There are small changes that engineers can make to their part designs that will lead to big savings when it comes time to manufacture. We've listed some of the easiest and most frequent problems that increase the time or expense of the machining process and offered several tips to optimize part design for CNC machining.
Avoid Excessively Thin Walls
Thin walls in parts are always a challenge since decreasing the wall thickness of material decreases its stiffness and decreases achievable accuracy of dimensions due to the inevitable vibrations that occur during machining. A common rule is to design walls with a thickness of 0.8 mm for metals and 1.5mm for plastics. The higher dimensional requirements for the wall thickness of plastic parts to be machined are due to their tendency to soften and warp.
Add A Radius on Internal Vertical Edges
End mills and many other cutting tools used in CNC machining are typically cylindrical, which results in the creation of a radius in corners that have been machined. Using smaller-diameter cutting tools can often shrink the radius, but it may still be impossible to achieve internal vertical corners due to the limitations of the small tools' diameter. What’s more, it leads to other issues such as delaying lead times and costing more.
When designing parts for CNC machining, it is recommended to add a vertical corner radius of one-third of the cavity or more.
Limit Thread Length
Taps are used to cut threads, while dies are used to cut external threads. Taps and dies can be used to cut threads down to M2. CNC threading tools are preferred by machinists due to their ability to reduce the risk of tap breakage. CNC threading tools are capable of cutting threads down to M6.
It is a common belief among people that the longer the thread, the stronger the connection. However, Increasing the thread length beyond 1.5 times the diameter does not improve the strength of the connection. It is recommended to design the thread with a length that is 1.5 times to 3 times the diameter. For threads in blind holes, add an unthreaded length equal to half the diameter at the bottom of the hole.
Avoid High Depth-to-width Ratios Cavities
Holes can be machined quickly and accurately when using standard drill bits. It is cost-effective to use standard hole diameters as much as possible. End mills or reamers are necessary to machine holes with non-standard dimensions, which could lead to an increase in costs. Generally, you should limit the hole length to 4 times the diameter. Deeper holes(up to 10 times the diameter) are available but they will cost more.
Use Tight Tolerance Where Necessary
Unnecessary tight tolerances can increase cost, machining time, and machining complexity, which may not have any impact on performance benefits.
If tolerances are not specified on the design, the parts will be machined using 2768 medium.
Avoid Small Features
It is a general rule to consider 2.5mm as the lower limit for cavity sizes. Micro-machining is defined as anything below this limit, and it has its own set of limitations and requirements. This process also entails additional costs, which is something you certainly want to avoid.
Design with Engraved Text and Letter
When text is necessary, opt for engraving instead of embossing text as engraving requires removing less material.
It is recommended to use Sans Serif fonts of at least 20 points to avoid small, unwanted features.
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