Efficient machining method for complex deep holes!
Complex deep hole machining has become increasingly challenging. Parts often require additional features, such as very small hole finishes, inner chambers, changes in aperture, contours, grooves, threads, and changing hole directions. To efficiently obtain such holes with small tolerances, not only does it require extensive experience and R&D resources, but also engineering capabilities, application facilities, and substantial customer involvement.
Deep Hole Machining (DHM)
It is a type of machining field dominated by cutting tools designed specifically for existing applications. Many different industries involve deep hole machining, but the most widely used are the energy and aerospace industries. At first, certain features of deep hole parts may seem impossible to form, but non-standard tool solutions designed by experts not only solve process problems, but also ensure that they are executed to some extent with high efficiency and error free features.
The increasing demand for complex holes and the urgent need to shorten processing time have promoted the development of modern deep hole processing technology. For decades, deep hole drilling has been an efficient machining method using hard alloy cutting tools, but the bottleneck of bottom hole boring has begun to emerge.
Nowadays, success in this machining field is usually based on a mixture of standard and specialized tool components, which have experience in designing specialized deep hole machining tools. These tools are equipped with extended high-precision tool holders, support functions, and integrated reamers, combined with the latest cutting edge groove and blade materials, as well as efficient coolant and chip control, to achieve the required high-quality results with the highest penetration rate and processing safety.
Figure 1
The parts that stop deep hole machining in Figure 1 first require drilling very deep holes, and then often involve various complex feature machining. The success of deep hole machining is usually based on a combination of application standards and common tool components, which have experience in designing non-standard tools. This type of non-standard tool based on T-Max 424.10 drill bit is a part of single tube application.
In deep hole drilling, small diameter holes below 1mm are machined using hard alloy gun drills. However, for holes 15mm and above, welding edge drills are generally used, while for holes 25mm and above, adjustable blade drills are used for highly efficient drilling. Modern indexable blade technology and drilling pipe systems also provide new possibilities for specialized cutting tools for deep hole machining.
When the hole depth exceeds 10 times the aperture, the processed hole is generally considered very deep. When the hole depth reaches 300 times the diameter, specialized techniques are required and single or double pipe systems can be used for drilling. In the long process of machining to the bottom of these holes, specialized motion mechanisms, tool configurations, and correct cutting edges are required to complete the machining of the inner chamber, grooves, threads, and cavities. Support plate technology is another important field, and it is also crucial in deep hole drilling. Now, as part of deep hole processing technology, it has made significant progress. This includes qualified cutting tools that are suitable for this field and can provide higher performance.
Figure 2
In deep hole machining, small diameter holes below 1mm are machined using hard alloy gun drills. However, for holes 15mm and above, welding edge drills are commonly used, while for holes 25mm and above, indexable blade drills are used to efficiently execute these processes in single tube and Ejector double tube systems. The Sandvik Keleman Deep Hole Processing Global Center can provide development, design, and testing resources for the development of part processes in the industry. In addition to small-scale applications, the center also collaborates closely with many industries that require higher parts output and touch a small number of high-quality holes, such as heat exchangers and steel billets.
Craft opportunities
The current manufacturing requirements require a deep hole machining solution that is completely different from that of deep hole drilling (which is usually carried out on other machine tools for subsequent single blade boring processes). Even on multitasking machines, this method is required for a single clamping. For example, when processing a hole several meters deep, its aperture is about 100mm, and one end must have a thread, and the inner chamber that penetrates into the hole must have a larger diameter. Usually, when drilling is completed, these features are added to the hole through the boring process after moving the part onto the lathe. Nowadays, deep hole machining combines the ability of a cutting tool to perform subsequent processes, and there are no machine tool adjustment restrictions. This new tool technology has actually expanded its operational capabilities, allowing for more efficient processing of these demanding features within a smaller range of limitations.
An example of using deep hole machining technology for efficient feature machining is petroleum exploration parts. This type of part is about 2.5m long and has some complex features with small tolerances. To achieve small tolerances and excellent surface finish, the tool solution first involves drilling holes with a diameter of 90mm, and then using a floating reamer for precision machining. Then, at a depth of 1.5m, the hole with a diameter of 115mm was enlarged and reamed. The other partition enters the hole approximately midway, and then it is also expanded and reamed, and processed through chamfering. Finally, perform boring and reaming to form two inner chambers with chamfers (also reamed to the finished size).
The common deep hole machining tools in the global center for deep hole machining bring non-standard disposal solutions suitable for parts in this power industry. The cutting time has been extended from over 30 hours to 7 and a half hours. This non-standard tool disposal plan can provide the required small tolerance and surface brightness throughout the relatively complex hole. The process includes one deep hole drilling and using a floating reamer to stop precision machining. Subsequently, reaching a depth of 1.5m, stop expanding and reaming the hole with a diameter of 115mm. Next, stop drilling and reaming the shorter part in another deep hole, and form a chamfer. Finally, stop boring and reaming to form two inner chambers with chamfers (also reamed to the finished size).
During routine machining, the time required to complete this part on the machine tool exceeds 30 hours. The deep hole machining solution equipped with specialized cutting tools can shorten the time to 7.5 hours.
Efficiency improvement
Completely different from multi operation clamping, using deep hole processing technology can also achieve production efficiency improvement in large batches. It is not surprising that the cutting time has been reduced by 80%. An example that can prove capability is that proprietary technology in tool and blade design can maximize the safety of cutting edge loads. Load balancing and optimizing cutting effects on the optimal number of blades can allow for higher penetration rates, thereby reducing processing time. In terms of accuracy, small tolerances are the specialty of deep hole machining, with 70% of the holes having concentric inner diameters, a typical tolerance of 0.2mm, and a diameter tolerance of 20 microns.
Deep holes deviating from the centerline
Another example of high requirements for cutting tools and proprietary technology during hole drilling is the machining of very deep holes in the generator shaft of a power plant. In this case, the power generation industry expert Generpro must process 90 tons of forged steel parts in an asymmetric manner with holes close to 5.5m long and diameters just over 100mm from the centerline of the shaft. This type of deep hole must be drilled at a certain angle deviation, and the positional tolerance must be within 8mm when exiting.
The drilling direction, chip breakage and removal, as well as the absolute absence of waste in the pre machined shaft, are crucial for this application. The tool solution includes a dedicated drill bit and a new type of support plate. Before applying on the shaft, drilling tests are required, and the results confirm that it is more efficient and reliable - and the exit position is within 2.5mm of the target.
In many cases, the use of modern hole processing technology indicates a significant reduction in processing time - from multiple hours to less than 1 hour - and makes many complex features machinable.
