Assessing The Safety of Magnetic Workholding

Assessing The Safety of Magnetic Workholding

Article by Patrick Stox

Resistance to the implementation of magnetic work holding usually begins with a concern for safety. These concerns can be allayed by assessing the technology, holding power and optimal operating conditions of magnetic work holding in terms of operational safety.

Despite the competitive benefits of magnetic workholding in reducing costs and improving productivity, there still exists a resistance to the implementation of magnetic technology as the primary work holder in machining operations. This resistance usually begins with a concern for safety. By assessing the technology, holding power and optimal operating conditions of magnetic work holding relative to operational safety, these concerns can be allayed.Magnetic Work Holding as a Safe Technology

If a machine operator has held workpieces with mechanical clamps for decades, the idea of relying on magnetism to hold workpieces, especially in heavy milling operations, boils down to an issue of trust: Is this really safe? While understandable this opinion is rooted in subjectivity not objective fact. More than likely, those who hold this point of view may not fully understand the facts of how safe magnetic work holding is.

So, how can magnetic work holding be considered as a safe technology? By definition, it produces a uniform, consistent, and infinite holding power that does not relax, give, or decrease until an operator de-energizes it.

In general, magnetic work holders are constructed with an array of individual magnets embedded into a magnetic chuck or plate. Each magnet has a north and south pole across which flows magnetic energy called flux. When a workpiece is placed across the poles of these magnets, flux flows into it. When placed in this flux field, a magnetic field of opposite polarity is induced into the workpiece thereby creating a magnetic attraction between the chuck and the workpiece. This attraction will remain consistent, uniform, infinite, and reliable as long as the magnetic field is energized. This reliability makes magnetic workholding a truly safe technology.

Magnetic Work Holding as a Safe Holding Force

Holding power or strength is another factor considered when forming an opinion about the safety of magnetic workholding. If an operator does not know how strong magnetic workholding is, he may mistakenly believe magnetic technology is not strong enough to do the job safely. This opinion can be allayed by two facts:

(1) magnetic workholding can have a clamping power up to 1000 daN and

(2) depending upon the application, an instantaneous clamping force of 12 tons per square foot can be generated by magnetic workholders. This level of holding force is more than comparable to mechanical clamps with one additional advantage: magnetic holding force is uniform, constant and infinite until the operator de-energizes it.

Optimal Operating Conditions

To implement magnetic work holding solutions may require some training to understand the technology’s optimal operating conditions. For example, magnetic work holding is best used with smooth-surfaced workpieces rather than rough ones because the smoothness decreases the air gap between the workpiece and the magnet; small air gaps increase magnetic attraction and the holding bond. Some materials are better conductors of magnetism than others. For example, annealed materials are ideal while hardened materials don’t absorb flux as easily and will retain some magnetism. This condition can be corrected within seconds with demagnetization. Finally, the direction of the holding force is yet another adjustment an operator may have to make to safely implement magnetic work holding. All magnets have 100 percent clamping force directly away from the face of the magnet, but only about 20 percent clamping force against side forces. So, the geometry of a cut must be considered in the machining process to reap the advantages of this type of workholding.

About the Author

DocMagnet Inc. designs and supplies Magnetic Work holding systems. Their Permanent Magnetic Chucks have all metal surfaces and are built and tested to the highest quality.

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