Complete collection of drilling techniques, collected

As the most common tool in hole machining, drill bits are widely used in mechanical manufacturing, especially for the machining of holes in cooling devices, tube plates of power generation equipment, and steam generators. Their application is particularly extensive and important.
1, The characteristics of drilling
A drill bit usually has two main cutting edges, and during machining, the drill bit performs cutting while rotating. The front angle of the drill bit increases from the central axis to the outer edge, and the cutting speed of the drill bit increases as it approaches the outer circle. The cutting speed towards the center decreases, and the cutting speed at the rotation center of the drill bit is zero. The lateral edge of the drill bit is located near the central axis of rotation, with a larger sub rake angle and no chip space. The cutting speed is low, resulting in significant axial resistance.
If the cutting edge of the transverse blade is ground to a type A or C in DIN1414, and the cutting edge near the central axis is a positive rake angle, it can reduce cutting resistance and significantly improve cutting performance.
According to the different shapes, materials, structures and functions of workpieces, drills can be divided into many types, such as high-speed steel drills (Fried Dough Twists drills, group drills, flat drills), integral carbide drills, indexable shallow hole drills, deep hole drills, nesting drills, and interchangeable head drills.
2, Chip breaking and chip removal
The cutting of the drill bit is carried out in narrow holes, and the chips must be discharged through the cutting groove of the drill bit. Therefore, the shape of the chips has a significant impact on the cutting performance of the drill bit. Common chip shapes include flake chips, tubular chips, needle chips, conical spiral chips, ribbon chips, fan-shaped chips, powder chips, etc.
The Key to Drilling Processing - Chip Control
When the chip shape is not suitable, the following problems will occur:
① Fine chips block the cutting edge groove, affecting drilling accuracy, reducing the lifespan of the drill bit, and even causing the drill bit to break (such as powdery chips, fan-shaped chips, etc.);
② Long chips entangle the drill bit, hindering operation, causing the drill bit to break or hindering the entry of cutting fluid into the hole (such as spiral chips, strip chips, etc.).
How to solve the problem of inappropriate chip shape:
① Methods such as increasing feed rate, intermittent feed, grinding the lateral edge, and installing chip breakers can be used separately or in combination to improve chip breaking and removal efficiency, and eliminate problems caused by chips.
② Professional chip breaking drills can be used to drill holes. For example, adding a designed chip breaking blade to the groove of the drill bit will break the chips into easier to remove debris. The debris is smoothly discharged along the trench without any blockage occurring inside the trench. Therefore, the new chip breaking drill has achieved much smoother cutting effects than traditional drill bits.
At the same time, the short and fragmented 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 machining process. And because the newly added chip cutting edge penetrates the entire groove of the drill bit, it can still maintain its shape and function after multiple rounds of grinding. In addition to the above functional improvements, it is worth mentioning that this design enhances the rigidity of the drill body and significantly increases the number of boreholes drilled before a single grinding.
3, Drilling accuracy
The accuracy of a hole is mainly composed of factors such as aperture size, positional accuracy, coaxiality, roundness, surface roughness, and hole burrs.
Factors that affect the accuracy of the machined hole during drilling processing:
① The clamping accuracy and cutting conditions of the drill bit, such as tool holder, cutting speed, feed rate, cutting fluid, etc;
② Drill size and shape, such as drill length, blade shape, drill core shape, etc;
③ The shape of the workpiece, such as the side shape of the hole, the hole shape, thickness, and clamping status.
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1. Expanding the hole
Expanding holes is caused by the swinging of the drill bit during processing. The swing of the tool holder has a significant impact on the aperture and positioning accuracy of the hole. Therefore, when the tool holder is severely worn, a new tool holder should be replaced in a timely manner. When drilling small holes, it is difficult to measure and adjust the swing, so it is best to use a coarse handle small diameter drill bit with good coaxiality between the blade and the handle. When using a regrinding drill bit for machining, the reason for the decrease in hole accuracy is often due to the asymmetric shape behind it. Controlling the height difference of the cutting edge can effectively suppress the cutting expansion of the hole.
Roundness of 2 holes
Due to the vibration of the drill bit, the drilled hole shape is easily polygonal, and there are double lines like patterns on the hole wall. The common polygonal holes are mostly triangles or pentagons. The reason for the formation of triangular holes is that the drill bit has two rotation centers during drilling, which vibrate at a frequency of 600 intervals. The main reason for vibration is the imbalanced cutting resistance. When the drill bit rotates one revolution, due to poor roundness of the processed hole, the resistance is imbalanced during the second round of cutting. The previous vibration is repeated, but the vibration phase has a certain deviation, resulting in the appearance of double line patterns on the hole wall. When the drilling depth reaches a certain level, the friction between the edge of the drill bit and the hole wall increases, the vibration attenuates, the involute disappears, and the roundness improves. This type of hole shape appears funnel-shaped when viewed from a longitudinal cross-section. For the same reason, pentagonal and heptagonal holes may also appear during cutting. To eliminate this phenomenon, in addition to controlling factors such as chuck vibration, cutting edge height difference, back and blade shape asymmetry, measures such as increasing drill bit rigidity, increasing feed rate per revolution, reducing back angle, and grinding the lateral edge should also be taken.
Drilling on inclined and curved surfaces
When the cutting surface or drilling through surface of the drill bit is inclined, curved or stepped, the positioning accuracy is poor. Due to the radial single-sided cutting of the drill bit at this time, the tool life is reduced.
To improve positioning accuracy, the following measures can be taken:
1. Drill the center hole first;
2. Use an end mill to mill the hole seat;
3. Choose drill bits with good penetration and rigidity;
4. Reduce the feed rate.
4 Burr treatment
During drilling, burrs may appear at the inlet and outlet of the hole, especially when processing materials and thin plates with high toughness. The reason is that when the drill bit is about to drill through, the material being processed undergoes plastic deformation. At this time, the triangular part that should have been cut by the edge near the outer edge of the drill bit is deformed and bent outward under the action of axial cutting force, and further curls under the action of the outer edge chamfer and edge edge surface of the drill bit, forming curls or burrs.
4, Processing conditions for drilling
The general catalog of drill bit products includes a "Basic Cutting Parameters Reference Table" arranged according to the processing materials. Users can refer to the cutting parameters provided to choose the cutting conditions for drilling processing. Whether the selection of cutting conditions is appropriate should be determined through trial cutting, based on factors such as machining accuracy, machining efficiency, and drill life.
1. Drill lifespan and machining efficiency
On the premise of meeting the technical requirements of the workpiece being processed, the appropriate use of the drill bit should be comprehensively measured based on the service life of the drill bit and processing efficiency. The evaluation index for the service life of drill bits can choose cutting distance; The evaluation index for machining efficiency can be selected as feed rate. For high-speed steel drill bits, the service life of the drill bit is greatly affected by the rotation speed, and is less affected by the feed rate per revolution. Therefore, increasing the feed rate per revolution can improve machining efficiency while ensuring a longer lifespan of the drill bit. However, it should be noted that if the feed rate per revolution is too large, the chips will thicken, causing difficulty in chip breaking. Therefore, it is necessary to determine the range of feed rate per revolution that can smoothly break chips through trial cutting. For hard alloy drill bits, there is a significant chamfer in the negative rake direction of the cutting edge, and the optional range of feed rate per revolution is smaller than that of high-speed steel drill bits. If the feed rate per revolution exceeds this range during machining, it will reduce the service life of the drill bit. Due to the higher heat resistance of hard alloy drill bits compared to high-speed steel drill bits, the impact of rotation speed on drill bit life is minimal. Therefore, increasing rotation speed can be used to improve the machining efficiency of hard alloy drill bits while ensuring drill bit life.
Reasonable use of cutting fluid
The cutting of drill bits is carried out in narrow holes, so the type and injection method of cutting fluid have a significant impact on the lifespan of drill bits and the machining accuracy of holes. Cutting fluids can be divided into two categories: water-soluble and non water-soluble. Non water-soluble cutting fluids have good lubrication, wetting, and adhesive resistance, as well as anti rust properties. Water soluble cutting fluid has good cooling properties, no smoke, and no flammability. Due to environmental protection considerations, water-soluble cutting fluids have been widely used in recent years. However, if the dilution ratio of water-soluble cutting fluid is improper or the cutting fluid deteriorates, it will greatly shorten the service life of the tool, so attention must be paid during use. Regardless of whether it is a water-soluble or non water-soluble cutting fluid, it is necessary to ensure that the cutting fluid reaches the cutting point fully during use. At the same time, the flow rate, pressure, number of nozzles, and cooling method (internal or external cooling) of the cutting fluid must be strictly controlled.
5, Re sharpening of drill bits
Drill bit regrinding discrimination
The discrimination criteria for re grinding drill bits are:
1. Wear amount of cutting edge, horizontal edge, and edge with edges;
2. The dimensional accuracy and surface roughness of the processed hole;
3. The color and shape of the chips;
4. Cutting resistance (indirect values such as spindle current, noise, vibration, etc.);
5. Processing quantity, etc.
In actual use, accurate and convenient discrimination criteria should be determined from the above indicators based on specific circumstances. When using wear as a criterion for discrimination, the most economical and optimal regrinding period should be identified. Due to the main grinding parts being the back of the head and the transverse edge, if the drill bit wears too much, the blade wears more and the grinding amount is large, the number of times it can be re ground is reduced (total service life of the tool=tool life after re grinding) × The number of times it can be re ground will actually shorten the total service life of the drill bit; When using the dimensional accuracy of the processed hole as the discrimination standard, column or limit gauges should be used to check the cutting and expansion amount, non straightness, etc. of the hole. Once the control value is exceeded, it should be re sharpened immediately; When using cutting resistance as the criterion for discrimination, methods such as automatic shutdown immediately after exceeding the set limit value (such as spindle current) can be used; When using processing quantity limit management, the above discrimination content should be comprehensively considered and discrimination standards should be set.
The grinding method of drill bits
When re grinding the drill bit, it is best to use a specialized drill bit grinding machine or a universal tool grinding machine, which is very important to ensure the service life and machining accuracy of the drill bit. If the original drilling shape is in good condition, it can be regraded according to the original drilling shape; If there are defects in the original drill shape, the subsequent shape can be improved appropriately according to the purpose of use and the lateral edge can be polished.
When grinding, attention should be paid to the following points:
1. Prevent overheating and avoid reducing the hardness of the drill bit;
2. Any damage on the drill bit, especially on the edges of the blade, should be completely removed;
3. The drilling pattern should be symmetrical;
4. During blade grinding, be careful not to damage the blade edge and remove any burrs after grinding;
5. For hard alloy drill bits, the grinding shape has a significant impact on the performance of the drill bit. The drill shape at the factory is the best drill shape obtained through scientific design and repeated testing. Therefore, when re grinding, the original blade shape should generally be maintained.