Ultra-efficiency in deep-hole drilling applications
Takahiro Yamamoto, OSG Corporation Applications Engineer (Drill Development Division)
For many years, gun drills and HSS long drills have been the tooling of choice for deep-hole applications. For drilling depth of 30xD or less, carbide twist drills capable of high-efficiency performance have become more and more widespread in recent times. However, for deep-hole applications exceeding 30xD, it is still a great challenge for carbide twist drills to achieve stable high-efficiency performance. Thus, gun drills continue to be commonly chosen for ultra-deep-hole scenarios.
OSG Corporation is pleased to introduce one of its latest drilling innovations for deep-hole applications – the ADO-40D and 50D coolant-through carbide long drills – engineered for ultra-efficiency and superior stability with performance equivalent to drilling 30xD or lower depth.
Features of ADO-40D and 50D
There are three key features of the ADO-40D and 50D that contribute to high-efficiency and stable machining of deep holes exceeding 30xD. The most important feature is its newly developed R gash geometry.
Figure 1. Newly developed R gash geometry. The newly developed R gash geometry enables a cutting force reduction of 30 percent or more compared to the conventional design with exceptional chip shape stability.
Although conventional carbide twist drills are capable of producing finely divided chips, when machining steel materials such as carbon steel, alloy steel and stainless steel, elongation of chips can easily occur. The unstable chip shape interferes with chip evacuation, which is especially problematic in deep-hole drilling, and may lead to sudden tool breakage.
The ADO’s newly developed R gash geometry expands the chip room at the center of the tool where chips are difficult to be discharged. With the optimized R shape to guide the direction of chip flow, chips can be evacuated smoothly. Moreover, with this new feature, the curling of chips is controlled, and the consistency of chip shape has significantly improved to allow superior chip separation versus the conventional design. In addition, the cutting force (thrust resistance) is reduced by approximately 30 percent compared to the conventional design, thereby enabling the suppression of machining vibration in high-feed machining and improves straightness during drilling.
The ADO coolant-through carbide long drill series is one of OSG’s latest drilling innovations for ultra-efficiency in deep-hole applications.
The second key feature of the ADO long drill is its new flute specification that enables smooth evacuation of the compact chips created by the R gash geometry, while maintaining high tool rigidity of the long tool body necessary for 40xD and 50xD applications. Chip evacuation capability has been greatly amplified by expanding the width of the flute, which functions as chip room. A 25-degree helical flute geometry is applied to enhance rigidity without interfering chip evacuation capability.
Last but not least, just as important as the previous two key features is the adoption of OSG’s original EgiAs coating for high durability. The EgiAs coating is consist of overlapping nano-periodical layers and wear-resistance layers, engineered to suppress the propagation of cracks that are likely to occur during drilling. The wear-resistance layer is composed of multiple hard layers; while the nano-periodical is a combination of hard and soft layers. With a mixture of hard and soft layers, internal stress can be relieved, allowing the EgiAs coating to achieve both high wear resistance and extreme toughness to ensure stable and consistent tool life under aggressive cutting conditions.
As mentioned previously, the most notable advantages of the ADO long drill are its consistent chip separation ability, low cutting resistance, and capability to achieve a fine balance between tool rigidity and trouble-free chip evacuation regardless of the long cutting depth to allow stable and efficiency processing.
1. Consistent Chip Separation Ability
Figure 2. Chip shapes in alloy steel SCM420H, which is highly viscous among steel materials.
As depicted in figure 2, the competitor carbide twist drill is unable to separate the chips effectively and ended up with elongated chips. The ADO-50D, on the other hand, demonstrates finely divided chips that are consistent in shape. The stability of cutting chips is one of the most important factors for achieving stable machining in deep-hole applications. As will be depicted later on in the article, this factor is the key to stable and extremely long tool life.
2. Low Resistance Processing
Figure 3. Cutting force resistance comparison when machining SCM440.
As shown in figure 3, the thrust resistance generated by the ADO-40D has been reduced by approximately 30 percent compared to the competitor drill (conventional design). The recorded waveform is calm and consistent, contributed by the ADO-40D’s smooth chip evacuation capability for stable performance.
3. High Tool Rigidity with Excellent Chip Evacuation for Achieving Stable Machining
For long drill lengths such as 30xD, 40xD and 50xD, the tool rigidity is reduced by nature due to the long overhang length. By increasing the bottom flute diameter or by reducing the helix angle can enhance tool rigidity. However, since the machining depth is deep, the path required for chip discharge is also lengthy. If too much emphasis is placed on the tool rigidity, chips cannot be evacuated smoothly. To resolve this challenge, the ADO-40D and 50D carbide long drills have employed a 25-degree helix angle versus the 30-degree helix angle commonly found in coolant-through carbide drills. This design ensures tool rigidity without impairing chip evacuation.
Figure 4. Helix angle’s effect on machining
As depicted in figure 4, vibration due to insufficient tool rigidity is observed during machining with the conventional 30-degree helix angle. While the 20-degree helix angle configuration has difficulty discharging cutting chips. The 25-degree helix angle demonstrates excellent stability and smooth chip evacuation.
With the previously mentioned key features of the ADO carbide long drill and the effect of OSG’s newly developed EgiAs coating, long tool life and stable machining is made possible in deep-hole applications. Figures 5 and 6 highlight the superior performance of the ADO long drills that far surpass gun drills and other competitor products.
Figure 5. Performance versus gun drill
Figure 5 introduces an example of using the ADO-50D to reduce the number of steps required for deep-hole drilling to improve higher processing efficiency while extending tool life.
Conventionally, deep-hole applications require the use of three tools – pilot hole drill, carbide twist drill (up to 27xD) and gun drill. However, in the cutting example illustrated in figure 5, the process is carried out in two steps, where only two tools – pilot hole drill and carbide long drill (50xD) are used to reduce the number of processes, increase efficiency and extend tool life. With the competitor long drill, machining is highly unstable and tool life is short. Thus, it is not possible to perform the operation in two steps. By employing the ADO-50D, on the other hand, significant processing time reduction and long tool life can be achieved. The long drilling process after the pilot hole can be completed with a single tool. Moreover, tool life is estimated to be 1.3 times longer with more than 2.5 times the drilling distance being machined. In this cutting trial, the ADO-50D is able to perform at more than 3 times the processing efficiency stably versus the conventional method.
Figure 6. Performance versus the competitor
As depicted in figure 6, the competitor carbide twist drill encountered sudden breakage due to unstable chip shape and chip evacuation, which can commonly occur at 100 holes or less. The ADO-50D, on the other hand, is able to machine under identical cutting condition as the competitor, but with 1.8 times the machining efficiency and more than 3 times the tool life consistently.
The ADO-40D and 50D are able to demonstrate their superior capability to eliminate machining troubles such as abrupt tool breakage, short tool life, long processing time and unstable performance commonly found in deep-hole applications.
The newly developed R gash geometry applied in the ADO long drill is also used in OSG’s ADO-TRS 3-flute carbide drill for ultra-machining efficiency and stability in steel applications. In the future, OSG will look to apply this unique specification to other products and evolve the company’s A-Drill series to better meet today’s demand of higher stability, efficiency, longer tool life, and greater precision machining.
For manufacturers who are struggling with deep-hole drilling, look to the ADO-40D and 50D to experience ultra-processing efficiency and stability.
The ADO-40D is available from diameter 3 mm up to 10 mm. The ADO-50D is available from diameter 3 mm up to 8 mm. Custom sizes are also available upon request. The manufacturable range of special sizes is indicated in figure 7.
Figure 7. Manufacturable range of special sizes
For more information on the ADO-40D and 50D coolant-through carbide long drills