Analysis of the influence of the helix angle of the drill bit on the service life of the drill bit

Helix Angle is the angle between the helix line on the helical groove and the bit axis after it expands into a straight line. Since the lead of each point on helical groove was the same, the helical angle was different at different diameters of the drill bit, with the maximum helical angle at the outer diameter, and the smaller the helical angle was the closer to the center. Increasing the helix angle will increase the front angle, which is conducive to chip removal, but the rigidity of the drill will decrease. Standard twist drill helix angle is 18 ° ~ 38 °. For bits with smaller diameter, the helix angle should be smaller to ensure the rigidity of the drill bit.

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According to the shape of twist drill, the helix angle of each point on the cutting edge is variable, and helix angle directly affects the front angle of the main cutting edge. The larger the helix angle is, the sharper the cutting edge will be and the lighter the cutting will be, otherwise it will cause severe machining hardening and wear the blade quickly. According to the cutting tool design data, helix angle of 30 ° can satisfy the use requirement, at the same time, it can be mass production.

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Manual grinding of high speed steel drill bits

The edge is placed flat against the grinding wheel surface

This is the first step in the bit’s position relative to the grinding wheel. Some inexperienced operators lean on the grinding wheel and start sharpening the edge before they even straighten it out. This must not wear well. The “edge” here is the main cutting edge. “Leveling” means that the main cutting edge of the sharpened part is in a horizontal position. “Wheel surface” refers to the surface of the grinding wheel, “against” is slowly close to the meaning. At this point, the drill bit cannot touch the grinding wheel;

Oblique drill shaft repair sharp Angle

Here refers to the axis of the bit line and the location of the relationship between grinding wheel surface, “Sharp Angle” is the half of the point Angle 118 ° ± 2 ° , it’s about 60 °. This position is very important, which directly affects the size of the point Angle of the drill bit, the shape of the major cutting lip and the chisel edge Angle. Do not neglect to lay down the bevel Angle in order to lay down the cutting edge, or to lay down the axis in order to lay down the cutting lip. These errors are common in practice. At this point, the drill bit is ready to contact the grinding wheel in the correct position;

From the edge to the back of the grinding

This refers to the grinding of the bit’s edge slowly along the entire back surface, starting from the edge of the bit. This facilitates heat dissipation and sharpening. At this point, the bit can gently contact the grinding wheel for a small amount of edge grinding. When grinding the edge, observe the uniformity of spark, adjust the hand pressure in time, and pay attention to the cooling of the drill bit. When the edge grinding starts again after cooling, continue to set the position.

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Manual grinding of high speed steel bit is subject to human factors. Manual grinding will result in a large error of the drill bit due to the difference between human experience and personal intuition. But machine repair and grinding completely avoid this problem. Drill bit grinding machine is more accurate, and the error is small, the human factors are relatively small. Operators do not need to go through professional drill grinding training can be on duty. The operation of the drill bit grinding machine is very simple and the efficiency of the drill bit grinder is very high. Therefore, now many companies that use drill bits choose to buy a drill bit grinding machine to repair the damaged drill bits, which saves a lot of cost. Our tool grinding machines are of very good quality and have been well received by our customers in the market. Welcome to inquire purchase.

Specification for high speed steel drill bits

Drill bit Materials and Steels

HSS bit is the most widely used bit in the industrial manufacturing of twist drill. We usually use high speed steel drill bits. When selecting the most suitable bit type for a particular hole processing task, the technologist needs to calculate the length-diameter ratio of the bit. What is the length-diameter ratio of the drill bit? Length-diameter ratio is the ratio of the depth of the hole processed to the diameter of the drill bit. For example, the drill bit diameter is 12.7mm and the hole depth to be processed is 38.1mm, so its length-diameter ratio is 3:1. When the length-diameter ratio is about 4:1 or less, the chip grooves of most standard high speed steel bits can discharge the chip removed from the cutting edge of the bit more smoothly.

When the length-diameter ratio exceeds the above range, a specially designed deep-hole drill is needed to achieve effective machining. The standard products of HSS drill bits are in accordance with international standards. Once the aspect ratio of the machined hole is greater than 4:1, it is difficult for the HSS bit to push the chip tip out of the cutting area. The chip will soon block the bit’s chip drain. At this point, we need to stop drilling, withdraw the bit from the hole, remove the chip in the chip removal groove, and then drill down again to continue cutting. The above operation needs to be repeated many times to produce the required hole depth. This drilling method is often called “pecking”.

The use of “peck” method to process deep holes will shorten the tool life, reduce the efficiency of machining, and affect the quality of the processed holes. Each time the drill bit is pulled out of the hole, and then the chip is removed and re-inserted into the hole, it is possible to deviate from the center line of the hole and make the hole diameter larger than the specified dimensional tolerance range. In order to solve the problem of deep hole machining, in recent years, drill bit manufacturers have developed two new types of deep hole machining bits — ordinary parabola bit and wide edge parabola bit.

Precautions for use of high speed steel drill bits

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1. Check whether all parts of the drilling machine are normal before use;
2. The high-speed steel bit and the workpiece must be clamped and tightened, and the workpiece cannot be held by hand, so as to avoid injury accident and equipment damage accident caused by the rotation of the bit;
3, focus on the operation, rocker arm and drag plate must be locked before work. When loading and unloading the drill bit, do not use hammer and other tools or objects to knock, and do not use the spindle up and down to hit the drill bit, should use a special key and wrench to load and unload. A drill chuck cannot be used to hold a bit with a tapered handle;
4, when drilling thin plate need to be padded with wood, and use a small amount of feed. When the dill bit is about to drill through the workpiece, the feed should be appropriately reduced. Gently apply pressure to avoid breaking the drill bit, damaging equipment or causing an accident;
5. It is prohibited to wipe the drilling machine and remove iron scraps with cotton yarn and towel when the high-speed steel drill bit is in operation. After work, the drilling machine must be wiped clean, cut off the power supply, stacking parts and keep the working site neat and tidy;
6. When the cuttings are wound on the workpiece or drill bit, the high speed steel drill bit should be raised to make it cut off, and special tools should be used to remove the cuttings after stopping drilling;
7. The drill must be drilled within the working range of the drilling machine, and the drill bit exceeding the rated diameter cannot be used;
8. When changing the belt speed change position, the power supply must be cut off;
9, in the work of any abnormal circumstances, should stop the machine for processing;
10. Before operation, operators must be familiar with the performance, use and precautions of the machine. Operators who are not familiar with the machine are strictly prohibited to operate the machine alone.

What are the differences between machining center and drilling & tapping center?

Now with the vigorous development of industrial manufacturing industry, various industries are using machining center equipment in abrasive tool processing. Many customers still know machining center better. When someone says drilling and tapping center, many people are not clear. Today, let’s talk about the similarities and differences between machining center and drilling & tapping center.

Same points

Machining center and drilling and tapping center, literally, have the word “center”. It can be seen that they are both metal cutting machine tools and CNC processing equipment. In terms of style and function, machining center and drilling and tapping center are very similar.

Difference

Application: Machining center is widely used, mainly for processing plane, surface and other shapes of equipment. Drilling and tapping centers are mainly used for drilling and tapping. Machining center can be used for milling, but machining center can only do slight milling, because the power of drilling and tapping center spindle is not very large, it can not carry out heavy milling.
Shape: drilling and tapping center is smaller than machining center in shape.
Tool library selection: machining center is mainly a hat-type tool library and a disc-type tool library, while drilling and tapping center is mainly a turret-type tool library and a turret-type tool library.
Fast moving speed: drilling and tapping center adopts linear guide rail, which is faster than machining center. The machine tool processing efficiency is obvious.
Price: As far as machinery is concerned, the price of machining center is higher than that of drilling and tapping center.

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Many machinery plants choose to use drilling and tapping centers. Both drilling and tapping centers and machining centers can cause tool damage and wear. In some cases the tool has not been completely damaged, many can be used after repaired with the drill bit grinding machine. For example, worn bits can be repaired with a drill bit sharpener for more than 90% of worn bits. The repaired bit can be reused. We produce a variety of tool grinding machines, you can choose the right tool grinding machine according to your needs to complete the repair work.

What is the reason for the rising price of cutting tools?

Why do the major brands of cutting tools in the same price? It is understood that the rise in the price of raw materials is the main reason for the rise in the price of tools.

In 2017, the price of raw materials for cemented carbides has been rising continuously, leading to a sharp rise in the production cost of enterprises producing cemented carbides. While the annual prices of cemented carbide products have not increased much, carbide tool manufacturers generally face the embarrassing situation of low profits. At present, manufacturers of cemented carbide cutting tools have been unable to bear the soaring cost of raw materials. At the end of the year, many cutting tools manufacturers were forced to raise their prices. Among the rising prices of raw materials, tungsten and cobalt rose the most.

Of course, there are many reasons for the price increase. The increase in raw material costs is only one of the reasons. In recent years, with the trend of consumption upgrading, the public demand is constantly increasing, and high quality products are accompanied by high prices. Therefore, the price increase will come naturally.

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Coating and grinding technology of tools

In the regrinding process of the drill bit or milling cutter, cutting lip should be ground to remove the original coating, so the grinding wheel used must be of sufficient hardness. Regrinding pretreatment of cutting lip is crucial, not only to ensure that the geometric shape of the original cutting lip after regrinding can be fully and accurately retained, but also to require regrinding to be “safe” for PVD coated cutting tools. Therefore, unreasonable grinding techniques must be avoided (e.g., rough or dry grinding that results in tool surface damage due to high temperature).

All existing coatings can be chemically removed before the tool is recoated. Chemical removal methods are commonly used for complex cutting tools (such as roller burnishing tool, rotary broaching tool), repeatedly coated tools, and tools that have problems due to the thickness of the coating. Chemical removal of coatings is usually limited to high speed steel cutters because it can damage the hard alloy matrix. Chemical removal of coatings will remove cobalt from the hard alloy matrix, resulting in loose surface of the matrix, generation of pores and difficulty in recoating.

At present, the typical recoating process is to remove the original coating by regrinding process.

The most common tool coatings are TiN, TiC, and TiAlN. Other superhard nitrogen/carbide coatings are also available, but not very common. PVD diamond coated tools can also be reground and recoated. The cutter should be “protected” from critical surface damage during recoating.

It is often the case that after the user has purchased an uncoated tool, a coating is applied when the tool needs to be reground, or a different coating is applied on a new tool or reground tool. In many cases, we remove the TiN coating from the cutter and reapply the TiAlN coating. Because users want to improve the production efficiency of tools, TiAlN coating tools are faster and more resistant to high temperature than TiN coating tools. Users often wish to get new coated tools with better performance from tool makers. So ‘tool makers may have to redevelop a new tool with a TiAlN coating’. But compared to redeveloping the new cutter, it takes much less time to remove the TiN coating from the old cutter and apply the TiAlN coating.

Just as a cutting tool can be reground multiple times, cutting lip of a cutting tool can be recoated multiple times. “The key to improve the performance of the tool is to obtain a coating with good adhesion on the surface of the tool that has been reground.” With the exception of cutting lip, the rest of the surface of the cutting tool may not need to be removed or recoated during each trim, depending on the type of cutting tool and the cutting parameters used in machining. Roller burnishing tool and rotary broaching tool are the tools that need to be removed from the original coating for recoating, otherwise the performance of the cutter will be reduced. When recoating without removing the old coating, a thickness is added to the outside diameter of the cutter. In the case of drill bit, that means the drill hole is getting larger. Therefore, the influence of the additional thickness of the coating on the outside diameter of the cutter must be considered.

A drill bit can be recoated 5 to 10 times without removing the old coating, but will face serious errors after that. The coating thickness is not a problem within the error range of 1. However, the effect of coating thickness must be considered when the error is within the range of 0.5-0.1 m. As long as the thickness of the coating does not become a problem, the recoated, reground cutter may well be better than the original performance.

What are the differences between normal wear and abnormal wear of cutting tools?

Tools in the production process will encounter a variety of problems, the master of mechanical processing often asked, “why can’t I use this cutter for so little time?”

Under the condition of high temperature, the tool will be gradually worn and damaged by the chip friction of the workpiece. But how can we distinguish the normal wear from the abnormal wear?

Normal wear and tear

Normal wear refers to the wear pattern that gradually expands with the increase of wear over time. There are two aspects that are clearly indicated as normal wear.

Front wear: there is crescent depression wear at the front edge of the blade, which is formed by friction and high-temperature and high-pressure action during chip outflow.
Main rear wear: the main rear wear is divided into three areas. It is assumed that blade tip wear C zone, and wear loss VC is caused by low strength and concentrated temperature near the blade tip. In the intermediate wear area B, except for uniform wear amount VB, the maximum wear amount in the severe wear area is VBmax, which is caused by friction and heat dissipation difference. The boundary wear N zone, where the cutting edge and the surface to be processed wear VN, is caused by high temperature oxidation and surface hardening.

Abnormal wear

Abnormal wear is usually caused by tool damage caused by impact, uneven heating and improper use during cutting.

Crushing: small crushing on the cutting edge is caused by low cutting edge strength, impact and hard points in cutting layer.
Cutting edge: it is easy to crack at the cutting point or cutting point, with brittle cutting material, low cutting strength and heavy cutting load.
Thermal cracking: small cracks in the vertical cutting edge are caused by uneven cutting temperature, discontinuous cutting and uneven pouring of cutting fluid.
Collapse: in the process of cutting, the cutting edge lost its cutting performance under the action of high temperature and high pressure, resulting in the collapse of the front or tip and cutting edge.

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Geometric angle of cutting tool

Choosing the appropriate geometric angle of the tool can help reduce the vibration of the tool, and in turn, the workpiece is not easy to collapse.

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1. Land angle

With the decrease of the absolute value of negative land angle, the wear area of the rear tool surface has little change, but the overall trend is decreasing. With the increase of the rake angle, the strength of the tool edge is weakened, which leads to the decrease of the wear area. The flank wear is aggravated. When negative land angle machining is used, the cutting resistance is large and the cutting vibration is increased. When large positive land angle machining is used, the tool wear is serious and the cutting vibration is also large.

2. Lip Relief Angle

If the lip relief angle increases, the strength of the tool edge will decrease, and the worn area of the flank will gradually increase. After cutting tool lip relief angle is too large, cutting vibration is strengthened.

3. Helix angle

When the helix angle is small, the cutting edge which cuts into the graphite workpiece simultaneously on the same cutting edge has the longest cutting edge length, the greatest cutting resistance and the greatest cutting impact force, so the tool wear, milling force and cutting vibration are the greatest. When the helix angle is large, the direction of milling resultant force deviates from the surface of the workpiece to a great extent, and the cutting impact caused by the collapse of graphite material is intensified, so the tool wear, milling force and cutting vibration are also increased. Therefore, the influence of tool angle change on tool wear, milling force and cutting vibration is caused by the combination of land angle, lip relief angle and spiral angle, so more attention must be paid to the selection.

Through a large number of scientific tests on tool grinding, our tool grinding machines optimizes the geometric angle of the relevant tool in the design, thus greatly improving the overall cutting performance of the tool.

Several methods of tool grinding

No matter what kind of cutter, after a certain period of use, it will be somewhat different from the prototype, which is not as smooth and sharp as it was when I bought it. In order to keep the cutter in its original shape, some grinding operations must be done, which can obviously remove the residue on it, make the blade tip sharper and effectively improve the speed of operation. Different methods should be chosen according to different types of cutter.

Tool grinding method:

Hollow Grind: a groove is excavated on both sides of the cutter surface of the shaping cutter and other cutting tools. Because it is easy to process and design, many factories in the market use this grinding method. The advantage is that this grinding will result in a very thin blade, and the thinner the blade the better. Its drawback is “thinner blade is more fragile”.

Chisel Grind: There is only one side to grind. The advantages are as follows: 1. Easy to process: one side grinding only needs half of the other grinding methods, and does not need to be too precise, so it saves time, labor and money. 2. Easy to grind: Only one side is needed unless there is serious damage, and the grinding technique need not be as advanced as other grinding methods. 3. strong blade: only a single edge, so the blade angle is large (about 30-45 degrees), and the blade is thick. 4. Save material: In the early hammering knife era, this kind of grinding method does not need to be like other grinding methods to generally remove excess steel, can save the most steel consumption.

There are three drawbacks: inaccurate cutting: when you cut apples with chisel grinding and other bilateral grinding knives, you will find that the two-sided grinding knife can cut the apple in two, and the chisel grinding knife will go out with the grinding angle. 2. Unable to puncture too deep: chisel grinding on the tip of the knife caused too much inclination, making it puncture on the formation of many obstacles. 3. Grinding surface error: right-handed knife grinding mode is (from the knife back down) the left side of the knife surface is flat, the right side is grinding; left-handed knife just the opposite. However, due to the differences in the traditional display of knife face and the usage of knife, most of the chisels made by Western knife factories are left-handed knives. When the blade is cut outward, the cutting angle of the knife must be increased to be used smoothly.

Flat Grind/V Grind: a grinding method for both sharpness and solidity. The back of the cutter, such as the shaping knife, has been ground to the blade from the beginning, so it has a fairly solid back and blade.

Saber Grind: Similar to the plane grinding method, they are both sides of the knife face without grooves. The difference is that the surface grinding method runs from the back of the knife to the blade, whereas the cavalry grinding method runs from the half. It also has excellent cutting and splitting ability. The early cavalry knife is the form of grinding, so it is called cavalry grinding.

Convex Grind: Also known as Moran Grind, Bill Moran is the best western master at developing this Grind. This grinding method is different from the above four grinding methods. The other grinding method is to form an inclined surface or groove on both sides of the knife, while the circular grinding method is to form a pair of convex arcs above the blade (also known as the blade in Japan because of its length like a hard clam). This type of grinding is as hard as flat grinding and as sharp as concave grinding. For a very difficult way of grinding. The downside is that if you don’t have a flat-belt Grinder, it can be hard to grind on your own when the blade is blunt.

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