Introduction
Computer numerically controlled (CNC) machining may be considered as a powerful, high-precision process in today's competitive manufacturing scenario. Instructions from a computer controlled program with the help of advanced electro-mechanical devices is used to manipulate tools across a number of axes. CNC machining is adopted to generate highly accurate and repeatable physical parts from Computer Aided Design (CAD) files generated with the help of computers.
Today, we shall discuss a simple guide to design products for CNC machining to ensure the solutions developed, meet and exceed expectations.
5-axis CNC machining, Source: https://waykenrm.com
Principles & Restrictions
Let’s start with the core principles and restrictions of CNC machining.:
Overview
As already discussed, CNC technology uses precise cutting tools to produce parts from a solid block of material. The design of each produced part is based on a highly accurate CAD model, which is perfectly replicated by the CNC machine at high speeds.
Advantages of CNC machining
1. Can cut parts from a wide variety of metals and plastics,
2. Can deliver exceptional dimensional accuracy and tight tolerances output.
3. Cost-efficient operation
4. Runs at high speed
5. Is ideal for medium- to high-volume production of products
6. Used for prototyping new components.
Restrictions
Despite its versatility, CNC machining does feature several restrictions
1. Size limitations: Every CNC machine has a finite range of access, making parts with incompatible dimensions and features impossible to produce. This can make crafting parts with substantial width-to-depth ratios difficult.
2. Tool geometry: It is another important restriction of CNC machining. Because most CNC cutting tools have a limited length and a cylindrical shape, they can restrict the potential geometry of machined parts.
Product Design Rules for CNC Machining
1. Material Selection
As discussed earlier, CNC machining is compatible with a wide range of metals and plastics. This provides designers more flexibility in choosing materials based on the required hardness, heat treatability, chemical resistance and other aspects of their products.
Some materials are more efficient for CNC machining than others. For example, parts made from plastics and softer metals (like aluminum) take less time to produce by CNC machining, which may reduce overall production costs. In contrast, hard metals like stainless or carbon steel can significantly reduce machine feed rates.
Designers should consider using softer, less expensive materials when designing the CNC-machined products.
2. Tolerances
Tolerances for CNC machining can vary dramatically based on the part features, materials and intended function. Mostly general tolerances are used by part manufacturers for component dimensions, wall thickness and surface treatments—and many allow customers to request custom part tolerances within a certain range.
It’s important that tight tolerances will often increase the overall costs of CNC machining, as well as the time, parts take to produce. As a result, most CNC experts recommend only applying tight tolerances to parts when absolutely essential.
3. Level of Complexity
More complex parts require more setup and processing time by CNC machining. This results in additional manufacturing cost. Some manufacturers often emphasize their time in the design phase to ensure their parts can be cut with as few axes as possible. For example, a part that can be cut with only two axes will be processed much faster—and with the simplest setup—thus reducing costs without impacting performance.
Some products demand more complex surfaces, making it impossible to design with only two axes cuts in mind. Thankfully, designers can still manage costs on complicated parts by prioritizing consistency. Minimizing the number of unique shapes and holes in parts will reduce the number of tool changes required—driving more efficient production in the process.
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