CNC machining process is widely used to produce custom machined parts, which is with strong strength and tight tolerance.It is the fast and cost-efficiently way to manufacture prototypes and mass production parts. An optimized designed CNC machined part will help to accelerate production time while saving cost.
To fully optimize your design for CNC machining parts, you should look at below design tips:
1. Round the Internal Corners
The CNC machining tools – such as an end mill or milling cutter – will leave rounded inside corners. The corner radius can be reduced by using a smaller diameter machining tool,but it requires both a smaller tool to machine away material and more passes – often at a lower speed to reduce the risk of deflection or tool breakage – Resulting in more machining time .
So we would suggest to add a inside corner radius of at least 1/3 of the depth of the cavity, and use the same radius in all internal edges,This helps eliminate tool changes, which adds complexity and can increase run time significantly.
2. Avoid Deep Cavities
The end mill cutting tools have limited cutting length, they typically work best when cutting cavities with a depth of up to 2-3 times their diameter. To minimize cost, we suggest limiting the depth of the cavity to the 4X diameter of the tool to ensure good results. Anything greater than that will increase the cost, as special tooling or multi-axis CNC systems are required.
If larger cavity depth is required, consider designing parts with a variable cavity depth.
3. Increase the Thickness of Thin Walls
CNC parts with thin walls have a tendency to chatter, which slows down machining speeds.They can also cause distortion, which makes it difficult to machine them accurately. The result can be additional machine time and cost.
In order to keep machining costs low, thin walls should have a minimum width of 0.8mm for metal parts, and 1.5 mm for plastic parts.
4. Optimize the Depth of Tapped Holes
Regarding to the Tapped holes, by increasing the length of thread in a hole does little to hold the bolt tighter. It’s really just the first two or three turns that do all the work.Going deeper just increases the risk of tap breakage and adds time to the tapping operation.
So we don’t suggest to thread a hold to more than 3 times of the hole’s diameter, normally, the thread length would be from 1.5X to 3X of the hole’s diameter .
5. Limit Use of Tight Tolerances
Typically, only a few surfaces of a part are critical to its function.The more features with tight tolerances,the more expensive a part to be
manufactured.Because it increases the machining time and cost.
So we would suggest to only assign tight tolerances on some critical features and surfaces, other less significant features should be controlled by standard tolerances of ± 0.125 mm,which is sufficient for those features .
6. Reduce Small Features
Small features such as micro-holes (less than 2.5mm in diameter) will increase the machining difficulty and machining time, thus should be avoided unless absolutely necessary.
7.Split Up Complex Parts
Machining multiple simple parts is less costly than machining one complex part. especially for parts with deep pockets, which would require hours of machining time to remove material, plus additional material costs.And most shops will charge a premium for more complicated parts. This is because if a mistake occurs it is costlier to redo a complex part than it is to redo a simple one.
So we would suggest to split up the complex parts to some simple parts and assemble them together if possible .
8. Design Holes with Standard Size
Holes can be CNC machined fast and to a great accuracy using standard drill bits. it won’t need end mills or reamers to finish the hole size to a non-standard dimension.This will helps reduce machine time and lower the cost . Also, limit the depth of all holes to 4 times their diameter.