Digital Design and Simulation Process
The production of high-speed PET preform molds begins with precise digital design. Through computer-aided design and simulation technology, the mold structure can be optimized before production, reducing rework and laying the foundation for efficient production.
Parametric and modular design is the core of high-speed mold design. Designers use 3D design software such as UG and SolidWorks to create parametric models based on preform parameters provided by the customer (such as weight, diameter, wall thickness, and draw ratio), linking the preform dimensions with the mold cavity, runner, cooling system, and other structures. By calling up modular component libraries (such as standard guide pillars and bushings, hot runner components, and ejection mechanisms), the overall mold structure can be quickly built, reducing repetitive design work. For example, for a 64-cavity high-speed mold, the design cycle can be shortened from the traditional 15 days to less than 7 days, while ensuring the consistency of the cavity structure.
CAE simulation analysis is used throughout the entire design process. By simulating key indicators such as melt flow, cooling effect, and structural strength, design defects can be identified in advance. In melt flow simulation, software such as Moldflow is used to analyze the filling time, pressure distribution, and temperature changes of different cavities, optimizing the runner layout and gate location to ensure that the filling time difference of each cavity in the 64-cavity mold is controlled within 0.3 seconds. Structural strength simulation uses ANSYS software to simulate the stress distribution of the mold during high-speed mold opening and closing, focusing on optimizing the thickness and layout of stress-bearing components such as templates and guide pillars to avoid deformation caused by long-term high-speed operation. Cooling system simulation can predict the uniformity of cooling of the preform by the water channels. By adjusting the water channel diameter, spacing, and inlet/outlet positions, the temperature difference of the preform during demolding is kept below 5℃.
Collaborative design and data management improve design efficiency. A PDM (Product Data Management) system is used for centralized management of design data, enabling real-time data sharing among designers, process engineers, and production personnel, avoiding design errors caused by version inconsistencies. Simultaneously, a cloud-based collaborative platform allows for real-time communication with customers and suppliers regarding design solutions, timely response to requirement changes, and shortens the design confirmation cycle by more than 30%. For example, when a customer adjusts the preform wall thickness, designers can quickly update the cavity dimensions through data correlation and simultaneously push the updates to the production department, ensuring timely adjustments to the production plan.
High-Performance Material Selection and Pretreatment Processes
High-speed PET preform molds have extremely high requirements for the mechanical properties, wear resistance, and stability of materials. Strict material selection and pretreatment processes are necessary to ensure the mold's long-term reliable operation under high-frequency, high-load conditions.
The precise selection of mold materials must be determined based on the functional differences of the mold components. Since the cavity and core directly contact the high-temperature, high-pressure PET melt, ultra-pure martensitic stainless steel (such as S136, STAVAX) must be used. Its carbon content should be controlled at 0.3%-0.5%, and the content of impurities such as sulfur and phosphorus should be less than 0.01%. After heat treatment, the hardness can reach HRC48-52, and it has excellent polishing performance, with a surface roughness of Ra0.01μm. Structural components such as templates and guide pillars are made of high-strength pre-hardened steel (e.g., 718H, NAK80), with a hardness controlled at HRC30-35 and a compressive strength ≥1200MPa, capable of withstanding tens of thousands of mold opening and closing impacts per hour. For ultra-high injection speed molds (producing over 100,000 preforms per hour), the cavity can be made of powder metallurgy high-speed steel (e.g., ASP-60), with a total alloying element content of ≥25% (tungsten, molybdenum, chromium, etc.), and wear resistance 3-5 times that of ordinary mold steel.
Material pretreatment is crucial for ensuring machining accuracy. After the steel is stored, it undergoes rigorous chemical composition and mechanical property testing. Elemental content is confirmed using a spectrometer, and initial hardness is measured with a hardness tester to ensure compliance with design requirements. Subsequently, aging treatment is performed, holding the steel at 500-550℃ for 4-6 hours and slowly cooling it to room temperature to eliminate internal stress generated during forging and prevent deformation after machining. For large molds, a stepped heating and isothermal cooling process must be adopted, controlling the cooling rate to ≤5℃/hour to achieve an internal stress relief rate of over 80%. Annealing treatment is also required before cutting the raw material to reduce material hardness (≤HRC25), improve cutting performance, and extend tool life.
Material dimensional accuracy control must be maintained throughout the entire pretreatment process. High-precision sawing machines (cutting accuracy ±0.1mm) are used for raw material cutting to ensure that the thickness deviation of the sheet metal does not exceed 0.2mm, leaving uniform allowance for subsequent processing. For cavity raw materials, rough grinding is performed using a surface grinder to control the flatness within 0.05mm/m, reducing the amount of cutting required in subsequent processing. Simultaneously, flaw detection (such as ultrasonic testing) is performed on the raw material to ensure the absence of internal cracks, pores, and other defects, preventing sudden breakage during mold use.
