A stepped drill for machining

Abstract

The utility model discloses a kind of special processing stepped drill, it is related to stepped drill technical field, including cylindrical shank and the cutter body on the cylindrical shank, the cutter body includes cutting edge portion and the transition neck portion connecting the cylindrical shank with the cutting edge portion, the cutting edge portion includes drill tip, first stepped cutting edge portion, second stepped cutting edge portion, second stepped cutting transition part and third stepped cutting edge portion, the cutting edge portion is equipped with chip flute, the chip flute and the cutter body solid portion intersection form two cutting sub-edge and two blade petal, the structure realizes the systematic optimization of cutting force, chip removal, precision and life, provides efficient solution for the machining of complex parts such as thin-walled, hollow.

Description

Technical Field

[0001] This utility model relates to the field of mechanical cutting tool technology, specifically a special step drill for machining. Background Technology

[0002] As is well known, in the field of machining, hole drilling differs significantly from milling or turning. Drilling is a semi-enclosed process, which leads to extreme friction between the tool and the workpiece during drilling, causing a sharp increase in cutting temperature and posing a severe challenge to tool performance. For multi-step countersunk hole machining of mechanical parts, a one-step drilling process is usually adopted to improve machining efficiency. Taking cylinder head machining in the automotive industry as an example, the phenomenon of stepped hole hollowing is quite common in the hole machining process of cast parts. However, during the machining of holes in such parts, the problem of oscillation and tool breakage is very likely to occur. Once the tool breaks into the part, it will directly lead to the scrapping of the workpiece, which will not only waste materials but also seriously affect production efficiency and cost control.

[0003] In existing technologies, stepped drills inevitably suffer from insufficient rigidity during drilling due to their long tool overhang. This defect directly leads to frequent tool vibration and even serious problems such as drill rod breakage. To address these issues, a special drill bit has been developed to meet the complex machining requirements of thin-walled, hollow, and countersunk holes with chamfers on special parts. This drill bit effectively reduces the cutting force when the tool enters the hole by optimizing the drill tip structure. The hollow part adopts a solid bar structure, which significantly increases the tool strength, thereby preventing tool breakage due to excessive cutting force during machining and greatly improving on-site machining efficiency. Therefore, it is necessary to propose a solution to this technical problem. Utility Model Content

[0004] The purpose of this utility model is to provide a special step drill for machining, so as to solve at least one aspect of the problems and defects mentioned in the background art.

[0005] To achieve the above objectives, this utility model provides the following technical solution: a special step drill for machining, comprising a cylindrical shank and a tool body disposed on the cylindrical shank, the tool body comprising a cutting edge and a transition neck connecting the cylindrical shank and the cutting edge, the cutting edge comprising a drill tip, a first step cutting edge, a second step cutting edge, a second step cutting transition portion and a third step cutting edge, the cutting edge being provided with a chip removal groove, the chip removal groove intersecting with the solid portion of the tool body to form two secondary cutting edges and two cutting edges.

[0006] According to the present invention, at least the following technical effects are achieved: This special stepped drill for machining uses a submicron-grained cemented carbide bar with a cobalt content of 10% for hollow machining conditions. The material has small grain size and strong grain boundary bonding. Cobalt, as a binder phase, improves bending strength and toughness, making the tool less prone to breakage under alternating cutting forces, thus enhancing tool rigidity and reducing the probability of vibration caused by excessive overhang. The cylindrical shank diameter is designed to be greater than or equal to the smallest even number of the cutting edge diameter, increasing the contact area between the shank and the machine tool spindle and reducing elastic deformation at the connection point. A specific section of the d3 stepped tail uses a solid cylindrical structure without slotting, increasing the proportion of the tool's solid portion. The chamfered slot at the root of the stepped section eliminates stress concentration points. These features... The optimized structure reduces weak points in rigidity; the center drill tip uses a specific included angle, combined with a corresponding clearance angle, to reduce the contact area between the drill tip and the workpiece, lowering the axial force during drilling and preventing hole deformation caused by excessive impact force during drilling in thin-walled castings; different combinations of the main cutting edge and the inner cutting edge rake angle cause different shear deformations in the chips, preventing long chips from wrapping around the tool; the outer diameter of the cutting edge is tapered, reducing the contact area between the tool and the hole wall, lowering frictional heat during cutting, and preventing tool coating failure or workpiece thermal deformation due to temperature rise; the two symmetrical helical chip removal grooves use a smooth arc transition, reducing chip flow resistance and preventing tool wear or workpiece surface scratches caused by chip accumulation; the chip removal grooves intersect with the tool body to form the cutting edge. The stepped drill, with its differentiated rake angle, subjects the chips to alternating shear forces, forming short chips that are easily collected by the automatic chip removal system, reducing the frequency of manual chip cleaning. The four-plane cutting edge shortens the transverse cutting edge length, improving centering accuracy and controlling hole axis misalignment. The stepped clearance angle is used for chamfering the hole opening, ensuring chamfering accuracy and surface roughness, meeting the precision requirements of automotive parts assembly surfaces. A specific section of cylindrical structure acts as a clearance, not participating in cutting, preventing interference between the tool and the machined hole wall, controlling the diameter tolerances of each step and the coaxiality of adjacent steps, meeting the fitting requirements of precision parts. The stepped drill can simultaneously complete drilling, countersinking, chamfering, and other multi-process machining, reducing process time and increasing the annual capacity of a single machine. Submicron-grained cemented carbide materials are used. With structural optimization, tool life is extended, tool replacement frequency is reduced, and the cost of machining a single part is lowered. The reduction of vibration and tool breakage phenomena lowers the scrap rate of workpieces, bringing economic benefits. The cemented carbide material with 10% cobalt content has both wear resistance and toughness, and can adapt to the machining of various materials. For the working conditions of uneven surface and thin wall thickness of castings, the inverted cone and solid structure design keeps the tool stable during eccentric cutting, reducing the machining quality risk caused by working condition fluctuations. This utility model breaks through the rigidity bottleneck of traditional stepped drills in overhanging conditions through multi-dimensional optimization of materials, structure, and parameters, and achieves systematic optimization of cutting force, chip removal, accuracy, and life, providing an efficient solution for machining complex parts such as thin-walled and hollow parts.

[0007] As a further embodiment of this utility model, the drill tip is provided with two angles and four flank faces, as well as two chip grooves. The intersection line of the two flank faces of the drill tip angle forms a transverse cutting edge, and the two central flank faces and the chip grooves form two inner cutting edges. The two flank faces of the drill tip second angle and the chip grooves intersect to form two main cutting edges, and the rake angles of the main cutting edges and the inner cutting edges are different.

[0008] As a further embodiment of this utility model, the rake angle of the main cutting edge is 18°, and the rake angle of the inner cutting edge is 4°-6°.

[0009] As a further embodiment of this utility model, the flank face of the cutting edge is a four-plane cutting edge type. The transverse cutting edge of the four-plane cutting edge type is relatively short, and the two central cutting edges form an included angle φ of 120°-130°. The flank face is provided with a cutting clearance angle β1 of 8°-10° and a second clearance angle β2 of 23°-25°.

[0010] As a further embodiment of this utility model, the diameter height d4 of the included angle φ is 0.3×d2, the transition from d4 to d2 is a planar transition, and its flank face angle is consistent with the central flank face angle, wherein d2 is the outer diameter of the first stepped cutting edge.

[0011] As a further embodiment of this utility model, the diameter d1 of the cylindrical shank is greater than or equal to the smallest even number of the diameter of the cutting edge of the blade body, and the outer diameters d2 and d3 of the cutting edge are both provided with a reverse cone, the length of the reverse cone is a step length, and the amount of the reverse cone is 0.3-0.35 / 100.

[0012] As a further embodiment of this utility model, the effective cutting depth and chip removal groove length are defined by the d3 stepped cutting to the tail of L2. The L3-L2 section is a cylindrical structure with a diameter set to d2-0.3 and without grooves.

[0013] As a further embodiment of this utility model, the root of the d2 step is provided with a chamfered groove of diameter d1, and the chamfer of the root of the step is set as the rear angle of the step, the angle of the rear angle of the step being 5°-11°.

[0014] As a further embodiment of this utility model, the cutting edge is provided with two symmetrical spiral chip removal grooves along the axis of the tool body, the chip removal grooves are smoothly transitioned by an arc, and the cutting edge is provided with four flank faces and chip collection grooves.

[0015] As a further improvement of this invention, the material selected has a cobalt content of 10% and a fracture toughness K... 1- High-C submicron grain cemented carbide bars. Attached Figure Description

[0016] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0017] Figure 1 This is a front view of the structure of this utility model; Figure 2 This utility model Figure 1 Top view of the middle blade body; Figure 3 This is a schematic diagram of the structure during the processing of the present invention. Figure 4 This is a schematic diagram of the structure during the processing of the present invention. Figure 5 This is a schematic diagram of the structure of the processed parts according to this utility model; Figure 6 This is a schematic diagram of the cutting angle of the back face of the present invention.

[0018] Figure label: 1. Cylindrical shank; 2. Tool body; 3. Drill tip. Detailed Implementation

[0019] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0020] Please see Figures 1 to 5 This utility model relates to a special stepped drill for machining, comprising a cylindrical shank 1 and a tool body 2 disposed on the cylindrical shank 1. The tool body 2 includes a cutting edge and a transition neck connecting the cylindrical shank 1 and the cutting edge. The cutting edge includes a drill tip 3, a first stepped cutting edge L1, a second stepped cutting edge L2-L1, a second stepped cutting transition portion L3-L2, and a third stepped cutting edge. The cutting edge is provided with a chip removal groove, which intersects with the solid part of the tool body 2 to form two secondary cutting edges and two cutting lobes. The stepped drill as a whole is L-shaped.

[0021] In this design, the drill tip 3 has two angles and four flank faces, as well as two chip grooves. The intersection of the two flank faces of the central drill tip 3 at the second angle forms a chisel edge. The two central flank faces and the chip grooves form two internal cutting edges. The two flank faces of the central drill tip 3 at the second angle intersect with the chip grooves to form two main cutting edges. The rake angles of the main cutting edges and the internal cutting edges are different. The dual-angle design reduces the axial force of the drill tip 3 by 18% when it enters the drill, reducing the deformation of thin-walled parts. The four flank faces, together with the chip grooves, form a three-dimensional chip breaking space, increasing the chip breaking frequency by 40% and preventing long chips from entangled. The difference in rake angles between the main cutting edges and the internal cutting edges (such as 18° and 5°) causes the chips to undergo different shear deformations, improving the chip breaking effect.

[0022] In this design, the rake angle of the main cutting edge is 18°, and the rake angle of the inner cutting edge is 4°-6°. The large rake angle of the main cutting edge reduces cutting resistance, making it suitable for external diameter cutting and reducing cutting force by 15%. The small rake angle of the inner cutting edge enhances cutting stability and prevents chipping of the inner hole wall, making it particularly suitable for brittle materials such as cast iron. The difference in rake angles causes the chips to generate torque when flowing out, forcing them to break into C-shaped chips, thus improving chip removal efficiency.

[0023] In this plan, see Figure 6 As shown, the flank face of the cutting edge is a four-faceted cutting edge type. The chisel edge of this type is relatively short, and the two central cutting edges form an included angle φ of 120°-130°. The flank face has a clearance angle β1 of 8°-10° and a second clearance angle β2 of 23°-25°. The four-faceted cutting edge type shortens the chisel edge length by 35%, the centering error is ≤0.02mm, and the hole axis misalignment is controlled within 0.04mm / 100mm. The β1 clearance angle reduces friction between the drill tip 3 and the workpiece, lowering the cutting temperature by 25℃. The β2 clearance angle increases the chip space, reducing chip flow resistance.

[0024] In this design, the diameter height d4 of the included angle φ is 0.3×d2, and the transition from d4 to d2 is planar, with its flank angle consistent with the central flank angle. Here, d2 is the outer diameter of the first stepped cutting edge. This planar transition structure increases the cross-sectional area of ​​the solid portion of the drill tip 3 by 15% and improves its bending strength by 20%. The d4=0.3d2 ratio optimizes the stress distribution of the drill tip 3, reduces stress concentration, and improves its resistance to deformation during hollow machining. The consistent angles ensure uniform wear across all sections of the cutting edge, extending tool life.

[0025] In this design, the diameter d1 of the cylindrical shank 1 is greater than or equal to the smallest even number of the cutting edge diameter of the tool body 2. The outer diameters d2 and d3 of the cutting edge are both provided with a reverse taper, the length of which is a step length, and the amount of the taper is 0.3-0.35 / 100. The design of d1 being no less than an even number of the smallest cutting edge diameter increases the contact area between the shank and the spindle by 20%, improves the connection rigidity, reduces the contact area between the tool and the hole wall by 40%, and reduces frictional heat by 20°C. Especially in deep hole machining, the tool wear is reduced by 30%, and the amount of the taper (0.3-0.35 / 100) can reduce the cutting resistance.

[0026] In this design, the effective cutting depth and chip flute length are defined by the d3 stepped cutting to the tail of L2. The L3-L2 section is a cylindrical structure with a diameter of d2-0.3 mm and no slot. The solid clearance section increases the tool's cross-sectional area by 12% and raises the first-order natural frequency by 15 Hz, avoiding common machine tool vibration frequencies. The d2-0.3 mm diameter design avoids interference with the machined hole wall, ensuring a coaxiality error of ≤0.03 mm. The slotless structure reduces stress concentration points and improves the tool's bending strength.

[0027] In this design, the root of step d2 is provided with a chamfered groove of diameter d1, with a groove length of 0.5D. The chamfer at the root of the step is set as the step back angle, with an angle of 6°-8°. The groove eliminates 30% of the stress concentration at the step transition, preventing the tool from breaking at this point. The hole chamfering process can be completed simultaneously, reducing the number of tool changes and shortening the process time by 30%. The groove length of 0.5D ensures sufficient stress release. Fatigue tests show that the tool cycle life is improved.

[0028] In this design, the cutting edge has two symmetrical spiral chip removal grooves along the axis of the tool body 2. The chip removal grooves have a smooth arc transition. The cutting edge has four flank faces and a chip collection groove. The spiral groove chip removal speed is 0.8m / s, which is 40% more efficient than the straight groove. It can run continuously for 2 hours without clogging in cast iron machining. The arc transition reduces chip flow resistance by 30%, which is suitable for preventing sticky materials such as aluminum alloys from sticking together. The four flank faces cooperate with the chip collection groove to form a three-dimensional chip breaking space, which improves the chip breaking rate.

[0029] In this design, the tool material is selected with a cobalt content of 10% and a fracture toughness of K. 1- High-cobalt submicrograin cemented carbide bars, with their submicrograin structure, achieve a hardness of 91.5 HRA, offering 30% higher wear resistance than ordinary cemented carbide, making them suitable for interrupted cutting of cast iron. A 10% cobalt content balances strength and toughness, resulting in a bending strength ≥2300 MPa, 40% improved impact resistance, reducing the risk of tool breakage, and a fracture toughness K1C = 12 MPa. m¹ / ², which extends fatigue life under hollow cantilever conditions.

[0030] This utility model discloses a special step drill for machining, mainly applicable to the machining of a special part. This part has complex working characteristics such as thin walls, hollow structure, countersunk hole with chamfer, and its local machining areas are as follows: Figure 5 As shown. These types of parts are commonly found in automotive trunk lids, and are typically castings. Some areas have thinner walls, and there are hollow areas between the stepped holes. In actual manufacturing, specific processing scenarios are as follows... Figure 3 and Figure 4 As shown. The drilling surface of castings may be uneven, or the wall thickness may be thin, leading to significant vibration during machining. Furthermore, the hollow dimensions are often large, placing higher demands on the strength and rigidity of the cutting tool. Based on these conditions, the tool shape is as follows... Figure 1 As shown. In the selection of tool material, a cobalt content of 10% and a fracture toughness K0 were chosen. 1- High-density (C) submicrograined cemented carbide bars. This material exhibits excellent wear resistance and impact resistance, meeting the machining requirements under complex conditions. The diameter d1 of the cylindrical shank is designed to be greater than or equal to the smallest even number of the cutting edge diameter (2) of the tool body. This design helps improve the connection stability between the tool and the machine tool spindle, further enhancing the rigidity of the tool. Figure 1As shown, due to the long overhang of the stepped drill, to reduce friction between the tool and the hole wall during drilling, the outer diameters of the cutting edges d2 and d3 are both tapered. The tapered length is consistent with the step length, and the tapered amount is typically 0.3-0.35 / 100. This tapered design effectively reduces the frictional resistance between the tool and the hole wall, reduces cutting heat generation, and also facilitates chip removal. The effective cutting depth and chip flute length are from step d3 to the tail of L2, while the cylindrical structure in the L3-L2 section is only used for clearance. To enhance tool strength, the diameter of this cylindrical structure can be set to d2-0.3, and it is not grooved. This design maximizes the solid portion of the tool while ensuring machining functionality, thus improving tool strength. The root of step d2 has a chamfered groove with a diameter of d1, and the groove length is typically 0.5D. The chamfer at the root of the stepped section is set as a stepped clearance angle, typically 5°-11°. This clearance angle design is mainly used for chamfering workpiece openings, ensuring the accuracy and surface quality of the chamfer. The cutting edge has two symmetrical spiral chip evacuation grooves along the axis of the tool body, with a smooth, rounded transition within the grooves. This spiral chip evacuation groove design provides a smooth discharge channel for chips, while the smooth rounded transition reduces resistance during chip removal, preventing chip blockage. The cutting edge has four flank faces and chip evacuation grooves. The two middle flank faces intersect to form a chisel edge, the two edge flank faces intersect with the chip evacuation grooves to form two inner cutting edges, and the two edge flank faces intersect with the chip evacuation grooves to form two main cutting edges. The rake angle of the main cutting edges is 18°, and the rake angle of the inner cutting edges is 4°-6°. This combination of different rake angles allows the chips to be subjected to different cutting forces during formation, making them easier to break and further improving chip removal efficiency. The flank face of the cutting edge is a four-faceted cutting edge. This type of cutting edge has a short transverse cutting edge length and high centering accuracy. See also Figure 6The two central cutting edges form an included angle φ of 120°-130°. The rake face has a cutting clearance angle β1 of 8° to 10° and a second clearance angle β2 of 23°-25°. These angular parameters effectively reduce frictional resistance during cutting, improving tool performance and service life. The diameter height d4 of the included angle φ is 0.3×d2, with a planar transition from d4 to d2, and its rake face angle is consistent with the central rake face angle. This transition design ensures the structural strength and cutting stability of the drill tip, allowing the tool to maintain good performance during drilling and cutting. In practical applications, this dedicated stepped drill has shown significant advantages for complex working conditions. Taking the multi-step countersunk hole machining of automotive hatch-type castings as an example, when using a stepped drill, the rigidity of the tool is effectively guaranteed, vibration is significantly reduced, and tool breakage almost never occurs. Because chips can be smoothly discharged, the cutting temperature during machining is effectively controlled, and the machining accuracy and surface quality of the workpiece are significantly improved. Meanwhile, the tool life is significantly extended, reducing the frequency of tool replacement, lowering production costs, and improving production efficiency. Through optimization of the tool structure and rational design of parameters, this utility model of a special-purpose stepped drill successfully solves the problems existing in the prior art, providing an efficient and reliable tooling solution for machining special parts. In the future field of machining, especially in industries such as automobile manufacturing where high precision and efficiency in parts machining are required, this stepped drill is expected to be widely used and promoted.

[0031] The above description is merely an example and illustration of the structure of this utility model. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the structure of the utility model or exceed the scope defined in the claims, they should all fall within the protection scope of this utility model.

Claims

1. A special step drill for machining, characterized in that, The tool includes a cylindrical shank (1) and a tool body (2) disposed on the cylindrical shank (1). The tool body (2) includes a cutting edge and a transition neck connecting the cylindrical shank (1) and the cutting edge. The cutting edge includes a drill tip (3), a first-step cutting edge, a second-step cutting edge, a second-step cutting transition portion, and a third-step cutting edge. The cutting edge is provided with a chip removal groove. The chip removal groove intersects with the solid part of the tool body (2) to form two secondary cutting edges and two cutting edges.

2. The special step drill for machining according to claim 1, characterized in that, The drill tip (3) has two angles and four back faces, as well as two chip grooves. The intersection of the two back faces of the drill tip (3) at the angle forms a transverse cutting edge. The two central back faces and the chip groove form two internal cutting edges. The two back faces of the drill tip (3) at the second angle intersect with the chip groove to form two main cutting edges. The cutting rake angle of the main cutting edges is different from that of the internal cutting edges.

3. A special step drill for machining according to claim 2, characterized in that, The rake angle of the main cutting edge is 18°, and the rake angle of the inner cutting edge is 4°-6°.

4. The special step drill for machining according to claim 3, characterized in that, The flank face of the cutting edge is a four-plane cutting edge type. The transverse cutting edge of the four-plane cutting edge type is relatively short. The two central cutting edges form an included angle φ of 120°-130°. The flank face is provided with a cutting clearance angle β1 of 8°-10° and a second clearance angle β2 of 23°-25°.

5. A special step drill for machining according to claim 4, characterized in that, The included angle φ has a diameter height d4 of 0.3×d2. The transition from d4 to d2 is a planar transition, and its flank face angle is consistent with the central flank face angle. Here, d2 is the outer diameter of the first stepped cutting edge.

6. A special step drill for machining according to claim 5, characterized in that, The diameter d1 of the cylindrical shank (1) is greater than or equal to the smallest even number of the diameter of the cutting edge of the blade body (2). The outer diameters d2 and d3 of the cutting edge are both provided with inverted cones. The length of the inverted cone is a step length, and the amount of inverted cone is 0.3~0.35 / 100.

7. A special step drill for machining according to claim 6, characterized in that, The effective cutting depth and chip removal groove length are defined by the d3 stepped cutting to the tail of L2. The L3-L2 section is a cylindrical structure with a diameter of d2-0.3 and is not grooved.

8. A special step drill for machining according to claim 7, characterized in that, The root of the d2 step is provided with a chamfered groove of diameter d1. The chamfer at the root of the step is set as the back angle of the step, and the angle of the back angle of the step is 5°-11°.

9. A special step drill for machining according to claim 8, characterized in that, The cutting edge is provided with two symmetrical spiral chip removal grooves along the axis of the tool body (2). The chip removal grooves are smoothly transitioned by a circular arc. The cutting edge is provided with four back face and chip removal grooves.

10. A special step drill for machining according to claim 9, characterized in that, The material selected has a cobalt content of 10% and a fracture toughness of K. 1- High-C submicron grain cemented carbide bars.

Images