Plastic Part Design Process Overview

Plastic Part Design Process

• Plastic part design involves many factors, including functional needs (e.g., mechanical strength, UV resistance), aesthetic concerns (e.g., color, transparency), and economic considerations (e.g., material cost, manufacturing expenses).
• Successful plastic part design requires teamwork, including conceptual designers, stylists, design engineers, materials suppliers, mold makers, manufacturing personnel, and more.
• Team input early in the design process is vital for optimizing overall product cost, not just individual components or steps.
• Designs should strive to maximize part function and appearance, define part requirements, evaluate process choices, and select appropriate materials to minimize manufacturing costs while ensuring prototype testing.

Defining Plastic Part Requirements

• Requirements should go beyond intended use conditions, considering harsher manufacturing and shipping conditions.
• Examine factors like chemical exposure (mold releases, solvents, etc.), radiation exposure (fluorescent lights), mechanical loading (static, impact, cyclic), temperature ranges, electrical performance, and weather resistance.
• Material compatibility with various chemicals is key. Environmental exposure requirements (e.g., outdoor decorations) may differ.
• Precisely evaluate the impact resistance that varies over various temperatures.
• Understand any agency approvals that your plastic part requires. Some examples include UL for electrical devices, MIL for military applications, FDA for food contact, USDA for meat/poultry equipment, and NSF for food processing and water applications.
• Define the product's life expectancy and expected conditions of use. Precisely evaluate part dimensional tolerances and how the load, temperature, and creep impact them.
• Overly stringent tolerance specifications add unnecessary cost. Consider processing demands, like filling difficulty or warpage susceptibility.

Production quantities and Cost Constraints

• Production volumes influence manufacturing strategies, materials, molds and assembly methods. Fewer production quantities can offset efficiency gains.
• Evaluate total system cost, covering more than just parts' and material costs.
• Look at assembly requirements, such as disassembly frequency and automation potential.
• Consider recycling necessities.

Thermoplastic Processing Methods

• Several thermoplastic processing methods exist, with various design requirements and limitations. Part size, shape, and concept often influence the chosen method.
• Injection molding, the most widespread method, forces molten plastic into molds under pressure. This process enables high production volume, wider part sizes, repeatability, and tight tolerances. It is suitable for intricate features, and structural components.
• Extrusion creates continuous profiles via a die. It's mainly for sheets, films, and pipes. Secondary operations are often needed for complex features.
• Thermoforming shapes thermoplastic sheets via vacuum or pressure. It's well-suited for large parts. But its feature limitations (e.g., projections like ribs, bosses) may require secondary operations.
• Blow molding efficiently creates hollow shapes, like bottles and containers. Two types are extrusion (e.g., parison) and injection (molded shape).
• Rotomolding involves heating and rotating a mold to coat a hollow shape with thermoplastic powder. It is effective for large hollow parts and low production quantities.

Optimizing Product Function

• Consolidation: Reduce the number of parts in an assembly, merging functionality and reducing part count.
• Hardware: Eliminate or reduce hardware (screws, etc.) by incorporating them directly into parts (e.g., molded hinges), reducing materials and assembly cost.
• Finishing: Using molded-in color instead of paint reduces costs.
• Markings/Logos: Molding-in markings/logos is more cost-effective than secondary methods.

Reducing Manufacturing Costs

• Materials: Find the best value-for-money material, minimizing usage and avoiding overly specific requirements.
• Overhead: Maximize hourly production, avoid thick sections, design molds for easy cooling/ejection, add mold cavities to increase production rate, evaluate whether mold cost increases are offset by machine cost savings.
• Labor: Simplify manual tasks; utilize automatic degating/proper gate placement; maintain parting lines for efficiency; streamline/automate assembly steps.
• Scrap/Rework: Follow design guidelines, avoid tight tolerances that aren't truly necessary, and place molds for parts in the middle of tolerances to avoid rework. Choose mold makers cautiously (check for material and mold quality).

Prototype Testing

• Prototype testing is crucial for optimizing design and material selection before production tooling investment. It should accurately mirror molding, processing, and assembly conditions.
• Thorough prototype testing helps avoid subsequent costly modifications to production tooling.