RU2519708C1 - Expanding mandrel - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: expanding mandrel includes a spindle with an external conical surface, a replaceable elastic element in the form of a sleeve with slots, which can be moved relative to conical surface in axial direction and fixed by fasteners. The part is equipped with a washer rigidly installed on the spindle; the sleeve is made from friction material and has longitudinal slots taken out to different end faces and alternating with each other; an external sleeve profile is identical to an internal profile of a mounting hole; when the part is being installed, the sleeve can be moved in axial direction by the value at which conditions are met, which correspond to the specified mathematical relationship.

EFFECT: improving processing quality of long parts.

2 dwg

Description

The invention relates to machine tool industry, and in particular to tooling for machining parts on metal cutting machines, and can be used in the processing of parts with a central hole, for example bushings, on the outer surface and at the ends for one installation, mainly on turning and circular grinding machines.

Known mandrel for the finishing of parts, containing a stepped roller, on which are placed a fixed stop flange and a clamping mechanism, made in the form of an expanding collet, nut and washer. In this case, the collet hole is made with a conical section, and the mandrel is equipped with a conical sleeve with a conical section on the outer surface, designed to interact with the conical section of the collet hole (RF patent No. 2119409, IPC B23B 31/40, publ. 09/27/1998).

The device has the following main disadvantages:

- the installation of the part is carried out on the end surface and the Central hole, which makes it impossible to install the workpiece, such as stamping, without preliminary machining of the base surfaces;

- the device does not have the ability to base parts with a central conical hole.

Known expandable mandrel containing a spindle with an outer conical surface, an elastic element in the form of a sleeve having a cylindrical outer and inner conical surface, and the outer surface is formed by cylindrical surfaces of different diameters. Slots are made on the sleeve, forming zones with a small cross section along which the sleeve is deformed. The sleeve slides onto the conical surface with a nut through a quick-change washer. The sleeve slides with a conical hole on the conical surface of the spindle and is deformed in places having the smallest section, as a result of which the part is centered on the axis of the spindle and fixed on the mandrel (RF patent No. 2030257, IPC B23B 31/40, publ. 10.03.1995, prototype).

This mandrel for installing and securing the workpieces provides a more accurate and reliable in comparison with the known solutions base and fastening of parts. It allows for one installation to process in addition to the outer surface of the parts and their ends, including the execution of both external and internal chamfers, as a result of which the accuracy of the location of the surfaces of the workpiece is ensured.

The prototype has the following main disadvantages:

- the elastic deformation of the sleeve occurs in zones having a small cross section, as a result of which its resistance is low;

- there is no possibility of basing and fastening parts significantly exceeding the length of the elastic sleeve, i.e. processing of long parts is not feasible;

- there is no possibility of calculating and selecting the necessary and sufficient clamping forces of the part on the mandrel;

- the device does not provide for mounting parts with a conical inner hole;

- the device does not protect against dynamic loads in the machine-tool-tool system that occurs during the cutting process.

The objective of the invention is the provision of the possibility of high-quality machining of long parts having increased hardness of the surface layer, for example, an alpha layer on titanium billets, at a low accuracy (large tolerance) of their landing hole having a conical or cylindrical surface.

The technical result is the ability to apply the proposed mandrel not only for finishing, but also for roughing of parts or workpieces, and without preliminary preparation of their landing holes, due to the rational placement of the seating surfaces of the mandrel, the use of friction materials and the regulation of the clamping forces of the part, allowing to reduce dynamic loads in the machine-tool-tool-system, including when processing products with a hardened surface layer.

The specified technical result is achieved by the fact that the expandable mandrel contains a spindle with an outer conical surface, a removable elastic element in the form of a sleeve with slots, while the sleeve moves axially relative to the conical surface and is fixed with fasteners, a rigidly mounted washer and sleeve are additionally placed on the spindle made of friction material and has longitudinal slots facing different ends and alternately alternating with each other, the outer profile of the sleeve is identical to morning profile bore, the sleeve parts during installation is moved in the axial direction by an amount at which the conditions are satisfied, the formula:

Mtr = K

where Mtr is the friction moment that occurs when the part is clamped between the contacting surfaces of the sleeve and the part’s bore hole, kg · m,

K = 1.5-2.5 - safety factor,

Msopr - the total moment of resistance of cutting forces, kg · m.

Figure 1 shows an expandable mandrel with a workpiece mounted on it; figure 2 - in isometric elastic sleeve.

The expanding mandrel contains a spindle 1, having at one end a mounting device 2, near which the washer 3 is placed, and at the other end, a threaded part 4, near which the outer conical surface 5 is made on the spindle. The outer conical surface of the spindle is mated with the inner conical surface of the sleeve 6 The longitudinal grooves are made on the sleeve 7. The clamping device consists of intermediate washers 8, a set of small split washers 9, a large split washer 10, a continuous washer 11, and nuts 12.

The spindle by means of the installation device 2 is clamped into the cam cartridge of a lathe (not shown). A replaceable sleeve 6 is installed on the conical surface 5 depending on the length, diameter and profile of the bore hole of the workpiece 13, it is fixed with washers 8 and 11, slightly tightened by nuts 12.

After installing the part 13 on the washer 3, the sleeve 6, the mandrel spindle is pressed by the tailstock quill (not shown). Then the part 13, by tightening the nuts 12, is centered relative to the axis of the spindle 1 and clamps motionlessly on the sleeve 6, while the inner conical surface of the sleeve 6 slides along the conical surface 5, unclenching the sleeve due to the grooves 7. The clamping forces are regulated by the selection of the number of split washers 9, subject to conditions:

Mtr = K

The continuous washer 11 and nuts 12 protect against accidental spontaneous disassembly of the part with the mandrel, ensuring the safety of the machinist.

Replacement of the workpieces is carried out with the help of a puller when removing the quill and holding the mandrel in the machine cartridge.

The use of friction material in the sleeve allowed the rotational movement of the part to be transmitted through friction, which allows smooth adhesion at different speeds. The design of the mandrel cannot transmit through itself a greater moment than the moment of friction forces, due to the fact that slipping of the sleeve relative to the workpiece begins. Therefore, this design protects the machine-tool-component-tool system from dynamic overloads arising, for example, from unevenly hardened surface layer, which improves the quality of the workpiece and the durability of the system.

Due to the presence of longitudinal slots extending to different ends and alternately alternating between each other, the sleeve is pressed uniformly with radial force to the inner surface of the hole of the workpiece, reliably fixing and centering it on the mandrel.

The presence of the outer profile of the sleeve, identical to the internal profile of the bore hole, allows you to process parts not only with cylindrical, but also with conical bore holes.

The moment of friction that occurs when the part is clamped between the contacting surfaces of the sleeve and the part’s bore hole, which exceeds the total moment of resistance of the cutting forces by 1.5–2.5 times, allows, on the one hand, to securely fix the workpiece and, on the other hand, minimize dynamic loads in the machine-tool-tool system.

The proposed mandrel was used for machining the flange part and the outer punching surface of VT6 titanium alloy with a maximum outer diameter of 232 mm, a length of 450 mm, an internal taper bore with a largest diameter of 141 ± 2 mm, and a weight of 32 kg on a M163 screw-cutting lathe. The end and outer surfaces were subjected to processing for visual inspection for the absence of pressed folds, hollow cracks and other inclusions in the starting part of the stamping. The estimated total moment of resistance of the cutting forces Msopr = 18 kg · m, the estimated moment of friction that occurs when the part is clamped between the contacting surfaces of the sleeve and the bore of the part, Mtr = 36 kg · m.

The proposed expanding mandrel for installing and securing the workpieces provides a stable process for processing long parts, the mounting holes of which are of low accuracy, the parts themselves have uneven increased strength and hardness of the surface layer, and it is possible to process their ends in addition to the outer surface of the part in one installation.

Claims (1)

An expanding mandrel containing a spindle with an outer conical surface, a replaceable elastic element in the form of a sleeve with slots, which can be moved relative to the conical surface in the axial direction and fixed with fasteners, characterized in that it is provided with a washer rigidly mounted on the spindle, while the sleeve is made of friction material and has longitudinal slots extending to different ends and alternately alternating with each other, the outer profile of the sleeve is identical to the internal profile of the landing hole, and the sleeve when installing the part has the ability to move in the axial direction by an amount that is determined by the conditions corresponding to the dependence:
Mtr = K
where Mtr is the friction moment that occurs when the part is clamped between the contacting surfaces of the sleeve and the part’s bore hole, kg · m;
K is the safety factor equal to 1.5-2.5;
Msopr - the total moment of resistance of cutting forces, kg · m.

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