Surface Roughness in CNC Manufacturing

In this competitive world, perfection is paramount. A minor flaw can affect the whole reputation of products and companies. However, CNC machines offer a high level of perfection that satisfies customers. Surface roughness in CNC manufacturing is something that ensures precision.

 

In simple words, surface roughness is the critical factor that controls the precision. Before using any product, you should check its surface roughness. Are you wondering what this terminology is and how to measure it? Worry not! In this comprehensive article, I will examine each aspect in detail. So, let’s get started!

 

Overview of Surface Roughness in CNC Manufacturing 

Surface roughness is the measurement of imperfections in a CNC machine’s products. These imperfections can be in the form of scars, valleys, or curves. This roughness is measured through the Ra (Roughness Average) value. The Ra value shows how much a product deviates from ideal perfection. 

 

Simply put, a product with less deviation from the ideal point has fewer flaws. On a roughness measuring scale, consider that the perfect perfection point is 0. Let me explain it with examples. If a product has a Ra value near 0, e.g., 0.4, it has a lower level of imperfection than a product with a Ra value of 2.3.  

 

Products with higher deviations are imperfect and need remanufacturing. Each manufacturer is responsible for checking the level of roughness. The nature of the tool or workpiece causes different levels of roughness. For example, if the cutting edges of tools are not sharp, they will create an uneven surface. 

 

This surface can cause severe issues in product functioning. Moreover, durability, shine, and resistance to pressure and temperature rely on surface roughness. However, this roughness cannot be seen with the naked eye. 

 

The product may seem very clear and perfect, but imperfections can be noted at the microscopic level. You may think that such micro-level irregularities cannot cause serious issues. You’re wrong, as many applications require 100% precision. Slight imperfection causes disturbance.

 

Quick Highlight: Products with lower Ra value are considered more towards precision. On the flip side, products with high Rw are imperfect. They undergo further surface finishing. As a manufacturer, you should focus on achieving lower Ra while making a product. 

 

What Are Typical Surface Roughnesses Levels for CNC Machining?

As I mentioned above, roughness levels indicate the extent of perfection. Different products show several levels of surface roughness during manufacturing. Remember, those roughness levels are measured in micrometers. Let’s explore the details of each level. 

 

1- 3.2 µm Ra

 

It is a significant level of surface roughness. Products that show this level of roughness have imperfections in their finishing. For instance, they have uneven upper surfaces. Some manufacturers overlook it for industrial parts where a smooth surface isn’t required. You can consider it a moderate-level roughness. Moreover, as it is in microns, it cannot be seen without a microscope. 

 

1.6 μm Ra

 

Products with 1.6 μm Ra are much smoother. But they still do not match the ultimate smoothness criteria. It is near the ideal perfection point compared to 3.2 μm Ra but far from other higher levels of perfection. This level of roughness enhances the gripping power. So, you can ignore this surface roughness if you need gripping in your product. 

 

0.4 μm Ra

 

It is the highest perfection level of surface roughness. You can see that it is much closer to the ideal perfection point. Products with 0.4 μm Ra have smoother surfaces, more shine, and excellent durability. Achieving this level of perfection is not a straightforward procedure. 

 

Many specialized finishing and cutting tools are required. This level of smoothness is crucial for your medical equipment. With an increased level of perfection, product prices also increase. Products containing 0.4 μm Ra are more costly than products with 3.2 µm Ra value. 

 

Types of Surface Roughness 

 

Based on irregularities, three types of surface roughness occur during CNC machining. Let’s take a bird’s eye view of each type. 

 

• Waviness: As the name suggests, this type of roughness occurs in the form of large waves. The continuous vibration of the CNC machining platform causes these waves. Specific parameters and filters are used to reduce this roughness.

• Lay: When surface roughness appears in conductive lines, it is known as lay. Different milling operations, i.e., grinding and turning, cause this pattern. These lines can interrupt a product’s sealing procedure.

• Flaws: Flaws appear as scratches, cracks, and pits on a product’s surface. They reduce a product’s pressure-bearing capability. The malfunctioning of any CNC tool causes them. Therefore, Proper tool inspection and flaw removal are essential for better product function.

 

How CNC Surface Roughness is Measured?

Measuring the surface roughness is a complex task. You know that those imperfections are too minor to detect with ordinary methods. Therefore, standard tools and techniques are used to examine surface roughness. Are you ready to learn those methods? Let’s dive and explore them deeply. 

 

1- Contact Profilometers

 

A contact profilometer uses a needle-like tool to measure surface roughness. That tool is known as a “stylus.” It seems like a needle, but it is more sharp and narrow. During the measuring process, the stylus travels across the surface of the products. 

 

It moves along with the ups and downs present on the surface. That needle creates a profile that helps the experts to measure those imperfections. A drawback of this method is that the needle can damage the product’s aesthetics.

 

2- Optical Methods

 

The optical method uses a laser or beam to measure the surface roughness. How does it work? A device produces an intense beam of light that strikes the product’s surface. It reflects the light that is captured by sensors. 

 

Those sensors are connected to computers and show a precise 2D image of curves, peaks, and valleys. Engineers estimate Ra values of valleys and curves to measure surface roughness. It is a fast and more accurate method, but it applies only to non-reflective products. 

 

3- Atomic Force Microscopy (AFM)

 

It is the most advanced method of measuring surface roughness. You can assess its precision by its detection of atomic-level irregularities. Like a contact profilometer, it also uses a needle known as a probe. But what sets it apart is its extra cantilever. This small tool is attached to the probe and emits the beam to reflect the imperfection on the screen. 

 

How does it measure the surface roughness? The prob moves to the surface. Different scars, waves, and valleys affect the smooth moment of the probe. The cantilever scans these imperfections. This cantilever sends data to a sensor that generates a 3D image on the screen. The AFM method is used to achieve a 0.4 μm level of surface roughness. 

 

Factors That Affect Surface Roughness in CNC Manufacturing

 

During CNC machining, several factors contribute to affecting the surface roughness. Understanding those factors is necessary to attain a higher level of accuracy. Moreover, by knowing these factors, you can reduce the level of roughness at the earlier stage. In the section below, I will debunk all possible factors briefly. 

 

• The efficiency of CNC machining tools highly affects the overall surface roughness. For example, tools with low cutting and shearing speeds create pits and scars on the surface. 

• Improper alignment of tools and workpieces creates uneven surfaces during the machining procedure. It increases the Ra value and makes it imperfect.

• Pollutants during machining considerably worsen the finish, leading to a rough product. 

• The level of roughness also depends on the material of the workpiece. A softer material is easy to operate and has fewer imperfections, and vice versa.

• Lastly, CNC machines in poor condition, with wear and tear and vibration, produce irregular surfaces.

 

How to Achieve the Desired Surface Roughness in CNC Manufacturing? 

 

What if you have prepared your product and it is not precise? No doubt it affects the reputation of your company and wastes your time. However, achieving the desired surface roughness is not impossible. You can easily attain it by following some considerations. These considerations give you accuracy and save you time and cost. Let’s discuss them below. 

 

• It is crucial to check the proper geometry and speed of cutting tools. Ensure the tool is speedy enough to cut the workpiece in one round. 
• Ensure that machining tool materials are robust enough for varying workpiece thicknesses. Using the wrong material tool affects the smoothness of products.

• Use lubricants for tools to make them efficient for machining. These lubricants reduce friction and maximize precision level. 

• Before starting CNC machining, ensure the workpiece’s platform is stable. It does not produce unwanted vibration. 

• Maintaining tools is crucial for reaching the desired surface roughness. If you find any wear and tear, replace those tools or parts. Those malfunctioned parts immensely affect the overall machining process. 

 

Frequently Asked Questions

 

Is higher Ra smoother?

No, a higher Ra value does not represent a smoother surface. Higher Ra values signify a more significant deviation from the standard perfection level. 

 

Why is surface roughness necessary?

Surface roughness is essential because it declares how durable a product is. Moreover, it reveals the pressure and temperature endurance capacity of any product. Therefore, it makes it easy for you to choose the best product for your project. 

 

How do you test surface roughness?

Several parameters are used to test surface roughness. Some of them include lasers, contact profilometers, and atomic force microscopy. All those instruments mark the Ra value, which identifies different roughness levels. 

 

Conclusion 

 

Measuring the surface roughness in CNC machining is very important. It indicates the levels of precision of various CNC machined products. In this elaborate article, I have cleared different queries about surface roughness. Such as surface roughness has multiple levels. All those levels vary due to the Ra values. 

 

A product with a higher Ra value deviates more from the ideal precision point. Therefore, reducing the Ra value of products should be a priority for manufacturers. This can be done through definite geometry of tools, proper maintenance, and the use of lubricants.