Transparent and translucent are two terms widely used in physics. Basically, these two words can be used to describe some physical properties of a material. Light can pass through translucent objects, while transparent objects not only allow light to pass through but also allow imaging.
Transparent and translucent materials are also used in many industries. To choose the correct method for producing transparent and translucent parts, it is important to have a good understanding of the concepts of both material properties.
What is transparent material?
The transparent material allows light to pass through (light passes through completely, not partially or scattered). Transparent media are air, glass, water and plastics. In most materials, unlike translucent materials, electrons do not exceed their available energy level in the visible range, preventing significant absorption and making certain materials transparent.
Of course, transparent materials are also subject to the law of refraction of light. Transparent materials have a clear appearance and an overall appearance of the same color. But they can also have a combination of colors, creating a bright spectrum of each color.
In fact, many liquids are highly transparent due to the absence of molecular structures and defects (voids, cracks). Diamond, cellophane, Pyrex, and soda-lime glass are considered popular examples of transparent materials.
Different materials allow most of the light that hits them to pass through and barely reflect it. Such materials are referred to as optically transparent, not translucent. Flat glass and clean water are examples of optically transparent materials. Other examples are:
What is translucent material?
Translucent materials allow light to pass through, but unlike transparent materials, translucent materials are not always subject to the laws of refraction of light. Light transmission occurs when a change in the refractive index of one of the two interfaces leads to photon scattering.
Translucent materials do not appear as clear as transparent materials. When light hits a material, it can interact with the material in several ways. This depends on the wavelength and material properties. Photons interact with materials by combining reflection, transmission and absorption. Translucent materials absorb more light than transparent materials. Frosted glass, colored glass, waxed paper, and ice are translucent. Other examples are:
- Colorful plastic bottle
- Transparent Paper
- jelly
- Paper Cups
- Cloud
- Colorful balloon
The difference between translucent and transparent
Although transparent and translucent materials transmit light, there are differences between them.
1. Transparent materials transmit more light than translucent materials.
2. Transparent materials are subject to the law of refraction, while translucent materials are not necessarily subject to the law of refraction.
3. Transparent materials are lighter than semi-transparent materials.
4. Transparent materials allow images to be formed, but translucent materials do not allow a clear image to be formed.
5. Transparent materials have fewer structural defects than translucent materials.
Why use transparent and translucent pieces?
Transparent enclosures allow a free and clear view of the various reactions within the part, helping to solve many unknown problems. Different transparencies can be used for different requirements to achieve the designer's goals.
Process for producing transparent and translucent parts
Stereolithography (SLA)
Stereolithography stands for “SLA”, a photopolymerizable three-dimensional molding process. This means that a laser with a specific wavelength and intensity is focused on the surface of the light-curing material, curing it gradually from point to line and line to surface. The drawing of one layer is completed, and then the lifting table is moved vertically to the height of one layer to harden another layer. In this way, the layers are stacked to form a three-dimensional structure.
The biggest advantage of 3D printing transparent parts is time savings. Using this process, a CAD model can be printed into a transparent solid (with some degree of translucent contact) within hours. For post-processing, only the staples and burrs need to be removed.
However, due to the material and process, SLA parts are less stable than parts made from other processes and often cannot be used as finished products in real life. I hope you understand. Transparent 3D printing is widely used in the dental and jewelry industries for transparent orthodontic models and aesthetic products.
Materials: thermosetting polymeric resins.
Advantages: high punctuality, suitable for the production of various complex structures, low cost in the manual printing stage.
Disadvantages: low strength, fragile, products become translucent after processing and require post-processing to obtain full transparency. Not suitable for mass production, low quality material and poor color choices.
CNC machining of transparent parts
CNC machining is one of the most popular processes for rapid prototyping service providers. Milling and turning are used to give the transparent materials of a sheet the appearance desired by the customer.
One of the most commonly used transparent CNC materials is acrylic. Acrylic is easy to mill, and CNC machining can achieve good surface roughness while maintaining precision. The processed acrylic surface is also translucent (absorbs light) and the surface has a knife pattern. After manual sanding and polishing, a highly transparent state or even an optically transparent state or directions can be achieved.
Therefore, acrylic is often used to make headlight parts. Other CNC transparent materials include PC, PS, etc. As with all machined parts, clear machined parts are often more robust than comparable 3D printed parts and therefore have a wider range of uses.
However, CNC machining is more expensive than some other processes and there are no economies of scale. CNC clear machined parts are more robust than clear SLA processes and are therefore used in more industries. However, CNC machining is more labor-intensive and time-consuming and often less economical than SLA. Furthermore, the structure of the part becomes more restricted and for more complex parts the only option is to disassemble and glue the part.
Material: PMMA, PC, PS.
Advantages: High material resistance and good performance. Close to the effect of the final product.
Disadvantages: more expensive than other methods.
Injection molding of transparent parts
Injection molding is also known as injection molding and is an injection molding process that uses injection molding. Molds must be made before injection molding. Mold manufacturing is expensive and has long lead times. Injection molding is therefore rarely used for one-off prototypes.
With the development of technology, aluminum material also began to be used in the manufacture of molds, which reduces production costs and improves the production cycle. The combination of aluminum and steel molds is a widely used rapid prototyping service.
Transparent injection molding materials such as PC, PET and PMMA can be used to produce transparent products, which can quickly adapt to the design and be manufactured into various transparent parts according to needs. However, various defects often occur in injection molding, such as flow marks, shrinkage, etc., which require more professional engineers to solve.
Material: PC, PET, PMMA etc.
Advantages: fast and efficient production, high quality, similar to end-use parts. A variety of materials and surface effects are available for you to choose from, from simple structures to complex structures that can be injection molded.
Disadvantages: long cycle times, high level of knowledge required, not suitable for small batches.
Vacuum casting of transparent parts
Vacuum injection molding is an excellent option for low-volume production that can significantly reduce budgets, increase production speeds, and produce parts with excellent results. Vacuum casting uses silicone molds instead of expensive metal molds, and one silicone mold can reproduce and customize about 20 parts in the desired color. However, the injection molding material is polyurethane, so the strength is not comparable to that of the finished product. It is often used for display prototypes or for coating various types of devices.
Material: PMMA-like polyurethane, PC-like, etc.
Advantages: Suitable for small batch production, short cycle time, low cost, good part effect, color matching possible.
Disadvantages: low strength, not suitable for large volume production
Other methods
In addition to these processes, laser cutting and waterjet cutting are also used for the production of parts. Both methods can be used to produce parts, but they are very expensive.
Post-processing of transparent and translucent parts
Among the above processes, SLA transparent parts and CNC transparent parts generally require post-treatment processes such as grinding, polishing, gassing, painting and sandblasting.
Grind
Grinding, a surface modification technique, is a processing method in which the physical properties of the material surface are changed by friction with rough objects (sandpaper with harder particles, etc.), mainly to achieve a certain surface roughness. This process is used very frequently; polishing, gassing, painting and sandblasting are the basic requirements for grinding.
Both finishing and sanding are suitable for complex shapes. Although it is difficult to obtain completely transparent objects using this method, with maximum effort you can create transparent objects like glass, as described previously.
Polishing and fumigation
The polishing process cannot improve the dimensional and geometric accuracy of the part. Its main objective is to obtain a smoother surface finish. Polishing is applicable to clear SLA parts and clear CNC acrylic parts. After polishing, it can greatly improve the transparency and surface of parts, and is widely used for products with high appearance requirements. PC and PS polished parts made by CNC do not achieve a more translucent effect, and acetone fumigation can achieve a very good transparent effect.
Spray paint or spray coating
There are transparent parts of the headlight, there are transparent red ones, there are beautiful textures, and there are multiple colors in one part. In fact, in addition to the mass application of the injection molding process, there are also many methods to achieve these effects at the artisanal stage. The spray painting method is the most commonly used.
By controlling the position of the paint, the color of the paint and the thickness of the paint layer, different effects can be achieved. Spray coating is a quick and easy way to make opaque objects clear. It gives the transparent material a shine that is difficult to obtain by grinding and polishing molecules. Helps hide layers and UV exposure when you want truly visible, reflected, opaque pieces.
Resin coating
This method is used when you need very light and transparent pieces of material. Works best on flat surfaces, not opaque materials and surfaces. A resin coating provides a very smooth finish.
In short: simply apply the resin to the piece using the syringe and it will absorb the drops that fall from the syringe. The resin covers all scratches and imperfections and smoothes the surface. Apply as thin and dense a layer as possible.
coloring
In addition to polishing, dyeing can also be used to clean parts. Mainly for an aesthetic appearance. During molding, autotexturing can be used for other additives and colorants. For coloring, CNC machining parts coloring, dyeing, sandbox and texture painting techniques are used. Most often primary colors such as red, green and blue are used, but other secondary colors are also used.
