Patent ID: 7172034

Claim:
A boring control method for a machine tool which automatically bores deep holes using a central control means ( 20 ) that performs a boring process by program control, while constantly detecting, by a torque detection means that detects load torque of a tool ( 1 ), a load current of a main shaft motor so as to read said load current at a specified sampling time (S TR ) and at a specified reading frequency (N S ), so that a mean value (TR) thereof is calculated and taken as a detected torque rate (TR), and said torque rate (TR) is compared with a torque limit value (TR LIM ) within a specified detection time (Î”T), and while checking a position of a tip end portion of said tool from a desired reference point (R) in a direction of Z axis of a workpiece ( 10 ) to a hole-bottom (Zf) using a Z axis movement device ( 6 ), characterized in that said boring process is executed so that: in a first step (S 1 ), a forward path step process (S 1 G) comprising a first forward path step cutting process (S 1 Gd) constituting a boring cutting process is initiated from said reference point (R) under fixed working conditions comprised of a specified pattern including working conditions comprised of a main shaft rotation number (S), which is a rotational speed of said tool, and a feeding rate (F) of said tool, said feeding rate (F) of said tool is stopped when said load torque exceeds a torque limit value (TR LIM ), which is a specified predetermined threshold value, thus taking a position where said tool is stopped as a first cut hole-bottom (Z 1 ), and said tool is withdrawn to said reference point (R) under fixed withdrawal conditions comprising a specified pattern in a return path step process (S 1 B); and subsequently, in a second step (S 2 ), said tool is moved from said reference point (R) to the vicinity of said first cut hole-bottom (Z 1 ) in a forward path step movement process (S 2 Gm) of a forward path step process (S 2 G), and a second forward path step cutting process (S 2 Gd) which is a boring cutting process is initiated under predetermined working conditions comprising a specified pattern, said feeding rate (F) of said tool is stopped when said load torque exceeds a torque limit value (TR LIM ) of said tool, thus taking a position where said tool is stopped as a second cut hole-bottom (Z 2 ), and said tool is withdrawn to said reference point (R) under predetermined withdrawal conditions comprising a specified pattern in a return path step process (S 2 B); and such a step (Sn) is repeated; and in a final (f) step (Sf), said tool reaches said hole-bottom (Zf), and the feeding rate (F) of said tool is stopped in a forward path step cutting process (SfGd), and said tool is withdrawn to said reference point (R) under predetermined withdrawal conditions comprising a specified pattern in a return path step process (SfB); and said boring process is ended.