Where is the "precision" in the often said precision injection molding technology? (two)

2021-03-25 09:54:52 admin

Last issue talked about two of the "precision" in precision injection molding technology. Today we will talk about the next department!


1. Precision injection screw


Compared with the traditional injection screw, the precision injection screw has the characteristics of relatively small compression, large aspect ratio and high wear resistance. Taking the aspect ratio as an example, the ordinary injection screw is 20 to 23, while the precision injection screw is 24 to 30.


Generally, the materials used for precision injection molding screws have high rigidity and strength, and the precision injection molding screws produced will vary according to the processing materials. In order to improve the flow-length ratio of injection molding and minimize the shrinkage of product molding, the injection pressure of the precision injection molding machine can reach 216 to 243 MPa, and the injection pressure of the ultra-high pressure machine can reach 243 to 392 MPa. In this case, the screw must have sufficient rigidity and strength to avoid failures such as bending and twisting during high-pressure injection molding.


Precision clamping device


Mold clamping device is an important part to protect precision molds and ensure product quality. Compared with the ordinary clamping device, the rigidity of the precision clamping device is 10% to 15% higher, and the standard of parallelism between the moving and fixed mold plates is also 30% to 40% higher, generally controlled within 0.05~0.08mm , So as to realize the low-pressure protection of the mold and the precise control of the clamping force.


1. Mold clamping device of precision toggle device


For the mold clamping device of the traditional toggle lever device, long-term stable parallelism cannot be obtained between the movable and fixed mold plates, and it is difficult to achieve low-pressure protection for precision molds. In order to overcome this shortcoming, the precision toggle lever device has made the following improvements: the use of high-precision ball guides to guide the movement of the moving platen ensures the stability of the moving platen operation accuracy; the dual functions of speed control and closed-loop pressure are applied. The servo valve realizes the low-pressure protection of the precision mold; the pin shaft and the steel sleeve adopt a friction pair with high wear resistance, which further stabilizes the parallelism between the moving and fixed mold plates; the application of the precision mold adjustment mechanism has realized The high-precision mold adjustment ensures that the movable platen can achieve stable parallelism at any position.


2. Precise full hydraulic clamping device


The clamping device for precision injection molding is mainly based on full hydraulic clamping device. In the traditional mold clamping device, the clamping force of the toggle lever device usually acts on the upper and lower (or left and right) sides, which will cause the middle part of the movable template to be deformed, thereby affecting the parallelism of the template. This kind of full hydraulic The mold clamping oil cylinder piston of the mold clamping device acts on the central position of the movable mold plate to ensure the long-term stable parallelism between the movable mold plate and the fixed mold plate.


With the improvement of application requirements, the precision full-hydraulic mold clamping device is constantly being reformed. The use of high-precision ball guide rails for the movement of the movable mold plate is the most obvious improvement, which has further improved the gap between the movable mold and the fixed mold plate. The requirements of parallelism stability.


3. No tie rod clamping device


Since the tie rodless mold clamping device does not use tie rods, the effect of tie rod deflection on the parallelism of the template is eliminated. In recent years, through the improvement of the "C"-shaped frame, which is susceptible to deformation, the accuracy and stability of the parallelism between the movable and fixed templates have been improved. For example, Milacron’s Freedom series tie-bar-less injection molding machine has a U-shaped mold clamping device with only two tie-rods at the bottom, which has higher rigidity. By configuring the patented balance cylinder structure, the parallelism between the fixed templates is more stable.


4. Divided one-piece headboard


Generally, the head plate of an injection molding machine with a tie rod clamping device adopts a monolithic structure, and such a structural design often causes the overall deformation of the head plate due to excessive force. The precision injection molding machine adopts a block-integrated head plate, which effectively improves the rigidity of the head plate, so as to reduce the deformation and deflection of the mold plate due to the force. This split-piece conjoined head plate separates the force-receiving function of the head plate and the installation mold function, which are respectively borne by their respective blocks, and a central ring body is used to connect the force-receiving block and the installation mold block.


In the process of bearing the clamping force, since the force area of the center ring body is smaller than the area of the force block, the deflection generated by the force of the head plate only transmits the deformation and deflection generated at the center center ring body to the mounting mold block. It can be seen that the deformation and deflection zone of the installation mold block due to the force is only in the central ring body, which will not produce deflection to the installation mold block as a whole, so as to achieve the purpose of improving the clamping accuracy.


Precision hydraulic control technology


The development of high-speed response integrated components and systems is the development direction of precision hydraulic control technology. To achieve high-speed response capabilities, not only the response speed of the valve itself must be improved, but the number of valves must be reduced under the premise of improving the control performance to achieve Respond to the speed requirements of the loop.


In order to meet this requirement, the hydraulic control technology of precision injection molding machines is accelerating its own technological development. The most obvious feature is the integration of digital electronic hydraulic technology and electronic computing technology to form a "smart" control system, so that no external controller is needed. Various operating functions can be completed independently, and accurate closed-loop control of each main parameter, such as flow, speed, position and pressure, can be achieved, so that the system can achieve better high-speed response control effects.


Multifunctional and highly integrated proportional hydraulic components are an important feature of the development of hydraulic components for precision injection molding machines. Different from the previous loop that requires the application of multiple valves with different functions, the current precision injection molding equipment integrates these multi-function control valves into one loop, which greatly improves the dynamic performance of the equipment. For example, Atos has developed a digital servo proportional cartridge compound valve for injection molding and plasticizing circuits. The component integrates a P/Q digital amplifier. By cooperating with an external pressure sensor, only one valve is required to complete the control task when injection molding. The original 3 to 5 valves are required. The component can also perform speed control and pressure control at the same time, and can achieve highly dynamic and accurate conversion in the pressure holding and plasticizing back pressure stages.