The advantages of precise electrochemical machining of cemented carbides

April 17, 2024

3:05 PM

Annabelle von Ritter zu Groenesteyn, social media manager, and Christopher Wacht, project engineer, PEMTec

Advanced technologies and precision engineering are synonymous in terms of their continually having to adapt to meet the evolving requirements of various industries. Among the advanced technologies having a significant impact in precision engineering is precise electrochemical machining (PECM). This article explores the fundamental principles of PECM, its ability to overcome the challenges of working with cemented carbides and the many advantages it affords across various applications, particularly those involving cemented carbides.

An overview of PECM

To comprehend the advantages of PECM of cemented carbides, it is crucial to grasp the fundamental principles that underpin this machining technology. In contrast to conventional machining technologies, PECM, an advanced form of classical electrochemical machining (ECM), enables the precise and contact-free machining of intricate shapes in hard-to-machine materials without introducing mechanical or thermal stress^1-5.

At its core, PECM involves the interaction between a negatively polarised tool electrode (cathode) and a positively polarised workpiece (anode), with an electrically conductive electrolyte solution, typically an aqueous solution of sodium nitrate, filling the gap between them. In this process, material is anodically removed from the workpiece, mirroring the negative shape of the electrode, as shown in figure 1. The key to precision in PECM lies in its controlled short current pulses, a synchronised oscillating tool electrode and an extremely narrow machining gap, typically around 20 µm (0.00078 inches).

Figure 1: A precise electrochemical machining (PECM) graphic.

The non-contact process allows high-precision and cost-effective manufacturing, all with minimal causing tool wear⁵. PECM excels in machining a broad range of materials, including superalloys, powder metallurgy (PM) steels and even materials with varying hardness. In essence, PECM provides a controlled and highly accurate means of material removal, making it ideal for applications where precision, intricate shapes and exceptional surface quality are paramount.

The complexities of machining cemented carbides

Cemented carbides, often referred to as hard metals, are celebrated for their extraordinary properties, such as high hardness and exceptional wear resistance, which make them a preferred choice for various applications. However, machining cemented carbides to meet the demands of precision engineering generally introduces a unique set of complexities.

Cemented carbides are known for their resilience, presenting challenges with conventional machining technologies due to their hardness. Achieving precision and high-quality surfaces while working with these hard metals can be a daunting task. The undesired consequences, especially caused by a high heat input, can range from a modified microstructure to a formation of micros that degrade the structural integrity of the workpiece. From a PECM perspective, it is important to note that machining cemented carbides can be intricate due to their heterogeneous composition of tungsten carbide and cobalt, which exhibit contrasting electrochemical behaviours⁶.

The challenges associated with machining cemented carbides using conventional machining technologies are multifaceted. These materials are abrasive and have the potential to quickly wear down cutting tools, necessitating frequent tool replacements and increasing production costs. Moreover, their brittleness can lead to sudden tool breakages, causing production disruptions and safety concerns.

Another critical challenge is the need for high dimensional accuracy. In applications where components must fit together with utmost precision, even the slightest deviation can be unacceptable. Conventional machining technologies often struggle to meet these requirements, especially for the machining of sophisticated geometries. Considering these challenges, the machining of cemented carbides calls for solutions that can maintain precision, surface quality and tool durability.

PECM of cemented carbides

PEMTec developed the PEM 3.1 SX CC PECM system, shown in figure 2, to cater for the complexities of machining cemented carbide parts.

Figure 2: PEMTec’s PEM 3.1 SX CC PECM system.

Key features of the PEM 3.1 SX CC include:

a versatile and robust software platform;
a free programmable axis;
a single oscillating tool electrode;
a newly developed electrolyte system;
a synchronised, ultra-short current pulse generator; and
an X, Y table.

PECM is an ideal solution for cemented carbides for a number of reasons. As is the case for ECM, neither hardness nor toughness of the material is relevant. Moreover, PECM, like ECM, preserves the material’s, and therefore the workpiece’s, structural integrity. Unlike conventional machining technologies that might introduce mechanical or thermal stress, PECM is non-contact and non-thermal, thus ensuring that the final product remains free from undesirable microcracks, melted layers or other structural compromises.

PECM also delivers levels of precision and surface quality that are often not achievable using ECM or conventional machining technologies. Precision is paramount in the machining of cemented carbides, since the smallest deviation can have a significant impact. Electrical discharge machining (EDM) typically requires the use of numerous electrodes to manufacture precise components, but PECM requires just one electrode that can be reused multiple times, achieves higher precision and, moreover, makes manual repolishing of the processed parts superfluous, as shown in figure 3.

Fig 3 roughness measurement PEM-Punch series.png

Figure 3: This graph shows the roughness and repeatability measured on 10 precise electrochemically machined punches.

Since PECM is non-contact and uses just one electrode, it also reduces the risk of tool wear, prolonging tool life and minimising production interruptions due to tool replacement.

Additionally, PECM delivers greater speeds than EDM in precision applications.

PECM applications

There are various PECM applications, as outlined below and shown in figures 4 to 9.

Punches for cutting tool inserts

The PEM 3.1 SX CC is used by PEMTec to produce punches, crafted from a sub-micron grade cemented carbide containing 13 percent cobalt, for processing cutting tool inserts, as shown in figures 4 and 5. The system achieves a machining speed of up to 150 µm/min, an Ra (surface finish) value of 0.05 µm and an Rz (surface roughness) value of 0.30 µm. This level of precision ensures that cutting inserts meet the uncompromising demands of industries.

1 of 6

Figure 4: A precise electrochemically machined punch series.

2 of 6

Figure 5: A precise electrochemically machined punch for processing cutting inserts. Material: 12-13 percent cobalt, sub-micron WC grain size; machining depth: 0.8 mm; machining time: 1h 30 min; Ra: 0.05 µm, Rz: 0.30 µm.

3 of 6

Figure 6: A precise electrochemically machined punch with a honeycomb structure.Material: powder metallurgical (PM) steel; machining depth: 3.2 mm; machining time: 100 min; Ra: 0.3 µm.

4 of 6

Figure 7: A precise electrochemically machined spur gearing.Material: 1.4034 stainless steel; machining depth: 1.7 mm; machining time: 8 min (4-fold processing, 2 min per part); Ra: 0.15 µm.

5 of 6

Figure 8: A precise electrochemically machined guiding vane.Material: Inconel 718; machining depth: 21.7 mm; machining time: 48 min; Ra: 0.64 µm.

6 of 6

Figure 9: A precise electrochemically machined gear.Material: 1.4301 stainless steel and SMC435 (a chromium-molybdenum through-hardening steel of medium hardenability); machining depth: 1.58 mm; machining time: 6 min; Ra: 0.086 µm.

Aerospace components

In the aerospace industry, precision is the foundation of safety and performance. PECM enables the machining of critical components made from cemented carbides and other special materials. The non-contact, non-thermal nature of PECM ensures that these components afford the required structural integrity and exacting surface finishes.

Automotive components and products

The automotive industry uses PECM for a spectrum of applications, from crafting high-performance engine components to manufacturing advanced sensors. The technology’s efficiency and precision streamline processes, resulting in cost savings and elevated product quality.

These practical applications underline the advantages of PECM of cemented carbides. The technology's exceptional precision means it is able to meet the exacting demands of various industries.

A summary of the advantages of PECM of cemented carbides

In the domain of cemented carbide machining, PECM is impacting working with cement carbides across diverse industries on account of the advantages summarised below.

Precision—PECM has a machining gap of just a few micrometres and delivers precision of ±5 µm and lower. This level of precision is critical when working with cemented carbides, where even the smallest deviation can compromise the quality and functionality of the final product.
Surface quality—PECM consistently delivers exceptional surface finishes, reaching surface roughness values as low as Ra 0.03 µm. This level of quality ensures that components meet stringent industry standards, particularly in fields such as precision tooling and cutting insert manufacturing.
Material integrity preservation—Perhaps one of PECM’s most significant advantages is its ability to preserve the integrity of the workpiece. Conventional machining technologies can introduce mechanical or thermal stress, resulting in microcracks and structural compromises. PECM operates in a non-contact, non-thermal manner, ensuring the material remains structurally sound.
Extended tool life—In the world of machining, tool wear is a constant challenge. PECM addresses this by minimising tool wear due to its non-contact nature. The extended lifetime of the electrode tool reduces production interruptions and tool replacement costs.
Single-step processing—PECM streamlines the manufacturing process by performing roughing, finishing and polishing in a single step. This efficiency reduces the need for multiple machining stages, leading to shorter production cycles and cost savings.
High imaging accuracy—The ability to accurately replicate complex shapes and microstructures is another hallmark of PECM. Due to the precision afforded by the process, intricate parts with an exceptionally high degree of accuracy can be manufactured.

Conclusion

PECM’s exceptional precision, non-contact methodology and versatility have benefited industries including automotive, aerospace and medical. The highlighted case study on punches for cutting tool inserts showcases the technology’s capabilities, i.e., the delivery of exceptional Ra values as well as high imaging accuracy.

The future of PECM looks promising, as ongoing development, broader application and sustainability efforts mean it is poised to have an even more significant impact on precision engineering.

PEMTechttps://pemtec.de/en

References¹Schubert, A., Meichsner, G., Hackert-Oschätzchen, M., Zinecker, M. and Edelmann, J. (2012). Precise electrochemical machining of powder metallurgical steels. Galvanotechnik, volume 103, pp.710–715.²Meichsner, G., Hackert-Oschätzchen, M., Krönert, M., Edelmann, J., Schubert, A. and Putz, M. (2016). Fast determination of the material removal characteristics in pulsed electrochemical machining. Procedia CIRP, volume 46, pp.123–126.

³Mankeekar, T., Bähre, D., Durneata, D., Hall, T., Lilischkis, R., Natter, H. and Saumer, M. (2021). Fabrication of micro-structured tools for the production of curved metal surfaces by pulsed electrochemical machining. The International Journal of Advanced Manufacturing Technology, volume 119, pp.2825–2833.

⁴Hall, T., Adam, B., Busch, R. and Bähre, D. (2022). Pulse electrochemical machining of bulk metallic glasses. Proceedings of the 18thInternational Symposium on Electrochemical Machining Technology, Tokyo (Japan), November 14–15, 2022, pp. 71–76.

⁵Ghasemiansafaei, M., Schaefer, F., Hall, T. and Baehre, D. (2023). Analysis of mechanisms affecting the tool in pulsed electrochemical machining. Journal of The Electrochemical Society, volume 170, number 6, article number 063504.

⁶Steuer, P., Weber, O. and Bähre, D. (2015). Structuring of wear-affected copper electrodes for electrical discharge machining using pulse electrochemical machining. Int. Journal of Refractory Metals and Hard Materials, volume 52, pp.85–89.