What Is Chemical Machining?- Working, And Process

What is Chemical Machining?

Chemical machining offers a precise method for removing metal from specific areas, all while preserving the material’s inherent properties. What sets this technique apart is its reliance on a photochemical process, which means there’s no risk of introducing heat-induced distortions or mechanical stress to the finished parts.

This approach finds its niche in the manufacture of intricate, thin metal components—particularly when the design complexity demands a level of detail that traditional machining methods might struggle to achieve without damaging the material.

The sequence begins with a thorough cleaning of the metal surface to eliminate any contaminants, such as oils or debris, that could interfere with later steps. Next, a photoresist coating is applied and baked onto the metal, ensuring it adheres evenly and provides a reliable foundation for the pattern.

Once the photoresist is set, a patterned artwork is carefully placed over the metal sheet. This assembly is then exposed to ultraviolet light, which helps transfer the desired design onto the metal with accuracy, meeting the required resolution and etching specifications.

After exposure, the artwork is removed, and the resist is either developed or taken off, depending on the process. Now, the metal is prepared for the crucial etching phase: it is submerged in a chemical solution that selectively dissolves the unprotected areas, leaving only the intended design intact.

With the etching complete, the resist is stripped away, and what remains are the finished metal parts. A final round of cleaning and inspection follows, after which the components are packaged and made ready for their intended application.

Chemical Machining Process

Different processes of chemical machining are givens below:

1. Cleaning

During the cleaning stage, workpieces are carefully treated to remove any contaminants such as oil, grease, dust, or other unwanted substances. This step is essential for ensuring that subsequent processes proceed smoothly and achieve the desired results.

One of the main reasons for thorough cleaning is to promote effective adhesion of masking materials to the workpiece. If this step is neglected or not done properly, issues like stray etching can arise, particularly during masking or debugging stages.

A variety of cleaning techniques can be used, including vapor degreasing and alkaline etching, with the choice often depending on the specific material of the workpiece and the depth of machining required. However, cleaning becomes especially challenging when dealing with porous materials, as contaminants can be trapped within their structure.

In general, cleaning methods fall into two broad categories: mechanical and chemical. Of these, chemical cleaning is often preferred because it is gentler on the workpiece and reduces the risk of damage compared to mechanical approaches.

The condition and thickness of the masking layer also influence the cleaning process. When a mask is either particularly thin or has undergone chemical cleaning, the cleaned areas tend to become more refined. Additionally, applying heat during the cleaning process can further improve its effectiveness.

2. Masking

Masking plays a crucial role in the chemical machining process. Essentially, masks are protective coatings applied to those areas of a workpiece that must remain untouched during machining. What makes these masks suitable is their inert nature—they do not interact with, or degrade due to, the chemicals involved. For efficiency and practicality, it’s important to select a mask that can be removed easily once the process is complete.

The way masking works is fairly straightforward. Before machining begins, the technician applies the mask to the sections of the material that need to be protected, leaving the areas to be machined exposed. This ensures that only the unmasked regions come into contact with the chemical etchants. Sometimes, the entire workpiece may be masked first, and then specific areas are selectively unmasked to create the desired pattern or design.

There are three common techniques for applying these masks:

1. Cut and Peel Method: This involves covering the entire surface and then cutting away the mask from areas that need to be exposed.
2. Screen Method: In this approach, the mask is applied through a screen, much like screen printing, allowing for precise patterns.
3. Photoresist Method: This technique uses light-sensitive materials to create highly detailed masks, often used when intricate designs are needed.

Each method has its own advantages, and the choice depends on the specific requirements of the machining task.

3. Scribing

Once the masking process is complete, the material intended for machining is uncovered, allowing the targeted section of the workpiece to undergo the desired chemical reaction.

Following scribing, only the specific areas designated for machining remain exposed. These sections are then subjected to the chemical machining process.

4. Etching

Once the workpiece has been filtered, it is placed into a container filled with a chemical agent designed to react with its surface. During immersion, the sections of the workpiece covered by a protective mask remain unaffected; only the exposed areas are subject to the chemical reaction. As a result, material is selectively removed from the unmasked regions.

Typically, the etching process is carried out at higher temperatures to enhance reaction efficiency. It is important to prevent gas bubbles from forming and becoming trapped on the workpiece surface, as this can lead to uneven material removal and compromise the uniformity of the final product.

5. Demasking

Once the etching process is complete, the masks are taken off from the non-mechanized regions of the workpiece. At the same time, the oxide layer is carefully removed from the mechanized areas of the workpiece.

6. Washing

Once the demasking stage is complete, the workpiece is carefully rinsed with clean water to ensure that any remaining residues or contaminants are fully washed away from its surface.

In addition to these main procedures, there is an optional step involving the adjustment of the etchant’s temperature. Depending on the requirements, the solution’s temperature in the container can be controlled by employing either a heating or cooling rod. This allows for precise temperature regulation as needed during the process.

Types of Chemical Machining Process

This process finds application across a diverse range of operations, including milling, blanking, and engraving. Chemical machining itself can be organized into several categories:

• Chemical Milling
• Chemical Blanking
• Chemical Engraving

In some specialized situations, reactive gases such as jets of chlorine are introduced directly into the machining zone. When this method is employed, it’s often referred to as gaseous chemical machining or hot chlorine machining. It proves especially useful for tasks like removing defects from metal components.

1. Chemical Milling

Chemical milling, also known as industrial etching, is a subtractive manufacturing method where materials are selectively removed by immersing them in carefully controlled chemical baths. These temperature-regulated solutions dissolve targeted areas, gradually shaping the workpiece into its intended form.

This process is referred to by several names, such as photo etching, chemical etching, photochemical etching, and photochemical machining. While metals are the most common materials involved, the technique has been adapted to work with a growing variety of other substrates as well.

The origins of chemical milling can be traced back to the Renaissance, when craftspeople sought alternatives to metal engraving for decorating armor and producing printing plates. They developed etching methods that eventually evolved into the industrial practices used today.

At its core, chemical milling relies on exposing select areas of a material to an etchant—a reactive chemical that dissolves those regions. To preserve the rest of the workpiece, maskants (materials resistant to the etchant) are applied as protective barriers, allowing only the desired areas to be affected during processing.

Applications

Etching plays a crucial role across several high-tech industries. In the realms of printed circuit board production and semiconductor manufacturing, it serves as a fundamental process. The aerospace sector also relies on etching, particularly for removing thin surface layers from substantial components like aircraft structures, missile panels, and extruded elements used in airframes.

Beyond these applications, etching is a standard technique in the fabrication of integrated circuits and microelectromechanical systems. While traditional liquid-based etching remains in use, plasma etching has become especially common within the semiconductor industry, offering greater precision and control for complex designs.

2. Chemical Blanking

Chemical blankets, chemical blanking, photo-making, photo vibration, and photochemical etching all fall under the broader category of chemical milling. In essence, these processes involve selectively removing material from specific areas using chemical reactions.

Typically, this technique is reserved for sheets and foils, and it works well with a wide range of metals. That said, it isn’t suitable for thinning materials thicker than about 2 mm—so that’s something to keep in mind if you’re choosing a method.

The first step is always thorough cleaning. The workpiece is washed with either acid or alkali to ensure a clean surface, then dried. After that, a photoresist—essentially a protective layer—is applied by dipping, whirl coating, or spraying, depending on what’s most practical for the situation.

Once coated, the workpiece is dried and the photoresist is cured. Photographic techniques come into play here: using special materials, a light-sensitive image is created in the photoresist. These masks only react to specific wavelengths, typically ultraviolet, rather than ordinary room light. At this point, the surface is exposed to light through a negative, much like how you’d develop a photographic print based on a particular design.

After exposure, the next step is developing the image. During this stage, the areas that aren’t protected by the image in the photoresist become exposed, revealing the bare metal underneath.

The prepared workpiece is then placed in equipment where it’s either sprayed with the etching chemicals or immersed in a slurry. The choice of etchant depends on the metal—hydrofluoric acid, for instance, is used for titanium, but there are many other options for different materials.

Within a span of one to fifteen minutes, the exposed metal is dissolved away, leaving behind the intended pattern or structure. Once etching is complete, any residue—sometimes referred to as “ashes”—is quickly removed, and the finished piece is ready.

3. Chemical Engraving

Photoresist maskants are commonly used to chemically blank printed circuit boards, perform various engraving tasks, and create intricate cuttings. This method is especially effective for working with extremely thin metals, down to about 0.005 mm, allowing for precise shaping.

It is possible to achieve accuracy within ±0.015 mm, which is particularly valuable for applications requiring tight tolerances. When automated photographic processes are employed, production rates can be significantly increased, making this approach efficient for large-scale manufacturing.

Application of Chemical Machining

• Chemical machining (CHM) is commonly employed in situations where precise control over the depth of metal removal is essential, often down to just a few microns, and where maintaining tight tolerances is critical.
• The process is known for delivering surface finishes typically between 0.5 and 2 microns, which meets the demands of many high-precision applications.
• Notably, CHM can selectively remove metal from specific areas rather than the entire surface, making it particularly useful for components with complex or irregular shapes—such as forgings, castings, extrusions, or formed wrought stock.
• A key advantage of chemical machining lies in its ability to produce intricate stampings that are free from burrs, which is highly valued in industries where clean and precise edges are non-negotiable.

Advantages and Disadvantages of Chemical Machining

• One of the main advantages of this process is that it preserves the integrity of the workpiece—it doesn’t cause distortion or create burrs. It’s also remarkably effective when dealing with materials that are typically challenging to machine.
• On the other hand, the process is relatively slow. Because of this, it’s generally not the preferred choice for producing large volumes or for working with materials thicker than 2 mm.
• In practice, some small parts are manufactured in batches of 10 to 100 on a single plate. This approach helps offset the slower pace and makes production more efficient.

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