Deep Hole Drilling Machine Technology Parameters
Drilling is one of the most versatile machining processes. As modern CNC machine tools are able to perform a number of different operations a deep hole drilling machine is an ideal tool for tackling deep hole drilling tasks. Deep hole drilling machines offer a number of advantages such as being able to accurately drill at high speeds and depths while maintaining excellent hole finish and hole tolerances.
The term “deep hole drilling” is often used to refer to any drilling operation that is deeper than the diameter of the drill bit. While this is technically true, the definition of deep hole drilling is often considered to cover any operation that has a drilling depth to diameter ratio of greater than 10:1. In the case of a conventional drilling machine the maximum depth is generally limited to the length of the spindle and the limit of the cutting speeds, this inside diameter depth being less than ten times the cutting diameter.
The main complexity of deep hole drilling is the control and management of the cutting tool through the entire process. To guarantee a successful cutting operation the cutting parameters that must be controlled include, but are not limited to, cutting speed, feed rate, depth of cut, chip load, undulation, and the correct cutting fluid for cooling.
Deep hole drilling machines are constructed to reduce the high length to diameter ratio of the drilled hole. Without the use of dedicated machine tools, deep hole drilling usually requires multiple passes on the hole which can cause built up edges, sacrificial drilling and inefficient cycle time. Many deep hole drilling operations require a single pass to produce the desired hole; however, the features of the deep hole drilling machine tools make it suitable for multiple passes as well.
Deep hole drilling machines come in a variety of sizes, shapes and features making them suitable for a variety of applications. They are typically tall and vertical, with a specialized set of drilling spindles that range in size from 4–24 mm. Deep hole machines feature multiple drilling spindles or drums allowing them to bore multiple holes at a time in a single setup. The main types of deep hole drilling machines are gun drilling, trepanning and boring.
Gun drilling is most appropriate for cylindrical deep holes, as well as for deep holes with a diameter greater than 6mm. It is a process that entails the use of a small, single-blade tool instead of a conventional drill bit to achieve high speed and accuracy in deep hole drilling. The result is a hole with a round, tapered bore well suited for hydraulic rams and other high pressure applications.
Trepanning is a process used to cut circular holes or interior surfaces. It is similar to gun drilling, in that it uses the same type of single blade cutter but with a larger diameter blade and a lower speed to produce the desired hole shape. Common applications of trepanning include custom shaped holes and stepped holes for internal gearing and bearing races.
Boring is an internal machining process where material is removed from an existing hole to make it larger. Boring machines typically feature more robust designs than gun drilling machines, as the cutting forces are significantly higher due to the higher material removal rate. Boring machines are generally used in larger diameter applications and are capable of producing exceptionally tight tolerances at various depths.
The performance of a deep hole drilling machine is highly dependent on the strength and rigidity of machine construction and stability of the cutting process. Many deep hole drilling machines feature unique construction to optimize operation and increase the life of machine components.
The chief amongst these features is the use of hydrostatic bearings, either in just one spindle or the multiple spindles of the machine. Hydrostatic bearings allow work to be fed quickly and accurately with low vibration levels and provide high precision cutting with superior surface finish, even when drilling in difficult materials.
Other features to look for in deep hole drilling machines include an accurate and stable mechanical feed system, robust motor and tool design, reliable cutting fluid and advanced control systems, as well as hardened and ground guideways for rigid and precise positioning of the spindle for accuracy.
The cutting parameters for deep hole drilling are also important, as they affect the overall cutting performance and the life of the cutting tool. In general, shorter cutting depths and higher cutting speeds are preferred as this minimizes heat development, reduces tool wear and increases the life of the cutting tool.
The specific cutting parameters for each application will depend on a variety of factors, including the material being cut, the depth of cut, the size of the spindle and the cutting fluid being used. For maximum life, deep hole drilling operations require a slow feed rate and a long cutting time, while shallow holes benefit from faster cutting speeds and shorter cutting times.
Many modern deep hole drilling machines feature the latest in closed-loop control systems, which can automatically adjust the cutting parameters based on the material and size of the workpiece being machined. This advanced cutting technology allows for superior cutting performance and improved accuracy as the cutting parameters are constantly modified to bring the finished part to completion exactly as designed.
In conclusion, deep hole drilling machines represent a major advance in drilling technology over conventional drilling operations. The precision and speed at which they can operate, along with their specialized design and features, allow for accurate and consistent deep hole drilling applications. The cutting parameters involved can vary greatly depending on the material and sizes required, but with proper setup and maintenance deep hole drilling machines can provide the best results and optimum productivity.
