Masami Masuda

Bending of Drill and Radial Forces in Micro Drilling

This paper describes theoretical analysis of bending deflection and anisotropic rigidity of drill, and the induced radial forces in micro drilling. The main results obtained are as follows. (1) There are two different modes of drilling which cause bending deflection of drill and induce radial forces. They are position error mode and run-out mode. (2) The radial forces induced behave quite differently between the two modes. (3) The radial forces increases as the depth of hole increases, because the rigidity of drill beam increases. (4) The position error mode induces a cyclic stress in the drill which may cause a fatigue breakage.

Influence of Thermal Behavior of Spindle on Machining Accuracy in Micro-Endmilling

This paper describes on the influence of thermal behavior of spindle on machining accuracy in micro-endmilling. In order to make clear the reasons why the depth of slot varies during slotting repeated, temperatures around the spindle head and the thermal expansion of spindle axis were investigated. The machine tool used for experiment was a small type of vertical machining center. The spindle used for experiment was a ball bearing spindle which rotated at 10000-40000 min-1. The spindle head made of aluminum alloy had various cooling systems for spindle motor and ball bearings, and the temperature of spindle head changed only a few degrees C. Therefore it seems difficult to assume that the primary cause was thermal deformation of spindle head structure, even though the coefficient of thermal expansion of aluminum alloy is approximately twice of that of steel. Finally the thermal expansion of spindle axis was partly measured and relation between the thermal expansion and the variation of depth of slots was investigated. The main results obtained are as follows, (1) Slotting after a long period warming-up of spindle resulted in a small change of depth of slot, but slotting without any warming-up caused an initial rapid increase and then saturation of depth of slot, (2) Temperature rise of spindle head and adjacent structure seemed out of relation to the variation of depth of slot, (3) The partially measured thermal expansion of spindle as well as temperature of lower flange of spindle showed qualitatively similar change corresponding to depth of slot.

Study on Micro Drilling — Rotating Bending Fatigue of Micro Carbide Drills

In micro drilling, the run-out of drill due to rotational motion error of spindle or eccentric chucking of drill causes machining error and larger radial forces which may break the drill. Furthermore, because the spindle speed is very high, rotating bending fatigue of drill may dominate the tool life. In the previous work, relationship between bending deflection and radial cutting force, and fatigue fracture of drill were investigated theoretically and experimentally. The objective of this paper is to investigate more in detail the relationship between the radial cutting force/deflection of drill and its fatigue life. A series of pseudo rotating bending fatigue tests was performed by using three types of ultrafine grain carbide drill blank with 0.1mm diameter. The main results obtained are as follows, (1) Rotating bending fatigue curve did not depend on cobalt content and tungsten carbide grain size. This differs from the results of conventional cemented carbides. (2) The fatigue fracture surface was dominantly occupied by fast fracture regions.

Study on Machining Accuracy in Micro-Endmilling

Micro end mills, for example, smaller than 0.5 mm in diameter have low strength and stiffness. They are rather difficult to be re-sharpened by grinding. Therefore they are usually used until their breakage or are exchanged for a new one when the machining results lose quality. In the previous study [, tool life up to breakage was experimentally investigated under various feed rates and some useful information was obtained to predict tool life considering a sort of bending fatigue. For each experiment, a new tool was used to machine slots till it broke due to fatigue and/or wear. In this study, in order to measure tool life based upon another point of reference, the machining accuracies of the above slots were investigated. The main results obtained are as follows: (1) Slot depth first increased due to thermal deformation of the spindle and then decreased due to tool wear, (2) Slot width decreased as the tool wear increased, (3) Slot bottom corner radius increased as the tool wear increased, (4) Burr size increased as the tool wear increased, (5) Surface roughness of the slot bottom seemed to be influenced by feed rate, tool wear and chatter.

Study on Tool Life by Breakage in Micro Endmilling

To obtain some knowledge to predict the tool life caused by breakage, a series of slotting experiments was performed at various feed rates for high carbon steel by using coated carbide square end mills of 0.5mm in diameter. The main results obtained are as follows, (1) There found a possibility to obtain an optimum feed rate for the maximum slotting distance. (2) Lower feed rate caused chatter but higher feed rate rarely caused chatter. (3) A newly defined cumulative damage seems to be useful in some extent to predict tool life by monitoring cutting force.

Study on Unique Cutting Phenomena in Micro Endmilling - Mechanism and Possibility to Occur-

In micro endmilling, because of small uncut chip thickness comparable to the tool edge radius and low rigidity of tool, the cutting process must frequently transit between rubbing/ploughing and cutting, and it may deteriorate the machining stability, surface finish and tool wear. In this report, such unique cutting phenomena are investigated by modeling a mechanism, computer simulations and experiments. As a result, a possibility of the unique cutting phenomena proposed has been certified.