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what is the parting line in injection molding
Learn what the parting line is in injection molding, its importance in mold design, and how it affects product quality. Discover tips to optimize parting lines for better results.
Definition and function of parting lines
The design of the injection mold parting line is a key link in mold manufacturing, mainly determined based on product structure, demolding requirements, and process feasibility. The core purpose is to ensure that the product can be demolded smoothly and the appearance meets the requirements. The following is a specific analysis of the key points of our company’s Shanghai Yunyan Prototype & Mould Manufacture Factory parting line design:
Definition and function of parting lines
The parting line is the contact line between the moving and fixed molds in the mold, and it is also the seam line left on the product after injection molding. It determines the demolding direction of the product, affects the appearance, dimensional accuracy, and difficulty of mold processing.
Design principles and methods
1. Priority given to demolding convenience
Classification along the maximum contour line of the product: Ensure that the product can be smoothly removed from the mold to avoid getting stuck during demolding. For example, the parting line of box-shaped products is always located at the maximum contour of the opening edge.
Avoid side core pulling structure: If the parting line design is unreasonable, additional side core pulling mechanisms (such as sliders and slanted tops) may be required to increase the complexity of the mold. So generally speaking, it is preferable to choose straight lines or simple curves for classification to reduce complex structures.
2. Balancing appearance and functionality
Hidden parting line: If the appearance requirements of the product are high, the parting line should be set in an inconspicuous place (such as the bottom of the product, in the groove, or in the part that is covered after assembly). For example, the parting line of the phone case is often designed at the edge of the side to reduce visual impact.
Avoid functional surfaces: Avoid setting parting lines on the assembly surface, sealing surface, or stress surface of the product to prevent affecting its performance (such as if the parting line of the seal is on the sealing surface, it may cause leakage).
3. Mold processing and strength considerations
Simplification of parting surface: The parting line should be as flat or regular as possible to facilitate mold processing (such as milling flat parting surfaces directly to reduce processing costs).
Ensure mold strength: The position of the parting line should avoid weak structures (such as thin steel positions and sharp corners) in the mold to prevent deformation or damage under injection pressure.
4. Coordination of pouring system
Coordinate with the gate position: The parting line needs to be designed with the gate (such as the position of the main and branch channels) to ensure that the molten plastic can evenly fill the mold and facilitate the removal of gate waste. For example, the side gate is always located on the parting line for easy mold repair and waste removal.
Common Types and Applications of Classification Lines
Flat parting line: suitable for products with simple structures (such as flat plates and cylindrical parts), with convenient mold processing and relatively low cost.
Surface parting line: used for complex curved products (such as car bumpers), parting along the contour surface of the product to ensure smooth demolding, but the difficulty of mold processing is relatively high.
Step by step parting line: When the product has a multi-layer structure, the parting line is stepped and needs to be matched with a multi-stage demolding mechanism. It is commonly used for parts with protrusions or grooves.
Design Considerations
Reserved mold repair space: Sufficient machining allowance should be reserved at the parting line for subsequent mold repair adjustments (such as trimming and size correction).
Consider shrinkage and deformation: Plastic cooling shrinkage may cause burrs or dimensional deviations at the parting line, and the precision of the parting surface needs to be adjusted based on material properties (such as shrinkage rate) during design.
Trial mold verification: After the preliminary design, the effect of the parting line needs to be inspected through trial molding, observing issues such as product flash and demolding resistance, and optimizing the position of the parting line if necessary.
Shanghai Yunyan Prototype & Mould Manufacture Factory ensures that every design of the parting line requires a comprehensive consideration of product structure, mold technology, and production requirements to balance demolding convenience, appearance quality, and manufacturing costs.
