The Shibaura series of UVM machining centres features a high-precision aerostatic spindle and linear motor driven system, allowing for the effective processing of hard materials in mould making. Demand for hard material moulds is increasing since they afford extended lifetime, superior surface quality and more accurate geometries, but these difficult to cut materials require the right equipment and expertise.
It is well known that most brittle materials have a ductile mode cutting region with a very small depth of cut, sometimes 10–50 nm. Indeed, many mould makers refuse jobs because the depth of cut must be kept within such a narrow range. Shibaura, through its extensive research and experience, concluded that this no longer needed to be the case providing key material processing factors were accommodated, which resulted in the development of the UVM machining centre. The machine, thanks to its in-house manufactured aerostatic spindle and original linear motor guideways, can deliver the extremely high quality material processing necessary for high-end lens mould making.
Case study 1An example of ductile mode cutting of cemented carbide is shown in figure 1. This material has an ultra-fine grain and is widely used for optical lens mould making. Due to the hardness of cemented carbide, it is traditionally machined using a grinding process. Shibaura has used a single crystal diamond cutting tool in the ductile mode cutting region and achieved a smooth surface without any cracks.
Texture of a cut surface.
The effect of positioning at the actual cutting location is shown in figure 2. This is a comparison of positioning error with linear motor drive and ball screw drive. In general, ball screw driven systems have some backlash in small ranges and cannot control positioning in nanometres. On the other hand, the linear motor driven system achieved a small error of less than 10 nm. This difference makes a case for keeping the ductile mode cutting region.
Comparison of the positioning error for a linear motor driven system and a ball screw motor driven system.
Case study 2
An example of ductile mode cutting of silicon is shown in figure 3. Silicon is a typically brittle material widely used for semiconductor products and night scopes. In production, the original diamond tool shape is usually applied to make ductile mode cutting easy.
Here, a lens shape was formed on a silicon substrate that was 0.2 mm thick and therefore prone to breakage. However, an excellent surface finish was achieved, indicating that the material was continuously and perfectly machined via ductile mode cutting.
Cut surface of a silicon substrate.
Conclusion
Precise positioning on the actual cutting location should be an essential technique for the processing of hard, brittle materials such as cemented carbide and silicone. Shibaura believes that the UVM, with its high-precision aerostatic spindle and linear motor driven system, offers the ideal configuration for hard material processing.
Shibaura