in a mold used to form ribs, bosses, or corners, as well as obstacles in a mold (such as core pins), and transitions (such as a change in thickness of a part to be molded, which may be a sudden stepped change in thickness or a gradual change in thickness, such as a tapered region). These can involve a transition from a relatively thick region to a relatively thin region, and then back to a relatively thick region, and may involve one or more changes in thickness. The portion of a mold cavity used to form a living hinge, which is typically an integral, relatively thin region of a molded part that permits one portion of the part, such as a flip-top of a cap, to rotate with respect to the rest of the part, poses a flow filling challenge. As the term flow filling challenge is used herein, it is contemplated that the region of the part affected by a particular challenge may be at a particular position of a mold cavity, along a region of a mold cavity, or downstream of a particular position or region of a mold cavity, and as such, a flow filling challenge need not be limited to a particular location of a change in shape of a mold cavity, but may extend beyond, i.e. downstream of, such a location. 
         [0006]    Ideally, sensors for measuring the pressure within a mold cavity and at a melt flow front would be indirect, easy to install, and inexpensive. Direct sensors, such as sensors placed within a mold cavity, leave undesirable marks on part surfaces. For example, while demand for injection molded parts with high gloss finishes has been increasing, direct sensors positioned in the mold cavity have a tendency to mar the high gloss finish of the parts. As a result, indirect sensors that are not located in the mold cavity are preferable. Additionally, when the molding system is being used to make products for medical applications, contact between a sensor and the thermoplastic material may be prohibited. Some current indirect sensors include parting line sensors, ejector or static pin sensors, and ultrasonic sensors. Unfortunately, these indirect sensors cannot always be placed in optimal locations, sometimes require that a mold apparatus undergo a period of downtime in order to be machined so that the sensor can be mounted, and can be expensive. Strain gauge sensors have been used in the past in conjunction with molding apparatuses having ejector sleeves or long core pins, but not all injection molding apparatuses are configured to include an ejector sleeve or long core pin. 
         [0007]    More recently, external sensors, such as strain gauges, have been placed on a mold surface in order to measure how a condition, such as strain, changes over the course of a standard injection molding process. In a typical injection molding apparatus, a mold cavity is formed between two mold sides, which are held together under pressure by a press or clamping unit. Thus, along the parting line of the mold, a closing force is exerted by the press or clamping unit. When molten thermoplastic material is injected into the mold cavity, the molten thermoplastic material exerts an opening force along the parting line of the mold. Ideally, the opening force exerted by the molten thermoplastic material is less than the closing force exerted by the clamping unit. If the opening force is greater than the closing force, the mold sides are forced apart and flashing, or leakage of the molten thermoplastic material, occurs. A strain gauge sensor placed on the exterior of the mold surface adjacent to a parting line of a mold is able to sense the surface strain changes on the mold surface that occur over time as a result of the closing and opening forces. In response to surface strain changes, the strain gauge sensor emits an electrical signal, typically in the range of −10 to 10 Volts. The signal emitted by the strain gauge sensor is received and used by a controller to approximate one or more conditions within the mold, such as the pressure within the mold cavity or the location of the melt flow front. In certain molds in which the ratio of the length of the flow channel to the thickness of the molded part is great, i.e. molds having a high length-to-thickness (L/t) ratio, the pressure at the melt flow front may be approximated based on the signals emitted by the strain gauge sensor(s). These approximations may be useful for adjusting the injection molding process. For example, the amount of pressure within the mold cavity may be approximated and compared to a maximum permissible mold cavity pressure in an effort to ensure that the mold cavity is not damaged by excessive mold cavity pressure. 
         [0008]    However, two key challenges make it difficult to approximate a condition within a mold cavity using an external sensor, such as a strain gauge, placed on a mold surface. First, not all areas of a mold surface experience a measurable condition, such as strain, in a way that accurately, reliably, and/or quantifiably corresponds with a condition within the mold, such as the pressure within the mold cavity or the location of the melt flow front, and therefore only some areas of a mold surface can be used to approximate one or more conditions within the mold, such as the pressure within the mold cavity or the location of the melt flow front. Injection molds come in a variety of shapes and sizes. Identifying areas of a mold surface that can be used to approximate a condition within the mold using an external strain gauge sensor has required testing a number of different areas on the mold surface, which can be time consuming, or making a blind guess that may turn out to be wrong. Second, even in areas on the surface mold that do experience a condition, such as strain, in a way that corresponds with a condition within the mold, external sensors often pick up some amount of “noise” generated during the molding process that does not correspond with a condition within the mold cavity. The noise measurements picked up by the external sensor must be distinguished from the meaningful measurements in order to accurately approximate one or more conditions within the mold. In some cases, the ratio of noise measurements to meaningful measurements is so high that conditions within the mold cannot be accurately approximated. 
       SUMMARY 
       [0009]    Embodiments within the scope of the present disclosure are directed to a sensor located in an adapter of a nozzle of an injection molding system in order to approximate conditions within a mold, such as pressure or the location of a melt flow front. Strain gauge sensors are the type of sensor primarily discussed, while other sensors capable of detecting movement of the nozzle as a proxy or tell-tale for internal conditions such as mold cavity pressure or flow front location, could achieve the same purpose as a strain gauge sensor and are within the scope of the present disclosure. For example, microwave sensor kits, x-ray sensor kits, ultrasonic sensor kits, air pressure sensor kits, air temperature sensor kits, and sub-surface temperature sensor kits, could all be substituted for the strain gauge sensors described and depicted below. Additionally, other types of external gauge sensors, such as electrical, electronic, mechanical, wireless, and fiber optic sensors, could be utilized instead of strain gauge sensors. 
         [0010]    The present disclosure is directed to a strain gauge nozzle adapter for use in injection molding systems. The strain gauge nozzle adapter is positioned between the barrel end cap and a nozzle tip of the injection molding system and allows molten thermoplastic material to flow through it. The strain created in the strain gauge nozzle adapter by the flowing molten thermoplastic material is measured by at least one strain gauge pin located in a strain gauge aperture that extends from an external wall of the adapter to a bottom located a minimum distance away from an internal wall of the melt flow conduit. Depending on the orientation and type of strain sensor(s), the strain may be linear strain along one or more axes or circumferential strain in one or more locations. In some embodiments within the scope of the present disclosure, the strain gauge aperture may be located in an alternative material insert that amplifies the strain experienced by the strain gauge nozzle adapter. The alternative material insert may have a lower flex modulus than the surrounding strain gauge nozzle adapter. For example, the alternative material insert may be made of brass or aluminum while the strain gauge nozzle adapter is made from steel. In some embodiments within the scope of the present disclosure, the injection molding system may also include one or more secondary sensor. Each strain gauge pin and each secondary sensor is connected to a controller, which is connected to a virtual cavity sensor that calculates data such as mold cavity pressure and optionally adjusts the injection molding process based on the strain information received. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that is regarded as the present disclosure, it is believed that the disclosure will be more fully understood from the following description taken in conjunction with the accompanying drawings. Some of the figures may have been simplified by the omission of selected elements for the purpose of more clearly showing other elements. Such omissions of elements in some figures are not necessarily indicative of the presence or absence of particular elements in any of the exemplary embodiments, except as may be explicitly delineated in the corresponding written description. None of the drawings are necessarily to scale. 
           [0012]      FIG. 1  is a front elevation view of an injection molding system; 
           [0013]      FIG. 2  is a front elevation view of an injection molding system including a strain gauge nozzle adapter of the present disclosure including a single strain gauge pin; 
           [0014]      FIG. 3  is a front elevation view of an injection molding system including a strain gauge nozzle adapter of the present disclosure including multiple strain gauge pins in the strain gauge nozzle adapter and a secondary sensor; 
           [0015]      FIG. 4  is an orthogonal view of a portion of an injection system and a mold assembly of an injection molding system, illustrating (exploded from the injection system) a porous metal insert and strain gauge pin for use in a strain gauge nozzle adapter of the injection system; 
           [0016]      FIG. 5  is a longitudinal cross-sectional view of a strain gauge nozzle adapter of the present disclosure; 
           [0017]      FIG. 6  is an enlarged view of the strain gauge pin aperture depicted in the cross-sectional view of a strain gauge nozzle adapter of  FIG. 3 ; 
           [0018]      FIG. 7  is a top view of a strain gauge nozzle adapter of the present disclosure; 
           [0019]      FIG. 8  is a cross-sectional view taken along lines  8 - 8  in  FIG. 7  of a strain gauge nozzle adapter of the present disclosure; and 
           [0020]      FIG. 9  is a front elevation view of an injection molding system including a strain gauge feed system adapter of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Referring to the figures in detail,  FIG. 1  illustrates an exemplary injection molding apparatus  10  for producing thermoplastic parts in high volumes (e.g., a class 101 injection mold, or an “ultra-high productivity mold”, a class 102 (medium-to-high productivity mold), or class 103 (a medium productivity mold)). The injection molding apparatus  10  generally includes an injection system  12  and a clamping system  14 . A thermoplastic material may be introduced to the injection system  12  in the form of thermoplastic pellets  16 . The thermoplastic pellets  16  may be placed into a hopper  18 , which feeds the thermoplastic pellets  16  into a heated barrel  20  of the injection system  12 . The thermoplastic pellets  16 , after being fed into the heated barrel  20 , may be driven to the end of the heated barrel  20  by a ram, such as a reciprocating screw  22 . The heating of the heated barrel  20  and the compression of the thermoplastic pellets  16  by the reciprocating screw  22  causes the thermoplastic pellets  16  to melt, forming a molten thermoplastic material  24 . The molten thermoplastic material is typically processed at a temperature of about 130° C. to about 410° C. 
         [0022]    The reciprocating screw  22  forces the molten thermoplastic material  24 , toward a nozzle  26  to form a shot of thermoplastic material, which will be injected into a mold cavity  32  of a mold  28  via one or more gates. A check ring  38  is provided within the barrel toward a tip end of the reciprocating screw  22 . The check ring  38  is coupled (e.g., attached) to a portion of the reciprocating screw  22 , preferably at a position proximate a tip end of the screw  22 . The check ring  38  is generally configured to prevent, or at least limit, a backflow of molten thermoplastic material  24  from flowing in a direction from the nozzle  26  toward the hopper  18 . The molten thermoplastic material  24  may be injected through a gate  30 , which directs the flow of the molten thermoplastic material  24  to the mold cavity  32 . In other embodiments the nozzle  26  may be separated from one or more gates  30  by a feed system (not shown). The mold cavity  32  is formed between first and second mold sides  25 ,  27  of the mold  28  and the first and second mold sides  25 ,  27  are held together under pressure by a press or clamping unit  34 . The press or clamping unit  34  applies a clamping force during the molding process that is greater than the force exerted by the injection pressure acting to separate the two mold halves  25 ,  27 , thereby holding the first and second mold sides  25 ,  27  together while the molten thermoplastic material  24  is injected into the mold cavity  32 . In a typical high variable pressure injection molding machine, the press typically exerts 30,000 psi or more because the clamping force is directly related to injection pressure. To support these clamping forces, the clamping system  14  may include a mold frame and a mold base. 
         [0023]    Once the shot of molten thermoplastic material  24  is injected into the mold cavity  32 , the reciprocating screw  22  stops traveling forward. The molten thermoplastic material  24  takes the form of the mold cavity  32  and the molten thermoplastic material  24  cools inside the mold  28  until the thermoplastic material  24  solidifies. Once the thermoplastic material  24  has solidified, the clamping unit  34  releases the first and second mold sides  25 ,  27 , the first and second mold sides  25 ,  27  are separated from one another, and the finished part may be ejected from the mold  28 . The mold  28  may include a plurality of mold cavities  32  to increase overall production rates. The shapes of the cavities of the plurality of mold cavities may be identical, similar or different from each other. (The latter may be considered a family of mold cavities). 
         [0024]      FIG. 2  illustrates an injection molding system  10  of the present disclosure that includes a strain gauge nozzle adapter  42  and strain gauge pin  52 . A controller  50  is communicatively connected with a strain gauge pin  52  and a screw control  36 . The strain gauge pin  52  is located on in a strain gauge adapter  42 , discussed in greater depth with respect to  FIG. 3 . The controller  50  may include a microprocessor (or another suitable processing unit, or several such units), a non-transitory memory, and one or more communication links. 
         [0025]    The strain gauge pin  52  senses strain experienced by the strain gauge nozzle adapter  42 . Data from the strain gauge pin  52  may be communicated to a processor that calculates the change in the strain of the strain gauge nozzle adapter  42 . Electric signals  54  from the strain gauge pin  52  may travel along one or more electrical paths, such as wires  54 , depicted in  FIG. 1  in solid lines, ranging in strength from −10 to 10 Volts. The controller  50  may be connected to the screw control  36  via wired connection  56 . In other embodiments, the controller  50  may be connected to the screw control  36  via a wireless connection, a mechanical connection, a hydraulic connection, a pneumatic connection, or any other type of communication connection known to those having ordinary skill in the art that will allow the controller  50  to communicate with the screw control  36 . 
         [0026]    The controller  50  may use the change in strain calculated from the information provided by the strain gauge pin  52  to approximate conditions, such as pressure or melt flow front position, within the mold cavity or, in certain molds, particularly in which the ratio of the length of the flow channel to the thickness of the molded part is large, at the melt flow front of the molten thermoplastic material  24 . These approximations may then be used to adjust the injection molding process. For example, the amount of pressure within the mold cavity  32  may be approximated and compared to a maximum permissible mold cavity pressure in order to ensure that the mold cavity  32  is not damaged by excessive mold cavity pressure. If the amount of pressure within the mold cavity  32  is approximated to be dangerously close to the maximum permissible mold cavity pressure, or even in excess of a safety threshold well below the maximum permissible mold cavity pressure, the controller  50  may direct the screw control  36  to cease injecting molten thermoplastic material. Other approximations may be used to control the molding process, such that variations in material viscosity, mold temperatures, melt temperatures, and other variations influencing filling rate, can be used to trigger adjustments to the injection molding system by the controller  50 . These adjustments may be made immediately during the molding cycle, or corrections can be made in subsequent cycles. Furthermore, the approximations may be averaged over a number of cycles and then used to make adjustments to the molding process by the controller  50 . 
         [0027]    Additionally, the controller  50  is in communication with a virtual cavity sensor  51 , which is implemented as a program, or a set of software instructions. More generally, however, a virtual cavity sensor can be implemented in hardware (e.g., as an application-specific integrated circuit (ASIC)), firmware, software, or any suitable combination thereof. In this disclosure, the term “virtual cavity sensor” can refer to a module that determines the value of a process variable, such as pressure, without directly measuring this process variable. For purposes of this application, determines” means “compares the signal indicative of the output from each external sensor to a stored database that correlates that signal value to an approximate pressure or melt flow front location and outputs a signal indicative of that approximate pressure or melt flow front location corresponding to the external sensor signal value.” The strain gauge pin  52  and the virtual cavity sensor  51  together form a pressure controlling system that generates data relevant to strategic controlling of the pressure within the mold cavity  32 . As used herein, the term “pressure controlling system” refers to any suitable group of components, which can include both software-implemented and hardware-implemented components, that generate a signal indicative of a condition within a mold cavity based on a signal indicative of another process variable. 
         [0028]    For example, if based on the strain information provided by the strain gauge sensor  52 , a processor associated with the controller  50  determines that pressure within the mold cavity exceeds a trigger point (or is outside of a predetermined acceptable range), the virtual cavity sensor  51  signals the controller to adjust the screw control  36  to bring the pressure within the mold cavity back to a level below the trigger point (or within the predetermined acceptable range). As another example, if based on the strain information provided by the strain gauge sensor  52 , a processor associated with the controller  50  detects that changes in plastic pressure have progressed beyond a trigger point (which may correlate to a percentage of the mold that has been filled), the virtual cavity sensor  51  signals the controller to adjust the screw control  36  to bring the pressure within the mold cavity to a predetermined acceptable finalizing pressure or range, which may involve a reduction in pressure to avoid over-packing a mold cavity, and thereby prevent unwanted flashing. 
         [0029]      FIG. 3  illustrates an injection molding system  10  having a strain gauge nozzle adapter  42  with multiple strain gauge pins  52 . In the embodiment depicted in  FIG. 3 , the strain gauge nozzle adapter  42  has two strain gauge pins  52  arranged in the same circumferential plane, both of which are connected to the controller  50 . In other embodiments within the scope of this disclosure, more than two strain gauge pins  52  may be included in the strain gauge nozzle adapter  42  and their location may be spread out along the length of the strain gauge nozzle adapter  42 .  FIG. 3  also depicts the injection molding system  10  including a secondary sensor  76 . The secondary sensor  76  is depicted as a pressure sensor in the mold cavity  32 , but in other embodiments within the scope of the present disclosure, the sensory sensor  76  may be another type of sensor, such as a strain gauge sensor, and may be located in another location. In addition, more than one secondary sensor  76  may be connected to the controller  50 . The controller  50  provides the signals received from the strain gauge pins  52  and any secondary sensor  76  to the virtual cavity sensor  51 . 
         [0030]    Turning to  FIG. 4 , a region of the injection molding apparatus  10  of the present disclosure is illustrated, with the mold  28  at the lower left and a portion of the injection system  12  at the upper right in the drawing figure. The heated barrel  20  is provided with a barrel end cap  40 . A strain gauge nozzle adapter  42  projects from the barrel end cap  40 . A strain gauge aperture  43  is provided in the strain gauge nozzle adapter  42 . The strain gauge aperture  43  receives a strain gauge  44  therein, which is secured by friction fit in the embodiment depicted. In other embodiments, the strain gauge  44  may be secured in place by screwing a screw into the walls of strain gauge aperture above the strain gauge  44 . While a single strain gauge aperture  43  is illustrated, it is understood that the strain gauge nozzle adapter  42  may be provided with a plurality of strain gauge apertures  43 , each having a strain gauge  44  secured therein as discussed above. 
         [0031]    The strain gauge nozzle adapter  42  is provided between a barrel end cap  40  and a nozzle body  48  having a nozzle provided at an end thereof. While the embodiments illustrated in the drawings show the strain gauge nozzle adapter  42  as a distinct component from the strain gauge nozzle body  48 , the strain gauge nozzle adapter  42  is considered part of what is referred to herein as the nozzle assembly, and could be formed integrally with the nozzle body  48  and still be considered within the scope of the appended claims. The nozzle body  48  is in fluid communication with at least one of the mold cavity  32 , a gate, a runner, or a manifold of the injection molding system. 
         [0032]      FIG. 5  illustrates a cross-sectional view of an embodiment of a strain gauge nozzle adapter  42  of the present disclosure. The strain gauge nozzle adapter  42  includes a melt flow inlet  60 , a melt flow outlet  62 , and a melt flow conduit  64  extending between the inlet  60  and outlet  64 . The strain gauge aperture  43  is provided on an external melt flow conduit wall  66 . In some embodiments, the longitudinal axis of strain gauge aperture  43  is perpendicular to the axis of the melt flow conduit  64 . A minimum distance  68  must be maintained between the bottom  70  of the strain gauge aperture  43  and an internal melt flow conduit wall  74  to avoid cracking or leaking through the internal melt flow conduit wall  66 . In some embodiments within the scope of the present disclosure, the minimum distance  68  is 0.5 mm. 
         [0033]    In some embodiments within the scope of the present disclosure, the strain gauge aperture may be formed in an alternative material insert  72  that is made of a different material than the rest of the strain gauge nozzle adapter  42 . An expanded view of an alternative material insert  72  is depicted in  FIG. 6 . In some embodiments, the strain gauge nozzle adapter  42  is made from stainless, pre-treated steel while the alternative material insert  72  is made from aluminum, brass, or another material that will better amplify the strain for detecting by the strain gauge pin  44 . In some embodiments, the alternative metal insert is formed from a modified metallurgy that expands at the same rate as steel. The minimum distance  68  may vary depending upon the material forming the alternative material insert. 
         [0034]      FIG. 7  illustrates a top view of a strain gauge nozzle adapter  42 . One of the benefits of a strain gauge nozzle adapter  42  is that it is easily compatible with various injection molding systems without the need for modifications to the injection molding systems. For example, most injection molding systems may be connected to the melt flow inlet  60  and melt flow outlet  62  of the strain gauge nozzle adapter  42  by a universal thread.  FIG. 8  provides a cross-sectional view of the strain gauge nozzle adapter  42  depicted in  FIG. 6 . The strain gauge pin  44  described in the present application could be chosen from a variety of commercially available strain gauge sensors. For example, the Kistler “Miniature Longitudinal Measuring Pin M5” Type 9247A would be suitable for use in embodiments within the scope of the present invention. 
         [0035]      FIG. 9  illustrates an injection molding system  10  having a strain gauge feed system adapter  142  with a strain gauge pin  152 . The strain gauge feed system adapter  142  works identically to the strain gauge nozzle adapter  42  discussed with respect to  FIG. 2 , except that strain is experienced by the strain gauge feed system adapter  142  and measured by the strain gauge pin  152  at a location along the feed system of the injection molding system  10  rather than at the nozzle  26 . Specifically, the strain gauge feed system adapter  142  may be attached to the injection molding system  10  between the nozzle  26  and the mold  28 . 
         [0036]    A person having skill in the art would recognize that many of the features provided in a strain gauge nozzle adapter  42  could also be provided in a strain gauge feed system adapter  142 . The strain gauge feed adapter  142  may include an aperture for the strain gauge pin  152 , and an alternative material insert may surround the aperture and amplify the strain experienced by the strain gauge feed system adapter. The alternative material insert may have a lower flex modulus than the surrounding external sensor feed system adapter, and the alternative material insert may be one of aluminum and brass. The aperture of the strain gauge feed system adapter has a bottom, and the strain gauge nozzle adapter may have a melt flow conduit having an internal melt flow conduit wall. The distance between the bottom of the aperture and an internal melt flow conduit wall may be a minimum distance necessary to prevent cracking or leakage, such as 0.5 mm. 
         [0037]    The strain gauge feed system adapter  142  may have a plurality of strain gauge pins  152  provided in a plurality of apertures, and the controller may determine at least one of an approximate pressure or melt flow front location using an output of each strain gauge pin and adjust the operation of the ram in view of the determined approximate pressure or melt flow front location. The plurality of apertures may be located in the same circumferential plane of the strain gauge feed system adapter. In some embodiments within the scope of the present disclosure, a secondary sensor may be used in conjunction with the strain gauge feed system adapter  142 . The controller may determine at least one of an approximate pressure or melt flow front location using an output of the strain gauge pin and the secondary sensor, and the injection molding apparatus  10  adjusts an operation of the ram in view of the determined approximate pressure or melt flow front location. 
         [0038]    The strain gauge feed system adapter may be used in a method of injection molding. The method may include measuring, using a strain gauge pin, the change in strain in a strain gauge feed system adapter. The method may further include approximating at least one of a pressure or a melt flow front location within the mold cavity based on the change in strain and comparing the approximated pressure or melt flow front location to a trigger point. If the approximated pressure or melt flow front location equals or exceeds the trigger point, the method may include activating a virtual cavity sensor, wherein upon activation, the virtual cavity sensor causes a controller to perform an action. 
         [0039]    The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.” 
         [0040]    Every document cited herein, including any cross referenced or related patent or application and any patent application or patent to which this application claims priority or benefit thereof, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern. 
         [0041]    While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.