What Is a Burnishing Drill?
A burnishing drill is a tool that can perform both drilling and burnishing at the same time.
Burnishing means polishing the surface and is widely used for drilling holes that require high surface roughness. A reamer (or burnishing reamer) is a tool with similar performance.
While reamers can finish the surface of an already drilled hole, burnishing drills have a cutting edge called a “chisel” with an angled tip that allows finishing at the same time the hole is drilled. Because finishing work after drilling generally takes time and tends to leave surface defects, simultaneous drilling with a burnishing drill is both efficient and precise.
However, when using burnishing drills, incorrect cutting edge angle or rotational speed may result in chipping or damage to the cutting edge during drilling. It is also important to note that burnishing drills have a higher load than reamers and must be properly cooled.
Uses of Burnishing Drills
Burnishing drills are suitable for high-precision drilling because they do not require surface finishing after drilling. For example, burnishing drills are widely used in the machining of automobile and aircraft engine parts, and are also indispensable in the machining of dies and molds.
Furthermore, many burnishing drills have a multi-stage shape, making them suitable for machining workpieces with multiple hole diameters. They can also be applied to the machining of soft materials such as resins and aluminum alloys.
Since drilling and burnishing can be performed simultaneously, machining time is reduced and the number of tools is reduced, making this tool applicable to a variety of manufacturing sites. Burnishing drill blades are basically straight, but some are equipped with a spike-shaped blade to accommodate high-speed feed and deep holes. Another feature is that there are a wide variety of types to suit different applications, such as those with oil holes and those that can handle small holes of 1 mm or less.
Principle of Burnishing Drills
Burnishing drills are machining tools that smoothly connect the cutting surface to the hole wall by means of a margin, called a burnishing margin, to achieve high-precision machining. The disadvantage is that the chisel and clearance grooves reduce rigidity, but they still offer advantages such as reduced cycle time and the elimination of the need for drilling for the downhole. This makes it an ideal tool for machining workpieces, where productivity is important.
Burnishing drills also have the advantage of machining more accurately in a shorter time than when using a reamer for drilling. When drilling, burnishing drills have a spherical tip, which distributes the cutting force evenly and provides a uniform finish on the workpiece surface. Therefore, burnishing drills provide a smoother surface finish than reamers.
Reamers are used for deep holes, but when using burnishing drills, it is recommended to use oil-hole compatible ones.
Types of Burnishing Drills
There are four types of burnishing drills: straight blade burnishing drills, gauge blade burnishing drills, multi-blade burnishing drills, and burnishing drills with oil holes.
1. Straight Blade Burnishing Drill
Straight blade burnishing drills are a type of drill with a straight cutting edge. It is used for simple hole drilling. Because of its straight shape, it has the disadvantage that the larger the diameter, the lower the machining accuracy.
2. Gauge-Blade Burnishing Drill
Gauge-blade burnishing drills are a type of drill with a conical cutting edge. It is used for drilling the bottom of holes because it can cleanly drill the bottom of holes. Also, when used in combination with a step drill, the range of hole diameters can be expanded.
3. Multi-Flute Burnishing Drill
A multi-blade burnishing drill is a type of drill with multiple blades. They are suited for mass production because they provide good chip removal and reduce machining time. However, there is a disadvantage in that the large number of blades results in a narrower distance between the cutting edges, which reduces the strength of the cutting edges.
4. Burnishing Drill With Oil Hole
Burnishing drills with an oil hole are a type of drill with a hole in the center of the cutting edge to supply coolant oil. Chips can be removed by coolant water pressure, making this type of drill suitable for high-speed and mass production.