Difficulties and solutions of the hottest tapping

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Tapping difficulties and solutions

speaking of difficult processes in processing, tapping should be classified as the most difficult one. In general metal processing, it is usually to quickly cut the metal and form a smooth surface. Even if the process ends, tapping is not exactly the case. First, the thread formed after tapping must comply with the standard and be able to screw with the matching fastener; Secondly, it is very simple to exit the tool at the end of the general process cutting, and it may take as much time to exit the tap after the tapping is completed as it takes to cut the thread. All these make tapping an indispensable, slow and boring process

in addition to the above common problems, other factors will also increase the difficulty of tapping: these factors can be mainly divided into two categories: material related and operation related. In any case, the correct choice of tap will have a completely different impact on the tapping effect: tapping is very porous, tapping a hole, or completely immovable. The following is a brief introduction of some work that has been done by process personnel and tool manufacturing technicians in overcoming tapping difficulties with remarkable achievements in on-site technology R & D and production utilization

problem of workpiece material

tapping on difficult to machine materials may be a labor-intensive and expensive thing

Dan gajolosik, the engineering manager of besly products, pointed out that the main difficulty of tapping on difficult to machine materials is that the heat generated during cutting and the shrinkage of workpiece material wrap the tool. Titanium alloy is the most obvious in this aspect. He suggested that when tapping on this material, the tap used should have a large tooth shape shovel back amount and reverse taper to prevent the tap from jamming

in addition, gajolosik pointed out that the strength of the tap matrix is also important. Due to the high hardness and strength of the workpiece, the tap crown is often blunt quickly. In this case, it is recommended to use high-performance high-speed steel wire cones, which have high toughness, red hardness, deformation resistance and wear resistance

Paul motzel, a tap application expert of guhring company, said that when designing taps for machining hard materials, it is very important to use a small front angle, which can make the tap have a larger support when cutting

Stellite is a nickel base superalloy, which is one of the most difficult materials to machine. Mike Brown, the owner of a computer integrated processing company, received a batch of orders. The fan blades of space engines should be processed with this material. There are 25 pieces of each engine, and a 10 ~ 32unf-2b threaded through hole shall be processed on each piece, which is used to screw in the jackscrew when disassembling the blade

at the beginning, the company learned that this material has a strong "memory" function - the tendency to retract after processing. In order to overcome this problem, Brown first made the bottom hole larger: the drawing stipulates that the bottom hole is 0.159 "(4.0386mm) larger than the diameter, and the actual drilling is 0.161" (4.0894mm), which is 0.002 "(0.0508mm), which can make the tapping workload a little lighter. However, during the test of the first tap, it was found that only 1 ~ 2 holes could be drilled and it would crack

brown found that the tap made a high pitched noise, just like stepping on the brake. To realize that there must be something wrong. The tap used in Brown's test costs $18 each, and can only tap 1 ~ 2 holes. He wanted to try to find a more suitable tap through repeated exploration, so that the number of processed holes could be a little more

finally, it is determined to use the high-speed steel exotap produced by OSG tool and die company, which can process 4 holes. Brown said, "this kind of tap is 12-15 dollars per tap, and the cost of each hole is 3-4 dollars, which is on the high side. However, the cost of processing this material is not high, but if you use a tap close to 20 dollars per tap and only tap one hole, it is unacceptable."

are carbide taps further used? Brown thought it was not feasible. He said, "for this kind of workpiece, it is possible to drill with cemented carbide tools. But it is too hard, and the tolerance of cemented carbide taps to processing conditions is small, so it is not suitable."

however, this does not mean that cemented carbide taps cannot be used for machining the workpiece at all. In fact, after tapping with exotap tap, the workpiece is removed from the fixture, and the second process is to manually correct the screw hole with a $60 cemented carbide tap

brown believes that selecting the appropriate tap is not everything. It is also important to choose the right lubricant. At the suggestion of a craftsman friend, he changed the lubricant of the tap. At present, the screw tap lubricating paste of Castrol company is used. Before each tapping, the paste with less lubrication of peripheral circuits is brushed onto the screw tap for use

Dan welter, the foreman of diamond tooling company, provided another example of tapping difficult to machine materials. This material is a super austenitic stainless steel al 6xn, which has anti-oxidation and corrosion properties, and is widely used for liquid conveying parts, such as original parts. The material has high chromium, nickel and Molybdenum Contents (20%, 24% and 6% respectively), and has high hardness (hrb88) and cold work hardening tendency

this is an ink delivery pump of a printer. Welter needs to tap six through holes with 4 ~ 40 threads on the part, with three holes on each side, and the hole depth is 6.35mm. It is required to drill the bottom hole on the workpiece at one time and then tap. At first, he used standard high-speed steel tin coated taps, but the hardness of the material was too high, causing the taps to crack. After testing six different high-speed steel wire taps, welter finally gave up the intention of using standard taps to solve the problem and began to seek new solutions. The development of extrusion taps can solve this problem, although it is believed that extrusion taps are only suitable for soft materials

he used a tap produced by OSG company. According to the relevant personnel of OSG company, the tap has an Electra lube coating with a thickness of 2.54 μ m. It is a soft solid lubricant, which deposits on the tap to form a smooth surface, "Reduce the torque of the tap during operation and prevent adhesion, blockage, abrasion, etc.

deep blind hole tapping

tapping meets not only the difficult machining problem of the workpiece material. Sometimes, the opening of the tapping electro-hydraulic proportional valve is controlled by the computer, and the operating skills of changing the overflow through regulating the opening of the valve to change the working pressure of the system are also complex and subtle. For example, blind hole tapping Dave sibinski, process engineer of TS Company, pointed out that the biggest difficulty of blind hole tapping is to discharge the chips at the bottom of the hole to prevent the tap from squeezing the chips

sibinski pointed out that although the drawing does not necessarily require screw root cleaning, the actual working condition requires root cleaning. Because he knows that in blind hole tapping, in order to meet the requirements specified in the drawing, space must be prepared for tapping the tap to a sufficient depth. This requires drilling the hole deeper. However, if it is drilled too deep beyond the notch to the next part, it will cause eccentricity. In addition, he also pointed out that when drilling deep blind holes, the center of the ending section will gradually shift

in diamond tooling company, Welter needs to tap a 5/16 "-18 thread blind hole, 1" deep, made of 304 stainless steel, with a tapping depth of 3 times the diameter (thread diameter 5/16 ", i.e. 7.9375mm) 。 Welter proposed that a tap with strong rigidity and good chip removal should be processed in one time. He quickly ruled out the use of extrusion Taps. Prototyp company provides a kind of parallel triple S-type tap, which is one of eco series taps for difficult to machine materials produced by the company. Prototyp is a member of Sandvik CTT. Mathias arbruster, the technical sales manager of the company, pointed out that the tap adopts a large spiral angle, so that the tapping depth can reach several times the diameter. At the same time, the large helix angle makes the chips roll tightly, which can prevent the chips from wrapping up in a ball on the handle

in addition to supplying cutting tools, tool manufacturers often work closely with users' technicians to solve tapping problems. For example, Sai Kin eng, a senior engineer of Firth Brown tool company, helped users solve thread tapping with a diameter of 18mm and a depth of 60mm. He said that deep hole tapping is difficult due to many factors. The first is the difficulty of coolant delivery. Because the chips are blocked in the hole, it is difficult for the coolant to reach the tool/workpiece contact area. Of course, if the elongation of the workpiece material is large, you can use an extrusion tap, which works without chips. However, the diameter of the thread bottom hole should be close to the pitch diameter, and the tolerance should be stricter than that of the ordinary tap

in order to help the transmission of coolant, internal cooling tap can be selected. Multiple oil grooves can also be opened on the tap, or special lubricating coating can be used. These measures can reduce the working temperature and prevent the cutting edge from softening. After helping users adopt a series of measures, Firth Brown finally increased the tool life by 35% (the original was reduced by 50%, suspected of printing error - translation note)

although it is difficult to include all kinds of potential problems that process personnel will encounter, the tapping problems discussed provide ideas and practices on how to solve problems in real production. We can clearly see from it that great patience is needed to solve the problems in tapping. (end)

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