- Unnecessary Features and Complexity
One of the easiest design mistakes is to overcomplicate the design which often results in longer lead times and manufacturing costs – and potential performance issues. CNC machines are very capable of producing complex designs but they are most efficient when creating simple shapes. Part complexity takes many forms and includes geometry, special features, surface finishes, and part size along with other specifications. OEMs should look for opportunities to simplify the design. They must also work with their CNC machining partner to look at design alternatives and ensure any complex features are “must-haves”. It is important that OEMs ensure that every aspect of the design is truly necessary to achieve the requisite functionality – and when in doubt, simplify and standardize to save costs during CNC machining, sub-assembly, and final product assembly.
Engraving is a specific example of a design feature that can drive up cost and reduce production efficiency. While CNC machines are capable of engraving, this step often requires a separate cutting tool resulting in more time to machine the part. Designers should consider if there are faster and more cost-effective methods for adding text to a part. If CNC machining must be used for engraving, designers should utilize simplified fonts and avoid really small text as well as embossed text. This may seem like a minimal design modification but embossed text requires the removal of millimeters of material all across the surface of the part which takes much longer than engraving which only involves milling the text itself.
- Unwarranted Use of Tight Tolerances
During the design of complex heavy fabrications for CNC machining, it is imperative that OEMs define the “right” tolerances and work with a fabricator that has expertise in tolerance setting. The team at ABS assists customers with tolerance setting and is known for their ability to produce high-quality and complex products including impellers for turbo machinery OEMs world-wide. Machining a part to excessively tight tolerances drives up cost without providing value. A recommended best practice for heavy fabrication projects is to only apply tolerances when necessary and to utilize tight tolerances on critical areas of the part. Additionally, designers should consider that not all surfaces of a part require tolerancing. Following these measures avoids costly design mistakes and helps ensure project success, especially for highly intricate parts.
- Designing Walls Too Thin or Cavities Too Deep
Designing walls for parts manufactured by CNC machining can be tricky and is often a source of problems. In fact, insufficient wall thickness is one of the most common causes of part performance issues or failure. There is a strong desire to minimize material usage, which leads designers to push the limits on wall thickness, often ending up with walls that are simply too thin and are susceptible to vibration that can lead to warping or failure. When designing wall thickness for CNC machining, material selection must be considered from the beginning of the design as not all materials require the same wall thickness. For example, the wall thickness that works for an aluminum part may not be suitable for a stainless-steel part.
Another costly design mistake to avoid is part cavities that are too deep. CNC machining tools have a limited and finite cutting length, which means these tools can only successfully mill to a given depth. As a general rule of thumb, CNC tooling is most effective when milling a cavity depth that is 2-3 times the diameter of the tool. Beyond this, special tooling may be necessary to achieve deep cavity milling – driving up the cost and time required to create the part.