The Complete Guide of CNC Machining Acrylic
Acrylic has the advantages of light weight, cheap price and easy molding. Its molding methods include CNC machining, casting, injection molding, thermoforming, etc. In particular, injection molding can be mass-produced, with simple process and low cost. Therefore, it is widely used in instrument parts, automotive lamps, optical lenses, transparent tubes, etc. If you want to make prototypes out of acrylic, CNC machining acrylic is an inescapable topic. Since acrylic has been used in the field of CNC machining for many years, this article will detail the precautions for CNC machining acrylic, which will take about 3 minutes to read.
Excellent properties of acrylic
Acrylic has excellent properties, which is a widely used plastic, and is thermoformed,has good processability , so to make acrylic prototype parts, CNC machining is a common solution.
As we all know, the strength of acrylic is 5 times that of glass, and it has more powerful shock-proof and anti-drop characteristics, and its density is only half of that of glass. Also, it is not as fragile as glass, and if shattered, it does not form sharp shards like glass.
Acrylic has a transparency of 92%, which is clearer than window glass which is with a transparency of 83-90%, and the light is soft; the transparency of PC is 90%. Of course, the differences between the three kind of material are small, but they do exist.
Acrylic sheet has excellent weather resistance, high surface hardness and gloss, good high temperature performance. For example, acrylic will not change its properties when exposed to ultraviolet rays for a long time, PC will turn yellow, and other plastics will become very fragile and brittle; and the surface is not easy to crack during CNC machining.
The wear resistance of acrylic is close to that of aluminum material, with good stability and resistance to various chemicals, making it very durable.
Acrylic also has good printability and sprayability. With proper printing and spraying process, it can give acrylic products an ideal surface decoration effect. This makes it have a wide range of applications, such as car lights, LED lights, shop advertising banners, etc. These applications require high precision and excellent surface finish.
Choose suitable acrylic raw material and size for CNC machining
Generally, acrylic blanks are manufactured by two methods: extrusion and casting. The extrusion process is used to make sheets, while the casting process is suitable for making sheets and other types of blanks. Usually the thickness of acrylic is between 1.5 and 25 mm. Extruded acrylic has more residual tension and is therefore more prone to breakage and is more brittle. Compared to extruded acrylic, cast acrylic is more chemical resistant and has no burrs on the cut edges, which means smoother edges. Cast acrylic is available in a variety of colors, so cast acrylic is more suitable for CNC machining.
Before CNC machining, acrylic was a one-piece blank, crystal clear, and very hard. Then, the first step is to use the laser cutting machine to cut the material according to the 3D drawing (prefer to STEP, IGS or X_T format.) or the size required by the customer, and use the flexible laser beam to cut the hard Acrylic without contact , so that the billet will not be crushed, the precision can reach the millimeter level, and the incision is smooth.
Choose the right fixture for CNC Machining Acrylic
Acrylic, despite being tough, is still plastic, and care needs to be taken to clamp long parts or large sheets along the entire area when CNC machining. Smaller parts can be clamped using simple clamps and vices. Usually, longer workpieces will be glued or taped to the table, but DDPROTOTYPE often utilizes CNC to process acrylic sheets, and purchased a vacuum table in 2019, so it can perfectly clamp and release acrylic workpieces, which is an important basis for ensuring the accuracy of the manufactured acrylic parts.
Details of CNC machined acrylic
Feed rate.Similar to CNC machined PC parts, a stable feed rate is generally used, and the RPM is 15,000-18,000. This is done to prevent the milling cutter from staying in the same position too much, which generates heat due to the friction generated during the cutting process and affects tolerances. If the feed rate is too low, the chips will start to re-weld onto the part, which will ruin the surface finish of the acrylic, also affecting accuracy.
Choose the right tool.Machining acrylic with CNC requires special cutting tools and flutes to ensure optimum chip removal and thus eusure optimum precision. In addition, when drilling acrylic, the top angle of the drill should be 60 degrees instead of 120 degrees of standard drills, which is for better chip removal.
Cooling liquid.The melting point of acrylic is 130–140°C (265–285°F), which is much lower than the melting point of glass, so when CNC machining, the temperature must be kept to a minimum, This is why many acrylic sheets are cooled before processing. In lower temperature environments, chip removal is more convenient,some standard cooling liquid also can be used, but extra attention is required, if the cooling liquid is oil, please be sure it does not chemically react with the PMMA.
Polished. After the required precision and shape is achieved, the acrylic still needs to be polished to restore the crystal-like clarity of the acrylic itself. Usually, this is done by sequentially using a smaller-grained polishing tool and then a linen towel with polishing paste. In addition, diamond polishing and fire polishing can also be used. The sequence is generally as follows: diamond polishing, and then fire polishing to remove the burrs at the corners, which makes the acrylic parts more rounded and smooth; finally, the cloth wheel is used for polishing, and after the polishing paste is applied on the cloth wheel, it can be thrown up to More than 95% transparency.
Bonding. Bonding is a very important process in CNC processing acrylic, which is finished by hand. At this time, the experience of skilled workers in hot bending processing is particularly important; the bonding process of acrylic products must be strictly controlled, Not only should the acrylic product be bonded according to the design position of the acrylic product drawing, but also there should be no sticking and blistering, insufficient bonding, etc. The quality of acrylic parts that have undergone such strict quality control will be guaranteed.
Assembly: Assembly is to combine the processed acrylic parts of various shapes, and then present a complete acrylic finished product.
Advantages of DDPROTOTYPE
DDPROTOTYPE as a professional manufacturer of prototype processing and small batch production, we are proud to manufacture clear acrylic optics in the plastics processing industry using 3-axis, 4-axis, 5-axis CNC machines from Japan and the United States. To continue our pursuit of more precise manufacturing, we use the latest diamond machining technology. This technique, called SPDM or SPDT, can be matched with the capabilities of 5-axis micro-milling to produce a range of lens and light guide parts with outstanding optical quality. We will continue to improve CNC machining services, and upgrade machining equipment and cutting tools, aiming to process customized parts of various complex shapes for customers. If you have any questions about CNC machining acrylic, please feel free to contact DDPROTOTYPE to verify the design and make feasible suggestions for free.