Process Encyclopaedia

Drilling

Other names / variants: Trepanning

Overview

One of the most common of the machining processes - as there are few other ways to produce a deep circular hole. One of the biggest challenges to the drill designer is how to remove the waste material out of the hole at the same time as getting the cutting fluid into the hole. Large shallow holes are made by trepanning, where a disc is removed rather than all the material.

Materials and shapes

Almost any material can be drilled, although difficulties arise with very brittle materials (e.g. ceramics) and very hard materials (e.g. tool steel).
Drilling is used for making circular holes, dimensional accuracy can be improved by subsequent reaming or boring.
Holes from 0.5 mm to 50mm are commonly drilled - although the design of the drill bit will vary quite a lot!
Drilling is often used to complete parts that have been formed by a near-net-shape process (e.g. casting or forging) as precision holes are difficult to form with these processes.
Threaded holes are made by first drilling a cylindrical hole and then "tapping" with a threaded cutting tool.

Economics

It is normal to try to reduce the amount of drilling required in a component by careful design - but when an accurate hole is required, drilling has little competition.
Where drilling is required industrially, it is usually done either as part of the function of a machining centre, or in a dedicated drill set with multiple heads so that all the holes can be made simultaneously.