Dificuldades na produção de protótipos de dispersão de luz

Difficulties in producing light scattering prototypes

Diffusion prototype

Elon Musk once said, “If you do nothing, there is nothing.” It's so simple to say, but so true. As a manufacturer specializing in prototyping, we make a lot of “things”, all kinds of “things” from every sector imaginable. We are very proud to say that we have gained a lot of experience in manufacturing many parts. Still, we experience our fair share of trial and error.

This article mainly addresses the difficulty of imitating diffusion properties during the prototype development phase.

What is light scattering?

The dictionary definition of light diffusion is “the scattering of light by reflection or transmission.” Diffuse reflection occurs when light strikes an uneven surface, such as a frosted window or the surface of a frosted or coated lamp. Diffuse light appears to surround objects. It is softer and does not show the harsh glare of direct light.

We met many customers who wanted to make a piece that diffuses light. There is often an LED light source behind or underneath the part. Sometimes the part is made of soft material with certain hardness requirements. Sometimes the material is made of hard plastic.

How to make pieces that emit diffused light

To make a plastic part light-diffusing, a light-scattering agent is usually introduced into the plastic part during the injection molding or vacuum casting process.

As you can see in the photo below, “fine particles” are what we call “light scattering agents”. These light scattering agents are generally composed of nanobarium sulfate, calcium carbonate, silica, etc. When viewed under a microscope, scattering agents are extremely small spheres. The base resin can be clear PC, PMMA for injection molding or polyurethane for vacuum casting.

Photo from the Internet

Another common method of making a plastic part light-diffusing is to coat the plastic surfaces with a diffusing agent. For example, after producing a transparent PC, PMMA or polyurethane part, a thin layer of glass beads (original glass beads are clear) can be blasted onto the surfaces of the parts. In this case, the glass spheres serve as a diffusion agent. Another diffusion medium for this method is the spraying of clear granular paint, such as VDI36. The following part is a CNC machined clear PMMA part. After polishing, VDI36 grain paint was applied.

The difficulty of making diffuser parts

As you can deduce from the above methods for making fuzzy prototypes, it is very easy to make a part fuzzy. The real difficulty is getting a piece to diffuse the desired amount of light.

Maximum full width (FWHM) and half angle (HA) values ​​are commonly used to quantify light scattering and are often used to describe the light scattering ability of plastic under a light source. For FWHM and HA, higher values ​​mean greater light scattering.

In one of our projects, a customer specified a FWHM diffusion degree greater than 70°. Although we have made many prototypes that mimic the possible diffusion property, we have had difficulty giving the part a diffusivity greater than 70°.

On the one hand, different colors, different wall thicknesses, different structures, different percentages of diffusing agents and even different base plastics cause a part to disperse light differently. For example, in urethane casting (or vacuum casting), if we add a certain amount of diffusion agent in the production of a part, achieving the diffusion level desired by the customer.

Then the next customer has a different piece for which they want the same diffusion effect. Even if this other part only differs in wall thickness, we could use the same proportion of diffusing agent as before, but we would not get the same diffusion results as before. Many attempts were required to achieve the correct diffusion level.

In mass production, the material used for mass production parts is different from the material used for prototypes. For example, PC for prototypes is made from block material, while PC for injection molding is made from plastic pellets. Although they are both called “PC”, they are actually two different materials. PC plastic pellets do not contain impurities and are more heat resistant than PC block materials.

Furthermore, the production processes for fuzzy PC prototypes differ from those for mass production (typically injection molding). The diffusion agent can only be applied to the surfaces of PC prototypes. Injection molding generally involves adding a diffusing agent to the molten plastic during the molding process. Once the parts come out of the mold, they contain a diffusion agent inside, which is not possible with PC prototypes.

University Degree

In short, while it is not difficult to make prototypes that scatter light, it will be extremely difficult to make prototypes that scatter a certain amount of light. Furthermore, if the diffuser formula used in a prototype is applied, the diffused light emitted by prototypes and mass-produced parts will be different.

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