SUSPENSION BUSHES UNDER TEST

Contributing editor Rex Narraway went along to Rivercircle to look at a new machine for the automotive industry

In its role as a manufacturer of special-purpose equipment and tooling, largely within the automotive industry, the Peterborough-based firm Rivercircle has designed a machine to perform a sizing operation and carry out a bond-test on car front suspension bushes. The original contract to build the machine was awarded by Metzeler (UK). The machine complements earlier equipment supplied by Rivercircle but incorporates more up-to-date control circuitry.

The suspension bush that is being sized and tested on the machine resembles an anti-vibration unit in that it comprises an inner steel tube vulcanised to an outer steel sleeve, thus creating a thick rubber mantle between the two parts. The actions of the machine include an initial check to establish that no rubber has been deposited within the inner bore during manufacture, followed by a swaging process which squeezes the outside diameter to the correct size, a bond test on the rubber mantle, and a final gauging-to-size on both outer and inner diameters. From the instant that a component is introduced to the first station by the hopper, to its acceptance at the end of the cycle, takes 12s.

After being vulcanised, the suspension bushes are fed to the hopper on the machine via a large vibratory bowl feeder and are held in a small queue above the first station where they are supported by a wedge-shaped tip formed on the rod of a pneumatic cylinder. Actuation of this cylinder allows the components to be fed, one at a time, into the test station where their presence is detected by an inductive proximity sensor. The component undergoing test on that station is clamped in position by the action of the rod of another cylinder which applies a thrust across the outer diameter and moves a location gate in front of the sleeve to prevent any axial movement while testing takes place.

To check for a clean bore, designers at Rivercircle devised a special-purpose ball gauge which is driven forward to penetrate the inner tube of the bush, and the component is deemed to have passed this test when the gauge has moved through a distance of 70mm. At this point, the rod of the clamping cylinder and the location gate are removed to allow the accepted component to be transferred to a Finn-Power P20M swager. In the event of a component not passing the initial test – that is: that the motion of the ball gauge is restricted by debris – a signal to a third cylinder on this station causes an escapement mechanism, mounted below the component, to open and allow it to fall into the reject chute.

The ball gauge has been designed with a cylindrical clamping arrangement which involves two spring-loaded segments mounted on Belleville washers and serves as the main fixture for the bush as it is moved through the machine. Its movement is effected by attaching the gauge to the end of a long cylindrical rod which acts as a transfer bar and is supported by a phosphor bronze bearing, mounted approximately at the mid-point of its travel along the axis. The segmented section of the ball gauge grips the inner surface of the suspension bush but allows the inner tube to butt up firmly against a location shoulder formed by the end of the transfer bar. The transfer bar carries the ball gauge, complete with the component attached, from the initial testing station into the swager for sizing and bond testing, then into the final gauging station and out of the machine.

The motion to provide the three strokes that allow the component to pass through these stations in sequence is controlled by a pair of pneumatic cylinders fitted in a back-to-back configuration. They are mounted so that the rod of the first is connected to the carriage block which drives the transfer bar forward, while the rod of the second is rigidly connected to the side of the machine. The first of these units is an SMC stroke-reading cylinder with a graduated scale etched into the rod. In addition to providing the final stroke to eject the bush from the machine, this acts as the movement sensing element used in the bond test. The earlier two strokes are provided by a second cylinder.

When the initial debris test is complete, the suspension bush is transferred to a position inside the jaws of the swager which can be set to produce diameters with an accuracy of 0.1mm. After swaging to size, a pneumatic cylinder brings down a hinged plate on which a Powerlok hydraulic `Miniram’ has been mounted. The hydraulic cylinder operates along the axis of the machine with the tip of the rod resting on the end of the transfer bar.

By means of a solenoid valve, the exhaust of the measuring cylinder is opened to allow any ambient air to escape and hydraulic pressure is applied to the Miniram. This thrusts the inner tube of the bush forward inside its rubber mantle, using the compressive forces generated by the swager to restrain the outer sleeve, while the actual deflection is logged by the controller of the measuring cylinder and is displayed on a digital readout. A correctly bonded component will allow an axial deflection in the rubber of no less than 9mm between the inner tube and outer sleeve.

When the bond test has been completed, the bush is released from the compressive force of the swager while the exhaust of the measuring cylinder is closed so that the unit can be activated to produce the final stroke. Under this action, the component is moved forward to locate in a three-fingered infeed guide where it automatically clicks into position behind an arrangement of three spring-loaded pawls. At this point, the travel of the transfer bar is reversed to remove the ball gauge to the initial station where it is ready to receive the next suspension bush while leaving the earlier one in situ within the infeed guide. On completion of its cycle through the swager, each suspension bush forces the earlier one out of the infeed guide, into the final gauging station, and takes up its own position behind the spring-loaded pawls.

While in the final gauging station, the suspension bush is located between two in-line sleeves leaving a length of the outer sleeve accessible for monitoring by two inductive proximity sensors and receiving two fixed calliper gauges which have been mounted overhead at 45 degrees to the vertical. Each of the gauges contains `Go’ and `No-go’ features to ensure that the swager has produced the specified outside diameter and is activated by a pneumatic cylinder. The gauges also provide an inspection test for roundness. A plug gauge, also with `Go’ and `No-go’ features, is applied by a third cylinder, mounted along the axis, to measure the inside diameter in case it has become distorted during the swaging process.

When the next bush is transferred from the swager, the component that has just undergone inspection is forced from the sleeves into the output chute. If any component proves to be out-of-spec, as verified by the bond deflection test or by the outer and inner diameter gauges, a pneumatic cylinder opens a diverter inside the main chute and re-directs the part to a reject chute.

Figure 1: To check for a clean bore, designers at Rivercircle devised a special-purpose ball gauge which is driven forward to penetrate the inner tube of the bush, and the component is deemed to have passed this test when the gauge has moved through a distance of 70mm

Figure 2: The transfer bar carries the ball gauge, complete with the component attached, from the initial testing station, first: into the swager for sizing and bond testing, then into the final gauging station and out of the machine

Figure 3: The machine did not warrant the cost of using an ASI system. Instead, a less-costly valve terminal was supplied as a pre-wired and tested monoblock including the PLC, I/O and solenoid valves

{{RivercircleTel: Peterborough (01733) 315101Enter 470

SMCTel: Milton Keynes (01908) 563888Enter 471