CNC machining has an excellent reputation for its ability to produce complex parts quickly and with minimal operator intervention, but it’s important to remember that the final product will strongly reflect the quality of the initial design. Most of the restrictions of CNC machining relate to tool geometry and access. As CNC machines observe to the letter the data inputted into Computer-Aided Design (CAD) software, the failure to consider these restrictions will likely lead to inadequately machined parts.
Although CNC machining is constantly evolving with the growth of new technologies, designers and engineers should be aware of known restrictions before embarking on their CNC project designs.
Key Principles When Designing Parts For CNC Machining
Achieving the perfect design prior to machining is essential to secure outstanding product quality so the following key principles should be observed:
- Parts should be designed to allow tools with the largest diameters to machine them.
- Cavity depth should not exceed four times their width.
- The features of a particular design should correspond with the principal directions allowed by the CNC machine (so give consideration to the number of axes available).
- Text and symbols are best engraved instead of embossed to limit the amount of material that is removed during the process.
In addition to observing these basic principles, it’s important to design parts that consider the following restrictions:
1) Ratio 0f Tool Diameter To Cavity Depth
CNC cutting tools have a limited cutting length, hence the recommendation that depth should not exceed four times the width of the cavity. The deeper the cavity, the greater the vibration during machining, which may lead to problems such as increased tool deflection and chip evacuation.
2) Tool Geometry
Most CNC cutting tools are cylindrical, therefore restricting their cutting length and affecting the final cut that can be made. For example, internal corners usually have a radius, even when machined with very small cutting tools. While specialist tools can help to mitigate the restrictions of CNC tools, other problems may occur. Tools with longer shafts, for instance, may allow a deeper cavity to be machined but may be prone to vibration, thereby affecting accuracy.
3) Tool Access
Because CNC machining is a subtractive process, the cutting tools always access the workpiece from above so that material can be removed. If a required feature cannot be accessed in this way, then it cannot be machined using CNC. A recommendation is to align desired features, such as cavities, holes, or vertical walls, to one of the principal directions, although with 5-axis CNC design the workpiece can be held in different ways to improve access.
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With expertise in the field of CNC machining, we can provide tailored advice to help you to achieve the results you require so, to find out more or request a free quotation, please get in touch.
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