Surface Finish

What is Deburring? The Complete Guide You Should Know

deburring process

In metalwork and machining, deburring emerges as a fundamental process. In straightforward terms, deburring is the act of eliminating rough edges or burrs from metal components. These burrs, often sharp and unwanted, result from cutting, shaping, or drilling procedures.

To execute this task, a specialized tool known as deburring equipment comes into play. In this article, we’ll explore how deburring contributes to achieving smooth, safe, and polished metal parts ready for their intended use.

burrs on the workpiece

What is a Burr and Why Does it Occur?

A burr is essentially an unwanted, raised edge or small piece of excess material that forms on the surface of a workpiece during various machining operations like cutting, drilling, or milling. It’s the rough, often sharp, residue left behind after these processes.

The occurrence of burrs is a natural byproduct of metalworking. When a cutting tool moves through a material, especially metals, it displaces small amounts of material, leading to the formation of these protruding edges. However, the presence of burrs can have several undesirable consequences, such as compromising the smoothness of the finished surface, impacting dimensional accuracy, and posing safety hazards.

What is Deburring?

In the metalwork industry, deburring is a crucial process aimed at refining machined metal products by eliminating small imperfections known as burrs. These burrs are undesired ridges or protrusions of excess material that may result from various machining processes such as stamping or milling.

In addition, these burrs, if left unaddressed, can compromise the overall quality of the final metal part. Therefore, deburring steps after machining or welding to meticulously remove these imperfections, ensuring a smooth and reliable finished metal product.

deburring metal

Benefits of the Deburring Process

Deburring metal offers a spectrum of advantages, enhancing the overall quality and safety across various industrial applications. Here, we explore key benefits in the deburring process.

Achieving a Smooth Surface Finish

One of the primary benefits of the CNC deburring process is its ability to deliver a smooth surface finish to machined metal products, by removing those unwanted protrusions or ridges that can arise during various machining operations. The deburring process ensures that the final surface is free from rough spots, contributing to an aesthetically pleasing and high-quality appearance.

Ensuring Dimensional Accuracy

Beyond aesthetics, the deburring process plays an important role in ensuring dimensional accuracy in machined metal parts. Burrs can distort the intended dimensions of a workpiece, impacting its functionality and fit.

Through the removal of burrs, deburring contributes to the precision and accuracy of the final product, meeting specified tolerances and enhancing the overall performance of the metal component.

Enhancing Safety and Functionality

Safety is paramount in any application involving machined metal products. Burrs left untreated can pose safety hazards, causing cuts, abrasions, or interference issues. The deburring process eliminates these risks by eliminating sharp edges and protrusions, thereby enhancing the safety of the finished product.

Additionally, by removing burrs, functionality is improved, preventing potential issues that could arise from irregularities in the metal surface.

Extended Product Lifespan

Deburring goes beyond aesthetics; it enhances the longevity of products by making them less susceptible to wear and tear. By eliminating burrs, machines, and tools are safeguarded against damage, allowing for a longer lifespan.

types of burr

Different Types of Burrs

In machining processes, various types of burrs can emerge during cutting, drilling, or milling operations, impacting the quality and safety of metal parts. Let’s check the identification of distinct burr varieties.

1. Mechanical Burrs

Mechanical burrs result from cutting or drilling machine parts, creating rough edges that can compromise performance and safety. These undesirable burrs can significantly affect the lifespan of the part and the overall quality of assembly. Utilizing a specialized deburring tool with high-speed rotation is a useful method to remove these undesirable burrs.

2. Thermal Burrs

While mechanical burrs are common in metal parts, thermal burrs in plastic components during molding or casting processes are caused by excess materials that result from these manufacturing methods. These excess materials can negatively impact the final product’s quality, affecting factors such as surface finish and dimensional accuracy. Therefore, the presence of thermal burrs can compromise the overall functionality and aesthetics of plastic components.

3. Poisson Burrs

Poisson burrs are raised edges on metal surfaces following machining operations like drilling or milling. These burrs are caused by the metal displacement during these processes. Skilled workers use deburring tools with precision to remove these excess metal protrusions. The presence of Poisson burrs can pose risks, including the potential for cuts from sharp edges and difficulties in fitting machinery parts.

4. Internal Burrs

Internal burrs form within holes after drilling and reaming operations. These concealed burrs are caused by the metal displacement during drilling and reaming. These concealed burrs can adversely affect the overall quality of the drilled and reamed holes and cause potential issues in the fitting of components.

5. External Burrs

External burrs protrude from edges due to cutting operations, resulting from material displacement during cutting processes. These protruding burrs can significantly impact the material’s integrity, leading to potential issues in machinery performance and increased wear and tear.

6. Residual Burrs

Residual burrs may appear after machining processes, posing potential risks to machinery and operators. These lingering burrs pose potential risks to both machinery and operators, affecting safety and overall functionality.

4 Deburring Methods You Should Know

Deburring, a critical step in the machining process, employs various techniques to remove unwanted burrs resulting from cutting, drilling, or milling operations. The choice of deburring method depends on factors such as the metal types, applications, and desired surface quality. Here, we explore the top four popular methods for effective CNC deburring.

mechanical burrs

Mechanical Deburring

Referred to as automated deburring, the mechanical deburring process utilizes cutting, grinding, milling, or brushing tools to eliminate burrs through direct contact with the workpiece. This approach is cost-effective as the deburring tool can be seamlessly integrated into machining centers, eliminating the need for secondary equipment.

Additionally, mechanical deburring offers advantages in terms of speed, accuracy, and repeatability compared to manual deburring methods. The use of cutting-edge tool holders with automatic compensation and float ensures consistent pressure and uniform finishing, allowing for rapid adjustments based on burr size and rigidity.

manual deburring

Manual Deburring

An economical and frequently employed method, manual deburring entails utilizing handheld tools to buff, sand, or scrape burrs from metal and plastic parts. This localized process targets specific areas without affecting the entire part.

While manual deburring is straightforward, it can be slow, impacting operational productivity. Methods within manual deburring include brushing, utilizing rotating brushes to scrape off burrs, sanding with abrasive materials for varying surface finishes, and sheet metal edging, a process employing grinding wheels to smooth sheet metal edges.

electrochemical deburring process

Electrochemical Deburring

Electrochemical deburring utilizes electrolysis to eliminate burrs through anodic metal dissolution. The workpiece is attached to a circuit and submerged in an electrolyte, while an insulated, cathodic tool focuses the electrolysis and anodic reaction on burr-affected areas. This accurate method is effective for challenging metals but involves the use of chemical compounds, impacting their environmental friendliness.

Thermal Deburring

Thermal deburring addresses burrs in hard-to-reach areas by using heat and combustive, corrosive gases. This method creates thermal energy and shockwaves, vaporizing and scalding burrs away from the metal.

The process works well for low-conductivity materials and burrs in cracks or crevices. Cryogenic deburring, a subset of thermal deburring, employs liquid nitrogen and a flashing process to cool the chamber, embrittling and removing burrs with the help of abrasives.

remove burrs on metal

How to Deburr Metal Parts: Step by Step

Deburring metal is a meticulous process that demands precision and attention to detail. Here’s a step-by-step to efficiently deburr metal parts.

1. Pre-deburring Steps

Before diving into the deburring process, proper setup and calibration are crucial. Securely place the metal part in the deburring tool, double-checking the placement to avoid errors.

Too much force can damage the part, while too little may leave burrs intact. Constant attention to detail and accurate calibration guarantee a smooth and efficient deburring operation.

2. Proper Tool Selection

You should take into account factors such as the material, size, and shape of the part. Robust tools are necessary for hard metals, while more delicate materials demand gentler methods. Making the right tool choice not only ensures effective deburring but also contributes to prolonging the lifespan of the part.

3. Adequate Lubrication

The use of ample oil or coolant is essential to facilitate the smooth movement of the deburring tool, resulting in a more uniformly smoothed surface. Proper lubrication serves to prevent the tool from overheating and causing potential damage to the metal.

deburring machine

4. Tool Path Planning

Whether deburring machine parts or pipes, smart paths help the tool catch all rough spots. CAD/CAM software can be used for accurate path planning, ensuring even contact between the tool and the workpiece.

5. Workpiece Securing

Firmly securing the workpiece during the deburring process is vital. Uneven pressure can result in unwanted burrs, affecting the precision and quality of the final product. Vices or clamps are useful tools for this step.

6. Depth Control

Too shallow a cut won’t remove burrs, and a cut too deep may damage the metal. Constant monitoring and careful execution for depth control, often using gauges, are essential in the deburring process.

7. Burr Location

Easily accessible burrs can be effectively managed using manual techniques, whereas those situated within holes or corners may require more sophisticated approaches. Accurate identification of burr location minimizes potential challenges in the future.

8. Post-deburring Procedure

The deburring process extends beyond the mere removal of burrs. Following this step, a meticulous cleanup is initiated, where parts undergo a thorough wash in hot soapy water to eliminate any lingering burrs or grinding dust. Subsequent air-drying or a swift rotation in a drying machine is employed to guarantee the complete dryness of the components.

metal surface after deburring

Key Considerations and Tips for Optimizing Deburring

The durring process simplifies assembly, enhances edge strength, and ensures a uniform finish. Here are key considerations and tips to optimize your deburring process.

Consider Cutting Tools

Burrs, raised edges, or sharp fragments, result from various machining processes. Stabilizing the upstream process by timely replacement or re-sharpening of cutting tools reduces variations in incoming workpieces. This stabilizing measure not only improves finished product quality but also extends the lifespan of deburring machines.

Understand Materials and Components

The type of material and finished product requirements impact the deburring process. Materials like stainless steel may require longer processing times and coarser abrasives.

Choosing the right deburring tool depends on surface finish, edge requirements, and radius specifications. Different operations, from removing raised burrs to applying a radius, may need varied deburring tools, emphasizing the need for a tailored approach.

Choose the Right Machine Settings

Flexible flap brushes are recommended for sheet metal with internal contours or variable relief. Proper machine setup ensures unobstructed and perpendicular access to the entire workpiece surface. Understanding material differences influences conveyor belt speed settings, and ensuring the motor has sufficient power for deburring.

Industrial Applications of Deburring

Let’s explore how deburring is applied in different industries.

Automotive Industry

In automotive manufacturing, precision is paramount, especially in gear production. Gears with numerous teeth often retain burrs post-machining. Deburring is useful for achieving precision, preventing potential car breakdowns, and ultimately enhancing safety.

Aerospace and Aviation

The aerospace and aviation sector demands burr-free components, particularly in critical parts like turbine blades. Even minor burrs can disrupt airflow, impacting an aircraft’s fuel efficiency and speed. Tube deburring, a process to smooth the inner and outer surfaces of tubes, is essential for flawless aircraft systems.

Other Manufacturing and Production Industries

Broad manufacturing industries rely on deburring for components such as shafts and bearings. Undesirable debris or rough edges, known as burrs, can lead to operational failures and affect the lifespan of products. Deburring in manufacturing promotes efficiency, contributing to longer machine life and improved output.

Conclusion

Beyond being a mere technique, deburring is a guardian of quality. As industries evolve, so does the significance of deburring in ensuring precision, safety, and operational excellence.

FAQs

What tools are commonly used for deburring?

Common tools for deburring include brushes, sanders, and scrapers for manual deburring. Automated deburring often utilizes machines with grinding wheels and abrasive tools.

How does deburring contribute to safety in manufacturing?

Deburring enhances safety by eliminating sharp edges on metal components, reducing the risk of cuts and abrasions. It also ensures smooth machinery operation, preventing interference issues that could compromise safety.

Can deburring be applied to all types of materials?

Yes, deburring is versatile and applicable to various materials such as metals (aluminum, steel) and plastics.

Table of Contents

Brushing Surface Finish: Process, Tips, and Applications

brushed finish

Machinists often have to perform surface finishing operations after manufacturing parts and metal components. These finishes help to enhance the appearance, texture, and aesthetic appeal of the manufactured parts.

Brushing is the common surface finish. It involves using an abrasive brush to enhance the metal surfaces. Beyond improved aesthetics, it also helps improve the mechanical properties of the finished parts. This article provides all the details you need to understand about this precision finish.

What is Brushing in Finishing?

Brushing refers to the post-processing operations that involve using abrasive brushes to enhance the surface appearance and texture of metal surfaces. The finish creates a uniform parallel line on the metal surface, imparting a unique aesthetic quality.

Brushing also aids in riding the surface roughness, and burrs, among other imperfections obtained during the parts manufacture. Moreover, it enhances grip, and adhesion, improving the physical and mechanical features of the metal component.

brush surface finish

Steps in Brushing a Metal Surface

The brushing process employs grain abrasive brushes to enhance the surface properties of metal surfaces. It involves gently rolling and pressing the brush’s abrasive filaments, usually against the metal surface. This process removes contours and other imperfections, creating a more rounded edge.

Achieving a high-quality brushed finish involves adhering to the three main stages involved in this surface finish.

1. Pre-Brushing

As the name suggests, this includes a series of activities you engage in before the actual metal brushing. The first step is surface cleaning, which helps prepare the metal surface and rids it of contaminants, grease, dirt, etc. After cleaning, you can use sandpaper to sand the metal to remove scratches and other machining defects.

2. Brushing

After cleaning and preparing the metal, you can begin the actual brushing process. Brushing involves moving an abrasive bush in a rotatory motion on the metal surface. As the brush moves over the metal surface, it removes blemishes, imperfections, and other defects. Also, it creates fine lines on the metal surface, giving it a unique brushed finish.

Generally, maintaining a particular brushing direction is crucial for achieving a consistent finish. That said, ensure to control the pressure you apply on the brush and the wheel speed. This helps you achieve your desired depth and texture of the brushed finish.

brush surface of metal parts

3. Post-Brushing

After brushing, you may still perform some processes to optimize the final product further. This involves rinsing the metal in water tanks containing purifying solvents such as alkalis, surfactants, or acids. You may also use a suitable polish to enhance the metal surface further.

In fact, brushing is not usually the last surface finishing process. It’s often used as an intermediary finish for other finishes like polishing, painting, powder coating, or electroplating.

Advantages and Limitations of Brushed Finishing

Brushed finishing enhances the physical and mechanical features of your machined parts. However, it also has some shortcomings. Let’s take a quick look at the advantages and the cons.

Advantages

  • Enhances appearance and aesthetic appeal;
  • Improves parts durability;
  • Promotes better adhesion to paints and other adhesives;
  • Hides scratches, blemishes, and other defects;
  • Enhances corrosion and chemical resistance;
  • It maintains the part’s tolerance and dimensional accuracy.

Limitations

  • The brushed finish may leave brush marks, especially if it’s too dense;
  • Achieving surface uniformity may be challenging;
  • Sometimes, brushed surfaces are difficult to clean.

types of brushes

Types of Brushes for Surface Finishes

Brushes for brushing metal surfaces are usually made of abrasive materials, often wires. These tools differ in length, fill density, and material type, allowing the creation of a consistent satin-like surface finish upon proper application. The two standard brush types used in brushed metal finish include the following.

Steel Wire Brushes

Steel wire brushes are typical for achieving a brushed metal surface finish. It’s a common choice for brushing because it maintains the parts’ tolerance and dimensional accuracy. These brushes are suitable for brushing various metal surfaces. However, it’s the only kind applicable to brushed stainless steel. Note that these tips often come in different styles and configurations, depending on the goal or application of the finishing.

For example, steel wire brushes with short filaments tend to move rapidly, supporting vast applications, while those with more extended tips are better suited for controlled brushing of contoured faces. As briefly mentioned, the wires may also differ in their fill density. The short-trim, high-density brushes afford swift brushing and is usually more durable. However, the low-dense brush affords better flexibility.

Furthermore, unlike typical brushes, these steel wire brushes are non-loading. That is, they do not accumulate the debris and contaminants they brush off on metal surfaces.

Power Brushes

A typical power brush has its abrasive components made from carbon steel, ferrous and non-ferrous wires, or fibers that are either natural or synthetic. Like steel wire brushes, they also provide extensive surface finish applications.

Power brushes are often grouped based on the pressure you must apply to achieve a particular finish. However, the filament length, fill density, and the surface of the workpiece also determine the kind of finish you’d obtain. The machinists must understand when to modify these parameters to achieve a high-quality, desirable finish.

For example, when looking to achieve an intensive, finer finish, the trim length must be short, with an increased fill density moving at slow speeds. On the other hand, longer abrasive filaments achieve faster speeds but milder finishing and less dense filling.

In addition, beyond the typical finishes – polishing, edge finishing, etc., power brushes are suitable for improving the mechanical and physical resistance of metal fabrications. They also help get rid of contaminants and rust from metal surfaces.

Mechanical Applications of Brushed Finish

A brushed finish, like any other surface finishing procedure, is performed to enhance the general properties of a manufactured part. Below are more specific applications of brushed finishing.

how to brush a part

Cleaning

A brushed finish allows the creation of fine parallel lines on the surface of machined parts. The finish allows easy removal and prevents the accumulation of dirt, rust, slags, grime, film, and other contaminants.

Deburring

The brushes used in this finishing help rid burrs and other imperfections of metal surfaces. The metal surfaces get smoothened during brushing, yielding smooth edges with fewer protrusions or burrs.

Roughening

Beyond producing smooth, shiny surfaces, a brushing finish may also help to roughen metal surfaces. This application is most important for achieving better surface adhesion, especially before other surface finishing like painting. Metal surfaces roughened with steel wire or power brush possess better adhesive properties.

Edge Blending

After machining, the edges of the workpiece may be too sharp, hence the need to blend and smoothen such edges. Brushing, especially with a power brush, helps create less sharp and rounded edges. It promotes a better transition between where two surfaces meet – the edge. Also, it does not alter the part’s tolerance or affect the dimensional accuracy.

brushing process

Factors and Tips to Determine the Quality of a Brushed Finishing

Indeed, the choice of brush and technique plays a crucial role in the finishing you obtain. However, other factors may affect your brushed finishing. As a machinist, you must understand these tips to achieve your intended finish.

Brush Types

The choice of brush type plays a crucial role in achieving your desired brushed finish. For example, whether you intend to clean, deburr, or roughen the surface, the kind of brush you select determines the texture and effects you achieve.

Also, the material you are working too will affect your brush choice. For example, you can only use a steel brush when working with stainless steel. Moreover, ensure that the brush you select adheres to your fabrication’s specified requirements. Beyond the type of brush, ensure to use a high-quality brush to produce a durable finish.

Brushing Direction

The direction in which the machinist brushes plays a significant role in the outcome of the finishing process. Maintaining consistency in the brushing direction helps to avoid brushing irregularities and maintain a suitable aesthetic appealing surface finish.

In the past, a typical brushed finish created unidirectional lines parallel to the motion of the brush. However, machinists are taking a new route. Experts advise against brushing along the brush’s movement, as it may cause the brush’s top to become dull after extended use, making the process less efficient. Consequently, you should create the brush lines opposite the brushing motion.

Wheel Speeding

The wheel of the brush refers to the rotating tool used in brushing. That said, the speed of the brushing wheel plays a crucial role in the kind of finish you achieve. Generally, brushing with high wheel speed gives the best outcome. However, it could cause heat build-up or even burn out metal surfaces. Moreover, it could even cause the quick bending of the brush filaments.

Manufacturers must know the limits of the wheel speed of their brush to prevent brushing defects. It’s best to brush below the speed limit – the maximum revolution per minute of the brush or the top safe speed.

Moreover, modulating the wheel speed is essential for customizing the brushed finish to fit your fabrication specifications. Gaining mastery of the wheel speed of your brush helps you achieve better precision and dimensional accuracy.

Level of Operator’s Expertise

Beyond all the factors discussed, the machinist’s skill level also comes into play when brushing. The quality of the finished part depends on the operator’s expertise and how they handle the finishing process.

In fact, a skilled technician understands the intricacies of selecting the right brush, optimizing the wheel speed, and brushing directions, among other nuances, to achieve a top-notch brushed finish.

Comparing Brushed Finishing to Other Surface Finishing

How does a brushed finish compare to other standard metal surface finishing? Let’s compare this finishing to two different typical surface finishes.

brushing and bead blasting

Brushed Finish vs. Bead Blasting

Both finishes involve using an abrasive tool on a metal surface. While brushed finishing involves cleaning and ridding the metal surfaces of blemishes and imperfections, bead blasting obscures or coats the metal’s original surface with specific beads. The process involves blasting the metal surface with abrasive particles, the beads. They are usually made of ceramics, glass, metal, or corundum.

The finish creates a uniform, homogenous matte texture with little reflectivity. In addition, while a brushed finish often forms parallel, unidirectional lines on the metal surfaces, the bead blasting procedure is usually non-directional.

Brushed Finish vs. Satin Finish

Again, both finishes share some similarities. In fact, they are more similar, with people using them interchangeably, because they both leave the metal surfaces with little shiny and reflective properties.

However, a satin finish often uses a sanding (or abrasive) process, providing a glossier finish than an abrasive brush in a brushed finish. Also, the satin metal surface has little to no lines, so they are usually smoother with a more consistent texture. That said, while brushing is restricted to using an abrasive brush, a satin finish may employ other abrasive materials, like sand or paper.

Furthermore, a satin finish tends to have more mechanical and chemical resistance, making it suitable as a final finish, unlike brushed finishing.

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Conclusion

While brushing operations are often the final post-processing operation, they help enhance the general features of the machined parts. Also, it’s a valuable surface finishing process, as it maintains the dimensional accuracy and precision of the manufactured parts. That said, it’s a crucial process you should perform before finally applying other finishes like plating and painting.

FAQs

What material is brushed finish?

A brushed finish is suitable for various materials, especially metals. Typical brushing operations include a brushed aluminum finish. It also suits other metals and alloys like stainless steel, bronze, and brass.

Is brushed finish the same as matte?

No, a brushed finish differs from a matte finish. However, both processes result in metal surfaces with a non-reflective appearance. In addition, a brushed finish creates parallel lines from the brush, while a matte finish is often more consistent and uniform.

Which type of brush is the best for a brushed finish?

The type of brush for a brushed finish depends on the intended texture and depth of the finish. For example, when looking to achieve a fine texture, you should use a softer brush. However, use a coarse brush for a more pronounced or profound texture.

Table of Contents

Surface Finish and Roughness in Machining – Ultimate Guide (with Chart)

surface roughness

Surface finishes define the final appearance of parts after machining. Aside from appearance, it also influences part strength, resistance to wear and tear, and functionality.

So, what are surface finishes in detail? What are the factors that affect the surface finish? How can you measure the surface roughness? Keep reading as we provide you with answers and other important information about surface finishes and roughness.

What is Surface Finish in Machining?

Surface finish involves altering a workpiece surface to improve its appearance, aesthetics, and functionality. The process entails removing or adding materials to the surface of the machined part. Several factors influence the type of surface finish ideal for a part, including the tool used in machining, machining parameters, and the material being machined.

Another factor determining the type of surface finish used on a part is the location it will be used. For instance, parts that form a seal, move against each other, or have to fit tightly together often get special surface finish considerations. Also, the machine is the determining factor, with 5-axis CNC machining producing better finishes than its counterparts.

3 Elements Make Up Surface Finish

Sometimes, the term surface finish is ambiguous, as it encompasses different elements. The elements that make up surface finish include:

surface finish elements

Lay

Lay defines the dominating pattern and its orientation on the surface of a part. Lay is typically created during the manufacturing process. What’s more, Lay could be isotropic (non-directional), circular, crosshatched, radial, or parallel.

Waviness

Waviness defines the periodic variations in surface finish present on a part. This element often results from machining flaws caused by chatter or deflection and warping from heat and cold. These periodic surface flaws are sufficiently small, brief, and regular, differentiating them from surface flaws.

A waviness profile is created based on the measurement over an evaluation length. The waviness profile includes no surface irregularities resulting from form variations, flatness, or roughness. The peak-to-peak spacing of the waves is known as the waviness spacing (Wsm), whereas the average or total waviness parameters determine the wave height.

waviness in surface finish

Roughness

Also known as surface roughness, it refers to imperfections in surface geometry. Since roughness is the feature of surface finish that is most frequently described, measured, and computed, many people use the term “Surface Finish” to refer to roughness.

Common Types of Surface Finishes

Surface finish is one of the most important aspects of CNC machining as it improves appearance and influences functionality. There are several types of surface finishes, but the common types include:

machined surface

1. As Machined

As-machined parts are just off the production line and contain light tool marks, an average amount of surface abrasion, and a particular texture or completed appearance. According to the use case, a component’s average surface roughness (Ra) is the difference between its real and ideal machining surface roughness.

Leaving the surface of a CNC machined part “As machined” is quite beneficial, especially when achieving tight dimensional tolerance and consistency across multiple units.

However, on the downside, parts or products with this CNC machined surface finish often have visible tool marks on their surface. They are often exposed to environmental forces due to their distinct lack of protective coating.

2. Bead Blasting

Bead blasting is a finishing method that uses a pressured air gun to blast components with tiny glass beads. This procedure primarily enhances aesthetics by producing a matte, satin, or light-textured finish. It’s a primary finish type that mechanically modifies the surface to change or erase machining marks by eliminating extra material, leaving a smooth surface in its wake.

The even and textured finish of bead blasting is a benefit. This machined surface finish has little impact on tolerances, but it can affect critical dimensions of the surface, which is why it is best not to cover key surface features.

3. Powder Coating

Powder coating is the method of applying powder by static electricity to the surface of components. The major difference between powder coating and spray painting is using dry powder rather than liquid. The powder used is uniformly adsorbed on the machined components’ surface before being baked into the pieces in the oven.

This produces a robust, wear- and corrosion-resistant coating that is more long-lasting than conventional spray coating techniques. Powder coatings are durable and highly environmentally friendly. It gives the surface a drip-free uniform finish, improving its mechanical strength, corrosion, and aging resistance.

4. Anodizing Surface

Anodization is a metal surface finish that involves thickening the natural oxide layer of a CNC machined part. Aside from thickening, this process also makes the material more durable, denser, and electrically non-conductive.

The first step in the process involves submerging the component which acts as an anode into an acid electrolyte bath. The next step is placing a cathode into the tank that contains the electrolyte bath and introducing electricity. With the introduction of electrolytes, the combination of the atoms from the alloy and oxygen ions from the electrolyte covers the surface of the parts. This improves the wear resistance of the parts.

5. Polishing Surface

Three main types of polishing are used on machined parts surface finish; conventional polishing, fire polishing, and vapor polishing.

Conventional polishing involves smoothing a surface by using an abrasive. It greatly improves the durability of parts, although there is a risk of chipping or cracking when using this surface finish.

Fire polishing involves using an open flame at a specific temperature and angle to melt a part’s surface layer. Fire polishing facilitates the reduction of ridges and bumps formed during machining.

Vapor polishing is an ideal machined plastic surface finish, as it helps clarify opaque and dull plastics. The final result after vapor polishing is often a shiny and smooth surface. It is best to sand machined parts with extreme imperfections before applying the vapor polish surface finish.

It is important to note that polishing generally requires skill not to damage the product, so it is best to leave it to skilled professionals.

Factors that Affect Surface Finish

Surface finishing is usually not straightforward as there are factors that affect the outcome of the surface finished part. These factors include;

Machined Material

The possible surface finish for a material depends chiefly on the machined material type. Hard materials, like metals, are smooth; in contrast, the surface finish of softer materials, like plastics, is rougher.

Feed Rate And Cutting Tool

While the CNC fixture holds the workpiece in place, the feed rate impacts the CNC machining surface finish since it increases the number of passes the tool makes over the material. In other words, when the feed rate is high, it often results in a rougher surface finish, while a lower feed rate results in a smoother finish.

In addition, CNC machining parts with blunt CNC cutting tools often produce a poor surface finish compared to cutting with a sharper tool.

Cutting Depth

The cut depth impacts the workpiece’s surface finish. A shallow depth of cut results in an even or smoother surface finish, whereas a large cut could result in a more irregular finish.

Surface Finishes Chart Symbols, Units, Callouts, and Standards

While reading or preparing technical drawings, you could run into many surface finish charts, symbols, and surface finish callouts. They represent how a surface appears after being machined.

Surface Units

Without a thorough understanding of these units, it can be challenging to measure surface roughness. These units include:

Rz

Rz calculates the average difference between the five biggest peaks and valleys. Five different sampling durations are used for this measurement to help weed out any potential inaccuracies.

Ra

Ra is a gauge of a surface’s general roughness. It is a number without units that expresses the average height of peaks and valleys on a certain length of surface imperfections.

RMS

The average roughness of a surface is measured using a surface called the RMS- roughness average magnitude surface. The RMS roughness magnitude of the surface is taken as an absolute number to build this surface.

Rmax

Anomalies like burrs and scrapes that Ra alone cannot see are more noticeable to Rmax.

Profile Roughness (PE)

Measured in terms of the depth of the deepest valley or height or the highest peak, profile roughness measures the size and distribution of imperfections present on the surface of parts.

Profile Tolerances (PT)

The permitted departures from a nominal profile are known as profile tolerances. They are crucial in ensuring that parts fit together properly and function as intended.

Profile Smoothness (PS)

The width of the surface’s flattest region or the thickness of its thinnest region are the conventional units of measurement for profile smoothness.

Surface Finish Symbols

These surface finish symbols represent how a surface appears after being machined. Each of these symbols denotes a particular meaning and can be used to express various features of a surface finish. These include:

surface roughness symbols

  • Basic graphical symbol for surface texture
  • The expanded graphical symbol indicating the removal of material required
  • An expanded graphical symbol indicating the removal of material not permitted
  • Surface texture graphical symbol

Surface Roughness Chart

The machining surface finish chart provides important instructions for gauging standard surface finish characteristics. Manufacturers consistently reference it to guarantee product quality during the manufacturing process.

surface roughness chart

Surface Finish Conversion Chart

The surface finish conversion chart here compares the different scales for roughness used during the manufacturing process.

surface finish conversion chart

Surface Callout Symbols

callout symbols

  • a: Single surface texture requirement
  • a & b: Two or more surface texture requirements
  • c: Manufacturing method
  • d: Surface lay and orientation
  • e: Machining allowance

How to Measure Surface Roughness?

Surface roughness (Ra) defines how smooth a surface’s profile is. There are several measuring systems for surface roughness.

measure roughness machine

Direct Measurement Methods

This method uses a stylus to measure the surface roughness of a surface. The process involves running the stylus at a perpendicular angle to the material’s surface and then determining the roughness parameters using a registered profile.

Non-Contact Methods

The machinist uses light or sound to measure the surface roughness for this method. This method often involves using light or sound instruments like confocal and white light to send an ultrasonic pulse onto the part’s surface. The instrument with sensors would pick up on the reflections caused by the uneven surface for measurement.

Comparison Methods

The comparison method uses samples with known roughness parameters. The process here is quite simple, albeit requiring a lot of skill. Here, the manufacturer uses visual and tactile senses to compare the surface roughness of a newly machined part to that of a sample with an already-known surface roughness parameter.

Inductance Methods (In Process Technique)

This method requires inductance, as it uses magnetic materials to measure the surface roughness of a material. The inductance pickup uses electromagnetic energy to determine the distance to the surface. Then, using the calculated parametric value, it is possible to compute comparative roughness parameters.

Choose the Suitable Surface Roughness for Your Project

Here are some factors to consider when choosing the right surface roughness for your project.

Project Budget

Your project budget is one of the main determining factors when choosing surface roughness. For low-budget projects exposed to polishing, painting, or other surface finishes, 3.2 μm surface finish Ra might be your best bet, although 1.6 μm would show fewer cuts. Where the budget is extensive, going for CNC precision machining and smoother surface finishes like 0.4 and 0.8 μm is perfect.

Product Application

The application of the product is another factor to consider when choosing the right machining surface finish. For products with high precision and dimensional tolerance, it is best to go for high-grade and smoother surface finishes. For instance, parts that would serve as moving surfaces would require a surface finish like powder coating as it helps reduce friction. While anodizing is better suited for products exposed to corrosive forces for long periods.

Additional Surface Finish

Product undergoing or not-undergoing additional surface finish would also determine the type of surface roughness suitable. Where no additional surface finish is obtainable, it is often best to ensure the surface is as smooth as possible, as it improves product aesthetics and functionality.

XinCheng Meets Your Machined Part Surface Finish Requirements

Knowing the rate at which a specific material’s surface hardens leads to a better knowledge of surface finish. At XinCheng, we have great knowledge and expertise in machining, including CNC machining, die casting, vacuum casting, injection molding, sheet metal fabrication, etc.

In addition, you can rest assured of getting the desired surface finish outcome at XinCheng since we provide thorough dimensional inspection reports. Besides, we do a variety of finishing procedures, including bead blasting, electroplating, anodizing, polishing, powder coating, brushing, and more. We guarantee surface finishes that meet your specific needs.

Conclusion

Getting the right surface finish in the machining process is almost as important as machining the part precisely. The reason is that the right surface finish not only influences part aesthetics and durability, it also determines its corrosion resistance.

FAQ

What is the difference between surface finish vs surface finishing?

Surface finish describes the attributes, general surface texture, and quality of a surface. Surface finishing, in contrast, describes the process of altering the surface to produce a desired finish.

What does a 32-surface finish mean?

The typical surface roughness is 32 micro inches or a surface finish of 32. It is equivalent to 1/32 inch to have a 32-micron roughness. The surface finish that is smoother and closer to a 32 finish is a 6-surface finish.

What differentiates Ra and Rz in the surface roughness chart?

Ra represents the average distance between peaks and valleys. It also quantifies the surface’s departure from the mean line within a sampling length. On the other hand, Rz assists in determining the vertical separation between the highest peak and the deepest valley. This is accomplished within five sampling intervals, after which the observed distances are averaged.

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