While manufacturers continue to develop new advanced materials and innovative part designs to maximize efficiency and performance of critical components, the machining processes for manufacturing This cutting-edge division isn’t necessarily catching up. However, new advanced machining methods use completely different resources to form metal parts. One such machining process known as pulse electrochemical machining (PECM) uses the principles of electrochemistry for machine parts.
Image credit: Voxel Innovations
Recent manufacturing innovations include miniaturization of critical components, continued rollout of additive manufacturing, and increased deployment of advanced materials such as metal matrix composites, metallic glass bulk and super alloy1. These improvements directly benefit manufacturers, however, their progress is being hampered by conventional manufacturing processes due to high costs, inadequate machinability/finishing. and inability to efficiently produce large volumes of parts2.
Challenges create innovation — and one of the advanced manufacturing processes that aim to alleviate some of these is called pulse electrochemical machining (PECM). In this article, we will describe the exact need for PECM technology and its benefits and shortcomings.
Outstanding problems in advanced manufacturing
In aerospace manufacturing, power generation, and medical imaging, critical components in these fields will continue to require materials that are both lightweight and able to withstand extreme temperature fluctuations. This is a direct response to the growing requirements for fuel efficiency and energy density. These temperature fluctuations can be as high as 1700°C (3000°F) heat in jet engines3, or 800°C (~1500°F) and 20MPa (~3000psi) in super CO2 heat exchangers critical and as low as 4°K (-269°C or -452°F) in pulse tube chillers. Materials with these capabilities still exist today — for example, some nickel superalloys and metal matrix composites — but these advanced materials come with a price tag. In particular, the abrasive, brittle qualities of these materials are difficult for conventional machining processes to produce efficiently without incurring great costs.
Part miniaturization is another major goal for engineers and designers in the manufacturing sector, especially in aerospace and medical devices. There are three driving factors that affect most industries. First, miniaturization reduces the amount and material required, which is especially important considering the high cost of many advanced materials and the effect of weight on efficiency in many applications. Second, miniaturization can improve the appearance, fit, and function of critical components, as miniaturization of key parts provides more room for other components. This is especially common in robotic surgical tools, where smaller devices lead to less invasive surgeries. Third, by reducing the resources required to fabricate the part, miniaturization can reduce fabrication time4.
Additive manufacturing (AM) is another example of manufacturing innovation that presents both advantages and challenges for manufacturers. There are several unique advantages of AM that are worth mentioning. First, AM has the potential to significantly reduce material waste compared to conventional “minus” processes5. Another inherent advantage of AM is its ability to be used for rapid turnaround during design iterations, allowing engineers to modify part prototypes with greater efficiency.
However, the limitations of AM are becoming increasingly apparent as the technology continues to advance across many industries. For example, AM is not capable of producing specific part features, such as super surface finishes and thin wall features, especially on down skin surfaces6. AM is usually limited to a surface quality Ra of about 5-60µm and a wall thickness of 0.6mm – acceptable for many non-critical parts, but AM alone is not sufficient for critical parts such as gas turbine blades or orthopedic devices. AM is also largely incapable of producing high-volume parts at an affordable cost comparable to conventional manufacturing processes (such as pressing, metal casting).
These shortcomings therefore require an advanced machining method that can simultaneously produce small features, super-finished surfaces, and high part volumes for advanced materials that are difficult to machine. One such solution is a unique technology known as pulse electrochemical machining, also known as PECM7 and being applied to medical, aerospace, energy and industrial applications.
What is PECM and how does it work?
PECM is an advanced material removal method that uses electrochemistry to machine a part, as opposed to conventional methods that use friction and/or heat. There are four main components of PECM:
Cathode: Also known as an instrument, it is manufactured specifically for each application. Usually, the cathode is the inverse of the desired shape of the workpiece.
Anode: Also known as ingot, is the final material that is dissolved to form the desired shape. The anode can be in the form of a quasi-grid, a conventionally machined part, an additionally manufactured part or raw material in the form of a plate or bar.
Electrolyte liquid: This liquid, usually a salt-formed electrolyte, is discharged between the cathode and anode, serving two purposes simultaneously. First, the electrolyte acts as a catalyst for the electric current, facilitating the electrochemical reaction. Second, the liquid washes away process by-products, including metal hydroxides of dissolved metals.
Gap: Known as electrode gap (IEG), this is the space between the cathode and anode through which the electrolyte liquid flows. This distance is a significant factor in the efficiency of the electrochemical process; PECM uses gap sizes from 10 to 100 µm (.0004 to .004”) and allows for machining much smaller features than conventional ECM methods.
Advantages and disadvantages of PECM
PECM has a number of distinct advantages that, in general, are not offered by any other conventional manufacturing process. However, PECM also has important disadvantages.
PECM can process a wide range of advanced materials, but has limitations. Since PECM does not rely on friction or heat to machine the workpiece, the toughness of that material is not a factor. Instead, the chemistry and electrical conductivity of the part are the key factors that determine the feasibility of PECM – offering both important advantages and significant disadvantages.
While the different toughness of metals such as aluminum and Inconel results in a significant difference in conventional CNC milling speeds, the distance between their conductivity is much smaller, thus allowing PECM to machine large parts. metals of different toughness with the same speed and capacity. This is particularly advantageous for industries that require difficult to fabricate materials to fabricate in high volumes, some examples include nitinol orthopedic devices and nickel superalloy components in jet engines. propeller.
However, relying on electrochemistry presents important material limitations. PECM can only process conductive materials; Non-conductive materials such as polymers and ceramics cannot be machined with PECM. In addition, some refractory metals and valves can be difficult to machine electrochemically, although some companies have made recent advances in these materials.
PECM can machine unique features with relative efficiency, but is not as competitive when tasked with machining simplified geometries. Electrochemical machining enables precise part features and low tolerances comparable to conventional machining processes. For example, PECM can machine thin-walled features, down to <0.075mm or <0.003″ with an aspect ratio of 20:1. This is because PECM has no friction or heat does not generate tool vibrations. or heat-affected areas, allowing for machining certain features that may be sensitive to vibrations or thermal distortion. Another inherent advantage of PECM is the ability to machine and finish parts parallel to each other; produces surface quality down to 0.005-.4µm Ra (0.2-16 µin Ra) without any secondary or post-processing required.
These qualities give PECM a distinct advantage when machining parts with complex shapes. However, more conventional processes may be more suitable for machining a part with simpler features. For example, CNC milling may be a more efficient process for machining larger features in a part, while processes such as laser cutting or photochemical etching may be more ideal than PECM for machining large parts. simpler 2D configuration. The applicability of PECM is therefore specific to industries, materials and part geometries.
PECM can significantly reduce production costs but requires high upfront costs. PECM is capable of manufacturing thousands of identical parts with <10µm repeatability, since the electrochemical process does not wear out the tool. For projects that require part volumes in the tens or hundreds of thousands to millions, PECM can significantly reduce manufacturing costs in a number of ways. First, PECM is uniquely scalable, and multiple parts or surfaces can be run simultaneously to increase throughput. Second, reduce costs by significantly reducing tool replacement costs and eliminating post-processing steps.
However, fabricating cathode and fixture for a particular application is an iterative process that requires considerable technical expertise and results in significant upfront costs for manufacturers. For jobs that require quick turnaround and/or lower part volumes, investing in PECM would simply make sense until part volume increases — depending on the application, there is can be tens of thousands of parts.
PECM arose from the need of manufacturers to produce larger volumes of critical components with small features and super surface finishes in a more efficient manner. However, manufacturers should also consider the various limitations of electrochemical machining, including its affordability and other limitations, such as its exclusivity to conductive materials. .
Story source
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Selection link: https://www.voxelinnovations.
Author’s biography
Kirk Gino Abolafia is the technical marketing director of Voxel Innovations, a company that develops PECM processes and manufactures parts as a contract manufacturer.
