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vapor polishing surface finishing

Vapor Polishing: Achieving the Smooth Surface Finish

Polishing plays a crucial role in eliminating micro-imperfections from the surfaces of manufactured products and machined parts. These imperfections may not be readily noticeable at first glance. The primary objective of polishing is to remove these imperfections and sanding marks while imparting a glossy finish to the parts.

Among the various polishing methods, this article will focus on vapor polishing. Vapor polishing is a widely used finishing method, particularly effective in achieving high transparency levels in plastic materials. This is especially valuable in cases where plastic is utilized to create lightweight optical lenses, demanding optimal transparency.

Now, let’s delve into the vapor polishing process and how vapor polishing works in producing clear parts using injection molding or vacuum casting.

What Is Vapor Polishing?

Vapor polishing is a specialized surface finishing technique employed in manufacturing. In this process, a solvent is transformed into vapor and directed onto the part or product in need of refinement, either through a pressurized air stream or by cycling it repeatedly within a chamber. The solvent reacts with the part’s surface, inducing a melting effect that results in a smoother texture and increased resistance to scratches.

This method is particularly suitable for enhancing the properties of materials like acrylic (PMMA) or polycarbonate, contributing to improved surface finishes on both internal and external surfaces. Its effectiveness is pronounced when applied to smaller parts. Notably, vapor polishing excels at refining delicate internal features that are challenging to polish manually, such as threads, channels, apertures, and sample inspection areas.

The Vapor Polishing Process: A Step-by-Step Guide

vapor polishing process
Vapor Polishing Process

Vapor polishing is a technique manufacturers employ to smooth certain plastic resin materials, utilizing the gaseous state of a heated Weld-On 4 solvent. The choice of this solvent is primarily based on its reactivity with polycarbonates. Here’s a stepwise look at how to perform vapor polishing:

Step 1: Preparing the Workpiece

Before initiating the vapor polishing process, the workpiece undergoes sanding to reduce the presence of deeper marks on its surface, facilitating even coverage by the vapor. This sanding process involves using 1000 and 1500-grit sandpaper on the part’s surface. Subsequently, the workpiece undergoes a thorough cleaning to eliminate dust and other contaminants that may interfere with the vapor polishing process.

Step 2: Heating the Weld-On 4 Solvent

The journey begins with the careful heating of the Weld-On 4 solvent to its boiling point, an impressive 1040°F or 400°C. This initial step demands a controlled environment to ensure the safety of the surroundings and the individuals involved. The meticulous regulation of parameters prevents potential threats posed by the generated gas and serves as a shield against contamination.

Step 3: Vapor Generation

As the Weld-On 4 solvent reaches its boiling point, a crucial transformation occurs – vapor generation. This chemical vapor is the cornerstone of the vapor polishing process; it has the power to refine surfaces with unmatched precision. The controlled parameters during heating play a pivotal role in shaping the quality of vapor generated, laying the foundation for a flawless outcome.

Step 4: Spraying the Vapor

With vapor in hand, the next step involves the strategic application by spraying it across the surface of the plastic workpiece. The inherent heat within the vapor works harmoniously, swiftly melting the plastic resin material to fill in microscopic voids and scratches. This transformative process elevates the aesthetic appeal and ensures structural integrity.

Step 5: Dwell Time for Optimal Results

Once the vapor has been expertly applied by spraying across the workpiece’s surface, a critical aspect comes into play – dwell time. Allowing the vapor to interact with the plastic surface for a specified duration is essential for achieving optimal results. This dwell time allows the vapor to penetrate deeper into the microscopic imperfections, ensuring a thorough and uniform surface refinement.

Step 6: Controlled Cooling Process

Post-application, a controlled cooling process becomes imperative to solidify the plastic rapidly, locking in the enhanced surface characteristics. This phase is as crucial as the heating process, as it influences the final integrity of the plastic workpiece. Careful management of cooling parameters ensures the material solidifies smoothly, preserving the meticulous improvements made during the vapor polishing process.

Step 7: Inspection and Quality Assurance

With the surface now refined and solidified, a meticulous inspection follows. Trained personnel evaluate the workpiece for imperfections, ensuring the vapor polishing process meets the desired quality standards. This step is the last checkpoint before the polished components move forward in the manufacturing pipeline.

Step 8: Finishing Touches and Final Checks

Any remaining traces of solvent or residue are meticulously removed to elevate the result to perfection. Finishing touches, such as additional polishing or smoothing, may be applied to address specific aesthetic or functional requirements. The trained personnel must conduct final checks on the vapor polished part to confirm that every detail aligns with the predefined specifications.

Materials Suitable for Vapor Polishing

custom abs vapor polished part
Custom ABS Vapor Polished Part

Vapor Polishing is more compatible with plastic materials than others. Below are some engineering plastic resins that work well with vapor polishing.

Polycarbonate (PC)

Polycarbonates belong to a category of thermoplastic polymers featuring the carbonate group. Plastics within this category are characterized by their strength, toughness, and ease of fabrication. Essentially, polycarbonates can be easily thermoformed, molded, or machined.

Moreover, specific grades of polycarbonate exhibit transparency. The chemical structure of polycarbonates makes them well-suited for vapor polishing, offering an uncomplicated and advantageous process.

To vapor polish polycarbonate, a sealed container is utilized, into which a small amount of acetone or MEK (methyl ethyl ketone) is introduced. The solvent condenses on the part’s surface, inducing partial melting. Following condensation, evaporation ensues, resulting in a smoother surface. The polycarbonate polishing process is often repeated multiple times for optimal purity and high-level smoothness.

Acrylic (PMMA)

acrylic pmma vapor polishing
Acrylic (PMMA) Vapor Polishing

Acrylic, an engineered thermoplastic known for its translucency and transparency, is often called acrylic glass due to its non-crystalline nature. This lightweight and shatter-resistant material is particularly suitable for crafting clear optical prototypes.

When vapor-polishing acrylic components, a sealed container is used to introduce a small quantity of solvent, such as dichloromethane or chloroform, along with the acrylic parts. The solvent undergoes condensation on the part’s surface, followed by evaporation, resulting in a smoother finish. It is essential to repeat this process multiple times to achieve the necessary levels of purity and smoothness for these parts.

Acrylonitrile Butadiene Styrene (ABS)

Acrylonitrile butadiene styrene, or ABS, is a terpolymer recognized for its strength, featuring a glossy and impervious surface. Its substantial hardness and rigidity contribute to the ease of plastic fabrication.

The surfaces of ABS-produced parts are amenable to polishing, resulting in a shiny and flawless finish. Vapor polishing is employed for this purpose, causing the ABS part’s surface to momentarily melt and reflow before solidification occurs, resulting in a smoother finish. The use of solvent vapor, such as acetone, is integral to this process.

Factors like part size, solvent concentration, and other relevant considerations influence the duration of vapor polishing ABS.


Nylon plastics, commonly called polyamides, boast exceptional mechanical properties that facilitate CNC fabrication. For parts crafted from nylon, vapor polishing is a standard finishing process involving solvents such as methyl ethyl ketone (MEK), ethylene dichloride, or acetone. The solvent undergoes evaporation and condensation on the part’s surface, resulting in a smoother surface finish.

Comparing Vapor Polishing to Traditional Methods

vapor polished cnc part
Vapor Polished CNC Part

The selection process can be challenging when deciding between vapor and traditional polishing. However, rest assured, we will delve into the advantages and disadvantages of these two polishing methods to assist you in making informed decisions.

Traditional Polishing

Manual polishing represents the conventional approach to polishing. This method finds application in smoothing the surfaces of wood, 3D printing plastics, CNC machined plastics, and metals. One advantage of manual polishing lies in the readily available equipment.

Moreover, it poses no adverse health effects, with the only challenge being the generation of dust during the polishing process, a concern easily addressed by using a high-quality nose mask and other safety gear.

On the flip side, manual polishing proves labor and time-intensive, especially when aiming for high-quality glossy finishes or superior optical clarity in parts. Additionally, achieving a uniform finish on parts with intricate geometries may pose a challenge within this polishing method.

Vapor Polishing

Vapor polishing stands out as an efficient and rapid surface finishing process. The resulting parts exhibit a consistently shiny finish and exceptional optical clarity, achieved through the vapor’s ability to reach challenging areas.

Notably, vapor polishing minimizes material removal, leading to cost savings on the materials used. This specialized technique finds practical applications in manufacturing medical devices and specialized equipment. Similarly, it is widely used in features like channels, undercuts, apertures, threads, and other intricate details.

However, it’s important to note that vapor polishing may not be suitable for every plastic material. The setup cost can also be relatively high, involving expensive materials and equipment for optimal operation. Furthermore, some materials undergoing this process may necessitate annealing before polishing, leading to increased production costs.

Benefits of Vapor Polishing in Custom Machining

comparison of vapor polishing results
Comparison of Vapor Polishing Results

Vapor polishing in custom manufacturing offers several key benefits that impact the overall quality and functionality of the produced parts. Here are some of the benefits:

Light Transmission Improvement

Vapor polishing finish is highly effective in enhancing the ability of parts to transmit light. The process ensures a smooth and optically clear surface, allowing light to pass through without obstruction. This feature is particularly beneficial in applications requiring precise light emission, such as in optical components, lenses, or light-guiding elements. The improved light transmission achieved through vapor polishing contributes to these components’ overall performance and functionality.

Improves Product Aesthetics

Beyond functional benefits, vapor polishing significantly contributes to the visual appeal of products and parts. Vapor polishing imparts excellent optical clarity, a water-clear appearance, and a high gloss finish to elevate the overall aesthetic quality. This improvement in appearance is not merely cosmetic; it enhances the product’s perceived value, making it more attractive to end-users and stakeholders. Whether it’s consumer goods, electronic devices, or precision components, the aesthetic benefits achieved through vapor polishing can positively impact market perception.

Surface Enhancement

Vapor polishing stands out compared to other surface finishing methods, such as sanding, by eliminating deep and shallow marks or fine cracks on the product’s surface. The process addresses surface roughness and markings, producing a flawlessly smooth finish. This is crucial in applications where surface quality is paramount, such as aerospace components, automotive parts, or any industry requiring precise and polished surfaces. The absence of visible imperfections enhances the overall quality and functionality of every finished part.

Ideal for Use in the Medical Industry

In the medical industry, where stringent cleanliness and sterility standards are imperative, vapor polishing emerges as a preferred surface finishing process. Producing smooth tools without visible tool marks is critical for medical equipment and devices. Tool marks can potentially serve as areas where debris and contaminants accumulate, compromising hygiene.

Vapor polishing addresses this concern, ensuring machined medical tools have a smooth, contaminant-free surface. This makes the process highly suitable for manufacturing surgical instruments, breathing respirator, diagnostic equipment, and other medical devices where cleanliness and precision are paramount.

Vapor Polishing in Various Industries

vapor polish for 3d print
Vapor Polish for 3D Print

Manufacturing industries favor vapor polishing as a critical surface finishing method, particularly in medical devices, food processing, and consumer products.

Medical Device

In the medical devices sector, vapor polishing is extensively employed to craft components that meet high aesthetic standards and exhibit optical clarity and a glossy finish. Vapor polishing cost-effective solution is crucial in refining gate areas, addressing surface irregularities, and eliminating marks on medical instruments. Beyond aesthetics, vapor polishing contributes to the elimination of debris that may settle on the surfaces of devices involved in blood pumping, ensuring a smooth and hygienic performance.

Food Processing

Within the food processing industry, vapor polishing is utilized to enhance the smoothness and shine of product parts that come into direct contact with food. The benefits extend beyond aesthetics, as vapor polishing also improves the cleanability of these parts, mitigating the growth of harmful microorganisms. The smooth and polished surfaces contribute to the visual appeal of food processing equipment and support hygiene and safety standards in food production.

Consumer Products

In the realm of consumer products, vapor polishing serves as a valuable process, enabling the production of parts with exceptionally smooth surfaces. This smoothness enhances the visual appeal and reduces friction, particularly when these products come into contact with the skin or other items. As a result, consumer goods manufactured using vapor polishing exhibit a high-quality finish that contributes to a positive user experience.

Choosing the Right Vapor Polishing Services

at machining surface finishing services
AT-Machining Surface Finishing Services

Vapor polishing presents numerous advantages, providing a smoother and optically clearer surface with high transparency. However, it would be best to be mindful of potential accidents and health hazards.

To ensure you reap the benefits of vapor polishing, it is crucial to execute the process correctly. Entrust your vapor polishing projects to AT-Machining for both production and finishing. As a manufacturing company with extensive experience, we specialize in producing parts with various post-treatments, including vapor polishing.

Furthermore, we offer an exceptional surface finish characterized by outstanding optical clarity, all at an affordable price and with a quick lead time. If you have a new project in mind, reach out to AT-Machining today for a complimentary quote. Your satisfaction is our priority.

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Hey there, I’m Sam!

From AT-Machining, I’m a CNC Machining Expert in this field for more than 20 years.  We offer cost-effective machining services from China. Ask for a quote for your ongoing or upcoming projects now!

Best Regards, Sam, Co-Founder

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