What is cutting speed when drilling. Drilling holes in metal: methods, tools, useful tips. Types of holes in metal and methods for drilling them

In the process of forming a hole, the drill simultaneously performs rotational and translational movements, while the cutting edges of the drill cut off thin layers of material, forming chips. The faster the drill rotates and the greater the distance in one revolution it overcomes in the direction of the axis of the hole being machined, the faster the cutting occurs.

Cutting speed depends on the frequency of rotation of the drill and its diameter, the movement of the drill along the axis of the workpiece in one revolution affects the thickness of the removed material (chips). The drill, in comparison with other cutting tools, works in rather difficult conditions, since when drilling it is difficult to remove chips and supply coolant.

The main elements of cutting during drilling are the speed and depth of cut, feed, chip thickness and width (Fig. 3.77).

Cutting speed V - the path traveled by the point on the cutting edge of the drill, the furthest from the axis of its rotation. The cutting speed is determined by the formula V = ndnl1000 (where V is the cutting speed, m/min; d is the drill diameter, mm; n is the spindle speed, rpm; n is constant number, equal to 3.14; the number 1 OOO is entered into the formula for converting the diameter of the drill to meters). The value of the cutting speed depends on the material of the workpiece, the material of the tool and the shape of its sharpening, feed, depth of cut and the presence of cooling during hole processing.

Feed 3 is measured in millimeters per revolution of the drill (mm/rev). The amount of feed during drilling is selected depending on the requirements for the roughness of the machined surface and the accuracy of machining, the material being machined and the material being drilled.

Depth of cut t measured in millimeters and represents the distance from the machined surface to the axis of the drill, i.e. when drilling, the depth of cut is half the diameter of the drill, and when reaming, it is half the difference between the diameter drilled hole and ohm drill diameter.

Cut thickness (chips) measured in a direction perpendicular to cutting edge drill, and is equal to half the amount of movement of the drill relative to the axis of the hole being processed in one of its revolutions, i.e. half the feed rate. Since a layer of material is removed in one revolution of the drill by two cutting teeth, each of these teeth removes a layer of material whose thickness is equal to half the amount of feed of the drill per one revolution.

Cutting width measured along the cutting edge and equal to its length. When reaming, the cut width is equal to the length of the cutting edge involved in cutting. The cutting width is measured in millimeters.

Cutting conditions are set to provide the best performance. In this case, it is necessary to take into account the physical and mechanical properties of the material of the workpiece being processed, the properties of the material of the tool and the requirements for the quality of the machined surface specified by the drawing or specifications for manufacturing.

Theoretical calculation of the elements of the cutting mode is performed in the sequence below.

1. According to special reference tables, the feed rate is selected depending on the machining xapat, the requirements for the quality of the machined surface, the material of the drill and other technological data.

2. Calculate the speed of the tool, taking into account technological capabilities, cutting properties of the tool material and physical and mechanical properties workpiece being processed.

3. Determine the calculated spindle speed in accordance with the found cutting speed. The resulting value is compared with the passport data of the machine and is taken equal to the nearest the smallest value this frequency.

4. Determine the actual cutting speed with which processing will be performed.

In practice, ready-made data is used to determine cutting conditions technological maps and reference tables.

The cutting modes for countersinking and reaming, as well as the criteria for their selection, practically do not differ from the choice of these parameters for drilling.

Hole allowances

An allowance is a layer of material to be removed during processing. The size of this Layer depends on the requirements for the machined surface and the type of treatment.

When drilling, the machining allowance is half the diameter of the drill. When reaming, the allowance is determined depending on the requirements for the machined surface and on the need for its further processing (reaming, reaming). The reaming allowance, depending on whether it is preliminary (before deployment) or final, is from 0.5 to 1.2 mm. The size of the allowance also depends on the diameter of the hole being machined. The reaming allowance depends on the diameter of the hole being machined and on the requirements for the quality of the machined surface and ranges from 0.05 to 0.3 mm. Typical Defects when processing holes, the reasons for their occurrence and methods of prevention are given in table. 3.2.

Second after turning, the most common type machining is drilling. Deployment, countersinking, reaming are equated to it. When calculating cutting conditions, it is possible, neglecting the rigidity of the processing system, to imagine that this is simultaneous boring with several cutters, so the calculation principle will be similar to turning. However, for small drill diameters, less than 10 mm, cutting conditions are calculated based on the integrity of the drill after processing. In other words, the modes are calculated in such a way that the drill does not break, so the calculation is based on the strength characteristics of the tool.

However, during experimentation with the technique, an error was identified in which the cutting speed was too high, this was expressed by the duration of the drilling, but the long tool life, and high quality processing. Plus or minus must be decided when specific task, since low feeds can cause rapid blunting of the cutting part (or even sticking), however, at too high feeds, tool breakage is likely, not to mention a decrease in machining safety.

Our methodology for calculating modes for drilling can be found below. In the corresponding forum topic, you can download a macro for automatic calculation of cutting conditions for drilling.

Method for calculating cutting conditions for drilling work

When drilling, it is recommended to set the modes based on the power of the equipment used. Most comfortable material cutting tool- high-speed steel (R18, R6M5). Calculate feeds during drilling operations by the formula:

S - feed, mm/rev

D - drill diameter, mm

C - coefficient depending on the material being processed and other technological factors (surface cleanliness, the presence of further processing, etc.) (table 1)

Kls - coefficient for feed, depending on the condition of the chip exit (table 2)

Table 1

Iinnings group- drilling of blind holes or reaming without tolerance according to the 5th accuracy class or for subsequent reaming

IIfeed group-drilling blind and through holes in parts of a non-rigid structure, drilling for threading and reaming for subsequent processing with a countersink or reamers

IIIfeed group-drilling blind and through holes and reaming for further processing

table 2

Drilling cutting conditions

The power consumed during drilling depends on the torque. Torque is calculated using the formula:

Mkr - torque perceived by the drill when cutting, N * m

See, q, y - coefficients for torque during drilling, depending on cutting conditions (table 3)

D - drill diameter, mm

S - feed, mm/rev

Kmr - coefficient for torque, depending on the mechanical properties of the material (table 4)

Table 3

Table 4

For normal drills with a diameter greater than 10 mm, there is no danger of breaking from excessively high torque, since for these diameters the greatest stresses that occur in the drill are usually limited by the blunting rate with increasing cutting speed and feed. For drill diameter less than 10 mm, it is recommended to calculate the torque according to the f-le,

to ensure the integrity of the instrument.

Equating and it is possible to calculate the maximum possible feeds for small diameter drills when drilling a given material (table 5).

Table 5

To ensure the rigidity of AIDS when drilling, it is necessary to install a drill in a chuck with the minimum possible overhang (more by 3-5 mm than the depth of the hole being processed).

The cutting speed during drilling is calculated by the formula:

Table for calculating modes when drilling on a 2A135 machine in Appendix 1.

Countersinking and reaming

The feed during countersinking and reaming is calculated similarly by the formula:

Torque is calculated using the formula:

The values ​​of the coefficients С m, x, y, q choose according to table 6

Table 6

D- drill diameter

d- pre-drilled hole diameter- feed per tool tooth (equal to s/z)

s - feed, mm/rev

Z - number of reamer teeth

Coefficients C p , x , y in table 7

Table 7

Cutting speed is calculated by the formula:

The rotational speed is calculated by the formula:

The table for calculating modes when deployed on the machine 2A135 in Appendix 2.

When introducing a calculation method in the TechnoPro system, it is recommended that for drilling and reaming, the calculated modes be entered into the information database, thereby avoiding programming the calculation conditions and simplifying the system operation. To calculate the modes for countersinking and reaming, it is necessary to program the conditions using the coefficients from Table 6.

In a part made of cast iron KCh35-10, it is necessary to obtain a through hole 45H8 with a roughness Rz = 8 microns. Hole depth 52 mm. The operation is performed on the machine 2170.

It is impossible to get a 45H8 hole with Rz=8 µm with one drill. Let's establish a technological processing route.

According to the reference data, we find that in order to obtain a hole of the above dimensions and roughness, it is necessary to apply:

drilling;

reaming;

Countersinking is fine;

Deployment.

This means that after drilling, it is necessary to leave an allowance for reaming, and after reaming, leave an allowance for reaming.

In the reference book, we find that for processing a hole with a diameter of up to 45 mm when countersinking t2=3.48mm, for finishing countersinking, t3=0.48 mm is recommended, and when reaming - t3=0.1 mm.

In the same place, we find that, depending on the sequence of transitions to the depth of cut, it is necessary to take the correction factor Kt:

Kt2=1.1; Kt3=1.55; Kt4=2.8.

Thus, taking into account the peculiarities of the processing route, it is necessary to have:

Let's determine the diameters of the tools:

Reamer diameter

Finishing countersink diameter

Countersink diameter

Drill diameter

We specify the diameter of the drill, rounding it to the nearest according to GOST. The gradation of diameters of twist drills is given in the reference book. Drills with a diameter of 30 to 50 mm are available tool industry with an interval of change of diameters equal to 0.5 mm. With that said, choose D1=35 mm. In connection with the correction of the diameter of the drill, we also correct the diameters of other tools.

In this case, we get:

Various coefficients necessary to determine the cutting parameters, characteristics of steels and alloys and recommendations were selected from the reference manual by V. I. Lepilin “Cutting conditions for aviation materials during drilling, countersinking and reaming”.

drilling

The material being processed is cast iron. Cast iron KCh35-10 has? b = 350 MPa.

Selection of the main dimensions and geometry of the tool.

Analyzing the list of standards for spiral high-speed drills, we establish that for cast iron according to GOST 10903-77, spiral long drills with tapered shank. We choose a 35 mm drill made of P18 steel with a total length L = 350 mm, a length of the spiral part l = 230 mm and a Morse taper shank No. 3. For drilling difficult-to-cut materials, double sharpening with undercutting of the jumper and ribbon is recommended - DPL.

Table 2.

We set the wear criterion and the optimal service life. For fast cutters when processing titanium alloys h3=0.02D1.2=1.43; T=3D or T=105 min.

Choice of cutting depth

When drilling t=D/2, and therefore for our case t=17.5 mm.

Feed selection. Feed allowed by the strength of the machine's feed mechanism.

for machine 2170

According to the guide:

Consequently,

Feed allowed by tool strength.

When drilling with tools made of high speed steels

Feeding according to the rigidity of the AIDS system in connection with the given accuracy and roughness of the machined surface.

When drilling hard-to-cut materials in rigid parts without a permit and with a tolerance of up to 12 grades for subsequent reaming or boring with a cutter

The choice of the largest technologically permissible feed

From the found values ​​s1=3.48mm/rev; s2=1.54mm/rev; s3=1.155 mm/r we choose the smallest one and compare it with the available values ​​on the machine 2170. We take the nearest smaller one to the smaller calculated one. We will have s0=1.05mm/rev. This is the highest technologically admissible feed.

Choice of cutting speed.

The spindle speed of the machine can be determined by the formula:

In the directory we find:

Substituting everything necessary into the formula, we get:

Comparing with the passport data of the machine, we find:

Determine the feed for nx+1:

Coordinating with the passport feed rates, we will have

Resolving the issue of the best combination s and n.

Cutting modes for drilling. Labor productivity during drilling largely depends on the speed of rotation of the drill and the amount of feed, i.e., how much the drill deepens in one revolution into the workpiece.

But the rotation speed of the drill and the feed cannot be increased indefinitely - if the rotation speed is too high, the drill will “burn out”, and if the feed is too high, it will break.

The cutting speed is expressed by the formula

where v - cutting speed, m/min; D - drill diameter, mm; n is the number of spindle revolutions per minute; π is a number equal to 3.14.

When choosing a cutting speed, the properties of the material being processed and the material of the drill, the diameter of the drill, the amount of feed and the drilling conditions (drilling depth, the presence of cooling, etc.) are taken into account.

The feed rate is determined taking into account the diameter of the drill. So, for example, when processing steel of medium hardness with a drill with a diameter of 6 mm, a feed of 0.15 mm / rev is allowed; with a drill diameter of 12 mm - 0.25 mm / rev; with a drill diameter of 20 mm - 0.30 mm / rev, etc.

The correct choice of speed and feed of the drill has big influence not only on productivity, but also on the durability of the cutting tool and the quality of the hole being machined. The drill works better at high cutting speed and low feed.

The number of revolutions, speed and feed can also be determined from tables.

Care of drilling machines. Drilling machines will work with the required accuracy, productivity and trouble-free long time only if they are properly cared for.

Care of the drilling machine consists primarily in keeping the workplace clean and systematic cleaning of chips. Especially it is necessary to protect the table from nicks and rusting. The nicks left on the table as a result of careless work reduce the accuracy of drilling and speed up the need for repairs to the machine.

To avoid the formation of nicks and wear on the table, the parts should be installed carefully, without impacts and significant movements on the table. The support surfaces with which the part is placed on the table must be clean and free of burrs.

At the end of the work, the machine table and its grooves must be thoroughly cleaned of dirt and chips, rubbed with dry ends and lubricated. thin layer rust prevention oils.

Before work, it is necessary to lubricate all the rubbing parts of the machine, lubrication points and pour oil into the oilers.

During operation, the heating of the bearings is checked by hand. The heat must be tolerable for the hand. In order to avoid an accident, before checking the degree of heating of the bearings, the electric motor should be stopped and the check should be carried out with the belt or gear drives inoperative. It is also necessary to ensure that the gears of the machine are always securely guarded.

Lab #6

Calculation of cutting conditions when drilling

Objective: learn to count the most optimal modes cutting when drilling according to analytical formulas.

1. Depth of cutt , mm. When drilling depth of cut t = 0,5 D, when reaming, reaming and reaming t = 0,5 (D – d) ,

where d- the initial diameter of the hole;

D- diameter of the hole after processing.

2. Submissions , mm/rev. When drilling holes without limiting factors, we select the maximum allowable feed for the strength of the drill (Table 24). When drilling holes, the feed recommended for drilling can be increased up to 2 times. In the presence of limiting factors, the feeds for drilling and reaming are equal. They are determined by multiplying the tabular feed value by the appropriate correction factor given in the note to the table. The obtained values ​​are corrected according to the machine passport(Appendix 3). Feeds during countersinking are given in table. 25, and during deployment - in Table 26.

3. Cutting speedv R , m/min. Drilling cutting speed

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Coefficient values FROMv and exponents m, x, y, q are given for drilling in table 27, for reaming, countersinking and deployment - in table. 28, and the values ​​of the period of resistance T- tab. thirty.

General correction factor for cutting speed, taking into account actual cutting conditions,

Kv = Kmv Kiv Kv,

where Kmv- coefficient for the processed material (see tables 1, 3, 7, 8);

Kiev- coefficient for tool material (see Table 4);

Kιv,- coefficient taking into account the depth of drilling (Table 29). When drilling and countersinking cast or stamped holes, an additional correction factor is introduced Kpv(see Table 2).

4. RPMn , rpm, calculated according to the formula

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5. TorqueM kr , N m, and axial force Ro, H, calculated by the formulas:

when drilling

Mcr = 10 cmDqsyCr;

Р0 = 10 СрDqsyCr;

when reaming and countersinking

Mcr = 10 cmDq tx syCr;

Р0 = 10 Срtx syCr;

Values Cm and Wed and exponents q, x, y are given in table. 31.

Coefficient Kp, which takes into account the actual processing conditions, in this case depends only on the material of the workpiece being processed and is determined by the expression

Kr = Kmr.

Coefficient values kmr are given for steel and cast iron in table. 11, and for copper and aluminum alloys - in table. ten.

To determine the reaming torque, each tooth of the tool can be considered as a boring tool. Then with the tool diameter D torque, H m,

;

here sz– feed, mm per tool tooth, equal to s/z,

where s– feed, mm/rev, z- the number of teeth of the reamer. The values ​​of the coefficients and exponents, see Table. 22.

6. Cutting powerNe , kW, determined by the formula:

where netc- frequency of rotation of the tool or workpiece, rpm,

The cutting power must not exceed the effective power of the main drive of the machine Ne< Nuh(, where Ndv- engine power, h- machine efficiency). If the condition is not met and Ne> Nuh, reduce the cutting speed. The overload factor is determined, a new lower cutting speed value is calculated https://pandia.ru/text/80/138/images/image011_47.gif" width="75" height="25 src=">, where Growth – axial force machine.

7. Regular time That, min, calculated according to the formula

where L – tool travel length, mm;

The length of the working stroke, mm, is equal to L= l+ l1 + l2 ,

where l– length of the processed surface, mm;

l1 and l2 - the value of the infeed and overrun of the tool, mm (see Appendix 4).

Table 1

Correction factor To mv, taking into account the influence of the physical and mechanical properties of the material being processed on the cutting speed.

table 2

Correction factor Kpv, which takes into account the influence of the state of the surface of the workpiece on the cutting speed.

Table 3

Correction factor kmv, which takes into account the influence of the physical and mechanical properties of copper and aluminum alloys to cutting speed.

Table 4

Correction factor Kiev, which takes into account the influence of the tool material on the cutting speed.