What is Chemical Machining?
Chemical Machining is the clean removal of metal from pre-described areas without altering the integrity or properties of the metal by means of a photochemical process. This process is primarily used in creating small thin metal parts of the complex design with no burns or stresses to the parts.
Chemical Machining is the clean removal of metal from pre-described areas without altering the integrity or properties of the metal by means of a photochemical process. This process is primarily used in creating small thin metal parts of the complex design with no burns or stresses to the parts.
The process starts by cleaning the dirt and oils from the metal. A photoresist is applied and baked to assure an even application. The artwork is then placed over the prepared sheet of metal and exposed to ultra-violet light, resulting in the desired resolution and etch specs.
The artwork is removed and the resist is ready to be developed or removed. At this point, the metal is ready to be etched by submerging the sheet in a chemical solution that dissolves all the material that is not integral to the part. After the etching is completed, the resist is removed and the metal parts are cleaned, inspected, and packaged.
Chemical Machining Process
Different processes of chemical machining are givens below:
1. Cleaning
In the cleaning process, the workpieces are cleaned to remove oil, grease, dust, or any substance from the workpiece so that further processing can be completed properly.
Cleanings are necessary to ensure proper adhesion of masking material to the workpiece. In the case of masking debugging, stray Etching occurs.
Various types of cleaning processes such as vapor degradation, alkaline Etching, etc., like maskants, are carried out depending on the work material and the required machining depth. Cleaning porous workpiece material is difficult.
There are mainly two methods of cleanings, mechanical & chemical methods. The chemical method is widely used because it causes much less damage than the mechanical method.
If the masked is thicker and thinner and chemically cleaned, then the thinner or cleaned parts of the masked are refined. Heating the cleaning process is helpful.
2. Masking
Masking is done using masking. These masks are inert in nature and do not react with the chemicals used in the machining process. The masked to be used should be an easy stripe mask.
In this masking process, the parts of the workpiece that are not machined are masked using a mask so that the machined part is exposed to the chemical used in the machining process. But when the masking process is performed, the entire workpiece is masked.
Masks are applied to any of the three methods below:
- Cut and peel method.
- Screen method.
- Photoresist method.
3. Scribing
After the masking process, masking is performed to remove from the area of the workpiece that is to be mechanized so that a chemical reaction can occur on that part of the workpiece. After the scribe process, only those areas that are to be mechanized are exposed to chemical machining.
4. Etching
After filtering the workpiece, it is immersed in a container containing a chemical that undergoes a chemical reaction with the workpiece.
When the workpiece is immersed inside the chemical, the area that is masked does not undergo any chemical reaction, and the area that is not masked undergoes a chemical reaction with the chemical and the material unmasked area of the workpiece. I will start moving away from it.
The etching process is usually performed at an elevated temperature. Gas bubbles should not be allowed to become trapped during the process to avoid non-uniform machining.
5. Demasking
After the etching process, the masks are removed from the area of the workpiece, which is not mechanized, and the oxide layer is also removed from the area of the workpiece, which is mechanized.
6. Washing
After the demasking process, the workpiece is thoroughly rinsed under fresh water to completely remove any substances, etc., from the surface of the workpiece.
Apart from all these steps, one step is used optionally, which is the Etchant of heating and cooling: – According to the temperature, the temperature of the waiter is maintained in the container using a heating or cooling rod.
Types of Chemical Machining Process
The process can be applied to a wide variety of operations such as milling, blanking, and engraving. The various chemical machining processes can be classified as follows:
- Chemical Milling
- Chemical Blanking
- Chemical Engraving
Chemical machining for some specials purposes can also be achieved by using reactive gases, e.g., jets of chlorine, in the machining area. This is known as gaseous chemical machining or hot chlorine machining and can be used for debugging metal parts.
1. Chemical Milling
Chemical milling or industrial etching is the subtractive manufacturing process of using baths of temperature-regulated etching chemicals to remove material to create an object with the desired shape.
Other names for chemical etching include photo etching, chemical etching, photochemical etching, and photochemical machining. It is mostly used on metals, though other materials are increasingly important. It was developed from armor-decorating and printing etching processes developed during the Renaissance as alternatives to engraving on metal.
The process essentially involves bathing the cutting areas in a corrosive chemical known as an etchant, which reacts with the material in the area to be cut and causes the solid material to be dissolved; inert substances known as maskants are used to protect specific areas of the material as resists.
Applications
Etching has applications in the printed circuit board and semiconductor fabrication industries. It is also used in the aerospace industry to remove shallow layers of material from large aircraft components, missile skin panels, and extruded parts for airframes.
Etching is used widely to manufacture integrated circuits and Microelectromechanical systems. In addition to the standard, liquid-based techniques, the semiconductor industry commonly uses plasma etching.
2. Chemical Blanking
Chemical blankets, chemical blanking, photo-making, photo vibration, or photochemical etching are variations of chemical milling. In this process, the materials are completely removed from many areas by chemical action.
This process is mainly used on their sheets and foils. Almost any metals can be worked by this process; however, it is not recommended for thinning of materials more than 2 mm.
The workpiece is cleaned, reduced, and selected by acid or alkali. The cleaned metal is dried, and the photoresist material is applied to the workpiece by dipping, whirl coating, or spraying. It is then dried and cured. Photography materials have been used to produce degradation-resistant images in photoresist materials.
This type of mask is sensitive to light of a particular frequency, ultraviolet light in general, and not to room light. This surface is now exposed to light through a negative, namely, a photographic plate of the required design, as in developing drawings. After exposure, the image is developed. Unexpected parts break apart during the developing process showing bare metal.
The metal used is kept in a machine, which is sprayed with chemical substances or is added to the slurry. The etching solution can be hydrofluoric acid (for titanium) or one of many other chemicals. After 1 to 15 minutes, the unwanted metal has been ingested, and the finished portion is ready to remove the ashes immediately.
3. Chemical Engraving
Printed circuit cards, other engraving operations, and cuttings of complex designs can be chemically blanked using photoresist maskants.
- Very thin metals (0.005 mm) can be dug well.
- High accuracy of the orders of +0.015 mm can be maintained.
- High production rates can be accomplished using an automated photographic technique.
Application of Chemical Machining
- CHM has been applied in a number of usages where the depth of metal removal is crucial to a few microns, and the tolerances are close.
- The surface finish obtained in the process is in the range of 0.5 to 2 microns.
- Besides, it removes metal from a portion of the entire surface of formed or irregularly shaped parts such as forgings, castings, extrusions or formed wrought stock.
- One of the major applications of chemical machining is in the manufacture of burr-free, intricate stampings.
Advantages and Disadvantages of Chemical Machining
- The advantages are that this process does not distort the workpiece, does not produce burrs, and can easily be used on the most difficult-to-machine materials.
- However, the process is slow, and thus it is not usually used to produce large quantities or to machine material thicker than 2 mm.
- Some small parts are made 10 to 100 at a time on a single plate, which speeds up production.
