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  • Writer's pictureKirk Abolafia

Tool Wear, Repeatability, and the Scalability of PECM

Tool wear can be a significant hinderance to production efficiency for a variety of high-volume manufacturers. In this article, we will explain exactly how tool wear burdens manufacturers and how Voxel's unique PECM process can avoid many of these challenges altogether, enabling better production efficiency.


Interested in learning more? Consider reading our collaborative article with KUKA Robotics, detailing our high-volume PECM process in action.


 

Manufacturers are always considering new, innovative ways to reduce production costs.  Some of the most lucrative opportunities to reduce costs are within high-volume manufacturing, as relatively minute optimization improvements today can accumulate into significant savings tomorrow. At the core of high-volume optimization, manufacturers must produce larger quantities of identical parts while reducing the energy, materials, time and labor necessary to produce them. 

Among the most efficient means to optimize production can be found in the machining process itself, as the drawbacks of tool wear are the source of many engineering and financial challenges for manufacturers. Conventional, contact-based material removal processes used by most manufacturers have largely been unable to avoid tool wear, impeding their scalability and production efficiency--especially for high-volume work.


Fortunately, Voxel’s pulsed electrochemical machining (PECM) process is a completely non-contact, non-thermal material removal process, and--under the right circumstances--can be capable of significantly reducing production costs and improving production efficiency for a variety of high-volume parts by either significantly reducing or outright eliminating the negative impacts associated with tool wear.  


Robotic equipment on PECM production line
PECM is a process with little tool wear and high repeatability, ideal for an automated production line such as Voxel's.

In this article, we’ll explain:  

  • Why tool wear is such a significant burden for manufacturers  

  • How PECM mitigates tool wear at the molecular level, and finally, 

  • What PECM’s lack of tool wear and high scalability can do for manufacturers  


 

Tool Wear: A High-Volume Burden  

Many manufacturing technologies inherently require contact between the tool and workpiece to remove material—making tool wear practically unavoidable for most manufacturers. Even relatively minute tool wear can impair a high-volume production operation’s costs and efficiency in a variety of ways, especially with tight-tolerance parts.  

For one, tool wear impacts the precision capabilities of machining processes over time. As the tool is worn down, irregularities on the tool’s surface can create uneven and distorted areas on the workpiece. For example, a tool with even minimal wear attempting to drill a high aspect-ratio hole can still distort the hole’s straightness. This tool can also create burrs or other surface irregularities, on the workpiece surface. 

Surface irregularities from a worn tool are especially problematic on parts serving critical industries. For example, poor surface quality on an implanted orthopedic device can release cytotoxic materials in the patient’s bloodstream over time, and a rougher surface on a turbine blade can create unwanted roughness, reducing fuel efficiency.  

The second issue with tool wear is that a worn tool reduces production speed. A worn tool may still be capable of producing a part with adequate tolerances (using tool wear compensation measurements) , but will reduce the cutting efficiency, adding load and deflection forces on the spindle. —This means more energy expended or additional labor and overhead costs to accommodate the additional time spent.  

Finally, the cost of tool replacement in and of itself can be significant. For low-volume, rapid-prototyping work, tool costs can be a rather negligible expense for manufacturers compared to setup, overhead, and labor costs. However, tool replacement costs can become significant when manufacturers are tasked with producing high quantities of parts— primarily, the cost of the tool itself and the time required to replace it. Furthermore, both the rate of tool wear and the costs of the tools themselves increases dramatically when machining tough-to-machine materials like nickel superalloys.    

No Tool Wear At The Molecular Level 

As opposed to conventional, contact-based machining, Voxel’s pulsed electrochemical machining (PECM) process is unique in that it incurs almost no tool wear—In PECM, the tool is able to remove the workpiece material without contacting it (alongside a variety of other benefits you can read about here). PECM, therefore, circumvents many of the aforementioned disadvantages of tool wear.  


But how exactly is this lack of tool wear achieved? This phenomenon can only be adequately explained by examining PECM on an atomic level.  


[Note: we recommend first reading this introductory article to PECM if you are unfamiliar with how the process works].  


Simplified, ECM’s material removal method can be loosely equated to a kind of “hyper-oxidation" that removes the workpiece surface-atom-by-atom with electrochemistry. The electrical current facilitates an imbalance of electrons between the positive anode (workpiece) and negative cathode (tool) that must be corrected via Coulomb’s law, which states that two of the same charged particles repel, while opposite charged particles will be attracted to one another. Surplus ions are, therefore, removed from the anode surface atom-by-atom.  


Demonstration of electrochemical process
The primary byproducts of the electrochemical reaction are metal hydroxides and hydrogen gas.


Voxel’s proprietary process is a unique combination of cathode design, material, and current density that allows these hydroxides to remain in the electrolytic fluid rather than be deposited on the surface of the tool, as may be expected in other electrochemical processes. This electrolytic fluid serves as both the medium for the ion exchange, as well as a flushing agent that removes waste products (primarily the metal hydroxides). 


Additionally, PECM utilizes Faraday’s Law, which posits that chemical reactions occur fastest where the current density is highest, as a means to control this electrochemical reaction to develop a specific geometry on the anode. This is why in PECM the cathode (tool) is always shaped as the inverse of the desired geometry of the workpiece and is also responsible for how PECM is capable of machining such tight tolerances.  

 

PECM & Scalability   

PECM can, therefore, attribute its high scalability to two distinct causes.   


For one, its lack of tool wear (down to the molecular level) makes it especially well-suited for a  fully-automated ECM production line, as a single tool can produce thousands (or potentially tens of thousands) of identical parts without incurring tool replacement costs or affecting part tolerances. This also means that the process requires less overall supervision-- ideal for an automated production line.  


Secondly, PECM’s ability to customize its tooling can also improve the process’s scalability, as a custom tool can parallel machine features of a single part in-tandem without incurring additional machining costs (aside from the resources needed to produce the tool itself and additional amperage).  


This second point can be seen, for instance, when PECM is tasked to machine microchannel heat exchangers, as these critical parts often have repeating feature patterns or high quantifies of features in the same vector to maximize heat transfer capabilities. As opposed to a conventional machining process machining one channel at a time, PECM is capable of machining tens or even hundreds of slots at a time with a custom tool, improving production throughput and thereby reducing costs for manufacturers.   


Microchannel features on heat exchanger
The lack of tool wear allows PECM to produce multiple features in-tandem, such as these complex heat exchanger profiles.


For many manufacturers, tool wear is a seemingly inevitable obstacle, as a worn tool can incur a variety of costs associated with lower cutting speeds, lower part resolution, and the replacement of the tool itself.  Unlike conventional processes, however, PECM is capable of producing high-volume parts without incurring significant tool wear, as the electrochemical reaction itself requires no contact, or heat, to remove material. PECM’s lack of tool wear makes it especially suitable for an automated production line, and its custom-tooling properties make it especially valuable for high-volume parts that have repeating features, such as certain heat exchangers. 

This article highlights one of many benefits of PECM. To learn more about PECM’s scalability, surface finishing capabilities, and its ability to machine some of the toughest metals with ease, see our education portal.  

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