GB2257077A

GB2257077A - A control system

Info

Publication number: GB2257077A
Application number: GB9213781A
Authority: GB
Inventors: Gordon Robert Blakemore
Original assignee: HYDRO MARINE SYSTEMS Ltd
Current assignee: HYDRO MARINE SYSTEMS Ltd
Priority date: 1991-06-29
Filing date: 1992-06-29
Publication date: 1993-01-06
Anticipated expiration: 2012-06-29
Also published as: GB2257077B; GB9213781D0

Abstract

The control system for friction welding apparatus comprises a hydraulic motor (1) and a hydraulic ram (2). The control system provides a number of sensors (14, 15, 16, 17 and 18) mounted in the apparatus which monitor variables of the apparatus and send signals to a control means (19) and processing means (21). The processing unit (21) controls the variable via the control means (19) in response to signals received from the sensors. The apparatus is portable and adapted to be used in an underwater environment. <IMAGE>

Description

"A Control System" This invention relates to a control system and in particular, a control system for friction welding apparatus.

Friction welding is a welding technique which is particularly advantageous for carrying out welding operations underwater as it relies on relative movement between the workpieces to create the weld and does not require an electrical discharge which can be difficult to control and isolate in an underwater environment.

The technique involves rotating a first workpiece which is typically in the form of a metal stud at a very high speed and then bringing the first workpiece into contact with a stationary second workpiece. The friction between the relatively rotating workpieces creates sufficient heat energy to melt the metal at the rotating interface and after sufficient metal has been melted the rotational power to the first workpiece is stopped while still urging the first workpiece on to the second workpiece. This pressure is maintained to forge the workpieces together and until the interface between the workpiec#es is no longer plastic.

Since about 1970 "portable" friction welding machines have been developed for use underwater so that the welding machines man be easily manipulated to the weld site by either a diver or a remote operated vehicle (ROV). It is common in these machines to use a fluid to power the machines either by using a pneumatic driven system or a hydraulic driven system.

One conventional hydraulic friction welding machine uses fluid flow and pressure to drive a motor which rotates the first workpiece, the delivery of hydraulic fluid to the motor being controlled by an on/off shuttle valve. The hydraulic fluid can also be made to operate a ram which forces the rotating first workpiece on to the second workpiece. As with the valve for the motor, the valve for the ram also comprises a on/off shuttle valve. Typically, the pressure exerted by the ram is set by a manually operated pressure control valve and motor speed is set by a manually operated flow control valve. Hence, when the weld cycle is initiated using this machine the motor can be switched on and off and the ram switched forward/backwards to bring the workpieces into contact with each other.

However, a major disadvantage of this previous hydraulic friction welding machine has been that the ram pressure and the motor speed have to be preset while the machine is on the surface and cannot be altered after the machine has been submerged. This means that if there is a change in oil viscosity, for example by a change in the ambient temperature and/or pressure, there is a corresponding, uncontrolled, change in both the speed of the motor and the pressure exerted by the ram from the original preset values.

This can be a serious draw back as an ambient temperature and pressure change will generally always occur when the machine is submerged and taken to the depth where the welding operation is to be carried out.

In addition, with this previous machine it is impossible to intentionally vary the motor speed and ram pressure during the weld cycle, as these are preset at constant values before the machine is submerged and cannot be reset without returning the machine to the surface. This can lead to particular problems when attempting to weld aluminium and exotic metals.

In accordance with the present invention, a control system for friction welding apparatus comprising mounting means for mounting a first workpiece on the apparatus, a motor to rotate the first workpiece on the apparatus and a translation means to move the first workpiece in a direction substantially parallel to the axis of rotation of the first workpiece, the system comprising at least one sensor mounted on the apparatus to monitor a variable of the apparatus, control means mounted on the apparatus to adjust the variable or another variable of the apparatus and a processing unit coupled to the at least one sensor and the control means, wherein the processing unit controls the variable or other variable via the control means in response to signals received from the at least one sensor.

The invention has the advantage of providing a control system which enables variables of a friction welding machine to be controlled and varied during the weld cycle.

Preferably, the control system comprises a number of sensors and the control means comprises a number of control devices which adjust a number of different variables of the apparatus under the control of the process unit in response to signals from the sensors.

Preferably, the translation means comprises a ram device.

Typically, the at least one sensor comprises one of a motor speed, a ram pressure or a ram position sensor and preferably, where there are a number of sensors, there is a sensor for each of motor speed, ram pressure and ram position.

Preferably, the control system is for use with friction welding apparatus which is powered by a fluid and in this case there is preferably, provided a motor pressure sensor to monitor the pressure of fluid driving the motor and a system pressure sensor to monitor the inlet pressure of the fluid into the apparatus. Preferably, the fluid is a hydraulic fluid.

However, it is possible that the fluid could be a pneumatic type fluid, such as air or another suitable gas.

Typically, a sensor and a control device is provided for each variable to be monitored and controlled, respectively.

Typically, where the friction welding apparatus is powered by a fluid, the control means comprises a control device to control fluid flow to the motor, a control device to control fluid pressure to the ram and a control device to control the direction of fluid flow to the ram in order to control the direction of linear movement of the ram device.

Preferably, the control device for the motor comprises a proportional forward/reverse flow control valve and preferably, the control device for the ram fluid pressure comprises a proportional pressure control valve and the control device for the ram fluid flow direction may comprise a forward/reverse shuttle valve.

Preferably, the friction welding apparatus is portable and typically, is designed to be used in an underwater environment.

In one example of the invention the processing unit may be at a remote location from the friction welding apparatus and connected to the friction welding apparatus via an umbilical connection, such as an electrical or fibre optic umbilical. Alternatively, the processing unit could be mounted on the apparatus or the processing unit could comprise two sub-units, one mounted on the apparatus and the other at a remote location. The two sub-units being connected by an umbilical.

Preferably, an input device and an output device are connected to the processing unit to enable an operator to monitor and modify the variables, as appropriate.

An example of a control system for friction welding apparatus will now be described with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram of a control system for controlling hydraulic friction welding apparatus; Figs. 2a to 2d are flow diagrams depicting the operation sequences of the control system shown in Fig. 1; Fig. 3 shows graphs of speed, ram pressure and burn off versus time for a weld cycle of conventional friction welding equipment; Fig. 4 shows graphs for speed, ram pressure and burn off versus time in a first example of a weld cycle for the system shown in Fig. 1; and, Fig. 5 shows graphs of speed, ram pressure and burn off versus time in a second example of a weld cycle which may be obtained using the apparatus shown in Fig. 1. Fig. 1 is a schematic diagram showing a control system for a hydraulic friction welding machine.The friction welding machine comprises a hydraulic motor 1 and a hydraulic ram 2. The hydraulic fluid is supplied to the machine through an inlet 3 from a hydraulic fluid power supply (not shown) and the hydraulic fluid is returned to the hydraulic power supply via an outlet 4.

The inlet 3 is connected via a hydraulic line 5 to the hydraulic ram 2 via a valve 6 which controls the hydraulic fluid pressure exerted on the ram 2 and which is typically, a proportional pressure control valve.

The fluid is also supplied via a valve 7 which controls the direction of fluid flow through the hydraulic ram 2 and hence controls the direction of movement of the hydraulic ram. Typically, the valve 7 is a forward/reverse shuttle valve. A hydraulic line 8 from the hydraulic ram 2 passes the fluid from the hydraulic ram 2 to the outlet 4.

A hydraulic line 9 passes fluid from the inlet 3 to a valve 10 which is typically, a proportional forward/reverse flow control valve. The valve 10 controls hydraulic fluid flow through a line 11 to the motor 1. A by-pass line 12 is also provided which enables fluid to be diverted directly to the outlet 4 via a line 13 without the fluid passing through and therefore driving, the motor 1. The fluid from the motor 1 also passes along the hydraulic line 13 to the outlet 4 and returns to the hydraulic fluid power supply.

The control system for controlling the friction welding machine described above comprises a number of sensors 14, 15, 16, 17, 18 which monitor variables of the friction welding machine and send signals to a control computer 19 via sensor and control lines 20. The sensors 14-18 consist of a system pressure sensor 14 which senses the hydraulic fluid pressure at the inlet 3; a motor pressure sensor 15 which senses the pressure of the hydraulic fluid in the hydraulic line 11 immediately before it enters the motor 1; a motor speed sensor 16 which senses the speed of rotation of the motor 1; a piston position sensor 17 which senses the position of the hydraulic ram 2; and, a ram pressure sensor 18 which senses the pressure being exerted by the ram on workpieces (not shown) during a weld cycle.

The control computer 19 is also connected to a top side processor 21 via a main electrical or fibre optic umbilical 22. The control computer 19 is also connected to the valves 6, 7, 10 via the control lines 20 so that the valves 6, 7, 10 may be controlled via the top side processor 21 and the control computer 19 in response to signals received from the sensors 14-18.

Figs. 2a to 2d show flow diagrams which illustrate the operation of the control system shown in Fig. 1. Fig.

2a shows a routine for control of the hydraulic ram 2, Fig. 2b shows a routine for control of the motor 1 and Figs. 2c and 2d are flow diagrams of sub-routines for the routines shown in Figs. 2a and 2b.

In operation, an operator sets up the control system while the friction welding machine is still above water level and inputs the desired weld characteristics of the particular weld cycle to be performed into the control computer 19 via the topside processor 21 which comprises a display 23 and a keyboard (not shown).

With the friction--welding machine still the surface the operator then instructs the processor 21 and the control computer 19 to perform a test sequence which involves running the motor for five seconds, applying forward ram movement, reading the position of the ram 2 at touch down and returning the ram 2 to the start position. The processor 21 verifies via the display 23 that all settings are per the required weld cycle to be used during the welding operation.

The welding machine is then submerged and taken to the site where the welding is to be carried out.

Typically, the machine may be mounted on a ROV or may be manoeuvred into position by a diver. When the welding apparatus is in position the operator on the surface commences the weld cycle by entering an appropriate command into the processor 21 which in turns sends a signal along the umbilical 22 to the control computer 19. The weld sequence is commenced by opening the valve 10 to permit fluid to flow along the hydraulic line 11 to the motor 1 in order to drive the motor 1. The speed of rotation of the motor 1 is monitored by the control computer 19 using the routine shown in Fig. 2b. The sub-routine shown in Fig. 2c is used to continuously update and display the motor speed on the display 23 at the surface.

When the motor reaches the required speed the control computer 19 commences the flow diagram sequence shown in Fig. 2a for the hydraulic ram 2. If there are any sudden dramatic changes in the signals from any of the sensors 14-18 then this could indicate a problem with the apparatus and the weld sequence enters the sub-routine shown in Fig. 2d which aborts the weld sequence by switching off 49 the motor and sending 50 information on the aborted weld sequence from the control computer 19 via the umbilical 22 to the top side processor 21 for display on the display 23.

When the weld sequence is commenced the signal from the sensor 16 is read at step 30 in the flow diagram in Fig. 2b. If the control computer 19 determines that the motor is rotating at the required speed then the sub-routine in Fig 2c is entered and the motor speed is sent 31 to the surface for display on the display 23.

If the motor is not rotating at the required speed then the control computer 19 determines 23 from the sensor 16 whether the motor is rotating too fast. If the motor is rotating too fast then the control computer reduces the flow 33 to the motor 1 by closing the valve 10. If the motor 1 is not rotating too fast then the control computer 19 determines that the motor 1 must be rotating too slowly and increases the flow 34 to the motor 1 by opening the valve 10. The control computer 19 continuously repeats the routine shown in Fig. 2b and when the motor reaches the required speed of rotation the routine shown in Fig. 2a is commenced by the control computer 19. After the routine shown in Fig. 2a is commenced, the control computer 19 continues to periodically monitor the motor speed using the routine of Fig. 2b until the weld cycle is completed.

In the routine of Fig. 2a the control computer 19 initially reads the ram pressure 35 by reading the signal from the sensor 18 and if there is no dramatic change 36 then the control computer 19 determines whether or not the ram 2 is extending 37. If the ram 2 is not extending then the control computer 19 determines 38 whether the ram is holding in an extended position and if it is not holding in an extended position whetherthe--ram-#is fully retracted 39. - - -If--the- ram is not fully retracted then the control computer 19 reads the motor pressure 40 from the sensor 15 and subsequently determines 41 whether there has been a dramatic change.If there is no dramatic change then the control computer 19 proceeds to read the supply pressure 42 from the sensor 14 and if there is no dramatic change 43 then the routine returns to reading the ram pressure 35.

If at step 37 the control computer 19 determines that the ram is extending then the control computer then proceeds to determine 44 how far the ram has extended and whether the preset burn off of the workpiece held by the welding apparatus has been reached. If the preset burn off has not been reached then the routine moves to step 40 and subsequently returns to step 35 if there are no dramatic changes 41, 43 in the motor pressure and the supply pressure.

If however, the control computer 19 determines 44 that burn off has been reached then the control computer 19 stops 45 the motor 1 by closing the valve 10 and proceeds through steps 40 to 43 before returning to step 35 at the beginning of the routine.

If at step 37 the control computer 19 determines that the ram is not extending but subsequently determines at step 38 that the ram is holding in the extended position then this indicates that the motor 1 has been stopped in a prior cycle of the routine. The control computer 19 then goes on to determine 46 whether the ram 2 has been held in the extended position for the preset time period to form the weld for the particular weld cycle being used. If the ram 2 has not been held in the extended position for the required period of time then the routine goes through steps 40 to 43 before returning to the read ram pressure step 35.If however, the required time for holding the ram 2 in the extended position has been reached then the control computer 19 activates valve 7 to reverse the direction of fluid flow to the hydraulic ram which causes the hydraulic ram 2 to retract 47 towards it starting position. When the valve 7 has been activated to start retraction of the ram 2 the routine then proceeds through steps 40 to 43, as before in order to return to the read ram pressure step 35.

On the next cycle through the routine the decision step 39 will be reached as the ram 2 is not extending 37 and is not holding 38. The control computer 19 determines 39 whether the ram 2 is fully retracted by reading the signal from the sensor 17. If the ram has not fully retracted then the routine progresses through steps 40 to 43 as before, before returning to the initial read ram pressure step 35. However, if the control computer 19 determines 39 that the ram 2 is fully retracted then the sub-routine shown in Fig. 2c is entered, the information on the weld is sent to the processor 21 at step 31 and the routine is stopped 48.

Therefore it can be seen that by using the control system shown in Fig. 1 the variables of the welding machine and weld cycle can be monitored and continuously varied in accordance with the desired weld cycle. As mentioned previously, with conventional hydraulic friction welding apparatus the parameters of the welding machine and sequence are preset before the welding machine is submerged and cannot be altered during the weld cycle.

Typical curves for motor speed 50, ram pressure 51 and burn off 52 for a conventional friction welding machine are shown in Fig. 3. From this it can be seen that at touch down 53 the high resistive force between two workpieces causes a dramatic decrease in the speed 50 of the motor 1 which is undesirable.

With the apparatus shown in Fig. 1 it is possible to reduce the decrease in speed on the motor 1 as the motor speed can be controlled. This means-that-it--is possible to obtain virtually no discernible change in the motor speed at touch down 53 so that the graphs for speed, ram pressure and burn off in the apparatus according to the invention are very close to the theoretical "perfect" graphs of speed 54, ram pressure 55 and burn off 56 as shown in Fig. 4.

In addition, by using the apparatus shown in Fig. 1 it is possible to customise weld cycles to a particular application, for example to tailor the weld cycle for use with particular metals and/or alloys or combinations of metals and/or alloys. Such an example is shown in Fig. 5 where it can be seen in the weld cycle shown that the speed 58 and ram pressure 59 can easily be varied to different levels during the weld cycle. In this particular example both the speed of the motor 1 and the pressure of the ram 2 are at a relatively low value Sl,Pl respectively at touch down 53 and then are increased to speed S2 and pressure P2 immediately prior to the final formation stage of the weld.This particular ability to use multiple speeds and ram pressures during the weld cycle is particularly advantageous when welding aluminium, which requires the ability to use one pressure to build up heat in the weld material and a second, higher pressure to complete the "forge" phase of the weld. This flexibility for tailoring the weld cycle is also particularly useful when welding exotic metals and alloys.

Clearly the apparatus shown enables the weld parameters to be changed at will by an operator or to be input as preset "defaults" for materials and/or sizes to be chosen from a menu on the processor 21. Alternatively, parameters for a single material combination on a specific contract can be permanently stored in the processor 21 or the control computer 19 so that the machine and control system may be operated by an unskilled person.

By continuously monitoring and controlling the motor speed and ram pressure the invention also has the advantage of being able to compensate for changes in ambient temperature and/or pressure which could effect the viscosity of the fluid being used to power the welding machine and so adversely affect the ram pressure and motor speed.

Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims

1. A control system for friction welding apparatus comprising mounting means for mounting a first workpiece on the apparatus, a motor to rotate the first workpiece on the apparatus and a translation means to move the first workpiece in a direction substantially parallel to the axis of rotation of the first workpiece, the control system comprising at least one sensor mounted on the apparatus to monitor a variable of the apparatus, control means mounted on the apparatus to adjust the variable or another variable of the apparatus, and a processing unit coupled to the at least one sensor and the control means, wherein the processing unit controls the variable or the other variable via the control means in response to signals received from the at least one sensor.

2. A control system according to Claim 1, which comprises a number of sensors and the control means comprises a number of control devices which adjust a number of different variables of the apparatus under the control of the processing unit in response to signals from the sensors.

3. A control system according to Claim 1 or Claim 2, wherein the translation means comprises a ram device.

4. A control system according to any of Claims 1 to 3, wherein the at least one sensor comprises one or more of a motor speed sensor, a ram pressure sensor and a ram position sensor.

5. A control system according to any of Claims 1 to 4, wherein the friction welding device is powered by fluid.

6. A control system according to Claim 5, which comprises a motor pressure sensor and a system pressure sensor.

7. A control system according to Claim 3 or any Claim dependent thereon, which comprises a control device to control fluid flow to the motor, a control device to control fluid pressure to the ram and a control device to control the direction of fluid flow to the ram.

8. A control system according to Claim 7, wherein the control device for the motor comprises a proportional forward/reverse flow control valve.

9. A control system according to Claim 7 or Claim 8, wherein the control device for the ram fluid pressure comprises a proportional pressure control valve and the control device for the ram fluid flow direction comprises a forward/reverse shuttle valve.

10. A control system according to any of the preceding Claims where the friction welding apparatus is portable and adapted to be used in an underwater environment.

11. A control system according to Claim 10, wherein at least part of the processing unit is remote from the remainder of the system and is connected thereto by an umbilical connection.

12. A control system according to any preceding#plaim, wherein the processing unit is provided with input/out#put means enabling an operator to monitor and modify the variables during operation of the system.

13. A control system for friction welding apparatus substantially as herinbefore described with reference to the accompanying drawings.