Controlled fracture machining method for producing through-holes

A method of producing a though-hole by controlled fracture machining in a plastic or metal workpiece material comprising the steps of:

• securing a workpiece to a table of a multi-axis machining apparatus without the use of a die;
• selecting the cutting tool so to match the size and shape of a desired through-hole;
• positioning a face of a cutting tool perpendicular to the centerline of a proposed through-hole;
• adjusting the cutting face of the machine tool by rotating the cutting tool or workpiece so that an optimal cutting force can be achieved;
• approaching the surface of the workpiece with the cutting tool to a level sufficient to clear obstructions and to allow acceleration of the cutting tool to the speed required for controlled fracturing;
• driving the cutting tool using linear force, without rotation, about its axis into the workpiece using an impact force of at least 20,000 lbs/sq-in through use of controlled fracturing to exceed the yield strength and the breaking strength of the workpiece material by an impact force which causes the axial projection of adiabatic shear banding of the material along the perimeter of the tool to produce a through-hole to a depth necessary to make a through-hole without driving completely though the workpiece or using a fixed surface to support the workpiece;
• and
• creating a hole conforming to the perimeter of the cutting tool's face using a drive mechanism striking the workpiece.

A method for producing a though-hole using controlled fracturing using a machine that includes a table section for supporting a fixtured workpiece, a cutting toolholder section for holding at least one cutting tool comprising the steps of:

• securing a workpiece to a table of a non-spindle CNC holemaking machine tool such that no die is used;
• securing the cutting tool to the column of the machine tool;
• positioning a face of the cutting tool perpendicular to a centerline of a proposed hole;
• approaching the surface of the workpiece with the cutting tool to a predetermined clearance level;
• providing an impact force of at least 20,000 lbs/sq-in to impact the location of a proposed hole in the workpiece;
• driving the cutting tool into the workpiece to a depth necessary to make the through-hole without driving completely through the workpiece using a linear force to exceed both the yield strength and the breaking strength of the workpiece material in a manner so to cause fracturing by adiabatic shear banding produced by the impact force;
• creating a plurality of adiabatic shear bands to emanate from the face of the cutting tool using the impact force of the cutting tool to form connecting cracks using the plurality of adiabatic shear bands;
• and
• forming a slug in the workpiece at the position of the hole using the force of the cutting tool such that a through-hole in the workpiece is formed at the position of the slug by striking the workpiece to create the through-hole of a desired size and shape at the predetermined clearance level.