It is not easy to bore a mirror-like deep hole in a special steel, and it is even more difficult to make a hole with a diameter of only 28 mm for an 8-metre-long steel pipe. Today I will talk to you about the case of deep hole processing in military enterprises. In the second part of this article, we introduced 6 common deep hole processing methods. From cases to theories, this article is very comprehensive and worth reading.
1
Write the legend of "deep hole boring".
As an important part of artillery, the quality of the gun barrel directly determines the shooting accuracy and performance power of the artillery. When the shell is fired, the temperature in the barrel of the cannon will instantly rise to more than 3,000 degrees Celsius, and the pressure will rise to more than 600 megapascals, which is equivalent to exerting 6 tons of pressure on an area the size of a fingernail.
The manufacture of artillery barrels belongs to the deep hole processing industry, that is, to punch holes in the alloy steel with ultra-high strength, this special process is also called deep tube boring, which is one of the more difficult processes to master in all processing technologies, so if you want to punch holes for the "king of steel", not everyone can do it, and the processing requirements are not bad at all.
Rong Pengqiang, Chief Technician of China North Industries Group: Because we are engaged in the military industry, the products cannot have a little problem, the products involve the lives of soldiers, and it may be a turning point in a battle when it is critical. If you can't hit it or hit it accurately, it's fatal, and it can be said to be a great responsibility.
After inspecting, measuring and sharpening the knives, and the complex preparation process, Rong Pengqiang began the day's work. As the chief technician of China's weapons, Rong Pengqiang has been assigned to the artillery barrel production line since he entered the industry, and since then, it has become his constant pursuit to boring deep holes as smooth as mirrors in special steel.
Rong Pengqiang, chief technician of China North Industries Group: This is the knife I have used for so many years, the boring blade is loaded into our special tooling, processing high-strength and high-quality alloy steel, and the inner hole is boring as smooth as a mirror, whether it is dimensional accuracy and straightness, it must meet the requirements. For more than 30 years, I have mainly dealt with them.
The smoothness of the inner wall of the barrel directly affects the shooting accuracy of the gun, and this process is difficult to see in the entire processing process, but Master Rong has his own unique secrets.
Through decades of exploration and practice in the production line, Rong Pengqiang has practiced the unique skill of using his hands as "eyes", and his innovative ultra-long small-caliber pipe body deep-hole drilling and boring operation method, with a tolerance of less than 0.01 mm, equivalent to one-tenth of a hair, greatly improving the accuracy of artillery straight line firing.
In 2012, Rong Pengqiang received the daunting task of drilling a hole with a diameter of only 28 millimeters for an 8-meter-long steel pipe, which is only the thickness of an adult's big finger and processed to a depth of three floors. Due to the extreme difficulty of processing and the extremely high precision requirements, there is no domestic manufacturer that can produce it.
A machine tool for one person, Rong Pengqiang a research is a day, dozens of drill bits, five or six types of tool holders, test again and again, millimeter by millimeter forward, a year and a half later, Rong Pengqiang finally overcame the 8-meter difficulty of the national problem, became the first person in China's small-diameter pipe body processing technology.
2
Six commonly used deep hole machining systems
What is Deep Hole Machining?
The so-called deep hole is a hole with a ratio of the length of the hole to the diameter of the hole greater than 10. In most cases, the depth-diameter ratio of general deep holes is L/d≥100. Such as cylinder bore, axial oil bore of shaft, hollow spindle bore and hydraulic valve bore and so on. Some of these holes require high machining accuracy and surface quality, and some of the processed materials have poor machinability, which often becomes a major difficulty in production. What methods can you think of for deep hole machining?
1. Traditional drilling
Deep hole processing originated from the twist drill invented by the Americans. The structure of this drill is relatively simple, and the cutting fluid is easily introduced, which makes it easy to manufacture drills of different diameters and lengths for machining holes of different sizes.
Demonstration of deep hole processing of ultra-long twist drilling in the United States:
2. Gun drill
Deep-hole barrel drill was originally applied to the barrel (commonly known as deep-hole tube, the barrel is not made of seamless precision tube, and the precision tube manufacturing process cannot meet the accuracy requirements at all) manufacturing industry, hence the name gun drill. With the continuous development of science and technology and the unremitting efforts of deep hole processing system manufacturers, deep hole machining has become a convenient and efficient processing method. And it is widely used in: automotive industry, aerospace industry, structural construction industry, medical equipment industry, mold/tool/fixture industry, hydraulic and air compressor industry and other fields.
Gun drill is an ideal solution for deep hole machining, the use of gun drill can obtain precise machining results, the processed hole position is accurate, straightness, coaxiality is high, and has a high surface finish and repeatability. It can easily process various forms of deep holes, and can also be well solved for special deep holes, such as cross holes, blind holes and flat bottom blind holes.
↑↑ Gun drill system composition ↑↑
↑↑ Gun drill bit ↑↑
Video:
3. BTA system
Invented by the International Hole Drilling Association, the drill bit and drill pipe in the BTA system are hollow cylinders, which improves the rigidity of the tool and the problem of quick disassembly and assembly. Its working principle is shown in the figure, the cutting fluid enters the oil feeder from the inlet under pressure and flows to the cutting part for cooling and lubrication through the sealed annular space formed by the drill pipe and the hole wall, and the chips are pressed into the chip outlet on the drill bit, and discharged from the outlet through the inner cavity of the drill pipe. The BTA system is mainly suitable for deep hole machining with a diameter of φ>12 mm.
↑↑BAT system composition ↑↑
↑↑BAT drill bit ↑↑
4. Spray suction drill system
The suction drilling system is a deep-hole drilling method invented by Sandvik Company in Sweden by using the principle of injection suction effect of fluid mechanics. The spray suction drilling system adopts a double-layer pipe cutter holder, and the cutting fluid enters from the inlet after pressurization, in which 2/3 of the cutting fluid enters the annular space between the inner and outer drill pipes, flows to the cutting part for cooling and lubrication, and pushes the chips into the inner cavity of the drill pipe; The remaining 1/3 of the cutting fluid is sprayed into the inner drill pipe at high speed from the crescent-shaped nozzle on the inner drill pipe, forming a low-pressure area in the inner cavity of the inner drill pipe, which has a suction effect on the cutting fluid carrying the chips, and promotes the chips to be quickly discharged from the outlet under the dual action of spraying and suction. The suction drilling system is mainly suitable for deep hole machining with a diameter of φ>18mm.
↑↑ Principle of suction drill system ↑↑
↑↑ Suction drill bit ↑↑
5. DF system
The DF system is a double-inlet single-pipe internal chip removal system developed by Japan Metallurgical Co., Ltd., in which the cutting fluid is divided into two branches, front and rear, which enter from two inlets respectively. The first 2/3 of the cutting fluid flows to the cutting part through the annular area formed by the drill pipe and the wall of the machined hole, and pushes the chips into the chip outlet on the drill bit into the drill pipe and flows to the chip extractor; The latter 1/3 of the cutting fluid directly enters the chip pump, and is accelerated through the flare-shaped narrow conical gap between the front and rear nozzles, resulting in negative pressure suction to achieve the purpose of accelerating chip removal. The structure of the first half of the DF system is similar to that of the BTA system, and the structure of the second half of the "suction" is similar to the spray suction drilling system, because the DF system adopts a double oil inlet device, and only one drill pipe is used to complete the chip method of pushing and suction, so the diameter of the drill pipe can be made very small, and smaller holes can be processed, at present, the minimum processing diameter of the DF system φ can reach 6mm.
↑↑ How the DF system works ↑↑
↑↑DF deep hole drill bit ↑↑
6. SIED system
The SIED system is a single-pipe internal chip removal suction drilling system invented by North University of China. This technology is based on the three internal chip removal drilling technologies of BTA, suction drill, and DF system, and adds a split-type power-added chip pumping device, which can realize independent control of cooling and chip evacuation fluid flow. The basic principle is shown in the figure, after the cutting fluid is output by the hydraulic pump, it is divided into two branches: the former cutting fluid flows into the oil conveyor, flows to the cutting part through the annular space between the drill pipe and the hole wall, and pushes the chips into the chip outlet of the drill bit; The latter cutting fluid flows into the chip pump, and enters the inner cavity of the rear nozzle through the gap between the conical nozzle pairs, generating a high-speed jet and negative pressure. The SIED system has independent regulators for each of the two streams, which can be adjusted to the optimal cooling and chip pumping conditions. The SlED system is a system that is gradually being promoted, and it is also the most advanced system at present. Currently, the SlED system can reduce the minimum drilling diameter by less than φ5mm.