完成CNC加工零件的最终指南 - beplay体育 ios下载

Welcome to part II of our three-part series about secondary operations. This article covers finishing options, while the others discussheat treatmentsandhardware installation.

When discussingCNC加工surface finishing options, you may have heard terms like as-machined, anodizing, powder coating, or media blasting. But before we dig into the details of those processes, we need to clearly define two terms that are time and again used incorrectly: surface finish and surface finishing.

Let’s clear up the confusion, shall we?

The Distinction Between Surface Finish and Surface Finishing

Surface finish:Surfaces have characteristics produced by the manufacturing process: lay, roughness and waviness. Each of these is a “surface finish” and basically they quantify how irregular a surface is (on a micro scale). Depending on the function of your product, you might need to target specific values for these characteristics.

Surface finishing:This term encompasses the processes that protect and improve the appearance of surfaces. Some of these processes add material, some remove material, and some use heat, electricity or chemicals to change the surface finish of a part. This article will expand on those processes with the goal of helping you to choose the best one(s) for your project.

但首先，表面表面表面效果更多。

Surface Finish

Surface finish should not be confused with the use ofgeometrical tolerancessuch as flatness, profile, or total runout. Different methods are used to measure surface finish, and the term describes the irregularities of a surface at the micro-level rather than dimensional inaccuracies. But you may wonder: if geometrical tolerances are defined on your drawing, and if the exterior surfaces of your machined component look ok, why bother with micro levels and layers?

Surface Finish is a Critical Consideration for Points of Contact

CNC surface finish and finishing methods are particularly important if your part is in contact with other components. For example, the purpose of a ball-bearing is to reduce rotational friction and support radial and axial loads. When one of the races rotates, the balls also rotate because of the contact between them. If the surfaces of the balls or the races have the wrong surface finish characteristics, then friction increases, creating additional wear and reducing component lifespan – even when the components were fabricated within geometrical tolerances.

三个表面饰面特性

Lay:主要表面图案的方向。一些示例：径向，垂直，水平，交叉盘，圆形和各向同性。
Roughness:Measure of the total spaced surface irregularities. These deviations can be plotted as a profile (see illustration below). There are different methods to quantify roughness, but the most popular defines averages like arithmetic mean deviation Ra, Root mean squared Rms, and others. Always check what method and parameters are being used in your project – they’ll affect product specifications and result in different values.
Waviness:Similar to roughness, these are surface irregularities but with greater spacing.

具有粗糙表面的块3D模型的图像，显示出不同的表面表面特征 — *Surface Finish Characteristics*

Pay Attention to Surface Roughness

您可以在下图中看到具有不同粗糙度值的表面的视觉比较。除了改变外观外，粗糙度在接触力学中还起着关键作用，因为较高的粗糙度值会增加摩擦并在组件上引起更快的磨损。更多的粗糙度也意味着更多的表面不规则性，这些表面不规则可能成为腐蚀和裂缝的成核位点。尽管如此，更高的粗糙度价值不一定是不好的。当您对粘附感兴趣时，如果您选择适当的材料和表面饰面选项，则粗糙度可能是有益的。

*Comparison between different surface roughnesses*

Pre-Finish Prep: Masking Holes and Surfaces

Now that you understand surface finish characteristics, we should talk about the prep work that happens before surface finishing processes are applied.

Masking may be required to protect a surface or hole during the finishing process because some finishes add a layer of material, and that added thickness can interfere with tight tolerances, threaded holes, and press fits.

For holes less than one inch in diameter, the hole is plugged with a piece of rubber, which prevents the finish from interfering with a tightly toleranced diameter or threaded hole. This process is manual and time-consuming, so each hole that needs to be masked can add to the cost of the part. For holes that are larger than one inch, some manufacturers have large rubber plugs, but some will use surface masking liquid to paint the inside of the holes.

Speaking of surface masking liquid, it’s used to protect surfaces that require a different finish for aesthetic reasons, or because a surface mates with another part and must maintain a certain tolerance.

为了掩盖表面，将保护性漆涂在零件上，然后用空气固化约一天。然后在应用完成时进行后处理，并且需要另一天才能治愈。最后，除去掩模液体，使未完成的表面裸露。表面掩盖总是需要更长的交货时间，因为这是一个需要固化时间的手动过程。

Surface Finishing Options

So, you understand surface finish characteristics and pre-finishing prep work, now it’s time to talk about the many finishing options for CNC parts – from conversion coatings and plating to abrasive and polishing processes.

钝化

钝化可防止钢和不锈钢腐蚀。该过程涉及一种化学处理，该化学处理可去除材料表面的游离铁，从而产生光滑，闪亮的饰面。它不是涂层，因此不会为零件增加任何厚度，因此不需要掩盖。

A circular metal part with holes drilled in it, finished using Alodine — *Gold Alodine*

18beplay官网

Alodine, the brand name of chromate conversion coating, is also known as chem film. It’s a thin coating used to passivate aluminum. The bath of chemicals used to apply the coating is often made with proprietary formulas, but all use Chromium as the main component. When requesting Alodine for your machined parts, you might see the process is to MIL-DTL-5541F spec, which refers to the US Military Specification of Chemical Conversion Coatings on Aluminum and Aluminum Alloys.

Alodine’s protective layer serves as a corrosion inhibitor and improves adherence for paints and adhesives, so it can be used in conjunction with decorative finishes. Alodine also allows aluminum to maintain its thermal and electrical conductivity, while other finishes mitigate that conductivity. The color can be clear, gold, yellow, or tan, depending on the exact product used. It’s typically a cheaper process, and the coating is prone to scratches and superficial damage.

Anodizing

类似于铬酸阳极化,阳极氧化钝化process that creates a protective layer on aluminum parts. The protective layer is formed using an acid electrolyte bath with a cathode passing electric current to the part, which serves as an anode (hence the name). Anodizing is a controlled way to oxidize a base material to improve durability and corrosion resistance. This outer layer is fully integrated with the substrate, so it does not flake or chip like paint and plating can. Due to the coating’s porous nature, anodized parts can also be dyed, painted, and sealed.

有不同类型的阳极氧化:I型,泰pe II, and Type III. Each is applied through a different process and results in different coating thicknesses and properties. All anodizing causes aluminum to be electrically non-conductive and prevents corrosion.

类型I。, chromic acid anodize creates the thinnest layer, so it doesn’t change part dimensions. This type of anodize appears grayer in color and does not absorb other colors well.

类型I。I, boric-sulfuric acid anodize, is a safer alternative to Type I. It also has better paint adhesion, so it can be used to give a part a wide range of colors, including blue, red, gold, clear, and many others (suppliers have color charts with all the options).

类型I。II，硬硫酸阳极氧化是最常见的类型，具有最清晰的效果，可以与最宽的颜色一起使用。但是，这种饰面比II型稍厚（范围为.001至.004英寸）。III型也可以与PTFE（通常称为Teflon）结合使用。PTFE导致干燥的润滑表面。

Black Oxide

黑色氧化物用于亚铁材料，例如钢and stainless steel and it creates a layer called magnetite (Fe₃O₄) that provides mild corrosion resistance. It’s applied using a high-temperature chemical bath that contains alkaline cleaner, water, caustic soda, and a sealant such as oil to provide a smooth, matte finish. There are also variations of this process that function at cooler temperatures, but they offer less abrasion resistance. Masking is not necessary with black oxide as its application does not significantly affect the dimensions of the part.

A circular metal part with holes drilled in it, finished using electroless nickel plating — *电子镍电镀*

2018beplay

This process is the deposit of a nickel-alloy coating by chemical reduction without using an electric current. Typical coatings are nickel-phosphorus where the higher phosphorus content improves corrosion resistance but decreases hardness. And if you’re using electroless nickel plating, do so only after heat treating to preserve the corrosion-resistant properties. Aluminum, steel, and stainless steel can all be electroless nickel plated.

A circular metal part with holes drilled in it, finished using zinc plating — *Zinc plating*

锌电镀

There are two similar, but distinct types of zinc plating, and both are called galvanization. In general, both methods are used to protect steel from corrosion. When the coating is damaged and the material is exposed to the atmosphere, the underlying steel does not corrode because zinc is more reactive and oxidizes first.

Electro-Galvanization:Sometimes called zinc plating, electro-galvanization applies zinc using an electrical current. This process is cheaper and the finished parts are easier to weld. However, the coating is less wear resistant, and therefore should not be used on parts that come in contact with others.
热浸镀锌：也称为锌镀锌，热浸镀锌浸入了熔融锌浴中的零件。此过程会产生更具抗性的外层。如果您的应用程序要在激进的环境中工作，则应考虑热浸镀锌。

Powder Coating

Powder coating is used on steel, stainless steel, and aluminum, and is similar to painting your part. In this process, powdered paint is applied electrostatically to a part and either cured in an oven heated to 325-450 degrees or cured using ultraviolet light. Powder coating comes in a variety of colors and gloss levels and creates a thick, smooth uniform coating to provide increased durability.

Powder coating does change part dimensions, however, so tolerance and roughness value control are critical, and holes and mating surfaces with tight tolerances must be masked beforehand. Additionally, powder coatings have low electrical conductivity.

A circular metal part with holes drilled in it, finished using electropolishing — *Electropolishing*

18beplay下载

Electropolishing can be applied to steel or stainless steel and is how you can achieve a super fine or mirror finish on those materials. It uses an electric current and chemical bath to dissolve a tightly controlled layer of the base material. The electropolishing process involves myriad parameters, including base material chemical composition, electrolyte chemical composition, electrolyte temperature, time of exposure, and current density. You can fine-tune those parameters to achieve different levels of polish. The process is cheaper and faster than manual polishing.

Media Blasting

Media blasting is an abrasive finishing process that removes debris and changes the surface roughness of parts. It works using a pressurized jet to fire an abrasive, usually glass or plastic beads or sand, toward the surface of a part. The effect is similar to using sandpaper, but it’s a faster process that provides a more even matte finish. It also works well finishing corners and fillets. A variation of this process uses water to lubricate the surface and trap dust, but bear in mind that using wet blasting on mild steel will result in immediate corrosion.

Media blasting can be used on most metals, including brass, bronze, and copper, and is often combined with other finishes, like anodizing, for its aesthetic benefits.

Tumbling

翻滚，也称为枪管饰面，通过将其旋转在装有磨料或非浸泡培养基的枪管中，从而为零件提供了磨砂。它类似于媒体的爆破，但由于使用的磨料尺寸较大，因此受到了较少的控制。这使其成为一个较低的忠诚过程，通常用于去除毛刺和锋利的边缘，并且不适用于小于1立方英寸（翻滚介质的大小）的零件。

它可以在任何金属上使用，并且是一个相对便宜的过程。但是，翻滚会在零件上产生不平衡的侧面和面部，因此请务必在选择此选项之前检查几何公差要求。对于3D打印的应用程序，此过程可以纠正工件和可见的缺陷。

Combining Multiple Finishes

Multiple finishes can sometimes be combined to take advantage of their different properties. For example, media blasting is often done before applying other finishes to hide machining marks and give parts a smooth, matte finish. By combining media blasting with anodizing, for example, you’ll get the surface finish found on Apple’s MacBook laptops.

a metal part finished with media blasting and red anodizing — *Combining media blasting and anodizing gives a smooth, matte, colorful look to your parts.*

类型I。I anodizing and Alodine can also be combined, though that combo requires masking areas you need to retain thermal and electrical conductivity. And passivation and black oxide are often applied in tandem to steel to provide both corrosion resistance and a nice cosmetic finish.

Key Takeaways

Hopefully, this article has helped you to understand the difference between surface finish and surface finishing, as well as introducing you to the various finishing options for CNC machined parts. To figure out which finishing options will deliver the right protection and aesthetics for your next project, remember to:

Evaluate the aesthetic and performance surface finish characteristics you want in your finished part, paying attention to the lay, roughness and waviness values you need for your application
Consider whether your part will contact other components, and the effects increased friction will have on the life of the part
考虑操作环境以及需要多少腐蚀和耐磨性

如果您仍然难以确定哪种CNC加工表面饰面适合您create a free account, upload your design and see what surface finishing options can be applied to your part — and our team of experienced technical application engineers can help, too!