1. What is a deep hole?
A deep hole is defined as having a length-to-hole diameter ratio greater than 10. Most deep holes have a depth-to-diameter ratio of L/d≥100, such as cylinder holes, shaft axial oil holes, hollow spindle holes, hydraulic valve holes, and more. These holes often require a high level of machining accuracy and surface quality, and some materials are difficult to work with, making production challenging. However, with reasonable processing conditions, a good understanding of deep hole processing characteristics, and mastery of the appropriate processing methods, it can be challenging but not impossible.
2. Processing characteristics of deep holes
The holder of the tool is limited by a narrow opening and extended length, which results in insufficient stiffness and low durability. This results in unwanted vibrations, irregularities, and tapering, which negatively affect the straightness and surface texture of deep holes during the cutting cnc manufacturing process.
When drilling and reaming holes, it’s challenging for the cooling lubricant to reach the cutting area without the use of special devices. These devices reduce the tool’s durability and hinder chip removal.
When drilling deep holes, it’s not possible to directly observe the cutting conditions of the tool. Therefore, one must rely on their work experience by paying attention to the sound produced during cutting, examining the chips, feeling for vibrations, monitoring the workpiece temperature, and observing the oil pressure gauge and electric meter to determine whether the cutting process is normal.
It’s essential to have reliable methods to break and control the length and shape of chips, preventing clogging when removing chips.
To ensure that deep holes are processed smoothly and achieve the required quality, it’s necessary to add internal or external chip removal devices, tool guidance and support devices, as well as high-pressure cooling and lubrication devices to the tool.
3. Difficulties in deep-hole processing
Observing the cutting conditions directly is not possible. To judge the chip removal and drill bit wear, one has to rely on sound, chips, machine tool load, oil pressure, and other parameters.
The transmission of cutting heat is not easy. Chip removal can be difficult, and if the chips get blocked, the drill bit may suffer damage.
The drill pipe is long and lacks rigidity, making it prone to vibration. This can cause the hole axis to deflect, resulting in reduced processing accuracy and production efficiency.
Deep hole drills can be classified into two types based on the chip removal method: external chip removal and internal chip removal. External chip removal includes gun drills and solid alloy deep hole drills, which can be subcategorized into two types: with cooling holes and without cooling holes. Internal chip removal can be further classified into three types: BTA deep hole drill, jet suction drill, and DF system deep hole drill.The cutting conditions cannot be directly observed. The chip removal and drill bit wear can be judged only by sound, chips, machine tool load, oil pressure, and other parameters.
Cutting heat is not easily transmitted.
It is difficult to remove chips. If the chips are blocked, the drill bit will be damaged.
Because the drill pipe is long, has poor rigidity, and is prone to vibration, the hole axis will easily deflect, affecting processing accuracy and production efficiency.
Deep hole drills are divided into two types according to chip removal methods: external chip removal and internal chip removal. External chip removal includes gun drills and solid alloy deep hole drills (which can be divided into two types: with cooling holes and without cooling holes); internal chip removal is also divided into three types: BTA deep hole drill, jet suction drill, and DF system deep hole drill.
Deep-hole gun barrel drills, also known as deep-hole tubes, were initially used for the manufacturing of gun barrels. As gun barrels cannot be made using seamless precision tubes, and the precision tube manufacturing process cannot meet the accuracy requirements, deep-hole processing became a popular method. Due to the continuous development of science and technology and the unremitting efforts of deep-hole processing system manufacturers, this technique has become a convenient and efficient processing method that is widely used in various industries, such as the automobile, aerospace, structural construction, medical equipment, mold/tool/jig, hydraulic and air pressure industries.
Gun drilling is an ideal solution for deep-hole processing, as it can achieve precise processing results. The processed holes have a precise position, high straightness, and coaxiality, as well as a high surface finish and repeatability. Gun drilling can easily process various forms of deep holes and can also solve special deep holes, such as cross holes, blind holes, and flat-bottomed blind holes.
Deep hole gun drill, deep hole drill, deep hole drill bit
Gun drill:
1. It is a special deep hole processing tool for external chip removal. The v-shaped angle is 120°.
2. Use of special machine tools for gun drilling.
3. The cooling and chip removal method is a high-pressure oil cooling system.
4. There are two types: ordinary carbide and coated cutter heads.
Deep hole drilling:
1. It is a special deep hole processing tool for external chip removal. The v-shaped angle is 160°.
2. Special for deep hole drilling system.
3. The cooling and chip removal method is pulse type high-pressure mist cooling.
4. There are two types: ordinary carbide and coated cutter heads.
The gun drill is a highly effective tool for deep-hole machining in a wide range of materials, including mold steel, fiberglass, Teflon, P20, and Inconel. It ensures precise hole dimensions, positional accuracy, and straightness in deep hole processing with strict tolerance and surface roughness requirements. It is designed for external chip removal with a 120° V-shaped angle and requires a special machine tool. The cooling and chip removal method is a high-pressure oil cooling system, and there are two types available: ordinary carbide and coated cutting heads.
Deep hole drilling is a similar process, but the V-shaped angle is 160°, and it is designed for use with special deep hole drilling systems. The cooling and chip removal method in this case is a pulse-type high-pressure mist cooling system, and it also has two types of cutting heads available: ordinary carbide and coated cutter heads.
Gun drilling is a highly effective tool for deep-hole machining which can be used for a wide range of processing activities. This includes deep-hole processing of mold steel and plastics such as fiberglass and Teflon, as well as high-strength alloys such as P20 and Inconel. Gun drilling can ensure the dimensional accuracy, positional accuracy, and straightness of the hole, making it ideal for deep hole processing with strict tolerance and surface roughness requirements.
To achieve satisfactory results when gun drilling deep holes, it is essential to have a good understanding of the gun drilling system, including cutting tools, machine tools, fixtures, accessories, workpieces, control units, coolants, and operating procedures. The skill level of the operator is also crucial. Depending on the structure of the workpiece, the hardness of the workpiece material, and the working conditions and quality requirements of the deep hole processing machine tool, selecting the appropriate cutting speed, feed, tool geometric parameters, carbide grade, and coolant parameters is essential to obtain excellent processing performance.
In production, straight groove gun drills are the most commonly used. Depending on the diameter of the gun drill and the internal cooling holes through the transmission part, shank, and cutter head, the gun drill can be made into two types: integral and welded. The coolant sprays out from the small hole on the flank surface. Gun drills can have one or two circular cooling holes or a single waist-shaped hole.
Gun drills are tools used for drilling holes in materials. They are capable of processing holes with diameters ranging from 1.5mm to 76.2mm, and the drilling depth can be up to 100 times the diameter. However, there are specially customized gun drills that can process deep holes with a diameter of 152.4mm and a depth of 5080mm.
Compared to twist drills, gun drills have a lower feed per revolution but a greater feed per minute. The cutting speed of gun drills is higher because the cutter head is made of carbide. This increases the feed per minute of the gun drill. Moreover, the use of high-pressure coolant during the drilling process ensures the effective discharge of chips from the hole being processed. There is no need to retract the tool regularly during the drilling process to discharge the chips.
Precautions when processing deep holes
1) Important considerations for deep hole machining operations include ensuring that the center lines of the spindle, tool guide sleeve, toolbar support sleeve, and machining prototype support sleeve are coaxial as required. The cutting fluid system should be smooth and operational. Additionally, the machined end face of the workpiece should not have a center hole, and inclined surfaces should be avoided during drilling. Maintaining a normal chip shape is crucial to prevent the generation of straight ribbon chips. For processing through holes, a higher speed should be used. However, the speed must be slowed down or stopped when the drill bit is about to drill through to avoid damaging it.
2) During deep hole machining, a large amount of cutting heat is generated, which can be difficult to disperse. To lubricate and cool the tool, sufficient cutting fluid needs to be supplied. Typically, a 1:100 emulsion or extreme pressure emulsion is used. For higher machining accuracy and surface quality, or when dealing with tough materials, an extreme pressure emulsion or high-concentration extreme pressure emulsion is preferred. The kinematic viscosity of the cutting oil is usually 10-20 cm2/s at 40℃, and the cutting oil flow rate is 15-18m/s. For small diameters, low-viscosity cutting oil should be chosen, while for deep hole processing that requires high precision, a cutting oil ratio of 40% extreme-pressure vulcanized oil, 40% kerosene, and 20% chlorinated paraffin can be used.
3) Precautions when using deep hole drill:
① The end face of the milled parts should be perpendicular to the axis of the workpiece to ensure reliable end-face sealing.
② Before formal processing, pre-drill a shallow hole in the workpiece hole position, which can serve as a guide and centering function when drilling.
③In order to ensure the service life of the tool, it is best to use automatic tool feeding.
④If the guide elements in the liquid inlet and the movable center support are worn, they should be replaced in time to avoid affecting the drilling accuracy.
The deep hole drilling machine is a specialized tool used for drilling deep holes with an aspect ratio greater than ten and precision shallow holes. It uses specific drilling technologies like gun drilling, BTA drilling, and jet suction drilling to achieve high precision, high efficiency, and high consistency. Deep hole drilling machines are advanced and efficient hole processing technology and are used in place of traditional hole processing methods.
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Post time: Apr-29-2024