Mechanical component pressing is a standard technique, widely employed in industrial processes. Wherever products containing numerous components are mass produced in factories, there is usually a requirement for some of the components to be pressed mechanically to fit other components.

Such components may be of metal or of plastics.

Currently methods of pressing, which have been used for many years, involve hydraulic or fly pressing techniques.

For example, in one technique, say for inserting a bearing into another component, to ensure that the bearing is stopped in an accurate position in relation to the other component, pillars are provided as stops for a hydraulic ram when it reaches the desired position. However, wear and tear will eventually result in inaccurate positioning.

In another technique, the bearing itself is used as a stop for the hydraulic ram movement. For this method in relation to an aluminium component, heating of the component to say 200°C is required to facilitate insertion of the bearing without damaging the aluminium component. The heating step is inconvenient and, if the aluminium component is not heated to a desired temperature damage can be caused to the aluminium component.

Another known pressing technique using a hydraulic ram relies on machinery of the other component to achieve accurate positioning of the bearings. The additional machinery step increases costs.

Conventional hydraulic assembly presses require pressing speeds to be controlled by the hydraulic pump, which is difficult to do consistently and accurately.

An object of this invention is to provide an improved press for use in assembling components.

According to the present invention there is provided a press comprising a ram arranged for linear movement, means for moving the ram linearly and means for monitoring pressing load exerted by the ram during a pressing operation.

The ram is preferably arranged for sliding linear movement. The ram is preferably mounted on a rotatable screw, whereby rotation of the screw causes the ram to move relative to a support.

A preferred arrangement of the press of the invention has the ram mounted on a screw connected to a motor, preferably via a gear box, the screw being supported in a threaded member, such as a threaded nut or sleeve, whereby rotation of the screw causes the assembly of the screw, ram and motor to move relative to the threaded member. The ram preferably has its side edges slidable in sides of a supporting frame.

The means for monitoring the pressing load is preferably a load cell and the load cell is preferably linked to a computer for recordal of the pressing loads.

The threaded member is preferably mounted on a secondary slide assembly movable between a pair of stops, one of which has the load cell.

When the press assembly contacts a part to be pressed, the threaded member will be caused to move oppositely so that it or a part associated therewith abuts the load cell. As the pressing load increases the load cell is compressed. The loads measured by the load cell can be recorded and held on a database for use in controlling like pressing operations. Of course, a desired pressing load can be pre-set and the load cell used to control the pressing operation, so that the pre-set load is not exceeded.

The press assembly is preferably counterbalanced, such as by means of a weight connected via say wires and pulleys to the press assembly, whereby the threaded member or part associated therewith can always be pushing against the load cell.

The preferred mounting of the load cell is in a linear movement arrangement, so that the load cell will not experience side loads, which would otherwise distort the load readings or even damage the load cell.

The press of the invention typically utilises a ball screw, planetary gearbox and a servo motor for its press assembly. Other preferred features of the presses of the invention includes the following: the speed of rapid advance of the press can be programmed (0.01mm per minute to 7500mm per minute); the speed of the pressing stroke can be programmed (0.01mm per minute to 1500mm per minute); the speed of the pressing mode can be changed, e. g. when pressing rubber seals, slower start speed allows the rubber to reshape itself before full insertion and so stops tearing of the rubber; the load that is being exerted on components may be monitored at all times; more than one press stroke, at different loads in one operation may be undertaken; and the ram of the press does not rotate, as is normal with a conventional hydraulic press. This enables complicated shaped tooling to be used without the need of a die set.

The preferred press of the invention is a mechanical press linked to a programmable, computer controlled unit providing ultra-high accuracy and sensitivity of control.

Preferably electronic measurement of load is available at all times during the press cycle.

The press measurement of load may be collecte on a machine controller and stored for records. These records can then be down-loaded to a central database using, for example, RS 232 RS 485 or Ethernet or modem for Internet.

A preferred machine control system has input facilities for barcode readers and other scanning devices, so that the recorded results can be referenced to specific components.

A preferred control system allows the operator to set limits of the load required to press components and will provide an alarm if components are out of tolerances.

The press of the invention may also be set so that, after a reject is detected, it will not restart until the operator completes a secondary operation e. g. place reject into a receptacle that senses its presence or simply presses a reset button.

The complete press cycle is preferably programmable for speed and load, (e. g. forward 50mm at 100mm/sec. Change to 1 mm/sec for 10mm with a maximum load of 5000kg. Change direction, returning at 2mm/sec for 10mm, followed by rapid return home.) The final position of the press is preferably ajustable by typing a new position from a keypad of the machine control system. The speed of the press is preferably pre-adjustable throughout the press cycle. The final position for the component being pressed may be load-controlled.

The speed of movement of the press can be constant, unlike hydraulic presses, which heat up and speed up.

This invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figures 1 to 4 show schematically prior art hydraulic presses; Figure 5 shows schematically a press according to the invention; Figure 6 is a further schematic diagram of a press according to the invention; Figures 7,8 and 9 are respectively corner, front and side elevations of a press according to the invention; and Figures 10 and 11 are front and side elevations of load cell assembly for the press of Figures 7 to 9.

Referring to Figure 1 of the accompanying drawings, a hydraulic press 10 has a ram 12 shown being used for pressing a bearing 14 into a water pump casing 16. The ram has a large ring 18 fitted thereto and a set of pillars 20 which act as stops for the ring 18 and hence the ram when the bearing 14 has been pressed into its desired position.

In Figure 2 hydraulic ram 30 is shown performing the same operation as shown in Figure 1. However, there is a stop 32 on pressing table 34 for the bearing 14. The pump casing being of aluminium has to be heated to about 200°C to expand it sufficiently to enable the bearing 14 to be pressed into it without causing damage.

The Figure 3 arrangement uses the pump face 16 as a stop for hydraulic ram 40 to ensure that the bearing 14 is positioned correctly. Thus, the full load of the press is exerted through the pump casing, which can cause damage thereto.

Figure 4 of the drawings shows a conventional hydraulic assembly press 60, wherein rapid approach speed is controlled with a valve trigger and change to a lower speed for pressing by means of a pilot valve 62. Press speed is controlled by throttling down the hydraulic oil returning to the oil reservoir.

All of the above have various disadvantages as described above in the preamble.

Turning now to Figures 5 to 11, an assembly press 70, shown performing the same operation as in Figures 1 to 3, comprises a ram 72, a ball screw 74 for moving the ram vertically as shown by the arrow Z, a load cell 76 for monitoring the pressing force and a control unit 78. The control unit 78 is or is linked to a computer and includes a display monitor 80 and input keyboard 82.

The press can be set so that, if the pressing force is not within pre-set parameters an alarm signal is generated.

The control unit can be used to program the press for the following: a) rapid approach speed of the ram; b) speed of pressing operation; c) final position of the ram and the end of a pressing stroke; and d) retract speed of the ram.

The stopping position of the press is controlled and set by the computer control unit enabiing the pressing load to be monitored.

In more detail (see Figure 6) the ram 72 is mounted on ball screw 74, which is driven by servo motor 84 through gearbox 86 and bearing unit 88. The ball screw 74 extends through threaded nut 90 on a slide mounting 92. The slide mounting 92 is on a fixed component 94 of the press. At opposite ends of the slide mounting 92 are stops 96 and 98 and stop 98 includes the load cell 76.

The ram 72 is slidably mounted in the press support frame 100 and is counterbalanced by weight 102 connected to the ram by wires 104 over pulleys 106.

The ram of the press is a rigid box section construction with linear guide ways that support and guide the ram. The ram preferably has four support bearings on the centre line of the press which can eliminate leverage on the bearings when the press is under load.

The rigid design of the press enables the press stroke to be four times longer than that of a conventional hydraulic press.

The ram of the press does not rotate like hydraulic presses, which can make tooling of the press for integrated shapes simpler and less expensive.

For easy repair the whole of the ram head assembly can be removed from the press frame by removal of retaining bolts 110. The head assembly can be interchanged with other heads, so that repairs can be effected quickly and efficiently.

The ram head assembly is counterbalanced to pull the head up, so that the ram is always pushing against the load cell.

By avoiding use of hydraulic power, the press of the invention is environmentally friendly, in that it only needs to use power when called for.

The press operates in the following manner. The motor rotates the screw 74 which causes the ram to move downwards relative to the nut 90.

The ram assembly being counterbalanced causes the nut to slide up to contact the load cell 76. When the ram exerts a pressing force on the bearing 12 being pressed into the pump casing 14, the load cell is compressed by the nut and the loads applied are measured and recorded.

Once the desired position of the bearing is achieved, the load measurements recorded can be used to set the press for repetitive operations of the same type. Furthermore, incompatible load measurements can indicate a fault allowing remedial action to be taken.

The design of the press of the invention is such that the load cell does not need to experience any lateral or side loads, which can cause inaccurate readings or even damage to the load cell.