Advances in Micromaching Technology

The manufacture of miniature parts is not new. Many companies have used various EDM technologies to produce ultra-fine and precision details for many years. The difference today is the sheer volume of products that require EDM machining. The accelerated rate of change is unbelievable.

New miniature products are changing how we view the world. Many manufacturers are developing micromachining technologies to support this growth, including micro EDM solutions. Companies are continuing to look for smaller parts, with smaller feature sizes, made out of more exotic, engineered materials.

The ability to machine with smaller and smaller electrodes and cutting tools is removing many of the manufacturing barriers previously encountered in the industry. EDM systems and new machining technologies are being employed in the manufacture of a wide variety of products and devices, including:

Machine resolution, control, construction and ancillary tools all become much more critical to the success in producing micro parts.

Besides being able to machine micro features and parts, simply handling micro parts and tools poses unique challenges. This also impacts the repeatability of a process that has a desired tolerance of less than a micron.

The need for finer resolution

Although high-resolution feedback systems have improved accuracy and eliminated servo drift, there is more that needs to be done. It is no longer good enough to have feedback systems and resolutions only in the micron range. When machining in the micromachining range, sub-micron control and feedback systems are necessary.

Due to this cumulative effect of errors, a good rule of thumb is that the systems employed for manufacturing should be 10 times more accurate than the repeatable tolerance desired. This would mean that to achieve a ±0.00020" (±5 micron) tolerance, the required system must provide at least 0.000020" (0.5 micron) precision. Feedback resolutions in the 10-50 nanometer range are now available to improve "resolution" accuracy on new machine tools, however this does not necessarily make a machine accurate. Resolution is the digital accuracy of the machine tool and does not correct for alignment problems.

Alignment is critical in producing accuracy, and depending upon the number of axes that are combined in a system, the perpendicularity, parallelism and straightness of the positioning axes to each other are just as critical to precision.

Micro Wire EDM

ED machining has been a mainstay of micromanufacturing for more than 50 years, providing unique capabilities to the job shop and manufacturer alike.

Miniature parts and components have been produced for many years using the non-contact capabilities of EDM systems. In fact, in the early 1960s, Life magazine published a photograph of a series of micro holes that were EDM'd through a needle and spelled out the magazines name.

The ability to automatically wire thread and machine parts with a 20 µ (0.00078 in.) wire and achieve corner radii of less than 15 µ would have been unthinkable just a few years ago. But, the problems of small-hole threading and hole proximity can now be conquered.

A key to this technology is the horizontal orientation of the wire and the utilization of air and vacuum rather than a fluid to thread the wire. This is a radical departure from conventional designs. Machining in the horizontal plane provides several advantages including an integrated "C" axis for workholding and automated part loading with slug removal systems that improve automation.

The open design of a V-type wire guide improves automatic wire threading reliability. The guide controls the cutting tool and must therefore be highly accurate. The V-type guide provides three-point contact with the wire for superior wire alignment.

Also, as discussed earlier, an environmental system for precise temperature control (within ± 0.5º C) must be used when machining ultra-fine details. And lastly, an oil dielectric fluid instead of deionized water must be used in order to provide:

Micro EDM sinking

Today's CNC die sinking EDM system is much more capable than its manual predecessors for conventional mold manufacturing and micromachining of complex parts for a wide range of applications.

When talking about machining in the micron range, it is necessary to look at machine design and construction as well as the ability to produce parts efficiently in a production environment. Successful EDM'ing requires minute orbital motion in order to achieve the speed and surface finish to make micromachining economical.

Machining of micro holes has become an immensely important micromachining application. From micro start holes for newer wire EDMs to production ED drilling of small holes, EDMing has produced tremendous results. Holes having an L to D of 100:1 are possible by incorporating a "high-pressure" dielectric pumping system (>800 psi) and using micro tubing down to 0.1mm. holes. High-pressure seals in the rotating head and high-precision rotation are necessary as well.

Submicron tooling

Precision work and toolholding systems (electrode) capable of positional repeatability in the 1 micron range have been commercially available since the late 1980s. Originally designed for the EDM industry, these systems are highly reliable, even in the harsh EDM environment, and are now found on virtually every type of machining application. From machining centers to grinders to coordinate measuring machines, these holding systems can be found in every type of manufacturing environment. Due to the demands for better accuracy, new innovations in tooling with submicron repeatability are necessary.

Conclusions

Micron and sub-micron manufacturing requirements will continue to grow offering unique challenges and immense opportunities to a wide group of manufacturers. The designs and construction of many machine tools, work and toolholders, cutting tools and electrodes will naturally evolve as greater demands are placed on them when machining these miniature parts. Many of the challenges will evolve around economically controlling the micromanufacturing process. Many of these systems would not have been developed had it not been for the demands of industry for more and more micromachining capability.

For these systems to perform successfully in the real world requires cooperation and imagination on everyone's part. In the end, it is the user that challenges the expertise of the OEM to develop effective micromachining systems, processes and applications techniques to support the business. TMD

John Shanahan is a Product Manager for Makino, Inc. (Mason, OH) and is responsible for the technical marketing for all EDM products. Besides holding several technical EDM sales and marketing positions, he has also managed an EDM job shop on the West Coast. He has published several articles and spoken at a large number of seminars on topics including automation, EDMing, High-Performance Machining and Die/Mold production processes throughout the United States and Canada.