The rapid growth of high-speed machining in the moldmaking industry continues to be facilitated by the parallel implementation of advances in machine tools.

Advances such as high technology spindles with speeds up to 40,000 rpm, balanced shrink-to-fit toolholders, advanced control strategies and very high feedrates are now commonplace.

These advanced machines produce surface finishes and forms on molds, which had previously not been achievable on a milling machine, and in a third of the time it would take on the more conventional EDMs.

While utilizing the latest machines, controls, software, tooling and monitoring, it is still true that in most cases clamps or vices will be used for holding the mold or die block in position. These traditional workholding systems are now limiting the productivity of the machine by obstructing cutter paths – making programming more difficult because of the need to ensure that cutters do not interfere – and by restricting the number of workpieces that can be loaded at once – typically only one at a time.

Magnetic chucking overcomes these limitations and provides an excellent workholding solution for high-speed machining. Clamping magnetically completely eliminates the need for the strap clamps or vices and replaces them with a clear clamping surface with exceptional holding power. And with heavy-duty milling magnetic chucks, it also is possible to raise the mold off of the chuck surface on pole extensions to further enhance possibilities for through machining and edge milling. Plus, by using innovative electro-permanent magnetic circuits, the need for electrical power is eliminated – except during switching – which allows the chuck to be disconnected from its controller for pallet applications.

These unique capabilities of magnetic workholding provide significant benefits for moldmaking, including:

Five-sided clear access for machining without obstructions from clamps or vises;
Through drilling and boring clearance by raising the mold on pole extensions; Multiple workpiece setup limited only by the available magnet area;

Pallet compatible – just unplug and go;

Exceptional stability – by clamping over the entire mold surface, vibration is virtually eliminated for improved tool life and surface finish; and,

Quick setup for optimal productivity.
However, just as other components of the machine required optimization for high-speed machining, there also are special requirements for magnetic chucks. The magnetic chuck needs to be designed and specifically optimized for exactly this type of operation.

The first change required to fine tune magnetic chuck design for high-speed machining is to control the magnetic power. Most milling chucks are actually far more powerful than required for high-speed machining and allow magnetism to penetrate too deeply into the mold.

When machining close to the magnet face, for example in a deep pocket in the mold, it may be possible for the magnetism from the chuck to penetrate into the machining area. When this happens, there is a tendency to hold chips in the cutting area, which can scuff the finished surface and chip the cutter. This becomes a very critical issue in high-speed machining since this is typically a finishing or semi-finishing operation.