Hey! Here is a new article called milling and its main types, because with it we will begin the study of this not a simple method of metal processing.
What is milling?
Milling- This is a processing that creates flat and shaped surfaces by using a cutting tool such as a milling cutter. Much more can be said about this type of machining, but I think that we will consider all its components in stages. And when we finish (which is not very soon :)) you will know almost everything about him.
Milling. Main types and methods.
I do not want to burden you with theory and boring definitions, which are already so full in any literature devoted to metal cutting. I just want to talk about the main types of milling for now. So…
Milling with a cylindrical cutter. Well, as the name implies, a cylindrical cutter is used for this method. The essence of the method lies in the processing of flat surfaces of the correct form (squares, rectangles, etc.). We will not go deeper, yet :).
Milling with a face mill. This method is basically similar to the previous one, but the difference is that here a face mill is used to obtain the same surfaces. What is the difference between them, we will understand in the following posts. So let's not forget subscribe to blog updates.
F gear reduction.As for the manufacture of a gear rim by milling on a horizontal milling machine, I will tell you right away that this method has long been outdated and is used only in repair shops, since it does not have the necessary productivity and quality of gear production. By the way, we will also consider getting gears :)
Shoulder milling with a three-sided disc cutter. As is clear from the name, the removal of the allowance is carried out with a three-sided disk cutter. Which is called so because it has three cutting edges at once - along the outer diameter and immediately from two ends. This allows her to mill shoulders as shown.
Milling with a set of two three-sided disc cutters. This method is similar to the previous one, but the difference is that in this case, two cutters are processed simultaneously, which is very convenient for making flats on cylindrical surfaces.
Milling a groove with an end mill. This type is used to obtain straight-sided grooves of various sizes and configurations on both flat and cylindrical parts.
Milling grooves with a slotted cutter. Well, here I will say that slots are meant by slotted grooves. This method is also outdated as it is low productive and does not provide sufficient accuracy in obtaining the part. The division is carried out using a dividing head.
Milling of a shaped surface. Under shaped surfaces, as you already understood from my previous post. These are surfaces that have not quite regular "shaped" shapes (ellipses, spheres, etc.). And as a result, to obtain them, special milling cutters are needed, which are called shaped (having a shape that must be obtained after milling).
Milling of an inclined plane. Angle cutters also work on the principle of copying, namely, the resulting inclined surface is ensured by the accuracy of the manufacturing of the cutting tool. This method is used for the manufacture of sliding guides for machine tools.
Milling a curved contour. With the help of an end mill, we can get almost any complex curved contour. Here the cutter describes the workpiece along the curved line that we need to get.
Milling of helical grooves. With the help of this milling method, as can be seen from the proposed sketch, drills, countersinks and other tools with helical chip removal grooves are made. Basically, these operations are performed on CNC machines (at present).
Cutting with a cutter. Well, in this case, the name speaks for itself. With the help of a cutting cutter, metal bars of various sizes can be cut.
Well, that's enough information for today. I think that I wrote about milling and its main types not badly. If you have any suggestions on what to add to this post, WRITE!!!
Andrew was with you!
A flat surface at an angle to the horizontal is called inclined plane. A short inclined plane on a part is commonly referred to as bevel.
Milling inclined planes and bevels can be done:
a) with the rotation of the workpiece to the required angle;
b) with the rotation of the machine spindle to the required angle;
c) using an angle cutter.
Let's consider each method of milling separately.
Milling with workpiece rotation
Installation in a universal vice. To install the part (Fig. 105, a) at an angle, you can use a universal vice (see Fig. 68, b).
Fixing the part in a universal vice is carried out, as in a conventional machine vice. When installing a universal vice at the desired angle, it should be borne in mind that the inclined plane to be processed must be located horizontally, that is, parallel to the table surface (Fig. 105, b).
Installation on a universal plate. On fig. 106 shows a workpiece mounted on a universal plate (see Fig. 62, c) for milling an inclined plane.
The workpiece is attached to the table of the universal plate with clamps or bolts, as when fixing it on the table of a milling machine.
Universal vices and universal plates are usually used in tool and mechanical repair shops for the processing of single parts and in mechanical shops for the manufacture of small batches of products.
In tool shops for processing inclined surfaces and bevels, universal milling machines with tilt table(mod. 675 and 679). Tilting the machine table to the required angle ensures the correct position of the work surface, as when machining in a universal vice and on a universal plate.
Installation in special fixtures. When processing inclined planes in a large batch of identical workpieces, special devices are usually used.
On fig. 107, and shows a device for milling bevels from metalwork hammers. The reference plane of the fixture provides a quick installation of the workpiece without marking at the desired angle.
On fig. 107, b shows a device for milling an inclined wedge plane. This fixture has two bevels. Two workpieces are installed in the fixture from both sides and milled simultaneously with one cylindrical cutter.
Milling of inclined planes with the rotation of workpieces at the required angle is carried out with cylindrical or end mills in the same way as milling of horizontal planes.
Milling with turning of the machine spindle
Instead of turning the workpiece when milling ramps and bevels, you can use spindle turning. This is possible on vertical milling machines, in which the milling head with spindle rotates around a horizontal axis in a vertical plane (see Fig. 9).
Very convenient for this purpose are universal milling machines of the 6M82Sh type (see Fig. 11), in which the vertical head has a rotation in the vertical and horizontal planes.
In the same way, it is possible to mill inclined planes on a horizontal milling machine if the machine has an overhead vertical head.
Consignment note vertical The head is a special accessory of the horizontal milling machine. The presence of an overhead vertical head allows you to perform various jobs on a horizontal milling machine that are usually performed on a vertical milling machine. On fig. 108, and one of the designs of the laid on vertical head is shown.
Frame 2
of the laid on vertical head is mounted on the vertical guides of the machine bed and fixed with bolts 1
. Spindle 5
rotates in the turntable 6
heads. Loosen the bolts connecting the turntable 6
head with its body, the spindle can be rotated in a vertical plane and placed at any angle on the scale 4
. Ring 3
serves to remove the head. Rotation from the machine spindle to the head spindle is transmitted using a pair of spur gears 7
and 8
. Wheel 8
with the help of a cone, it is mounted on the spindle of a horizontal milling machine and transfers rotation from the machine spindle to the wheel 7
, and then through a pair of bevel wheels to the spindle 5
laid on vertical head. In the spindle seat 5
cutter is installed.
Due to the presence of a pair of bevel gears, the attachment spindle can be rotated around the milling machine spindle by 360°, i.e. a full turn. Such a device of an overhead vertical head allows you to install the cutter not only vertically, but also at any angle (Fig. 108, b). The presence of an overhead vertical head greatly expands the possibility of using horizontal milling machines.
On fig. 109a shows the end mill set at a 60° angle to the vertical for bevel milling. The desired angle of inclination is set by turning the vertical head until the marks 0 and 60° are aligned on the scale.
On fig. 109, b shows a face milling cutter set at an angle of 30 ° to the vertical for bevel milling, the angle is set by turning the vertical head until the marks O and 30 ° are aligned on the scale.
Milling of inclined planes with angle cutters
Small inclined planes and bevels can be milled with angle cutters. In this case, there is no need to rotate the part or spindle, the angle of inclination of the plane of the milled part is provided by the shape of the cutter itself.
Angle cutters. On fig. 110, a shows a single-angle cutter designed to process a plane inclined to the cutter axis at a certain angle. There are single-angle cutters with an angle Θ equal to 55, 60, 65, 70, 85 and 90 °.
two-angle a cutter is called, in which the second cutting edge also mills an inclined plane. Distinguish
milling cutters symmetrical(Fig. 110, b) and asymmetrical(Fig. 110, c). The angle of inclination δ of the second face of an asymmetrical double-angle cutter is usually 15, 20 and 25°.
Angle cutters are made with pointed teeth.
Milling with angle cutters is carried out on horizontal milling machines. Angle cutters are installed and fixed on mandrels in the same way as cylindrical cutters.
cutting modes. When working with angle cutters, the cutting speed and feed per tooth are set to be lower than when working with cylindrical cutters, since the working conditions of these cutters are much more difficult.
Processing example. Consider milling two conjugate inclined planes. On fig. 111, and a drawing of a prism is given, and in fig. 111, b - sketch of the processing of the corner recess. For milling, a two-angle symmetrical cutter with a 45° edge angle is required. We take the cutter diameter equal to 75 mm. This cutter has 22 teeth.
Cutting conditions: milling depth t=12 mm, feed 0.03 mm/tooth, cutting speed 11.8 m/min, which corresponds to 50 rpm.
We select the spindle speed available on the machine 6M82G, equal to 50- rpm. In this case, the minute feed should be 0.03X22X50 = 33 mm/min. We select the feed available on the machine 31.5 mm/min. We set up the machine for the selected cutting speed and feed, we perform milling like milling horizontal planes. The processed plane is checked with a template.
Possible scrap when milling inclined planes and bevels
When milling inclined planes and bevels with cylindrical, face and angle cutters, in addition to defects in surface finish and dimensional defects, marriage is possible due to non-compliance with the specified angle of inclination of the machined plane.
The reasons for such a marriage may be incorrect marking, incorrect installation of the workpiece, poor cleaning of the machine table and vise from chips, poor fastening of the vise or rotary table at an angle, and runout of the cutter.
Cylindrical cutters used for surface treatment. The teeth of a cylindrical cutter are arranged along a helical line with a certain angle of inclination of the helical groove co.
Cylindrical cutters are manufactured in accordance with GOST 3752-71 with fine teeth and with large teeth, with insert knives in accordance with GOST 9926-61 and with compound insert knives. Milling cutters equipped with hard alloy helical blades are manufactured in accordance with GOST 8721 - 69.
The main dimensions of cylindrical cutters are cutter length L, cutter diameter D, hole diameter d, number of teeth z.
Cylindrical cutters are made of high speed steel, and are also equipped with hard alloy plates. The manufacture of cylindrical cutters with insert knives (teeth) allows more economical use of expensive tool material.
According to the direction of rotation, the cutters are divided into right-cutting and left-cutting. right cutting they are called such cutters that, during operation, must rotate clockwise, if you look at the cutter from the side of the rear end of the spindle (or counterclockwise, if you look from the side of the suspension-earring). left cutting milling cutters are those cutters that, when working, must rotate counterclockwise when viewed from the rear end of the spindle (or clockwise when viewed from the suspension side).
When looking at the cutter from the side of the suspension, then the right-hand cutter throws chips to the right, and the left-hand cutter throws chips to the left.
Cylindrical cutters, depending on which side they are mounted on the mandrel, can be used both as right-cutting and left-cutting. The cutting direction can be changed by turning the cutter over on the arbor.
Selecting the type and size of a cylindrical cutter
The choice of the type and size of the cutter depends on these specific processing conditions (dimensions of the workpiece being processed, the grade of the material being processed, the size of the machining allowance, etc.).
Cutters with a large tooth are used for roughing and semi-finishing of planes, cutters with a small tooth - for semi-finishing and finishing.
Rice. 31. Nomogram for choosing the optimal size of solid cylindrical cutters
On fig. 31 shows a nomogram for choosing the optimal size of solid cylindrical cutters with fine and coarse teeth for given machining conditions. On fig. 31 adopted the following material designations:
T - hard-to-cut materials (stainless heat-resistant steel, etc.);
C - materials of medium processing difficulty (structural steel, gray cast iron, etc.);
L - easily processed materials (copper and its alloys, aluminum and its alloys, etc.);
I - roughing;
II - finishing.
We will explain the procedure for using the nomogram with an example. It is required to determine the dimensions of a solid cylindrical cutter during rough milling of a workpiece made of steel 45 (σ в = 75 kg / mm 2), milling width В = 15 mm, cutting depth t = 5 mm.
1. Determine the length of the cutter. The length of the cutter must be greater than the width of the workpiece to be machined. In the upper right part of the nomogram along the abscissa axis, two scales are given: the lower one, along which the milling width B is plotted, and the upper one, along which the standard lengths of cylindrical cutters are plotted, corresponding to different values of the milling width. So, for our case, for a width of B = 75 mm, the nearest cutter length is L = 80 mm.
2. Next, you need to determine the diameter of the cutter hole (or the diameter of the mandrel). From the point corresponding to L = 80 mm, we draw a vertical line until it intersects with an inclined line corresponding to the processing conditions - C-I (roughing of a material of medium machinability). From the obtained point we draw a horizontal line until it intersects with the d axis (mandrel diameter). The point of intersection is closer to d - 40 mm. Therefore, we choose a cutter with a hole diameter d = 40 mm.
3. Determine the diameter of the cutter. From the point corresponding to d = 40 mm, we draw a horizontal line until it intersects with the inclined line I (roughing). From the point obtained in this way, we draw a vertical line down to the intersection with the D axis - the diameter of the cutter. As can be seen from the graph, the nearest cutter diameter is 100 mm.
4. Find the number of cutter teeth. From the point corresponding to D = 100 mm, we draw a vertical line down to the intersection with the line corresponding to the specified processing conditions C-b From the intersection point of these lines, we draw a horizontal line to the intersection with the z axis (number of cutter teeth) - the lower left part of the nomogram. This point is between z = 12 and z = 14. We accept z = 12, since there are no cutters with obtained parameters with z = 14 according to the standard. Thus, the required cutter parameters are: a cylindrical cutter with large teeth L = 80 mm, D = 100 mm, d = 40 mm, z = 12.
For given milling conditions, we determine the optimal geometric parameters of the cutter according to the technologist's reference books: γ = 15°, α = 5°.
On fig. 32 shows a nomogram that can be used to select the optimal size of cylindrical cutters with insert knives.
Rice. 32. Nomogram for choosing the optimal size of cylindrical cutters with insert knives
Adjustment and setup
milling machine for
performance of various works
Adjustment- preparation of technological equipment and tooling for the performance of a certain technological operation (installation of a mandrel on a machine; installation of a cutter and setting rings on a mandrel; checking the runout of a cutter; installing a fixture on a machine; alignment of the workpiece relative to the tool; arrangement of stops that limit the course of the table, etc.).
Setting milling machine is to set the required number of revolutions of the machine spindle, the specified minute feed and milling depth.
Installing and fixing the cutter. After the optimal size of the cylindrical cutter for the given processing conditions is selected, it is installed and fixed. In accordance with the size of the hole diameter of the cutter, the required diameter of the mandrel is selected.
At domestic factories, mandrels of standard diameters are used: 16, 22, 27, 32, 40, 50 and 60 mm. On fig. 33 shows a milling mandrel 3 for fastening a cylindrical or disk milling cutter or a set of milling cutters with mounting rings 5.
Rice. 33. Mandrel for fixing cutters
The milling mandrel is placed in the spindle cone and tightened with a ramrod 7. Mounting (spacer) rings are put on the mandrel and cutter 4 at the required distance from the end of the spindle. A set of rings with a cutter (or a set of cutters) and a conical sleeve is tightened on the mandrel with nut 1. After that, the earring moves onto the conical sleeve of the mandrel to failure and is attached to the trunk of nut 2. The trunk must also be fixed on the frame with nuts 6. In heavy work, a second one is installed earring, for which the second cone bushing is included in the set.
To locate one or more cutters on the mandrel, two types of adjusting rings of different widths are used (Fig. 34, a, b).
Rice. 34. Setting rings
The normal set of setting rings supplied with the milling machine consists of * rings with a width of 1 to 50 mm; 1.0; 1.1; 1.2; 1.3; 1.4; 1.5; 1.6; 1.7; 1.8; 1.9; 2.0; 3.0; 5.0; 8.0;10; 15.20; thirty; 40 and 50 mm.
When one cutter is installed on the mandrel, it is desirable to place it closer to the machine spindle, since in this position the deflection of the mandrel will be minimal. The required location of the cutter relative to the workpiece being processed is achieved by appropriate setting of the table in the transverse direction.
If it is impossible to install the cutter near the spindle, it is recommended to use an additional hanging earring 1 (Fig. 35). If several cutters that do not have end contact should be installed on the mandrel, then the correctness of their relative position is achieved by a set of intermediate rings 2 that are installed between them.
Rice. 35.
The order of installation and fixing of the cutter
1. Pull out the trunk of the machine by turning the socket wrench, having previously unscrewed the locking screws (Fig. 36).
Rice. 36. Extension of the trunk and removal of the earring
2. Remove the earring by first unscrewing the screw.
3. Insert the mandrel with its end end into the spindle hole, align the grooves in the mandrel flange with the crackers at the end of the spindle and secure the mandrel with a ramrod. The taper tail of the mandrel must fit snugly into the taper hole of the spindle. Therefore, it is necessary to protect the conical tail of the mandrel and the seat in the spindle from nicks, and thoroughly clean them from dust before fixing.
4. Slide the selected setting rings and cutter onto the arbor. Pay attention to the correspondence of the direction of rotation of the machine spindle to the direction of the helical grooves of the cutter
It should be remembered that it is necessary to choose necessarily schemes with opposite directions of the helical grooves of the cutter and the direction of rotation of the spindle.
When working on horizontal milling machines, cylindrical cutters with the left direction of the helical grooves should be used with the right rotation of the cutter or with the right direction of the helical grooves with the left direction of rotation of the cutter. This is explained by the fact that in cases with a different direction of the helical grooves of the cutter and the direction of its rotation, the axial component of the cutting force Px is directed towards the spindle, i.e., a more rigid support. At the same time, it will press the mandrel into the spindle hole, and not pull the cutter with the mandrel out of the spindle socket and press on the less rigid support - the earring. Now let's return to the installation and fixing of the cutter. After putting the adjusting rings and the cutter on the mandrel, then put the rest of the adjusting rings on the mandrel and tighten the nut on the end of the mandrel. In this case, it is necessary to ensure that the nut does not cover the neck of the mandrel, which enters the earring bearing.
5. Install the earring so that the end of the mandrel (neck) enters the earring bearing (Fig. 37, a).
Rice. 37. Fixing the cutter on the mandrel
6. Fix the cutter on the mandrel by tightening the nut with a wrench (Fig. 37, 6).
7. Fix the trunk and lubricate the earring bearing.
8. Check the runout of the cutter and the mandrel, which must comply with existing standards. To check the runout of the mandrel and the cutter, use an indicator with a tripod.
Checking cutter runout
To check the runout of the cutter, use the device shown in Fig. 38. The radial runout of the cutting edges relative to the hole for cutters with a diameter of up to 100 mm should not exceed 0.02 mm for two adjacent teeth and 0.04 for two opposite teeth. The runout of the supporting ends when checking on the mandrel is 0.02 mm for cutters up to 50 mm long and 0.03 mm for cutters over 50 mm long.
Rice. 38. Device for checking milling cutters for runout
Radial runout of two adjacent teeth of cutters with a diameter of 100 to 125 mm is not more than 0.02 mm, and cutters - not more than 0.05 mm; for cutters with a diameter of over 125 mm - 0.03 mm and 0.08 mm, respectively.
Application of stops. Milling machines are equipped with devices for automating the work cycle, which allow you to set the machine to quickly approach the table, switch it to the working feed and stop at the end position. On fig. 39 shows the arrangement of the stops that limit the longitudinal travel of the table of the 6P82Sh wide-purpose machine. Thrust cams 7 and 2 are installed and fixed in the side longitudinal groove of the table, in a position corresponding to the beginning and end of the working stroke of the table, depending on the required milling length. After switching to the right by the lever 3 of the mechanical feed, the table with the workpiece being processed begins to move from left to right until the cam 1 rests on the protrusion of the lever 3 and puts it in the middle position, thereby turning off the mechanical feed.
Rice. 39. Arrangement of stops for automatic shutdown of the longitudinal feed
After turning lever 3 to the left, the table will automatically feed from right to left and will move until cam 2 rests on the ledge on lever 3 and puts it in the middle position, turning off the mechanical feed. Similar devices are used in milling machines to limit and automatically turn off the transverse and vertical feed. In those cases when, according to the processing conditions, automatic shutdown of the table feed is not required, the cams are installed and fixed in the extreme working positions of the table.
Coolant supply. It is necessary to select the appropriate coolant for these conditions (see § 7) and make sure that the fluid supply system works reliably.
Choice of milling modes. Selecting milling modes means that for the given processing conditions (material and brand of the workpiece, its profile and size), select the optimal type and size of the cutter, grade of material of the cutter and geometric parameters of the cutting part, as well as the optimal parameters of the milling modes: milling width, milling depth, feed per tooth, cutting speed, spindle speed, minute feed, effective milling power and machine time.
In ch. IX, the issue of establishing milling modes is analyzed in detail. Here we restrict ourselves to only some information on this issue (in serial production, all data for choosing a cutter and milling modes are indicated in operational technological maps).
The choice of the type and size of cylindrical cutters and their geometric parameters was discussed earlier. The cutting mode is determined according to the tables that are given in the manuals of the milling machine, technologist, standardizer or in the manuals on cutting modes. The milling width, as a rule, is not chosen, since it depends on the dimensions of the workpiece. The depth of rough milling depends on the machining allowance and the power of the machine's electric motor. It is desirable to remove the allowance for processing in one pass. When finishing milling, the depth of cut does not exceed 1-2 mm.
The feed per tooth of the cutter is selected depending on the nature of the processing (rough or finish milling). In rough milling, the feed per tooth is greater than in fine milling, since the smaller the feed per tooth, the higher the roughness class of the machined surface.
Based on the selected depth, milling width and feed per tooth, the cutting speed is determined. Let us analyze in detail the setting of a 6P82 horizontal milling machine for the case of rough milling of a workpiece made of steel 45 (σ of 75 kg / mm 2), milling width B 15 mm, cutting depth t 5 mm. In this example, we will choose the standard size of a cylindrical cutter with insert knives, and not a solid one.
Solution. According to the nomogram (see Fig. 32), we determine the standard size of a cylindrical cutter with insert knives. The solution of the example in fig. 32 is shown by arrows. For milling width B = 15 mm, the nearest cutter length dimension is 100 mm. From the point marked L = 100 mm, we draw a vertical straight line until it intersects with the C-I line (roughing, material of medium processing difficulty). Further, from the obtained point, we draw a horizontal line until it intersects with the d axis (mandrel diameter). The closest mandrel size is d = 40 mm. From the point marked d = 40 mm, we draw a horizontal straight line until it intersects with line I (roughing). Then, from the obtained point, we draw a vertical line down until it intersects with the axis on which the diameter of the cutter D is indicated. We obtain an intermediate value for the diameter of the cutter (between 90 and 110 mm). From a point corresponding to the selected diameter, for example 110 mm, we draw a vertical line until it intersects with the C-I line. From the obtained point we draw a horizontal line until it intersects with the z line (number of cutter teeth). Thus, for this case, the optimal dimensions of the cutter will be: L = 100 mm, d = 40 mm, D = 90 mm, z = 8 or L = 100 mm, d = 40 mm, D = 110 mm, z = 10.
It is preferable to take the second option, since here z=10, and not 8, as in the first case. Now, for a given workpiece material and the material of the cutting part of the R6M5 cutter, we find from the tables the optimal geometric parameters of the cutting part γ = 15°, α = 8°.
In the order indicated earlier, we determine the cutting mode according to the tables. For cutters with insert knives and large teeth, the feed per tooth is set within 0.05-0.4 mm/tooth. Let's take the feed per tooth S z 0.02 mm/tooth. The cutting speed when processing steel with these cutters is set within 35-55 m/min. For our case v = 42 m/min.
To determine the number of spindle revolutions for a given cutting speed and the selected cutter diameter, you can use the graph (Fig. 40). From the point corresponding to the accepted cutting speed, a horizontal line is drawn, and from a point with a mark of the selected diameter of the cutter - a vertical line. At the point of intersection of these lines, the nearest step of the number of revolutions of the cutter available on this machine is determined. So, for example, in our example, the number of spindle revolutions when milling with a cylindrical cutter with a diameter of D = 110 mm at a cutting speed of 42 m/min according to the graph will be 125 rpm.
Rice. 40. Graph for selecting the number of revolutions of the cutter
The desired speed is usually between two adjacent values of the spindle speed. In such cases, choose the nearest speed step to the found value according to the graph (Fig. 40).
The numerical value of the minute feed and, accordingly, the choice of the value S m available on this machine can be determined without counting, using the graph (Fig. 41).
Rice. 41. Graph for selecting minute feed
For our example, let's determine the minute feed when milling with a cutter with the number of teeth z = 10, with s z = 0.2 mm/tooth and n = 125 rpm. From the point corresponding to the feed per tooth, sz = 0.2 mm / tooth, we draw a vertical line until it intersects with an inclined line corresponding to the number of cutter teeth z = 10. From the obtained point, we draw a horizontal line until it intersects with an inclined line corresponding to the accepted number of spindle revolutions n = 125 rpm. Next, draw a vertical line from the resulting point. The intersection point of this line with the lower scale of minute feeds available on this machine determines the nearest step of minute feeds.
For our example, as can be seen from the graph, the minute feed coincides with one of the minute feed steps available on the horizontal milling machines of the M and P series, and is equal to 250 mm / min. For other types of machines, it is easy to build similar graphs.
If in the example discussed above, a workpiece would be given not from steel, but from gray cast iron with a hardness of HB - 180, then with the same milling width B = 75 mm and cutting depth t = 5 mm and for the same milling cutter with insert knives (L = 100 mm, d = 40 mm, D = 110 mm, z = 10), the following changes should be made. The geometric parameters of the cutter for this case are γ = 0°, α = 15°. The feed per tooth when machining cast iron is selected in the range of 0.1-0.5 mm / tooth, i.e., respectively, more than when machining steel. The cutting speed when machining cast iron is set within 15-45 m/min, i.e., less than when machining steel 45.
The finishing milling mode differs from the rough milling modes in that when finishing milling steel and cast iron, a relatively small feed per cutter tooth (sz = 0.05-0.12 mm / tooth) is assigned at high cutting speeds (according to the above upper speed limit for both cases).
Milling modes are usually indicated in the operating charts of machining. It should be borne in mind that non-observance of these milling modes leads to irrational use of the machine and tools, a decrease in labor productivity, or even to defective parts.
Setting the gearbox and feeds to a given number of revolutions per minute feed is carried out by setting the handle and dial for switching speeds and feeds to the appropriate positions.
Milling depth setting. Loosen the locking screws before raising or lowering the table. With the spindle rotating, carefully guide the table, together with the fixed workpiece, under the cutter by hand until it touches lightly. Then, by manually moving the table in the longitudinal direction, remove the workpiece from under the cutter.
Then, by turning the vertical feed handle, raise the table by an amount equal to the depth of cut. The reading of the amount of movement of the table is made along the limb, i.e., the ring with divisions (Fig. 42). The reading on the limb can in principle be carried out from any division of the scale, however, for convenience and simplification of the reading, after the cutter has touched the workpiece being processed, the limb should be set to zero (i.e., the risk of the limb with the O mark should be aligned with the target risk).
Rice. 42. Limb for counting movements
The price of division The limb is the amount by which the machine table will move if the handle of the table feed screw is turned one division of the limb. If, for example, the price of the dial division is 0.05 mm and the limb ring has 40 divisions, then this means that for one turn of the manual lifting handle of the table, it will move by 0.05 x 40 = 2 mm. To raise the table by 3 mm, you need to turn the dial by 3: 0.05 = 60 divisions, that is, one and a half turns.
When rotating the handle of the vertical feed of the table, it is necessary to take into account the presence of a "dead stroke". As a result of wear of the screw and nut, a gap is formed in the screw-nut connection. Therefore, if you turn the screw feed handle in one direction, and then change the direction of rotation of the screw, then it will turn idle for some part of the turn (until the gap in the screw-nut connection is selected), i.e. the table will not move.
Therefore, it is necessary to bring the limb to the desired division very smoothly and, if possible, carefully (without jerks). If, however, they accidentally turned it, say, to the 40th division, but it is necessary to the 35th, then you cannot correct the error by turning the dial in the opposite direction by 5 divisions. In such cases, it is necessary to turn the handwheel with the dial in the opposite direction almost a full turn and carefully move the dial again to the desired division.
After setting the cutter to the required milling depth, it is necessary to lock the console and the cross feed slide and set the power feed enable cams to the desired milling length.
After adjusting and adjusting the machine, by smoothly rotating the handle of the longitudinal feed of the table, bring the workpiece to be processed to the cutter, without bringing it up a little, turn on the machine, turn on the mechanical feed and start working.
Before moving the table to its original position (removing the part from under the cutter), remove all chips from the machined surface with a brush, and lower the table a little so as not to spoil the machined surface of the part during the reverse stroke. Then measure the machined part, the dimensions of which must correspond to the dimensions indicated in the operating card. If necessary, correct the size by an additional pass.
Milling inclined planes and bevels. The plane of the part, located at some angle to the horizontal plane, is called inclined plane. The inclined plane of a small part is called bevel. Milling of inclined planes and bevels with cylindrical cutters can be carried out by setting the workpiece at the required angle to the cutter axis. This rotation can be done in different ways.
Mounting the workpiece in a universal vice. When setting the universal vice to the required angle, it should be borne in mind that the inclined plane to be processed must be located horizontally, i.e. parallel to the axis of the cutter.
Mounting the workpiece on the universal turntable. On fig. 43 shows the workpiece set at the desired angle on the universal turntable.
Rice. 43. Milling an inclined plane on a universal rotary plate
Rotary plates allow processing planes with any angle of inclination ranging from 0 to 90° with the possibility of simultaneous rotation of the workpiece in a horizontal plane at an angle of up to 180°. The workpiece is attached to the table of the universal plate with clamps or bolts, as in the case of fixing it to the table of a milling machine. Universal vices and universal rotary plates are used in single or small-scale production.
Installation of workpieces in special fixtures. When processing workpieces with inclined planes or bevels in conditions of large-scale and mass production, it is advisable to install workpieces at the required angle to the cutter axis in special devices.
On fig. 44 shows a device for milling inclined planes. Two workpieces are installed in the fixture and milled simultaneously with a face or cylindrical cutter.
Rice. 44. Device for milling inclined planes
In mass production, milling completely supplanted the planing and partially chiselling used earlier. When processing by milling, it is possible to achieve significantly greater productivity - thanks to the use of a multi-edge tool, a much larger surface can be machined per unit time.
Milling productivity is also higher because several workpieces can be processed simultaneously with several simultaneously working tools. In addition, the duration of working and idle strokes of the workpiece and tool is reduced.
The main milling methods that provide an increase in processing productivity are:
- parallel, i.e. simultaneous, milling of several workpieces or several surfaces of one workpiece. To do this, several cylindrical, disk and shaped milling cutters or several face milling cutters on different spindles are installed on one mandrel. Processing is also carried out using one end mill of a larger diameter or one cylindrical cutter of sufficient length. With such milling, the labor intensity of processing is sharply reduced due to the combination of the machine time of individual transitions and the reduction of auxiliary time;
- sequential milling of several workpieces installed in a row on the machine table (or several surfaces of one workpiece), as they approach the cutter during the working movement of the machine table. In this case, auxiliary time is sharply reduced, since it is overlapped by machine time;
- parallel-serial milling (Fig. 3.86), in which the simultaneous processing of several workpieces (or several surfaces of one workpiece) installed in one or more rows on the machine table is combined with sequential processing. The use of this method, along with a reduction in labor intensity due to the reduction of auxiliary time, can drastically reduce machine time;
Figure 3.86 milling parts installed in rows:
1 - workpieces; 2 - a set of cutters; 3 - machine table; 4 - fixture
- milling on rotary tables and devices (Fig. 3.87). In this case, the complexity of processing is reduced due to the combination of a large part of the auxiliary time with machine time, since the processed workpiece is removed and a new one is installed during milling of the part at a different position on the table or in the fixture;
Figure 3.87. Scheme of milling on a rotary table. 1,2 - workpieces, 4 - rotary table
-milling With feeding in both directions(pendulum feed). This processing method is a variation of the previous one. It is used for small surfaces of long workpieces, for which the use of rotary devices is difficult;
Figure 3.88. Milling scheme.
1,2 - workpieces, 3 - machine table
- continuous milling(Fig.3.89) lies in the fact that the workpieces are mounted on a round continuously rotating table or in a drum device and milled with end mills mounted on the machine spindles. With such milling, the piece time can be very close or equal to the machine time. The processing of planes with end mills in serial and mass production is increasingly replacing milling with cylindrical cutters, since this method is more productive, and also allows processing workpieces of considerable width with a rigid tool holder. In addition, the surface roughness is also reduced to R a =0.8...0.4 µm.
When milling, the surface is processed not with a single-blade tool - a cutter, as in planing, but with a multi-blade rotating tool - a milling cutter. The feed is carried out by moving the workpiece fixed on the machine table. The cutter receives rotation from the machine spindle.
Flat surfaces can be milled with face and cylindrical cutters. Milling with face mills is more productive than with cylindrical ones. This is explained by the fact that during face milling, metal is simultaneously cut with several teeth, and it is possible to use cutters of large diameter with a large number of teeth.
Milling with cylindrical cutters is performed in two ways. The first method is counter milling (Fig. 2, a), when the rotation of the cutter is directed against the feed; the second method is climb milling (Fig. 2, b), when the direction of rotation of the cutter coincides with the direction of feed.
Rice. 2. Milling schemes: a- counter; b - passing
In the first method of milling, the chip thickness gradually increases when cutting metal with each cutter tooth, reaching a value and tah. Before cutting starts, there is a slight slippage of the cutting edge of the tooth along the cutting surface, which causes work hardening of the machined surface and dulls the teeth.
With the second milling method, the chip thickness gradually decreases. Productivity can be greater and the quality of the machined surface is better than with the first, but with the second milling, the cutter tooth grabs the metal immediately to the full depth of cut and, thus, cutting occurs with shocks. In view of this, the second milling method can only be used to work on machines with high structural rigidity and a device for eliminating gaps in the feed mechanisms. For this reason, the first milling method is used more often than the second.
Milling machines are divided into the following types: 1) horizontal milling, 2) vertical milling, 3) universal milling, 4) longitudinal milling, 5) rotary milling, 6) drum milling and 7) special.
Milling machines of the first three types are general purpose machines and are used in all types of production; the rest are high-performance and are used in serial, mainly large-scale and mass production. On horizontal milling and vertical milling machines can be installed on the machine table 3 one detail 1 or several parts in rows, processing them simultaneously or sequentially (Fig. 3) with cutters 2, fixed in fixture 4
Rice. 3. Milling of parts installed in rows: 1 - workpieces; 2 - a set of cutters; 3 - machine table; 4 - adaptation.
Rice. 4. Productive milling methods:
1 and 2 - workpieces; 3 - machine table; 4 - Rotary table
On fig. 4, a shows the milling of parts with a face mill on a vertical milling machine using the so-called pendulum feed method (feed in both directions); while auxiliary time is spent only on moving the table 3 the length of the distance between the parts. The use of this method can significantly increase the productivity of the machine. Universal milling machines, unlike horizontal milling machines, have a rotary table, which can be positioned in a horizontal plane at an angle to the spindle axis. This makes it possible to mill helical surfaces when using a universal dividing head.
Longitudinal milling machines come with horizontal and vertical spindles in various combinations: with one horizontal or one vertical spindle; with two horizontal with two horizontal and one vertical; with two horizontal and two vertical. Such machines come in large sizes (with a table stroke of up to 8 m, and sometimes more) they are used to process large parts - simultaneously from two or three sides.
On fig. 4 shows high-performance milling on a planer (a) and horizontal milling (b) machines using a turntable 4, thanks to which the change of machined parts 1, 2 produced during milling; auxiliary time is spent only on the reverse retraction of the table and its rotation, which does not exceed 0.2-0.5 minutes for two parts.
Carousel-milling machines have round rotating tables of large diameter and one (Fig. 5, a) or two (Fig. 5, b) vertical spindles.
