Técnicas avançadas de usinagem de furos da CNC Services

Advanced hole machining techniques from CNC Services

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Hole making is largely underrated because most of the holes we drill are trivial in precision, shallow in depth, and are only designed to accommodate screws. However, modern high-tech industries (especially aerospace and automotive) are entering the CNC services market with the need to produce parts with extremely precise or deep holes, or holes with very precise location. In addition to advanced CNC machining services, such requirements require special techniques and careful planning.

Hole Processing Issues

The process of making holes is quite strenuous from a manufacturing perspective. The tool and blank can easily overheat because it is difficult to introduce coolant into the hole. The process is not visible to the machine operator, so he can only rely on the information from the machine tool and has to cut blindly. Taking measurements is difficult, especially for small diameter holes. And these are just some of the problems with hole making. Therefore, to produce accurate holes, CNC services constantly develop and improve machining strategies and invent new tools and tools to meet customer needs.

Deep drilling

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Well, drilling itself is a common process and there is nothing interesting about drilling short holes, but the deeper the hole, the harder it is to keep its shaft straight while drilling. This is because a longer bit is less rigid even though it has two cutting edges that cannot be the same length. Therefore, the cutting force of the sides of the drill is different, and the drill often deviates from the straight axis and leaves the hole crooked. This is not acceptable for high precision CNC parts.

This is why deep drilling was invented. As the name suggests, it was first used to make long-stocked weapons, where a long but accurate bore is the main requirement. However, as production technologies developed, other industries also adopted deep drilling for their own purposes. The main difference in this strategy is the tools. A deep drill bit has a single cutting edge, so it doesn't deviate from its path like a simple drill bit. It has a larger chip removal groove that also serves as a cooling channel. The coolant is pumped through the groove under high pressure and removes the chips and cools the drill much better. The disadvantage of this method is that this drill cannot be mounted on an ordinary CNC milling center, but requires additional tools.

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CNC shops use deep drills in the most extreme cases, but most of the time they try to stick to universal tools and that is why there are certain strategies that allow you to make deep holes with simple drills. First, the length of the hole is divided into segments with depths of approximately 3-4 hole diameters. Each time the drill reaches the end of a segment, it is ejected to allow the blank and tool to cool and any chips to be removed from the hole.

High precision hole machining

To create a precise hole, CNC drilling typically involves using multiple tools, with the first one being significantly smaller than the diameter of the hole and increasing in size with the next tool. This is done to reduce the cutting force and therefore axis runout for the reason mentioned above. Additionally, sequential methods often differ from simple drilling:

Core drilling occurs directly after drilling. A core drill has three cutting edges instead of one and is therefore more stable. Drills typically produce a cut whose depth is only 0.5 mm, but their absolute advantage lies in the possibility of axis correction.

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To scrub. If your customer needs a hole with a tolerance of up to IT6 and a very smooth surface finish, take a reamer and set the machining feed extremely low. A reamer is a tool with many long cutting edges on the sides of the tool. It has front cutting blades, but these are extremely small, so the cutting depth during flaring is about 0.1-0.05 mm. For this reason and due to the extreme precision of the cutting edges, large holes are obtained when reaming. For smaller holes, reaming is done manually.

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Honing is a grinding process, but it can be done on a CNC machine tool. However, special honing machines are definitely better. A honing tool is basically a reamer with grinding plates instead of cutting blades. Another difference is that the plates can be adjusted to the correct diameter. The honing tool is inserted into the hole and rotates on its axis while the plates grind the material. As soon as the honing tool is ejected, the direction of rotation is reversed. As a result, the hole surface has microscopic cross grooves that make lubrication much more efficient.

Strategies for drilling holes

Many holes require threads that consist of thin, complex surfaces and are quite difficult to machine. There are several threading strategies, but it is essential to countersink or countersink beforehand. These two processes create a conical or cylindrical groove at the hole entrance. It allows the threading tool to penetrate correctly and also helps with the assembly of the parts themselves. So here are some thread cutting strategies.

Tapping uses a single tool that resembles a screw but has grooves for chip evacuation and a long tapered section at the front to gradually increase the depth of cut. The machining feed when cutting tapered threads (and any other thread) corresponds to the thread pitch. The tap is slowly inserted into the hole, where each of its spiral cutting edges gradually cuts a piece of material to form the thread. Small holes are drilled manually, the drilling process being similar to screwing in a tightly tightened screw. The tap must be ejected very carefully in the same way it was inserted. If you forget this and try to eject the faucet without loosening it, you could damage it and have to use EDM to get it out.

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Thread milling produces better results because the process temperature is lower and coolants are much easier to apply. A special cutter, 30-40% smaller than the hole diameter, moves in a spiral along the path of the drill grooves and rotates around its axis to provide efficient cutting. The minimum hole diameter depends on the minimum cutter diameter.

Another strategy is to tap. In fact, it is the same as turning in terms of part configuration and main movements, but the tool is made to imitate the shape of the thread groove. Thus, it is inserted into the hole of the part with a thread pitch and cuts the spiral surfaces of the thread. It is important to note that drilling works well for large holes, but cannot handle holes smaller than 20mm.

Contact Us-Wayken to learn how you can use precision CNC machining to design part holes for your project.

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