In mechanical processing, hole processing accounts for about 1/5 of the total processing volume, and drilling accounts for about 30% of the entire hole processing. I believe that gold enthusiasts who work on the front lines of drilling will not be strangers to drill bits. When purchasing drill bits, there will be drill bits made in different materials and colors. So, what are the differences between drill bits of different colors? What is the best color for the drill bit? buy?
Is there a relationship between color and drill bit quality?
First of all: it is impossible to determine the quality of drill bits simply by color. There is no direct and inevitable relationship between color and quality. Different colored drill bits are mainly due to different processing techniques. rough judgment based on color, but current low-quality drill bits will also process their own color to achieve the appearance of high-quality drill bits.
What is the difference between different colored drill bits?
High-quality, fully ground high-speed steel drill bits often appear white. Of course, laminated drill bits can also be made white by fine grinding the outer circle. The reason why they are high quality is not only the material itself, but also. the quality control during the grinding process is quite strict and there will be no burns on the tool surface. The black ones are nitrided drills. This is a chemical method of improving tool durability by placing the finished tool in a mixture of ammonia and water vapor and subjecting it to a heat preservation treatment of 540 to 560°C. Most of the black drill bits currently on the market are only black in color (in order to conceal burns or black skin on the tool surface), but the actual use effect has not been effectively improved.
There are three processes to produce drill bits, black is rolled, which is the worst. The blanks are cleared and polished. Because unlike rolling, no high temperature oxidation occurs, the grain structure of the steel is not destroyed and it can be used to drill parts of slightly higher hardness. Yellow-brown drills are called cobalt-containing drills in the industry. This is an unwritten rule in the drill bit industry. Cobalt-containing diamonds are originally white and are produced by grinding when atomized later they become yellowish brown (commonly known as amber). They are currently the best in circulation. M35 (Co 5%) also has a golden color. This type of drill bit is called titanium plated drill bit, which is divided into decorative plating and industrial plating. The decorative plating has no effect, it just looks nice and golden. Industrial plating is very good, the hardness can reach HRC78, which is higher than the hardness of cobalt diamond (HRC54).
How to choose a drill bit
Since color is not a criterion for judging the quality of a drill bit, how do you choose a drill bit?
Judging from experience, generally speaking, white drill bits are generally fully ground high speed steel drill bits and should have the best quality. The gold ones are coated with titanium nitride and are usually the best or worst ones that fool people. The quality of black also varies, and some are made from poor quality carbon tool steel that is easy to anneal and rust, so it must be blackened.
Usually, when purchasing a drill bit, you can look at the brand and diameter tolerance mark on the drill bit shank. The marks are clear and the quality of laser or electrical corrosion will not be too bad. If it is a cast word, if the edge of the word is bulging, the quality of the drill bit is poor, because the bulging outline of the word will prevent the tightening accuracy of the drill bit from meeting the requirements, and the edge of the word word is clear and well bonded to the cylindrical surface of the drill shank. The borderlines are of good quality. Additionally, look at the sharpness at the tip of the drill bit. The cutting edge of the fully ground drill bit is very good and the spiral surface meets the requirements, while the quality of the drill bit is poor at the back corner. the surface is very poor.
Drilling accuracy
After selecting the drill bit, let’s look at the drilling accuracy. Hole accuracy is mainly composed of factors such as aperture size, position accuracy, coaxiality, roundness, surface roughness and hole burrs.
Factors that affect the accuracy of the hole being processed during drilling:
①Drill clamping accuracy and cutting conditions, such as tool holder, cutting speed, feed amount, cutting fluid, etc. ;
②Drill bit size and shape, such as drill bit length, blade shape, sprue shape, etc. ;
③ Workpiece shape, such as hole side shape, hole shape, thickness, clamping state, etc.
1. Expansion
The enlargement of the hole is caused by the oscillation of the drill bit during processing. The oscillation of the tool holder has a great influence on the hole diameter and hole positioning accuracy. Therefore, when the tool holder is seriously worn, a new tool holder should be replaced in time. When drilling small holes, it is difficult to measure and adjust the wobble, so it is better to use a drill bit with a thick handle and a small blade diameter that has good coaxiality between the blade and the shank . When using resharpening drills, the decrease in hole accuracy is mainly due to the asymmetry of the subsequent shape. Controlling the edge height difference can effectively suppress the cutting expansion of the hole.
2. Hole roundness
Due to the vibration of the drill bit, the drilled hole can easily become polygonal, with lines like scratched lines appearing on the wall of the hole. Common polygonal holes are mostly triangles or pentagons. The reason for the triangular hole is that the drill bit has two centers of rotation when drilling. They vibrate at a frequency that is exchanged every 600. The main reason for the vibration is unbalanced cutting resistance as the bit rotates for one revolution. the roundness of the treated hole will be uneven. Well, the resistance is unbalanced in the second round of cutting and the last vibration is repeated again, but the vibration phase is shifted to a certain extent, causing scratch lines to appear on the hole wall. . When the drilling depth reaches a certain level, the friction between the surface of the drill edge and the hole wall increases, the vibration becomes attenuated, the scratched line disappears, and the roundness improves. This type of hole has a funnel-shaped opening seen in longitudinal section. For the same reason, pentagonal and heptagonal holes may also appear when cutting. In order to eliminate this phenomenon, in addition to controlling factors such as chuck vibration, cutting height difference, asymmetry of the back surface and blade shape, etc., measurements should also be taken. taken to improve the rigidity of the drill, increase the feed per revolution, reduce the relief. angle and grinding of chisel blade and other measurements.
3. Drilling holes on inclined and curved surfaces
When the cutting surface or drilling surface of the drill bit is a beveled, curved or stepping surface, the positioning accuracy is poor. Since the bit cuts on one side in a radial direction, tool life is reduced.
To improve positioning accuracy, the following measures can be taken:
1) Drill the center hole first;
2) Use an end mill to countersink the hole seat;
3) Choose a drill bit with good penetration and good rigidity;
4) Reduce the feed speed.
4. Burr treatment
When drilling, burrs will appear at the entrance and exit of the hole, especially when processing hard materials and thin plates. The reason is that when the drill bit is about to drill, the processed material undergoes plastic deformation. At this time, the triangular part that needs to be cut by the edge of the drill bit near the outer edge is deformed and bent outward. the axial cutting force, and is curved outward at the outer edge of the drill bit. It is then curved under the action of chamfers and edge surfaces to form curved edges or burrs.
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