With the development of the global economy, companies increase their capital investment in the research and development of new products. Rapid prototyping is still a must to verify the R&D work. The most commonly applied prototypes are CNC machining plastic prototypes. This article discusses four things you must know about them.
1. Materials for CNC plastic prototypes
Many plastics are available to make CNC rapid prototypes. The commonly used ones are ABS, PC, PC＋ABS, PS, PMMA (acrylic), PA (nylon), PP, POM, and PTFE. It will take another article to explain them in detail. You only need to remember the following points:
- ABS is the most commonly used plastic material for CNC machining prototypes. And it is cheap.
- To make transparent or semi-transparent parts, you can choose PC or PMMA. And The transparency of PMMA can be over 93%.
- To make structural parts, you can pick PP or POM. They are highly resistant and have high tenacity but are hard to be painted.
2. CNC machines applied
The CNC machines for making prototypes are usually 3-axis, 4-axis, and 5-axis machines.
- 3-axis CNC machines
The 3-axis CNC machines can only machine one face of the workpiece at a time, which is suitable for machining disk-shaped parts. It is hard to machine holes or recesses on multiple surfaces.
- 4-axis CNC machines
4-axis CNC machines add a rotary axis compared to the 3-axis. There is generally 360° rotation in a horizontal plane. However, it cannot rotate at high speed and is suitable for machining box-shaped parts.
If you need to drill holes in the side of a piece or the curved surface of a cylinder part, 4-axis CNC machining is the way to go. It largely speeds up the machining process. And the machining accuracy is high.
- 5-axis CNC machines
5-axis CNC machines have one more rotary axis than 4-axis machines, generally 360° rotation on the upright side. By clamping once, they can machine in all directions, thereby reducing clamping costs and avoiding scratching and bruising of the parts.
Due to their high versatility, 5-axis CNC machines can manufacture high-precision parts, such as prosthesis or skeleton medical parts, aerospace parts, titanium parts, oil and gas mechanical parts, and military products.
It is not essential to make all prototypes with 5-axis CNC machines, even though they offer many advantages. Making CNC rapid prototypes that can be machined using 3-axis CNC machines through 5-axis machining will not only increase the cost, but you also might not get the desired results.
3. General tolerances of CNC rapid prototypes
Generally, the highest tolerance can be +/- 0.01 mm inner tolerance. With some Japanese CNC machines, the tolerance can be within +/- 0.001 mm.
However, the actual tolerance of the CNC machining prototypes depends on many factors such as the machines, the systems, the tools, the processing methods, etc. It would be wise to confirm with your CNC machining manufacturer per project.
4. Common surface treatments for CNC rapid plastic prototypes
For marketing purposes or to test the appearance of the design, you will need to post-treat the prototypes after they are machined. The main surface treatments are painting (matte, glossy, textured, etc.), silk screening, electroplating, vacuum plating, sandblasting, and water plating. After finishing, the CNC machining rapid prototypes look like the mass-produced ones.