I. Overview
Plastic injection molding machines, commonly known as injection molding machines, are essential equipment in modern manufacturing. These machines heat granular plastic to a molten, flowable state before injecting it into a mold cavity at high speed and pressure. After a specified holding pressure period and cooling process, the material solidifies into the desired plastic product shape. The hydro drive transmission technology is fundamental to achieving these precise operations.
The XS-ZY-250A injection molding machine is classified as a medium-small sized equipment, featuring impressive capabilities for its class. Its theoretical maximum injection capacities are 201cm³, 254cm³, and 314cm³, corresponding to barrel screw diameters of φ40mm, φ45mm, and φ50mm respectively. This particular model comes standard with the φ50mm barrel screw configuration, with other options available for separate purchase based on specific production requirements.
With a clamping force of 1600kN, the XS-ZY-250A is engineered to handle a wide range of plastic molding applications. The machine's hydro drive transmission system enables several key operational movements: mold closing and opening, injection unit forward and backward movement, injection, pressure holding, and ejection. These movements follow a specific sequence as dictated by the plastic injection molding process, forming a complete working cycle that the hydro drive transmission precisely controls.
Fig. 8-9: Injection Molding Machine Working Cycle
Mold Closing → Injection Unit Forward → Injection & Pressure Holding → Injection Unit Backward → Mold Opening → Product Ejection → Ejection Cylinder Retraction
II. XS-ZY-250A Injection Molding Machine Hydraulic System
Figure 8-10 illustrates the hydraulic system schematic of the XS-ZY-250A injection molding machine. This advanced system employs a hydraulic-mechanical design where the hydro drive transmission plays a central role in all operational phases. The clamping cylinder acts through a symmetric five-link mechanism to move the mold plates during opening and closing operations. This linkage mechanism provides both force amplification and self-locking capabilities, relying on the preload force generated by the elastic deformation of the connecting rods to ensure the required clamping force.
A key feature of this hydraulic system is its utilization of proportional pressure valves and proportional flow valves for precise pressure and flow control. Compared to other types of injection molding machine hydraulic systems, this configuration employs fewer hydraulic components and features a simpler circuit design. The hydro drive transmission enables smooth transitions between pressure and speed settings, minimizing shock during these transitions and facilitating remote control and program control implementation. This design foundation makes it ideal for computerized control integration.
Table 8-1 provides a comprehensive overview of the XS-ZY-250A injection molding machine's operational cycle and solenoid valve activation sequence. Understanding this sequence is crucial for optimizing the performance of the hydro drive transmission system and ensuring efficient, high-quality production cycles.
Hydraulic System Components
- 1 Clamping cylinder
- 2,4 Mold clamping device
- 3 Ejection cylinder
- 5 Nozzle
- 6 Heater
- 7 Hopper
- 8 Feeding screw
- 9 Injection cylinder
- 10 Injection unit moving cylinder
- 11,12 Proportional pressure valves
- 13 Proportional flow valve
- 14,15 Check valves
- 16-19 Directional control valves
- 20 Check throttle valve
- 21 Pressure relay
- 22 Check sequence valve
- 23 Core filter
- 24 Cooler
Fig. 8-10: XS-ZY-250A Injection Molding Machine Hydraulic System Schematic
The diagram illustrates the complete hydro drive transmission system, showing the integration of all components in the hydraulic circuit.
III. Hydraulic System Working Principles
1. Mold Closing
The mold closing process operates in a sequence of fast and slow speeds, with the hydro drive transmission precisely controlling each phase. The entire mold closing process consists of three distinct stages, each optimized for specific operational requirements.
Solenoid 7YA is energized, while control signals (0-10V voltage or 4-20mA current) are applied to proportional valves E1, E2, and E3 to control the corresponding pressure and flow in the system. The hydraulic pump delivers hydraulic oil (low pressure, high flow due to small load) through the proportional flow valve 13 and directional valve 16 into the left cavity of the clamping cylinder. This action pushes the piston, driving the connecting rods for fast mold closing. Oil in the right cavity of the clamping cylinder returns to the tank through directional valve 16, filter 23, and cooler 24. The hydro drive transmission ensures rapid movement while maintaining system stability.
During this phase, the cylinder generates relatively small thrust due to the low pressure setting. This design feature protects the mold surface from damage even if hard foreign objects are present between the two mold plates. The speed of the clamping cylinder is regulated by the proportional flow valve 13, with the hydro drive transmission ensuring smooth, controlled movement. This stage represents a critical safety mechanism in the molding process, preventing costly mold damage.
The voltage signal for control signal E2 is increased, causing the pressure output from proportional pressure valve 12 to rise accordingly. Meanwhile, the voltage signal for control signal E1 is set to zero (de-energized), enabling the double pump to unload. The combination of high pressure and low flow achieves high-pressure mold closing, causing the mold to close completely and the connecting rods to undergo elastic deformation, thereby securely locking the mold. The hydro drive transmission system's precision ensures that the exact pressure required for proper mold locking is achieved and maintained.
Stages of mold closing process showing the transition from fast to slow movement, controlled by the precision hydro drive transmission system.
2. Injection Unit Forward Movement
Solenoid 3YA is energized, and the proportional pressure valve 12 controls the system pressure during this phase. Hydraulic oil from the hydraulic pump flows through the directional valve 18 into the right cavity of the injection unit moving cylinder 10, pushing the entire injection unit forward. Oil in the left cavity of cylinder 10 returns to the tank through valve 18, filter 23, and cooler 24.
The hydro drive transmission system ensures precise positioning of the injection unit, which is critical for proper nozzle alignment with the mold gate. This alignment directly affects the quality of the final product, as misalignment can cause material leakage, pressure loss, or imperfect filling of the mold cavity. The proportional control capabilities of the hydro drive transmission allow for fine adjustments to the forward movement speed and position, accommodating different mold designs and production requirements.
Injection Unit Forward Movement
Precise positioning controlled by hydro drive transmission
3. Injection Process
The injection process operates in three speed stages: slow, fast, and slow again, with corresponding control signals applied to proportional valves E1, E2, and E3. The injection speed is controlled by the voltage signal to the proportional flow valve 13, demonstrating the versatility of the hydro drive transmission system in adapting to different material properties and product requirements.
During injection, solenoid 1YA is energized, directing hydraulic oil from the hydraulic pump through valve 19 and valve 22 into the right cavity of the injection cylinder 9. Oil in the left cavity of cylinder 9 returns to the tank through valve 19, filter 23, and cooler 24. The hydro drive transmission system's ability to precisely control both pressure and flow rates during this critical phase ensures uniform filling of the mold cavity, preventing defects such as air bubbles, uneven density, or incomplete filling.
The initial slow injection phase allows the molten plastic to begin filling the mold without splashing or creating turbulence that could trap air. The subsequent fast injection phase rapidly fills most of the mold cavity, optimizing cycle time while maintaining product quality. The final slow injection phase ensures complete filling of intricate details and helps prevent excessive material pressure at the mold gate. Throughout all these phases, the hydro drive transmission maintains precise control over the injection parameters, which is essential for consistent production quality.
4. Pressure Holding
Following the completion of the injection phase, the pressure holding phase begins, during which the hydro drive transmission system maintains a specified pressure within the mold cavity. This is essential because molten plastic continues to cool and shrink after injection, requiring additional material to be pushed into the mold to compensate for this shrinkage. The pressure holding phase ensures that the final product maintains its intended dimensions and density.
The proportional pressure valve 12 plays a key role in the pressure holding phase, precisely regulating the system pressure as dictated by the control signal E2. The pressure is typically maintained at a level lower than the maximum injection pressure but sufficient to ensure proper compensation for material shrinkage. The duration of the pressure holding phase varies depending on factors such as the plastic material, product thickness, and mold design. Throughout this phase, the hydro drive transmission system maintains consistent pressure control, which is critical for producing high-quality parts with minimal dimensional variation.
IV. Characteristics of XS-ZY-250A Injection Molding Machine Hydraulic System
1. Advanced Clamping Mechanism
Injection molding machines typically require molten plastic to be injected into the mold cavity at high pressures ranging from 40-150MPa. This necessitates a substantial clamping force to prevent mold separation during injection, which would cause flash on the finished product.
The XS-ZY-250A employs a hydraulic-mechanical clamping mechanism where the clamping cylinder acts through a five-link mechanism with force amplification and self-locking capabilities. This innovative design reduces the required clamping cylinder pressure while ensuring stable and reliable mold clamping. The final clamping force is achieved by maintaining high pressure in the clamping cylinder, causing elastic deformation in the linkage mechanism that securely locks the mold. This approach, combined with the precision of the hydro drive transmission, ensures consistent clamping performance throughout production runs.
2. Optimized Speed Control
To maximize productivity by minimizing idle time while ensuring process stability and preventing damage to products and molds, the clamping mechanism requires variable speed control during both mold closing and opening operations. This typically follows a slow-fast-slow sequence.
The XS-ZY-250A's hydro drive transmission system achieves rapid movements through low-pressure, high-flow oil supply from the hydraulic pump. This approach optimizes cycle times while maintaining the precision required for high-quality production. The proportional flow control valve allows for smooth transitions between speed stages, eliminating sudden movements that could cause mold damage or product defects. The hydro drive transmission's ability to precisely control these speed variations contributes significantly to the machine's overall efficiency and product quality.
3. Flexible Process Parameters
Recognizing that different plastic materials, product geometries, and mold gating systems require different processing conditions, the XS-ZY-250A's hydraulic system is designed with proportional adjustment capabilities for both pressure and speed. This flexibility is primarily achieved through the use of proportional pressure and flow valves that form the core of the hydro drive transmission system.
Material Adaptability
Different plastics have varying viscosity and flow characteristics. The hydro drive transmission allows operators to adjust injection pressure and speed to match these characteristics, ensuring optimal filling and packing of the mold cavity regardless of the material being processed.
Product Geometry
Complex part geometries with thin walls or intricate details require different processing parameters than simple, thick-walled parts. The proportional control offered by the hydro drive transmission enables precise adjustments to meet these varying requirements, ensuring consistent quality across different product designs.
Production Optimization
The ability to fine-tune pressure and speed parameters through the hydro drive transmission system allows for optimization of production cycles, reducing cycle times where possible while maintaining product quality. This results in improved productivity and reduced energy consumption.
Discover More About Our Hydraulic Systems
Explore the full range of capabilities and technical specifications for the XS-ZY-250A injection molding machine and its advanced hydro drive transmission system.
Learn more