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Guide of LED Lens Injection Molding Defects And Solutions

LED technology has revolutionized the lighting industry, offering energy-efficient and durable solutions. Central to the effectiveness of LED lighting systems are the lenses that shape and direct the light. LED lens injection molding is a critical process in achieving precision and quality, but it comes with its own set of challenges. In this article, we will delve into the most commonly used plastic materials for LED lenses, quality standards, common defects, and their solutions, as well as the requirements for injection molds, injection molding machines, and workshops.

Plastic Materials for LED Lenses

Acrylic (PMMA):

Acrylic, or Polymethyl Methacrylate (PMMA), is a popular choice for LED lenses due to its optical clarity and excellent light transmission properties.

Advantages include:

1. High light transmittance, making it suitable for applications requiring bright and clear lighting.

2. UV resistance, ensuring longevity in outdoor environments.

3. Cost-effectiveness compared to other materials.

However, PMMA also has its disadvantages:

1. Prone to scratching, requiring additional coatings for protection.

2. Lower impact resistance compared to some alternatives.

Acrylic (PMMA) LED Lens Applications:

Indoor lighting fixtures

Automotive lighting

Polycarbonate (PC):

Polycarbonate is another commonly used material for LED lenses, known for its impact resistance and durability. Advantages include:

1. High impact strength, making it suitable for rugged applications.

2. Resistance to shattering, enhancing safety in certain environments.

3. Lightweight nature.

Disadvantages of PC:

1. Lower light transmittance compared to PMMA.

2. Susceptible to scratches, though less than PMMA.

Polycarbonate (PC) LED Lens Applications:

Outdoor lighting fixtures

Industrial lighting

Quality Standard of Led Lens

As the optical lens plays a crucial role in the application of light sources, it is imperative for LED lens products to adhere to specific requirements to ensure their qualification. These stringent criteria encompass the absence of bubbles, dents, sink marks, flow lines, and weld marks within acceptable limits—ensuring that these imperfections do not compromise the packaging or functionality of the lens. Furthermore, it is crucial that warping deformation remains within a controllable range, preventing any adverse effects on assembly or subsequent injection molding processes.

Common LED Lens Injection Molding Defects and Solutions

Shrink in lens injection molding

The root cause of shrinkage is uneven wall thickness, and plastic condensation cannot be fed.

For shrinkage, the solution is summarized as follows:

A: The water inlet of the mold is small, the sprue is long, and the plastic is difficult to glue in. Increase the water inlet or improve the glue feeding method.

B: If the material temperature is too low, increase the material temperature, such as thicker products should increase the material temperature to increase fluidity and reduce shrinkage.

C: Increase the holding pressure and prolong the holding time due to early switch to holding pressure or insufficient holding pressure.

D: The cooling time is not enough, increase the cooling time. For example, for thick-walled lenses with a mirror surface, proper cooling time is beneficial to improve shrinkage.

Flow lines in lens injection molding

Usually, flow lines appear in the glue inlet and wall thickness. Generally, flow lines are mostly caused by plastic melt injection, and when the melts enter the mold cavity successively, the temperature difference between the two leads to flow lines.

So the summary for flow lines is as follows:

1. Process reason:

A: The mold temperature is high and the material temperature is low.

B: The injection pressure is too high and the speed is too fast to cause injection. You can find the position and reduce the injection pressure and speed.

2. Mold reason: The gate is too small or the shape is wrong, resulting in jetting, and the size and shape of the gate should be trimmed (for example, fan-shaped according to the situation) to prevent jetting.

Water ripple in lens injection molding

The water ripple is easier to understand, its shape is like a wave, as shown in the figure. Usually, due to the low mold temperature, the plastic condenses in advance, and the melt enters later to promote the formation, which can properly increase the mold temperature, material temperature, and injection rate, or improve the mold water inlet.

Air marks in lens injection molding

Air marks are the appearance of aerosol on the surface of plastic products.

Airmarks on the surface of the lens affect the appearance and light effect, which can be solved from the injection mold and machine adjustment process:

A: If the mold exhaust is not good, add exhaust. If the product allows, you can add exhaust needles or add exhaust grooves on the mold. 80% of injection molding failures are caused by injection molds. This is a once-and-for-all method, and the requirements for adjusting the machine are low.

B: Adjusting the machine to solve the problem, relatively requires the ability to adjust the machine, control the rate of injection in sections, and switch to low-speed injection at the position where air marks are generated.

Black spots, yellowing and color mixing on the product

Black dots, yellowing and color mixing are absolutely unacceptable defects of lens products.


A: Check whether the temperature of the material is too high, causing the material to burn black and carbonize in the barrel, check whether there is a gap in the nozzle flange, and whether there is accumulated material carbonization inside.

B: Color mixing checks whether the gun barrel is cleaned when changing the material and changing the color, and whether there is any miscellaneous material in the material.

Air bubbles and vacuum bubbles in lens injection molding

To improve air bubbles and vacuum bubbles, you can try the following solutions:

A: Improve the mold. The gate of the mold is too small, the position arrangement is unreasonable, the runner is too small, the water transportation is unreasonable, and the uneven cooling is easy to generate air bubbles.

B: If the air bubbles are caused by poor mold exhaust and trapped air, the mold exhaust can be improved by adding exhaust needles or exhaust grooves.

C: If it is a vacuum bubble caused by uneven cooling and shrinkage of the thick book, you can properly increase the mold temperature, increase the back pressure, increase the holding pressure and cooling time to make it fuller and solve the vacuum shrinkage.

Finding Expert LED Lens Manufacturers

Selecting a reliable LED lens manufacturer is crucial for product quality and reliability.

Sung Precision Mould & Plastic Co., Ltd is a leading LED lens injection molding supplier in China. Precision plastic tooling and injection molding are our core, while prototyping can better support low volume production needs. When you choose Sungplastic, you get a professional partner through the entire production cycle. Timely, professional, and effective communication is always with you, taking your product from concept or drawing to reality.

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