CNC machining is a suitable technique to employ whether you want to produce a prototype or manufacture end-use products in large quantities. However, the cost of machining is a prominent barrier that causes people to give up. Several factors, such as materials, quantity, designs, finishing, turnaround time, etc., influence the cost of CNC machined parts.
But the good news is that you can drastically reduce the CNC machining costs by making some effective design optimizations. Here is a comprehensive guide that covers numerous proven ways to help you reduce the cost of CNC machining by implementing key design changes.
1. Minimize or avoid deep pockets (internal cavities)
Deep pockets can negatively impact the cost of CNC machining since they require extensive material removal. It takes time to remove material, and you might need specialized equipment to get to the desired depth.
Try to keep the depth of your design’s internal cavities to four times their length. CNC tools can only go as deep as two or three times their diameter whenever it involves cutting pockets. Although you can cut up to four times the diameter, the cost involved will be on the higher end.
2. Avoid designing thin walls
Firstly, since they are so delicate, machined items with excessively thin walls would take longer to manufacture. Secondly, it is challenging to maintain precise tolerances since they frequently vibrate or distort. These thin-walled parts are more costly owing to their slow processing, high scrap rate, and the requirement of distinctive processing technologies.
Hence, prevent designing parts with thin walls. Ideally, the walls of metal components should be wider than 0.8 mm, and for plastic parts, they should be greater than 1.5 mm, as they are more durable and less expensive to machine.
3. Optimize tapped hole sizes
The tap size and the depth of the hole when designing a machined product will determine the final cost. You won’t need to thread a hole longer than three times the diameter, and you should try to keep it lesser because, generally speaking, adding thread length to the hole will not make the part any sturdier. It will take longer to machine, and it further raises the probability of breaking if the thread is three times longer than the diameter.
Moreover, since smaller threads necessitate manual tapping, it increases the overall production costs. Therefore, using conventional tap sizes can lower cost and risk. For instance, using a tap with a 4-40 size is more practical and economical than one with a 3-38 size. Additionally, if at all possible, make the threaded holes larger than 2-56′′. You’ll save money by doing that.
4. Limit designing features with a high aspect ratio
It is challenging to accurately machine finer features having a high width-to-height aspect ratio because they are susceptible to vibrations. You can achieve significant cost reduction by designing features that maintain a width-to-height aspect ratio under four and providing bracing support or linking them to a wall to increase their stiffness.
5. Avoid 90° internal corners in the design
90-degree internal corners will require more machining operations, which will not only take longer but also add to the cost. However, most internal angles have rounded corners and don’t require 90 degrees, making it easier to employ functions.
If you modify your design to add rounded corners, the CNC machine can produce your part without interruption. Internal corners get rounded automatically by CNC machining tools like end mills and milling cutters. A short internal corner radius necessitates additional passes and specialized finer tools, which lengthens the machining process and necessitates tool changes. In contrast, larger tools can carve them precisely because the corners have a bigger radius.
Thus, you must ensure that your interior corners have a length-to-diameter ratio of 3:1 or less for optimal design. Additionally, maintaining the same radius on all internal corners can speed up the machining process.
6. Limit using tighter tolerances
A tighter tolerance in your product design increases the cost since it requires more manufacturing time and physical inspections. Sadly, internal features of your product find it particularly problematic to hold to precise tolerances because burrs can form on the edges of holes and some other cavities during machining.
If the design doesn’t specify a particular tolerance, the conventional tolerance of 0.010 thousandths or superior is applied. You must analyze any strict tolerances you want and only stipulate when it’s critical because this conventional tolerance performs well for numerous design characteristics.
Most of the above-discussed tips for cutting CNC machining expenses emphasize design simplicity as their overarching theme. When you design a complicated part, you’ll probably need specific equipment or fixtures, multiple machine configurations, or expensive specialized materials. So the ultimate advice is to keep things simple and follow the designing and manufacturing standards to reduce CNC machining costs without compromising product quality.
About the Author:
Peter Jacobs is the Senior Director of Marketing at CNC Masters. He is actively involved in manufacturing processes and regularly contributes his insights to various blogs on CNC machining, 3D printing, rapid tooling, injection molding, metal casting, and manufacturing in general.