Overview
Known for their expertise in plastic injection molding, The YuanCheng Mold solves problems with efficiency. We were approached by a customer from the PET preform industry to provide advice on the process of molding a hot runner injection mold with 24 cavities in one mold for PET preforms.
It was through the application of CAE to the design of the mold, YuanCheng Mold sought to further improve the limitations that existed in the injection molding process of the 24-cavity PET preform injection molding in order to help further improve the product quality. In order to ensure future production of the product, the customer was looking for a value-based solution.
24-cavity PET preform injection molding
Problem
The objective is to improve the mold structure and the success rate of testing molds, to ensure the quality of plastic parts, to reduce the cost of production, and to reap significant benefits to the enterprise’s bottom line.
24-cavity PET preform injection molding process solution:
Using Moldflow software, plastic injection molding is analyzed. Using simulation analysis, accurately predict plastic parts shrinkage and warpage in plastic, and more. Ensures the rationalization of the mould design through targeted optimisation of the moulding process parameters. Enables the designer to optimize the design in the planning phase at minimal cost and in the shortest possible time, shortening the development phase. Reduce the production cycle and reduce production costs.
Simulation part
Manufacture analysis of plastic parts structure
Figure 2: The preform of lightweight bottle of 9. 8 g
Figure 2 shows a preform for a lightweight 9.8 g 500 mL water bottle. A polyethylene terephthalate (PET) preform has a volume of 7.5 cm3. Additionally, the neck and body of the bottle have 1.25 mm wall thicknesses.
To achieve excellent performance, plastic parts should be clear, homogeneous and colourless. Free from air bubbles, stretch marks, stiffness, voids, spillage, black rings and stains. There is no white haze, a smooth, intact thread, and a sealed bottom door of the blank. uniform wall thickness is essential.
Of course, the uniform wall thickness of the PET preform is also essential.
Design of gating system and cooling system
- Hot runner system
A hot runner reduces plastic parts stress, deformation, and gating system aggregates. Choose a mold with 24 cavities to make high-quality PET preforms. A hot runner is composed of a flow channel plate, 24 nozzles, and a temperature controller. This is a needle valve nozzle designed to prevent feed scars at the bottom of the preform.
There are separate controls for each cavity. There are three shunt channels: a 10 mm shunt channel at the top, a 6 mm shunt channel at the bottom, and a 10 mm nozzle inlet. The material opening is 1 mm in diameter and 60° in angle.
- Cooling system
The mold is cooled by a 16 water circuit cooling system. Cooling tube diameter is 6 mm, nozzle diameter is 8 mm, temperature is 25°C, and power is 10000 watts. All cooling systems use water as a cooling medium.
Molding process
Figure 3: Meshing
Convert the three-dimensional model in Moldflow software to IGES format, using surface mesh (fusion) partitions for the finite element mesh. In order to ensure analysis effect, the original plastic part model is simplified so that the bottle mouth threads appear as stripes.
The grid side length should be 1.5 to 2 times the minimum wall thickness to ensure accurate analysis. Multiply the edge length of the mesh with a double layer. To meet the computational accuracy requirements, the grid matching rate is 87.3% and the grid matching percentage is 83.7%.
Molding process setting
It takes a long time for PET to crystallize due to its crystalline nature. Incorrect mold temperatures, injection pressures, and cooling during molding will cause PET preforms to crystallize and influence PET preforms’ physical and mechanical properties. Set the injection temperature and pressure reasonably: nozzle 260 °C, hot runner 285 °C, injection pressure 4.5 mPa, injection time 3.0 s, cooling time 3.45 s. Surface temperature 50-60°C, mold temperature 60-120°C, melt temperature 265-290°C. Select Mold-PET from the flow material library (Cleartuf-8006, Shell Co. manage).
Result: 24-cavity PET preform injection molding
Using Zhejiang Shenda Machinery Manufacturing Co., Ltd SE220 injection molding machine for mold trial, based on Moldflow analysis and optimization results. Compared to the CAE simulation, the wall thickness of the formed preform is uniform, beautiful, and does not show any obvious differences in color, bubbles, or white fog.
Injecting molds and their structure can be continuously optimized, thus avoiding repeated mold trials and mold repairs caused by the use of traditional experiences. Improve plastic part production efficiency and molding quality, reduce mold trial, mold repair, and production costs, resulting in high-quality plastic products, which contribute significant economic benefits to production enterprises.
