Drilling a Dole

 Drilling means drilling a hole

Cutting process range

There is a wide range of processes available for drilling processes. Different tools can be used on the drilling machine to complete centering, drilling, reaming, reaming, tapping, boring, and boring face, as shown in the figure. The drilling precision of the drilling machine is low, but the holes with high precision (IT6~IT8, the surface roughness is 1.6-0.4μm) can also be processed by drilling-reaming-reaming. The fixture can be used to process hole systems with location requirements.

When machining on a drilling machine, the workpiece is fixed and the tool moves axially (feed motion) while rotating (main motion).

driller

The main types of drilling machines are bench drilling machines, vertical drilling machines, radial drilling machines, milling and drilling machines, and center hole drilling machines. The main parameter of a drilling machine is usually the maximum hole diameter.

Vertical drilling machine is one of the widely used drilling machines. It is characterized in that the axis of the main shaft is vertically arranged and the position is fixed. The position of the workpiece needs to be adjusted so that the centerline of the machined hole is aligned with the centerline of rotation of the tool. The main movement is achieved by the rotation of the tool while moving in the axial direction of the feed movement. Therefore, the operation of the vertical drilling machine is inconvenient and the productivity is not high. It is suitable for the processing of small and medium-sized parts in single-piece and small-batch production.

•Transmission principle of vertical drilling machine.

Main movement: A single-speed motor is driven by a gear stepper transmission mechanism; the rotation direction of the main shaft is changed by the forward and reverse rotation of the motor.

Feed motion: The spindle and spindle sleeve move linearly in the spindle box. The axial movement of the spindle is represented by the axial movement of the spindle per revolution. Second, the bench drill. A bench drill press is called a bench drill. It is essentially a vertical drill press for machining small holes. It has a simple and compact structure, is flexible and convenient, and is suitable for processing small holes in small parts. The diameter of the drill hole is usually less than 15mm.

Three, radial drilling machine

For large and heavy workpieces, it is very inconvenient to process them on a vertical drilling machine. At this time, a radial drilling machine can be used for processing.

The headstock can be adjusted laterally along the guide rails on the rocker's arm. The rocker arm can be adjusted along the cylindrical surface of the column and rotated around the column. During the machining process, the workpiece is fixed, and the position of the spindle is adjusted so that the center is aligned with the center of the hole to be machined and quickly clamped to maintain an accurate position. Radial drilling machines are widely used in single, medium, and small batch production to process large and medium-sized parts.

If you want to machine holes and holes in any direction and in any position, you can use a universal radial drilling machine. A machine tool spindle can rotate about a specific axis in space. There is also a lifting ring on the top of the machine so it can be hung in any position. Therefore, it is suitable for processing large and medium-sized workpieces in single-batch and small-batch production.

drilling tool

twist drill

Structure of twist drill

A twist drill consists of three parts: the working part, the neck, and the handle.

(1) Working part: The working part of the twist drill has two spiral grooves, and its shape is very similar to the shape of the twist. It is the main part of the drill bit and consists of the cutting part and the guide part.

  deal with

The handle is the clamping part of the drill bit, which is used to connect with the machine tool and transmit torque and axial force during the drilling process. There are two types of handles for twist drills: tapered handle and straight handle. Straight shanks are mainly used for small twist drills with a diameter of less than 12mm. The taper shank is used for large-diameter twist drills, which can be directly inserted into the taper hole of the spindle or inserted into the taper hole of the spindle through the taper sleeve. The flat end of the taper shank is used to transmit torque and to remove the bit easily.

neck

When grinding the handle of a drill, the neck groove of the twist drill is the overrunning groove of the grinding wheel. The bottom of the groove is usually engraved with the drill's specifications and factory markings. Straight shank drill bits have no neck.

The composition of the cutting part

The cutting part is responsible for the cutting work and it consists of two fronts, a main back, back, a main cutting edge, a secondary cutting edge, and a chisel edge. As shown in the figure, the chisel edge is the edge formed by the intersection of two trunks, and the back is the two belts of the drill bit, which are opposite to the wall of the workpiece hole (that is, the processing surface) when working.

The guide part is the guiding function when the cutting part cuts into the workpiece, and it is also the grinding part of the cutting part. In order to reduce the friction between the guide part and the hole wall, the outer diameter (that is, on the two margins) is ground with an inverted cone of (0.03-0.12)/100. (0.03-0.12 inverted taper per 100mm length)

In addition, in order to improve the rigidity of the drill bit, the diameter of the core between the two blades of the working part is made to be a positive taper of (1.4 to 1.8)/100 in the axial direction.

(1) Rake face: The rake face is the surface of the spiral groove, which is the flow of chips through the surface, acting as chips and chips. Polishing is required to allow smooth chip removal.

(2) Main side: The main side is opposite to the processing surface and is located at the front end of the drill. The shape is determined by the sharpening method. It can be helicoidal, conical, and flat, or any manually sharpened surface.

(3) Secondary side: The secondary side is the narrow end face on the outer cylindrical surface of the drill bit opposite to the machined surface.

(4) Main cutting edge: The main cutting edge is the intersection of the rake face (spiral groove surface) and the main side. The main turning edge of a standard twist drill is straight (or nearly straight)

(5) Minor cutting edge: The minor cutting edge is the intersection of the rake face (the surface of the spiral groove) and the minor side (narrow face), that is, the cutting edge.

(6) Transverse blade: The chisel edge is the intersection of the two main sides and is located at the front end of the two drill bits, also called the drill bit.

Geometric parameters of twist drill

coordinate plane

(1) Cutting plane Ps: It is a plane including the cutting speed direction at this time, and this plane is tangent to the surface cut by the cutting edge at this time.

(2) Base plane Pr: The base plane Pr of the selected point on the main cutting edge of the drill bit is a plane that passes through the point and is perpendicular to the cutting speed of the point. The bottom surface is always a plane that passes through the drill axis and is perpendicular to the direction of the cutting speed.

Geometry of the drill bit

(1) Helix angle: The intersection line between the helical groove surface of the drill bit and the outer cylindrical surface is the helix, and the angle between the helix and the axis of the drill bit is called the angle of the helix drill bit and is recorded as β. (see textbook)

(2) Edge angle and end face inclination angle

Since the main cutting edge does not pass through the axis, the insert tilt angle is formed. The inclination angle of the insert is also different for each point on the cutting edge, mainly because the bottom surface of each point is different from the cutting plane. To facilitate the description of this concept, we introduce the concept of panel tilt.

•Face angle: The angle of the end face of a selected point on the main cutting edge is the angle between the base of the point measured in the end projection view and the main cutting edge. For different selection points, the inclination angle of the end face is also different, and the maximum value (minimum absolute value) of the outer edge near the core is smaller.

(3) Vertex angle (rake angle) and lead angle:

The apex angle of a drill is the angle between the projections of the two major cutting edges in a plane measured in a plane parallel to the two major cutting edges. Recorded as 2φ, standard twist drill 2φ= 118°

The advance angle is the angle between the protrusion of the main cutting edge and the feed direction measured in the base plane, expressed as κrx. Since the base surfaces of points on the main cutting edge are different, the main deflection angles at each point are also different.

(4) Rake angle: Measure the rake angle of the selected point on the main cutting edge on the orthogonal plane of the point.

References

(5) Relief angle: The relief angle selected on the main cutting edge is measured in the tangent plane with the cutting head axis as the axis and passing through the cylindrical point at this point, expressed as αf.

3. Other drill bits

Carbide twist drill

When machining hard and brittle materials, using carbide drills can significantly improve cutting efficiency.

The following carbide twist drills are made into an integral structure and can be made into straight shank carbide twist drills or used as tapered shank carbide twist drills.

Compared with high-speed steel twist drills, this core has a larger diameter, smaller helix angle and shorter working part. The blade body is made of 9SiCr alloy steel and hardened to 50-52HRC. These measures are designed to increase the stiffness and strength of the drill bit to reduce chipping caused by vibration during drilling.

(2) Deep hole drilling

Deep holes usually refer to holes with an aspect ratio greater than 5 times. When drilling deep holes, issues such as chip breaking, chip removal, cooling and lubrication, and guidance must be solved.

gun drill

Gun drills were originally used to drill gun barrels, hence the name gun drills. It is usually used for processing small diameter deep holes.

1. Structure and working principle

A gun drill consists of cutting parts and drill rods. The cutting part is made of high-speed steel or hard alloy to make the chip flute long; the drill rod is made of seamless steel pipe, and the chip flute rolls near the drill bit, and its diameter is 0.5~1mm smaller than the drill bit diameter. They are joined together by welding, and the flutes are aligned during the welding process.

Working principle: When drilling, the workpiece rotates, and the drill bit feeds. The cutting fluid is injected into the cutting area from the inner hole of the drill pipe and the oil inlet hole of the cutting part by high pressure to cool and lubricate and flush the chips out of the chip groove. Since the chips are expelled from the outside of the drill bit, they are called external chips.

2. Features

(1) Since the cutting fluid enters and exits separately, the cutting fluid is not disturbed under high pressure and can easily reach the cutting area, which better solves the problem of cooling and lubrication during deep hole drilling;

(2) Since the cutting edge is divided into an inner cutting edge and an outer cutting edge, and the cutting edge has an eccentricity e, chip action can be performed during the cutting process, the chip is narrowed, and the cutting fluid is convenient for punching the chip. , making chip removal easy;

(3) Since the core column with a diameter of 2h is left after drilling, it can ensure that the support surface of the drill bit is always in close contact with the hole wall so that the drill bit has reliable guidance and solves the problem of guiding deep hole drilling.

2. Deep hole drilling with internal chip removal

The drill bit consists of a drill body, three cutting edges distributed on different circumferences and two guide blocks.

During operation, high-pressure cutting fluid is delivered to the cutting area from the gap between the drill pipe and the hole wall to provide cooling and lubrication. At the same time, chips are punched out of the drill bit’s internal chip hole and the drill rod’s internal hole.

This kind of deep hole drill bit has three teeth arranged on different circumferences, so it plays the role of cutting chips and facilitates chip removal. Moreover, when the chips are discharged, they will not rub against the machining surface, so the production efficiency and processing quality are higher than those of external chips. This structure has no chiseled edges, thus reducing axial forces. The guide block bears unbalanced circumferential force and radial force on the circumference, and the deep hole drill has better-guiding performance.

jet drilling

The suction drill consists of three parts: drill bit, inner tube, and outer tube.

When working, 2/3 of the cutting fluid enters the cutting area through the gap between the inner and outer tubes to play a cooling and lubricating role. The remaining 1/3 of the cutting fluid is sprayed into the tube through the slit of the crescent groove on the inner tube wall so that the pressure difference between the front end and the rear end of the inner tube produces "suction" to accelerate the discharge of cutting fluid and chips.

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