Composites and the Secret to Lightweighting CNC Machined Parts

Originally published on fastradius.com on February 10, 2021

Lightweighting is the process of reducing a part’s weight for environmental and/or economic reasons. Engineers achieve lightweight parts at the design level by removing unnecessary material, either by coring parts out, employing lattices in their designs, or taking advantage of topology optimization. Another effective method of lightweighting is swapping out a heavy material for a lighter one that meets critical mechanical requirements. Lighter parts are easier on the environment, more cost-efficient, and more fuel-efficient, plus they often offer product teams more material options.

Lightweighting is a very popular technique in the automotive, aerospace, and construction industries. Common applications for lightweighting in the automotive industry — one of its most prominent use-cases — include engine blocks, chassis, and a wide variety of other parts. If a product team is not pursuing lightweighting through design elements such as lattices, but through the incorporation of lighter materials, it’s important that they employ a material that does not sacrifice strength or durability — composites often fit the bill.

What is a composite material?

Composite materials are heterogeneous mixtures of two or more materials designed to achieve specific properties. The final properties of the composite material will ultimately depend on its makeup, but generally speaking, composites are stronger than either base material on its own.

Composite materials are ideal for lightweighting because, by weight, they are stronger than most high-performance homogeneous materials on the market. The most common structure for composites consists of fibers held together by a binding matrix. These components work together to combine the strongest aspects of each one. The reinforcing fibers in the composite carry the load while the surrounding matrix, often consisting of polymers, ensures the fibers maintain their relative positions. As a result, in some cases composites can be up to 10 times stronger than steel and 8 times stronger than aluminum, but still remarkably light. CNC-machined parts built with lightweight composite materials are more fuel-efficient and easier to transport or install.

In addition to high strength, durability, and low weight, composite materials tend to offer increased design flexibility. They can be easily molded to fit complex geometries, making them ideal for use with CNC machining. And since there are so many material combinations available for composites, designers can find tailor-made CNC composites that will fit their unique requirements.

Common composite building materials

The two classifications of composite materials most applicable to lightweighting are polymer matrix composites (PMCs) and metal matrix composites (MMCs). PMCs, also known as fiber-reinforced polymers, are the most common and use a polymer-based resin for the matrix and a carbon or glass fiber for the reinforcement. MMCs are popular for lightweighting in the automotive industry and use a metal like aluminum for the matrix and silicon carbide for fiber reinforcement.

Lightweighting composites can be made from many different combinations of materials, so engineers have a lot of ground to cover when it comes to material selection. Here are three common composite building materials that are used for lightweighting CNC-machined parts.

1. Carbon

Carbon fibers come in two main varieties — polyacrylonitrile-based (PAN) carbon and pitch-derived carbon. 90% of the carbon fibers on the market today are polyacrylonitrile-based, and these fibers offer high stiffness and modulus values, as well as an impressive strength-to-weight value. Carbon is well-suited for lightweighting because it is a low-density composite material with a high weight reduction potential — in fact, it’s 50% lighter than steel.

Common applications for CNC-machined carbon fiber composites include frames, chassis, and other components in the aerospace and automotive industries. Unfortunately, cost is carbon’s most significant limitation. It’s 570% more expensive than steel, according to the International Research Journal of Engineering and Technology, which is prohibitively expensive for many product teams. Also, carbon fibers have a low impact resistance, which engineers should keep in mind for lightweighting in the automotive industry.

2. Glass

Glass composite filling materials come in five different commercial compositions — E-glass, C-glass, S-glass, R-glass, and T-glass. E-glass is the most common glass fiber used in polymer matrices for lightweighting and offers excellent mechanical properties, high electrical insulation, and low susceptibility to moisture. C-glass fibers are best for applications where the part requires chemical-resistance, but S-glass has higher strength, heat resistance, and modulus.

Fibers — *In general, glass fibers are denser and heavier than carbon fibers. They are also less stiff.*

Glass fillers can still be used as a composite material for lightweighting, but engineers should know that glass-fiber-reinforced parts will be heavier than carbon-fiber-reinforced parts and require special design accommodations in applications where high stiffness is required. Product teams and designers should keep these factors in mind during the design phase. Despite these limitations, many products use glass fibers because they are considerably more cost-effective than carbon fibers.

3. Aluminum

Aluminum-based metal matrix composites are very popular for lightweighting in the automotive industry. In general, aluminum alloys have some of the highest strength-to-weight ratios of commonly available metals, offer excellent electrical conductivity, and are highly corrosion-resistant. What’s more, aluminum composites weigh about a third of what steel does.

When aluminum is included in an MMC, the composite material can have a higher modulus, lower coefficient of thermal expansion, and higher hardness than unreinforced aluminum. Common applications in the automotive industry include vehicle frames, electrical wiring, wheels, engine parts, and more. Unfortunately, working with aluminum can drive up manufacturing costs.

Getting started with CNC composites

For engineers looking to machine strong, flexible, and damage-resistant parts without adding extra bulk, composite materials are the perfect choice for lightweighting. Polymer matrix and metal matrix composites represent two broad categories of composite materials, and any composite that falls into one of these categories can be made up of many different combinations of materials. As such, it can be challenging for product teams to ensure they’re choosing the right composite material for their project.

An experienced manufacturing partner like SyBridge Technologies can help product teams master the material selection process. Our team of expert designers, engineers, machinists, and technologists have decades of experience in ushering teams through the entire product development process, so we know that an exceptional part starts with the right materials. Contact us today — we’re here to help.

Polyoxymethylene (POM), more commonly known as acetal or its branded name Delrin®, is an engineering plastic offering low friction, high stiffness, and excellent dimensional stability. Polyoxymethylene is a category of thermoplastics and includes many different formulations of the material, all of which vary slightly. As such, it’s important to learn as much as you can about each type before choosing one for your next project. Delrin® is a semi-crystalline engineering-grade thermoplastic widely used to create highly precise parts. In general, Delrin® provides impressive dimensional stability and sliding properties. It’s known for its high strength, wide operating temperature range (-40°C to 120°C), and excellent mechanical properties. Here’s everything you need to know about this material, from how it’s made to its best-fit applications. Inside the polyoxymethylene production process Acetal was first discovered by German chemist Hermann Staudinger in 1920 before it was commercially synthesized by research chemists at DuPont, the original manufacturers of Delrin® plastic, in 1956. Like all other plastics, acetal is created by distilling hydrocarbon fuels down into lighter groups called “fractions,” which can then be combined with other catalysts via polymerization or polycondensation to produce a finished plastic. To make an acetal homopolymer like Delrin®, anhydrous formaldehyde must be generated by causing a reaction between aqueous formaldehyde and alcohol to form a hemiformal. The hemiformal is then heated to release the formaldehyde, and the formaldehyde is polymerized by anionic catalysis. The resulting polymer is stabilized when it reacts with acetic anhydride, which creates polyoxymethylene homopolymer. Acetal comes in many different commercial varieties and formulations, each with its own advantages and disadvantages. For example, Delrin® 500 is medium-viscosity, all-purpose polyoxymethylene that has a good balance of flow and physical properties. It can be used to produce parts via CNC machining and injection molding and is frequently used to manufacture mechanical parts, fuel systems, and fasteners. Delrin® 1700P, on the other hand, is a very low- viscosity, fast-molding resin that is best suited for parts with complex shapes, thin walls, long flow paths, or multi-cavity tools. It also offers the best molding thermal stability for deposit-free molding in demanding conditions. Since there are dozens of different formulations of acetal, it’s important to do your research and make sure your prospective plastic offers all of the properties you need for your application. Delrin® plastic properties and mechanical specifications small black Delrin pieces Delrin® can also be found in all-purpose industrial equipment like bearings, gears, pumps, and meters. Acetal’s excellent mechanical properties make it extremely versatile, offering a unique blend of properties that you won’t find in most metals or other plastics. Delrin® plastic is strong, rigid, and resistant to impact, creep, abrasion, friction, and fatigue. It’s also well known for its excellent dimensional stability during high-precision machining. Acetal can also stand up to moisture, gasoline, solvents, and a wide range of other neutral chemicals at room temperature. From a design standpoint, parts made with extruded POM naturally have a glossy surface finish. Since acetal is compatible with CNC machining, injection molding, extrusion, compression molding, rotational casting, and more, product teams are free to choose the manufacturing process that works best for their budget and their needs. However, it’s worth noting that Delrin® plastic is typically very challenging to bond. Acetal material properties vary by formulation, but the mechanical properties for Delrin® 100 NC010, one of the most popular formulations, include: Tensile modulus: 2900 MPa Yield stress: 71 MPa Yield strain: 26% Density: 1420 kg/m3 Charpy notched impact strength, +23°C: 15 kJ/m2 Coefficient of linear thermal expansion, normal: 110 E-6/K Water absorption: 0.9% Delrin® does have a few limitations. For instance, even though Delrin® is resistant to many chemicals and solvents, it’s not very resistant to strong acids, oxidizing agents, or UV radiation. Prolonged exposure to radiation can warp the color and cause the part to lose its strength. Also, this material isn’t readily available in a flame-retardant grade, which limits its utility for certain high-temperature applications. Why choose Delrin® plastic? These limitations notwithstanding, there are many reasons to choose acetal over other materials. When compared to other plastics, acetal offers better creep, impact, and chemical resistance, better dimensional stability, and higher strength. It also has a lower coefficient of friction. Acetal outpaces certain metals as well. Parts built with this material have a higher strength-to-weight ratio, better corrosion resistance, and offer more opportunities for part consolidation. You can build thinner and lighter parts faster and at a lower price point with acetal than with a comparable metal. Delrin® plastic can be found in almost every major manufacturing sector. In the automotive industry, common applications include heavy load-bearing gears, fuel system components, loudspeaker grilles, and safety system components like seatbelt hardware. Delrin® can also be found in all-purpose industrial equipment like bearings, gears, pumps, and meters. In the consumer goods and appliances space, this material can be used to make anything from zippers and pens to knife handles and lawn sprinklers. Getting started with Delrin® There’s a lot for product teams to love about Delrin®. It’s strong, stable, versatile, and its excellent mechanical properties make it a good choice for a wide variety of applications in a number of industries. However, with dozens of different formulations of acetal on the market, it can be very challenging to determine which one might be the best fit for your unique project. A seasoned manufacturing partner can help demystify the material selection process. When you partner with Fast Radius, you partner with a team of on-demand manufacturing experts who have years of experience helping product teams navigate material selection. We’re well-versed in the wide range of materials that can be used for both traditional and additive manufacturing — including Delrin®. Once you’ve selected the Delrin® formulation that’s the right fit for your application, our team of experts can help facilitate the entire manufacturing process — from design and prototyping to production and fulfillment. With a full suite of manufacturing services including CNC machining and injection molding, Fast Radius can bring your vision to life quickly and easily. Contact us today to get started.

Composites and the Secret to Lightweighting CNC Machined Parts

What is a composite material?