Una guida per i progettisti di stampi: Principi, tecniche e innovazioni

Mold design is the backbone of modern manufacturing, enabling the mass production of precision components across industries such as automotive, medical, and consumer goods. A well-designed mold ensures product consistency, reduces waste, and optimizes production efficiency. This guide synthesizes critical principles, challenges, and emerging trends to empower mold designers in mastering this intricate discipline.

Core Principles of Mold Design

Uniform Wall Thickness

Maintaining consistent wall thickness is paramount to avoid defects like sink marks, warping, and uneven cooling. Thick sections cool slower, causing shrinkage imbalances, while thin walls risk incomplete filling. For example:

• ABS: Optimal wall thickness ranges from 1.14–3.56 mm.
• Polycarbonate: 1.02–3.81 mm.

Gradual transitions (using fillets or chamfers) between varying thicknesses minimize stress concentrations

Draft Angles

Draft angles facilitate part ejection and reduce tool wear. Recommendations vary by material and surface finish:

• Smooth surfaces: 1–2° draft.
• Textured surfaces: Up to 5° or more.

Heavily textured parts (e.g., SPI/VDI standards) require additional draft to prevent sticking.

Radii and Fillets

Sharp corners hinder material flow and create stress points. Design guidelines include:

• Internal radii ≥50% of wall thickness.
• External radii = internal radius + wall thickness.

Rounded edges improve structural integrity and reduce machining costs.

Critical Mold Components and Design Strategies

Cavity and Core

• Cavity: Defines the part’s exterior shape.
• Core: Shapes internal features.

Both must withstand high pressure and heat. Tool steels (e.g., SKD11, SKD61) are preferred for durability, while aluminum suits prototyping. Thermal expansion and material shrinkage rates must align with resin properties (e.g., PPS requires ±0.5% tolerance)

Cooling System Design

Effective cooling minimizes cycle time and defects:

• Conformal cooling: 3D-printed channels follow part contours for uniform heat dissipation.
• Channel placement: Position near thick sections to prevent warping. Water or oil coolants are common.

Poor cooling accounts for 70% of cycle time; optimized systems can reduce it by 30%.

Ejection System

• Ejector pins: Place on flat surfaces to avoid marks. Use stripper plates for complex geometries.
• Draft alignment: Ensure pins align with the mold’s draw direction to prevent damage.

Soft materials (e.g., TPE) may require wider pins to distribute force.

Gates and Runners

• Gate types: Edge gates (cost-effective), hot tip gates (cosmetic parts), and tunnel gates (auto-trimming).
• Runner design: Balance flow across multi-cavity molds. Hot runners reduce waste in high-volume production.

Gate placement in thick sections ensures proper filling and minimizes jetting.

Material Selection for Molds

Design Workflow for Mold Engineers

1. Product Analysis: Assess manufacturability, identify undercuts, thin walls, and tolerance requirements.
2. Material Selection: Match resin properties (e.g., shrinkage, thermal stability) with mold material.
3. Cooling Layout: Use CAE simulations to optimize channel placement.
4. Mold Layout: Decide cavity count (single vs. multi-cavity) and gate positioning.
5. Simulation & Testing: Validate flow, cooling, and ejection via software (e.g., Moldflow) before prototyping.

Future Trends in Mold Design

1. Additive Manufacturing: 3D-printed molds enable rapid prototyping and complex geometries (e.g., lattice structures).
2. AI-Driven Design: Machine learning optimizes gate placement, cooling, and material selection.
3. Sustainability: Biodegradable resins and recycled materials reduce environmental impact.
4. Industry 4.0 Integration: Real-time monitoring of pressure, temperature, and flow via embedded sensors.

Conclusion

Mold designers bridge creativity and engineering, transforming product concepts into manufacturable realities. By adhering to principles like uniform wall thickness, strategic cooling, and material optimization—while embracing innovations like AI and additive manufacturing—they drive efficiency and quality in modern production. As industries evolve, the role of mold designers will remain pivotal in achieving sustainable, high-precision manufacturing.