EDM control system: Smooth surface finish and connectivity included

Nov 15, 2023

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With a wire machine it is all about producing sharp radii and smooth surfaces, especially on the interior of ejector pin holes. For mould maker BM Injection, that is exactly what the U32j from Makino has produced right from the start due to a combination of rigid machine build, thermal stability and the Hyper-i control.

Established over 30 years ago, mould maker BM Injection operates from a 10,000 square feet manufacturing facility in Whitchurch, UK. Out of every ten moulds produced, eight are used for on-site production of injection moulded plastic products for numerous sectors including aerospace, automotive, domestic appliance, sports, safety, optics and transportation.

Before it is complete and ready for use, every mould has to visit both a die-sink and a wire-cut electric discharge machine (EDM) as well as a machining centre for hard milling. The proportion of time spent on each machine varies. In the production of BM Injection's mould tools, unless any are hard-milled on an Okuma 3-axis machining centre on-site, all three production platforms used for manufacturing the moulds were built by Makino in Japan and supplied through sole UK agent NCMT.

Latest to be installed in May 2022 was a U32j wire EDM machine fitted with the same Hyper-i control system as a Makino Edaf 3 Heat EDM die-sinker that arrived in 2019, at the same time as a Makino D200Z 5-axis machining centre from the same Japanese source.

The Hyper-i Windows-based, twin-touch-screen CNC system, with an intuitive interface similar to that found on tablets and smartphones, includes advanced functions to support operators of all skill levels at every step of the machining process. The control contains an extensive library of cutting conditions that automatically optimises the erosion process, even for sealed and poor flush applications. It also enables easy access to and selection of power settings to produce accurate results in the fastest possible cycle times.

The control employs Hypercut technology, a process developed by Makino to produce surface finishes as fine as three microns Rz in standard tool steels in a three- or four-pass process. The machine ordered by Mark Combes, a director of BM Injection, was a high-accuracy package with 0.05-micron scale feedback capable of producing extremely smooth surfaces down to 0.7-micron Ra if a 7-pass process is adopted.

Of particular note is the bidirectional Hyperconnect Industry 4.0 network connectivity for remote machine monitoring and interlinking of all manufacturing information. This standard software allows access via the cloud to BM Injection's Open Mind Opticam wire EDM computer-aided manufacturing software. The CAD/CAM information occupies the top monitor of the twin-screen control and can be viewed and operated as if it were on-board, while Makino's process control screen occupies the lower monitor.

Another feature worthy of mention is the standard Crystal II machining functionality built into the Hyper-i control, which is effective for machining shapes that are hard to polish while enhancing surface finish for improved mould release. It requires no special insulated jigs and is performed with uncoated wire, Bedra brass wire of 0.25 mm diameter with a high zinc content being the standard consumable at the Whitchurch facility.

The U32j is capable of utilising wire down to 0.07 mm diameter, however, smaller than most machines are able to accommodate. There will be a need for smaller gauges and the accompanying diamond guides for the future production of BM Injection's optical industry moulds. Combes points to a reduction in wire consumption coupled with an increase in cutting speed on every job completed so far on the U32j compared with the nearly 20-year-old wire-cut EDM machine that was replaced.

He continued: "When the time came to install new, modern wire EDM technology, we looked at a number of options. We decided again in favour of the Makino offering not only because of the control and its synergy with our die-sink CNC system, but also due to the U32j's impressive working volume (370 x 270 x 220 mm) for the footprint (2,580 × 3,165 mm). We get a very compact machine while gaining an extra 20 mm of travel in X, Y and Z."

He was also impressed with the user-friendly, fixed-table, rise-and-fall tank design, which gives access on three sides for efficient loading and unloading of components and for easy cleaning and maintenance. Reliable unattended running is achieved throughout the night and into the next day, depending on the cycle, helped in part by the effective, automatic, jet-less wire rethreading system. It uses the X, Y, U and V axes to hunt unerringly for an optimum cutting restart position with the wire clear of the workpiece surface.

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Another effective technology from Makino is the Protech galvanic protection option, enabling the prevention of rusting and oxidation of steel, carbide and aluminium. By placing an electrode plate in the bottom of the tank and giving it a positive charge, ensuring that the workpiece is held at a negative potential constantly attracts the positive ions and prevents oxidation.

Combes summed up: "Makino is an excellent product but equally important to us is after-sales service. We have always received good back-up from NCMT ever since they delivered, installed and commissioned an Okuma 3-axis vertical machining centre in 2016."

Extensive product knowledge and being able to impart it to the operators during training is even more crucial with EDM technology. Unless parameters are kept within close limits, machining efficiency can fall off quite quickly. "It is important our staff know how to keep an eye on this. NCMT's engineers provided a week's instruction at the outset and are always available online or at the end of a telephone for troubleshooting or if technical advice is needed", says Combes.

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