Deep Hole Drilling

August 18, 2011 12:03 pm

As such ‘Drilling’ is the most commonly used process. You would find people using this technology even at home with an easy to use hand-drill machine. Once it comes to deep hole drilling very few people know about it. I have come across highly experienced engineers oblivious to this technology. Of course the main reason for this being that the process of Deep Hole Drilling is not commonly used in the industry compared to conventional machining processes like turning, milling, conventional drilling etc. This technology dates back to the late 19th century, when it was invented to manufacture gun barrels. Earlier gun barrels were made by forging a long strip of steel around a mandrel in a helical fashion. This hand forging process formed the barrel bore around the mandrel and also welded the strip at the spiral joints. This used to be a highly skilled as well as cumbersome process. On the other hand Deep Hole Drilling made the barrel bore making process highly reliable and fast. Obviously being an armament technology, it remained closely guarded subject. Therefore even today you won’t find information in this area in the public domain. Even many Deep Hole Drilling solutions provider do not involve themselves into research in this field. Subsequently it started being used in other industries like oil exploration, automotive, nuclear, power generation etc.
Generally, Deep Hole Drilling is used in applications where the ratio of hole depth to hole diameter (L/D) is more than 10. Major challenge in drilling Deep Hole Drilling is removal of chips from the hole. Peck Drilling is one way of tackling this issue. But there are still issues of lower productivity, hole quality and straightness etc. There are applications where Deep Hole Drilling is used for holes with L/D ratio less than 10 due to its inherent capability of producing Holes with Higher accuracies and surface finish. But Deep Hole Drilling is the only option when it comes to larger L/D ratios where these ratios can go up to 100!
For implementing Deep Hole Drilling process the first thing required is an investment in Deep Hole Drilling Equipment. You will find many companies converting their conventional lathe machines into drilling deep holes and ending up losing money with breakages of costly tooling’s and compromising on quality of the component being drilled. Also the coolant required in this process is special cutting oil with EP additives. As already mentioned the expertise in this technology is very limited and hence troubleshooting becomes a challenge. Companies promoting this technology like Precihole are planning to conduct workshops and seminar for educating the Indian industry. As India is poised to become a global manufacturing hub after China, it is imperative to keep updated with the latest manufacturing technologies and Deep Hole Drilling is one of them. In fact the government should promote research in this field through various engineering and research institute.
There are mainly three categories in Deep Hole Drilling Systems viz. Gun Drilling, BTA/STS drilling and Ejector Drilling. Generally for smaller diameters Gun Drilling is a preferred option. The range can be anywhere from Dia. 2 to 25. There are applications where up to Dia. 1 gun drilling is done on the lower side and up to Dia. 40 on the higher side. BTA/ STS drilling generally starts from Dia. 18 to 250 solid drilling and counter boring can go up to Dia. 500. Even here BTA is being used up to Dia. 12 in some special applications. Ejector technology has been developed by Sandvik mainly introduced to retrofit a conventional machine with Deep Hole drilling system.

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