Minimizing a part’s weight increases structural efficiency and optimizes overall performance, while maintaining the required strength and stiffness.
In the case of aerospace applications, lighter components contribute to improved fuel efficiency, increased speed, and enhanced handling. For design and mechanical engineers who want to specialize in the aerospace industry, designing lightweight, functional parts is an essential skill.
CNC machining enables highly accurate material removal, making it particularly well-suited for producing lightweight components with intricate geometries.
One of the primary challenges in designing lightweight CNC parts is controlling part vibration and tool chatter throughout the manufacturing process. Features such as thin-walled ribs, flanges, and pocket floors are especially prone to vibration during machining, which can lead to resonance, damage, and dimensional inaccuracies.
In this article, we’ll explore key considerations for designing lightweight parts, including design drivers, material choice, and part geometries.
As we’re focusing on CNC machined components, the two main considerations we’ll review in this article are design drivers and material.
If you were still considering which manufacturing process to use for your components, you would also need to take that into account. This could include 3D printing, sheet metal, welding, or metal stamping.
Begin by thoroughly evaluating a part's primary design requirements. For lightweight components, determine whether the application primarily requires stiffness or strength.
Applications that are stiffness-driven focus on minimizing deflection under anticipated loads or maximizing properties such as flexural modulus, modal response, and other relevant stiffness measures.
In strength-driven scenarios, the main objective is for the component to withstand loading conditions without failure. Here, the design can generally accommodate some degree of displacement, so long as it does not compromise overall functionality.
Related Read: Understanding Mechanical Properties in Metal - Strength
Establishing whether stiffness or strength is the critical factor early in the development process assists with both material and manufacturing process selection.
It's important to note that manufacturing constraints sometimes define the feasible design envelope. For example, in the case of CNC machined parts, factors like vibration often dictate wall thickness specifications that exceed what is practically manufacturable. In those cases, you would need to prioritize DFM over strength or stiffness as a primary driver.
Selecting materials for lightweight applications demands a comprehensive evaluation of cost, manufacturability, mechanical strength, and rigidity. In aerospace engineering, commonly utilized metals include aluminum alloys, titanium, stainless and high-strength steels, Inconel, Hastelloy, and other advanced nickel-based alloys, along with magnesium.
In addition to metals, high-performance composites such as carbon fiber-reinforced plastics, glass fiber, and Kevlar are essential to the advancement of modern lightweight solutions. With the breadth of available options, engineers must thoroughly assess the specific requirements and trade-offs to identify the optimal material for each application—a process that requires both technical expertise and informed decision-making.
Related Read: Material Selection Strategy for Machined Components
These Ashby charts illustrate how materials rank according to strength, Young's modulus, and density (respectively). Click an image to view in more detail.
Several design patterns can help with load distribution while also reducing a part’s weight, including webs, ribs, beams, and isogrids.
Webs and ribs are the most commonly used geometries for designing lightweight parts, especially in the case of machined aerospace components.
A web is a relatively thin, flat section of material that connects thicker regions of a part that serves as a load-transmitting surface between structural elements. In addition to distributing loads, webs allow manufacturers to use less material while maintaining stiffness, which results in reduced weight in components.
A rib is a reinforcing feature (typically a narrow, elongated protrusion) that adds stiffness to a web or flat surface. Ribs increase bending resistance, prevent warping, and support thinner sections without adding excessive material. Note that ribs should be designed with tool access in mind – too narrow or too deep, and it will make the part more difficult or expensive to machine.
A beam is a type of geometry that spans between supports or interfaces to prevent deformation under load. In machined components, beams are typically linear or curved features that are either supported at their ends or along their length. They are subjected to bending, shear forces, and axial loads.
An isogrid is a lattice pattern that’s machined into a part’s surface, typically a flat or curved panel, and creates a stiffened shell for bending and shearing loads. The pattern of intersecting ribs forms equilateral shapes (often triangles) that aid in stiffness, load distribution, and weight reduction.
|
Feature |
Primary Function |
Typical Geometry |
Load Type |
|
Beam |
Carries loads across a span; resists bending and shear |
Long, slender member; often rectangular or I-shaped in cross-section |
Bending, shear, axial |
|
Rib |
Reinforces thin sections; increases local stiffness |
Narrow, protruding feature; often perpendicular to a surface |
Local bending, shear |
|
Web |
Connects structural elements; distributes loads |
Thin, planar surface between thicker regions |
Shear, tension/compression |
|
Isogrid |
Maximizes stiffness-to-weight ratio with isotropic properties |
Triangular lattice of intersecting ribs; machined into a surface |
Multi-directional bending, shear, membrane loads |
Developing lightweight machined components is essential for enhancing performance in aerospace components. While it presents unique engineering and manufacturing challenges, a structured approach and the right machining partner will help ensure successful outcomes.