HK1058647B - A drive system for and injection molding apparatus - Google Patents

Description

Transmission system for injection molding equipment

Technical Field

The present invention relates generally to molding machines and more particularly to an injection molding machine that utilizes a single electric motor to drive a hydraulic motor and transmission for loading an accumulator, such as a feed screw and/or a mold clamping unit.

Background

The injection unit of an injection molding machine has two main functions, injection and extrusion, during the normal operating cycle. In a standard reciprocating screw injection molding machine, the extrusion function is accomplished by the plastic melt gradually moving toward the forward end of the screw as the screw rotates, and creating a pressure or force as the melt accumulates to move the screw back to its pre-injection position. When a sufficient amount of material has been accumulated ("injected"), the screw is rapidly moved forward (without rotation) to inject melt directly into the mold, thus performing the injection function. Injection molding processing requirements for commercially important plastic materials involve injection pressures of at least 15,000 pounds per inch²And often up to 30,000 lbs/inch²。

The injection unit of the molding machine can also be designed as a "two-stage" system, where the extrusion and injection functions are performed by separate machine parts. In two-stage injection molding systems, the extrusion or plasticizing function is still performed by the feed screw in the heating cylinder, but all or part of the plastic melt is transferred to the "melt reservoir" instead of being directly transferred to the mold. Thereafter, the melt reservoir is operated to perform, or at least assist in performing, the injection molding function. The advantages of the two-stage injection molding unit include more uniform material plasticization, reduced wear on the screw and the cylinder, and higher injection molding pressure potential. The main disadvantage is the high cost.

The injection and extrusion functions require associated gearing in the injection unit. In prior art hydraulic machines, the injection function movement is typically accomplished by a hydraulic cylinder, while the feed screw rotation for the extrusion operation is typically accomplished by a hydraulic motor. More recently, electric motors in combination with mechanical systems have been used as a direct power source in injection molding units. Some prior art electrical systems have used separate motors for various functions, i.e., one motor for rotation of the feed screw and another motor in conjunction with a mechanism such as a ball screw to convert the rotational motion to the linear motion required for injection molding. Other prior art "hybrid" machines have used an electric motor to turn the feed screw with the remaining functions of the machine being hydraulically driven, the power being from the electric motor driving one or more hydraulic motors.

Although "hybrid" machines have some of the advantages of electric motors (better control of screw rotation) and hydraulic machines (lower overall cost), there is still room for improvement. In particular, because the motor that turns the screw has excess power, there is the potential for a more economical system. Such motors are used only during the cycle in which the injection of the extruded (plasticized) thermoplastic occurs. Due to the relatively high cost of the electric motor and associated variable speed drive, it is desirable to maximize the use of this motor. In addition, with the currently used injection molding machines with variable speed motors, either the motors are used on special shafts (e.g., with electromechanical systems) or are redundant to standard hydraulic lines, such that the variable speed motors and transmissions do not achieve effective control.

Therefore, it is typical to apply new processes to existing products in an effort to maximize the performance of the processes of previous injection molding systems to reduce risks and maintain product identity. This is especially true in all-electric injection molding machine designs where hydraulic mechanism control has been replaced with electromechanical mechanism control. Because of this limited design approach, many of the significant advantages of variable speed motor drives have not been realized in their injection molded applications.

It is very true that the replacement of the hydraulic drive train by an electromechanical drive train achieves a significant modest improvement in the accuracy, stability and reproducibility of the driven device, which is a consequence of the reduction of the number of components in the drive train, eliminating the inherent variation of the hydraulic oil with temperature, viscosity variations. This change is due to the fact that extreme chemical breakdown of the oil itself may occur, among other things, increasing the concentration of contaminants. However, while the desired performance improvement is achieved by merely replacing the hydraulic drive train with servo electrical/mechanical components, all possible improvements are still accomplished.

Another consideration is that the footprint of the injection molding machine has become an especially important criterion. When resources once available to equipment are transferred to other assets to increase productivity, the length x width x height of a machine becomes an issue of extra importance for machine design competition.

In addition to the need to increase the productivity of the electric injection unit, it is possible to improve the precision, stability, reproducibility and durability of the driven device and to reduce the overall length of the machine, finding a way to overcome the obstacles that present the limits of the use of electromechanical processes for reciprocating screw injection units.

There is also a need for an improved and efficient system when the closing or clamping mechanism of an injection molding machine is operated while the two mold halves can be moved toward or away from each other to open and close the injection mold. With this arrangement, the injection mold must withstand relatively large mold clamping forces during the injection cycle, and the prior art has focused on using a fully hydraulic drive for the long stroke portion of the open mold and for the equipment used to apply the clamping force. More recently, electric motors have been used for long opening and closing strokes and utilize hydraulic pressure to apply large clamping forces during the injection molding cycle. However, the prior art still needs to provide a small and efficient transmission system using an electric motor and a hydraulic motor.

Disclosure of Invention

It is therefore an object of the present invention to provide an improved transmission apparatus that can use an optimal single motor to provide the power required by the various parts of an injection molding machine.

Another object of the invention is to provide a simplified apparatus that can drive both the extrusion screw and the hydraulic motor.

It is a further object of the present invention to provide an injection unit for a molding machine which is inexpensive to assemble, reliable and easy to maintain.

It is a further object of the present invention to provide a highly efficient drive system for an injection molding machine that employs an electric motor to simultaneously drive an extrusion screw and a hydraulic motor to simultaneously load a hydraulic accumulator, thereby utilizing the load in the accumulator to impact the screw during the injection cycle.

It is still another object of the present invention to provide an efficient drive system for an injection molding machine. It uses an electric motor to drive an extrusion screw and a hydraulic motor that loads an accumulator. A clutch is disposed between the motor and the screw to allow the motor to continuously drive the hydraulic motor even during the injection cycle.

It is a further object of the present invention to provide a highly efficient drive train for an injection molding machine that utilizes an electric motor to close the mold while loading an accumulator and utilizes the load in the accumulator to apply a clamping force during the injection/molding cycle.

To this end, the invention provides an injection molding machine equipped with a transmission system including an injection unit, comprising: a feed screw housed in a barrel having an inlet and an outlet; a hydraulic motor selectively in communication with the at least one hydraulic accumulator via at least one hydraulic valve; a rotary drive unit simultaneously rotating the feed screw to plasticize the material within the barrel and transport it from the inlet to the outlet; and driving the hydraulic motor to store energy in the accumulator; a hydraulic piston is in selective communication with the accumulator through the hydraulic valve, the piston being in communication with the feed screw, wherein pressure and flow from the accumulator translates the piston which in turn translates the feed screw to inject material through the outlet.

The injection molding machine further comprising a clutch mechanism provided between the rotary transmission unit and the feed screw, whereby the feed screw is selectively disengaged from the rotary transmission unit; the hydraulic valve is a spring-loaded solenoid valve; the hydraulic valve is a servo control valve; the hydraulic valve is a hydraulic pilot valve; the rotary transmission unit is an electric motor; the rotary transmission is a variable speed motor; the rotary transmission unit is communicated with the hydraulic motor by adopting at least one torque transmission belt; the rotary transmission unit is communicated with the hydraulic motor by adopting at least one gear set; the accumulator is a gas-filled piston type; the accumulator is of the gas-filled bag type.

One embodiment of the present invention is directed to a hybrid injection molding machine that simultaneously drives an extrusion screw and a hydraulic motor with an optimally variable speed electric motor during the plasticizing process. In the course of the plasticizing process, the hydraulic motor loads the hydraulic accumulator. When sufficient plastic has been extruded and the desired "shot" size is produced, the load in the accumulator is used to impact the screw or a separate piston to inject melt into the mold cavity.

Alternatively, a clutch can be provided between the electric motor and the extrusion screw, whereby the electric motor can continuously charge the accumulator by driving the hydraulic motor. The clutch is actuated to disengage the extrusion screw once the desired shot size is produced, thereby stopping the rotation of the extrusion screw so that the screw can be impacted by a piston driven by the load in the accumulator, which is constantly being continuously charged by the motor.

In another embodiment of the invention, a separate motor is provided on the clamping side of the injection molding machine. The motor is connected with a mechanical transmission mechanism for opening and closing the mold. In addition, a hydraulic motor is connected to the electric motor, which supplies a separate energy store. When the electric motor closes, it also drives a hydraulic motor that loads the accumulator, and once fully closed, the load in the accumulator is utilized. To apply the large clamping forces to the mold that are required during the injection/molding cycle.

In this embodiment, an optional clutch mechanism is provided between the electric motor and the mechanical transmission, so that the electric motor continuously drives the hydraulic motor and charges the accumulator, although the mold is fully closed. Once the mold is fully closed, which disengages the transmission from the electric motor, the clutch is actuated, thereby allowing the electric motor to continue to drive the hydraulic motor and charge the accumulator.

As long as a single motor is best suited for a given load, the drive system will be simpler and cheaper. Also, a separate hydraulic motor is best suited for accumulator loading, as is required for different sizes of injection molding machines. Furthermore, the overall efficiency of the machine is improved by using the electric motor to perform both functions simultaneously. The addition of the clutch enables the motor to continuously load the accumulator, which not only results in shorter cycle times, but also improves the overall efficiency of the machine.

In general, the present invention provides a unique hybrid drive system for an injection molding machine that allows for optimization of various drive components and a more efficient drive system for the extrusion screw and clamping mechanism.

Drawings

The present invention will be better understood in view of the detailed description of the preferred embodiments taken in conjunction with the following drawings.

FIG. 1 is a diagrammatic view of an injection molding machine injection system push-type screw unit with its associated indexing and/or drive force transmission apparatus;

FIG. 2 is an enlarged diagrammatic view, partly in section, of a two-stage injection molding apparatus modified from an injection molding machine;

FIG. 3 is a hydraulic schematic of the injection unit of the present invention;

FIG. 4 is a simplified plan view of an improved clamping unit for an injection molding machine incorporating an improved drive train.

Reference numbers used in the figures

12-motor

14-moving plate

16-hydraulic motor

18-first drive belt

20-second drive belt

22-piston assembly

24-Hydraulic accumulator

26-first fixing plate

28-second fixing plate

29-extrusion assembly

30-hopper

34-Heater

36-feed screw

38-extrusion Shell

40-discharge port

42-base

46-hydraulic valve

48-guide beam

50-catheter

52-melt reservoir

54-oil tank

56-check valve

58-Clutch mechanism

59-Cylinder

60-first fixed platen

62-second stationary platen

64-linkage mechanism (transmission means)

66-Movable mold half

68-Tie rod

70-stationary mold half

72-Movable platen

74-Transmission mechanism

Detailed Description

The present invention relates to an injection unit for an injection molding machine; it will therefore be described in the context of a "representative" machine. Because the general structure and operation of injection molding machines are well known, significant emphasis has been placed on those aspects of having different or new uses for the injection molding machine equipment.

Fig. 1 depicts the basic structure of an injection unit of an injection molding machine, a single-stage pusher screw unit 10 of which is mounted on a base 42. The extrusion assembly 29 includes an extrusion housing 38, a hopper 30 for feeding solid plastic, and a rotary and replaceable pusher feed screw 36. In heat exchange relationship with the housing 38 is a heater 34 which maintains the melt in a molten state for injection through a discharge port 40.

The device of fig. 1 has several parallel guide beams 48, two fixed plates 26, 28 and a movable plate 14. The plate 14 is moved along the guide beam 48 by the piston assembly 22. Mounted on the plate 14 is a motor 12 which is connected to a feed screw 36 by a first drive belt or other linkage 18. Also mounted on the plate 14 is a hydraulic motor 16 which is driven by a feed screw 36 via a second drive belt or another linkage 20. In this configuration, the reader can readily see that the electric motor 12 simultaneously provides power to both the feed screw 36 and the hydraulic motor 16. It should be noted that the position of the hydraulic motor 16 can be easily changed so as to be directly driven by the electric motor 12.

Communicating with the hydraulic motor 16 is a tank 54 for the hydraulic oil and a hydraulic accumulator 24 via the hydraulic valve 46, wherein the electric motor 12 drives the hydraulic motor 16, which in turn charges the hydraulic accumulator 24, so that energy is stored in the accumulator 24.

Operatively mounted between the fixed plate 26 and the movable plate 14 is a piston assembly 22. During the injection molding process, the energy stored by the accumulator 24 extends the piston assembly 22 in the "B" direction. The piston assembly 22 is retracted by the force of the melt as it accumulates in front of the feed screw 36.

To fill an injection mold (not shown) with plastic melt, the motor 12 is stopped and the piston assembly 22 is selectively actuated by the hydraulic valve 46 to direct the energy stored in the accumulator 24 to extend the piston assembly 22 in the "B" direction, and then the pusher feed screw 36 is pushed forward by the plate 14 into the housing 38 to inject the melt material through the discharge port 40.

On the other hand, a selectable clutch mechanism 58 is provided to disengage the motor 12 from the feed screw 36 during the injection cycle. This arrangement enables the electric motor 12 to continuously drive the hydraulic motor 16 and load the hydraulic accumulator 24.

Referring to fig. 2, the apparatus of the present invention is used in conjunction with an injection molding machine 100. The general construction of molding machine 100 includes a two-stage electric/hydraulic injection unit mounted on an elongated support or base 42. The components of the injection unit 100 are specifically designed to incorporate the motor drive process into a two-stage injection unit. Preferably, the primary components are a motorized extrusion assembly 29 and a melt reservoir 52. The extruder assembly 29 is provided for continuous plastication and therefore has a non-reversing feed screw 36. However, the principles of the present invention can also be applied to a two-stage injection molding system incorporating a reciprocating feed screw as shown and described with respect to FIG. 1, if desired.

As is generally known in the art, the material is fed to the extrusion apparatus in a convenient manner, for example, via a hopper 30. The rotational power of the feed screw 36 is also supplied in a conventional manner, such as by a motor 12 connected to a belt or other drive pattern 18 that drives the screw 36. Since the feed screw 36 is only rotating, the drive train is much simpler than an injection molding apparatus having a screw that also reciprocates.

The melt reservoir 52 is essentially a container of variable volume by means of a cylindrical barrel 59 and a piston assembly 22 that moves linearly within the barrel 59. The relative dimensions of the piston assembly 22 and cylinder 59, as well as the stroke of the piston 22, will vary depending on the amount of melt required for injection into the mold. The end shapes of the piston 22 and cylinder 59 are preferably configured to minimize the amount of resin remaining in the cylinder 59 when the piston 22 is fully extended during shrinkage of the melt reservoir 52.

The discharge port of the feed screw 36 is connected to a reservoir 52 by a suitable conduit 50. A check ball valve 56 or other suitable one-way safety device is conveniently provided between the feed screw 36 and the feed port of the melt reservoir 52 to control the flow direction in the conduit 50. the check valve 56 prevents backflow of melt to the feed screw 36 due to pressure differential when the hydraulic accumulator 24 is actuated to inject plastic into the mold cavity and maintain pressure during filling and storage. The outlet of melt reservoir 52 is connected to an injection mold (not shown) through a suitable outlet port 40.

The piston 22 of the melt reservoir 52 is preferably selectively actuated by a hydraulic valve 46 that controls the stored energy in the hydraulic accumulator 24 to extend the piston 22.

The electric motor 12 is connected to the hydraulic motor 16 by a linkage such as belts 18 and 20. When the electric motor turns the feed screw 36, the hydraulic motor 16 is also driven, causing the hydraulic motor 16 to load the accumulator 24. The stored hydraulic energy in the accumulator 24 is then used to impact the piston 22 and inject melt into the discharge port 40.

Operation of the injection molding machine 100 incorporating the two-stage injection unit of the present invention will now be described, with the feed screw 36 being rotated within the extruder housing 38 by the extruder motor 12 to initiate plasticization of the material, which is delivered to the melt reservoir 52 as a plastic melt. Rotation of the screw 36 generates pressure at the end of the feed screw 36, which actuates (opens) the ball check valve 56, allowing material to flow through the conduit 50 and into the melt reservoir 52. When the plastic melt pressure reaches a certain level, it begins to force the piston 22 backwards.

When sufficient plastic melt load is accumulated in front of the piston 22 in the melt reservoir 52 for injection into the mold cavity, the extrusion operation is completed and the rotation of the feed screw 36 is stopped, at which time the hydraulic valve 46 is actuated to control the pressure and flow to the feed port of the piston 22. The advancing movement of the piston 22 forces the accumulated plastic melt through the discharge orifice 40 into the mold cavity. The injection pressure created by the movement of piston 22 moves ball check valve 56 to a position that prevents the molten resin from turning into extruded housing 38.

Optionally, a clutch mechanism 58 may be provided between the electric motor 12 and the feed screw 36 so that the electric motor 12 may be disengaged from the feed screw 36, allowing the electric motor 12 to continuously drive the hydraulic motor 16 and charge the hydraulic accumulator 24. Thus, the clutch mechanism 58 allows the motor 12 to continue to operate, loading the accumulator 24, during the injection cycle.

Referring now to FIG. 3, a simplified diagram of the hydraulic system of the present invention is shown, with the hydraulic accumulator 24 selectively actuated by a four-way, two-position hydraulic valve 46, as previously described. The valve train is spring loaded to its normal state to allow the hydraulic motor 16 to charge the accumulator 24 and return hydraulic oil from the piston 22 to the tank 54 as the piston 22 retracts during the extrusion process. When valve 46 is actuated, hydraulic fluid is directed from accumulator 24 to piston 22 to inject melt into a mold cavity (not shown). The valve 46 may be solenoid-controlled or servo-controlled, with the preferred embodiment being a servo-valve, as it facilitates infinite adjustment of the time-pressure profile delivered to the piston 22 during the injection molding process.

Referring now to FIG. 4, an improved injection molding clamping system 200 is generally described. The motor 12 is mounted on a base (not shown) using many of the same high efficiency principles previously discussed. The base communicates with a drive mechanism 74 through a linkage 64. Mounted on the transmission 74 is an optional clutch mechanism 58 for selectively engaging the transmission 74 with the motor 12, rigidly secured to the first stationary platen 60 distal to the plurality of tie rods 68. Rigidly affixed to the other distal end of the plurality of tie bars 68 is a second fixed platen 62, and between the first and second fixed platens and guided by the plurality of tie bars 68 is a movable platen 72. The movable platen 72 is in communication with a transmission mechanism 74, whereby rotation of the transmission mechanism 74 translates the movable platen 72 relative to the stationary platen along the long axis of the plurality of tie bars 68.

Mechanically connected to the electric motor 12 is a hydraulic motor 16. The hydraulic motor 16 is in fluid communication with the hydraulic accumulator 24 through the use of a hydraulic valve 46. When the electric motor 12 drives the hydraulic motor 16, pressure and oil flow from the oil reservoir 54 is selectively communicated through the hydraulic valve 46 to the hydraulic accumulator 24 to store energy.

Rigidly affixed to the movable platen 72 is the movable mold half 66. Rigidly fixed to the first stationary platen 60 is a stationary mold half 70. As the actuator 74 moves the movable platen 72, the movable mold half 66 translates to open the mold, thereby releasing the finished plastic part.

The hydraulic accumulator 24 is in selective communication with the piston assembly 22 through a hydraulic valve 46. The hydraulic piston assembly 22 is operatively secured between one of the fixed platens 60 or 62 and the movable platen 72. In the preferred embodiment, the piston assembly 22 is a single-acting hydraulic piston mounted on the second stationary platen 62.

In the configuration shown in fig. 4, the motor performs two functions, one of which is to open and close the mold halves 66 and 70. Upon completion of this function, the selectable clutch mechanism 58 is engaged, causing the motor 12 to start the transmission 74. In a preferred embodiment, the transmission mechanism is of the ball screw type. The second function of the electric motor 12 is to drive the hydraulic motor 16, which hydraulic motor 16 charges the accumulator 24 with stored energy.

Once the mold halves are fully assembled by actuator 74 and ready for the injection cycle, the pressure and fluid load stored in accumulator 24 is transferred to piston assembly 22 through hydraulic valve 46. The pressure transmitted from the accumulator 24 to the piston assembly 22 is required to bring the two mold halves 66 and 70 together tightly and withstand the injection pressure that acts to open the mold halves. Once the molded part is injected and the molded part is set at the predetermined dwell time, deactivation plug assembly 22 is depressurized via hydraulic valve 46. At this point, the motor 12 communicates with the actuator 74 to open the mold, thereby releasing the molded article from the mold cavity.

Although the present invention has been described in some detail with reference to preferred embodiments thereof as illustrated in the accompanying drawings, and while the preferred embodiments have been described in some detail, the invention is not limited to the details thereof. Rather, the invention is intended to cover all modifications, alterations and equivalents which may fall within the scope and spirit of the appended claims, for example, although the drive coupling is typically a belt or pulley, other mechanical couplings, such as suitable gearing, may be used to accomplish the same function.

Claims (11)

1. An injection molding machine equipped with a transmission system including an injection unit, comprising:

a feed screw housed in a barrel having an inlet and an outlet;

a hydraulic motor selectively in communication with the at least one hydraulic accumulator via at least one hydraulic valve;

a rotary drive unit simultaneously rotating the feed screw to plasticize the material within the barrel and transport it from the inlet to the outlet; and

and driving the hydraulic motor to store energy in the accumulator;

a hydraulic piston is in selective communication with the accumulator through the hydraulic valve, the piston being in communication with the feed screw, wherein pressure and flow from the accumulator translates the piston which in turn translates the feed screw to inject material through the outlet.

2. The injection molding machine of claim 1, further comprising a clutch mechanism disposed between the rotary drive unit and the feed screw, whereby the feed screw is selectively disengaged from the rotary drive unit.

3. The injection molding machine of claim 1 wherein said hydraulic valve is a spring-loaded solenoid valve.

4. The injection molding machine of claim 1 wherein said hydraulic valve is a servo controlled valve.

5. The injection molding machine of claim 1 wherein said hydraulic valve is a hydraulic pilot valve.

6. The injection molding machine of claim 1 wherein the rotary drive unit is an electric motor.

7. The injection molding machine of claim 1 wherein said rotary drive is a variable speed motor.

8. The injection molding machine of claim 1 wherein said rotary drive unit communicates with said hydraulic motor using at least one torque transmission belt.

9. The injection molding machine of claim 1 wherein said rotary drive unit communicates with said hydraulic motor using at least one gear set.

10. The injection molding machine of claim 1 wherein said accumulator is a gas-filled piston type.

11. The injection molding machine of claim 1 wherein said accumulator is of the gas-filled bladder type.