Daily Archives: October 31, 2022

What is Pulsed Electrochemical Machining?

With pulsed electrochemical machining, it is possible to achieve high-repeatability production parts. This advanced process is a completely non-thermal and non-contact material removal process. It is capable of forming small features and high-quality surfaces.

Although its fundamentals remain the same as electromechanical machining or ECM, the variant, PECM or the pulsed electrochemical machining process is newer and more precise, using a pulsed power supply. Similar to other machining processes, like EDM and more, there is no contact between the tool and the workpiece. Material very close to the tool dissolves by an electrochemical process and the flowing electrolyte washes away the by-products. The remaining part takes on a shape like an inverse of the tool.

The PECM process has some key terms that it uses routinely. The first is the cathode—representing the tool in the process. Other names for the cathode are tool and electrode. Typically, its manufacturing is specific for each application and its design is the inverse of the shape the process wants to achieve.

The second is the anode—it refers to the workpiece or the material that the process works on. Therefore, the anode can assume many forms. This can include a cast piece of near net shape, wrought stock, an additively manufactured or 3D printed part, a part conventionally machined, and so on.

The third key item is the electrolyte—referring to the working fluid in the PECM process that flows between the cathode and the anode. Commonly a salt-based solution, the electrolyte serves two purposes. It allows electrical current to flow between the cathode and anode. It also flushes away the by-products of the electrochemical process such as hydroxides of the metals dissolved by the process.

The final key item is the gap—this is also the IEG or inter-electrode gap and is the space between the anode and the cathode. This space is an important part of the process, and it is necessary to maintain this gap during the machining process as the gap is a major contributor to the performance of the entire process. The PECM process allows gap sizes as small as 0.0004” to 0.004” (10 µm to 100 µm). This is the primary reason for PECM’s capability to resolve minuscule features in the final workpiece.

Compared to other manufacturing processes, pulsed electrochemical machining has some important advantages:

The pulsed electrochemical machining process of metal removal is unaffected by the hardness of the material it is removing. Moreover, the hardness also does not affect the speed of the process.

Being a non-thermal and non-contact process, PECM does not change the properties of the material on which it is working.

As it is a metal removal process using electrochemical means, it does not leave any burrs behind. In fact, many deburring processes use this method as a zero-risk method of machining to avoid burrs.

It is possible to achieve highly polished surfaces with the PECM process. For instance, surfaces of 0.2-8 µin Ra (0.005-0.2 µm Ra) are very common in a variety of materials.

Because of non-contact, there is no wear and tear in the cathode, and it has practically near-infinite tool life.

PECM can form an entire surface of a part at a time. The tool room can easily parallel it to manufacture multiple parts in a single operation.

The Battery of the Future — Sodium Ion

Currently, Lithium-ion batteries rule the roost. However, there are several disadvantages to this technology. The first is that Lithium is not an abundant material. Compared to this, Sodium is one of the most abundantly available materials on the earth, therefore it is cheap. That makes it the most prime promising candidate for new battery technology. So far, however, the limited performance of Sodium-ion batteries has not allowed them a large-scale integration into the industry.

PNNL, or the Pacific Northwest National Laboratory, of the Department of Energy, is about to turn the tides in favor of Sodium-ion technology. They are in the process of developing a Sodium-ion battery that has excelled in laboratory tests for extended longevity. By ingeniously changing the ingredients of the liquid core of the battery, they have been able to overcome the performance issues that have plagued this technology so far. They have described their findings in the journal Nature Energy, and it is a promising recipe for a battery type that may one day replace Lithium-ion.

According to the lead author of the team at PNNL, they have shown in principle that Sodium-ion battery technology can be long-lasting and environmentally friendly. And all this is due to the use of the right salt for the electrolyte.

Batteries require an electrolyte that helps in keeping the energy flowing. By dissolving salts in a solvent, the electrolyte forms charged ions that flow between the two electrodes. As time passes, the charged ions and electrochemical reactions helping to keep the energy flowing get slower, and the battery is unable to recharge anymore. In the present Sodium-ion battery technologies, this process was happening much faster than in Lithium-ion batteries of similar construction.

A battery loses its ability to charge itself through repeated cycles of charging and discharging. The new battery technology developed by PNNL can hold its ability to be charged far longer than the present Sodium-ion batteries can.

The team at PNNL approached the problem by first removing the liquid solution and the salt solution in it and replacing it with a new electrolyte recipe. Laboratory tests proved the design to be durable, being able to hold up to 90 percent of its cell capacity even after 300 cycles of charges and discharges. This is significantly higher than the present chemistry of Sodium-ion batteries available today.

The present chemistry of the Sodium-ion batteries causes the dissolution of the protective film on the anode or the negative electrode over time. The film allows Sodium ions to pass through while preserving the life of the battery, and therefore, quite significantly critical. The PNNL technology protects this film by stabilizing it. Additionally, the new electrolyte places an ultra-thin protective layer on the cathode or positive electrode, thereby helping to further contribute to the stability of the entire unit.

The new electrolyte that PNNL has developed for the Sodium-ion batteries is a natural fire-extinguishing solution. It also remains non-changing with temperature excursions, making the battery operable at high temperatures. The key to this feature is the ultra-thin protection layer the electrolyte forms on the anode. Once formed, the thin layer remains a durable cover, allowing the long cycle life of the battery.