The traditional concept of "spiral groove bit is irreplaceable" is now being subverted by the processing efficiency of the straight bit. In some processing applications, the straight groove drill is becoming a better tool choice than the twist drill.
        The "pioneer" of the modern straight slot drill is a die drills, which are short in size, rigid and well-bore, suitable for drilling hard steel at lower spindle speeds and smaller feed rates, Its high strength and high rigidity make it possible to process straight and rounded holes. Mold bit has been able to achieve good processing results, because the design of the drill when the processing material is usually produced short chip metal. Chip control is still a key issue in the machining applications of straight slot drills. (P / M), medium-high silicon content (6% or higher) of silicon-aluminum (P / M), medium-high silicon content (6% or higher) is only possible in the case of processing materials that do not produce long rolls of chips Alloy and so on.
However, with the machine tool technology, coolant transport technology and tool geometry design progress, straight groove drilling processing applications are constantly expanding. The traditional way of thinking that the spiral groove of the drill bit is essential for chip removal, straight groove drilling can only be used in aluminum and cast iron drilling hole depth of 2D ~ 3D (D for the aperture) of the shallow hole. But now the development of high-pressure cooling system and higher machine tool spindle speed, making the use of internal cooling straight groove drill chip and chip performance greatly improved.
In the case of suitable processing conditions, the straight bit drill can show far better than the spiral groove bit good processing performance. The advantage of the straight bit is to be able to process rounded and straightened holes with faster cutting speeds than standard cobalt or high speed steel drills. For example, the cutting speed of the twist drill is 50sfm (15m / min) and the feedrate is 0.005ipr (0.127mm / r) when the tiles are machined with a Guhring RT150GG straight groove with a diameter of 0.394 "(φ10mm) The cutting speed of the straight groove is up to 800sfm (245m / min) and the feed rate is 0.007ipr (0.178mm / r). The cutting time of the straight groove is only 1/10 of the twist drill.
Partial reasons for the significant improvement in machining efficiency by straight-groove drilling are based on the basic design of the drill bit, which provides a direct channel for the chip discharge orifice. However, since the cutting edge of the straight bit bit lacks a positive rake angle, its crumb and chip breaking capacity is poor, especially when machining ductile materials.
Cutting speed (especially high enough cutting speed) is another factor in the successful application of straight groove drilling. The faster the cutting speed, the smaller the chip is formed. Straight groove drilling is achieved by a faster spindle speed rather than a higher feed rate to achieve high productivity.
Many high-performance, high-drilled twist drills have a large chamfer on the cutting edge, which requires the drill to enter the work of the feed should be more than the cutting edge of the chamfer size, so that the cutting edge to the workpiece material Cut it and not just push it. For some processing applications and machined materials, the cutting edges of the twist drill are in good working condition, and these twist drills are usually drilled at a feed rate higher than the straight slot and a cutting speed below the straight slot The
Take the car manufacturer Saturn's drilling as an example. The drill bits used by the company were previously processed at a cutting speed of about 500sfm (150m / min). Later, they decided to do some cutting test, would like to determine the drill in the end to how high the speed of processing. As a result, they found that when the speed increased, the tool life is extended, the processing cycle is shortened, chip efficiency is improved. When using uncoated monolithic carbide bit, the cutting speed can reach 1000smm (300m / min), while the tool life and the quality of the hole are significantly improved.
Through the use of a reasonable combination of coolant pressure and cutting speed, straight slot drill can also be effective processing of those who do not necessarily produce short pieces of the workpiece material. For example, with the straight groove drilling 1144 resistant steel effect is very good, broken chip smooth and chip small, also did not form BUE. The drill bit is HAM Precision's 294-0500 uncoated cooling straight bit (diameter φ5mm) with a drilling depth of 48mm and a cutting speed of 185sfm (63m / min) with a feed rate of 0.003ipr (0.076mm / R), the coolant pressure is 1500 psi. 1144 alloy manganese sulfide content is high, is conducive to chip breaking. However, to successfully process this material requires a high coolant pressure (experience has shown that the coolant pressure should be above 600 psi, preferably 1000 psi, 1200 psi or more).

For straight groove drilling, in addition to chip control, the chip may also become a problem. This is because the workpiece material is removed from the center of the straight groove when the cutting edge, and was pushed to the drill bit tip. One of the ways to avoid the formation of BUE is to use a well with a smooth surface and a high finish. The use of a coated drill bit also helps to prevent the formation of BUE, such as molybdenum disulfide (MoS2) coatings, which are widely used in aluminum processing, Teflon (Teflon) similar characteristics, difficult to bond with other substances, the need to prevent the formation of the chip in the processing of the use of this coating drill bit effect is excellent.
The drill bit has the tip structure so that it can sharpen the two cutting edges at the outer edge of each straight groove. As the drill bit has four contact points with the workpiece, the drill bit is more stable in the processing, which can improve the machining precision The
The large vertex of the straight bit also helps to improve its machining performance. For example, H.A.M. Precision's standard straight-bit drill uses a 140 ° vertex, similar to a separate drill roof, which can be drilled into the hole with very small thrust. In addition, the big vertex can ensure that the entire diameter of the drill bit and the workpiece material quickly joined, so that the drill bit "deviation" may be minimized.
In many processing cases, it is advisable to use a guide bit (center drill) with a vertex angle greater than the apex of the carbide crown to produce a starting hole (pre-hole), so that it is possible to ensure that the machining is straight The drill tip center (horizontal blade) of the drill bit first enters the pre-hole to avoid the chipping of the carbide cutting edge which is relatively brittle. Another strategy for the use of straight-groove drilling is to simply define the hole before starting the drilling, since even the surface of the workpiece that has been machined may be defective, and the operator simply touches the pre-hole with a drill to determine its position The As long as the drill bit by the first contact with the workpiece, the drill will not "deviation", positioning holes can play a similar role in drilling.
The straightness of the hole measured at the φ10 mm hole in the cast iron material with three different drill bits indicates that the cutting speed of the high speed steel spiral groove bit is 98 sfm (30 m / min) and the feed rate is 7.66 ipm (195 mm / min ), The external cooling method, the hole processing quality to IT12 level; overall carbide spiral groove bit cutting speed of 295sfm (90m / min), feed rate of 34.5ipm (876mm / min), the use of coolant pressure The machining speed of the hole is up to IT9 grade; the cutting speed of the straight groove bit is 425smm (130m / min), the feed rate is 33.3ipm (845mm / min), the coolant pressure is For the internal cooling mode of 735psi / 3.2-gpm, the processing quality of the hole reaches IT8 grade.
Many people will be all the straight groove drill is called "G drill", but this is not exact, in fact, "G drilling" is only Accuromm USA Int. The company produced a class of straight slot drill trademark name, The outer edge of the tail can play a role in squeezing the hole.
Comparison of a variety of hole processing tool can achieve the hole wall finish, in general, high-speed steel drill bit is about 125-rms, carbide spiral groove efficient drill about 63-rms, three-slot reamer is about 32-rms , While the G drill can reach 16-rms or less, has reached the finishing level of finishing.
In order to process holes of different quality levels, Accuromm has designed a different drill bit, the company's G drill can generally meet the H9 level tolerance standard hole processing requirements, and the company's G-7 drill set with drilling and reaming function One, can meet the H7-level tolerance of processing requirements. For example, Accuromm listed an example of a drill with a straight groove G drilling on an aluminum material with a diameter of 0.394 "(φ10mm) with a cutting speed of 330 ft.min (100 m / min) (0.008 mmr), the results show that the hole machining accuracy is significantly improved, the aperture error from the original ± 0.0032 "(0.08mm) reduced to ± 0.0012" (0.03mm). In the same cutting Parameters, such as with G-7 drill processing, aperture error can be reduced to ± 0.0008 "(0.02mm).
Due to the high quality of the borehole drilling, it is also beneficial for other hole processing processes. Accuromm pointed out that if you need to drill the hole of the straight bit drill, its excellent dimensional accuracy can increase the tap life by about 50%.
The improvement in cutting tool performance is almost always required to narrow the scope of its processing. Although the straight groove drill is far from being a general tool, but its use is constantly expanding. The application of straight groove drilling can improve the processing efficiency and improve the quality of the workpiece to obtain two very significant benefits.
HAM Precision's Solid Carbide Straight Ladders "Muilt-Drill" is a TiAlN coating and an internal cooling channel designed for drilling, stepped and chamfering on short-chip aluminum alloys The
Competitive Carbide Int.'s "Insatiable G-Spot" special compound tool combines the company's G-Spot straight slot drill with the end mill and uses a tool to complete a variety of machining of the workpiece geometry The The tool can perform a total of nine machining operations, including drilling, OD chamfering and countersinking, ID chamfering and countersinking, outside diameter turning (pre-machining of threaded workpieces). Due to the large contact area between the tool and the workpiece, the drill bit has 4 points of contact with the workpiece, so the two-piece tool helps to keep the workpiece position stable and can be used to clamp the workpiece. As the straight groove drill has two cutting edge, the tool can not only drill, but also can play a role in the hole squeeze. This means that the machined hole finish is higher and the straightness is better, and the specific size requirements for the hole can be better served than the conventional drill bit with only one cutting edge of the cutting edge. The use of Insatiable G-Spot composite tool can replace at least 3 to 4 kinds of tools, that is, if the original tool processing, need 3 times the knife to complete the four kinds of processing operations. Therefore, the use of this multi-functional composite tool, for improving the processing efficiency, shorten the processing time of great benefit.