Complex deep hole machining is becoming more and more challenging. Parts often require additional features such as very small hole finishes, inner chambers, hole diameter variations, contours, grooves, threads, and varying hole orientations. Efficiently obtaining such tight tolerance holes requires not only extensive experience and R&D resources, but also engineering capabilities, application facilities, and substantial customer involvement.

Deep Hole Machining (DHM)

is a machining field dominated by tools designed for existing applications. Deep hole machining is involved in many different industries, but the most widely used are the energy and aerospace industries. At first, some deep hole part features often seem impossible to form, but special tool solutions designed by experts not only solve process problems, but also ensure that they are executed in a way that is characterized by high efficiency and error-free.The ever-increasing demand for complex holes and the urgent need to reduce machining times has led to the development of modern deep hole machining techniques. Deep hole drilling has been an efficient method of machining with carbide tools for decades, but bottom hole boring is starting to emerge as a bottleneck.
Today, success in this area of ​​machining is often based on a mix of standard and specialized tool elements that have experience designed as specialized deep-hole machining tools. These tools feature an extended, high-precision shank with support features and an integrated reamer, combined with the latest cutting edge geometries and insert grades, as well as efficient coolant and chip control, for the highest penetration and Get the high-quality results you need with process safety.

Figure 1 Parts that stop deep hole machining first require drilling very deep holes, often followed by machining of various complex features. Success in deep hole machining is often based on a mix of specifications and special tool elements that have a history of being designed as non-standard tools. Such non-standard tools based on T-Max 424.10 drills are part of a single-pipe application.In deep hole drilling, small-diameter holes below 1mm are machined with carbide gun drills, but for holes of 15mm and above, welded edge drills are generally used, and for holes of 25mm and above, indexable inserts are used. The drill can perform very efficient drilling. Modern indexable insert technology and drill pipe systems also offer new possibilities for deep hole machining with specialized tools.

When the hole depth exceeds 10 times the hole diameter, the machined hole is generally considered to be very deep. Special techniques are required for holes as deep as 300 diameters and can be drilled with single or double pipe systems. The long process of machining to the bottom of these holes requires specialized kinematics, tool configuration, and the correct cutting edge to complete the chambers, grooves, threads and cavities.  Support plate technology is another important field, and it is also very important in deep hole drilling. Now it is also making great progress as part of deep hole machining technology. These include qualified knives for this field that offer higher performance.

Fig. 2 In deep hole processing, small diameter holes below 1mm are processed by carbide gun drills, but for holes of 15mm and above, welding-edged drills are generally used, and for holes of 25mm and above, rotary drills are used. Bit-blade drills can perform these operations very efficiently in both the single-pipe system and the Ejector double-pipe system. Drillstar global centers for deep hole machining provide development, design and testing resources for developing part processes in the industry. In addition to low-volume applications, the center works closely with industries that demand higher part output and touch a small number of high-quality holes, such as heat exchangers and billets.

Craft opportunities

Today’s manufacturing requirements require deep-hole machining solutions that are completely different from deep-hole drilling (which is followed by a subsequent single-edge boring operation, which often has to be performed on other machines). Even on multitasking machines, this method is required for a single setup. For example, to machine a hole several meters deep, the diameter of which is about 100mm, one end must be threaded, and the inner chamber that penetrates into the hole has a larger diameter. Usually, , when the drilling is completed, after the part is moved to the lathe, these features are then added to the hole through the boring process. Deep hole machining now combines the ability of one tool to perform subsequent operations without the limitations of machine adjustments. This new tool technology has instead broadened its operational capabilities to more efficiently machine these demanding features within tighter constraints.

An example of efficient feature machining using deep hole machining techniques is oil exploration parts. Such parts are about 2.5m long and have some complex features with tight tolerances. To achieve tight tolerances and an excellent surface finish, the tool solution first involved drilling a 90mm diameter hole, followed by finishing with a floating reamer. The 115mm diameter hole was then reamed and reamed to a depth of 1.5m. The other partition goes into the hole about halfway through, and is then also reamed and reamed, and finished by chamfering. Finally, boring and reaming are performed to create two inner chambers that are chamfered (also reamed to finished size).

The special deep hole machining tool of the deep hole machining global center brings a non-standard disposal solution suitable for this power industry part. Cutting time was extended from more than 30 hours to 7.5 hours. This custom tool handling solution provides the required tight tolerances and surface finish throughout a relatively complex hole. The process consists of one deep hole drilling and finishing with a floating reamer stop. After reaching a depth of 1.5m, the reaming and reaming of the 115mm diameter hole was stopped. Then stop reaming and reaming and chamfer the shorter part in the other deep hole. Finally, stop boring and reaming create two chambers that are chamfered (also reamed to finished size).

In conventional machining, this part takes more than 30 hours to complete on the machine. A deep hole machining solution with a dedicated tool reduces the time to 7.5 hours.

Efficiency improvement

Completely different from multi-operation clamping, the use of deep hole machining technology can also improve production efficiency in large batches. It is not surprising that the cutting time is reduced by 80%. An example of a proven capability is the know-how in tool and insert design to maximize cutting edge load safety. Load balancing and optimized cutting action on the optimal number of inserts allow for higher penetration rates, resulting in shorter machining times. In terms of accuracy, small tolerances are the specialty of deep hole machining, where 70% of the holes have a concentric inner diameter, with a typical tolerance of 0.2mm and a diameter tolerance of 20 microns.

Deep hole off centerline

Another example of the high tool and application know-how required for hole drilling is the machining of very deep holes in generator shafts in power stations. In this case, the power generation industry expert DrillStar must process 90 tons of forged steel parts in a way that is asymmetrical to the shaft centerline, in which the hole is close to 5.5m long , just over 100mm in diameter. Such deep holes must be drilled off a certain angle, and the position tolerance must be within 8mm when withdrawing.

Drilling direction, chip breaking and evacuation, and the absolute absence of scrap from the pre-machined shaft are critical for this application. The tool solution includes a special drill and a new support plate. Drilling tests were performed prior to application on shafts, which proved to be more efficient and reliable – and the exit position was within 2.5mm of the target.

In many cases the use of modern hole-making techniques has shown significant reductions in machining time – from many hours to less than an hour – and made many complex features machinable.

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