As computers and televisions continue to become thinner, medical technology has also advanced to the point where increasingly miniaturized devices can be implanted in the human body—even cameras small enough to navigate within it.
Not only are things getting smaller, but they are also being equipped with more components, delivering greater power and functionality. Micro-components now have a wide range of applications in industries such as aerospace, automotive, biomedical, electronics, information technology, optics, and telecommunications.
The development of all these products is driving higher demands for smaller parts and assemblies. To continuously reduce costs, most of these miniature components are produced using molds. These trends are placing new and diverse challenges on mold makers, from utilizing new aerospace-grade materials and special mold coatings to milling with 0.1 mm diameter tools and achieving submicron precision.
At the same time, the intrinsic complexity of micro-components also creates new opportunities. As the production of simple and moderately complex molds shifts to countries with lower labor costs, mold makers in the U.S. and Europe can maintain their competitive edge by turning to advanced technologies such as micro-molding and micro-milling.
Challenges of Small Part Manufacturing
One of the main challenges in producing molds for miniature components is the actual machining of these tiny parts. Both direct milling of functional mold areas and the production of small EDM electrodes place extremely high demands on milling technology.
Micro-milling challenges include the use of ultra-small tools—sometimes as small as 100 microns (μm) or less—operating at spindle speeds up to 150,000 rpm. Required surface roughness often reaches Ra 0.2 microns. Since polishing such small features is usually impractical, micro-milling must achieve a polish-free finish.
Milling an EDM electrode with a 0.1 mm tool (photo courtesy of Cimatron).
Micro-Milling Technology
To meet both quality and precision demands while staying economically viable, the entire manufacturing chain must be optimized and synchronized. Suppliers of CNC machines, tools, tool holders, fixtures, and quality control equipment must all provide competitive and precise solutions.
Key Considerations in a Micro-Milling Environment:
1) Tools, Holders, and Spindles
Small-diameter tools are fundamental to micro-milling. Depending on the workpiece size, tools may be as small as 0.1 mm, and possibly smaller in the future. Availability and cost of such tools must be considered early.
High spindle speeds are essential for small-diameter tools. For instance, at 10,000 rpm using a 0.1 mm tool, the cutting speed (Vc) is only 3.3 m/min—which is far too low.
For spindles operating between 20,000 and 150,000 rpm, it’s critical to achieve perfect dynamic balance and zero runout using high-precision heat-shrink tool holders. Otherwise, surface finish will suffer, and tool life will decrease significantly.
2) Fixturing and Process Integration
Micro-milling parts should typically be machined in a single setup. Combining EDM and milling in separate operations may lead to unacceptable misalignment and visible tool marks.
3) Machine Tools and Workshop Environment
Machines must offer consistent accuracy and resolution to four decimal places (i.e., micron-level).
Micro-milling benefits greatly from five-axis capabilities, allowing shorter tools by tilting away from surfaces. However, since current five-axis accuracy often lags behind three-axis systems, any five-axis implementation for micro-milling must be thoroughly validated.
Temperature control and vibration isolation are critical. Even a heavy truck driving by the workshop can leave marks on a surface if the machine is not properly insulated.
4) Milling Strategies
Depending on geometry, micro-milling may require strategies beyond simple scale-downs. In many cases, climb milling (rather than conventional milling) is the preferred approach.
CAD/CAM solutions for high-precision micro-milling in mold manufacturing must offer easy-to-use 3D tools.
CAD/CAM Requirements
While it’s intuitive to think of machines, holders, and tools as the main challenges in scaling down to micro-manufacturing, the software is equally complex. At first glance, software may seem easier—it should handle numbers like 0.0001 just as well as 1.0 or 10. But in reality, it’s far more nuanced.
Essential Features for CAD Systems:
Reliable and accurate model interpretation is crucial. Reducing data translation between systems helps maintain model fidelity.
Ultra-tight geometric tolerances (0.1–0.01 microns) are essential for creating parting lines or geometry for sliders, ejector pins, and lifters. Gaps between parting surfaces must be eliminated, maintaining C1 and C2 continuity.
Support for very small, multi-cavity molds, including sample parts and complex assemblies.
CAM System Requirements for Micro-Milling:
Support for tight tolerances and ultra-high precision machining.
Since manual intervention is impossible during operation, CAM must precisely manage chip load throughout the toolpath.
Use of high-resolution mathematical models to maintain geometric fidelity. Integrated CAD/CAM platforms are ideal as they eliminate translation errors.
Built-in high-precision modeling functions (e.g., surface capping, extension) with appropriate tangent control.
Support for toolpath deviation as low as 0.1 microns—critical when machining fine features on large parts.
Capability to define micro-milling level parameters—such as using a 0.1 mm tool, 0.005 mm stepovers, and 0.05 mm tool radius. The resulting toolpath must be accurate to five decimal places.
Strategies combining roughing, semi-finishing, and finishing in one continuous operation.
Intelligent feedrate control based on actual remaining stock to protect fragile tools and reduce machining time.
Conclusion
Micro-systems, micro-molds, and micro-milling are emerging as exciting technologies for mass-producing miniature parts. With submicron precision and cutting tools nearly invisible to the naked eye, this fast-growing field presents many challenges and opportunities for mold makers and suppliers alike.
It requires in-depth knowledge of new materials, ultra-fine tools, special coatings, and advanced CAD/CAM software. However, micro-milling also provides a competitive edge for manufacturers looking to differentiate themselves from low-cost competitors.
Effective development in this field demands collaboration between industry, research institutions, and governments—a model already underway in Europe. The EU’s CRAFT initiative, led by the Fraunhofer IPT, has partnered with leading suppliers of CAD/CAM, CNC machines, tools, and fixtures to develop next-generation materials, machines, and software tools for micro-manufacturing.
It’s time for the North American toolmaking industry to join in and capitalize on this emerging and highly profitable market segment.
Micro-Milling at a Glance
Micro-system technology has become one of the fastest-growing industries globally. Sectors like biomedical devices, optics, and microelectronics (including mobile and computer components) are generating enormous demand for tiny, high-precision parts.
Components requiring micro-manufacturing often measure 5 mm or less, with surface finish demands of 0.2 microns or better, and material hardness reaching 45 HRC or more.
Micro-milling is a cutting-edge technology designed specifically for manufacturing such miniature and ultra-precise components. It involves tools smaller than 0.1 mm in diameter, achieving ultra-smooth surfaces and micron-level tolerances—far beyond the capabilities of standard NC software.
To achieve this level of precision, manufacturers must overcome challenges such as part deformation, increasing complexity, and the use of specialized tools. Key micro-milling capabilities include:
Tool diameters of 100 µm or smaller
Tool aspect ratios (L/D) of 10 to 100
Spindle speeds of 150,000 rpm or more
Machining tolerances of 0.1 mm or less
Geometry correction and ultra-precise toolpaths
Micro-milling represents the future of high-speed milling. Companies mastering micro-precision moldmaking will enjoy a powerful competitive advantage.
