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Home / Resources / 3 Common CNC Machining Pain Points and How to Solve Them

3 Common CNC Machining Pain Points and How to Solve Them

November 24, 2020 by SyBridge Technologies
CNC Machining

Originally published on fastradius.com on November 24, 2020

Computer numerical control machining, or CNC machining, is a manufacturing method that uses computer-programmed tools to create fully-customizable, highly precise parts. CNC machining’s precision, accuracy, and flexibility makes it the manufacturing method of choice for industries requiring a high ratio of critical parts — in which the smallest error can have dire consequences — such as the aerospace, automotive, and healthcare sectors.

Unlike injection molding or cast urethane, CNC machining ensures that every part produced is created exactly to specifications, as each part receives individualized attention while being machined. A relatively reliable, repeatable, and effective process, CNC machining is not without its downsides.

Its most significant pitfall by far is its cost, and the main driver of cost in CNC machining is time. Fortunately, smart design for manufacturability can help eliminate or reduce features that demand more machining time, thereby minimizing cost. Here are three of the most common pain points associated with CNC machining, and how product teams can solve or avoid them to make CNC machining more cost-effective.

1. Internal sharp corners

Internal sharp corners are most machinists’ biggest pet peeve. That’s because CNC machines generally use a rotating, round cutting tool, which makes it incredibly difficult to cut an inside square corner. While it’s sometimes possible to achieve an internal sharp corner, it will likely require special tools or exotic machining processes like electrical discharge machining (EDM), which will drive costs up.

Fortunately, it’s typically possible — and fairly easy — to avoid internal sharp corners. They’re rarely necessary to a part’s functionality, and there are several alternatives that are much easier to machine, including radiused corners.

2. Undercut features

Undercuts are features that can’t be machined using standard cutting tools because some of their surfaces are not accessible from above. The two main types of undercuts are T-slots and dovetails, both of which can be difficult to CNC machine as the features can’t be reached with a standard mill.

Fortunately, undercut features aren’t always a problem. Product teams can work around undercut features in several ways: by adding setups to a part, altering the design to eliminate them, by utilizing specialized tools, or by bringing the features close to the edge of the part to increase the ease of manufacturing.

3. Workholding

“Workholding” refers to the fixturing of a part in the machine, or how a part is held in place once cutting begins. Workholding can easily become a pain point in CNC machining because, if a part is difficult to hold while machining, it will take longer to produce and therefore be more costly.

Unlike other CNC machining challenges, workholding is addressed most effectively during manufacturing rather than during the design phase. However, certain design features can help optimize workholding and thus reduce cost.

There are several solutions for parts that are tricky to workhold. During the design phase, product teams can add flat sides to the part that will make it easier to clamp. Alternatively, some parts can be held down with simple and affordable solutions like hot glue or double-sided tape. The most effective workholding solution — and the most expensive — are soft jaws, which are clamps custom-made to fit a particular part.

Best practices for CNC machining

Engineers and product designers can incorporate features that make for an easier and faster CNC machining manufacturing process.

The most foolproof way to reduce the time and cost associated with CNC machining is to design for manufacturability (DFM). Engineers and product designers can incorporate features that make for an easier and faster manufacturing process, including:

  • Putting key features on the same side to reduce setups
  • Avoiding deep features, which often require more expensive tools
  • Using softer materials if possible, as harder materials take longer to cut
  • Making the part smaller and simpler if possible, as large and complex parts take more time to cut

A manufacturing partner like SyBridge can not only help product teams identify and take advantage of cost-saving opportunities during the CNC machining process, but also to determine whether CNC machining is the best option for a given project and to aid in the material selection process. Unlike other manufacturing partners, SyBridge is technology-agnostic and highly flexible, ready to adapt to suit every customer’s unique project requirements and price point. Our team of seasoned design and engineering experts are ready to help make your concept a reality. Contact us today to get started.

Category: Knowledge CenterTag: CNC Machining

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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.

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