Prototype of Cutting Machine by Wire-sawing in Vacuum for In-situ Investigation of Rocks

Introduction: A bullet type sampler is sometimes used to obtain a sample from an asteroid on samplereturn missions [1]. On the other hand, in-situ analysis is demanded for the investigation of more amount of rock samples. Many drilling or coring devices have been developed [2-5]. Slicing the rock sample is preferable to observe its interior rather than shaving [6]. Because coolant cannot use in vacuum environment, tool life will be shorten. It is expected for a wire saw to maintain cutting performance due to successive supply of cutting edges. This abstract describes a prototype of a cutting machine by wiresawing and some demonstrations. Preliminary Experiments: Fig. 1 and Table 1 show a setup and conditions for a preliminary experiments, respectively. A terrestrial basalt block, which has a similar structure and strength to a lunar mare basalt rock, with a width of 10 mm was cut with 0.2-mm wire saws with a tungsten carbide coating deposited by electrical discharge machining [7] or diamond abrasive electroplated with nickel. Cutting loads of 2.5 N in air and 3.8 N in vacuum were applied with a dead weight. The saw was reciprocated with a motor-driven xy stage from the outside of a vacuum chamber. After 2000 stroke-cutting, abrasive layers were completely removed and the core was exposed. The short stroke caused heavy wear. The cutting depth was 0.2 mm in both environments. The requirements for the cutting machine were clarified as follows. (1) Use a long wire saw to decrease the reciprocation. (2) Increase the feeding velocity of the wire saw to decrease the machining time. Design of Cutting Machine: Fig. 2 and Table 2 show an appearance and specifications of a prototype with two motors, respectively. It was placed in the chamber and the motors were mounted on the side wall with rotational feedthroughs. While the wire saw was reciprocated, one motor wound at a constant velocity and another applied the tension by a PID control. The maximum speed of the wire saw was 2 m/s by the limitation of the motor torque. A workpiece was mounted on an end of a lever and a cutting load was applied with a constant force spring. Cutting Experiments: The cutting performance in vacuum was compared with that in air. Table 3 shows cutting conditions. A wire saw with 30-40-μm diamond grits was used. The length of the wire saw was set to 7 m (5 m at a constant speed of 1 m/s) for the acceleration test of the wear. The machining time was 20 min. The pressure during cutting was 5.1-