Injection molding apparatus control system and method of injection molding

There is shown an injection molding apparatus, which comprises a source of a fluid molding material and a molding die into which the molding material is forced under pressure. The apparatus includes a control means for initiating and controlling an injection cycle in which the fluid molding material is injected into the molding die in a particular and predetermined manner. The control means generally comprises a programmable logic controller (PLC) which is programmed to receive signals from sensors adapted to sense variable parameters of the injection cycle. The PLC is programmed to generate control signals based upon the signals from the sensors so as to control the variable parameters of the injection cycle. The output control signals of the PLC are coupled through an interface circuit to a servo-control circuit which in turn is operatively coupled to control various parameters of the injection cycle. The control system allows the user to pre-set multiple flow rates to accomplish desired acceleration/deceleration characteristics during the injection cycle so as to optimize fabrication of high quality patterns while reducing scrap patterns. The control system may also be implemented to prevent a machine operator from making unauthorized changes of injection parameters to assure the integrity of injection parameters on a continuous basis. The use of a high level PLC also enables generation and collection of data relevant to the injection processes to visually monitor the process dynamic parameters, to display an injection profile with tolerances, to facilitate diagnostics as well as other valuable functions.

BACKGROUND OF THE INVENTION 
The present invention relates generally to an injection molding apparatus 
and process of injection molding utilizing a novel control system which 
allows dynamic parameters of the injection process to be more accurately 
and easily controlled and which enhances the flexibility of operation of 
the apparatus. More particularly, the invention is directed to an 
injection molding apparatus and process of injection molding which 
utilizes a programmable logic controller to control certain variable 
dynamic parameters encountered in an injection molding process such as for 
example, the making intricate disposable wax patterns or the like for use 
in metal casting techniques. 
In various injection molding procedures, it has been found that control 
over the injection process is less than adequate, resulting in defective 
molding which renders the procedure less efficient and adds to the cost 
thereof. It is desired in injection molding techniques such as die 
casting, plastic injection and wax injection techniques to provide a 
greater amount of control and flexibility in the injection process to 
enable more efficient, cost-effective production and manufacturing 
capabilities. For example, in metal casting techniques, such as investment 
casting, disposable wax patterns are utilized to generate a mold form used 
in the metal casting process. A molten metal will be poured into the mold 
form to produce metal castings which are often intricate in their geometry 
and require close tolerances with respect to characteristics such as 
dimension and surface finish. In the investment casting process, a 
disposable wax pattern is formed and thereafter covered with one or more 
layers of a suitable "investment" materials, such as a ceramic material, 
wherein the coating is permitted to solidify about the wax pattern. The 
wax pattern may then be removed by melting or dissolving the wax to leave 
a mold cavity in the investment material, being an exact replica of the 
wax pattern and having the desired intricate geometry and close tolerances 
of the metal part to be cast therein. Conventionally, such disposable wax 
patterns are produced by injecting a specially formulated liquid wax into 
a master mold using an injection molding apparatus, wherein the injected 
wax will be solidified under pressure within the master mold by means of 
the injection molding apparatus. 
The intricate disposable wax patterns for use in investment casting or 
other metal casting techniques must be of high quality in order to be used 
to generate a suitable mold cavity as described. Similarly, cost effective 
production of such disposable wax patterns requires a high degree of 
uniformity and reduction of scrap patterns produced in the injection 
molding apparatus. As the intricate metal parts to be cast are configured 
in a broad range of size, geometry and other specifications, the master 
molds utilized for production of the disposable wax patterns similarly 
vary over a wide range. The broad variations in the size, geometry, 
orientation and runner systems of the various master molds require that 
the injection molding apparatus be capable of a great amount of 
flexibility, so as to be applicable for use in fabricating the desired wax 
pattern. The quality and uniformity of wax patterns produced in this 
manner are directly related to the ability of the injection molding 
apparatus to accurately control parameters of the pattern molding process. 
For example, the dynamics of fluid flow and pressure must be controlled 
with a high degree of accuracy to produce acceptable and desired wax 
patterns. As a wide variety of molds are to be used in the fabrication of 
wax patterns, a similar wide variety of wax flow characteristics and 
injection pressure control must be achievable in the wax injection molding 
apparatus. Similar criteria exist for various die casting, plastic 
injection and other injection molding techniques. 
It is also been found that in many instances the final metal part to be 
cast includes hollow portions, requiring the wax pattern to be molded 
about a fragile ceramic core to enable production of such hollow castings. 
In such instances, the lack of adequate control of wax flow and pressure 
may result in breakage and/or structural damage of the fragile ceramic 
core thereby producing an unacceptable wax pattern. Further, in the wax 
injection process or any other injection molding process, the lack of 
adequate control in the injection process may also result in such 
imperfections as air bubbles, wax flow lines, knit lines, cracking or 
fracturing, incomplete fill, sink, incorrect size or dimensions and 
various other surface imperfections which may result in unusable patterns. 
Various injection molding apparatus have been developed, as for example for 
use in fabrication of expendable wax patterns used in investment casting 
techniques, such as the assignees prior U.S. Pat. No. 4,274,823. The 
injection molding apparatus shown in this patent included a control system 
which allowed a high degree of control to be obtained over injection 
parameters such as the acceleration, maximum flow velocity and maximum 
pressure of the liquid wax with a high degree of accuracy throughout the 
injection and solidification cycle. A servo-control system was described 
which was operable to continuously monitor and variably control dynamic 
parameters of the injection molding cycle to achieve a high degree of 
quality and uniformity of the produced wax patterns. Although the wax 
injection molding apparatus greatly improved with the ability to properly 
fabricate desired disposable wax pattern for use in metal casting 
techniques in a cost effective manner, the apparatus comprised a dedicated 
system, wherein limitations for application of the system have been 
encountered. Under many circumstances, the wax injection molding apparatus 
of this prior patent was set up to act as a stand-alone dedicated machine 
capable of fabricating a single selected pattern with a high degree of 
quality and uniformity. It has been found that the basic inability to 
customize the wax injection molding apparatus to various needs of the user 
simply and effectively resulted in the need to provide a separate 
injection molding apparatus for each master mold to be used. It has also 
been found with the prior art injection apparatus, that the operator of 
the apparatus had the ability to modify the injection parameters to some 
degree, which may have resulted in less than adequate fabrication of the 
patterns if the operator was not extremely knowledgeable about the 
injection process. It has also be found to be desirable to provide the 
user with the ability to monitor operation of the injection molding 
apparatus and provide feedback to the user to allow optimization of the 
pattern fabrication process. 
SUMMARY OF THE INVENTION 
Based upon the foregoing, there has been found a need to provide an 
injection molding apparatus and control system which allows the user a 
greater amount of flexibility and enables the injection apparatus to be 
customized to the users needs and for a variety of different applications. 
It is therefore a main object of the invention to provide a injection 
molding apparatus having a control system for accurately controlling 
process parameters of an injection cycles such as 
acceleration/deceleration, flow velocity, pressure of the injection 
material and other machine functions to improve quality, reduce core 
breakage or otherwise optimize the injection process. 
Another object of the invention is to provide an injection molding 
apparatus having a control system which allows a wide variety of process 
parameters to be effectively controlled, such that the apparatus can be 
used in the fabrication of a wide variety of patterns in different 
injection molding processes in an easy and convenient manner. 
Another object of the invention is to provide an injection molding 
apparatus and control system which allows set up of a plurality of die 
recipes for various master mold dies to be used in conjunction with the 
apparatus, wherein any of the die recipes may be chosen and machine set up 
is provided automatically for a particular die. 
Yet another object of the invention is to provide an injection molding 
apparatus and control system which allows visual monitoring of the dynamic 
parameters in the injection process, and automatically indicates any 
deviation from a predefined injection profile and given tolerance band 
about such a profile. 
It is yet another object of the invention to provide an injection molding 
apparatus and control system which allows the user to compare the function 
of the apparatus over time with respect to patterns produced thereby, to 
facilitate trouble shooting any problems which may arise in the 
fabrication process. 
Another object of the invention is to provide an injection molding 
apparatus and control system which allows the user to set up operation of 
the apparatus and to prevent modification of the dynamic parameters 
encountered in the molding process. 
Still another object of the invention is to provide a wax injection molding 
apparatus and control system which will facilitate generation of various 
reports regarding production control and quality control in the molding 
fabrication process. 
Another object of the invention is to provide an injection molding 
apparatus control system which allows the user to pre-set multiple flow 
rates to accomplish acceleration or deceleration of the flow during an 
injection cycle, wherein such multiple flow rates may be related to time, 
material back pressure or both during the injection process. 
Yet another object of the invention is to provide an injection molding 
apparatus control system which allows the apparatus to be networked with a 
plurality of other injection molding apparatus by means of a central 
computing facility which allows monitoring and control of each of the wax 
injection molding apparatus from the central control facility. 
Another object of the invention is to provide a method of injection molding 
utilizing a novel control system wherein process parameters and variable 
parameters of an injection cycle are closely monitored and controlled for 
more efficient, cost-effective fabrication. 
These and other objects of the invention are accomplished by means of an 
injection molding apparatus control system which is capable of producing 
injection molded parts such as disposable wax patterns or the like wherein 
the control system including a high level programmable logic controller 
(PLC) to control all of the various dynamic parameters which may be 
encountered in the process of molding intricate patterns or the like. The 
control system including the PLC is capable of storing a plurality of 
master mold die recipes, each of the recipes being identifiable and being 
capable of being down loaded to the apparatus for automatic parameter set 
up. The ability to down load a particular die recipe will reduce set up 
time and ensure that the proper process parameters are implemented for 
producing high quality patterns. The control system of the injection 
molding apparatus allows a system to be customized to the users needs and 
provide the system which is not only flexible but provides extended 
injection capability from a particular machine so as to be much more 
versatile. The control system allows the user to pre-set multiple flow 
rates to accomplish desired acceleration/deceleration characteristics 
during the injection cycle so as to optimize fabrication of high quality 
patterns while reducing scrap patterns. The control system may also be 
implemented to prevent a machine operator from making unauthorized changes 
of injection parameters to assure the integrity of injection parameters on 
a continuous basis. The use of a high level PLC also enables generation 
and collection of data relevant to the injection processes to visually 
monitor the process dynamic parameters, to display an injection profile 
with tolerances, to facilitate diagnostics as well as other valuable 
functions. The collection of such data may also facilitate analysis of the 
fabrication process to facilitate production and quality control as well 
as to implement preventative maintenance systems and ensure machine 
operation is consistent over time. Another aspect of the invention is 
found in that the control system of a particular injection molding 
apparatus may be networked into a central control facility, wherein a 
plurality of injection machines may be easily and effectively controlled 
from a central location to ensure optimization of the injection processes 
for each of the injection machines. 
In general, the invention provides an injection molding apparatus, which 
comprises a source of a fluid molding material and a molding die into 
which the molding material is forced under pressure. The apparatus 
includes a control means for initiating and controlling an injection cycle 
in which the fluid molding material is injected into the molding die in a 
particular and predetermined manner. The control means generally comprises 
a programmable logic controller (PLC) which is programmed to receive 
signals from sensors adapted to sense variable parameters of the injection 
cycle. The PLC is programmed to generate control signals based upon the 
signals from the sensors so as to control the variable parameters of the 
injection cycle. The output control signals of the PLC are coupled through 
an interface circuit to a servo-control circuit which in turn is 
operatively coupled to control various parameters of the injection cycle, 
such as the velocity and acceleration of an injection ram, the injection 
cycle time, the temperature of the fluid molding material, the 
characteristics of the molding die or platens associated therewith, as 
well as a variety of other variable dynamic parameters of the injection 
cycle. The use of a PLC enables a variety of distinct advantages to be 
obtained, such as allowing the user to program the process parameters for 
a plurality of mold dies directly into the PLC, such that the process 
parameters for a particular die may be easily and conveniently called up 
to reduce set up time in using a particular die. The PLC also includes a 
memory capacity which allows information regarding the injection process 
to be collected and stored so as to increase the capability to generate 
and collect data regarding injection processes for use by management, 
engineering or otherwise. In this way, the injection molding apparatus has 
improved cost performance, is easier to operate and provides improved 
process control capabilities. 
It has additionally been found that the use of the PLC allows process 
parameters for a particular mold die to be initially set up and thereafter 
prevents changing such process parameters, except by authorized personnel, 
so as to ensure continuity in fabricated parts, and improve the 
reliability of the injection process. The use of a PLC also facilitates 
maintenance and diagnostic analysis of the injection apparatus so as to 
reduce problems or possible down time of the apparatus.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the figures, the injection molding apparatus of the 
invention will be described with reference to a wax injection molding 
process, but it should be recognized that the apparatus is also usable in 
other injection processes, such as die casting and plastic injection 
techniques for example. The injection molding apparatus is shown 
diagrammatically in FIG. 1, and is generally of the structure as shown and 
described in the assignees prior U.S. Pat. No. 4,274,823. The injection 
molding apparatus generally indicated at 10 comprises a reservoir 12 which 
will hold a fluid molding material 14, such as a molding wax, wherein the 
reservoir 12 is open to the atmosphere and connected to a fluid passage 
opening 16. A suitable heating and/or agitating means (not shown) may be 
disposed in the reservoir 12 to maintain the fluid molding material 14 in 
a fluid condition and at a temperature suitable for injection molding. The 
passage 16 communicates at its lower end to a chamber 18 as well as a 
second fluid passage 20 which is formed centrally in movable nozzle means 
22 of the molding apparatus 10. Within the chamber 18, is positioned an 
injection ram 24 movable within the chamber 18 so as to act on any fluid 
molding material therein. A first valve 26 is positioned within fluid 
passage 16, wherein the location of the valve 26 is diagrammatically 
illustrated in FIG. 1. The valve 26 is intended to allow or cut off flow 
of the fluid molding material 14 from the reservoir 12 into the wax 
injection chamber 18. Similarly, a second valve 28 is positioned within 
fluid channel 20 of the movable nozzle 22 and is intended to seal the 
nozzle opening or allow flow of the fluid molding material therethrough. A 
pressure transducer 25 is shown schematically in coupling relation to 
fluid channel 20 of the injection nozzle. The pressure transducer 25 will 
provide an indication of the back pressure on the fluid molding material 
flowing through injection nozzle 22, and may be used to control an 
injection cycle as will be hereinafter described. It should be understood 
that the fluid molding material may be drawn into injection chamber 18 by 
opening valve 26 and retracting ram 24 within chamber 18. The wax or other 
suitable molding material will also be drawn into channel 20 with valve 28 
closed to prevent further flow of the material out of nozzle 22. 
Retraction of ram 24 is accomplished by means of hydraulic actuation, and 
may comprise hydraulic chambers 30 and 32 separated by a piston 34 
connected to piston rods 36 and 38. Piston rod 38 is operatively connected 
to ram 24, such that upon movement of piston 34, corresponding movement of 
ram 24 within chamber 18 will occur. Movement of ram 24 within chamber 18 
is also facilitated by a vent 19 provided in association with chamber 18. 
Similarly, movement of piston 34 will result in corresponding movement of 
piston rod 36, which has coupled therewith a potentiometer slider 40 and 
slider arm 42 of a linear potentiometer 44 adapted to monitor movement of 
piston arm 36 and therefore movement of injection ram 24. 
The hydraulic actuation system for injection ram 24 comprises a suitable 
hydraulic pump and hydraulic control system generally comprising hydraulic 
feed conduits 46 and 48, each of which communicates with one of the 
hydraulic chambers 30 and 32 respectively. The conduits 46 and 48 are in 
turn coupled to a hydraulic valve housing 50 of a servo-valve assembly 52. 
The valve housing 50 communicates with a hydraulic supply conduit 54 and 
exhaust conduits 56 and 58, each of which communicates with a suitable 
hydraulic fluid source or sump. Within the valve housing 50 are provided a 
spool valve 64 having two raised spool elements 60 and 62 formed thereon 
in spaced relation to one another so as to divide the interior of housing 
50 into three chamber 66, 67 and 68, which will be of variable volume 
depending upon the position of spool valve 64. Each of the chambers 66-68 
in turn communicates with the supply conduit 54 or exhaust conduits 56 and 
58 respectively, and chamber 66 and chamber 67 may in turn communicate 
with feed conduit 46 to supply or exhaust hydraulic fluid from hydraulic 
chamber 30 depending upon the position of spool valve 64. Similarly, 
chambers 67 and 68 may communicate with feed conduit 48 to allow supply or 
exhaust of hydraulic fluid from hydraulic chamber 32 depending upon the 
position of spool valve 64. The spool valve 64 is movable within housing 
50 by means of an injection servo-valve coil 70, and as should be 
recognized will supply hydraulic fluid to one of the hydraulic chambers 30 
or 32 to initiate retraction or extension of ram 24 in conjunction with 
piston 34 and piston rods 36 and 38. 
In operation of the injection molding apparatus 10, the movable nozzle 22 
is positioned within a nozzle opening of a suitable mold die 72, which in 
turn may be properly positioned with respect to nozzle 22 by means of 
upper and lower platens 74 and 76 respectively. The upper platen 74 may be 
movably supported on the injection molding apparatus and vertically 
movable toward and away from the lower platen 76 so as to clamp the 
injection mold die 72 therebetween. A suitable hydraulically actuated jack 
78 may be utilized to raise and lower the upper platen 74 with respect to 
lower platen 76. The basic structure of the injection molding apparatus 10 
is described in more detail in the assignees prior U.S. Pat. No. 
4,274,823, which is hereby incorporated herein by reference. 
Referring now to FIGS. 2a-2d, operation of the injection molding apparatus 
10 will be described with respect thereto. As seen in FIG. 2a, the initial 
"at rest" position of the injection molding apparatus 10 is shown 
diagrammatically, wherein the fluid molding material 14, such as a molding 
wax, is maintained in a liquified state within reservoir 12. The reservoir 
valve 26 is maintained in an open position such that wax is able to flow 
within channels 16 and 20, but the nozzle valve 28 is closed to prevent 
flow of the material from the nozzle 22. Flow of material from channel 16 
into injection chamber 18 is inhibited by the fully extended position of 
injection ram 24 by means of hydraulic fluid acting on piston 34 within 
the hydraulic chamber. The position of the injection ram 24 is monitored 
by means of the position sensor or linear potentiometer 44 and feedback of 
this position is supplied to the control system of the injection apparatus 
as indicated by arrow 80. Similarly, the pressure of the molding material 
within injection nozzle 22 is monitored by the pressure transducer 25 and 
feedback from the pressure sensor 25 is supplied to the control system of 
the apparatus. The injection molding die 72 is not coupled to the 
injection nozzle at this point, and the status of the apparatus may be 
maintained in this configuration for an indefinite amount of time. 
Upon initiation of an injection cycle, the hydraulic actuation system 
supplies a hydraulic fluid to operate on piston 34 within the hydraulic 
chamber so as to move piston 34 downwardly as indicated in FIG. 2b. 
Hydraulic fluid within the hydraulic chamber below piston 34 will be 
exhausted therefrom, such that as piston 34 moves downwardly, the 
injection ram 24 will also move downwardly so as to draw material into 
injection chamber 18. The position of injection ram 24 is again monitored 
by means of position sensor 44 as injection chamber 18 is filled. Once 
injection chamber 18 is filled with the proper amount of molding material, 
the molding die 72 may be coupled to injection nozzle 22 as seen in FIG. 
2c, such that the injection process can begin. For injection of the 
molding material, the reservoir valve 26 is closed and the injection 
nozzle valve 28 is opened as seen in FIG. 2c. Injection of the material 
from injection chamber 18 may then be performed by means of upward 
movement of injection ram 24 upon actuation of the hydraulic system in 
which hydraulic fluid is supplied below piston 34 and exhausted from an 
upper portion of the hydraulic cylinder to cause upward movement of piston 
34. Upon upward movement of piston 34, the injection ram 24 will be moved 
upwardly and material within injection chamber 18 will be forced through 
passage 16 and into injection nozzle 22 so as to be fed into molding die 
72. Again, the position of the injection ram 24 is continuously monitored 
by means of position sensor 44 and the pressure of the material flowing 
through injection nozzle 22 is also continuously monitored by pressure 
sensor 25. It should be understood that the speed at which injection ram 
moves upwardly can be controlled so that material can be injected into the 
molding die 72 at a pre-selected flow rate and acceleration. Similarly, as 
the mold cavity of molding die 72 becomes completely filled, the back 
pressure of the material can be continuously monitored for precise control 
of the injection process. As seen in FIG. 2d, the injection process is 
continued until the mold die 72 is completely filled, wherein a 
pre-selected pressure may be maintained on the material within die 72 
during a solidification cycle of the molded pattern. 
It has been found that the quality and uniformity of molded patterns, such 
as disposable wax patterns, are directly related to the ability of the 
injection machine 10 to accurately control the parameters of the pattern 
molding process, specifically the dynamics of fluid flow and pressure. The 
broad variation in size, geometry, orientation and runner systems of 
various molding dies 72 require that correspondingly wide variations in 
wax flow characteristics and injection pressure control be available by 
means of the injection apparatus. As previously mentioned, the further 
aspect that some wax patterns are to be molded around fragile ceramic 
cores to produce hollow castings, require precise control of wax 
acceleration, flow and injection pressure to eliminate breakage of the 
ceramic core which may be caused by excessive pressures or wax flow. 
Additionally, the lack of adequate control of flow and pressure may result 
in such pattern imperfections as air entrapment, flow lines, knit lines, 
cracking, incomplete fill, sink or cavitation, incorrect size, core 
breakage, and various other surface imperfections causing the pattern to 
be unusable. In the injection molding apparatus 10, the control system 
provides a means of controlling the acceleration, maximum flow velocity, 
maximum pressure and other parameters with a high degree of accuracy 
throughout the injection and solidification cycles as desired. 
Turning now to FIG. 3, a simplified block diagram of the improved control 
system for the injection molding apparatus of the invention is shown. The 
control system of the invention comprises a computer interface injection 
control system which greatly simplifies use of the injection molding 
apparatus and allows a great amount of flexibility to be obtained in the 
operation thereof. Input variable parameters such as shot size 100, 
acceleration 102, maximum flow velocity 104, injection pressure 106, cycle 
time 108, and temperature control 110 show basic parameters which may be 
effectively controlled by the control system. Although these parameters 
represent basic parameters which are desired to be precisely controlled in 
operation of the injection molding apparatus, a variety of other dynamic 
variable parameters may be similarly controlled by selection of the 
desired parameters as inputs to the control system. In the preferred form, 
each of the dynamic variable parameters relating to the function of the 
injection apparatus may be controlled by selecting input values of these 
variables for set up of the injection cycle to be performed by the 
apparatus. A selected shot size value may be manually entered via a key 
board interfaced either integrally or selectively to an input register 
module 112. The shot size parameter of an injection cycle relates to a 
predetermined quantity of liquid molding material which is to be drawn 
into the injection chamber 18 as seen with respect to FIG. 1. Setting of 
the shot size parameter for an injection cycle will relate to the 
particular configuration of the molding die being utilized, and the amount 
of molding material to be used and filling of the injection chamber 18 can 
be optimized in a particular injection cycle. Setting of the shot size 
parameter 100 will in turn control retraction of the injection ram 24 by 
means of the linear potentiometer 44 as described with reference to FIG. 
1. As will be described hereinafter, after the shot size parameter is set 
for a particular molding die, this parameter may be stored in the control 
system and automatically downloaded for automatic set up of the injection 
apparatus for a particular injection cycle to be performed. It should also 
be understood that inputting of a selected shot size parameter may be 
performed by an alternative source from a key board such as push buttons, 
limit switches or the like as desired. 
Similarly, the acceleration parameter 102 forming an input to the control 
system may be manually entered from a key board into the input register 
module 112 to control acceleration of the injection ram during a 
particular injection cycle. As will be described in more detail 
hereinafter, a portion of the control system includes a novel 
servo-control system wherein the acceleration parameter of the injection 
ram during an injection cycle is continuously monitored and compared with 
preselected parameters which represent the desired acceleration parameter 
so as to continuously control acceleration of the injection ram during the 
injection cycle. For a particular pattern to be fabricated, the 
acceleration parameter of the injection ram may be critical to achieve a 
high quality pattern and preclude pattern imperfections such as air 
entrapment, surface imperfections, incomplete fill or the like. The 
acceleration parameter 102 along with flow and pressure are critical to 
obtain the best results in the injection process. 
The injection parameter of maximum flow 104 similarly relates to achieving 
the proper operation of the injection ram during an injection cycle. In 
the servo-control system, the maximum flow parameter 104 is repeatedly 
compared against the continuous monitoring of the injection ram velocity 
which corresponds to the material flow rate in the injection cycle. The 
maximum flow rate parameter 104 may be similarly entered from a key board 
to the input register module or by other suitable means, and once input 
for a particular molding die may be subsequently downloaded for automatic 
operation. 
The injection pressure parameter 106 will also be precisely and accurately 
controlled by means of feedback obtained from the pressure transducer 25 
as described with reference to FIG. 1. The pressure transducer 25 may be 
situated directly within the flow of molding material in the injection 
nozzle of the injection molding apparatus to continuously monitor the back 
pressure of the wax during the injection cycle which will be compared to 
the pre-selected injection pressure chosen for a particular injection 
cycle. The injection pressure parameter 106 may be similarly manually 
entered from a key board to the input register module 112, and may also be 
automatically downloaded subsequent to initial set up as previously 
described. It has also been found that the injection pressure parameter, 
being particularly critical in the fabrication process, may be desirably 
displayed, wherein both the selected injection pressure as well as 
realized injection pressure from the pressure transducer may be displayed 
for observation by the operator during an injection cycle. 
Another parameter which is advantageously selected as an input is the cycle 
time 108 of the injection cycle. The input parameter of cycle time may 
again be manually input to input register module 112 via a key board or 
the like and subsequently downloaded for automatic operation for a 
particular injection cycle relating to a selected molding die. Again it 
may be advantageous for the operator of the apparatus to have an 
indication of the time remaining in an injection cycle to monitor proper 
operation of the apparatus, and therefore a display of the time remaining 
may be generated from this input variable. Generally, the cycle time and 
display of time remaining will be obtained by means of an internal timer 
within the control system, but may otherwise be generated with reference 
to a remote timing source or the like. 
Another input variable is the temperature control 110, which generally 
refers to temperature control of a variety of components in the injection 
molding apparatus. For example, in many instances the temperature of the 
nozzle tip of the injection apparatus is important to yield proper 
injection characteristics. Similarly, the temperature of the molding die 
itself may be important and may be controlled by adjusting the temperature 
of the upper and lower platens clamped about the molding die. It also 
should be of noted that the temperature of the molding material in the 
reservoir tank should be controlled to maintain the molding material in a 
molten state and at a temperature corresponding to the temperature of the 
molding die for example. Thus, temperature control of these various 
aspects of the injection molding apparatus can be affectively accomplished 
by individual temperature controllers. The temperature controllers may be 
interfaced with the control system of the invention, wherein the input 
values set for each of these parameters at 110 will be fed to the 
controller and continuously monitored. 
It should be recognized that the dynamic variable input parameters as 
described above generally will comprise only a partial number of the 
parameters which are desirably controlled during an injection cycle. For 
example, other parameters such as clamp position or velocity control, 
clamp pressure, injection nozzle height as well as a variety of other 
variable parameters may be preselected for a particular molding die and 
pattern to be fabricated so as to ensure speedy and reliable set up of an 
injection cycle and ensure optimization of the injection cycle for high 
quality production of injection molded parts such as expendable patterns 
used in metal casting processes. 
The preselected dynamic variable parameters which are input into the input 
register module 112 are thereafter supplied to a programmable logic 
controller 114 which is programmed and adapted to provide automatic 
operation of an injection cycle and a molding process. The PLC 114 of the 
injection control system enables inputting and monitoring of process 
control parameters in a user friendly and extremely flexible manner. The 
process parameters as described above as well as any other process 
parameters may be initially input into the PLC 114, which has an internal 
random access memory (RAM) which may be utilized to store a large number 
of molding die recipes or process parameters within the control system. 
The die recipes may be identified by any suitable designation, wherein 
upon any use of a particular molding die, the die recipe may be downloaded 
from the control system to automatically set up the process parameters for 
a particular die to greatly reduce set up time and to minimize operator 
activities with respect to initiating an injection cycle. Thus, once an 
acceptable wax pattern is produced for a particular molding die, the 
injection parameters for that particular die would be established and 
could thereafter be locked into the control system for subsequent use. Any 
subsequent use would merely require inputting of a tool identification 
number assigned to a particular molding die to be used, wherein all 
process parameters and subsequent operation of the injection cycle would 
occur without operator intervention. The PLC 114 may also have the 
capability to lock in the process parameters, wherein the operator would 
not be capable of modifying such parameters to ensure the preservation of 
product integrity as well as to facilitate diagnostic analysis and trouble 
shooting of any problems which may arise in the molding process. This 
system also provides the capability of generating quality control and 
production control reports relating to use of the injection molding 
apparatus and enables the user to trace parts made on a particular 
injection apparatus. The traceability of parts gives the user the ability 
to determine whether a particular part was made according to desired 
specifications, which is extremely important with todays stringent 
tightening of quality control standards, especially in industries such as 
aircraft and ordinance manufacturing. 
It should be recognized that the use of a PLC 114 greatly extends the 
injection capabilities of the injection molding apparatus as it allows an 
infinite number of combinations of process control parameters to be easily 
and effectively implemented. The infinite number of process control 
parameters which may be implemented essentially removes the limitations of 
the injection molding apparatus for example in the process of metal 
casting using an expendable injection molded pattern. In one aspect of the 
control system of the invention, precise control of the injection process 
allows various acceleration/deceleration functions to be implemented. For 
example, five pre-selected acceleration/deceleration functions may be 
initially set up and subsequently selected by an operator in association 
with a particular die recipe. The parameters of flow rate and acceleration 
which are of critical importance in the fabrication of a high quality 
patterns may be varied within an injection cycle to achieve optimal 
pattern forming capabilities by allowing both acceleration and 
deceleration as well as different wax flow rates during a single injection 
cycle. It should also be understood that any acceleration/deceleration 
function may be easily and conveniently generated or modified to customize 
the injection apparatus for a particular use. The use of a PLC 114 also 
gives the control system a great amount of flexibility as various options 
may be easily added or subtracted as the PLC 114 has available various 
input and output communication ports for linking with various other 
processing devices or otherwise. 
In a first preferred embodiment, the PLC 114 is operatively coupled to a 
digital output module 116 which may generate output signals corresponding 
to various of the input process parameters, such as cycle time 108 or 
temperature control variables 110. The PLC 114 may provide digital signals 
to the temperature controllers as well as the timer circuit of the 
injection apparatus. Additionally, digital output signals generated from 
digital output module 116 may be fed through a digital to analog converter 
118 to generate analog signals used to set injection process parameters. 
Additional process parameters may also be supplied from the PLC 114 
directly to the D/A converter 118 for setting of the injection parameters 
for a particular molding die. Output signals from the processing circuit 
comprising PLC 114, digital output module 116 and the D/A converter 118 
are thereafter coupled to an interface circuit 120, which is adapted to 
interface the PLC 114 and associated processing equipment to a 
servo-control circuit 122 which controls and implements machine functions 
124 and receives feedback for control of various process parameters. The 
servo-control circuit 122 forms a closed-loop servo-control which provides 
dynamic feedback of measured process parameters for comparison with the 
control inputs generated by PLC 114. The difference between the 
pre-selected input and the measured output may then be used to drive the 
system toward a dynamic state which reduces any differences to zero, so as 
to obtain an extremely precise control of acceleration, flow, injection 
pressure and other parameters. Additionally, as will be described more 
fully hereinafter, the PLC 114 interfaced with the servo-control circuit 
122 via interface circuit 120 allows velocity, pressure and other 
parameter profiles to be created in the system, wherein any deviation from 
such profiles may be indicated and used for process control as well as 
information and data collection. It is also seen in FIG. 3 that feedback 
control signals from the servo-control circuit 122 are also coupled via 
interface circuit 120 to analog input module 126, adapted to receive 
various analog signals from measured process parameters which are 
converted to digital signals and fed back into PLC 114 for continuous 
process control and monitoring as well as data collection. Additionally, a 
variety of machine functions as well as input variables may be displayed 
on a suitable display device 128 for visual feedback to the machine 
operator as to the status of an injection cycle, various process 
parameters and a variety of other information. 
As a preferred but non-limiting example, a suitable PLC 114 may be the 
Square D Sy/Max.RTM. programmable controller Model 401 or alternatively a 
Honeywell IPC620-11 PLC, but it should be recognized that a wide variety 
of PLCs may be used in the control system and are contemplated for use in 
the present invention. In the Square D series 401 PLC, an on board RAM 
will allow the storage of approximately 300 sets of injection parameters 
or die recipes which may be recalled to automatically load the machine 
with the proper injection parameters for a particular die. This type of 
PLC also includes various input and output ports which allow direct 
communication with other compatible processors or other devices, such as a 
class 8030 type ROM122 isolated analog output module or type RIM126 
isolated analog-thermocouple input module also manufactured by Square D 
Company. Such input or output modules may be suitably coupled to the PLC 
114 to achieve the desired processing characteristics of the control 
system of the invention. 
Turning now to FIG. 4, there is shown a generally schematic circuit diagram 
of the servo-control circuit used in conjunction with the PLC processing 
circuitry 111 of the control system in the invention. Many aspects of the 
servo-control circuit are described in greater detail in the assignee's 
prior U.S. Pat. No. 4,274,823 which has been incorporated herein by 
reference, and details of various aspects of the circuit can be referred 
to therein. The servo-control circuit generally comprises a system 
specially designed to monitor and variably control certain dynamic 
operational parameters which are encountered in the injection molding. As 
mentioned previously, the acceleration, velocity and pressure of the 
liquid molding material used in the molding process is continuously 
monitored, and the servo-control system is responsive to these parameters 
to variably control the magnitudes thereof with a high degree of accuracy 
through the injection and solidification cycles. The servo-control system 
compares a desired value of a variable process parameter to the actual 
value of the parameter and provides an error signal which is used to 
adjust the apparatus so the actual value of the parameter under 
surveillance closely approximates the pre-selected and desired value. The 
servo-control system generally comprises two servo-control loops, one 
being a pressure control loop and the second being a velocity control loop 
which will in turn control the acceleration parameter of the injection 
process. The pressure control loop generally comprises a pressure 
transducer which is mounted within the injection nozzle so as to be 
exposed to and responsive to the fluid pressure of the material flow 
between the injection cylinder and injection nozzle of the apparatus. The 
output of the pressure transducer is coupled to an operational amplifier 
130 which in turn is connected to a comparator 132 which is also supplied 
with a pre-selected control signal from the control system representative 
of the maximum pressure. The output of the comparator 132 is then supplied 
to amplifier 134 which controls the injection servo-valve coil operating 
the control valve of the hydraulic system and in turn the piston within 
the hydraulic cylinder and the injection ram. The output signal of the 
pressure control loop will thus be representative of any differences 
between the pre-selected maximum pressure and that sensed by the pressure 
transducer and will control the injection servo-valve to adjust actuation 
of the injection ram and result in increase or decrease in the fluid 
pressure as desired. 
In the velocity control loop, any movement of the injection ram will result 
in corresponding movement of the wiper arm 42 of the linear potentiometer 
44, and a feedback signal from linear potentiometer 44 will be fed to an 
instrumentation amplifier 136. The output of the amplifier 136 is 
proportional to the position of the injection ram and is supplied to a 
differentiating amplifier circuit 138 which will have an output 
proportional to the time rate of change of position or the velocity of the 
injection ram. The output of the amplifier circuit 138 is supplied to an 
amplifier 140 which acts as a comparator, and which is also supplied a 
velocity clamping voltage from the control system. The amplifier 140 
generally acts as voltage summing amplifier and will compare in the 
feedback signal from the linear potentiometer indicative of the velocity 
of the injection ram with a desired reference voltage derived from 
amplifier 141. The velocity control of the injection ram during an 
injection cycle enables a high quality casting to be fabricated for a 
particular part being molded, allows repeatable results with a particular 
mold die and ensures integrity of the molding process. 
It should also be understood that the acceleration of the injection ram 
will be defined by the rate of change of its velocity with respect to 
time, and control of the acceleration will also enable high quality and 
repeatable molding of a desired pattern to be achieved. The control system 
of the invention is adapted to generate an acceleration/deceleration 
function for an injection cycle, wherein the acceleration function will be 
applied to the servo-control circuit as a voltage waveform via amplifier 
144. An integrating amplifier 142 is supplied with a voltage in 
conjunction with an output voltage of amplifier 146 to generate the proper 
acceleration signal which is thereafter applied to comparator 140 to be 
compared with actual movement of the injection ram. Any deviation from the 
desired acceleration or deceleration characteristics of the injection ram 
will then be supplied as a voltage waveform to invertor amplifier stage 
143 and current amplifier 134 to the injection servo-valve coil. An output 
signal representative of the proper acceleration or deceleration desired 
will be supplied as a sufficient current which is made to flow through the 
coil to actuate the spool valve within the control valve of the hydraulic 
system to cause movement of the injection ram in a desired manner. 
The control system of the invention including the PLC processing, generates 
control signals which are supplied to the servo-control circuit. Process 
control signals developed by the PLC and associated peripheral processing 
devices have eliminated the need for adjustment potentiometer for the 
process control variables which were initially set by the operator in the 
prior injection molding apparatus. Elimination of the control 
potentiometer has resulted in elimination of any possible misadjustment of 
such potentiometer and again reduces setup time and initiation of an 
injection cycle. Additionally, the ability of locking out the inputs to 
the PLC in the control system also enable process parameters to be set and 
secured without allowing an operator to modify or vary the process 
parameters as desired. The control system of the invention has also 
eliminated the need for the logic control system and its associated CMOS 
devices and FET switches as part of the control system described in U.S. 
Pat. No. 4,274,823, which were not isolated and created significant noise 
within the control system. The control system utilizing the PLC also 
increases the current capacity of output relays associated with the 
control system. 
Turning now to FIG. 5, there is shown the interface circuit adapted to 
couple the PLC processing system to the servo-control circuit. The 
interface circuit generally comprises an edge connector adapted to connect 
to each connector of the servo-control circuit as well as a buffer circuit 
and comparator circuit which allows use of the servo-control circuit with 
the PLC. As seen in FIG. 5, the interface circuit may include a 
potentiometer 150 controlled by a user adjustable knob on a front panel of 
the injection molding apparatus, which has an output thereof coupled to 
amplifier 152. The linear potentiometer 44 associated with the injection 
piston also has an output thereof coupled to the buffer amplifier 154, 
wherein an output signal proportional to movement of the injection ram 
will then be supplied to an input of amplifier 152 for comparison with the 
selected shot size process control signal selected by the operator or 
download from a die recipe. The output of amplifier 152 may be termed an 
injector retracting signal which is coupled to the PLC in the control 
system. The output of amplifier 154, indicative of the position of the 
injection ram, is also supplied to a comparator circuit 156, which is also 
supplied with an injector extending reference signal from a reference 
potentiometer 158. The reference potentiometer 158 allows the control 
system to be zeroed relative to full extension of the injection piston and 
injection ram for a particular injection molding machine, to ensure that 
all subsequent indications of ram position, velocity and acceleration are 
accurate. The output of the comparator circuit 156 is also supplied to the 
PLC as an injector extended signal. The edge connector of the interface 
circuit comprises a plurality of coupling sites from the PLC, which as 
shown in FIG. 5 include retract injector 160, extend injector 162 and 
cycle on 164 communication ports. Each of the PLC communication ports 160, 
162 and 164 are coupled via buffer amplifiers to servo-control circuit 
communication ports 163, 164 and 165 respectively. The servo-control 
circuit coupling sites for the retract injector and extend injector 
process control signals are indicated on FIG. 4, and other similar 
coupling sites are provided for each of the process control parameters to 
be controlled by the control system and actuated by the servo-control 
circuit. 
Turning now to FIG. 6, there is shown a flow chart indicating set up and 
functioning of the control system in various aspects of the injection 
process. In the control system, the PLC 114 as described with reference to 
FIG. 3 essentially comprises a two fold system having a run mode and a 
program mode associated with a particular molding die, a die recipe is 
prepared in accordance with the process control parameters which are found 
to produce high quality patterns when using a particular die. The PLC is 
initially placed in program mode, wherein a keyboard may be coupled to a 
communication port of the PLC for input of the various process control 
parameters for a particular die. The PLC may be programmed to provide menu 
driven programming of a die recipe into the PLC. As seen in FIG. 6a, a 
main menu is generated from the control system and PLC 114 as indicated at 
170, wherein various alternatives of system display, injection parameters 
or die recipes programmed or to be programmed can be displayed. In the 
system display option as seen in FIG. 6c at 172, various process 
parameters of an injection cycle will be displayed on a video display 
terminal (VDT), digital display or other suitable display device. Various 
functions of the injection molding apparatus and the status of these 
functions may be displayed as indicated at 174, such as whether the upper 
platen of the apparatus is clamped onto a molding die for which an 
injection cycle to be performed, whether the press is up or various other 
status conditions of the apparatus. The operator may also select an option 
to display the selected injection pressure and/or cycle time of an 
injection cycle for a particular die recipe down loaded for operation. The 
time remaining in an injection cycle may also be displayed to give the 
operator an indication of the time remaining in an injection cycle. 
Various other parameters, such as nozzle tip height or other status 
conditions, may also be displayed for a particular molding die used. 
Alternatively, the operator may select a display of the injection 
parameters as indicated in FIG. 6a at 176, wherein parameters such as wax 
pressure, cycle time, acceleration, shot size, the 
acceleration/deceleration function to be implemented including the flow 
rates and times or pressures at which they are initiated, back pressure, 
temperature settings of various portions of the apparatus and nozzle tip 
heights. If an operator who is knowledgeable with respect to the injection 
process is implementing an injection cycle, the control system may be 
switched into a run-edit mode wherein the operator can modify any of the 
process parameters which are deemed necessary. For example, if various 
external factors are found to affect the temperature control settings of 
various portions of the apparatus, the operator may adjust the temperature 
settings to compensate for the external factors. Alternatively, the 
control system may be switched into a run-only mode, wherein the process 
parameters may not be modified by the operator. This feature essentially 
allows the operator to be taken out of the pattern fabrication operation 
to ensure consistency and increase overall control of the injection 
process. Thus, the operator does not necessarily need to be particularly 
competent with respect to setting up and operating the injection molding 
apparatus to achieve high quality patterns and the injection molding 
process may be performed more cost effectively and efficiently. As all 
functions of the injection molding apparatus are effectively controlled by 
the control system, operation of the apparatus can be carried out 
essentially automatically. 
To enable automatic operation of the apparatus, a large number of die 
recipes may be programmed into and stored within the control system. As 
indicated in FIG. 6b at 178, the operator may select the die recipe option 
from the main menu 170, wherein a programmed die recipe may be run, a new 
recipe may be created or an existing recipe may be listed. As indicated at 
180, initiation of an injection cycle using a programmed die recipe may be 
selected by indicating the die recipe to be used, wherein the control 
system will download the selected recipe or indicate that such a recipe 
does not exist. Alternatively, a process engineer or knowledgeable 
operator may program in a new die recipe or edit an existing recipe, 
wherein each of the process parameters will be displayed if existing, and 
editing thereof can be performed, or a new recipe may be created. As 
another option,.any die recipe may be listed, whereby the process 
parameters may be viewed accordingly. It is also contemplated that a 
particular die recipe may be selected by means of a bar-code designation 
which may be attached to a particular die, and simply read by a bar-code 
reader associated with the injection machine and downloaded for operation. 
In another aspect of the invention, an acceleration/deceleration function 
may be implemented to closely control flow within an injection cycle to 
optimize fabrication of an expendable pattern. The control system may be 
programmed to carry out a particular acceleration function which may also 
be displayed on the display device of the control system, wherein an 
example of such an acceleration function is shown in FIG. 7. As seen 
therein, the acceleration function may comprise a series of different flow 
rates which will cause acceleration and deceleration of the injected wax 
flow to form a high quality pattern for a particular injection die. As 
merely an example, the function shown in FIG. 7 indicates an acceleration 
flow rate of 3 in..sup.3 /sec. for two seconds, in which the actual flow 
of wax will accelerate to this rate until two seconds have elapsed and 
thereafter, the control system is adapted to decelerate the flow to a rate 
of approximately 1.5 in..sup.3 /sec. for three seconds after the initial 
flow rate. The flow rate may again be accelerated in the time period from 
five to six seconds to a flow rate of approximately 4.5 in..sup.3 /sec. 
Thereafter, the flow rate may be decelerated as the die cavity is becoming 
increasingly filled to a rate of approximately 1.5 in..sup.3 /sec., until 
complete fill is achieved. It should be apparent that the control system 
of the invention allows an infinite number of acceleration/deceleration 
functions to be controlled with respect to time in a precise manner to 
achieve acceleration and deceleration characteristics in the injection 
cycle which will optimize high quality fabrication. As previously 
mentioned with respect to the control system, the programming of the PLC 
may be implemented to allow five preset flow rates to be entered for a 
particular die recipe. These five preset flow rates are initiated at 
pre-selected times during an injection cycle, although any number of flow 
rates may be selected to generate a particular acceleration function for a 
particular die recipe as desired. 
Turning to FIGS. 8a and 8b, volume and pressure profiles for the 
acceleration function as described in FIG. 7 are shown. In FIG. 8a, the 
actual flow of injected wax into a die during an injection cycle is shown, 
wherein at initial stages of the injection cycle, the injection nozzle is 
retracted as indicated at 200 and an amount of molding material in 
accordance with the selected shot size is introduced into the injection 
chamber of the apparatus as previously described. After the injection 
chamber is filled with the desired shot size, the injection nozzle is 
extended over a period of time as indicated by T, and thereafter injection 
of the material into the mold cavity from the chamber is accomplished by 
the injection ram. The pre-selected first accelerating flow rate as 
indicated in FIG. 7 is then implemented by the injection apparatus as 
indicated at 202 for a period of two seconds. Thereafter the second flow 
rate as indicated at 204 is initiated, wherein the reduced or decelerating 
flow rate over the next three second period is indicated by a flattening 
of the curve in FIG. 8a. The third flow rate is then initiated for a 
period of one second, with the increased or decelerating flow rate 
indicated by a steepening of the curve at 206, and thereafter, the fourth 
and final decelerating flow rate is initiated until the die cavity is 
completely filled as indicated at 208. With reference to FIG. 8b, the 
pressure profile of the material flowing through the injection nozzle is 
shown, wherein back pressure as sensed by the pressure transducer located 
adjacent the injection nozzle only senses a pressure upon initiation of 
the injection into the mold cavity. An initial pressure rise at 210 is 
seen to correspond with the initial flow rate as indicated at 202 in FIG. 
8a. A reduction in pressure is seen to occur at 212 upon initiation of the 
decelerating second flow rate 204 as indicated in the flow profile of FIG. 
8a, and similarly, a pressure rise at 214 corresponds to the third 
accelerating flow rate at 206. The final decelerating flow rate at 208 is 
indicated by the pressure drop at 216 in FIG. 8b which continues until the 
die cavity is completely filled. The flexibility of performing any desired 
acceleration function in the injection cycle allows much better control 
over the injection process and significantly reduces mold imperfections 
such as air bubbles, flow lines, cracking or fracturing, incomplete fill, 
cavitation and the like. 
As an alternative to the acceleration/deceleration function as described 
with reference to FIG. 7, the ramping function may also be set up and 
performed relative to back pressure sensed by the pressure transducer in 
the injection molding apparatus. It has been found that implementing an 
acceleration function based upon time during an injection cycle may not 
fully account for actual circumstances occurring during an injection 
cycle. For example, if the die cavity fills more quickly than expected, an 
acceleration function based upon time of an injection cycle may not be 
adequately controlling the injection process parameters to achieve the 
best results for a particular die. For example, it has been found that as 
the die cavity fills with the injected wax material, various venting 
orifices in the die structure will become closed as the level of wax 
within the cavity rises. As the injection cycle continues, the reduction 
in venting of the die cavity effectively results in higher back pressures 
which can be sensed with the pressure transducer provided in the injection 
apparatus. When the die cavity is nearly completely filled, it is very 
important to maintain the flow of wax into the cavity at a rate to 
maintain sufficient pressure upon the material within the die cavity and 
to eliminate problems of cavitation, cracking or surface imperfections 
which would make the mold formed unusable. Upon monitoring the back 
pressure in an injection cycle, it has been found that each particular die 
has a critical point after which flow of material into the die cavity must 
be very closely and accurately controlled to result in the desired product 
quality in the formed mold. As the pressure transducer in the apparatus 
will provide a feedback signal representative of the injection process in 
real time, use of this information to develop and initiate an acceleration 
function may provide a more accurate means by which a desired function may 
be implemented. 
As seen in FIG. 9, the acceleration/deceleration profile may be based upon 
the actual back pressure measured by the pressure transducer wherein the 
flow rate of the molding material is modified according to the pressure 
detected. For example, an injection cycle may be initiated wherein a 
molding die is injected at approximately 3 in..sup.3 /sec., with the 
injection cycle being modified according to at least one sensed pressure. 
For example, the injection profile may reduce the flow rate to 
approximately 1.5 in..sup.3 /sec. upon reaching a back pressure of 50 psi. 
The deceleration performed at the critical point in the injection cycle 
will facilitate the reduction of various defects and increase the quality 
of the mold forms produced. For any particular molding die, it will be 
known what the maximum pressure is desired to be, and thus the 
acceleration/deceleration function may be implemented based upon actual 
pressure readings from the pressure transducer as the pressure nears the 
maximum. 
For the example shown in FIG. 9, the actual flow and pressure profiles for 
this acceleration function are shown in FIGS. 10a and 10b. In FIG. 10a, 
the flow profile indicates retraction of the injector in filling of the 
injection chamber at 220 wherein the amount of filling of the chamber 
equals the shot size selected for the particular die cavity being used. 
The injection nozzle is then extended during period T and an accelerating 
flow which, as indicated in FIG. 9 of this example, is approximately 3 
in..sup.3 /sec. is initiated at 222. Corresponding to the flow profile is 
the pressure profile of FIG. 10b, wherein it is seen that an initial rise 
in back pressure at 226 occurs upon the accelerating flow of material into 
the die cavity corresponding to the first flow rate 222. Upon reaching the 
pre-selected back pressure of 50 psi in this example, which is shown at 
228 in FIG. 10b, the second decelerating flow rate is initiated as 
indicated at 224 in FIG. 10a causing a deceleration in the injection 
profile. This deceleration causes a reduced back pressure to be sensed as 
indicated at 230, and upon continued filling of the die cavity, the sensed 
back pressure will slowly rise until the die is completely filled at 232 
and the maximum pressure selected is imposed for a solidification cycle. 
The pressure encountered during an injection cycle is indicative of the 
filling process, and the ability to judge when the die is almost filled by 
means of a pressure feedback signal will allow precise and accurate 
control of the injection process by means of an appropriately tailored 
acceleration/deceleration function based upon detected pressures. It again 
should be recognized that the particular acceleration function as shown in 
FIGS. 9 and 10 is merely an example, and a plurality of acceleration 
functions based upon pressure may be easily provided by the control system 
of the invention. 
It should also be recognized from the foregoing that an 
acceleration/deceleration function or profile for a particular injection 
cycle may be implemented as based both on time and pressure variables. For 
example, at initial stages of an injection cycle, various accelerating or 
decelerating flow rates may be implemented at particular times until a 
selected pressure is encountered in the injection process. Upon reaching a 
selected pressure, a decelerating (or accelerating) flow rate may be 
implemented such that advantageous characteristics of both methods of 
controlling the injection cycle may be relied upon to optimize the 
injection process. 
Turning now to FIG. 11a, an alternate embodiment of the invention is shown, 
wherein a plurality of injection molding machines may be networked 
together and operated from a central control facility to achieve distinct 
and extremely advantageous capabilities. The control system of the 
invention including a PLC, has the capability of being networked with a 
central control facility as indicated at 240 and 242. The central control 
facility may simply comprise a host computer, which need be no more than a 
standard personal computer, such as a 386SX, having a sufficient amount of 
memory to handle the number of injection machines on a particular network. 
The host computer may be coupled to the injection molding machines by 
means of a local area network (LAN) as indicated at 244, which is adapted 
to communicate with the PLC of the control system for each individual 
molding apparatus. For example, the Square D Company Sy/Max.RTM. Class 
8020 type SPC-401 PLC may be networked using the Square D Sy/Net.RTM. LAN 
utilizing a network interface module (NIM) as an example. The LAN is 
adapted to allow communication from the host computer to a work cell 
indicated at 246, which may typically comprise 8 PLCs and associated 
control systems. As seen in FIG. 11b, a work cell coupled to the LAN, may 
comprise an operator interface control station 248, which for example may 
be a Sy/View.RTM. industrial color work station with a key pad produced by 
the Square D Company. The operator interface provides a display for the 
operator on which system parameters and function of the injection molding 
machine may be viewed. A plurality of PLCs including input/output 
registers are shown at 250 and are coupled to the LAN 244,and forming part 
of the control system for an injection molding machine. The individual 
PLCs may be programmed or edited via a programmable controller operator 
interface module 252 which may be selectively coupled to the PLCs as 
necessary. The PLCs may in turn be coupled to a plurality of temperature 
controllers indicated at 254 for control of the temperature of various 
components of the injection molding machines as previously described. 
The networking of a plurality of injection molding apparatus to a central 
control facility allows a variety of distinct advantages to be gained. 
Injection parameters, as well as product analysis may be removed from the 
operator station and placed in control of the process engineer at the 
central control facility so as to ensure process integrity, security and 
consistency. As previously mentioned, the security of the injection 
process is extremely important to eliminate operator error and reduce the 
necessity for a knowledgeable operator. At the central control facility, a 
particular injection molding machine may be selected, and all process 
parameters of that machine displayed, with the ability to modify or edit 
any existing parameters or generate new die recipes as previously 
described. Each injection molding apparatus may therefore be set up from 
the central station and monitoring of an injection cycle may be performed 
from the central station. In either the stand alone or network embodiments 
of the invention, the control system of the injection molding machine(s) 
may be set up so as to generate alarms upon the occurrence of deviations 
from the preset injection parameters to allow continuous monitoring of the 
injection processes on each machine and appropriate modification if 
necessary. As previously mentioned, once an acceptable die recipe is 
generated for a particular molding die, each of the process parameters may 
be provided with tolerance bands about the optimum desired parameters, 
wherein deviation from the pre-selected values beyond a given tolerance 
band will result in an alarm being triggered. The networking of a large 
number of injection molding machines also allows greatly enhanced data 
collection as the central control facility may be provided with suitable 
storage facilities such that every injection profile from a single machine 
could be monitored over time for quality control and production control 
activities. Various management reports may then be generated such as 
production rates, costs, scrap generation, product flow data as well as a 
variety of other reporting capabilities which will greatly enhance the 
user's ability to efficiently and cost effectively produce high quality 
expendable patterns, and document traceability of product fabrication 
historically and comparatively. As previously mentioned the ability to 
trace the manufacturing history of a particular molded product is becoming 
increasingly important under more stringent quality control standards, and 
also gives the user the ability to monitor the fabrication process over 
time. 
It should be evident from the foregoing, that the injection molding 
apparatus and control system of the invention provides a novel and 
significant improvement relating to injection molding apparatus for use in 
producing expendable patterns for metal casting techniques. The control 
system of the invention greatly reduces set up time, and increases the 
ability to generate and collect technical and accounting data to allow 
improved cost performance and process control capabilities. The control 
system provides security to ensure the consistency and integrity of the 
production process and reduces maintenance requirements by allowing 
diagnostic analysis of the machine operation on a continuous basis. 
Although the invention has been described relative to particular preferred 
embodiments thereof, it should be apparent that various modifications or 
variations in the apparatus or details of operation are contemplated 
herein and would occur to those skilled in the art. The invention is 
therefore not to be limited by the details of the description of the 
preferred embodiments, but rather is intended to encompass all such 
modifications which are within the spirit and scope of the invention as 
defined by the appended claims.