What cutting oil can be selected for deep hole machining to solve the difficulty of chip removal?
July 13, 2023
Deep hole processing is divided into six types:
deep hole drilling, deep hole gun drilling, deep hole boring, deep hole drilling, deep hole honing, scraping and rolling machine tool processing, and more! Of course, the cutting oil used is also different.
Processing characteristics of deep hole drilling machine tools: 1. The tool holder is limited by the aperture, with small diameter and large length, resulting in poor rigidity and low strength. During cutting, it is prone to vibration, ripple, and taper, which affect the straightness and surface roughness of deep holes. 2. When drilling and expanding holes, it is difficult to input cooling lubricant into the cutting area without using special devices, which reduces tool durability and makes chip removal difficult. 3. In the process of deep hole processing, it is not allowed to directly observe the cutting condition of the tool, but to judge whether the cutting process is normal or not by listening to the sound of cutting, watching chips, touching vibration and workpiece temperature, and observing instruments (oil pressure gauge and electricity meter) based on work experience. 4. It is difficult to remove chips, and reliable methods must be used to break and control the length and shape of chips, in order to facilitate smooth removal and prevent chip blockage. In order to ensure the smooth progress of deep hole machining and achieve the required machining quality, it is necessary to add internal (external) chip removal devices, tool guidance and support devices, and high-pressure cooling and lubrication devices for the tool. Generally, a hole with a depth of more than 3-5 times of the hole diameter is called a deep hole. Its difficulty lies in the fact that Fried Dough Twists drills can be used for holes with a relatively small depth of chip removal and cooling holes. In order to remove chips smoothly, iron chips should be straight out in a thin strip shape and bring out smaller pieces, while coolant is easy to enter. It is recommended to use a relatively simple grinding method for the drill bit. 1. Increase the angle between the drill blade to 130-140 degrees to increase the chip thickness and change the direction of chip discharge (the direction of chip discharge is perpendicular to the edge). 2. Grind the horizontal edge to reduce the axial cutting tool, and at the same time, create a corner near the drill core to facilitate chip separation. 3. If the drilling diameter is large, the chip groove can be ground on one side of the cutting edge, which should be one foot wide to balance the cutting force of the two cutting edges; If the diameter is large, the chip separation groove can be ground between the two cutting edges. 4. Chamfer the outer corner of the blade by 1 millimeter and 45 degrees to reduce wear and improve smoothness. 5. The drilling speed should be slightly lower, and the feed amount should be taken larger to thicken the chips and discharge them in a strip shape. 6. The nozzle of the coolant should face inward towards the hole to facilitate the coolant entering the cutting area.
Deep hole drilling can be divided into two types: external chip removal and internal chip removal. For smaller diameters, external chip removal is used, as the drill pipe is too small to remove chips. The drill rod with a larger diameter has sufficient space for chip removal, and high-pressure oil is pressed between the hole wall and the drill rod to remove chips and heat from the rod. The drill bit is specially made of hard alloy, which is divided into two parts: the guide and the chip blade. The chip blade is ground into a trapezoidal shape to separate chips. The height and width of the chip groove depend on the material and feed rate of the workpiece to ensure that the chip shape is tight and small, preferably in the shape of a C-shaped or tile.
In the process of deep hole drilling, it is difficult to remove chips during drilling and it is not easy to emit cutting heat, which often leads to blade annealing and affects the service life and processing efficiency of the drill bit. Poor heat dissipation conditions can generate a large amount of cutting heat, and the direction of chip discharge is opposite to the feed direction of the drill bit. Cutting fluid needs to penetrate into the edge of the drill bit to lubricate, cool, and assist in chip removal. Cutting fluid should first have good permeability, and the supply method, flow rate, and pressure should also meet the requirements.
Solving the selection of cutting oil for deep hole drilling
Although deep hole drilling is a cutting process, it is different from traditional cutting. In practice, it has been found that traditional cutting involves multiple cutting tools working simultaneously, resulting in different torques for each process. In the early stage of deep hole drilling, as soon as the drill bit comes into contact with the workpiece, the pressure reaches around 2000N, and the temperature instantly increases. It is required that the selected oil has low viscosity, good permeability, good cooling ability, and smooth chip removal; At the end of processing, the pressure is about 4000N. If the extreme pressure value (PD) of the selected oil is lower than 4000N or if the release speed of the extreme pressure agent in the oil is slow, then smoking and fast wear of the drill bit are inevitable.
Generally, a 1:100 emulsion or extreme pressure emulsion is selected; When high machining accuracy and surface quality or toughness materials are required, extreme pressure emulsions or high concentration extreme pressure emulsions are selected. The kinematic viscosity of the cutting oil is usually 10-20cm2/s (40 ℃), and the cutting oil flow rate is 15-18m/s; Select cutting oil with low viscosity when the machining diameter is small; For deep hole machining with high precision, the cutting oil ratio can be 40% extreme pressure sulfide oil+40% kerosene+20% Chlorinated paraffins.
