Cutting Tool Design

1 calculation and design of round drawing

Stretching is one of the most effective methods of machining, which allows you to obtain products of high accuracy (up to the 6th quota) and roughness of the treated surface up to 0.32 microns. Drawing is also the most productive metal cutting. The high pull performance is due to the large total length of the cutting edges simultaneously involved in metal cutting. Stretching is mainly used in large-scale and mass production, but this method is also successfully used in small-scale production and even single production, when stretching is the only possible or most economical method of processing.

Different types of draws are used as a cutting tool in sweeps. A pulling tool is a multi-blade tool with a series of successive blades in a direction perpendicular to the direction of the main movement speed, designed for processing in a translational or rotational main cutting movement and the absence of feed movement.

Sweep is used to treat internal (open) surfaces. Accordingly, internal and external rails are distinguished. A variety of links are piercings, the design of which is not fundamentally different from the design of the links, however, during the cutting process, piercings are mainly subjected to compressive forces, while the links work for tension. The applications of the sweep are very diverse. Internal drawing is used for treatment of holes of various shapes, including round, square, polyhedral, splined ones with splines of different profile, as well as key and other slots. The external draws mainly treat flat and shaped surfaces, slots, ledges, corrugations, etc.

Advantages of the sweep process:

1) high productivity, since during cutting the allowance is removed simultaneously by several teeth, while the active length of the cutting edges is very long, although the cutting speed is low (6... 12 m/min). For example, when pulling a hole with a diameter of 30 mm simultaneously with five teeth, the width of the cut layer is about 470 mm. Overall, stretching performance is 312 times higher than other treatments;

2) high accuracy (JT7... JT8) and low roughness (Ra 0.32... 2.5) of the treated surfaces due to the presence of draft, finish and calibrating teeth, and in some designs of bracing and ironing teeth. Stretching replaces milling, construction, countersinking, deployment, and sometimes grinding;

3) high resistance of the tool, calculated by several thousand parts. This is achieved due to optimal cutting conditions and large overflow reserves;

4) simplicity of machine design, since there is no feed movement during drawing, therefore the machines do not have feed boxes, and the main movement is carried out using power hydraulic cylinders.

The disadvantages of trails include:

1) high labor intensity and cost of the tool due to the complexity of the drawing structures and high requirements for the accuracy of their manufacture;

2) rails are special tools designed for the manufacture of parts of only one type;

3) high costs of rework due to the complexity of the structures of these tools.

The following features of their operation shall be taken into account when designing the rails:

1) the rails experience very high tensile loads, so the internal rails are necessarily checked for strength along the weakest sections;

2) the chips cut during drawing must be freely placed in the chip grooves during the entire time of the cutting teeth in contact with the workpiece and freely leave the groove after the cutting process stops. Therefore, the placement and separation of chips in width requires a lot of attention. So, for example, when pulling round holes, annular chips are not allowed, because it would take a long time to release them;

3) the length of the rails shall correspond to the working travel of the drawing machine, as well as to the capabilities of the equipment for their thermal and mechanical treatment. The rails must have sufficient rigidity during manufacture and operation, so lunettes and other devices are sometimes used in drawing.

Of all the varieties of internal carts, the most used (up to 60%) were carts for the treatment of round holes, therefore, the basis for the design of these carts will be discussed below. For other types of rails (faceted, splined, external), only the distinctive features of calculating their cutting part will be considered.

Despite the variety of internal carvings, their various varieties contain basically the same structural elements as carvings for processing round holes.

Drawing features. The rails consist of the following main parts: shank, neck, front and rear guides, cutting and calibrating parts, rear shank (Fig. 3.2).

The shank is used to connect the link to the cartridge of the machine. The main types and dimensions of shanks are standardized (GOST 404470). At the same time, the diameter of the shank should be less than the diameter of the extension hole by 1.. 2 mm.

The neck and the next transition cone perform an auxiliary role. Their length should provide the possibility of connecting the pulling to the cartridge before the start of pulling. Transition cone allows free entry of front guide into hole to be pulled. The diameter of the neck is made less than the diameter of the tail by 0.3... 1.0 mm.

The front guide serves to center the axis of the workpiece with respect to the pulling axis before pulling in order to avoid skewing of the workpiece, which can lead to breakage of the pulling or damage of the treated surface. The length of the front guide shall be equal to the length Lo of the hole to be pulled, and at long lengths - not less than 0.6L0. The shape of the front guide must correspond to the shape of the hole in the blank, and the tolerance for the diameter of the guide is taken along e8.

The rear guide performs the same role as the front guide, preventing the drawing from skewing when its calibrating part leaves the treated hole. It is slightly smaller in length than the length of the front guide, and its diameter is made more precisely, with a tolerance as per IT7. The shape of the rear guide shall be the same as that of the extended hole.

The shape of the rear guide shall be the same as that of the extended hole.

In order to automatically return the pulling to its original position after pulling, especially at large length and diameter of the pulling, a rear shank is sometimes provided after the rear guide, which is fixed in the cartridge of the carriage of the machine, and which is similar in shape to the front shank. The presence of the rear shank also prevents the drawing from sagging and skewing in the hole and avoids distortion in the shape and size of the processed hole.

The cutting (working) part of the pulling serves to remove the allowance and form the surface of the extended hole. It contains rough and finished, and in the group cutting scheme there are also transition teeth located on the stepped-conical surface. The length of the cutting part is equal to the product of the number of teeth per their pitch, which, in turn, depends on the requirements for the accuracy of the hole being pulled, the roughness of its surface and the amount of allowance to be taken. Tooth diameters are calculated based on the accepted cutting scheme.

The calibrating part contains 4... 10 teeth of the same diameter, equal to the diameter of the last finish tooth, and serves to calibrate the hole, reduce the scattering of its dimensions, and is also a reserve for reeling: as the finish teeth wear, the calibrating teeth can be sharpened to the finish teeth, thereby increasing the overall life of the draw.

The sizing teeth of the allowance are not cut, but remove the micro-irregularities of the surface remaining after the passage of the finishing teeth, and provide the direction of drawing in the hole.

The design of the cutting part of the pulling is determined by the accepted cutting scheme, which means the accepted order of sequential cutting of the allowance.

The following cutting schemes are distinguished:

a) according to the method of dividing the allowance by thickness and width - single and group;

b) according to the method of forming the treated surface - profile, generator and combined.

Let's consider the first two diagrams using the example of processing round holes.

The single cutting scheme is characterized by the fact that each cutting tooth cuts a certain thickness allowance along the entire perimeter of the treated hole due to the fact that the diameter of each subsequent tooth is more than the diameter of the previous one by 2az, where az is the lift or supply to the tooth (az = Sz).

Conclusion

During the course work, the design and calculation of the geometric parameters of the round drawing were carried out. Also, the spur shank was calculated, the parameters in the initial section were calculated, the drawing dimensions on the front surface were carried out.

check calculation.

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