Offering unparalleled freedom to produce complex components in a limited number of setups, frequently one, 5-axis prismatic machining delivers high accuracy parts by minimising tolerance build-up and virtually eliminates scrap by removing the risk of manual handling errors. Yet the significant investment required to purchase such high-technology machine tools is often undermined by insufficient attention to a simple element: the workholding.
Traditional manual clamping solutions such as vices and fixtures invariably obstruct the cutter’s access to the component, making it more difficult to remove material, while complicating and lengthening the programmed tool paths. Obstacles that impede tool access often necessitate the use of tools with longer and hence less rigid shanks to reach the material surface. This inevitably increases deflection, making it more difficult to meet drawing tolerance and raising the risk of costly collisions.
If pneumatics or hydraulics is involved in workholding, an additional point of potential failure is introduced, not to mention extra expense. Crucially, such methods of mechanical clamping cause in the workpiece internal mechanical stress and torsional forces that can deform it. When the clamps are released after machining, the stored energy rebounds, leading to measurable dimensional inaccuracy and sabotaging the very precision 5-axis machining is designed to deliver. This is especially problematic when dealing with thin-walled components or those demanding an elevated level of precision.
If a manufacturer is lucky enough to be processing ferromagnetic materials such as iron, steel and cobalt, they have at their disposal a workholding solution that avoids most of the foregoing issues: electro-permanent magnetic (EPM) and permanent magnetic clamping. A leading supplier of the technology is Walmag in the Czech Republic, whose products are sold exclusively into the UK and Irish markets by 1st Machine Tool Accessories, Salisbury (www.1mta.com).
Walmag’s principal solution for 5-axis workholding in its EPM technology, which avoids the trade-offs found in earlier magnetic solutions by combining the safety of permanent magnets with the controllability of electromagnets, without the need for a continuous power supply. The core principle of an EPM device uses an internal circuit comprising two distinct magnetic elements: magnetically ‘hard’ permanent magnets, typically Neodymium, which supply the constant holding force, and magnetically ‘soft’ core materials, whose polarity can be switched.
The entire clamping mechanism is controlled by a momentary electrical pulse. A short, powerful current is applied to the internal coils, aligning the magnetically soft cores in the same direction as the permanent magnets. This causes the magnetic flux lines to extend outward through the pole plates and into the ferrous workpiece, creating a high-force, closed circuit.
No power is required to maintain the clamped state, a feature that ensures the holding force remains constant, even if there is a sudden power outage, providing a degree of safety unmatched by hydraulic or pneumatic systems. To release the part, an equally brief electrical pulse of the opposite polarity is applied, reversing the soft core magnetisation and causing the two fields to oppose and internally cancel each other out, instantly releasing the workpiece.
EPM systems are inherently well suited to Industry 4.0 integration, as the mag/demag cycle is electronic and fully controllable via the machine’s PLC interface, making such workholding the ideal partner for robotic loading and unloading and various zero-point palletising solutions.
The performance profile of Walmag’s EPM chucks is tailored for aggressive material removal, offering holding forces that can reach up to 170 N/cm² in heavy-duty milling applications. The high force is distributed uniformly across the entire contact surface of the part’s base, rather than being concentrated at localised points, avoiding workpiece deformation and suppressing vibration.
Maximum competitive advantage is found during 5-axis milling and drilling, as all barriers between the cutting tool and the workpiece are effectively removed. By securing the component solely from the base, the entire periphery and top surface are accessible, allowing the machine to leverage its full all-round metal cutting capability for efficient, single setup production.
Walmag supplies pole extensions that may be placed on the surface of the magnetic plate to transfer the flux directly into irregularly shaped locations on a workpiece. The system includes both fixed pole extensions, used to create a rigid, elevated reference surface for prismatic parts, and flexible or conical extensions that adapt to the rough, uneven contours of castings or forgings, ensuring consistent clamping force across an entire contact area. The EPM top plate can be pre-machined to create custom locating features or pockets for repeatability during dedicated component runs.
The comprehensive Walmag portfolio offers magnetic solutions for the full range of 5-axis machining operations. The Mastermill series provides rectangular electro-permanent chucks for high-force milling of prismatic components, while the Neopower and Neomill Compact permanent magnetic chucks offer robust rigidity and a low-profile construction to maximize Z-axis travel.
For rotary applications, the Neostar and Circu EP circular magnetic chucks are designed specifically for use on rotary tables and in turning operations, enabling single-setup machining of inner diameter, outer diameter and face features. The complete range ensures that, regardless of whether the job demands rapid roughing on a large block or high-precision finishing on a small component, a suitable EPM solution can be implemented.
As for all of the globally-sourced workholding and automation equipment it supplies, 1st MTA offers a comprehensive consultancy and demonstration service to companies looking to streamline their production operations using Walmag products. Moreover, the manufacturer in the Czech Republic is more than willing to modify its standard products to suit special custom applications. Further information and contact details may be found at: www.1mta.com/manufacturer/walmag
