Carefully study the product geometry, including wall thickness, ribs, undercuts, side holes, and other structural features. For instance, if a product has uneven wall thickness, the mold design must ensure the plastic flows evenly in different thickness areas to prevent defects like sink marks or warping.
Material Analysis
Clarify the type of plastic material used for the product. Different materials, such as ABS (good flowability) or PC (high strength but lower flowability), have distinct characteristics like flowability and shrinkage rates. The gating, runner, and cooling systems should be designed based on these material properties.
Mold Structure Design
Parting Line Design
The parting line is where the upper and lower or moving and stationary mold halves separate. A reasonable parting line ensures easier ejection of the product and maintains product quality. For aesthetically sensitive products, the parting line should be positioned where it doesn't affect the appearance.
Core and Cavity Design
The core forms the internal shape of the product, and the cavity forms the external shape. During design, precision, surface roughness, and compatibility with other components must be considered. For high-precision products, extra processing allowances and appropriate draft angles must be accounted for.
Gate Design
The gate is where the molten plastic enters the mold cavity. Common gate types include side gates, pin gates, and latent gates. Gate position and form affect product appearance, molding efficiency, and internal stress distribution. For small, appearance-critical products, a pin gate may leave minimal marks on the surface.
Runner System Design
The runner system, including main runners, branch runners, and cold runners, directs the molten plastic from the injection machine nozzle into the mold cavity. The shape (circular, trapezoidal) and size of the runners, as well as their surface roughness, affect flow resistance and filling efficiency. For example, circular runners have lower flow resistance, allowing smoother filling.
Cooling System Design
The cooling system controls mold temperature, improving production efficiency and product quality. It typically includes the layout of cooling channels, coolant flow rate, and temperature control. Cooling channels should be as close to the cavity surface as possible to ensure uniform cooling and prevent product deformation.
Ejection System Design
The ejection system helps remove the molded product from the mold. Common methods include ejector pins and ejector plates. The choice of ejector positions and numbers depends on the product shape and structure to avoid damaging the product during ejection. For large, flat products, ejector plates are often used for smooth ejection.
Selection of Mold Standard Components
Choosing Suitable Standard Mold Bases
Based on mold size, structure, and usage requirements, select a standard mold base. Standard mold bases offer good interchangeability, high precision, and low cost. For example, Blector mold bases are commonly used and come in various specifications.
Using Standard Mold Parts
Standard parts like ejector pins, guide posts, and bushings should be selected wherever possible. These components are reliable, easy to source, and reduce mold manufacturing time.
Mold Size and Strength Calculations
Mold Dimensional Calculation
Based on the mold structure, cavity number, layout, and injection machine installation requirements, calculate the mold dimensions to ensure it fits the selected injection machine and leaves enough space for operation.
Strength Calculation of Mold Components
For mold parts that bear significant pressure and friction, such as templates and cores, strength and stiffness calculations are necessary. For instance, the template thickness must be calculated to prevent deformation during the injection process.
Mold Drawing Preparation
Assembly Drawing
Clearly indicate the assembly relationships and positional accuracy requirements of various mold components. The assembly drawing should include multiple views (front, top, sectional) for easy understanding of the overall structure.
Part Drawings
Draw detailed part drawings for each component, including cavity, core, ejector pins, etc. These drawings should specify dimensions, tolerances, surface roughness, and material requirements to provide accurate machining instructions.
Modifications for Inadequate Mold Design
When a mold design is deemed unreasonable or inefficient, several modifications may be necessary to improve its functionality, manufacturability, and overall performance. We can help do such modifications.
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