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Key Factors in Plastic Mold Design

2025-06-30

Plastic mold is a tool for producing plastic products. It is composed of several groups of parts, and there is a molding cavity within this combination. During injection molding, the mold is clamped on an injection molding machine, and the molten plastic is injected into the molding cavity. The plastic cools and takes shape in the cavity, after which the upper and lower molds separate. The product is ejected from the cavity by the ejection system and leaves the mold. Finally, the mold closes again for the next injection molding, and the entire injection molding process is carried out cyclically.

This is the table of contents for this article

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1. Parting Surface
2. Structural Components
3. Mold Precision
4. Gating System
5. Shrinkage Compensation And Dimensional Control
6. CAD/CAM Integration
Design Optimization Strategies

1. Parting Surface

The contact surface where the cavity and core meet when the mold closes. Its position and configuration are influenced by:

· Product shape, appearance requirements, wall thickness

· Molding method (e.g., injection, extrusion)

· Post-processing needs (e.g., trimming, assembly)

· Mold type (e.g., two-plate, three-plate)

· Ejection mechanism and molding machine specifications

2. Structural Components

Critical elements like slides, lifters, and ejector pins impact:

· Mold lifespan: Material selection (e.g., hardened steel for high-wear areas)

· Cycle time: Efficient cooling channel integration

· Cost: Simplifying complex mechanisms (e.g., replacing multiple slides with angled pins)

· Product quality: Preventing deformation through balanced ejection

3. Mold Precision

Positioning systems ensure alignment and durability:

· Anti-binding features: Clearance tolerances (e.g., 0.02-0.05mm)

· Precision guides: Linear bearings or dowel pins for high-precision molds

· Wear resistance: Surface treatments (e.g., nitriding) for guide components

4. Gating System

The pathway from the injection unit to the cavity includes:

· Sprue: Connects nozzle to runner system

· Runners: Distributes melt to cavities (balanced for multi-cavity molds)

· Gates: Entry points into the cavity (types: edge, pin, submarine, etc.)

· Cold slug wells: Traps solidified plastic from nozzle

5. Shrinkage Compensation And Dimensional Control

Account for:

· Material shrinkage: Varies by resin (e.g., 0.5-2% for ABS vs. 2-3% for polypropylene)

· Manufacturing tolerances: CNC machining accuracy (±0.01mm typical)

· Mold wear: Hard chrome plating for high-friction areas

· Machine-mold compatibility: Clamping force, injection pressure, and stroke length

6. CAD/CAM Integration

Modern practices include

Simulation tools: Analyze melt flow (e.g., Moldflow), cooling efficiency, and warpage

Parametric modeling: Enables quick design iterations

Automated manufacturing: CNC milling, EDM for complex geometries

Design Optimization Strategies

Factor	Optimization Approach	Example Application
Parting Surface	Minimize undercuts; align with cosmetic surfaces	Smartphone housing (visible seams)
Structural Parts	Replace complex slides with collapsible cores	Threaded bottle caps
Precision	Use interchangeable inserts for high-wear zones	Medical device components
Gating System	Position gates to avoid weld lines in critical areas	Transparent lenses
Shrinkage	Apply differential shrinkage ratios for multi-material parts	Overmolded grips

Effective mold design balances these factors through iterative analysis and prototyping, leveraging CAD/CAM tools to ensure manufacturability and cost-efficiency.

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FAQ

FAQs

Can Bost customize modified plastics with special properties?

Yes! We offer modification services such as reinforcement, flame retardancy, conductivity, wear resistance, and UV resistance, for example:
• Adding carbon fiber to enhance stiffness
• Reducing the coefficient of friction through PTFE modification
• Customizing food-grade or medical-grade certified materials

What is the delivery lead time? Do you offer global logistics?

Standard products: 5–15 working days; custom modifications: 2–4 weeks. We support global air/sea freight and provide export customs clearance documents (including REACH/UL certifications).

What is the minimum order quantity (MOQ)? Do you support small-batch trial production?

The MOQ for standard products is ≥100kg. We support small-batch trial production (as low as 20kg) and provide mold testing reports and performance data feedback.

What are the core advantages of Bost engineering plastics compared to ordinary plastics?

Bost engineering plastics feature ultra-high mechanical strength, high-temperature resistance (-50°C to 300°C), chemical corrosion resistance, and wear resistance. Compared to ordinary plastics, their service life is extended by 3 to 8 times, making them suitable for replacing metals in harsh environments.

How do I select the appropriate engineering plastic grade for my product?

Selection should be based on parameters such as load conditions (e.g., pressure/friction), temperature range, medium contact (e.g., oil/acid), and regulatory requirements (e.g., FDA/RoHS). Our engineers can provide free material selection consulting and sample testing.