Rotary Table Intelligent Assembly Machine processing five key issues? As the most common tool in hole processing, drill is widely used in mechanical manufacturing, especially for the processing of parts such as cooling devices, tube plates of power generation equipment and steam generators, etc., the application is particularly extensive and important.

First, the characteristics of drilling

The drill usually has two main cutting edges, and when machining, the drill is rotated at the same time. The front Angle of the bit becomes larger and larger from the central axis to the outer edge, and the cutting speed of the bit is higher the closer it is to the outer circular part, and the cutting speed decreases to the center, and the cutting speed of the rotating center of the bit is zero. The transverse edge of the drill is located near the center axis of rotation, the secondary front Angle of the transverse edge is large, there is no space for chip, and the cutting speed is low, so it will produce a large axial resistance. If the transverse edge is polished into type A or type C in DIN1414, and the cutting edge near the central axis is a positive front Angle, the cutting resistance can be reduced and the cutting performance can be significantly improved.

According to the shape of the workpiece, material, structure, function, etc., the drill can be divided into many types, such as high-speed steel drill (twist drill, group drill, flat drill), integral carbide drill, indexable shallow hole drill, deep hole drill, casing drill and interchangeable bit.

Second, chip breaking and chip removal

The cutting of the bit is carried out in the narrow space of the hole, the chip must be discharged through the bit edge groove, so the chip shape has a great influence on the cutting performance of the bit. The common chip shapes are flake chip, tubular chip, needle chip, conical spiral chip, ribbon chip, fan chip, powder chip and so on.

Chip control is the key of drilling

When the chip shape is not appropriate, the following problems will occur:

① Fine chips block the edge groove, affect the drilling accuracy, reduce the bit life, and even break the bit (such as powder chips, fan chips, etc.).

② Long chips wrap around the drill, hindering operation, causing damage to the drill or preventing cutting fluid from entering the hole (such as spiral chips, ribbon chips, etc.).

How to solve the problem of improper chip shape:

① Methods such as increasing the feed rate, intermittent feed, grinding the cross edge and installing the chip breaker can be used separately or jointly to improve the chip breaking and removing effect and eliminate the problems caused by chips.

② Professional chip breaking drill can be used for drilling. For example, the addition of a designed chip breaking edge to the groove of the drill breaks the chip into more easily removed debris. Debris is removed smoothly along the trench, and no blockage occurs in the trench. Therefore, the new chip breaking drill obtains a much smoother cutting effect than the traditional drill.

At the same time, the short broken iron filings make it easier for the coolant to flow to the drill tip, further improving the heat dissipation effect and cutting performance during the processing. And because the new chip cutter cuts through the entire groove of the bit, it can maintain its shape and function after multiple refinements. In addition to the above functional improvements, it is worth mentioning that the design strengthens the rigidity of the drill body and significantly increases the number of holes drilled before a single grind.

3. Drilling accuracy

The accuracy of the hole is mainly composed of the size of the aperture, the accuracy of the position, the coaxiality, the roundness, the surface roughness and the burr of the hole.

Factors affecting the accuracy of the drilled hole during drilling:

The clamping accuracy and cutting conditions of the drill, such as the tool holder, cutting speed, feed rate, cutting fluid, etc.

The size and shape of the drill bit, such as the length of the drill bit, the shape of the edge, the shape of the drill core, etc.

③ Workpiece shape, such as orifice side shape, orifice shape, thickness, clamping state, etc.

reaming

Reaming is caused by the swing of the bit during machining. The swing of the tool holder has a great influence on the aperture and the positioning accuracy of the hole, so the new tool holder should be replaced in time when the tool holder is seriously worn. When drilling small holes, it is difficult to measure and adjust the swing, so it is best to use a thick handle small edge diameter drill with a good coaxiality between the edge and the handle. When using the regrinding bit, the reason for the decline in hole accuracy is mostly caused by the asymmetry of the shape behind. Controlling the edge height difference can effectively restrain the cutting and expanding amount of the hole.

Roundness of the hole

Due to the vibration of the drill bit, the hole shape is easy to be polygon, and the hole wall appears like a rifle-like line. Common polygonal holes are triangles or pentagons. The reason for the triangular hole is that the drill has two rotating centers when drilling, and they vibrate at a frequency of 600 exchange per interval. The main cause of vibration is the imbalance of cutting resistance. When the drill turns once, due to the roundness of the hole processed, the resistance is not balanced during the second turn cutting, and the vibration is repeated again, but the vibration phase has a certain offset. Resulting in ribbed lines on the hole wall. When the drilling depth reaches a certain degree, the friction between the bit edge and the hole wall increases, the vibration attenuates, the rifle line disappears, and the roundness becomes better. From the longitudinal section, the orifice of this pass is a funnel type. For the same reason, there may also be pentagonal and heptagonal holes in the cutting. In order to eliminate this phenomenon, in addition to the control of chuck vibration, cutting edge height difference, rear and blade shape asymmetry, we should also take measures to improve the rigidity of the bit, increase the feed rate per revolution, reduce the back Angle, and trim the transverse edge.

Drill holes on bevels and curved surfaces

When the cutting surface or drilling through surface of the bit is inclined, curved or stepped, the positioning accuracy is poor, because the bit is radial single-sided cutting, so the tool life is reduced.

To improve the positioning accuracy, the following measures can be taken:

① Drill the center hole first.

②. Mill the hole seat with the end mill.

③ Choose a good cutting ability, good rigidity drill.

④ Reduce feed speed.

Treatment of burrs

During drilling, burrs will appear at the entrance and exit of the hole, especially when processing materials and sheets with high toughness. The reason is that when the bit is about to drill through, the material to be processed has plastic deformation, and the triangular part that should be cut by the bit near the edge of the outer edge is deformed and bent to the outside by the axial cutting force, and further crimped under the action of the chamfer on the outer edge of the bit and the edge with the edge edge, forming a curling or rough edge.

Four, drilling processing conditions

The general drill product sample catalog has the "Basic Cutting parameters Reference Table" arranged according to the processing material, and the user can choose the cutting conditions of drilling processing by referring to the cutting parameters provided. The choice of cutting conditions is appropriate, should be through the test cutting, according to the processing accuracy, processing efficiency, bit life and other factors comprehensive judgment.

1 Bit life and processing efficiency

Under the premise of meeting the technical requirements of the workpiece to be machined, whether the use of the drill is proper should mainly be measured according to the service life of the drill and the processing efficiency. The evaluation index of bit service life can be selected cutting distance; The evaluation index of processing efficiency can be selected feed speed. For high-speed steel bits, the service life of the bit is more affected by the rotation speed and less affected by the feed per revolution, so the processing efficiency can be improved by increasing the feed per revolution and ensuring a long bit life. However, it should be noted that if the feed rate per turn is too large, the chips will thicken and cause chip breaking difficulties, so it is necessary to determine the feed rate range per turn that can successfully chip breaking by test cutting. For carbide bits, the negative front Angle of the cutting edge has a large chamfer, and the optional range of feed per revolution is smaller than that of high-speed steel bits. If the feed per revolution exceeds this range during processing, the service life of the bit will be reduced. Since the heat resistance of the carbide bit is higher than that of the high-speed steel bit, the rotary speed has little effect on the bit life, so the method of increasing the rotary speed can be used to improve the processing efficiency of the carbide bit and ensure the bit life.

2. Reasonable use of cutting fluid

The cutting of the drill is carried out in the narrow space of the hole, so the type of cutting fluid and the way of feeding have a great impact on the life of the drill and the machining accuracy of the hole. Cutting fluid can be divided into water-soluble and insoluble two categories. The non-water-soluble cutting fluid has good lubricity, wettability and adhesion resistance, and also has anti-rust effect. Water-soluble cutting fluid has better cooling, no smoke and no flammability. Due to the consideration of environmental protection, the use of water-soluble cutting fluid is larger in recent years. However, if the dilution rate of water-soluble cutting fluid is improper or the cutting fluid deteriorates, it will greatly shorten the service life of the tool, so it must be paid attention to in use. Whether water-soluble or non-water-soluble cutting fluid, the cutting fluid must be fully reached the cutting point in use, and the flow rate, pressure, number of nozzles, and cooling mode (internal or external cold) of the cutting fluid must be strictly controlled.

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