Why micromachining?
Micromanufacturing can be viewed as the production of components with geometric features that have at least one dimension less than 1mm. Like with their macroscale manufacturing, companies depend on a number of manufacturing processes to fabricate microparts. These processes include micromolding, microforming, laser machining, microEDMing, microECMing and mechanical micromachining. This article examines the mechanical micromachining process and provides guidelines to help determine applications that may be a good fit for such a process.
Mechanical micromachining is a subtractive manufacturing process where material is removed in the form of chips by a rotating cutting tool. Through extensive research, it has been found that micromachining is a drastically different process than its macro counterpart. Cutting mechanics, such as the way in which the tool interacts with the material being machined, and process parameters, such as feeds and speeds, do not translate directly from the macroworld to the microenvironment. These differences are the primary reason why machine tools that work well for macroscale machining do not always perform well in micromachining applications.
Mechanical micromachining is a process that can address a range of applications across various industries. EDM and ECM processes require the material being processed to be conductive, but mechanical micromachining can process an array of materials, including plastics, aluminum and brass to harder materials, such as stainless steel, titanium and ceramics.
As with other manufacturing processes, design for manufacturability is an important issue in micromachining. Achievable feature dimensions in mechanical micromachining are limited by commercially available cutting tools. Therefore, during the design phase, it is important to examine the manufacturing process and consider which cutting tool is more appropriate to make a feature.
Because micromachining is typically performed on a 3-, 4- or 5-axis CNC machine, full 3-D free-form geometry, such as smooth contoured surfaces, can be achieved.
An in-house micromachining capability allows product development engineers, for example, to make quick design changes and fabricate products from functional materials, thereby moving through the design process faster and cheaper than continually outsourcing this fabrication. The difficulties faced by many companies is that the more traditional CNC machining equipment in their machine shops and toolrooms are not well equipped to handle these tight-tolerance, small-part applications. The ultrahigh precision machine tools currently on the market can also be quite expensive and still beg the question, “Why am I using such a big machine to make such little parts?” Micro machine tool builders have developed a new breed of machine tools that are fundamentally rooted in the concept that small parts should be manufactured on specially designed small machines. Through the development of these micro machine tools, many of the shortcomings and pains experienced in current micromachining practices are directly addressed and mitigated.
Easily integrated into an office, laboratory or production floor environment, CNC micromilling machines provide solutions for machining small, high-precision parts.
For example, CNC micromilling machines from Chicago-based Microlution Inc. are available with a 36-pocket automatic toolchanger and have a 2-micron positioning accuracy, 80-nanometer resolution and 200-nanometer repeatability—within a 4-sq.-ft. footprint. A ball and vee-type kinematic mounting system for both the workpiece pallet and the spindle is utilized on Microlution’s machine tools. This quick-change mounting system allows the workpiece pallet or spindle to be removed and replaced with submicron repeatability. This capability allows, for example, a machining operation to be interrupted and the workpiece pallet to be removed, inspected and replaced without the need to reregister the part.
When the machine is being used for multiple jobs, each job can have its own kinematic workpiece pallet. This enables multiple users to easily transition from one setup to the next without losing their part registration. The kinematic mounting system also allows the spindle to be removed and replaced with, for example, a laser sensor to perform metrology operations, such as surface roughness and profile measurements. Similarly, multiple spindles—each with its own kinematic spindle mount—can be accurately implemented during a single machining process. Microlution’s micromilling machines are built off of precision-ground granite support structures and incorporate AC linear motors and Heidenhain linear optical encoders on the X, Y and Z stages. —Onik Bhattacharyya, sales and marketing coordinator, Microlution Inc. |
