Countersinking is an operation associated with the processing of pre-drilled, stamped, cast, or other methods of holes in order to give them a more regular geometric shape (eliminate deviations from roundness and other defects), as well as achieve a higher accuracy compared to drilling (up to Grade 8) and lower roughness (up to Ra 1.25). Countersinking is carried out either on table-top drilling machines (with small hole diameters), or on stationary drilling equipment installed on the foundation. Manual drilling equipment for countersinking is not used, since it cannot provide the required accuracy and surface roughness. Types of countersinking include countersinking and counterblowing.
Basic rules for countersinking holes:
drilling and countersinking of holes must be done with one setting of the part (workpiece) on the machine, that is, changing only the processing tool;
when countersinking untreated holes in body parts, special attention should be paid to the reliability of the installation and the strength of the fastening of the part;
it is necessary to accurately observe the amount of allowance for countersinking, guided by the corresponding table;
countersinking should be done in the same modes as drilling;
the same labor protection rules must be observed as when drilling.
Hole machining. Drilling, countersinking, countersinking, reaming.
After the holes are made in the solid material, they are processed to increase the size and reduce the roughness of the surfaces, as well as the processing of the previously obtained holes (for example, by casting, punching, etc.). Hole machining is performed in several ways, depending on which parameters of accuracy and roughness of the hole surface are specified in the drawing. In accordance with the selected processing method, the tool for its implementation is also selected. When machining holes, there are three main types of operations: drilling, countersinking, reaming and their varieties: reaming, countersinking, counterbore.
Drilling is an operation to form through and blind holes in a solid material, performed using a cutting tool. a drill. Distinguish between manual drilling. manual pneumatic and electric drilling devices (drills) and drilling on drilling machines. Hand-held drilling devices are used to produce holes with a diameter of up to 12 mm in materials of low and medium hardness (plastics, non-ferrous metals, structural steels, etc.). For drilling and processing of holes of larger diameter, increasing labor productivity and quality of processing, table-top drilling and stationary machines are used. vertical drilling and radial drilling.
One of the types of drilling is reaming. increasing the diameter of the hole drilled earlier. Drills are used as tools for reaming holes, as well as for drilling. It is not recommended to ream holes made in a workpiece by casting, forging or stamping. Such holes have different hardness along the surface of the hole due to the scale formed during casting, as well as due to the uneven concentration of internal stresses in the metal in different parts of the surface of holes obtained by forging or stamping. The presence of places with uneven and increased surface hardness leads to a change in the radial loads on the drill during the machining of the hole, which leads to a displacement of its axis, and also causes breakage of the drill. Hole machining by drilling and reaming allows you to obtain the accuracy of the dimensions of the machined hole up to the 10th quality and the roughness of the machined surface up to Rz 80.
Countersinking is the processing at the top of drilled holes of cylindrical or conical grooves for screw and rivet heads, as well as chamfers. The operation is performed using a special tool. countersink.
Basic rules for countersinking holes:
it is necessary to observe the correct sequence of countersinking holes: first drill a hole, and then carry out its countersinking;
drilling of a hole and its countersinking should be done from one installation of the workpiece (part), changing only the tool;
countersinking should be performed with manual feed of countersinks and a low spindle speed (no more than 100 rpm) using an emulsion, the depth of countersinking should be checked with a vernier caliper or a ruler;
When countersinking holes with a cylindrical countersink, when the journal diameter is larger than the hole diameter, you must first drill a hole along the journal diameter, and then countersink the hole. Final operation. reaming the hole to the specified size.
Counterbore is an operation for cleaning the end surfaces when processing bosses for washers, nuts, and retaining rings. The operation is performed using a special tool. a counter forging, which is installed on special mandrels.
Reaming is an operation for machining previously drilled holes with a high degree of accuracy (up to grade 6) and low roughness (up to Ra 0.63). Reaming processing is performed after pre-drilling, reaming and countersinking the hole with reamers, which are divided into roughing and finishing, manual and machine. Deployment is carried out both manually and on machines, as a rule, stationary. The design of the tool is selected depending on the applied processing method.
Basic rules for reaming holes:
it is necessary to accurately observe the size of the reaming allowance, guided by the corresponding table;
Drilling glass sinks and countersinks for drains with Electroplated and Sintered Core drills
manual deployment should be performed in two steps: first, rough, and then fine;
in the process of opening a hole in a steel workpiece, it is necessary to abundantly lubricate the surface to be treated with emulsion or mineral oil, cast iron workpieces should be deployed dry;
manual deployment should be carried out only clockwise to avoid scoring of the hole walls by chips;
during processing, the reamer should be periodically cleaned of chips;
the accuracy of processing reamed holes should be checked with gauges: cylindrical. through and non-through; conical. according to the marginal risks on the caliber. It is allowed to check the expanded conical hole with a control pin “on a pencil”;
drilling and reaming of holes on a drilling machine with a machine reamer must be done from one workpiece installation, changing only the processing tool.
Drilling, countersinking and reaming
Drilling. this is the process of obtaining by cutting deaf and through-
cylindrical holes in solid material, carried out on drilling and turning machines. If the diameter of the hole that you want to get during the processing is 30 mm, then two drills are used to make it. First, for drilling. and the second, for reaming.
Drilling (reaming) is rough machining of holes, during which accuracy is ensured within 12. 14 grades and roughness microns.
In our country, a unified gradation of drill diameters is adopted, regulated by GOST 885-77 and covering almost all hole sizes up to 80 mm found in machine parts and devices.
The following types of drills are produced: spiral, feather, single-sided cutting (gun), annular and combined [11, 13].
Spiral or twist drills are most widespread when machining holes with a depth of up to (5. 10) d. The design of a twist drill with a taper shank is shown in Fig. 40.
Fig. 40. Taper Shank Twist Drill Design
The twist drill consists of a working part and a shank. On the working part, in turn, the cutting part and the guiding part can be distinguished. A foot is provided for knocking out drills with a taper shank from the spindle bore.
Between the working part and the taper shank of the drill, there is
often has a neck-like transitional part of the drill.
Twist drills can have a cylindrical shank (at a diameter of mm) or a taper shank (at a mm).
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Drilling, countersinking, reaming
Drilling is the main method for producing blind and through cylindrical holes in solid material of the workpiece. As a tool for drilling, a drill is used (Fig. 7.15), which has two main cutting edges, ne-
Fig. 7.15. Parameters and elements of the twist drill: /. working part; one. cutting part; / 2. calibrating part; / 3. neck; / 4. shank; /. ribbon; 2. cutting edge; 3. back surface; four. front surface; five.
middle edge and two helical grooves for chip evacuation.
Drills can be:
- with plates made of hard alloys;
- for deep holes.
Twist drills are made with a diameter of 0.1 to 80 mm. Working part / drills (fig.7.15, and) has two screw grooves. The cutting part /, has two cutting teeth. The cutting tooth has: front surface four (fig. 7.15, in), back surface 3 and cutting edge 2. The border of the cutting teeth is the transverse edge 5. On the gauging part / 2 there are bands /, which provide the direction of the drill during cutting. The shank / 4 is made tapered for fixing in the spindle of the machine (directly or using adapter sleeves) or cylindrical (Fig.7.15, b) for fixing in the chuck. The drill is marked on the neck / 3.
The angle 2ph at the tip of the drill (between the cutting edges) can range from 80 ° (for aluminum, babbits, plastics and other soft materials) to 140 ° (for marble and other brittle materials). For drilling steel and cast iron, this angle is 116-118 °. The angle from the slope of the helical groove determines the value of the rake angle, its values range from 10 (for drilling brittle materials) to 45 ° (for soft materials); for steel and cast iron. 30 °.
When drilling, there is a “drift” of the drill due to the presence of a transverse edge, which, when the drill is in operation, does not cut, but presses on the workpiece. It was found that up to 65% of the feed force falls on the transverse edge. To facilitate the work of the drill, the transverse edge is sharpened (Fig.7.15, d); from for the same purpose, double sharpening of drills working on cast iron and steel is performed with an angle of 2 (p, from 75 to 80 ° (Fig. 7.15, e). B the rear surface of the second sharpening is selected in the range from 0.18 /) to 0.22 /) (/). drill diameter). As a result of double sharpening, the width of the chip increases due to its thickness, the angle at the tip decreases, therefore, the durability of the drill increases.
Drilling machines are used for drilling and lathes. On drilling machines, the drill performs a rotary (main) cutting movement and a longitudinal (feed movement) along the axis of the hole, the workpiece is stationary. When working on lathes, the rotary (main) movement is performed by the workpiece, and the translational movement along the axis of the hole (feed movement) is performed by the drill.
The process of chip formation during drilling takes place in more severe conditions compared to turning, since during drilling, the exit of chips is more constrained and the supply of cutting fluid to the cutting zone is more difficult.
Drilling also provides surface roughness Yaa = 10- ^ 20 μm.
To obtain holes of higher accuracy, countersinking and reaming are performed on the same machine.
Countersinking. processing by cutting the walls or the entrance part of the hole. is carried out on black surfaces in castings and forgings or on drilled holes. The purpose of countersinking is to obtain more accurate hole sizes and surface locations, to process the end or inlet part of the screw head hole, etc.
Cutting during countersinking is similar to the simultaneous operation of several boring bits, which in this case can
Fig. 7.16. Countersinks and countersinks: and. countersink three-toothed tail; b. one-piece four-tooth countersink; c, d, e. countersinks
count the countersink teeth. Countersinks (tools for processing holes per pass) are made with trident tail (Fig.7.16, and) with a diameter of 10 to 50 mm and four-pronged. Four-tooth countersinks can be mounted, solid (Fig. 7.16, b) and prefabricated (with plug-in knives made of high-speed steel or with plates of hard alloys) with a diameter of 45-80 mm.
Countersinks (a type of countersinks) are used to process the inlet part of the holes for the heads of bolts, studs (Fig.7.16, in), have a guide pin, which is manufactured as one piece with the countersink body (in some designs it can be replaceable). Countersinks for processing the inlet part of the hole on a cone (for screw heads, rivets) have an angle (60, 75, 90 or 120 °) at the top of the cone (Fig.7.16, d). In fig. 7.16, d shows a countersink for trimming bosses. Combined countersinks are also produced to obtain stepped holes.
Deployment. final finishing of holes with surface roughness Yaa = 0, Zch-2 microns. When reaming from the walls of a hole, previously processed by drilling and countersinking (or just drilling), a layer of metal is removed in a few tenths of a millimeter.
According to the shape of the hole being machined, the reamers are divided into cylindrical (Fig. 7.17, and) and conical (fig. 7.17, b). Time-
Fig. 7.17. Sweep: and. cylindrical; b. conical
vertices, like countersinks, are made tail and mounted. The working part / cylindrical reamer consists of a cutting part /, a gauging part / 2 and an inverse taper / 3. To prevent the cutting of the hole being machined, the angular pitch of the teeth of the reamers is made unequal so that pairwise opposite teeth lie in the same diametrical plane to control the dimensions of the reamers. According to the method of application, reamers are divided into machine and manual, according to their design. into solid and prefabricated with plug-in knives.
Drilling, reaming and countersinking holes
Operating allowances for hole processing. Allowance for the processing of parts is a layer of metal to be removed during processing.
The size of the “allowance for machining holes should be minimal, but sufficient to obtain the correct geometric shape, specified dimensions and roughness of the hole with the minimum number of required tools and the number of passes. Thus, the most advantageous hole machining allowance ensures compliance with specifications along with high productivity and cost-effectiveness of machining.
The minimum size of the allowance for machining holes depends on the rigidity of the machine. tool. part system and, mainly, the rigidity of the mandrels and boring bars, on the type of tool used, the type of holes and their location, the nature of the operation performed, the size of the holes and the body.
The required number of passes when machining holes decreases with an increase in the rigidity of mandrels and boring bars, in the presence of a multi-cutter tool, a symmetrical arrangement of the allowance, a decrease in the length of the hole and (spindle overhang.
The rigidity of mandrels and boring bars, in turn, increases with the use of a support in the back rack or rests.
Drilling It is used for making holes in solid material with accuracy and roughness up to Rz 40. The required length of the cutting part of the drill depends on the required drilling depth and is determined from the drawing of the workpiece. Extra long drills are used when drilling deep holes.
The drills are installed with a tapered shank in the bore of the adapter sleeve or extension, and the latter in the cone of the machine spindle. Pre-mating conical surfaces are wiped with ends or a napkin. The drills are removed from the mandrel or extension using a drift wedge. It must be borne in mind that all taper shank tools can only work properly if the taper surfaces are well mated and there are no nicks. To guide the drill at the beginning of processing, pre-center the hole with a short drill with a diameter of up to 30 mm.
The cutting mode for drilling and reaming is selected depending on the material of the workpiece, the diameter and geometry of the drill sharpening, the length of the hole to be machined, “drill protrusion.
Drilling feed is carried out by axial movement of the spindle relative to the workpiece fixed on a stationary table, or by moving the table with the workpiece relative to the rotating spindle (drill). Manual drill feed is used when drilling along the crust, setting movement until the tool touches the part and when removing the tool from the hole to remove chips. Due to the significant axial forces, drilling is performed with power feed.
When drilling, the following rules must be observed: do not use drills with a spiral flute length less than the drilling depth; bring the drill to the part only when it rotates; plunge in manually, and then turn on the power feed; do not stop the drill while cutting without first turning off the drill feed; when drilling through holes, the end face of the part must be perpendicular to the axis of the drill at the entrance and exit.
Blind holes are drilled on horizontal boring machines as follows. The worker brings the drill until it touches the part and notices the graduation on the circular spindle feed dial that coincides with zero risk. Then he drills the hole manually and, turning on the mechanical feed of the spindle, monitors the rotation of the circular dial until the division corresponding to the depth of the hole. The worker then turns off the power feed and manually pulls the drill out of the hole. When drilling blind holes, the worker manually brings the second drill until it touches the outer diameter of the drill to the end face of the part, after which, turning on the power feed, he counts the drilling depth along the spindle feed dial.
Holes with a length of less than five drill diameters with a normal spindle overhang are drilled according to the marking without the direction of the drill. When the hole is precisely positioned (the ratio of the hole length to the diameter is greater than 5), the drills are guided through bushings installed in the fixture, or pre-machined holes in one of the walls of the part. If the hole is located at a significant distance from the end of the spindle, an elongated arbor is used, which enters with a slip fit.
Cooling during drilling is carried out by cutting fluids: emulsion or kerosene. The flow rate of the emulsion should be 10-12 l / min. The use of cooling when processing steel allows you to increase the cutting speed by 25-30%.
Drill breakage can occur due to chipped cutting edges, dullness, wear or damage to the tape edges, or breakage of the shank foot. To prevent breakage of the drills from the indicated reasons, it is necessary to reduce the cutting speed, sharpen the drill, reduce the feed, replace the guide sleeve with a loose hole diameter, clean the drill from chips in a timely manner, ensure the correct mating of the tapered surfaces of the tool, adapter sleeve and spindle.
When drilling parts on boring machines, the following processing errors may occur: drill drift from the specified axis, hole breakdown by diameter, unsatisfactory roughness of processing or offset of the hole axis from the reference surfaces.
Reasons for the drift of the drill from the specified axis: longitudinal bending of the drill, loose fit of the drill taper in the machine spindle, non-parallelism of the spindle axis with the machine guides or non-perpendicularity of the surface of the part to the direction of the drill feed.
Reasons for breaking the hole during drilling: misalignment of the axes of the shank and the working part of the drill, displacement of the axis of the intake cone relative to the shank, inequality of cutting edges during sharpening or runout of the machine spindle axis.
The unsatisfactory roughness of the hole machining with a drill and the offset of the hole axis from the reference surfaces are also a consequence of the above reasons, but, in addition, depend on the quality of sharpening, the condition of the cutting edges and tape, the correct coordination of the tool during installation.
Drill drift from a given axis can be prevented by double sharpening with sharpening of the bridge and tape, preliminary drilling with a rigid shortened drill, using elongated guide bushings when drilling holes in several walls, eliminating nicks and contamination of the tool and spindle tapers, moving the spindle (and not the table) during machining and milling the end face of the part before drilling.
The breakdown of the hole by diameter can also be prevented if the technical conditions for the runout of the working part of the drill relative to the shank are observed (drill diameter up to 20 mm, beating, no more than 0.12 mm, diameter 20-50 mm. 0.15 mm, diameter over 50 mm. 0.18 mm), sharpen the cutting edges of the drill with a base from the shank and control the equality of the lengths of the cutting edges.
By reaming drilling a pre-drilled hole. Reaming is used when machining holes in solid material with a diameter of over 30 mm.
Machining large holes with two or three drills is more productive than with a single drill, since a large diameter drill has a wide transverse edge that generates significant axial forces. This results in lower feed rates and longer drilling times. Three drills are used when machining holes with a diameter over 50 mm. When drilling holes, the side allowance for each next drill is 10-12 mm.
The MultiSink® Combination Drill & Countersink Tool
Hole countersinking produced by countersinks to improve the roughness and accuracy of holes obtained by preliminary drilling or by casting, forging, stamping. The choice of the type of countersink depends on the material, the size and condition of the surfaces, the holes of the workpiece, the nature of the operation being performed (machining a hole, recess, boss, stepped holes, etc.).
The average values of the allowance for the diameter removed during countersinking are: for a hole diameter of 20 mm. 1 mm, for a diameter of 30 mm. 2 mm, for a diameter of 50 mm. 3 mm, for a diameter of 65 mm. 4 mm, for a diameter of 80 mm. 5 mm.
Countersink, being a multi-edge tool, somewhat straightens the axis of the hole obtained by preliminary processing. However, if the hole axis is severely curved, the countersink allowance is unevenly distributed and a difference in cutting force occurs on opposite sides of the hole, which bends the counterbore mandrel and causes the hole axis to bend after countersinking. The straightness of the hole axis after countersinking can be ensured provided that a rigid short mandrel is used and the hole is sequentially machined with two countersinks with a large angle in plan j.
Countersinking allows you to get the accuracy of machined holes up to the 11th grade and roughness up to Ra 2.5.
Countersinking of cylindrical and conical grooves and counterbore (stripping) of the end surfaces of the bosses are used to install screw heads in a flush or to form support areas for screw heads or washers.
When countersinking, surface and hole processing defects may appear: scoring and deep scratches from adhesion of metal particles to the tool, breaking the hole diameter beyond the reamer allowance, the appearance of a crushed surface and chipping of the cutting edge due to the vibration of the countersink. To prevent these defects, the countersink should be lubricated with kerosene or industrial oil, the sharpening geometry (angle j) should be changed, the diameter of the countersink should be reduced or the feed should be increased to the maximum permissible tool strength.
Holes are measured during drilling and countersinking with a vernier caliper, depth gauge or an indicator bore gauge.
The accuracy of machining and the shape of the hole will be the higher, the smaller and more uniform the machining allowance, the better the direction of the tool and the tool has more blades with sufficient rigidity.
DRILLING, ROOTING, COUNTERSINGING, REAMING AND BORING
FEATURES OF TECHNOLOGICAL OPERATIONS
Drilling used for processing blind and through holes of cylindrical, conical and multifaceted internal surfaces.
Two types of drilling are used:
actual drilling (making holes in solid material);
reaming (an increase in the diameter of a previously drilled, cast, punched out during stamping, pierced, obtained by methods of electrophysical or electrochemical machining of a hole).
Drilling and reaming ensures the accuracy of hole processing according to 10.11 grades and surface quality Rz 80.20 microns (when machining small diameter holes in non-ferrous metals and alloys up to Ra 2.5 μm). To obtain more accurate holes, use countersinking and reaming.
Countersinking, as well as reaming, they are used to increase the diameter of a previously obtained cylindrical hole, as well as to obtain conical (conical countersinks) and flat (countersink ends when processing stepped holes) surfaces. When countersinking after drilling, accuracy is obtained according to 9.10 grades, surface quality up to Ra 2.5 μm.
Deployment used for final (finishing) processing of mainly cylindrical holes, less often. for finishing conical and end surfaces. Accuracy 6.8 grade, surface quality Ra 2.50. 0.32 μm.
GEOMETRIC PARAMETERS OF THE CUTTING PART OF DRILLS, RADIANT DRILLS AND READERS
Elements of the cutting part of the most common twist drill are shown in Fig. one a, b.
The twist drill has two teeth, each of which has its own apex, main and auxiliary cutting edges, its own front surface, main and auxiliary back surfaces. The drill also has a transverse cutting edge (bridge) that allows the drill to cut holes in solid material.
The twist drill geometry is determined by the following sharpening angles.
Front corner gx at the point in question x the main cutting edge is measured in the I-I plane, normal to the main cutting edge, between the tangent to the leading surface at the point in question x and normal to the surface formed by the rotation of the main cutting edge around the axis of the drill.
Back angle aх measured in a plane tangent to the cylinder coaxial with the drill, on the surface of which the point under consideration lies x the main cutting edge, between the tangent to the flank surface at the point x cutting edge and tangent at the same point to the circle of its rotation around the axis of the drill. At the outer surface, the angle gx the largest, and the angle aх – the smallest.
Drill Nose Angle 2j measured between the main cutting edges. Corner 2j appointed depending on the material to be processed: for processing steel, hard bronze 2j = 116.118 °, for processing non-ferrous metals and their alloys of medium hardness 2j = 130.140 °.
one. main cutting edge; 2. main back surface; 3. the top of the tooth; 4. auxiliary rear surface [ribbon]; 5. auxiliary cutting edge; 6. groove; 7. the back of the tooth; 8. front surface; 9. jumper (at the drill); ten. guiding part (at the sweep); L, lslave, lsh, lx, lp, lk, ll, lc. lo.k. the length, respectively, of the tool, its working part, neck, shank, cutting part, calibrating part, foot of the cylindrical section and the section with reverse taper; Dr. main movement; d. drill diameter; (j, j1. main and auxiliary angles in the plan; gx, ax. front and back angles at point x; a0. back angle of the bulkhead at point O; w is the angle of inclination of the tooth; y. angle of inclination of the lintel; AB. jumper; al. back angle on the ribbon; q. diameter of the backs of the teeth
The angle of inclination of the transverse cutting edge y measured between the projections of the transverse and main cutting edges on a plane perpendicular to the axis of the drill.
The angle of inclination of the helical groove w is measured by the outer diameter. As the angle c increases, the rake angle g increasesX1 this facilitates the cutting process and improves chip yield. Recommended geometrical parameters of the drill are given in the reference literature.
The auxiliary entering angle jx is created by the reverse taper on the working part of the drill within 0.03. 0.12 mm per 100 mm length. The rear surfaces of the drills are sharpened along the conical surface, along the plane and along the helical surface.
Elements of the cutting part of countersinks and reamers are shown in Fig. 1.1, in. e. The working part of countersinks consists of a cutting part and a gauging part. with a reverse taper. The cutting part is inclined to the axis at an angle j in front of the axis and performs the main cutting work.
The twist countersink has 3.4 teeth, practically the same geometry as the twist drill teeth.
The working part of the reamers consists of a guide cone with a length lH, cutting part length ip and gauging part length lK. The calibrating part of the reamers consists of two sections: cylindrical length lC and tapered length 70 k with reverse taper. Reverse taper is done to reduce the friction of the tool on the machined surface and reduce the amount of hole breakout.
The reamer has 6.12 teeth. Corners g, ak and w the sweeps are usually zero.
Drills, countersinks and reamers are made of tool and high-speed steels, hard alloys VK6, VK8, VK3M, VK6M, VK8V. Solid carbide drills are widely used for machining holes in heat-resistant and stainless steels and alloys, titanium and its alloys, thermosetting plastics.
ELEMENTS OF CUTTING MODE AND CUT LAYER
The main movement for drilling, reaming, countersinking and reaming is rotary Dr, and the feed movement is translational Ds. Cutting patterns for drilling, reaming, countersinking and reaming are shown in Fig. 2. Cutting speed, m / min or m / s, at the periphery of the tool
Where D. diameter of the processed surface, mm; n. tool rotation frequency, rpm.
a. drilling; b. reaming; in. countersinking; d. deployment; one. blank; 2. drill; 3. countersink; 4. scan; D, D0. diameters of the processed and processed surfaces; Dr. main movement; Ds. feed movement; and, and b.thickness and length of the cut layer; s. feed for one revolution; sz.feed per tooth; t. cutting depth; j. main angle in the plan
Innings s. the amount of movement of the tool along the axis for one revolution. Innings sz, per tool tooth, sz = s / z (z. number of teeth of the tool).
Thickness and the cut layer is measured in the direction perpendicular to the main cutting edge of the tool, and the width b cut layer. along this cutting edge.
When drilling under the depth of cut t means the distance from the machined surface to the axis of the drill (t = D / 2), and when drilling, countersinking and reaming. the distance from the processed to the processed surface: t = (D. D0) / 2.
When drilling, axial force P0 (feed force, N), calculated by the formula
Torque Mcr, Nm, cutting when drilling
When drilling, countersinking and reaming, an axial force (usually a small amount) and a torque act on the tool Mcr, Nm, cutting
Where Wed and Cm – constant coefficients characterizing the processed material and the conditions of its processing; zP, ur, zM, hmm, um– degree indicators; D mm, t, mm, and s, mm / rev. respectively, the diameter of the machined surface, depth of cut, and feed; cr and km – general correction factors, taking into account specific processing conditions. Effective power, kW, cutting
Where Mcr. cutting torque, Nm; n. rotation frequency of the tool or product, rpm.
When drilling, cutting speed, m / min or m / s,
When reaming, countersinking and reaming
Where Cv – constant coefficient characterizing the processed material and specific processing conditions; zv, xv, yv – degree indicators; t. indicator of relative resistance; kv – general correction factor, taking into account specific processing conditions; T. durability period.
The drilling and boring group of machines, the second group according to the ENIMS classification, consists of two subgroups: drilling and boring. Drilling machines are designed to work with drills, countersinks, reamers, taps, etc., and boring machines, in addition, are mainly designed to work with boring tools of various designs. Depending on the location of the spindle, drilling machines are divided into vertical and horizontal drilling, and depending on the number of spindles. into single and multi-spindle. Bench-drilling machines are manufactured for drilling holes with a diameter of up to 16 mm; vertical drilling and radial drilling. for drilling holes with a diameter of up to 100 mm. Horizontal drilling machines are designed to produce deep holes with special drills.
CUTTING TOOLS AND TECHNOLOGICAL EQUIPMENT OF DRILLING MACHINES
Holes on drilling machines are processed with drills, countersinks, reamers and taps. All of these tools are pivotal. Machining with these tools is carried out with the main rotary motion. Dr tool or workpiece and with one feed motion Ds (more often a tool) along the axis of the tool or work surface.
When machining with axial tools, three kinematic schemes are possible:
Countersink Selection- Everything you need to know (for aluminum)
the main movement and the feed movement are transmitted to the tool. Such a scheme is implemented on drilling, jig boring, aggregate-drilling and aggregate-boring machines. With this scheme, there is a deviation of the tool axis if this axis does not coincide with the feed direction of the workpiece or tool;
the main movement is transferred to the workpiece, and the feed movement to the workpiece or tool. They are used on lathes, turret lathes and automatic lathes. Tool axis drift can take place in this case only due to uneven sharpening of the tool teeth;
the rotary movement is imparted to the workpiece (v3, m / min or m / s), and the tool (v and m / min or m / s). The main movement Dr in this case, it will be the one whose speed is greater (usually this is the speed of rotation of the tool v and).
Cutting speed (total), m / min or m / s, is determined by the formula v = v3 v and.
The feed motion is communicated to either the tool or the workpiece.
This scheme is used only for drilling on some machines and special machines. The diametral dimension is more accurate than with the previous scheme.
Drill by design and purpose, they are subdivided into spiral, centering and special. The most common tool for drilling and reaming is a twist drill (see Fig.1.1, a, b), consisting of a working part l slave, necks lsh, shank lx and paws ll.
In the working part l slave distinguish between cutting lp and calibrating guide lk parts with helical grooves. Neck lsh connects the working part of the drill to the shank. Shank lx required to install the drill in the machine spindle. Foot ll serves as a stop when knocking the drill out of the spindle hole.
The elements of the working part and the geometric parameters of the twist drill are shown in Fig. 1.1, b. The drill has two main cutting edges 1 formed by the intersection of the front 8 and main rear 2 blade surfaces and performing the main cutting work; transverse cutting edge 9 (bridge) and two auxiliary cutting edges 5. On the calibrating (guide, with a reverse taper) part of the drill along the helical groove there are two narrow bands four (auxiliary rear surfaces), which provide the direction of the drill during cutting and the required accuracy and quality of the processed surface.
Countersinks according to the type of holes to be machined, they are subdivided into spiral cylindrical (see Fig. 1.1, in, d), conical (fig. 1.3, and) and end (Fig.9.3, b). Countersinks are solid with a tapered shank (see Fig.1.1, c, d) and mounted (see Fig.1.3, b).
The spiral cylindrical countersink differs from the twist drill mainly in the large number of teeth (three to four) and the absence of a bridge.
Countersinking, as mentioned earlier, is used when machining previously obtained holes and end surfaces.
Sweeps, as indicated in subsection. 1.1, the holes are finished. By the shape of the hole to be machined, cylindrical are distinguished (Fig.1.1, d and 1.3, c) and conical (Fig. 1.3, d) sweeps. The reamers have 6.12 main cutting edges lK, located on the cutting edge lp with guide cone lH, auxiliary cutting edges are located on the calibrating part 7K.
According to the fastening design, the reamers are subdivided into tail (see Fig. 1.1, d and 1.3, c, d) and mounted (Fig. 1.3, d, which shows a machine shell reamer with mechanical fastening of cutting blades in its body).
Taps used for cutting internal threads. The tap (Fig. 9.3, e) is a screw with cut straight or helical grooves that form cutting edges. The working part of the tap has a cutting lp and calibrating lK parts. The thread profile of the tap must match the profile of the thread to be cut. The tap is fixed in a special cartridge.
With countersinks, reamers, taps, like drills, the cutting parts do the main cutting work. Calibrating parts serve to guide the tool in the hole and provide the required accuracy and surface quality.
During operation, the cutting elements of axial tools are subjected to abrasion along the front, main rear and auxiliary surfaces with simultaneous heat exposure. This leads to wear on the surfaces of the tools (fig.9.4, a, b), contacting with the workpiece and the cut layer. The intensity of wear of the areas of drills, countersinks and reamers depends on the cutting mode, material of the cutting part and workpiece, on other processing conditions.
The wear of the high-speed drill (see Fig. 9.4, a) proceeds along the front 1, the main 2 and subsidiary 3 back surfaces. The most intense wear occurs on the auxiliary rear surfaces 3 (strips), having a significant surface of friction, and along the back surface in the area of conjugation of the main and auxiliary cutting edges. The value of ii3, which characterizes this wear, is used to judge the possibility of further exploitation of the drill.
Flank wear h3 for different cases of drilling is given in the reference literature. For example, for a 20 mm HSS drill h3 = 0.8 mm. Failure to comply with the recommendations on the permissible amount of wear reduces the service life of the tool: with high wear on tool regrinds, you have to remove a lot of material, and with low wear, you have to do a lot of regrinds.
The wear of the countersinks and reamers occurs along the tape and the back surface of the intake part, forming the most vulnerable point of the tool (see Fig. 1.4, b). Permissible wear is set by the value h3. For high speed countersinks with a diameter D = 10. 50 mm, this value lies within 1.2 mm, for carbide 0.4. 0.6 mm. The wear of high-speed reamers should not exceed 0.6. 0.8 mm.
one. front surface; 2, 3, 4. main, auxiliary, additional rear surfaces; K1, K2. cams; P1t, P2, P3. the clamping forces of the drill in the fixture; DSnp. longitudinal feed; DSкp. circular reciprocating rotary drill feed; DSy1, DSy2. setting rotational movements of the cams K1 and K2; Ds2p and Ds2b. respectively, the working and auxiliary strokes of the cross feed of the drill; h3. wear width
When the specified wear value is reached, the axial tools are resharpened to restore their cutting properties. Re-sharpening of drills, countersinks and reamers is carried out along the main rear surfaces and, in some cases, along the front surface. For sharpening twist drills, special sharpening machines are used. Some drills sharpening schemes are shown in Fig. 9.4, c, d, d.
TECHNOLOGICAL EQUIPMENT OF DRILLING MACHINES
When processing on drilling machines, various devices are used to install and strengthen workpieces on tables and tools on machine tool spindles.
The workpieces are installed on the machine table, equipped with T-shaped slots, in the following ways: by fixing with clamping bars or in a machine vice; on a square with a table that can rotate to the required angle and which has T-shaped grooves that allow you to fix a device with a workpiece on this table; in three- or four-jaw chucks (cylindrical blanks); on a prism with fixing the workpiece with clamps; with the help of jigs equipped with guide bushings, which provide a certain position of the cutting tool relative to the workpiece being processed, which is fixed in the jig body. There is no need for marking when using conductors.
The cutting tool in the spindle of the drilling machine is fixed using an auxiliary tool: adapter sleeves for drill chucks and mandrels. The tool holder can be rigid or floating. Rigid fastening of the tool is used when machining inaccurate holes.
When reaming the holes with an accuracy of the 7th grade with the direction of the tool along the drill bushings or along the previously machined hole, it is necessary to use self-aligning chucks (swinging and floating), which allow you to eliminate deformations of the tool and spindle and freely orient the tool relative to the drill bushings or the hole being machined.
Taper shank cutting tools are clamped directly into the taper bore of the drill spindle. If the size of the taper of the tool shank is less than the size of the tapered bore of the spindle, then tapered bushings are used. Tools with a cylindrical shank are clamped in two-, three-jaw or collet chucks.
SCHEMES FOR PROCESSING BILLS ON DRILLING MACHINES
Drilling machines perform drilling, reaming, countersinking, reaming, counterbiting, countersinking, tapping and machining complex holes.
Schemes for processing blanks, cutting tools and the possibilities of drilling, reaming, countersinking, reaming are given in subsection. 1.1 and 1.2.
We add that drilling and reaming Is rough processing.
Depending on the required accuracy and the size of the batch of workpieces to be processed, holes are drilled in a jig or along a marking.
The diameter of the hole for reaming is chosen so that the transverse cutting edge does not participate in the work. In this case, the axial force decreases.
Countersinking refers to a semi-finishing type of surface treatment of holes, with this method, small allowances of 0.5 are removed. 3 mm. A countersink is a tougher tool than a drill, and therefore it corrects the bending of the axis of the hole to be machined after retraction of the drill, improves machining accuracy and surface quality of a cylindrical hole.
Deployment. finishing method of hole machining. A small allowance on the side of 0.05 is left for deployment. 0.5 mm, and therefore the reamer cannot correct the curvature of the hole axis, but increases the accuracy of the diametral dimension and the quality of the machined surface.
Single, double and triple deployments are used. A one-time deployment is carried out by a rough scan, it provides accuracy according to 8. 9th grade; double deployment is carried out by rough and semi-finishing sweeps, accuracy. according to the 7th grade; three-fold deployment is carried out by rough, semi-finishing and finishing sweeps, accuracy. up to the 6th quality.
Cecuring. processing of the end surface of the hole with an end countersink to achieve perpendicularity of the flat end surface to the axis (Figure 1.5, a).
a. countering; b, c. countersinking; d. threading; d. combined processing fixed support;
Date added: 2015-08-21; views: 16280; ORDER WRITING WORK