Main parts and elements of the cutter.
Geometry of the cut layer.
Cutting elements.
Main features of cutting during turning.
Topic 26. Metal cutting, elements and geometry of the cutter
Questions:
1. Let's consider the main features of cutting during turning. In Fig. Figure 37 shows a diagram of turning a shaft with a cutter. Workpiece the main rotational movement is transmitted from the machine spindle, the feed movement is transmitted to the cutter by the machine support; both movements are carried out continuously. The surface of the workpiece from which chips are removed is called processed; surface, formed after chip removal - processed; the surface formed by the cutting edge of the tool during the cutting process - cutting surface.
Fig.37
2. The cutting elements during turning include cutting speed, feed and depth of cut (Fig. 37). The combination of these values is called the cutting mode.
Cutting speed υ (m/min) is the path of movement of the cutting blade of the tool relative to the workpiece in the direction of the main movement per unit time. If the main movement is rotational (turning), then the cutting speed is determined by the formula:
Where D zag – the largest diameter of the workpiece being processed, mm;
P– workpiece rotation speed, rpm.
By filing S(mm/rev) is the path of the point of the cutting blade of the tool relative to the workpiece in the direction of the feed movement per revolution.
Depth of cut t(mm) is the distance between the machined and machined surfaces of the workpiece, measured perpendicular to the latter, in one pass of the tool relative to the machined surface. In external turning, the depth of cut is determined as half the difference in diameters before and after processing:
The volume of metal cut in one minute is determined by the formula:
G=υS t, cm 3 /min.
3. Geometry of the cut layer characterized by thickness, width and cross-sectional area.
Thickness of the cut layerA(mm) – the length of the normal to the cutting surface, drawn through the point of the cutting edge under consideration, limited by the cross-section of the layer being cut.
Width of the cut layer (cut width, mm) – length of the cross-sectional side of the cut layer formed by the cutting surface.
Nominal area of cut layer f ABCD (mm 2) (see Fig. 37) is determined by the formula: f ABC D =aв = tS.
Actual area of the cut layer f BSDE due to the fact that two movements are involved (υ and S), will be less than nominal f ABCD on the value of the axial sectional area of the scallop f ABE remaining on the treated surface. These ridges determine the surface roughness, which increases with increasing t, S and angles φ, φ 1.
4. A cutter is the most common tool used in processing materials and removing chips on machine tools.
Turning straight cutter(Fig. 38) consists of two parts - working part, having cutting edges that cut off a layer of metal from the workpiece, and fastening part(rod) designed for installation and fastening in the tool holder of the machine.
The working (cutting) part is formed by a number of surfaces, which, intersecting, form (cutting edges and the tip of the cutter. Front surface- this is the surface that comes into contact with the cut layer and chips during the cutting process. The rear surfaces of the cutter are in contact with the surfaces of the workpiece during the cutting process. Main back surface– the surface facing the cutting surface of the workpiece. Auxiliary back surface– the surface facing the machined surface of the workpiece. The anterior and main posterior surfaces at the intersection form main cutting edge, forming the larger side of the section of the cut layer. The anterior and auxiliary posterior surfaces, intersecting, form auxiliary cutting edge, forming the smaller side of the section of the cut layer. Cutter tip– the intersection point of the main and auxiliary cutting edges.
Rice. 38. Parts and surfaces of a through turning cutter:
1 – mounting part (rod) of the cutter; 2 – working part; 3 – front surface; 4 – auxiliary cutting blade (edge); 5 – top; 6 – auxiliary rear surface; 7 – main rear surface; 8 – main cutting blade (edge)
5. The angles of the cutter are considered in a stationary (static) state of the cutter and the workpiece - this is necessary so that it can be manufactured in metal and the working part can be sharpened.
Main rake angle γ– the angle between the front surface of the cutter and the plane perpendicular to the cutting plane passing through the main cutting blade (point M).
Main clearance angle α formed by the main rear surface and the cutting plane, it is taken equal to 6...12°. It serves to reduce friction between the main flank of the cutter and the cutting surface.
Rice. 39. Sharpening angles of the cutting part of the cutter
Principal taper angle β– the angle between the front and main rear surfaces.
Cutting angle δ form the front surface and cutting plane.
From Figure 41 it is clear that angles β and δ depend on angles α and γ and are related to them by the following dependencies:
β = 90° – (α + γ) and δ = 90°– γ.
Auxiliary angles α 1 and γ 1 are measured in the auxiliary cutting plane B– B, perpendicular to the projection of the auxiliary cutting blade onto the main plane. The main purpose of the angle γ 1 is to reduce friction between the auxiliary rear surface of the cutter and the machined surface of the workpiece.
Rice. 40
The plan angles φ, φ 1, ε are determined in the main plane. Principal angle φ– the angle between the projection of the main cutting blade onto the main plane and the feed direction, it varies within 30...90°. Reducing the angle φ increases the cleanliness of the machined surface and reduces wear of the cutter, but leads to an increase in the radial component of the cutting force, so most often the angle φ is taken equal to 45°. Auxiliary plan angle φ 1 is the angle between the projection of the auxiliary cutting blade onto the main plane and the direction opposite to the feed. Typically its values are chosen within 5...10°. With a decrease in φ 1, the cleanliness of the machined surface increases, the strength of the cutter tip increases and its wear decreases. Plane apex angle ε is formed by the projections of the cutting blades onto the main plane, and is determined from the relation ε = 180°– (φ + φ 1).
The angle between the main cutting blade and a plane drawn parallel to the main plane through the tip of the cutter is called angle of inclination of the main cutting blade λ.
In Fig. Figure 42 shows the effect of angle λ on the direction of chip flow.
At λ = 0 the main cutting edge is located parallel to the main plane and during cutting the chips curl into a spiral (Fig. 40, a). If the angle λ negative (Fig. 40, b), then the tip of the cutter is higher than other points of the main cutting edge, so the chips will move towards the machined surface. At a positive angle λ (Fig. 40, c) the tip of the cutter lies below the main cutting edge, as a result, the allowance is removed first by the parts of the cutting edge distant from the tip and, lastly, by the tip of the cutter, so the chips move towards the machined surface. At positive angles, the cutter is more resistant, however, the machined surface can be damaged by falling chips, so such cutters are used for preliminary (roughing) processing.
Cutter elements can always be found in other cutting tools (drills, cutters, broaches, reamers).
The cutter consists of a rod and a cutting part (head), manufactured at the same time.
The rod is also designed to secure the cutter in the tool holder of the machine support.
Rice. 4 Surfaces and elements of the cutter.
The following elements of the cutting part of the cutter are distinguished:
1. the front surface along which the chips flow;
2. main rear surface, facing the cutting surface;
3. auxiliary rear surface, facing the machined surface of the workpiece;
4. the main cutting edge, formed by the intersection of the front and main rear surfaces (it performs the main cutting work).
5. auxiliary cutting edge formed by the intersection of the front and auxiliary rear surfaces;
6. tip of the cutter - the point of intersection of the main and auxiliary cutting edges.
To consider static cutter angles (sharpening angles), the following conditions are necessary: the tip of the cutter is located in height at the level of the workpiece axis and the cutter shaft is perpendicular to the workpiece axis. The cutter angles determine the performance of the cutter, the relative position of the surfaces and cutting edges relative to the machined surfaces. The cutter angles are considered in the main and auxiliary cutting planes and in plan.
The main cutting plane of the cutter is a plane perpendicular to the projection of the main cutting edge onto the main plane and the main plane
Auxiliary cutting plane of the cutter is a plane perpendicular to the projection of the auxiliary cutting edge onto the main plane and the main plane. The main plane for a turning cutter is the lower supporting surface of the cutter rod (holder).
The following angles are considered in the main cutting plane: Fig. 5.
Rice. 5 Angles of the cutter in cutting planes.
a - the main relief angle is located between the main rear surface of the cutter and the cutting plane (the cutting plane is the plane tangent to the cutting surface at the point of contact with the main cutting edge).
Can have values from 6...12 0.
b - sharpening angle, located between the front and main rear surfaces. Its values depend on the magnitude of the angles a and g.
g - rake angle, located between the front surface and the normal to the cutting plane, can be positive and negative and
have values from -8 to +25 0.
d - cutting angle, located between the front surface and the cutting plane, is the sum of the angles (a + b).
In the auxiliary cutting plane, auxiliary angles a 1, β 1, γ 1, δ 1 are considered
When examining the through cutter from above (in plan), the following cutter angles are visible: (Fig. 5).
j - the main angle in the plan is located between the projection of the main cutting edge onto the main plane and the direction of the direct longitudinal feed. It determines the relationship between radial and axial cutting forces.
j 1 – auxiliary angle in plan is located between the projection of the auxiliary cutting edge onto the main plane and the direction of the reverse longitudinal feed. For finishing cutters j 1 → 0.
e - the angle at the tip of the cutter is formed by the intersection of the main and auxiliary cutting edges.
l - the inclination angle of the main cutting edge is located between the main cutting edge and a line drawn in the cutting plane through the tip of the cutter parallel to the main plane. (Fig.6), l is considered positive when the tip of the cutter is the lowest point of the cutting edge; negative when the tip of the cutter is the highest point of the cutting edge; equal to zero when the main cutting edge is parallel to the main plane. The angle of inclination of the main cutting edge determines the direction of chip flow; most often it is zero.
Rice. 6 Angle of inclination of the main cutting edge.
The considered cutter angles are static, i.e. their values are determined when the cutter and workpiece are stationary. During turning, the workpiece rotates and the cutter moves in a straight line, constantly curving the cutting surface (since the feed is constant), but the cutting plane is tangent to the cutting surface, so it rotates in space following the cutting surface, the amount of rotation depends on the feed rate.
Angles a and g are measured relative to the cutting plane, so their values change during processing. Angle a decreases and angle g increases.
Changes in a and g depend on the feed rate and workpiece diameter.
Control questions:
1. How are incisors classified according to their purpose?
2. What materials are used for the cutting part of the incisors?
3. What do the concepts mean – “right incisor”, “left incisor”?
4. How are incisors classified by design?
5. What angles of the cutter are considered in the main cutting plane?
6. What angles of the cutter are considered in the auxiliary cutting plane?
7. What angles of the cutter are located in plan?
8. Where is the rake angle of the incisor located?
9. How and why is the workpiece secured only in the chuck?
10. Why is there a need to secure the workpiece in the centers?
11. Is a conical surface formed if the upper rotating part of the support along with the cutter is rotated at a certain angle, but a mechanical longitudinal feed is used?
12. Why are cutters for processing internal surfaces installed parallel to the axis of the workpiece?
13. Why, before processing, is it necessary to touch the surface with the cutter and record the readings of the dial at this moment?
14. Why is the surface quality unsatisfactory when machining a conical surface using the upper rotating part of the caliper?
15. What can happen if cutting is done at a considerable distance from the chuck when securing a workpiece of small diameter only in the chuck?
Literature:
1. Gorbunov B.I. Metal cutting processing. – M.: Mashinostroenie, 1981. 287 p., ill. With. 17...20.
6. Technology of structural materials / A. M. Dalsky, I. A. Arutyunova, T. M. Barsukova, etc. Under the general direction. ed. A. M. Dalsky. M.: Mechanical Engineering, 1985.-448 p., ill. With. 446…470
Topic 3: Cutting Conditions
Target: Study the parameters that make up the cutting mode and their influence on the quality of processing.
1. Depth of cut.
2. Submission.
3. Cutting speed.
Turning of parts involves the use of different types of cutters: through, boring, threaded, shaped. They carry out roughing and finishing machining of part surfaces, internal sampling, and thread cutting. has many signs. They are structurally formed by the following main parts: a holder, a working head (for some types of cutters it can be replaceable).
Correct sharpening means giving a certain geometric shape to the cutter head - ensuring the required values of angular parameters.
The correct orientation of the cutting edge is determined by three planes. They have names established by standards: front, rear and additional (auxiliary).
Along the first, the movement of the resulting chips occurs. This is called the main back surface. The second is directed along the back surface of the incisor. It is called the auxiliary back surface. Both surfaces of the cutter are called edges. They are turned with the front side towards the workpiece. During sharpening, attention is paid to the characteristics of the meeting of both edges. Incorrect operation reduces the quality of processing. Leads to mechanical damage to the cutter.
Of particular interest is the point where the planes intersect, called the vertex. It bears the heaviest load.
The angles that determine the characteristics of the cutter are divided into the following categories:
- main ones (two);
- auxiliary (same amount);
- angles in plan or projection (three angles are considered).
The values of the listed indicators depend on the following characteristics:
- shape of the selected workpiece;
- purpose and design of cutters;
- specified processing quality;
- material of the cutting head (if it is removable);
- physical and mechanical characteristics of the metal product;
- allowable allowance;
- spindle rotation speed.
Structurally, cutters have four types:
- straight (their holder and head are located in two versions, along one axis or on two parallel axes);
- curved (has a curved holder);
- bent (deviated to the side from the direction of translational movement of the workpiece);
- retracted (the width of the head is smaller in size than the holder). The quality of the required operation plays a big role in the shape of the tip. They are divided into the following categories:
- rough processing (called stripping);
- semi-finish;
- finishing;
- precision (high accuracy).
When setting angles, pay attention to the feed side. The process can occur on the left or on the right.
The main plane is the plane oriented along the movement of the cutter. It is located perpendicular to the previous one - called the cutting plane.
The third is the auxiliary plane. Its trace determines the angles of the cutter. To obtain a high-quality product, attention is paid to the cutting angle and sharpening.
Principal angles
One received the name - the main front angle. The second one is called the main rear one.
Each influences the processing result:
- The first directly determines the quality of the surface being removed (the resulting chips). If it increases, increased deformation occurs in the upper layer. A low value allows the tool to remove excess metal much easier. Does not cause increased compression of this layer. Significantly facilitates the process of removing and draining excess metal.
- An increase in the numerical value of the second weakens the reliability of fastening the tool to the tool holder. Promotes an increase in the frequency and amplitude of vibrations. Changing the characteristics increases the wear rate of the cutter. Decreasing the value increases the contact area of the cutting edge with the machined surface. This leads to an increase in the temperature of the cutter.
Auxiliary angles
Located on the auxiliary plane. The first is formed by its angular difference with the direction oriented by the continuation of the cutting edge.
The second is the parameter formed by a straight line segment passing through the vertex and the surface of the edge location.
Plan angles
For they have the following names of plan angles:
- main angle;
- auxiliary;
- corner located at the apex.
The first is formed between the plane of the edge projection and the main plane of the tool.
The second is determined between the continuation of the projection of the cutting edge with a plane directed along the movement of the workpiece.
The third is between the first listed plane and the main plane.
The numerical values of the parameter located at the vertex can take positive and negative values. It turns out positive when the top of the sharpening point is at the lowest point of the workpiece. Minus sign - the peak reaches its highest point.
Measuring cutter angles
Each sample undergoes a procedure for measuring the listed characteristics. They are carried out using special measuring instruments. Use a table goniometer, or a mechanical one equipped with a vernier. The results obtained must be recorded in a journal.
The first type of meter allows you to determine the parameters of angles located on the main plane. Structurally, it consists of the following parts:
- massive base;
- stands with a moving template (to set the direction of the planes);
- measuring sector (equipped with a degree ruler);
- locking screw (to fix the received direction).
The sequence of measurements is carried out as follows. The selected sample is placed on the base. The surface of the edge is combined with one plane of the stand. The second is directed parallel to the edge being examined. The resulting values on the degree ruler are the value of the measured indicator. A prerequisite for carrying out measurements is to ensure a tight fit of the template to the corresponding surface of the cutter.
The measurement of such specific parameters as plan angles is carried out with a mechanical inclinometer equipped with a vernier. Its design includes the following main elements:
- two special sectors, each of which has its own angular scale;
- two independent measuring guides;
- special movable vernier.
The sequence of measurements is somewhat different from the sequence of operations of a desktop inclinometer.
To obtain the exact value of the parameter, it is necessary to accurately align one strip with the side surface of the case. The cutting edge should be directed parallel to the second bar. Numerical values are read using the existing built-in vernier. The obtained values are recorded in the documentation.
Geometry of turning tool.
Machining of parts on lathes is carried out with cutters, which, depending on the type of operation performed, can have different designs.
The cutter consists of two parts:
- working part (head)
- fastening part (holder)
Main elements of the cutting part Fig. (A):
1- Front surface 4. Main cutting edge
2- Main rear surface 5. Auxiliary dir. edge
3- Auxiliary back surface 6. Apex
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Basic turning tool angles
To determine the angles, four coordinate planes are adopted:
R v – main plane – the plane passing through the dir point. edges perpendicular to the direction of the velocity vector
R n – cutting plane – tangent to the cut. edge and perpendicular to the main plane.
R τ - main cutting plane - perpendicular to line p e cuttingPvAndPn(perpendicular to the cutting edge).
P s – working plane – the plane in which the vectors of the main movement and feed are located.
1) In the main cutting plane ( R τ ) The main angles of the cutter are measured:
γ - front angle - angle between the front surface and the main planeP v .
α – clearance angle – the angle between the flank surface and the cutting plane.
β – sharpening angle – the angle between the front and main back surface.
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2) In the main plane (Pv) measure plan angles:
φ - main angle in plan – the angle between the main cutting edge(Pp) and work plane (Ps)
φ` - auxiliary plan angle – angle between the working plane(Ps) and projections of the main and auxiliary cutting edges onPv.
ε – apex angle
3) In the cutting plane, the inclination angle of the main cutting edge is measured -λ- the angle between the cutting edge and the main planePv.
(+λ ;-λ; λ=0)
Positive (+λ) strengthens the cutting edge because the force falls not on the top, but on the stronger part of the cutting edge. (When finishing machining, λ is taken negative (up to -5°) so that the chips do not scratch the machined surface.
When roughing – vice versa (up to +5°)
The influence of turning tool angles on the cutting process
The angles of the cutting part of the tool have a greater influence on the cutting process. By correctly setting the angles, you can significantly reduce its wear, cutting forces, and power spent on the cutting process. The quality of the machined surface and processing productivity also depend on the angles.
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Front corner γ 10°…+30° |
Choose depending on: · Processed material · Instrumental material · Processing conditions Has the greatest influence on the cutting process. As γ increases, the work expended decreases. May on the cutting process, the conditions for coming off are improved chips, the quality of the processed surface increases. However, this reduces the strength of the blade, tool wear increases, retraction decreases heat. When arr. plastic and soft materials < γ - increase, and at arr. brittle and hard< γ -уменьшают. When arr. hardened steels with carbide cutters and intermittent cutting< γ делают отрицательным. |
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Main clearance angle α 6…12° |
Choose depending on: · Processed material · Instrumental material · Processing conditions Serves to reduce friction between the rear blade surface and cutting surface. When increasing< α, снижается прочность лезвия, therefore when choosing< α необходимо учитывать properties of the processed material and conditions cutting When arr. viscous metals< α – увеличивают, at arr. fragile materials<α – уменьшают. |
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Main plan angle φ 30…90 ° |
Affects the durability of the cutting tool and on surface roughness. As the angle φ decreases, the roughness of the workpiece decreases. surface, the length of the active part increases dir. edges (width of the cut layer), which leads to reducing thermal and force load on the cutter Consequently, the wear of the instrument is reduced. However, at small angles φ increases greatly component of the cutting force pushing the cutter away from blanks. Vibrations may occur. At φ=90° |
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Auxiliary approach angle φ` 5…30 0 |
Serves to reduce auxiliary friction back surface against the surface being processed. With decreasing<φ`- уменьшается шероховатость surface, increases the strength of the blade tip and tool wear is reduced. <φ`=5…10°(при обр. жестких заготовок) <φ`=30…45°(при обр. нежестких заготовок |
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Main cutting edge angle λ -5…15 0 |
Determines the direction of chip flow · if λ=0- the chips come off perpendicularly main cutting edge. · if λ - (+)- the tip of the cutter is the lowest point of the cutter, place of initial contact further from the top, higher durability. Chips flow towards the machined surface (rough processing). · if λ-(-)- the chips go to the processed surfaces(finishing). |
The influence of the cutter installation during processing on the angle values.
The value of the angles α and γ changes during the cutting process when the cutter tip is positioned above or below the axis of rotation of the workpiece. Angles φ and φ` - depending on the location of the cutter axis relative to the workpiece axis.
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Of all the types of turning tools, the most common are the through cutters. They are designed for turning external surfaces, trimming ends, ledges, etc.
The prismatic body of a walking cutter (Fig. 1), like any other, consists of a cutting part (head) and a holder. The cutter head contains a front 1, main back 2 and auxiliary back 3 surfaces. The intersections of these surfaces form the main 4 and auxiliary 5 cutting edges.
Rice. 1. Structural elements of a turning tool:
1 – front surface; 2 – main rear surface;
3 – auxiliary rear surface; 4 – main cutting edge;
5 – auxiliary cutting edge
The chips removed by the cutter flow along the front surface. The main flank surface faces the cutting surface formed by the main cutting edge, and the auxiliary flank surface faces the machined surface of the part.
The specified surfaces and cutting edges after sharpening are located at certain angles relative to two coordinate planes and the feed direction, selected taking into account the kinematics of the machine.
Two mutually perpendicular planes are taken as coordinate planes (Fig. 2):
1) the cutting plane passing through the main cutting edge and the cutting speed vector tangent to the cutting surface;
2) the main plane passing through the same edge and the normal to the cutting speed vector.
There is another definition of the main plane: this is the plane passing through the vectors of the longitudinal Spr and radial Sp feeds; in a particular case, it may coincide with the base of the cutter, in which case it is possible to measure the angles of the cutter outside the machine in its static position.
Rice. 2. Geometric parameters of a continuous turning tool
For the cutting speed vector, in relation to cutters, as well as to many other tools, the vector of the peripheral speed of the part is taken without taking into account the longitudinal feed vector, which is many times smaller than the peripheral speed vector and does not have a noticeable effect on the magnitude of the front and rear angles. Only in certain cases, in relation to drills, for example, at points of the cutting edges adjacent to the drill axis, does this influence become significant.
In Fig. Figure 2 shows the plan view of the workpiece and the cutter and the geometric parameters that must be indicated on the working drawings of the cutters: γ, α, α1, φ, φ1. Below are definitions and recommendations for the purpose of their values.
The front and rear angles of the main cutting edge are usually measured in the main cutting plane N–N, which runs normal to the projection of this edge onto the main plane, which in this case coincides with the plane of the drawing. The N–N plane was chosen due to the fact that it is in it that the metal deforms during cutting.
Rake angle γ is the angle between the main plane and the plane tangent to the front surface. The magnitude of this angle has a decisive influence on the cutting process, since the degree of deformation of the metal during the transition to chips, power and thermal loads on the cutting wedge, the strength of the wedge and the conditions for heat removal from the cutting zone depend on it. The optimal value of the rake angle γ is determined experimentally depending on the physical and mechanical properties of the processed and cutting materials, cutting mode factors (V, S, t) and other processing conditions. Possible values of the angle γ are in the range 0...30°. To strengthen the cutting wedge, especially those made of brittle cutting materials, a chamfer with a zero or negative rake angle (γf = 0...–5°), width f, depending on the feed, is sharpened on the front surface.
Relief angle α is the angle between the cutting plane and the plane tangent to the rear surface. This is actually the clearance angle that prevents the flank of the cutter from rubbing against the cutting surface. It affects the wear rate of the cutter and, in combination with the angle γ, affects the strength of the cutting wedge and the conditions for heat removal from the cutting zone.
The less load the cutting wedge experiences and the stronger it is, the greater the value of angle a, the value of which depends, therefore, on the combination of properties of the processed and cutting materials, on the feed rate and other cutting conditions. For example, for high-speed steel cutters during roughing of structural steels α = 6...8°, for finishing operations α = 10...12°.
Angle of inclination of the main cutting edge λ- this is the angle between the main plane drawn through the tip of the cutter and the cutting edge. It is measured in the cutting plane and serves to protect the tip of cutter A from chipping, especially under impact load, and also to change the direction of the flowing chips. The angle λ is considered positive when the tip of the cutter is lower compared to other points of the main cutting edge and is the last to come into contact with the workpiece. In this case, the chips move in the direction of the machined surface (from point B to point A), which can significantly increase its roughness. During roughing, this is acceptable, since it is followed by a finishing operation that removes these irregularities. But during finishing operations, when the load on the cutting wedge is small, the task of removing chips from the machined surface becomes of paramount importance. For this purpose, negative angle values (–λ) are assigned. In this case, the tip of the cutter A is the highest point of the cutting edge, and the chips flow in the direction from point A to point B.
The presence of the angle λ complicates the sharpening of cutters, so the practical values of this angle are small and range from λ = +5...–5°.
Plane angles φ and φ 1 (main and auxiliary)– these are the angles between the direction of the longitudinal feed Spr and, accordingly, the projections of the main and auxiliary cutting edges onto the main plane.
The principal angle φ determines the relationship between the thickness and width of the cut layer. As the angle φ decreases, the chips become thinner, heat dissipation conditions improve, and thereby the tool life increases, but at the same time the radial component of the cutting force increases.
When turning long workpieces of small diameter, the above can lead to their deformation and vibration, and in this case φ = 90° is assumed.
– during finishing φ = 10...20°;
– when roughing shafts (l/d = 6...12) φ = 60...75°;
– when roughing harder workpieces φ = 30...45°.
Passing cutters usually have an angle φ1 = 10...15°. As the angle γ1 decreases to 0, the value of h also decreases to 0, which makes it possible to significantly increase the feed rate, and therefore the productivity of the cutting process.
The auxiliary relief angle α1, measured in the section N1 - N1, perpendicular to the auxiliary cutting edge, is taken approximately equal to α; α1 forms a gap between the auxiliary flank surface and the machined surface of the workpiece.
The auxiliary rake angle γ1 is determined by sharpening the front surface and is usually not indicated in the drawing.
In order to increase the strength of the cutting part of the cutter, the rounding radius of its tip in plan is also provided: r = 0.1...3.0 mm. In this case, a larger radius value is used when processing hard workpieces, since with an increase in this radius, the radial component of the cutting force increases.
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