GB2200313A - Pneumatic ejector for pressed components - Google Patents

Abstract

A pneumatic lifter or ejector (10) for components formed in presses includes a piston/cylinder unit (15) of which the piston rod (20) carries an engaging member (23) designed to engage the cushion (3) of the press tool with the purpose of lifting the pressed component (7) from the tool ram (1). Connected to the engaging member (23) is a cylindrical bearing bush (30) received in a corresponding bore (29) in a guide bush (9) in the press tool and which fits around the cylinder (14) of the piston/cylinder unit (15) with minimum radial clearance over substantially its whole length. The bearing bush (30) has radial holes (33) containing solid lubricant. <IMAGE>

Description

Pneumatic Ejector for Pressed Components The invention relates to a pneumatic ejector for components formed in power presses,of the kind in particular for deep drawing presses, designed for mounting in a recess in a press tool and including a pneumatic piston/cylinder unit with which is associated a linear guide means acting in the direction of operation of the piston/cylinder unit and of which the piston rod carries an engaging member which is designed to engage the pressed component or a cushion of the press tool for the purpose of ejecting the pressed component from the tool.

Such ejectors engage the pressed component immediately after the pressing operation in order to free it from the press tool and to ease its subsequent removal. In other cases the ejectors engage the cushion of the press and lift it after the pressing operation, thus only acting on the pressed component indirectly.

A preferred field of use of the invention is in high speed bodywork press tools used on deep drawing presses which are capable of operating at forty to fifty strokes per minute. On every working stroke each of the ejectors which are present has to complete a stroke of the order of magnitude of 50 to 80mm.

In this operation there must neither be any tilting nor any jamming. If the press or more important, if an entire production line is brought to a halt on account of the inadequacy of even a relatively small item such as a press ejector the consequential damage and cost can be substantial. The standards set for reliability of such ejectors are therefore very high and are difficult to fulfil when one takes into account the conditions of loading, involving a number of strokes of relatively long travel following each other in rapid succession.

In one known ejector for pressed components of the kind described there are guide rods which lie on diametrically opposite sides of the pneumatic piston/cylinder unit, and they are mounted on the engaging member which engages the pressed component, the guide rods being guided in bushes connected to the piston/cylinder unit so that the guiding of the engaging member as tha piston/cylinder unit operates is trouble-free and does not leave the piston/cylinder unit itself behind. Only with such provisions of additional guiding of the engaging member can adequate reliability be achieved.

However, the presence of the lateral guide rods present in addition to the piston/cylinder unit and the associated guide bushes restricts the introduction of such pneumatic ejectors only to those situations where in practice sufficient space is available in the press tool. Unfortunately in many cases this is not present for various structural and design reasons.

The aim of the invention is to arrange in a more compact form a pneumatic ejector for pressed components of the kind set forth in the introductory paragraph above whilst retaining effective guiding of the engaging member.

This problem is solved according to the invention by the features that the linear guide means is formed by a cylindrical bearing bush connected to the engaging member and designed for insertion in a corresponding bore in the press tool, the bearing bush enclosing the cylinder of the piston/cylinder unit with radial clearance over a length which is equal to at least the stroke of the piston/cylinder unit plus a supporting length equal to at least the outside diameter of the bearing bush.

By virtue of the bush hardly any more space is needed for guiding the engaging member than for the piston/cylinder unit itself. The ejector as a whole is a cylindrical structure of a diameter which exceeds the diameter of the piston/cylinder unit itself by only the amount of the wall thickness of the bush plus the necessary clearance. In this way the recess in the press tool to receive the unit can be made of simple cylindrical form and furthermore a very effective guiding over a large supporting surface is obtained, with correspondingly low surface loadings.

The length of the bearing bush is determined primarily by the stroke of the piston/cylinder unit.

When the piston/cylinder unit is fully extended the bush must still have a sufficient support present to prevent tilting. Practical experience has shown that this is the case when the supported length corresponds to at least the diameter of the component which is guided, i.e. in this case the bush. In this way the overall length of the bush corresponds substantially to the overall length of the piston/cylinder unit itself.

As materials for the bearing bush one can consider any of those materials which have sufficient mechanical strength combined with long-term lubricating qualities.

In one embodiment the bush can be in the form of a metal matrix with lubricant distributed evenly over it. The metal matrix can be porous or honeycombed and can contain the supply of lubricant in its cavities, sufficient for operation over a long period. An arrangement has been found particularly satisfactory in which solid lubricant, for example graphite or molybdenum disulphide, is arranged in radial holes or bores in the wall of the sliding bush, either extending right through it or extending in only from one side. Such an arrangement of a sliding bush is in itself part of the state of the art.

Preferably the bearing bush fits onto the outside of the engaging member, which is forms the itself secured on the projecting end of the piston rod.

The invention extends also to the construction of a press tool equipped with at least one pneumatic ejector of the kind defined above.

As high standards with regard to surface finish and tolerances are set for the guide bore in the press tool for co-operating with the bush, it is preferred to form the bore in a separate guide bush.

An embodiment of the invention by way of example is illustrated in the accompanying drawing, which shows a vertical partial section through one side of a press tool in the form of a deep drawing tool with an ejector in accordance with the invention.

The press tool includes a ram 1 co-operating with an upper tool 2. The ram 1 is surrounded by a cushion or shoulder 3 which rests on an outer part 4 of the tool 1, this part being connected to the ram 1. The cushion 3 is separated from the outer part 4 of the tool at a plane 5 and can be lifted away from it in the direction of the arrow 6 in order to detach the pressed component 7, for example a deep-drawn bodywork component, from the ram 1 when the ram moves downwards away from the upper tool 2, and to ease the unloading of the pressed component 7 by automatic equipment (not shown).

In the outer part 4 of the tool there is a stepped bore 8, of which the axis is parallel to the direction of stroke 6 of the press and is perpendicular to the plane 5. Seated in the inner portion of the bore 8 is a guide bush 9 for receiving an ejector for the pressed components, indicated generally at 10. The guide bush 9 has a flange 11 at its upper end secured to the outer part 4 by screws 12 indicated only diagrammatically, so that the guide bush 9 is secured in the stepped bore 8 in an axial direction. The upper face of the flange 11 does not project beyond the plane 5.

The stepped bore 8 has a narrower portion 8' below it, provided with a screw thread, into which is screwed the end cap 13 of a piston/cylinder unit indicated generally at 15. The end cap 13 closes the lower end of the cylinder 14 of the unit 15 apart from an inlet 16 for compressed air, which can be introduced through a connection 17 and a feed pipe 18. The piston 19 of the piston/cylinder unit 15 carries an upwardly extending piston rod 20 which passes through the upper end cap 21 of the cylinder 14 and carries on its outwardly projecting end a cylindrical portion 22, parallel to the axis, of an engaging. member indicated generally at 23, secured to the end of the piston rod 20 by a grub screw 24. The engaging member 23 in the embodiment illustrated has a pin-shaped projection 26 engaging in a bore 25 in the cushion 3.The shape of the engaging member in this region could however be of constructionally different form. For example in other situations it may be of advantage for the upper end of the engaging member 23 to be forked.

Engaging the outer surface of the cylindrical portion 22 is the upper end of a linear sliding bearing bush of cylindrical shape, which is indicated as a whole at 30 and which extends over practically the entire length of the piston/cylinder unit 15 and of which the inner surface 31 provides a minimum clearance around the outer surface of the cylinder 14. The outer surface 32 of the bearing bush 30 is ground to a high degree of precision and co-operates with a correspondingly finished bore 29 in the guide bush 9, with only a very small degree of clearance necessary for the sliding movement.

The wall of the bearing bush 30 has over its entire surface uniformly distributed holes 33 of a few millimetres diameter, in which is embedded a solid lubricant forming a long-term lubricant reservoir for lubricating the longitudinal movement of the bush 30 in the bore 29.

When pressure is applied below the piston 19 through the pipe 18 the piston rod 20 is extended upwards and takes with it the engaging member 23 and thereby the cushion 3 as well as the bush 30. The bearing bush 30 and thereby the cushion 3 are guided laterally in the guide bush 9 so that the piston/cylinder unit 15 is relieved of any lateral forces which arise during the lifting process.

During the stroke of the piston 19 the interior space of the cylinder 14 above the piston is vented to the space 28 outside the cylinder through an opening 27 so that there is no resistance offered from this cause.

In contrast to a spring ejector, the travel of the ejector 10 takes place with a constant force over the whole stroke. When the pneumatic pressure is cut off the cushion 3 sinks under its own weight to return to the starting position illustrated in the drawing, the air returning from the outer space 28 through the opening 27.

Claims (8)

Claims

1. A pneumatic ejector for pressed components in presses, in particular for deep drawing presses, designed for mounting in a recess in a press tool and including a pneumatic piston/cylinder unit with which is associated a linear guide means acting in the direction of operation of the piston/cylinder unit and of which the piston rod carries an engaging member which is designed to engage the pressed component or a cushion of the press tool for the purpose of ejecting the pressed component from the tool, in which the linear guide means is formed by a cylindrical bearing bush connected to the engaging member and designed for insertion in a corresponding bore in the press tool, the bearing bush enclosing the cylinder of the pistpn/cylinder unit with radial clearance over a length which is equal to at least the stroke of the piston/cylinder unit plus a supporting length equal to at least the outside diameter of the bearing bush.

2. An ejector for pressed components according to claim 1 in which the bearing bush comprises a metal matrix with embedded lubricant distributed uniformly over its surface.

3. An ejector for pressed components according to claim 2 in which the bearing bush has radial holes with solid lubricant embedded in them distributed over its surface.

4. An ejector for pressed parts according to any one of claims 1 to 3 in which the engaging member includes a cylindrical portion secured on that end of the piston rod which projects from the cylinder and on which portion the associated end of the bearing bush fits.

5. A press tool, in particular a deep drawing tool, equipped with at least one pneumatic ejector for the pressed components arranged in a recess in a tool,and constructed in accordance with any one of claims 1 to 4, the recess being formed by a bore in the tool.

6. A pressed tool according to claim 5 in which a guide bush is arranged in the bore for receiving the bearing bush.

7. An ejector for pressed components in presses, substantially as described with reference to the accompanying drawing.

8. A press tool equipped with at least one pneumatic ejector according to claim 7, the ejector being received in a recess in the tool.