Manufacture and application of ultra-small micro end mills

https://doi.org/10.1016/j.cirp.2012.03.012Get rights and content

Abstract

The use of micro parts and micro structured elements has constantly grown over the past decade. Milling with micro end-mills belongs to the manufacturing technologies which offer a high potential for competitive micro machining. However, the design criteria for the micro end-mills and their manufacture pose many challenges. In this paper, first the design and manufacture of single-edge micro end-mills with diameters between 10 and 50 μm and a variable helix angle is described. Second, the use of these end-mills in titanium and polymethyl methacrylate (PMMA) is described to demonstrate their potential.

Introduction

The demand for micro products and related components increases rapidly along with possible applications in optical, mechanical, electrical, medical, and biochemical devices. Therefore, micro manufacturing processes are a fast-evolving area of research. Micro end milling provides the advantage of a relatively high material removal rate and at the same time allows for the manufacture of complex three dimensional structures.

Micro end milling is a highly flexible manufacturing process. It is for example used to machine small features in molds used for mass production, to structure medical implants for better biocompatibility, to generate deep X-ray lithography masks, and to manufacture microfluidic devices [1], [2]. Different from alternative manufacturing processes, it is even possible to manufacture undercuts by using profiled milling tools [3]. The quality of the micro machined parts depends on the cutting parameters, the milling strategy, the work piece material, and to a large extend on the micro end milling tool itself [4], [5], [6]. The tool may vary in material, overall geometry, cutting edge radius, surface conditions and coating. The tool design influences dimensional accuracy, surface quality, burr formation, and tool life [7]. Therefore, it is of high importance for micro end milling.

Several researchers have reported the development of micro end mills with various geometries and tool manufacturing processes. Vasile [8] used a focused ion beam to manufacture micro end mills with 25 μm diameter. Schaller [9] described a grinding process to manufacture micro end mills with 50 μm diameter whereas Egashira [10] reported the use of electrical discharge machining to produce micro ball end mills with 10 μm radius. Goto [11] describes CBN micro end mills with 30 μm diameter and their performance.

In this paper, a geometrically optimized tool design, the manufacture of micro end mills with diameters down to 10 μm by grinding, and the application of these micro end mills in two different material classes, a titanium alloy (Ti–6Al–7Nb) and polymethyl methacrylate (PMMA), are described.

Section snippets

Tool design

A good end mill tool design needs to fulfill various, partly conflicting, specifications and requirements. The tool must:

  • allow for good chip formation and removal,

  • have a sharp cutting edge leading to a low cutting force and a small minimal undeformed chip thickness,

  • have a flank geometry which prohibits contact to the workpiece at the side walls, and

  • be manufactured by a robust and fast process in order to be economically feasible.

The main geometrical characteristics of the micro end mills which

Experimental set-up

The studies were performed using a CNC 3-axis precision milling machine. This desktop machine tool is mounted on a vibration-isolated granite base. The X- and Y-motions of the work table are performed with air bearing linear stages. A 50,000 rpm air bearing spindle is vertically mounted on the Z-axis, which is equipped with cross-roller bearings. The machine tool provides a resolution of 20 nm and a repeating positioning accuracy of 1 μm. All tested tools have the same radial clearance angle (αr)

Results

The experiments have been carried out with micro end mills with diameters between 10 (for PMMA) and 20 (for titanium) to 50 μm (for both materials). Fig. 7 shows structures milled in Ti–6Al–7Nb and PMMA.

The effect of using a micro profile end mill can be seen in Fig. 8. This undercut was machined in a single step with 22 μm depth of cut. It show the possibility to vary the cutting edge angle (χr) in order to machine undercuts or to design tools with χr smaller than 90° for milling inclined side

Conclusions and outlook

It could be shown that grinding is a suitable technology for the manufacture of ultra-small micro end mills. It combines geometrical accuracy with the possibility to achieve very small cutting edge radii at a comparatively short processing time. The kinematics of the process allow to manufacture micro end mills with customized end geometry, i.e. ball end, straight end or even dovetail end. In milling tests it was possible to machine a titanium alloy with tool diameters down to 20 μm and PMMA

Acknowledgments

This research was funded by the German Science Foundation (DFG) within the CRC 926 “Microscale Morphology of Component Surfaces” and the European Regional Development Fund within the RWB EFRE Program Rheinland-Pfalz.

References (12)

There are more references available in the full text version of this article.

Cited by (126)

View all citing articles on Scopus
View full text