The metal parts machined by CNC usually leave tool marks, uneven surface textures, or appearance differences. Metal sandblasting improves the surface texture, cleanliness, and roughness by blasting abrasives at high speed.
This article will introduce the working principle, abrasive selection, process parameters, and applications of metal sandblasting for different metals.
What Is Metal Sandblasting?
Sandblasting is a surface treatment method that uses high-speed projection of abrasive materials to alter the cleanliness, surface texture, and roughness of metal surfaces.
When abrasive particles strike your part’s surface at high velocity, they generate impact, cutting, and slight plastic deformation, effectively removing contaminants, oxide layers, old coatings, and some machining marks while creating a new surface texture and roughness.
Sandblasting vs. Abrasive Blasting
Sandblasting originally refers to the spraying of quartz sand, while abrasive blasting is a broad term that encompasses all processes of treating surfaces with high-speed spraying of various abrasives. Sandblasting is one of the types within the category of abrasive blasting.
Sandblasting: Initially, it specifically referred to the surface spraying process using quartz sand as the abrasive material. However, modern industrial applications often use alternative abrasive blasting media because of the dust and occupational health risks associated with crystalline silica.
Abrasive Blasting: Broadly speaking, it refers to all surface treatment processes that involve high-speed spraying of solid abrasives. Processes such as sandblasting, bead blasting, shot blasting, and grit blasting are all forms of abrasive blasting.
In simple terms, all sandblasting is abrasive blasting, but abrasive blasting does not equal sandblasting. When selecting the process, you need to accurately mark the actual working conditions to avoid process mismatch.
How Does Sandblasting Work?
The basic principle of metal sandblasting is to accelerate abrasive particles through compressed air or other blasting systems and project them onto the metal surface at high velocity through a nozzle. During impact, the abrasive particles remove contaminants, modify the surface texture, and create a controlled surface roughness.
The final sandblasted finish is not only determined by the abrasive. Factors such as abrasive type, particle size, blast pressure, nozzle distance, blasting angle, processing time, and raw material all work together to define the final surface result. For example, spherical abrasives such as glass beads or ceramic beads typically create a more uniform matte or satin finish, while angular abrasives produce a more aggressive textured surface.
Different Types of Metal Sandblasting
Matte Finish
The matte surface usually has a lower degree of specular reflection. If you want the metal parts to have a more understated and uniform appearance, sandblasting is a very common method.
Satin Finish
It is usually more refined than the rough sandblasted surface, while maintaining a certain soft luster.
Frosted Finish
Frosted Finish typically emphasizes a delicate and soft “sanded” visual effect. If your product is visually driven, you need to pay particular attention to controlling particle size, abrasive type, and sanding uniformity.
How the Metal Sandblasting Process Works
A stable metal sandblasting process is not merely about “just spraying with a gun”. To achieve stable results for a batch of machined parts, reproducible parameters, and controllable yield, your parts must go through the following 8 steps.
Step 1 — Surface Inspection
After CNC machining, conduct a comprehensive inspection of the raw material condition, confirming the metal type, types of surface defects (rust, scratches, oxide layer thickness), and the parts’ dimensional accuracy requirements.
At this point, an exclusive processing plan needs to be formulated to avoid damaging precision tolerance parts.
Step 2 — Cleaning and Masking
Before sandblasting, your parts need to be cleaned. At the same time, according to the design requirements, the positions that do not need sandblasting should be masked, such as threads, precision holes, mating surfaces, sealing surfaces, optical surfaces, and electrical contact areas.
Especially for precision CNC parts, masking is an important step to ensure the dimensions and functions.
Step 3 — Select Abrasive Media
Select the abrasive based on the material, the target surface, and the subsequent processing.
Step 4 — Set Blast Pressure
Adjust the pressure of compressed air according to the hardness and precision requirements of the processed parts:
For soft metals (aluminum, copper, brass): use low pressure to avoid damage to the base material.
For hard metals (carbon steel, titanium alloy, cast iron): use medium to high pressure to ensure the effect of impurity removal and texture.
Step 5 — Control Nozzle Distance and Angle
Sandblasting nozzle distance and angle of the nozzle also affect the result.
If the nozzle is too close, the local impact may be too strong.
If the nozzle is too far away, the kinetic energy of the abrasive will decrease, and the processing efficiency and surface effect may also change.
For edge, chamfer, groove, and deep hole areas, more attention should be paid to the differences brought by the sandblasting angle.
Step 6 — Blast the Surface
During the formal sandblasting process, the following should be maintained as much as possible:
- Stable spraying speed
- Consistent nozzle distance
- Reasonable spraying angle
- Uniform movement path
- Consistent treatment time
If the operation trajectory is unstable, it is very likely to result in inconsistent depths in certain areas. This is especially important for your products with high appearance requirements.
Step 7 — Clean and Inspect
After finishing sandblasting, it is necessary to remove the remaining abrasive and dust and conduct the following checks on:
- Surface color
- Surface texture Roughness
- Uniformity
- Edge condition
- Hole and thread condition
If your part requires subsequent anodizing, you also need to consider whether the surface condition after sandblasting meets the requirements for anodizing.
Step 8 — Apply the Next Surface Treatment
Sandblasting is usually just one step in the entire surface treatment process. The metal surface after sandblasting has extremely high activity and is highly prone to secondary oxidation.
Therefore, subsequent processes such as anodizing, spraying, electroplating, and passivation need to be completed within the specified time.
What Does Sandblasting Do to Metal?
Remove Contaminants
During CNC machining, the surfaces may still have the following residues:
- Oil spill
- Dust
- Metal particles
- Oxides
- Processing residues
Sandblasting can help remove these surface contaminants, making the subsequent surface treatment more stable.
However, if there is a large amount of grease on the part surface, it is usually not recommended to solve the problem directly by sandblasting. First, clean it, and then sandblast.
Otherwise, the abrasive may further carry the contaminants onto the surface.
Remove Coatings
Sandblasting can also be used to remove:
- Painting
- Powder coating
- Oxide layer
- Old coating
- Part of surface treatment layer
If your part needs re-finishing or surface repair, the abrasive and sanding pressure need to be selected based on the substrate and the original coating.
Remove or Reduce Machining Marks
The metal surface machined by CNC usually leaves directional tool marks. If your product requires a matte finish, sandblasting can reduce the visual presence of the processing texture, making the overall surface texture more uniform.
However, you should be aware that sandblasting can reduce the visual impact of the processing texture, but it does not mean that it can “eliminate the tool marks” without limit.
If the tool marks are deep, the correct approach is usually to improve the tool path and surface quality during machining, rather than relying on sandblasting to forcibly cover them.
Create a Uniform Surface Texture
This is one of the most common applications of sandblasting aluminum and other metals.
After CNC machining, there are obvious tool marks on the surface of your aluminum enclosures, and the gloss of different areas is not completely consistent.
Through an appropriate sandblasting process, a more uniform microscopic texture can be formed on the surface. If anodizing is to be carried out later, this uniform pre-treatment surface usually also helps to achieve a more consistent visual effect.
Create Surface Profile for Coating Adhesion
This is one of the most fundamental industrial values of sandblasting. The high-speed impact of abrasive materials forms a dense micro-roughness structure on the metal surface, significantly increasing the contact area between the coating, glue, coating layer, and the substrate, helping improve coating adhesion and reduce the risk of delamination and peeling in painting, powder spraying, and anodizing.
Cleaning/Finishing: Its core purpose is to remove impurities, level the surface, beautify, and enhance the adhesion of the coating. It mainly uses angular abrasive materials, changing the surface roughness and cleanliness, without focusing on the improvement of mechanical properties. It is mostly used for appearance parts and pre-treatment of coating.
Shot Peening: Its core purpose is to modify the mechanical properties of the metal. It uses spherical abrasive materials to generate compressive residual stress through controlled impact, primarily improving the fatigue performance of the part, not pursuing an extremely smooth appearance. It is mostly used for mechanical structural parts and aerospace parts.
Sandblasting Media: Which Abrasive Should You Use?
Choosing the wrong abrasive material will prevent even the most precise parameters from achieving a satisfactory result. The hardness and particle shape of different abrasive materials directly determine the surface effect and applications.
You can directly select based on the table below to meet the requirements of various metals and processing methods:
| Media | Hardness | Particle Shape | Surface Effect | Typical Applications |
| Glass Bead | Medium | Spherical | Smooth satin/matte | Aluminum, stainless, brass |
| Aluminum Oxide | High | Angular | Aggressive/textured | Steel, aluminum, coating prep |
| Garnet | High | Angular | Medium aggressive | Stainless, aluminum, steel |
| Silicon Carbide | Very High | Angular | Very aggressive | Hard metals |
| Steel Grit | High | Angular | Deep profile | Carbon steel |
| Steel Shot | High | Spherical | Peening | Steel |
| Ceramic Bead | Medium/High | Spherical | Fine uniform finish | Precision components |
| Plastic Media | Low | Angular | Gentle cleaning | Sensitive surfaces |
| Walnut Shell | Low | Irregular | Very gentle | Cleaning / delicate surfaces |
How Grit Size and Blast Parameters Affect Surface Finish
Even if you choose the right abrasive material, if the parameters are not controlled correctly, the final surface may still not meet the requirements.
What Does Grit Size Mean
Grit size is typically used to describe the size classification of abrasive particles.
Fine vs. Coarse Abrasives
Fine abrasive: Primarily used to create a fine matte and frosted texture, with low surface roughness, suitable for fine surface finishing and processing of precision parts, without obvious grinding marks.
Coarse abrasive: With stronger cutting force, it can quickly remove thick oxide layers and deep tool marks, forming a high-roughness surface. Specifically designed for high-adhesion coating and severe descaling scenarios.
Blast Pressure
The sandblasting pressure directly affects the energy with which the abrasive strikes your part. When the pressure is increased, it usually leads to an increase in processing efficiency and surface action intensity.
However, for thin-walled aluminum parts, precision components, and appearance parts, you cannot simply pursue high pressure.
Nozzle Distance
The distance between the nozzle and the part will affect the energy density of the abrasive when it reaches the workpiece.
Blast Angle
The blast angle also affects the material removal and surface texture. For flat parts, the angle is relatively easy to control.
Exposure Time
The longer the machining time, the longer the surface is exposed to the abrasive action. If you want a uniform surface, what really matters is not “how long to sandblast”, but rather ensuring that different areas receive as consistent treatment as possible.
The following is a chart for your reference to check all details.
| Parameter | Typical Starting Range | Main Effect | Notes |
| Blast Pressure | 30–80 psi (2.1–5.5 bar) | Impact intensity | Lower pressure for thin-wall aluminum |
| Nozzle Distance | 100–300 mm | Energy density | Shorter distance increases local impact |
| Blast Angle | 45–90° | Texture/material removal | 90° gives stronger direct impact |
| Exposure Time | 10–60 s per area | Surface development | Depends strongly on media and part geometry |
| Abrasive Size | ~50–250 μm | Texture/roughness | Finer media generally produce finer texture |
| Nozzle Diameter | 4–10 mm | Coverage/flow | Must match equipment and abrasive |
| Surface Roughness | ~Ra 1.6–6.3 μm | Final texture | Must be validated by actual process |
These values are process-development starting points, not universal specifications. Final parameters should be validated using the actual abrasive, equipment, material, geometry, and required surface finish.
Sandblasting Different Metals
The hardness, ductility, and surface condition of different metals vary, so the sandblasting process cannot be universally applied.
Sandblasting Aluminum
Aluminum is more susceptible to surface impact, so if you are aiming for a consistent appearance, you need to pay special attention to the abrasive material, pressure, and processing time.
For CNC aluminum parts that require anodizing, sandblasting can also serve as an important pre-treatment step. Sandblasted aluminum is commonly used in:
- CNC aluminum enclosures
- Keyboard cases
- Consumer electronics
- Mechanical equipment enclosures
- Automobile parts
Sandblasting Stainless Steel
Stainless steel has good hardness and corrosion resistance. For stainless steel machining parts with high appearance requirements, it is necessary to pay special attention to controlling the uniformity of the surface.
Sandblasting Brass/Copper
Copper/brass has high ductility, and the sandblasting parameters need to be controlled carefully. If the pressure is too high or the treatment is excessive, it may affect the surface condition.
For precision copper parts and brass parts, it is recommended to confirm the final surface through sample pieces before formal production.
Copper and brass are prone to oxidation, so after sandblasting, other treatments can be carried out to prevent oxidation. For keyboard cases and weight, we usually apply clear coatings to protect them from oxidation.
Sandblasting Carbon Steel
Carbon steel can generally be treated with abrasives that have greater cutting ability for the following purposes:
- Removing rust
- Removing the oxide layer
- Removing old coatings
- Pre-treatment before painting
If powder coating is ultimately required, special attention should be paid to surface cleanliness and surface profile.
Sandblasting Titanium
The machining cost of titanium alloys is high, and they are sensitive to the surface condition. If your parts are used in aerospace or medical applications, sandblasting should not only consider the appearance.
FAQ
Why Blast Aluminum Before Anodizing?
Sandblasting can create a uniform surface texture on the surface of your parts, allowing the oxide film to grow more evenly.
Does Sandblasting Change Part Dimensions?
Yes, but it usually depends on the process strength, the material, and the structure of the part.
How to Specify a Sandblasted Finish on a Technical Drawing?
You can mark the grit of the sandblast, abrasive type, and surface roughness Ra value.
Sandblasting vs Bead Blasting: Which is Better for Aluminum?
For aluminum parts, bead blasting is often preferred when you want a fine, uniform satin or matte finish. More aggressive abrasives such as aluminum oxide may be selected when stronger cleaning, coating preparation, or a more textured surface is required. The better option depends on the required finish, alloy, dimensional tolerance, and subsequent treatment such as anodizing.
Final Thoughts
Metal sandblasting may seem like a very simple surface treatment process, but for precision CNC parts, what truly determines the outcome is the control of the entire process.
Shanghai Yecheng provides CNC machining and in-house sandblasting for aluminum, stainless steel, brass, copper, titanium, and other metal parts. If you have a drawing or surface finish requirement, send us your specifications, and we can help evaluate the appropriate blasting process, media, and subsequent finishing.
