Today we will look at the manufacturing processes for acrylic polymers or optical prototypes. It is one of the most used plastics around the world and a strong competitor to glass and polycarbonate. Since acrylic parts are used in many industries, it is a good idea to look at the manufacturing processes, particularly CNC acrylic machining, as this is the process that is present in almost all types of acrylic production. In this article, you will learn how to choose the right blank, cut and engrave it with CNC milling machines, and what to do after finishing the cutting operations.
The Benefits of Acrylic and Why Machining is Best for It
Acrylic is a widely used material due to its excellent properties. Firstly and most importantly, it is 5 times more resistant than glass. And by stronger I mean shockproof and unbreakable. It is also very transparent. Acrylic has a transparency of 92%, which means that only 8% of incident light is lost in transit. For comparison: window glass is 83-90% transparent, polycarbonate is 90% transparent. Of course, the difference is small, but it exists. In addition to being transparent, and unlike other plastics, acrylic does not deteriorate when exposed to UV light for long periods of time. For example, PC turns yellow, other plastics become brittle. The same applies to corrosion and water resistance.
What do these properties tell us? That acrylic pieces are very durable, resistant and transparent. This makes them perfect for many applications. Car lights, store and advertising banners and emblems, light tubes and more. All mentioned applications require the highest precision and excellent surface quality. And since acrylic is quite strong and rigid, CNC machined acrylic is a perfect solution.
What type of acrylic is best for CNC machining
Typically, acrylic blanks are made by two methods: extrusion and casting. The first method is used to make plates while the other is used to make plates and other shapes. Acrylic thickness for both methods generally varies between 1.5 and 25 mm. This variety of thicknesses makes acrylic a good choice for cutting flat emblems and signs. Let's see which types of blanks have the best properties for CNC acrylic cutting.
Extrusion involves melting large quantities of acrylic pellets in a special tank and extruding the resulting liquid through a specially shaped orifice – an extrusion nozzle. Pouring acrylic is similar to pouring other materials. The pellets are melted and poured into a mold, which is then cooled and removed. Extruded and cast blanks behave differently under a cutting tool. Extruded acrylic has more residual stress and is therefore more prone to cracking and generally more brittle. This is why the editing is such a disaster. Additionally, extrusion makes its properties anisotropic, so you essentially machine different materials along the X and Y axes.
If you want to use acrylic CNC machining in your manufacturing process, please choose castings only. Extruded blanks are not worth the effort.
Clamping acrylic parts for machining operations
Now that we have decided on the type of blank we will use, let's discuss the specifics of fixing acrylic. I won't go into detail about CNC routers for acrylic, as any type of metal or plastic CNC router will do the job well. However, I do not recommend using wood routers as they are less rigid. So, back to devices. There are several ways to attach acrylic, but what you really want to consider is the size of the raw piece. Although acrylic is quite rigid, it is still plastic and you need to ensure that long pieces or large panels are securely attached across the entire surface. Smaller parts can be clamped using simple jigs and vices. Longer pieces are usually glued or glued to the work table, and if you plan to process acrylic panels frequently, you need to purchase a vacuum table. It will secure and release your panels perfectly.
The peculiarities of acrylic processing
feed speeds
Once you've secured the acrylic in place, you can get to work, so to speak. Most acrylic blanks are milled. The actual machining of acrylic on a CNC router is similar in many ways to machining polycarbonate. First, use a similar speed: 15,000-18,000 rpm. Then use a stable, fairly aggressive feed rate. This is necessary to prevent the tool from remaining in the same place for too long and generating heat due to the friction created during cutting. If the feed rate is too slow, the chips will start to weld back into the part and you will ruin the valuable surface finish and precision.
cutting tools
Special cutting tools are mandatory. You need to purchase special acrylic cutting bits, as they have grooves that guarantee optimal chip flow and, therefore, accuracy. Additionally, when drilling acrylic, the angle of the drill tip should be much smaller than with a standard drill bit. Instead of 120 degrees, it should be 60 degrees. This is also adjusted for better chip evacuation. And don't worry if you don't get a perfectly transparent surface after processing. This is impossible. To obtain a completely transparent piece, you need to put a little more effort into the finishing operations.
refrigerator
Maintaining the minimum temperature is essential in any CNC acrylic cutting process. For this reason, many acrylic sheets are cooled before processing. This ensures better chip removal and a lower starting temperature. Other than that, you can use some standard coolants. However, if they contain oils, make sure they do not react with the PMMA.
CNC acrylic engraving
Engraving is a variant of the acrylic machining process. Acrylic engraving is done in the same way as milling, but with a different cutting tool. It is a very common method, as many acrylic pieces are used for advertising or aesthetic purposes. Modern CNC systems allow you to engrave the most complex designs on a plastic plate. The resulting groove can then be filled with some paint to make the design more visible.
Post-processing of processed acrylic
Once the desired precision and shape of the acrylic pieces has been achieved, the pieces always need to be sanded and polished. This is usually done using successively finer grit polishing tools and finally a linen cloth with polishing paste. Additionally, there are some chemical polishing processes that involve introducing special gas to melt the outer layer of acrylic. Last but not least, there are exotic single-point milling processes with diamond tools, where a small amount of plastic is cut from the surface using a very sharp and durable single-point milling cutter.
Our Advantages in Acrylic CNC Processing
In the future, we will continue to improve our CNC prototyping services and modernize our machining equipment and cutting tools to ensure the highest quality of machined transparent plastic parts in the industry. To this end, we aim to provide the best service to customers who need to process all types of optical components into arbitrarily complicated shapes.
