Indexable inserts for drilling are removable cutting tips used in drilling applications. They can be rotated (indexed) so that when one of the cutting edges wears down, another cutting edge can be used without affecting the overall quality of the insert. They are placed in an insert holder made for drilling on a machine and remove material when placed in contact with the workpiece. Indexable drilling inserts may be designated as either central or peripheral. A central insert is designed for use in the center of the drilling insert holder, while a peripheral insert is designed for use on the outer rim of the drilling insert holder. Inserts for drilling are used to make holes in material during standard drilling, boring, step drilling, milling, and circular ramping operations.
Drilling inserts come in a variety of shapes which are selected based on the specific indexable insert holder being used.
An important consideration when selecting indexable drilling inserts is the cutter material, also known as the substrate. Most inserts for drilling are made of carbide, which resists abrasion and is harder than high-speed steel.
Also consider the insert's finish or coating. To strengthen or add wear resistance to the substrate, many inserts have single or multilayer coatings applied through processes such as medium temperature chemical vapor deposition (MTCVD) or physical vapor deposition (PVD).
The pairing of the cutter material and finish is referred to as the manufacturer grade. The grade determines how effectively the insert can machine specific materials in a range of operating conditions. It also determines the balance of wear resistance and toughness the insert offers in certain applications and operating conditions. Manufacturer grades are often proprietary compositions determined by a particular manufacturer.
Another factor is insert style, designated by a series of letters and/or numbers that reference the shape and size of the drilling insert. The shape and size are chosen based on the specific indexable insert holder being used. Insert styles vary for drilling inserts depending on the type of tool, application, and operating conditions. Each indexable drilling insert has more than one cutting edge and a special geometry designed for controlling evacuation of chips at a specific range of feeds and speeds on different materials. Some drilling insert style names also indicate corner radius (the rounded tip on the cutting edge), represented by numbers.
Each insert has a chipbreaker geometry that allows the insert to break off and evacuate chips most efficiently in specific applications, such as roughing and finishing, and in operating conditions related to the machine and workpiece material. Chipbreaker geometries are designated with two or more letters or numbers.