Drilling work control method and drilling work device

A drilling work device, comprising:

• a tool that forms a hole in a workpiece;
• drive systems that make the workpiece and the tool execute relative rotating motion and relative feeding motion therebetween;
• and
• a control system that controls the drive systems, wherein:
• the workpiece includes forming areas of a predetermined number that is a plurality divided by being formed of materials of different qualities;
• and
• the control system includes:
• load torque detecting means that detects load torque applied to the tool;
• working start determining means that determines working start of drilling work for the workpiece;
• working object layer determining means that determines the two or more forming areas respectively in order of drilling work as two or more working object layers arrayed in a feeding direction that is a direction of the feeding motion based on a times of occurrence of variation of the load torque by a predetermined variation coefficient or more after the working start and a layout of the working object layers of the workpiece;
• working condition deciding means that decides spindle speed and feeding speed corresponding to materials that form the working object layers determined by the working object layer determining means;
• drive controlling means that controls the drive systems so as to execute the rotating motion at the spindle speed and the feeding motion at the feeding speed so that the tool forms the hole over the two or more working object layers;
• an immediately before penetration determining means that determines that the tool is at an immediately before penetration position that is immediately before penetrating the workpiece in a working finishing layer by detecting a load torque reduction is a predetermined reduction rate or more in the working finishing layer, wherein the immediately before penetration determining means determines that a working object layer of the working object layers is the working finishing layer and determines that the load torque has reduced by a predetermined reduction rate or more;
• a working finishing position detecting means that detects a working finishing position where the tool penetrates the workpiece and finishes drilling work;
• and
• a working condition deciding means makes the feeding speed a slow feeding speed that is slower than a working feeding speed in the working finishing layer;
• wherein
• the control system determines that the tool is at the immediately before penetration position when reduction of the load torque of the predetermined reduction rate or more has been determined in the working finishing layer in the immediately before penetration determining means;
• and
• the control system controls the drive systems so that the tool moves forward at the slow speed from the immediately before penetration position to the working finishing position.