GB2295340A - Adjusting bending machines - Google Patents

Description

1 1 Adjustincy Bending Machines 2295340 The present invention relates to a

method of adjusting bending machines and in particular to the setting up in a reproducible manner of machines for bending elongate articles such as tubes or rods.

There is at present no well-defined method of setting up a tube bending machine for a particular task. If it is incorrectly set up prior to bending, problems arise such wrinkling, bumps and necking of the tube. Existing computer controlled or CNC machines are capable of facilitating relatively small batch production of, say, 20 to 30 parts before setting up for some other product. This has the advantage that the manufacturer need only make parts as required and not for stock. The computer only takes a fraction of a second to set up the bending and set-up parameters for a tube via a look up table, which might have as a reference the part number or description. The time taken in setting up a machine for the next component is all in the mechanical setting up of the tooling. For complex parts this can take up to an hour if the part is critical or of very tight bending parameters, i.e. bend radius.

The present invention seeks to overcome or reduce this problem.

According to a first aspect of the present invention there is provided a method of adjusting a bending machine comprising one or more adjusting mechanisms for respective parameters of a bending process, the method comprising recording the torque or force values applied by the or each mechanism when producing a part of acceptable quality and subsequently using said values when setting up the machine to produce similar parts.

2 The or each adjusting mechanism preferably comprises a low friction slide operated by a motor with torque control for final load setting.

The present invention does not eliminate the original setting up correctly of the bending machine to do a particular job, e.g. to produce an exhaust or seat f rame, but does enable the machine to be reset to the original parameters when a good product was previously made.

According to a second aspect of the present invention, there is provided a bending machine comprising adjusting mechanisms for respective parameters of a bending process, at least one of the adjusting mechanisms incorporating a low friction slide.

The or each adjusting mechanism incorporating the low friction slide may be controlled by a motor operating in torque mode, e.g. by a ball screw and nut drive arrangement.

Alternatively the position of the adjusting mechanism may be precisely determined by a motor or otherwise.

The adjusting mechanism preferably adjusts the clamping die pressure, the pressure die pressure or the powered follower pressure. In a preferred embodiment separate adjusting mechanisms are provided for all three parameters, although one or two only may be provided.

Further similar adjusting mechanisms may be provided for other parameters of a bending machine, or indeed any material deforming machine.

A preferred embodiment of the present invention will 3 now be described, by way of example only, with reference to the accompanying drawings, of which:

Figs.. la to if illustrate the steps in a typical tubebending process; Fig.2 is a schematic view of an adjusting mechanism for a clamping die of a bending machine in accordance with the present invention.

Referring to the drawings, Figs la to if illustrate a process for bending a tube 20 and employing a two ball mandrel plus a wiper die. The bending machine 10 comprises a bending former or centre former 11, a pressure die 12, a clamp die 13, a mandrel 14 with two articulated balls 14a, and a wiper die 15, which holds the tube wall steady against the mandrel.

A bend arm 31, Fig.2, carries the clamp die 13 and the tooling carrier 32 therefor, and produces rotation thereof and of the former 11. The pressure die 12 is fixed to the main bed of the bending machine. Fig.1a shows tube 20 inserted ready for bending.

In Fig.1b the pressure die 12 and clamp die 13 are closed. The bending former 11 and clamp die 13 then rotate to bend the tube 20, Fig.1c, and to pull it through the machine. During this process, the pressure die 12 "follows" the tube i.e. moves to the left in Fig.1c.

The pressure die 12 usually consists of a steel or aluminium bar, one side of which is machined to fit half way round the tube 20 and running along the straight portion of the tube. This component is free to slide, either by mounting on a roller slide or being mounted 4 directly in a bearing system. During bending i.e. the rotation of the centre former 11, and hence bending the straight tube into the circular centre former, the pressure die forms the reaction system necessary to bend the tube. Thus the only loads in the pressure die are those induced during bending.

For producing bends with a tight radius and/or of high quality a controlled force, indicated by arrow 21, can be exerted on the pressure die to control its leftward movement; this is known as a powered follower arrangement.

Fig. 1d shows the mandrel 14 retracting, and then the pressure die 12 opens and the clamp die 13 drops away, Fig.le. Finally the components 11 to 14 return to their original locations and the tube 20 is fed forward and rotated as required for the next bending operation.

There are a plurality of bending parameters required to make a good part and these are determined by the settings of the various adjustment mechanisms of the components of the bending machine. The best settings for both machine and quality of bend correspond to minimal preloads on the pressure die consistent with minimal ovality at the bend region of the tube. The bending parameters concerned are: clamp die pressure, pressure die pressure, powered follower pressure. Of course, these depend not only upon the material and dimensions of the tube but also upon the particular bend angle required. In general the other parameters such as bend angle, carriage position and other controls in the three main axes can be set up by a computer for different parts.

In existing bending machines, the adjusting mechanisms for the clamping die, the pressure die slide and the powered follower have mechanical slideways utilising brass wear plates with steel slides carrying the tooling moving in and out as required. The friction in these slides is such that it cannot be predicted easily due to the possibility of wear and slackness in the slides. This friction is a significant proportion of the forces used in the eventual control parameters and hence this allows too much tolerance in the setting up.

In the present bending machine, there are employed low friction slides (as used in many machine tool beds) to carry the three sets of tooling and AC servo motors with torque control setting for the final setting of the loads. The torque setting of the motors is done by the CNC controller in a similar manner to that normally used for setting position.

One of the low friction slide adjustment mechanisms 30 is shown in Fig.2, viz the adjustment mechanism for the clamping die tooling 13. The bend arm 31 has a main shaft 33 with a chain sprocket 34 for controlling rotation of the bend arm. The fine control for the clamp die 13 is provided by a tooling carrier block 40, mounted on a low friction slide 41, and a ball screw 42 and nut 43 mechanism driven via a gear box 45 by an AC servo motor 46 running in torque mode. When a good part has been produced, the motor is run up to the same torque when it is desired to repeat the process to an inserted tube.

Similar adjusting mechanisms are provided for the pressure die 12 and powered follower, but these of course are attached to the main bed of the bending machine 10.

d 6 The above - described arrangement has numerous advantages. The foremost advantage is that of speed - a process which previously could take up to one hour can now be performed in a few seconds. The parameters clamp die pressure, pressure die pressure and powered follower pressure can be set simultaneously with the other parameters being determined by a computer. Moreover, the process is precise so that waste is avoided. In addition it is easy to perform so that highly-skilled labour is no longer required, which leads to further cost saving.

Existing bending machines can be retro-fitted to have servo control such that the set up is faithfully repeated when a previously correct part has been made and the data stored.

The process can be employed in the aerospace, automotive and furniture industries, for example, to make fuel lines, brake pipes, exhaust pipes etc. In all such industries manufacturing quality is improving continuously and tolerances on shapes are getting tighter, and the process is capable of meeting this need.

Various modifications may be made to the above-described arrangement. In particular only one or two of the three parameters may be set in accordance with the process of the invention, with the others being set conventionally. The mandrel 14 may be omitted if desired, but is usually retained since it reduces the tendency of the bent tube to spring back. The wiper die 15 may also be omitted.

By interfacing with a robot, the machine may also be capable of automatic tool changing when required.

The motor 46 can be used in position mode instead of 7 torque mode if desired. Because of the low friction slides (e.g. 41), this still provides an advantageous arrangement compared with conventional machines with high friction adjustment mechanisms which were difficult to position precisely. However, torque control is more convenient and leads to better results. In a modification both torque (i. e. pressure or load at the machine component) and position determinations are employed during setting up.

Although a draw bending method has been described, methods according to the invention can be applied to any other bending or deformation process or machine.

A 11.

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Claims (9)

1. A method of adjusting a bending machine comprising one or more adjusting mechanisms for respective parameters of a bending process, the method comprising recording the torque or force values applied by the or each mechanism when producing a part of acceptable quality and subsequently using said values when setting up the machine to produce similar parts.

2. A method according to claim 1, wherein the or each adjusting mechanism comprises a low friction slide operated by a motor with torque control.

3. A method according to claim 1 or 2, wherein the parameter(s) adjusted is/are clamping die pressure and/or pressure die pressure and/or powered follower pressure.

4. A method of adjusting a bending machine substantially as herein described with reference to the accompanying drawings.

5. A bending machine comprising adjusting mechanisms for respective parameters of a bending process, at least one of the adjusting mechanisms incorporating a low friction slide.

6. A machine according to claim 5, wherein the or each adjusting mechanism incorporating a low friction slide is controlled by a motor operating in torque mode.

7. A machine according to claim 6, wherein the friction slide has a ball screw and nut drive arrangement.

8. A machine according to any of claims 5 to 7, wherein the adjusting mechanisms adjust the clamping die pressure and/or the pressure die pressure and/or the powered follower pressure.

9. A machine substantially as herein described with reference to the accompanying drawings.