Layout of parts (general information). Milling curved contours How to place parts with curved contours

Not all machine parts have contours delineated by straight lines; many parts represent flat surfaces, limited from the sides by curvilinear contours. On fig. 156 shows parts with curvilinear contours: a wrench (Fig. 156, a), a clamp (Fig. 156, b), a cam to a lathe (Fig. 156, c), an engine connecting rod (Fig. 156, d). The contours of these parts consist of straight line segments conjugated with curves or circular arcs of various diameters, and can be obtained by milling on a conventional vertical milling or special copy milling machine.

Curved contours can be milled on a vertical milling machine:
a) according to the marking by combining manual feeds;
b) by marking with a round turntable;
c) by copy.

Milling a curved contour by combining manual feeds

Milling by combining manual feeds is that a pre-marked workpiece (fixed or on the table milling machine, either in a vice or in a fixture) is processed with an end mill, moving the table by hand at the same time in the longitudinal and transverse directions so that the cutter removes the metal layer in accordance with the marked curvilinear contour.

To explain this method of processing a curved contour, consider the example of milling the contour of the bar shown in fig. 157.
Cutter selection. Let's choose end mill, the diameter of which would make it possible to obtain a rounding R = 18 mm, required by the contour of the part according to the drawing. We take an end mill made of high-speed steel P18 with a diameter of 36 mm with normal teeth and tapered shank according to GOST 8237-57; This cutter has 6 teeth.
preparation for work. The bar is installed directly on the table of the vertical milling machine, fixing it with clamps and bolts, as shown in fig. 158. A parallel lining is used to ensure that the cutter does not touch the working surface of the machine table during processing.
When installing, care must be taken to ensure that chips or dirt do not get between the mating surfaces of the machine table, pad and workpiece.
Setting the machine for cutting mode. Set the machine to a given cutting speed of 40 m/min. According to the beam diagram (see Fig. 54) cutting speeds 40 m/min with cutter diameter D = 36 mm corresponds to the number of revolutions between n 11 = 315 and n 12 = 400 rpm. We accept the next smaller number of revolutions n 11 = 315 and set the gearbox dial to this stage. In this case, the cutting speed according to the formula (1):

Contour milling. Milling will be carried out with manual feed, following the markings, for which milling must be started from the area where there is the smallest allowance, or cut with a cutter gradually in several passes to avoid breakage of the cutter (Fig. 159).

Milling is carried out with simultaneous feed in the longitudinal and transverse directions, respectively, of the marking line. It is impossible to mill the contour cleanly in one pass, therefore, the curvilinear contour is first milled in draft form, and then completely along the marking line, including the roundings at the wide part of the plank.
milling a central slot 18 wide mm and length 50 mm produced by the method of milling a closed groove (see Fig. 131).

Milling with a rotary table

Curved contours, having the shape of an arc of a circle, in combination with straight line segments or without them, are processed on a round rotary rotary table, which is a normal accessory of a vertical milling machine.
Turning round table with manual feed. On fig. 160 shows a round turntable for manual feed operation. Plate 1 The turntable is attached to the machine table with bolts inserted into the grooves of the table. When turning the handwheel 4 , impaled on a roller 3 , rotating part of the table 2 . Degree divisions are applied on the side surface of the table to count the rotation of the table to the required angle. Workpieces for processing are fixed on the turntable in any way: in a vice, directly with the help of clamps, in special devices.

When turning the handwheel 4 the workpiece, mounted and fixed on a round rotary table, will rotate around the vertical axis of the table. In this case, each point of the workpiece surface will move along a circle with a radius equal to the distance of this point from the table axis. The farther the surface point is from the table axis, the larger circle it will describe when the table rotates.
If you bring the workpiece to a rotating cutter at any point and continue to turn the table, then the cutter will process an arc of a circle on it with a radius equal to the distance from the center to this point of the workpiece.
Thus, when machining on a circular rotary table, the contour of the arc is formed without combining two feeds as a result of the circular feed of the rotary table, and the accuracy of the contour here does not depend on the ability to combine two feeds, but on correct installation blanks on the table.
With the help of a round rotary table, both external contours and internal grooves can be milled.
Contour pattern processing. Consider an example of manufacturing a part by milling, which combines the processing of an external contour with the processing of internal circular grooves.
Let it be required to process the contour pattern shown in Fig. 161.

The workpiece has the form of a rectangle measuring 210x260 mm, thickness 12 mm. The workpiece is pre-drilled with a central hole with a diameter of 30 mm(for mounting it on a round table) and four auxiliary holes with a diameter of 32 mm(for milling). The workpiece is pre-marked.
Milling will be carried out on a vertical milling machine.
Since the outer and inner contours are subject to processing, milling must be carried out in two installations.
1. Having fixed the workpiece on the round table with bolts passed through any two holes in it, we mill the outer contour along the marking using the rotational movement of the round table (Fig. 162, a).

2. Having fixed the workpiece on the round table with clamps, we mill the internal circular grooves according to the marking, using the rotational movement of the round table (Fig. 162, b).
Cutter selection. Since it is desirable to process the outer contour and internal grooves without changing the cutter, we choose an end mill made of high-speed steel R18 (according to GOST 8237-57) with a diameter of 32 mm(corresponding to the width of the circular groove) with a normal tooth (z = 5) and a tapered shank.
Installing a round turntable. To install a round table you need:
1 Place the round table on its edge, wipe the base and place it on the machine table. When installing, insert clamping bolts with nuts and washers into the grooves of the machine table on both sides and fix the round table with bolts.
2 Insert a centering pin with a diameter of 30 mm into the center hole of the round table. mm.
To fix the workpiece, we use the centering pin and bolts for the first installation (Fig. 162, a) and the centering pin and clamps for the second installation (Fig. 162.6).
Setting the machine to milling mode. For this operation, the cutting speed is set υ = 31.5 m/min, that with a cutter diameter D = 32 mm according to the ray diagram (see Fig. 54) corresponds to 315 rpm. Cutter feed set 0.08 mm/tooth, which at n = 315 rpm and the number of cutter teeth z = 5 gives a minute feed of 0.08X5x315= 126 mm/min.
Set the gearbox dial to 315 rpm and the limb of the feed box at 125 mm/min.
External contour milling. Fixing the workpiece is clear from Fig. 162, a.
Having fixed the end mill in the spindle of the machine, turn on the machine and bring the workpiece to the cutter in the place where there is the smallest allowance (Fig. 162, a).
A rotating cutter is cut into the workpiece by manual feed to the marking line and, by turning on the mechanical longitudinal feed, a straight section is milled. 1-2 (Fig. 161). With manual rotation of the round table, a curved section is milled 2-3 . After that, a straight section is milled with mechanical longitudinal feed 3-4 and, finally, again, with the manual rotation of the round table, a curved section is milled 4-1 .
Circular slot milling. The workpiece for milling circular grooves is installed as shown in Fig. 162b.
By rotating the handle of the vertical, longitudinal and transverse feeds, the cutter is brought in (see Fig. 162, b) and inserted into the hole 5 (see fig. 161). Then you need to raise the table, lock the table console and smoothly with manual circular feed of the round table, slowly turning the handwheel, mill the inner groove 5-6 . At the end of the pass, lower the table to its original position and remove the cutter from the groove.
By rotating the handles of circular and vertical feeds, the cutter is inserted into the hole and the inner groove is milled in the same way with circular feed. 7-5 .
Round rotary table with mechanical feed. On fig. 163 a more perfect design of a round table is given, the circular movement of which is mechanically driven by the drive of the machine. If on the square end of the roller 6 put on the handwheel, you can rotate the table manually, as shown in Fig. 160 tables with manual feed. Mechanical rotation of the table is obtained by connecting the lead screw of the longitudinal feed of the machine table through a system of gears with a hinged shaft 3-4 associated with the worm gear located in the body of a round machine. Turning on the mechanical feed of the table is made by handle 5. Automatic shutdown of the mechanical feed is made by the cam 2 , which can be moved along the groove for installation 1 round table and secure in position with two bolts.

The work on the mechanical feed rotary table is similar to the disassembled example of manual feed rotary table processing, but the miller does not have to manually turn the handwheel. Circular mechanical feed is also expressed in terms of mm/min. It is determined based on the expanded length of the processing circle and the number of revolutions of the round table per minute.

Example 7 . Determine the circular feed when machining along the outer contour of the workpiece shown in fig. 161, on a power feed rotary table, if the table is known to make 0.25 rpm.
The outer contour of the part according to fig. 161 outlined by arcs of a circle D = 250 mm, therefore, the length of the path of the cutter along this circle is π D= 3.14 X 250 = 785.4 mm. At one revolution of the table per minute, the circular feed rate is 785.4 mm/min, and at 0.25 rpm, as given by the machining conditions, the circular feed rate will be: 785.4-0.25= 197.35 mm/min.

Copier milling

For the production of parts having a curved contour, curved grooves and other complex shapes, it is possible to mill the workpiece, as we have seen, either by combining two feeds, or by using a rotary table; in these cases, preliminary markup is required.
In the manufacture of large batches of identical parts with curvilinear contours, copiers are used or special copy-milling machines are used.
The principle of operation of copiers for milling is based on the use of longitudinal, transverse and circular feeds of the machine table to communicate the workpiece with a curvilinear movement that exactly matches the contour of the finished part. To automatically obtain the desired contour, copiers are used, that is, templates that replace markup.
Milling according to the copier - template. For milling the contour of the large head of the engine connecting rod (Fig. 164, b) copier 1 put on a detail 2 and securely fastened to it. By operating the circular feed handwheel of the round rotary table and the longitudinal and transverse feed handles, the miller ensures that the neck of the end mill 3 all the time pressed against the surface of the copier 1 .

The end mill for processing on a copier is shown in Fig. 164, a.
On fig. 165 is a diagram of a copier for milling the contour of a large head of an engine connecting rod, similar to that shown in fig. 164, but with the use, in addition to the copier, of a roller and a load.

On the table 7 machine installed copier 5 , having a round rotary table with manual feed; a copier is fixed on the faceplate of the table 6 . under the influence of the load 1 copier 6 always pressed to the roller 2 . The lead screws of the longitudinal and transverse feeds of the machine table are released and, when the round rotary table is rotated, the fixture together with the fixed workpiece 4 will “follow” the copier under the action of the load 6 , and the cutter 3 will process the workpiece 4 along a given contour.
The device has, in comparison with that shown in Fig. 164 with the advantage that the miller is relieved of the need to continuously create contact between the finger and the copier, which is carried out automatically under the action of the load. In order to further automate copy-milling work along the contour, special contour copy-milling machines are used. Chapter XXIII discusses the basic principles of automatic contour reproduction and describes copy-milling machines for these works.

Not all machine parts are contoured with straight lines, as discussed in previous chapters; many parts are flat surfaces bounded laterally by curvilinear contours. On fig. 222 shows details with curvilinear contours: a wrench (Fig. 222, a), a clamp (Fig. 222.6), a cam for a lathe (Fig. 222, c), an engine connecting rod (Fig. 222, d).

The curvilinear contour shown in fig. 222 parts consist of straight segments conjugated with curves or circular arcs of various diameters, and can be obtained by milling on a conventional vertical milling or special copy-milling machine.

Milling curvilinear contours on a vertical milling machine, it can be carried out: by marking by combining manual feeds, by marking using a round rotary table and by a copier.

Milling a curved contour by combining manual feeds. Milling by combining manual feeds consists in the fact that a pre-marked workpiece (fixed either on the table of a milling machine, or in a vice, or in a special device) is processed with an end mill, moving the table by manual feed simultaneously in the longitudinal and transverse directions so that the cutter removes the metal layer in accordance with the marked curvilinear contour.

Let's consider an example of milling by marking by combining manual feeds of the contour of the bar shown in fig. 223.

Choice of cutter. For milling, we choose an end mill, the diameter of which would make it possible to obtain a rounding R = 18 mm, required according to the drawing. We take an end mill with a diameter of 36 mm with six teeth. The cutter material is high-speed steel.

Preparation for work. The bar is installed directly on the table of the vertical milling machine, fixing it with clamps and bolts as shown in Fig. 224. A parallel lining is used to ensure that the milling cutter does not touch the working surface of the machine table during processing.

When installing, care must be taken to ensure that chips or dirt do not get between the mating surfaces of the machine table, lining and workpiece.

Setting the machine for cutting mode. Since for our case the feed is carried out manually, we will take it equal to 0.08 mm / tooth, assuming a depth of cut of 5 mm. According to the table 211 of the "Young Miller's Handbook" for these conditions, the recommended cutting speed will be 27 m / min and the corresponding number of revolutions of the cutter n \u003d 240 rpm.

Let's choose the nearest number of revolutions available on the machine and set the dial of the gearbox to n = 235 rpm, which corresponds to a cutting speed of 26.6 m/min.

Contour milling. Milling will be carried out with manual feed, following the markup, for which we will start processing from the area where there is the smallest allowance, or we will plunge in gradually, in several passes, in order to avoid breakage of the cutter.

Milling is carried out by simultaneous feed in the longitudinal and transverse directions, respectively, the marking line. It is impossible to mill the contour cleanly in one pass, therefore, first the curvilinear contour is milled in draft form, and then completely along the marking line, including the roundings at the wide part of the plank.

Milling of the central groove with a width of 18 mm and a length of 50 mm is carried out according to the method of milling a closed groove (see Fig. 202).

Curvilinear contours, having the shape of an arc of a circle, in combination with straight line segments or without them, are processed on a round rotary table (see Fig. 146 and 147).

When processing on a round rotary table, the arc contour is formed without combining two feeds as a result of the circular feed of the rotary table, and the accuracy of the contour here does not depend on the ability to combine two feeds, but on the correct installation of the workpiece on the table.

Consider an example of milling a part, which combines the processing of an external contour with the processing of internal circular grooves.

Let it be required to process the contour pattern shown in Fig. 225.

The workpiece has the form of a rectangle 210×260 mm in size, 12 mm thick. The workpiece is pre-drilled with a central hole with a diameter of 30 mm (for mounting it on a round table) and four auxiliary holes with a diameter of 30 mm (for milling). The contour of the part is marked on the workpiece.

Milling will be carried out on a vertical milling machine. Since external and internal contours are subject to processing, milling must be carried out in two settings:

1. Having fixed the workpiece on the round table with bolts passed through any two holes on the workpiece, we mill the outer contour according to the marking using the rotational movement of the round table (Fig. 226, a).

2. Having fixed the workpiece on the round table with clamping strips, we mill the internal circular grooves according to the marking, using the rotational movement of the round table (Fig. 226,

Since it is desirable to process the outer contour and internal grooves without changing the cutter, we select an end mill made of high-speed steel with a diameter of 30 mm, corresponding to the width of the circular groove.

Before installation, the round table must be placed on edge and its base wiped. Then insert clamping bolts with nuts and washers into the grooves of the machine table on both sides and fix the round table with bolts. To base the workpiece, insert a centering pin with a diameter of 30 mm into the central hole of the round table.

We fix the workpiece with a centering pin and bolts during the first installation (Fig. 226, a) and with a centering pin and tacks during the second installation (Fig. 226, b).

Setting the machine to milling mode. We select the cutting speed according to the table. 211 of the "Young Miller's Handbook" for a cutter with a diameter of 30 mm and feed for £ tooth = 0.08 mm / tooth, with the greatest depth of cut t = 5 mm. Cutting speed v = 23.7 m/min and, accordingly, n = 250 rpm.

We set the machine to the nearest speed n = 235 rpm, which corresponds to a cutting speed v = 22.2 m/min, and proceed to the processing of the outer contour.

Having fixed the end mill in the spindle of the machine, turn on the machine and bring the part to the cutter in the place where there is the smallest allowance (Fig. 226, a).

A rotating cutter is cut into the workpiece by hand feed to the marking line and, turning on the mechanical longitudinal feed, a straight section 1-2 is milled (Fig. 225). With manual rotation of the round table, a curvilinear section 2-3 of the outer contour is milled. After that, the straight section 3-4 of the outer contour is milled with mechanical longitudinal feed, and finally, the curved section 4-1 of the outer contour is milled again with manual rotation of the round table.

The installation of the workpiece for milling circular grooves is carried out as shown in Fig. 226b.

By rotating the handle of the vertical, longitudinal and transverse feeds, the cutter is brought in (see Fig. 226, b) and inserted into hole 5 (see Fig. 225). Then the table is lifted, the table console is stopped and the inner groove 5-6 is milled smoothly by manual circular feed of the round table, slowly rotating the handwheel. At the end of the passage, lower the table to its original position and remove the cutter from the groove. By rotating the handles of the circular and vertical feeds, the cutter is inserted into the hole 7 and the inner groove 7-8 is milled in the same way with the circular feed.

Copier milling. Milling of parts having a curved contour, curved grooves and other complex shapes, can be done, as we have seen, either by combining two feeds, or using a rotary round table; in these cases, preliminary markup is required.

In the manufacture of large batches of identical parts with a curvilinear contour, special copiers are used, or special copy-milling machines.

The principle of operation of copiers is based on the use of longitudinal, transverse and arc feed of the machine table to communicate the workpiece with a curvilinear movement that exactly matches the contour of the finished part.

To automatically obtain this contour, copiers are used, that is, templates that replace the markup. On fig. 227, b shows the milling of the contour of the large head of the engine connecting rod. Copier 1 is applied to item 2 and securely fastened to it. Acting with the handwheel of the circular feed of the round rotary table and the handles of the longitudinal and transverse feeds, the miller ensures that the neck 3 of the end mill is pressed against the surface of the copier 1 all the time.

copier processing,

The end mill used for is shown in fig. 227 a.

On fig. 228 is a diagram of a copier for milling the contour of a large head of an engine connecting rod, similar to that shown in fig. 227, but with the use, in addition to the copier, of a roller and a load. Under the action of load 1, roller 2 is always pressed against copier 5, which is rigidly connected to the table of copier 5, on which the connecting rod 4 is fixed. .

Marking is the initial operation of the process of processing body parts. Sheets and profiles are received for marking, the details of which will be cut on mechanical equipment, portable machines for thermal cutting or hand-held gas cutters. Marking can be done manually, using photo projection, sketch or template methods, on marking and marking machines with program control and using other methods.

The photoprojection method is used for marking sheet steel parts. With this method, negatives from large-scale drawings-templates are issued from the plaza to the site of the shop marking.

The actual markup process is as follows. A sheet of metal is fed onto the marking table. If the sheet does not fit tightly on the table (there are gaps between the sheet and the table top), then it is pressed against the table with clamps. They turn on the projection equipment, into which the corresponding negative is previously inserted, and set it up. Since the lines and signs of a scale drawing are drawn in black ink, these lines and signs turn out to be light on the negative and its projection. On the light lines and signs on the surface of the sheet to be marked, the contours of the parts and their marking are fixed (kern).

The sketch marking method is used mainly for marking parts from profiled rolled products. The use of this method for parts from sheet metal is allowed only in cases of marking dimensional waste, the absence of photoprojection equipment and marking and marking machines.

Marking parts using sketches comes down to the fact that the scribe builds on a sheet or profile in full size the contours of the parts shown on the sketches. The contours of the parts are obtained by performing simple geometric constructions using conventional measuring and marking tool. To mark the most complex details, rails or templates are attached to the sketches, which are specially stipulated in the sketches. Both sketches and slats, as well as templates, arrive at the workshop marking section from the plaza.

Parts with curved edges, the construction of which presents significant difficulties geometrically, as well as parts made of bent profiles, are subjected to marking according to templates.

Mark the parts according to the templates as follows. A template is placed on the sheet to be marked. After that, the outline of the part along the edges of the template is outlined with a scriber. Then all the cutouts on the template are outlined. Next, the template is removed and the parts are marked. After that, break lines, welding lines and all other lines necessary for processing and assembling parts are punched or drawn (along the serifs).

Rice. 11.5. Measuring tool: a - steel tape measure; b - folding rule; c - caliper; g - micrometer.

As measuring tool when performing marking work, they use (Fig. 11.5):
- tape measures with a metal tape up to 20 m long, metal rulers up to 3 m long, folding rules for measuring lengths;
- calipers and calipers for measuring internal and external diameters, as well as material thickness with an accuracy of 0.1 mm;
- goniometers, protractors for measuring and constructing angles;
- micrometers for measuring the thickness of the material with an accuracy of 0.01 mm.

Rice. 11.6. Marking tool: a - compass; b - caliper; in - squares; g - center punch; e - control center punch; e - thread; g - gage.

As a marking tool, they are used (Fig. 11.6):
- compasses and calipers for drawing circles and building perpendiculars;
- squares for building perpendiculars;
- cores for drawing points on metal;
- threads for drawing straight chalk lines;
- thickness gauges for drawing parallel lines on profile steel shelves, etc.;
- scribers for drawing lines.

All dimensions applied to parts that do not have allowances must correspond to the projection or drawing.

Below are the values of permissible deviations of the actual dimensions of the marked parts from the nominal ones (in millimeters):
From overall dimensions for sheet parts:
with a length (width) up to 3 m .............. ±0.5
with a length (width) of more than 3 m ............. ± 1.0
From overall dimensions for profile parts:
with a length of up to 3 m .............. ± 1.0
with a length of more than 3 m ................. ± 2.0
From the dimensions of the cutouts for the set, etc. ........... 1.0
Diagonal Difference................... 2.0
From straightness or other edge shape:
with a length of edges or chords (with curved edges) up to 3 m. .............. ± 0.5
with an edge or chord length of more than 3 m ........ ± 1.0
When marking, the width of the chalk line should not exceed 0.7 mm. The width and depth of the line drawn by the scriber should not exceed 0.3 mm.

When marking some parts, allowances are left along their edges. An allowance is called a part of the metal removed from the workpiece to obtain parts in drawing or plaza sizes. Allowances are designed to compensate for possible deviations from the dimensions that occur during the processing of parts, assembly and welding of assemblies and sections. The values of allowances assigned from the conditions of manufacture of parts are usually taken within the range of 5-50 mm.

To save traces of the markup until the end of processing and assembly of parts and to restore the markup (if necessary), all markup lines are crossed.

Light alloy body parts are marked with a simple soft pencil. It is allowed to punch only the centers of the holes, the installation sites of the set (subject to the obligatory further overlapping of their welded parts), as well as contour lines removed during subsequent processing.

A mark must be applied to each marked detail.

The appearance of automatic machines for thermal cutting of parts made it possible to exclude the operation of marking these sheets, but the marking of parts remained. In order to automate the process of marking parts on production lines for thermal cutting of parts, marking machines with program control have been created. At present, a sample of a laser marking and marking machine has been created.

* Details about drawings-templates were said in Ch. ten.

Before cutting a part from a sheet, you need to mark its contours in exact accordance with the dimensions indicated in the drawing.

There are the following types of markup:

1. Template marking in the manufacture or assembly of a large number of homogeneous parts.

2. Marking with a marking tool. This type of markup, in turn, can be divided into:

- marking with a ruler and a compass;

- marking with the help of an outline for bending and flanging the edge, as well as for trimming the edge;

- marking with punching centers before drilling holes;

- marking with a thickness gauge.

Marking when assembling units and installing them on an aircraft is carried out both using a marking tool and using templates.

Marking tool

Steel ruler, steel meter, scriber, pencil (simple), square, outline, compasses, center punch, hammer, templates, protractor, thickness gauge, prism, goniometer, plumb line.

Marking the contour of the part according to the template

1. Apply the template to the sheet so that when cutting the part out of it, as little waste as possible is obtained.

2. Mark the part by tracing around the outline of the template with a sharp scriber (Fig. 13).

Marking a part with a marking tool

a) Marking with a ruler and a compass

Mark a part with rectilinear contours by drawing parallel lines

1) draw a vertical line a parallel to the edge of the sheet using a steel ruler;

2) draw line b with a square at a right angle to line a;

3) apply strokes to draw contour lines parallel to sides a and b, setting aside the dimensions according to the drawing in full size (Fig. 15 and 16);