GB2074490A

GB2074490A - Tailstock Centre in Cutting and Rolling Machine

Info

Publication number: GB2074490A
Application number: GB8109015A
Authority: GB
Original assignee: NII TEKHNOL TRAKTOR I SELSKOKH
Current assignee: NII TEKHNOL TRAKTOR I SELSKOKH
Priority date: 1980-04-25
Filing date: 1981-03-23
Publication date: 1981-11-04
Also published as: IT1170919B; DE3107365A1; JPS56163802A; FR2481167A1; SU1032669A2; GB2074490B; IT8148345A1; DE3107365C2; IT8148345A0; FR2481167B1; JPH0244641B2

Abstract

A headstock centre 6 and a tailstock centre 7 support a workpiece 8. A tool head 3 and a head 4 with deforming rollers 5 spaced equidistantly apart along a circumference are consecutively arranged in a housing 2 fitted on the carriage 1 of a machine tool. A length of the tailstock centre 7 contiguous in operation end-to-end with the workpiece 8 serves as a guide for the rollers 5, being given a diameter substantially equal to the diameter to which the rollers 5 are set, and its end next to the workpiece has a chamfer or groove to accommodate the point of the tool 9 in a position preparatory to machining. The centre 7 may have a centreing cone 32 engaging a smaller diameter end part of the workpiece 8. The axial holding pressure is produced by a hydraulic cylinder 47. The headstock and tailstock may have flexible portions in their centres to allow lateral workpiece movement for high precision machinery. <IMAGE>

Description

SPECIFICATION Machining of Cylindrical Surfaces The present invention relates to apparatus for machining workpieces with a cylindrical surfaces, such as shafts, piston rods of hydraulic actuators, and axles. The apparatus can be employed in the automotive, tractor, and agricultural machine industries, and in road machinery building, for example.

The invention provides a contrivance for the machining of cylindrical surfaces on machine tools having headstock and tailstock centres to support the work placed therebetween, a tool head, and a head with deforming rollers spaced equidistantly apart all the way along a circumference, the head being consecutively arranged in a housing mounted on the carriage of a machine tool, a length of the tailstock centre contiguous in operation face to face with the work and serving as the guide for the deforming rollers is given a diameter virtually equal to the diameter set at which are the deforming rollers, and its end facing the work is adapted to accommodate the point of the tool in a position preparatory to machining.

It is expedient that the tailstock centre is shaped cylindrically, at least within the length serving as the guide for the rollers, and has an axial blind bore containing a spring-loaded centering cone. The tailstock in such a form ensures reliable fixing of shafts and effective machining of shafts which are of a low mass and which have an end portion of smaller diameter with a central hole.

Alternatively the tailstock centre is provided, at least within the length serving as the guide for the rollers, with a spring-loaded cylindrical sleeve and a centering cone contained therein. This may advantageously be used in machining highmass shafts with a central hole in an end portion of smaller diameter. In operation, the tailstock centre will be always pressed against the end face of the workpiece due to the action of the spring without a play even if the linear dimensions of the central hole are variable.

In one embodiment, the end of the tailstock centre which is contiguous with the end face of the workpiece in the course of machining is provided with a chamfer at the outside diameter to accommodate the tool point in its position preparatory to machining. Alternatively, the end of the tailstock centre which is contiguous with the end face of the workpiece is provided with an annular groove, preferably not wider than three millimetres, to accommodate the tool point in its initial position preparatory to machining. To provide the chamfer or groove for the tool point is a simple operation requiring no effort.

It is expedient that the end of the said length of the tailstock centre which is contiguous with the end face of the workpiece is provided with a rearward converging taper to receive a chamfered end of the workpiece. The use of chamfer as a datum surface ensures precise positioning of the workpiece with respect to a lathe spindle and, as a result, high accuracy of machining.

It is possible that a portion of the tailstock centre (and also the headstock centre) is given a stiffness which is less than elsewhere, the lowstiffness portion of the tailstock centre being located behind the length serving as the guide for the rollers. The provision of a low-stiffness portion minimizes the effect of an erroneous setting of the workpiece at the datum surface and of the tailstock and the apparatus as a whole relative to a lathe spindle.

Preferably, the tailstock centre is movably linked with the mobile member of a hydraulic piston-and-cylinder device so as to be capable of axial travel. This arrangement ensures constant optimum effort to be applied for the clamping of the workpiece during machining so as to prevent slip at the headstock centre and to eliminate the possibility of bending.

The apparatus is operationally reliable and enables a surface to be machined in one set-up, in spite of being of a comparatively simple construction, without sacrificing quality. Practical implementation of the invention will reduce machine tool outlay and productive area requirements, and will increase labour productivity at the same time.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic general view, partly cut away, of apparatus for the machining of the external cylindrical surface of a workpiece; Figure 2 is a view of a tailstock with a springloaded centering cone, the tool head and rollers being in an initial position; Figure 3 is a view of a tailstock centre with a spring-loaded cylindrical sleeve and a centering cone; Figure 4 is a view of a tailstock in another embodiment; Figure 5 is a view of a solid tailstock centre with a rearward converging internal taper; and Figure 6 is a view of tailstock and headstock centres with low-stiffness sections.

A plate 1 (Figure 1) is secured to the carriage (not shown) of a lathe. A housing 2 secured to the plate 1 contains a tool head 3 and a head 4 with deforming rollers 5, the heads being consecutively arranged in the direction of axial feed indicated by arrow S. A headstock centre 6 and a tailstock centre 7 support a workpiece 8 between them for machining.

The tool head 3 accommodates a tool 9 attached to a slide 10 fitting into guides 11 provided in the housing 2. The slide 10 is linked with a drum 13 by a tie rod 12, and the drum can be turned in a supporting slide 14 by means of a handle 15. The drum 13 has a curvilinear groove receiving the lower end of the tie rod 12 and serves the purpose of speedily withdrawing the slide 10 integrally with the tool 9 after, or setting it preparatory to, machining.

The tool 9 is set for a given turning diameter with the aid of a slide 14 which can be actuated by a handwheel 17 through the intermediary of a kinematic pair 16 consisting of a nut and a screw.

The setting of the tool 9 is monitored by means of a dial gauge 18 whose input is connected to the slide 10.

The head 4 contains a cage 19 with slots accommodating the rollers 5, which are spaced equidistantly apart all the way around the circumference and rest on a supporting cone 20 fitted inside the housing 2. A spring 21 provided in the housing 2 automatically sets the cage 19 integrally with rollers 5 at a driven turning diameter. The axial loads coming into play during turning are sustained by a thrust bearing 22. The rollers 5 are set at the given turning diameter with the aid of a nut 23 which, engaging with its male thread a female thread cut in the housing 2, acts upon a ring 24 also contained in the housing 2.

A ring 25 of elastic material fitted in the cage 19 serves to prevent leakage of lubricant-coolant out of the zone of surface rolling. A cover plate 26 at the side of the head 4 facing the tool head 3 keeps chips out of the zone in which the rollers 5 are arranged to operate.

The tailstock centre 7 is of a revolving type, fitting into a poppet sleeve 27 of the tailstock 28 resting on the frame 29 of the lathe, and is given, over some length, a diameter virtually equal to the diameter at which the rollers 5 are set. The said length should be sufficient to accommodate the housing 2, enabling the tool 9 to be set at the end face of the workpiece 8 as shown in Fig. 2; the tailstock centre 7, serving as the guide for the rollers 5, abuts the end face of the workpiece 8, enabiing the rollers to contact the work in a gradual way so as to ensure high precision of machining.To facilitate the setting of the point of the tool 9 into the initial position preparatory to machining, a chamfer 30 (Fig. is provided at the outside diameter of that end of the tailstock centre 7 which is contiguous with the workpiece 8.

To cope with the turning of a workpiece 8 which has a low mass and an end of a smaller diameter with a central hole, the tailstock centre 7 is provided with a hollow cylindrical portion 31 having a blind bore containing a centering cone 32 acted upon by a spring 33. The outside diameter of the cylindrical portion 31 is virtually the same as the diameter at which the rollers 5 are set.

To enable the turning of a workpiece 8 which is chamfered at its end face contiguous with the cylindrical portion 31, the latter is provided with a rearward converging taper 32a at its inner diameter.

To cope with the turning of a workpiece 8 which has a high mass and an end of a smaller diameter with a central hole, the tailstock centre 7a (Fig. 3) in an alternative embodiment is provided with a cylindrical sleeve 34 and a centering cone 35. The diameter of the cylindrical sleeve 34 is again virtually equal to the diameter at which the rollers 5 are set. A spring 37 serving to press the sleeve 34 against the end face of the workpiece 8 during turning is fitted on the centering cone 35 between the poppet sleeve 27 and a retainer 36.

To facilitate the setting of the point of the tool 9 into the initial position in another embodiment, an annular groove 38 (Fig. 4) is provided at the end of a cylindrical sleeve 34a of the tailstock centre 7b, which is contiguous with the end face of the workpiece 8 in the course of turning. By virtue of the small width of this groove, which preferably does not exceed 3 mm, the rollers 5 are smoothly transferred from the tailstock centre 7b to the workpiece 8.

To enable the turning of a workpiece 39 (Fig.

5) which is only chamfered at an end, in another embodiment the tailstock centre 40 is given a rearward converging internal taper 40a and is of a diameter virtually equal to the diameter at which the rollers 5 are set; a chamfer 41 cut at its end at the outer diameter serves to accommodate the point of the tool 9. Alternatively, an annular groove similar to that described above with reference to Fig. 4 can be cut at the end of the tailstock centre to accommodate the point of the tool 9.

To provide for high precision of work, in another embodiment a section 44 of a headstock centre 42 (Fig. 6) and a similar section 44 of the tailstock centre 43 are of a stiffness which is less then elsewhere. The section 44 of the taiistock centre 43 is arranged behind a section 45 which is of a diameter virtually equal to the diameter at which the rollers 5 are set and serves as the guide thereto. The diameter of the sections 44 is less than that of the section 45.

The low-stiffness sections can be provided in any other way suitable to that end. They minimize the effect of an erroneous setting of the work at the datum surface or of a misalignment of the tailstock 28 and the headstock 46 is well as of the housing 2 integrally with the tool head 3 and the head 4 with the rollers 5 relative to the spindle of the lathe.

A hydraulic cylinder 47 (Figs 1 and 4) fitted to the tailstock 28 serves to provide a constant optimum effort for the clamping of a workpiece. A movable member of the cylinder 47, its piston rod 48 (Fig. 4), is movably linked with the tailstock centre.

The apparatus disclosed is provided with a system for feeding the lubricant-coolant which is neither described nor shown in the drawings, since it is not directly relevant to the present invention. The apparatus operates on the following lines.

On placing a standard workpiece between the headstock centre 6 and a tailstock centre 7, the tool 9 is fed through a given cutting depth, using the handwheel 1 7. The amount of travel of the tool 9 is noted on the dial gauge 18, the tool 9 is speedily withdrawn into the inoperative position by turning the handle 15, and the standard workpiece is removed from the centres 6 and 7.

The housing 2 with the heads 3 and 4 is moved back into the initial position, and a workpiece 8 is placed between the headstock centre 6 and the tailstock centre 7, being then clamped by the constant effort due to the pressure in the hydraulic cylinder 47. The rollers 5 are set so as to provide for a given turning diameter of the workpiece 8 by rotating the nut 23 which displaces the cage 19. As a result, the rollers 5 contact the cylindrical portion 31 of the tailstock centre 7, whose diameter is virtually equal to the diameter at which the rollers 5 are set. The tool 9 is in a position between the end face of the work 8 and the contiguous end of the tailstock centre 7.

Upon setting the tool 9 into the cutting position by means of the handle 1 5, the workpiece is set rotating, the system feeding the lubricant-coolant is set into operation, and so is the drive of the lengthwise feed. The tool 9 starts cutting, and the rollers 5 begin to move around the guide surface of the tailstock centre 7, functioning as a follow rest system which prevents chattering and ensures precision turning.

When the housing 2 has travelled through a distance equal to that between the point of the tool 9 and the apices of the rollers 5, these come up to the workpiece 8 and begin the operation of plastic deforming thereof at a given pressure (interference) without ceasing to function as the follow rest.

At the end of the pass, the tool 9 is rapidly withdrawn into the inoperative position, using the handle 15, whereas the rollers 5 proceed with their job to the end of the pass, where the supporting cone 20 moves them apart, clearing of the setting. The length with feed and spindle drive are then brought at rest, the feed of the lubricantcoolant is discontinued, and the housing is returned to the original position together with the heads 3 and 4, the rollers 5 staying clear of the workpiece 8. The workpiece is then removed from the machine tool.

A pilot model of a universal lathe embodying the above-described apparatus has been used to turn steel shafts in a single pass to quality requirements between IT6 and 1T1 7. The degree of surface roughness has varied between 0.1 and 0.16 microns.

Claims

1. Apparatus for machining a workpiece with a cylindrical surface, comprising headstock and tailstock centres to support the workpiece between them, a carriage movable along the workpiece, a tool head, and a forming head with rollers spaced equidistantly on a circumference, the heads being mounted at longitudinally spaced position on the carriage, in which a length of the tailstock centre contiguous in operation end-toend with the workpiece serves as a guide for the rollers and its end facing the work is adapted to accommodate the point of a tool carried by the tool head in a position preparatory to machining.

2. Apparatus as claimed in claim 1, in which the tailstock centre has an axial blind bore containing a spring-loaded cone.

3. Apparatus as claimed in claim 1, in which the tailstock centre a spring-loaded cylindrical sleeve slidably mounted on a centering cone.

4. Apparatus as claimed in any of claims 1 to 3, in which the said end of the tailstock centre is provided with a chamfer at its circumference to accommodate the point of the tool in a position preparatory to machining.

5. Apparatus as claimed in claims 1 to 3, in which the said end of the tailstock centre is provided with an annular groove to accommodate the point of the tool in a position preparatory to machining.

6. Apparatus as claimed in claim 5, in which the groove is not wider than 3 mm.

7. Apparatus as claimed in any of claims 1 to 6, in which the said end of the tailstock centre is provided with a rearward converging internal taper.

8. Apparatus as claimed in claim 1, in which the tailstock centre has a portion of reduced stiffness located behind the said length.

9. Apparatus as claimed in any of claims 1 to 8, including a hydraulic piston-and-cylinder device having a fixed member and a movable member which is linked with the tailstock centre to impart axial motion thereto.

10. Apparatus as claimed in any of claims 1 to 9, in which the said length of the tailstock centre has a diameter substantially equal to the diameter to which the rollers are set.

11. Apparatus for machining a workpiece with a cylindrical surface, substantially as described with reference to, and as shown in, Figure 1 and any of Figures 2 to 6 of the accompanying drawings.

12. A method of machining a workpiece with a cylindrical surface, in which apparatus according to any preceding claim is used, the diameter of the said length of the tailstock centre being substantially equal to the final diameter of the workpiece.