Thin Wall Injection Molding Process: Streamlining Your Production

Thin-wall injection molding is a specialized plastic molding process characterized by the production of parts with wall thicknesses less than 1mm. More comprehensively, the definition of thin-wall molding is related to the procedure/thickness ratio, plastic viscosity, and heat transfer coefficient. When the length from the mold’s sprue to the farthest point of the product (L) divided by the product’s thickness (t), known as the L/t ratio, is 100 or more, it is considered thin-wall injection molding.

What is Thin Wall Injection Molding?

Thin wall injection molding is a specialized process within the injection molding realm, aimed at producing lightweight and slim plastic components while ensuring their durability. This method is defined by wall thicknesses of less than 1 mm and a flow length to wall thickness ratio greater than 200, making it well-suited for high-volume manufacturing.

Utilizing this technique allows manufacturers to significantly decrease cycle times—often reducing them by up to 50%—as the smaller volume of material cools at a faster rate. Consequently, companies can achieve quicker delivery times and lower costs per unit, facilitating faster market entry while minimizing material and shipping expenses.

Thin Wall Injection Molding Process Overview

The thin wall injection molding process begins with the preparation of the polymer granules, which are heated until they melt. The molten plastic is then injected into a precisely designed mold at high speeds. Because the walls are thin, the material cools quickly, allowing for rapid solidification and reduced cycle times. After the mold is filled, the part is ejected, and the cycle begins anew.

Advantages of Thin Wall Injection Molding

Thin-wall injection molding offers several key advantages that drive its increasing demand:

• By minimizing material usage, thin-wall molding can lower production costs significantly, with plastic materials often comprising 50% to 80% of total expenses.
• The lightweight and compact nature of thin-wall parts allows for integrated design and easier assembly, resulting in shorter production cycles and additional cost savings.
• The rise of portable electronic devices—like smartphones, MP3 players, and tablets—demands thinner and more compact plastic components, making thin-wall injection molding techniques essential.

Challenges and Solutions

However, thin wall injection molding does come with its own set of challenges. The injection process necessitates higher pressures and accelerated molding speeds to ensure the molten plastic adequately fills the thin cavities without solidifying prematurely. For instance, while a standard part might require two seconds for filling, a component with walls 25% thinner could need just one second.

Techniques and Machine for Thin-Wall Molding

Producing thin-wall parts requires specialized machine and techniques:

1. High-Speed Injection Molding Machines: Traditional injection molding machines are often unsuitable for thin-wall molding due to their inability to follow the required speed curves within short injection times. High-resolution microcontrollers (MCUs) and machines capable of independent pressure and speed control are necessary.
2. Smaller Barrels: Thin-wall parts require less plastic material. Therefore, molding machines with smaller barrels are used to prevent material dissociation due to prolonged residence times.
3. Mold Temperature Control: Mold temperature directly affects the melt flow behavior, cooling rate, and final part quality. Traditional heating methods, such as water, oil, or electric heating, are often inadequate for thin-wall molding due to their limited ability to rapidly heat and cool the mold. Variable mold temperature control technology, which rapidly heats the mold cavity surface during injection and quickly cools it after injection, has emerged as an effective solution. This technology utilizes heating systems such as steam, electrode, and induction heating, combined with traditional cooling methods, to achieve rapid heating and cooling cycles.

Thin Wall Injection Molding Design Tips

Thin walls frequently appear in design, but they can introduce various challenges for injection-molded components. To avoid potential problems, consider reinforcing your design with thicker walls or making minor adjustments. If thin walls are necessary for functionality, it’s important to focus on specific design and material considerations.

Understanding Thin-Walled Geometries

Thin walls can disrupt the smooth flow of plastic during the injection molding process, leading to issues such as:

Challenges	Description
Cracking	Potential fractures in the part.
Incomplete Fill	Areas may not fill properly due to flow issues.
Uneven Cooling and Warping	Results in dimensional inconsistencies.
Weak Knit Lines	Points of weakness in the material structure.
Surface Texture Inconsistencies	Variations in the finish of the part.

Submitting your CAD model early in the design phase allows for early detection of potential issues, enabling timely modifications. Our quoting software can highlight concerns related to thin walls (generally under 0.015-0.020 inches or 0.381-0.508 mm, depending on material). Our applications engineers will suggest improvements, such as adding draft angles or increasing thickness in critical areas.

Material Considerations

Choosing the right material is essential for ensuring optimal flow in thin-walled designs. Suitable thermoplastics include:

Material	Benefits
HDPE	Good flow properties.
LDPE	Flexible and easy to mold.
Polypropylene (PP)	Lightweight and durable.
Nylon (PA)	Strong and versatile for various applications.
Liquid Silicone Rubber (LSR)	Excellent flow but may create flash risks.

These materials offer good flow characteristics for thin sections, making them suitable for components with living hinges. Liquid silicone rubber (LSR) also fills well but may pose a flash risk at parting lines. In contrast, polycarbonate can present challenges in thin geometries due to its stickiness.

Ideal Machinery for Thin Wall Applications

• Wall Thickness: Specialized equipment is essential for parts with diminishing wall thickness, especially those under 1 mm.
• Filling Times: Thin components may require fill times of less than 0.5 seconds, with injection pressures often exceeding 30,000 psi.
• Types of Machines:
  • Hydraulic machines typically use accumulators.
  • Increasingly available high-speed all-electric or hybrid machines.
• Clamp Force: Generally needs to be between 5 to 7 tons per square inch to handle high pressures.
• Heavy-Duty Platens: Minimize flexing, ensuring greater stability during the molding process.
• Tiebar to Platen Ratio: Usually maintained at 2:1 or less for adequate support during injection.
• Control Mechanisms: Closed-loop systems for injection speed and transfer pressure enhance filling and packing efficiency.
• Recommended Shot Sizes:
  • Optimal shot sizes should be between 40% and 70% of barrel capacity.
  • Possible reductions of 20% to 30% in shot size if assessed for material degradation.
• Material Considerations: Parts must be evaluated for potential material degradation due to smaller shot sizes.

Wall Thickness Recommendations

Maintaining appropriate wall thickness is crucial to minimizing cosmetic defects. Aim for a consistent wall thickness of 0.060 to 0.120 inches (1.5 to 3.0 mm) to ensure even cooling and prevent warping. Ribs should be about 50-60% of the main wall thickness to avoid excess material buildup.

Design Tips

To facilitate material flow into thin areas, consider adding flow paths and radii. The placement of parting lines can significantly affect the appearance of molded components; strategic adjustments can lead to less visible seams. Early submission of your CAD file enables us to offer valuable feedback and guidance throughout the injection molding process, ensuring any wall thickness or geometry issues are swiftly addressed to meet your production deadlines.

Additional Design Considerations

For demanding thin wall applications, stronger steel grades such as H-13 or D-2 should be used for gate inserts. Mold interlocks can also help prevent flexing and misalignment. Utilizing telescoped cores reduces the risk of core displacement and breakage. Ensure robust support plates and preloaded support pillars for added structural strength.

To facilitate part release, consider diamond polishing for cores and ribs or using surface treatments like nickel-PTFE. Effective venting is essential, and employing vented core pins and ejector pins can aid in gas evacuation. As injection speeds increase, larger gates help minimize shear and gate wear, while gate inserts should ideally have a Rockwell hardness exceeding 55 to withstand high pressures.

Defects and Solutions in Thin-Wall Injection Molding

Warpage

Warpage is caused by uneven internal stresses within the part. Orientation stress and thermal stress are two primary types of stresses that contribute to warpage. Orientation stress arises from the alignment of fibers, macromolecules, or chain segments in the melt during filling. Thermal stress occurs due to temperature differences between the melt and mold cavity wall, leading to uneven cooling and the formation of mechanical stresses.

Solution: Proper mold design, including runner and gating configurations, can help minimize orientation stress. Variable mold temperature control technology can help reduce thermal stress by ensuring more uniform cooling.

Flow Marks

Flow marks are spiral or annular stripe patterns on the part’s surface caused by unstable melt flow in the mold cavity.

Solution: Optimizing the mold design, particularly the runner system and gating, can help stabilize the melt flow and reduce flow marks. High-injection pressures and rapid filling rates may also contribute to flow marks, and adjusting these parameters can help mitigate the issue.

Weld Lines

Weld lines form where two or more melt fronts meet in the mold cavity. In thin-wall parts, weld lines are more pronounced due to increased filling resistance.

Solution: Proper mold design and melt flow optimization can help reduce the visibility of weld lines and improve their mechanical strength. Techniques such as using higher injection pressures, temperatures, and shear rates can also help improve weld line quality.

Using BOYI for Thin Wall Plastic Parts

Transform your designs with BOYI’s thin wall injection molding services! Our advanced technology delivers lightweight, high-quality plastic parts quickly and cost-effectively. Ready to elevate your products? Contact us today and let’s start creating!