Metal processing industry in Germany, according to a study of drilling processing is one of the most time consuming process machining workshop. In fact, of all the processing time, 36% of consumption on the hole machining operation. Corresponding to this is that turning processing time was 25%, the milling time is 26%. Therefore, the use of high performance overall carbide drill instead of high speed steel and ordinary carbide drill, can greatly reduce the working hours required for the drilling process, thus reduce the machining cost.

In the past few years, cutting parameters (especially the cutting speed) on the constantly improve, especially high performance overall carbide drill cutting speed increase obviously. Twenty years ago, solid carbide drill bits of typical cutting speed is 60 ~ 80 m/min. Now, in the machine tool can provide enough power transmission capacity, stability, and coolant conditions, with 200 m/min the cutting speed of drilling steel has been a surprise. However, compared with the average cutting speed turning or milling, drilling process on the machining efficiency and great potential for improving.

Solid carbide drill bits for the high demand for the toughness of the matrix, and bit wear under the condition of the controllable and uniform stability is acceptable. As a result, the typical drilling tool brand contains more than turning or milling cutter of cobalt element.

A fine grain cemented carbide drill material usually used to improve the cutting edge strength, to ensure uniform wear without collapse edge. With carbide drill process usually water-based cutting fluid is used, so the cutting edge of temperature is not high, but it requires the drill bit has a thermal shock. Best performance of the bit number is typical of pure tungsten carbide material, without the need for a large number of add tantalum carbide or titanium carbide.

For solid carbide drill bits, coating must do more than just improve the surface hardness and abrasion resistance. Coating must be provided between cutter and workpiece material insulating layer and maintain chemical inert; The bonding effect between workpiece materials and coating must be reduced to a minimum to reduce the friction; The coating surface must be smooth as possible; In addition, the coating of twist drill must also has the ability to resist crack spread. Dynamic characteristics of drilling machining of micro cracks may cause, in order to keep the knives' service life, you must stop the spread of the crack. By choosing the correct coating process and generate the appropriate coating microstructure, can make the coating material under a compressive stress state, thus greatly extend the life of cutter.

The use of use multilayer coatings can obtain good effect. Multilayer coatings to hopefully stop the spread of the micro cracks between the layers of coating, even with individual coating damage and spalling, other coating to protect the carbide substrate. Nano coating for drilling tools, and precision custom coating has great potential for development.

For example, a top level using a new type of TiAlN nano TiN coating can make encountered many of the problems in drilling process of stainless steel. Smooth TiN top coating can reduce the cutting tool and workpiece material bonding and friction, and lower TiAlN nano coating can provide hardness and abrasion resistance for cutting tools. This kind of coating has excellent anti crack diffusivity and heat shock resistance, when drilling stainless steel cutting speed can reach 70 ~ 80 m/min, is almost 2 times of conventional bit.

In order to give full play to the modern the excellent properties of cemented carbide substrate and the surface coating, we must optimize the geometric parameters and drill bit type design, must according to the processing and use of drilling, point Angle, blade shape, cutting edge preparation, chip groove, chip groove and the number of blade with make reasonable adjustments, etc.

Efficient cutting bit generally use one of the four kinds of drill tip geometry. With chisel edge of tetrahedron micro-drill point is easy to manufacture, and easy to control the grinding of tolerance, but it is the center of the clearance is small, when feeding large knife surface contact with the bottom of the hole, so the influence of feed rate increase. The other is a conical drill point, compared with the tetrahedron drill point it at the center of the clearance is bigger, so that, when drilling axial thrust is small, but this kind of drill tip geometry is more complicated, difficult to guarantee the consistency of the tool manufacturing and management. Apart from the above two kinds of drill point type, alternative and helical drill point, it is divided into two types: the traditional spiral drill point with a chip groove, chip can discharge from center area; New spiral drill tip is at the same time after the grinding chip groove and blade surface, which can eliminate drilling steps, further improve chip flow. Because these two kinds of design at the center of the drill tip clearance is greater than other kinds of drill tip geometry shape, so has the very high ability of feed. In addition, the new spiral drill tip also has high speed cutting ability, and can in the axial thrust of the smaller drilling. The only drawback of the drill tip geometry is needed for manufacturing drill grinding process is more complex.

When choosing a bit, besides the knives' service life and processing speed, another main factor to consider is the hole machining quality. In recent years, how to reduce the burr became the focus of attention. Deburring is a kind of typical manual process, the manufacturing cost is very high, if improper operation, may cause serious problems.

Solid carbide drill bit in high speed rotation and feeding the workpiece material will produce a lot of pressure. Therefore, the conventional drilling design or drill tip Angle processing, can produce larger burrs in the hole exit. To solve this problem, the simplest method is to drill Angle increases to 135 ° ~ 145 °, point Angle at the bit in this range can be produced in the hole at the exit of a disk, and remain the tensile stress under the action of the workpiece material, make the material easy to cut and not just its launch outside of work. Cutting edge preparation, drilling and chamfering top and other geometrical parameters optimization measures to reduce burr play a large role.

When drilling in grey cast iron and ductile cast iron can produce totally different problems. These material brittleness is larger, more prone to material at the exit to the hole collapse phenomenon rather than the formation of burr. Material collapse will not only affect the quality of workpiece, can also cause bit damaged. Specially designed for cast iron processing drill top chamfering can make bit drilling work piece in a very smooth manner, and keep cutting until the last turn, help to avoid the happening of material collapse fragile phenomenon.

Drill tip design need according to the geometrical parameters of chip groove and adjust. Number of cutting edges, chisel edge thickness, chip groove width, blade width, etc are all factors to consider when designing drill point. In addition, the influence of the workpiece material also nots allow to ignore.

Two slots hole on steel, twist drill is usually the best tool to choose. This bit is convenient to use, easy to heavy grinding, has the extremely good fault tolerance, enough to minimize diameter jump error, and tolerant of instability of machine tool and workpiece.

Has more than 2 chip groove drill in drilling hole with large length to diameter ratio or in a workpiece materials such as cast steel with internal stress on drilling has a performance advantage. Three slot bit with 3 belt of blade and three cutting edges, so when drilling has a better orientation and self-centering capability. But as a result of such a bit cannot bear too big torque, so only recommended for processing of grey cast iron and nonferrous materials. With two cutting edges and 4 belt of blade bit also can be used as an alternative tool scheme (especially in need of cutting tools in the cooling case).

Have 4 belt of blade twist drill performance when machining steel and cast iron materials, because of its fault tolerance is very good, and to be able to more than the single slot bit about twice as high feed rate using the drilling process. This bit is also drilling depth of processing can be up to 30 times the aperture of the tool of choice for deep hole, the drilling speed of about five times to conventional gun drill.

For processing of aluminum alloy material, USES the straight flute drill can get the best drilling precision, and can work out in the form of relatively simple complex ladder groove. Straight flute bit of cutting tool are the shortcomings of gripping high accuracy requirement, this kind of bit of radial runout, high cutting speed and feed rate or low coolant pressure lack of tolerance.

Deep hole drilling in the drilling process, especially) in a very serious problem, is if a bit off the hole at the beginning of the centerline (wandering), so in the back of the processing is almost unable to rectify, blade belt will guide drill drill down along the eccentric position until the bottom of the hole. But because the drill bit has spiral Angle, and drill hole will spiral. To avoid this problem, the most important thing is that there must be a good self-centering capability of drill point correctly. In addition, the orientation of improving bit also helps to prevent running deviation. 2 belt of the blade of the drill in drilling beginning can only get 25% support, so even a small force, also easy to deviate from the center to the most direction. And 4 belt of blade bit can be supported in all directions, so can work out a better roundness and cylindricity hole. Blade with 4 bit in non-uniform drilling or drilling hole can also provide a better support performance, and such drilling operation in the machining process of hydraulic parts, such as is very common.

In drilling today, chip removal must be fully control, rather than in the past, as long as the operator feel drilling force increase, can adopt the way of lift drill pecking at any time. A crucial question is, from the chip at the beginning of the drill point form, must be in a can make the chip and chip removal tank to implement in a way that is easy to match into chip and the chip breaker, and the chip with smaller friction smooth outside vent.

Kinematics principle of the drilling process actually helps chip control, due to the drilling center of the cutting speed is zero, so the chip will more or less in the horizontal flow around the blade, and will be fully formed inside the chip groove, as long as the chip groove with the correct geometry, it is easy to generate the size as a chip. In addition, the chip groove until both ends all adopt the chisel edge of negative taper trench wall surface grinding, and will also help to form a free chip flow, implemented in a controlled state using the drilling process.

Using the right drilling bit and reasonable process parameters, can improve the production efficiency, reduce the processing cost. But how should see tooling cost? First of all, these advanced drill geometry compared with the traditional drill geometry manufacturing difficulty bigger, so in general the price of the new type of bit is also more expensive than traditional bits. However, this new type of bit can resharpening 4 ~ 5 times, although every time after resharpening tool life will reduce about 10%, but it is still possible to save tooling costs more than 50%.

However, every time after resharpening cause to reduce the bit life may also bring some problems. In order to ensure the safety of the processing, can only be used for processing the bit with high safety factor, so the user must use a set of monitoring and tracking system to timely replace the heavy ground drill. To solve this problem, the only way is to use "used to abandon" type product, but the use of disposable solid carbide drill bits are usually very uneconomical.

A new modular bit design can effectively avoid the above problems. This drill adopts the removable carbide drill tip, the cutting performance and cutting tool life and efficient overall carbide drill. Drill point with steel or other USES threaded coupling between the drill shank not on small diameter bit difficult way of connection. Because don't have to consider when designing drill point grinding need, therefore can optimize the drill tip geometry, chisel edge of drill point district, adopted positive rake Angle to reduce the cutting force and improve the self-centering capability. Compared with alloy steel with solid carbide drill bit rigid, so the positive rake Angle is very important to compensate bit rigid.

Unlike conventional carbide drill, modular drill clearance groove is not used to after all use the same spiral Angle, but in the front of chip removal tank using the right hand spiral to speed up the chip flow, at the rear, the use of the small negative clearance groove spiral Angle, a negative spiral Angle for increased stability and reduce the vibration of the bit is particularly useful, also, this steel drill to compensate for lower rigidity is also very important.

Compared with the solid carbide drill bits, modular bit of another difference is that the export of coolant in the chip groove, directed at rake face of cutting edge (solid carbide drill cooling hole exports is in) on the side of the drill tip, the importance of this design is the cutting edge blade is usually a processing temperature before the highest area, very need to provide effective cooling between the chip and tool materials. The design of the cooling hole in optimizing the cooling effect at the same time, also can have a thermal shock effects on chip, help to improve the control chip. Due to drill horizontal blade not directly exposed to the impact of cooling fluid, thus is advantageous to the chip in the chisel edge area of the cutting speed is very low.

Besides the knives' service life good consistency, the use of modular bit can greatly reduce is another important advantage of tool stock. When using conventional cemented carbide drill bit, since there are a large number of bit often in heavy grinding process again, so demand for bit stock is very large. The use of disposable drill out the heavy grinding process again, tool inventory is equal to the number of the bit in machining (perhaps more tools on the shelf in the prepared a small amount of spare parts).