Acrylic (PMMA) is a highly desirable material due to its strength, toughness and transparency. However, it may not be practical to rely on conventional processing to cut acrylic as the material is very fragile and any excessive force can lead to unwanted breakage. Nevertheless, CNC machining offers a reliable method of manufacturing acrylic parts safely, with high precision and minimal waste of trim. CNC machining produces very few errors, allowing the manufacture of high quality acrylic parts and prototypes such as headlamps, housings, jewellery and more.

Advantages of Acrylic CNC Machining

As a CNC machined plastic, acrylic has many inherent advantages. Excellent transparency comparable to glass, Lighter weight than glass, Excellent dimensional stability, Good tensile and flexural strength, Good insulation level, Anti-wear, Anti-UV & sunlight, Good biocompatibility, Relatively low cost, Can be solvent bonded, Easy to polish, Available in a wide range of colours, Recyclable.

Choosing CNC machined acrylic over molding or 3D printing can bring additional benefits, some of the main advantages of machined acrylic include:

1.Material compatibility
Acrylic is a thermoplastic that is malleable when heated, making it ideal for CNC machining. This inherent property makes it easy to fabricate and shape acrylic using this precise and efficient process.

2.Manufacture of High-Precision parts
CNC machines offer extremely high cutting accuracy with tolerances down to thousandths of an inch. This level of high accuracy is particularly important when working with materials such as acrylic, where the need for neat edges and dimensional accuracy is critical.

3.Increasing productivity
CNC machining is one of the most efficient ways to manufacture acrylic materials, especially when producing small batches of acrylic parts. The process allows for faster production speeds compared to manual methods, resulting in increased efficiency and productivity in acrylic manufacturing.

4.Reducing waste
Thanks to its precise manufacturing method, the CNC machining is able to cut acrylics with optimum force, avoiding irreversible damage. This enables fast and efficient production of acrylic components with precise shapes and sizes. Using CNC machining increases accuracy and minimises waste in the manufacturing process.

5.Achieve high repeatability
The automated CNC process ensures consistency across multiple parts or batches, thus ensuring consistent reproduction accuracy for each part. This reliability is a key benefit of CNC machining, especially in maintaining uniformity and accuracy in the production of acrylic parts.

6.Saving on manufacturing costs
CNC machining can provide significant manufacturing cost savings due to reduced material waste, increased efficiency and lower labour costs. The precision and automation of CNC helps to achieve a leaner, more cost-effective production process.

Applications of Acrylic CNC Machining

CNC machined acrylic has many industrial uses, with the material being most widely used in the optical and automotive industries.

Alternatives to Glass

Due to its excellent transparency and clarity, acrylic is used as a replacement for shatterproof glass in many industries, including automotive, aerospace and optical.

Acrylic is commonly used as a glass replacement for window structures in aquariums, submarines, and hockey arenas. It is also used in the manufacture of lighting components such as headlights in the automotive industry. However, lights used in optical and automotive applications often have complex shapes and may also require very tight tolerances to provide optimal performance.

Medical and Dental

Due to its good biocompatibility, acrylic can be used in a variety of medical applications, including cosmetic surgery, where it can be used as a dermal filler. Acrylic can also be used as a bone cement in orthopaedic surgery (often used in fracture repair, joint replacement surgery or in vertebroplasty to fix the vertebrae, stabilize the spine and alleviate pain), as well as in dentistry for a variety of purposes (e.g. dentures).

Consumer goods

The aesthetics of acrylic make it suitable for a wide range of consumer products from furniture to consumer electronics to musical instruments.

Precautions When Machining Acrylic

Acrylic is a useful and versatile material, but it usually fails when subjected to compressive and tensile forces. This means that machining the desired shapes and cavities into acrylic panels requires care and attention.

However, the digital precision of CNC machining greatly simplifies this task. It also greatly increases the speed of acrylic machining and allows input parameters to be programmed to meet a wide range of needs.

Workpiece clamping

Plastics and metals have different workpiece clamping requirements, and acrylic is no exception in this regard. All areas of the material must be clamped using jigs and vises (smaller parts) or using adhesives to secure the entire part to the table (larger parts). If budget allows, a vacuum table is best suited for acrylic machining because it can effectively clamp and unclamp the material without damaging it.

Machining

CNC machining of acrylic typically requires a steady feed rate. Feed rates that are too low can lead to heat build-up and chips sticking back to the part, which can greatly reduce the quality of the surface finish. Another way to prevent heat build-up is to pre-cool the acrylic material before machining begins to allow for better chip removal. During machining, it is best to use oil-free coolants as they do not react with the plastic.

Surface finishing

For an aesthetically pleasing product, acrylic needs to be polished after CNC machining to produce optimum clarity and light transmission in the part. This is usually done by using progressively finer grit sandpaper followed by hand polishing with a linen towel and polishing paste. For high-quality prototypes, such as automotive headlight lenses or taillight lenses, or windows for electronics, polishing must be done by hand, a job done by the most experienced and skilled employees.

To create a diffusion effect on acrylic parts, the surface can be sandblasted and textured, while milky white paint offers another aesthetic option. Or to colour the part while maintaining transparency, it can be painted and coloured after hand polishing.

Conclusion

Acrylic is widely used for its strength, toughness and transparency, and CNC machining provides a reliable method for manufacturing high-quality acrylic parts. Acrylic machining has a variety of industrial applications, such as optical, automotive, and medical, but requires care and attention to post-processing such as clamping and polishing. Benefits include good material compatibility, manufacturing high precision parts, increasing productivity, reducing waste, achieving high repeatability and saving manufacturing costs.