CNC machined parts – definition, materials, tolerances, surface treatment, advantages, design

In today’s world, CNC machined parts are everywhere and it’s easy to see why, mainly because CNC parts manufacturers are constantly improving their machining technology. They are an integral part of most machinery as they offer precision and efficiency in an affordable manner.

But what exactly are machined parts? What makes them so important?

In this article, I have compiled a lot of the latest information about CNC machining and CNC machined parts to help you get a comprehensive understanding. Let’s take a deeper look together!

1.What are CNC machined parts?

CNC machined parts are components that are made using machining processes. But what exactly is machining?

Machining involves the use of subtractive cutting machines such as milling machines, lathes, and grinders to create the desired parts. Although these machines use different technologies, the ultimate goal is the same – to remove material from the workpiece and form the desired shape.

Machining can be a manual or digital process.

1. Manual machining – A skilled machinist will use a manually operated cutting machine to shape the component.

2. Digital machining – As the name suggests, this is an automated cutting method that involves the use of computer numerical control (CNC) machines. In this digital manufacturing process, pre-programmed instructions are fed into the CNC machine and the part is cut according to those specifications. The result? Unmatched precision, uniformity, and efficient machining of parts.

CNC machines are a revolutionary technology in the manufacturing industry. And with online CNC machining services, you can easily get CNC parts that fit your unique business needs.

That being said, there is still a place for hand machining and other manufacturing processes such as molding, casting, and forging.

2.Materials Used for Machined Parts

CNC machining can handle a wide range of materials, from metals to plastics and ceramics. However, not all machined materials are created equal.

When choosing a material for your CNC machined parts, I recommend considering a combination of factors such as cost, part weight, conductivity, heat resistance, surface finish, and the intended use of the component.

Additionally, some CNC machined materials are easier to machine than others. Particularly hard materials are difficult to cut and can damage cutting tools. The manufacturing process can also generate severe vibrations that affect the accuracy and surface finish of the part.

Conversely, materials that are too soft tend to warp under the forces of cutting. This, of course, affects the quality of your CNC machined parts.

A custom CNC machining shop can advise on the best material for your specific project. In this section, I will cover some of the materials that are frequently used with CNC machines.

1) Metal Products

Metal is one of the most commonly used materials in CNC machining services. Metal parts have a variety of industrial applications due to their electrical conductivity, high strength, and good mechanical properties.

Different metals have different outstanding properties. For example, stainless steel is popular for its corrosion resistance, versatility, and high strength. On the other hand, we will use aluminum because of its lightweight, thermal conductivity, and corrosion resistance.

Some of the most commonly used metals in CNC machining services include aluminum, stainless steel, copper, titanium, magnesium, zinc, and mild steel. Sometimes, we may use metal alloys in the production of machined parts. Bronze is a popular metal alloy that is favored for its attractive surface finish, ductility, and chemical resistance.

2) Plastics

Another material used in CNC machining is plastic. Plastic parts are lightweight, versatile, and corrosion-resistant.

Commonly used plastics in CNC machining services include nylon, acrylic, polycarbonate, ABS, PVC, polyethylene, and Delrin.

Due to their versatility, plastic parts are used in consumer electronics, medical devices, and the automotive industry. Plastic parts are also used to make electrical insulation parts.

In addition to metals and plastics, CNC machining centers also use ceramics and composites to make parts. Composite materials are composed of two or more component materials with different properties. They have matrix materials such as fiberglass and epoxy resin.

3.Tolerances of Mechanical Parts

Machinery part tolerance refers to the acceptable deviation from the specified dimensions. Some of the factors that affect the tolerance of CNC machine parts are:

1. Processing method

2. Materials used

3. Complexity of design

4. Cost impact

CNC machining is known for its excellent ability to produce parts that meet tight tolerances. This is convenient, especially for critical dimensions such as diameter, length, and hole size.

Adherence to specified machining tolerances is essential to the function of the part. Tighter tolerances require precise CNC machining procedures, which increases production costs.

Conversely, looser tolerances allow for easier machining methods, but they may compromise the performance of the part. These looser specifications are common in prototypes and non-mechanical components.

4.Surface treatment of mechanical parts

After CNC machining, we can treat the surface of machine parts to enhance their appearance and texture. Surface finish is both functional and aesthetic.

1) Machined Surfaces

As the name implies, machined surfaces are not treated in any way after the CNC machining process. Instead, they remain as is and retain their natural surface finish. Machined surfaces are often used for internal parts as they only contribute to functionality rather than aesthetics.

2) Sandblasted Finishes

Sandblasting involves the use of abrasive media to create a matte surface finish on machined parts. The final surface finish will vary depending on the level of roughness.

The sandblasting process is not compatible with delicate machined parts. This is because it can alter their geometry by removing material.

3) Anodizing

After the CNC machining service is completed, we may anodize the final part. Anodizing is a common treatment process used for aluminum machined parts. This process creates a strong, corrosion-resistant surface.

The coating also provides wear resistance to the part.

4) Powder Coating

This surface treatment method requires applying a powder coating to the surface of the machined part and then baking it in an oven. The resulting wear- and corrosion-resistant layer is more durable than a paint coating.

Additionally, powder coatings come in a variety of beautiful colors, so beautiful custom machined parts can be made.

5.Advantages of Machined Parts

Compared to parts made using other production processes, CNC machined parts have a variety of advantages. In this section, I will cover some of these advantages.

1) No MOQ

One of the most notable benefits of CNC machined parts is that there is no minimum order quantity or minimum order quantity. This means that we can efficiently manufacture small batches or even one-off custom parts at a relatively low cost.

This is not always possible with other manufacturing methods. For example, for molded parts, metal molds need to be made first. This is an expensive process, so it is not cost-effective to make some custom parts.

Given that there is no minimum order quantity for machined parts, the CNC machining process is suitable for businesses with different quantity needs, custom designs, and prototyping. This brings me to the second point.

2) Good Prototypes

One of the outstanding features of CNC machining is accuracy and speed. We can create high-quality prototypes quickly and with high accuracy. Such prototypes are similar to the final product, which is very useful in the evaluation and design verification process.

Rapid prototyping can also create multiple variations of a part for testing and verification processes. We will then manufacture the CNC machined parts based on the prototypes that perform best.

This is not always possible with other manufacturing methods. For example, for molded parts, a metal mold needs to be made first. This is an expensive process, so it is not cost-effective to manufacture some custom parts.

Given that there is no minimum order quantity for machined parts, the CNC machining process is suitable for businesses with varying quantity needs, custom designs, and prototyping. This brings me to my second point.

3) Design Freedom

CNC machining offers unparalleled design freedom. We can manufacture high-precision machined parts with intricate details and complex geometries.

This makes it possible to realize imaginative concepts that might otherwise be tricky or impossible to realize. The flexibility of CNC machining services facilitates the creation of custom machined parts.

4) Quality

CNC machining enables us to manufacture top-notch machined parts. The production process meets tight tolerances, excellent surface finish, precision, and the highest quality standards. As a result, you can expect components that exactly meet your design specifications.

This makes CNC machining the production process of choice for industries such as aerospace, medical, and military, where high-quality parts are essential.

5) Lead Time

CNC machining has very short lead times. The design and prototyping process can be completed relatively quickly, especially since there is no lengthy machining process like other production methods.

Once the prototype is approved, we begin production of the part. Again, the manufacturing process is fast and efficient, which means shorter lead times. Businesses that choose CNC machined parts tend to see shorter time to market, which is a competitive advantage.

6) Alterations

Sometimes, it is necessary to adjust the part design. Since CNC machined parts are manufactured using digital CAD files, it is relatively easy to make these changes. All we have to do is update the technical drawings and then produce the new part to the revised specifications.

Easy modification, effectively reducing CNC machining service costs and duration. These simple adjustments also give CNC machining an advantage over other production processes.

For example, if a modification to molding is required, it may mean a lot of restructuring. Of course, this comes with huge cost and time implications.

7) Strength

Performance and durability are always a concern in the manufacture of parts. Machined parts tend to be stronger and more resilient than parts produced using other processes. This is because CNC machining does not generate the internal stresses that are characteristic of other production methods.

In addition, machined parts are derived from a solid block of material. This makes the part structure stronger and more durable.

6.Design Guidelines for Machined Parts

1) Undercuts

An undercut is a feature that cannot be created using standard cutting tools. The part usually obscures certain surfaces, making it inaccessible from the top.

There are two types of undercuts: T-slots and dovetail slots. To machine such cuts, we need to use specialized cutting tools. The width of an undercut ranges from 3 to 40 mm. The depth of an undercut should not exceed twice its width.

In addition, if the design has an undercut on the inner wall, you also need to consider the clearance of the cutting tool. The general rule is to ensure that the space between the machined wall and the inner wall is at least four times the depth of the undercut.

I recommend sticking to undercut sizes that are standard (i.e., whole millimeters). This is because cutting tools come in standard sizes.

If a design has a non-standard undercut, the manufacturer needs to create a custom cutting tool first. Of course, this increases lead time and production costs. If your business is concerned about speed and cost, I recommend avoiding this type of undercut.

2) Wall Thickness

Injection molded parts can deform if the walls are too thick. The opposite is true for CNC machined parts. Too little thickness leads to decreased part stiffness and more vibration during CNC machining. Overall, this tends to reduce the achievable accuracy.

For metal machined parts, a wall thickness of 0.8mm is recommended. Plastic machined parts should have a wall thickness of at least 1.5mm. If you choose a smaller wall thickness, plastic parts tend to deform (due to residual stresses) and soften due to higher temperatures.

If possible, choose a larger minimum wall thickness for your design. However, if this is not feasible, you can use a different manufacturing method, such as injection molding.

3) Protrusions

Protruding features are difficult to achieve with machining processes. Just like thin walls, these features can easily be damaged by vibration during machining. In addition, vibrations can reduce the achievable accuracy.

A good rule of thumb is to make sure that the height of a protrusion is no more than four times its width.

4) Cavities, Holes, and Threads

The holes and cavities on your parts will vary depending on your tooling. It is recommended that the cavity depth is 4 times its width. Shallower cavities will result in increased vibration. With deeper cavities, you may also end up with rounded edges instead of potentially sharp edges.

CNC technology can cut threads as small as M6. When designing threaded features, remember that the thread length should be at least 1.5 times its diameter.

However, the recommended thread length is 3 times its diameter. Any length above that is practically pointless. This is because the first few teeth carry most of the load.

Holes are usually created using drills or end mill tools. Since drills come in standardized sizes, I recommend taking a hole diameter that matches the standard drill size.

Also, keep in mind that the maximum recommended hole depth is 4 times its diameter.

5) Scale

The size of the part that can be machined is determined by the machine working range, which varies depending on the type of material and the CNC machine deployed.

The size of the milled part is usually limited to a maximum of 400 x 250 x150 mm. The maximum size of a turned part is ⌀ 500 mm x 1000 mm.

If you use a larger machine, you can make larger parts. You can seek advice from your manufacturing partner before going for a custom CNC machining process.

7.Conclusion

CNC machining has changed the game for industrial production of parts. It offers many advantages, from no minimum order quantity and rapid prototyping to shorter delivery times and improved quality control.Online CNC machining services make it more convenient to get quality CNC parts.

If you are looking for an experienced CNC machining manufacturer, Xavier is your ideal choice. The Xavier team is well-equipped to provide high-quality CNC machining solutions. If you need more information or to discuss your machining needs with us, please feel free to contact us.