The efficiency of machining deep hole with solid carbide bit is increased by 8 times

More and more processing workshops are replacing gun drill with solid carbide drill to process deep holes.

In the deep hole machining tool market dominated by gun drills in the past, the new generation of integral carbide fried dough twist drills that can drill deep holes up to 16-40 times the aperture are occupying an increasing share. In order to improve the machining accuracy and chip removal performance, this kind of integral cemented carbide bit adopts the horizontal edge and spiral groove, and uses high-density cemented carbide materials to improve the hardness, so that it can be drilled 5-10 times faster than the gun drill.

Some solid carbide bit manufacturers believe that the performance advantages of such bits are becoming more and more attractive to manufacturers who use gun drill to process deep holes on their own lathes or subcontract deep hole processing tasks to gun drill processing workshops. However, they also pointed out that compared with gun drills, which usually use cemented carbide or hardened high-speed steel drill tips, hardened steel shanks and straight grooves, solid carbide deep hole drills also have some limitations. For example, their drilling depth limit (dimensioned) is 40 times the hole diameter, while gun drills can easily drill deep holes with a depth of more than 50 times the hole diameter.

Tomedler, the hole processing product manager of iska company, which not only manufactures gun drills, but also produces integral cemented carbide drills, pointed out that gun drills can drill and process all kinds of difficult to process materials, "Because the processing speed of gun drill is slow, it is easy to remove chips. When drilling titanium alloy and stainless steel, chip removal is a big problem, and gun drill has better versatility when processing difficult materials. In these processes, gun drill will still be widely used."

Another obstacle to the use of solid carbide deep hole drills is that the machining personnel are worried about their brittleness and the potential risk of fracture. For example, raydomingue, an operator of CNC lathe in Bosco processing workshop, once doubted whether a solid carbide drill with a diameter of 6.35mm could drill 240mm deep holes in an extremely difficult alloy material such as nitronic50 Nitrogen Strengthened austenitic stainless steel in less than 4 minutes, while the drill could still remain intact (as claimed by a tool salesman).

However, Domingue must try. Last year, like most processing workshops, his boss made simplifying operations and cutting costs a priority. In August last year, the company decided to change the gun drilling deep hole processing previously subcontracted to other units to self processing by the workshop. The processing task includes drilling a deep hole with a depth of 240mm on 120 oil parts called gamma tandem. The workpiece is made of nitronic50 stainless steel, which contains 22% chromium and nearly 12% nickel. It is highly abrasive and difficult to drill.

The workshop plans to use gun drill to process these deep holes on its own haassl30 lathe. Domingue said, "we bought several gun drills with a diameter of 6.35mm. I compiled the processing program, started the machine tool for processing, and it took about 24 minutes to drill a 240mm deep hole." After machining several parts, the sales representative of the tool manufacturer guhring company came to the workshop to visit the users. "He told me that if they use their integral carbide drill, they can drill the same hole in only 3-4 minutes. I said, 'is this really the case? We will try. If I can, I will buy this tool.' to be honest, I don't believe that the integral carbide drill can do this. Drilling nitronic stainless steel is the most difficult process, and the brittleness of cemented carbide is very large."

Domingue first clamped a standard length cemented carbide bit on the lathe, drilled a guide hole twice the hole depth (about 13mm), and then used the rt100t internal cooling integral cemented carbide bit (6.35mm in diameter and 30 times in length) of guhring company for drilling. He said, "after I switched to the guhring drill bit, I compiled an M00 code. Then I used the high-pressure nozzle of the lathe cooling system to provide 2000psi, 3.5gpm high-pressure coolant. Because of the high-pressure cooling, I chose the sealed sleeve collet to hold the drill bit. When the drill bit was drilled into the hole, I turned on the high-pressure cooling nozzle." Cutting parameters: circumferential cutting speed 42m/min (140sfm), spindle speed 2140r/min, and feed rate 0.089mm/r. The processing time for drilling each hole (including drilling the guide hole) is about 3.5 minutes. A total of 65 holes were machined before the drill had to be reground and recoated (TiAlN coating).

Domingue added that the chips produced by the solid carbide bit are "small and tight", and 2000psi high-pressure cooling helps to ensure that the chips are discharged quickly. In addition, this drill has proved to have high machining accuracy, and the end diameter jump of the hole is less than 0.25mm.

From the point of view of productivity, the machining efficiency of solid carbide bit is 8 times higher than that of gun drill; From the perspective of processing cost, Bosco processing workshop saves the labor cost and transportation cost of outsourced processing. Although the overall price of cemented carbide bits ($375) is more than five times higher than that of gun drills ($70), the significant increase in productivity will soon offset and exceed the increase in tool costs.

Tool performance test

In a tool performance test conducted in September last year, guhring company compared the cutting performance of its rt100t solid carbide bit with that of gun drill. These two kinds of drill bits with diameter of 6.35mm are used to drill 1000 holes with depth of 240mm on nitronic50 material respectively. Guhring's cemented carbide drill completed all processing in 22.59 hours, while gun drill took 323.48 hours. According to the average level of the workshop, the processing cost of $65 per hour is converted into the processing cost per hole. The rt100t cemented carbide bit is $4.46, while the gun drill is $37.06.

In addition to the series of integral cemented carbide drill bits listed 3 years ago for processing deep holes with length diameter ratio of 20 and 30, guhring also launched a deep hole drill bit with length diameter ratio of 40 in November last year. Hellinger of the company said, "in fact, deeper holes can be drilled, depending on the diameter of the bit. For example, the spiral groove length of a 3.2mm diameter bit is about 150mm, so deep holes with a length diameter ratio of 45 can be drilled."

Like edler of iska, Hellinger is well aware of the limitations of cemented carbide bits. He believes that, "Stainless steel, hardened steel and alloy steel are relatively easy to process for integral cemented carbide bits. We also use them to process cast iron. It also performs well when processing nickel based alloys. However, this kind of bit may not be the best choice for processing chilled cast iron or aluminum alloy. However, we have specially designed a kind of cemented carbide bit for processing aluminum alloy, and its spiral groove design is relatively flat. After about 6 months, this kind of bit Can be listed as a standard product. "

Reduce drilling force

The solid carbide deep hole drill introduced by iska 3 years ago can process holes with a length diameter ratio of 22. The drill adopts a 140 ° straight drill sharp angle and a four sided belt design, which can minimize the drilling force, assist in centering and protect the cutting edge. The company has coated and polished the spiral groove, edge belt and cutting edge of the drill bit to reduce friction and torque required for machining. The tool material is made of sub micron Grain Cemented Carbide with cobalt content of 10%, which has the key characteristics of rapid drilling. Edler said, "the grain size of this brand is 0.8 μ m. Its high-density composition makes the drill bit have good hardness and toughness. " According to the traditional theory, hardness and toughness are two opposite characteristics. "Generally speaking, in order to obtain the required strength for such a long drill bit, hard alloy with good toughness must be used, but good toughness cannot be converted into good wear resistance."

Edler added, "deep hole drilling is an extremely difficult process, because it is carried out in a closed environment, and the cutting heat is difficult to dissipate. When processing some workpiece materials, the heat cannot be transferred into the material, and will be transferred into the cemented carbide bit. Therefore, only with high hardness can we take into account the strength and wear resistance of the cemented carbide bit, so that we can process with a large feed."

Edler pointed out that another key factor for large feed machining with solid carbide bits is cooling.

The higher the coolant pressure, the better the cooling effect. He recommended the pressure of 1000-1400psi. "The ideal effect is to flush out the chips. This is always a difficult problem when drilling deep holes." He added that when drilling deep holes with solid carbide bits, the minimum lubrication (MQL) method is also very effective.

Enhanced drill point design

Secotoolsinc It is one of the tool manufacturers that have recently entered the market of solid carbide deep hole drills. Earlier this year, it launched the sd16 drill bit. As part of its feedmax product series, the drill bit can process deep holes with a depth of 16 times the aperture (the company can also customize deep hole drills with a length diameter ratio of 25).

Tomsandrud, the hole processing manager of shangao company, said, "we chose a drill point geometry design that is different from the standard conical drill bit. This is a tetrahedral drill point shape with a main rear angle and a secondary rear angle, which can better protect the drill point at the center of the drill bit. It can produce a free cutting edge and help the drill bit position."

He added that the structural design of the sd216 integral cemented carbide bit eliminates the need for pre drilling guide holes before formal machining. In addition, the design of double arris and wide side sub arris adopted by the drill enables it to "cut into the workpiece at the beginning of drilling, which helps to process a good hole shape, maintain a small geometric error, and ensure the straightness of the hole."

Sandrud said that although the company has only recently started to set foot in the overall cemented carbide deep hole drill Market, the sales volume of its new drill bits is growing steadily - and he predicted that the deep hole drilling technology will further develop. "In the last four to five years, more enterprises like sandrud will add deep hole drill bits to their product lines. Our competitors are working in the same direction as us." This development direction is to make the drill bit as long as possible to make its processing efficiency higher.