GB2041799A - Workholders - Google Patents

Abstract

A workholder comprises a base 1 formed with channels 6 containing pads 4 which have means for attaching to a workpiece. The channels can be "opened" and "closed" e.g. by exerting hydraulic pressure on a sidewall, thereby allowing the pads to tilt and attach to the undersurface of a workpiece before re-closing the channel to grip the pads in the work engaging position. The attachment means of the pads may be magnetic, suction or adhesion. <IMAGE>

Description

SPECIFICATION Improvements in and relating to workpiece holding with particular reference to surface production.

This device has for an object a means whereby a table for holding workpieces can be made to conform to the profile of the resting surface of the workpiece and is capable of being locked in this condition so as to allow the workpiece to be fully supported whilst machining takes place on its opposite side.

In accordance with the invention there is provided a series of sections or pads capable of attaching themselves to the workpiece in its natural state either by magnetism, adhesion or vacuum means and then the pads being gripped in their precise positions in a rigid manner so that the workpiece is held or supported on a perfect 'bed' ready for machining.

This device consists generally of a plurality of pads housed in a vice like construction each pad being independently capable of attaching itself to the underside of a workpiece and the shape of the pad in its housing being such that it is capable of compound movement and the shape to allow its vice-like housing to grip it in a rigid manner without any movement of the pad taking place when gripping occurs.

In a particular application there is a steel construction in the form of a unit having a series of channels across the length and means are provided to open these channels so that sections or pads that are normally trapped between the walls of the channels can be allowed to move freely.

The pads which are also made of a robust material such as steel consists of a generally rectangular slab of metal of a width slightly in excess of the unstressed width of its associated channel and is formed on the sides that register in the channel to a true radius that is half the width of the channel. When the channels are open the pads can move in a completely compound manner within the limit of their dimensions.

Instead of a radius a very narrow locating area may be used. The gripping jaws or channel, may be either machined from a solid piece of metal or they may be formed by a bolted construction to have the same affect. The means to stress open the 'jaws' takes the form of a small section thrust unit housed in a slot machined as a continuation below the surface on the same line or approximately as the jaw face and included in the assembly as a means of hydraulically pressurizing the thrust unit in the form of a sealed screwed piston. Also included is another screwed piston to be used as a means of adjusting the displacement of the hydraulic fluid so as to avoid over-stressing the jaws.The said pads tape the form of rectangular steel blocks whose sides which are in contact with the jaws, are machined to a dimension equal to the width of the jaw gap plus sufficient extras so as to be severe interference fit between the 'jaw' faces or have a very narrow contact edge. The face of the pads is machined to house the unit for making contact with the part.

There are four types of pads as follows: 1. This is machined to house a permanent magnet with the face of the magnet and pad coincident.

2. This is machined to accept the installation of a small electromagnet.

3. This is machined to house a cup seal with the lips of the cup slightly protruding above the bass face but with sufficient clearance in its housing to allow the pad to be sucked into the part to be held. This cap is flexibly piped to a manifold which in turn is connected to a vacuum pump.

4. This is machined with a plain boss so as to accept double sided adhesive tape to be adhered to it.

The pads mentioned may have a groove turned in a boss diameter just below its face to accept a swarf seal said swarf being a sheet of resilient material with holes which are a tight fit in the boss grooves and produced at centre distances to suit the boss positions and all around the assembly is machine a groove to complete the sealing of the complete unit.

It will now be seen that if pressure is applied to the trust strips which are in circuit with the pump the pad gap will open allowing the pads to be moved in a compound direction i.e. they can tilt slightly in any direction and can also be moved away from their underside seating. It will also be seen that if Pad Type 1 is used and the part is ferreous and is placed on the pad surfaces which form almost a complete surface, the magnets will pull themselves to be in contact with the underside of the part and will form an almost perfect profile with it, even though the part may be distorted or in its cast form.

When the pump pressure is taken off the jaws will try to assume their natural position and will close in on each pad in its new position without any movement of the pad. The part can now be machined in its natural shape without distortion due to magnetic pull-down or clamping and the unit is operating in a fail safe manner. It will also be seen that when Pad Type 2 is used the same affect is obtained. It will also be seen that when Pad Type 3 is used and the pad cap seals are evacuated and the same procedure is adopted, again the same effect is obtained. Pad 4 is used for surfacing thin non ferrerous parts in which case the part is pressed down onto the pads so as to contact the adhesion surface and the return of the part to its natural shape will carry the pads with it and again a near perfect unstressed bed is obtained on which to machine the plate.

The pressurising means to generate thrust in the thrust units may also be remote and operated automatically from an outside source such as a hydraulic power pack. All of the foregoing relates to a plate on one plane and implies a rectangular shape.

The Workpiece holder may be ring shaped or circular and may be on different planes and angles to suit the requirements of the part to be machined or held without distortion.

In another application the sworf seal may be dispensed with and the workpiece may be lifted off of the unit carrying the adhering pads with it for them to be removed from the workpiece individually.

The invention will be more fully understood by reference to the drawings where Fig. 1 sheet 1 shows a cross section of such a table in which 1 is the Main Body of the unit and is shown channeled to grip a series of Sections or Pads 2 and to house the opening means 5.

The opening means shown 5 consist of an open ended channel in a strip of steel machined to a depth to accommodate an '0' seal that is bounded at its extremities by two pump housings which are shown as 3 and 4 on fig. 1 sheet 3.

Also in the channel fitting its width is another strip of material which could be steel or a resilient material such as nylon or P.T.F.E. which would act an an anti-extrusion agent.

The total depth of the channel is such that the '0' seal is trapped thereby preventing any fluid that is forced in the channel from escaping thus causing a face pressure on the inside of the jaws 6 fig. 1 sheet 1 6 r 7 fig 2 sheet 1 and Sand 6 on fig 3 sheet 1. Trapped between the above jaws are a series of pads 2 shown on Figs. 1 8 2 sheet 1 and shown as 2 on fig. 1. sheet 3.

Sheet 1 figs. 1.2.3. and sheet 2 figs. 1 and 2 show various ways of achieving the object of having the jaws constructed in a manner to allow them to be stressed open by means of the pumps 6 7 7 fig. 1. sheet 3 shown dotted.

It will also be seen that pump 6 is screwed into a positive stop 8 and the pump 7 is unrestricted endwise so that it can be used for opening the jaws when the pump 6 is fully screwed to its stop.

It will also be seen that if after this adjustment has been made the pump 6 becomes the operating pump thereby preventing any damage to the channel unit due to over-opening. Further explanations are as follows.

Referring to sheet 1 fig. 1 is the Unit Body 2 is the adhesive pad 3 is the channeled strip to house the oil seal 5. 4 is the magnetic insert.

Sheet 1 figs. 2 1 is the Unit Body. 2 is the adhesive pad. 3 is the channeled strip to house the fluid seal 3. 4 is the magnetic insert. 5 is the resilient swarf seal 6 and 7 are narrow jaw faces.

Sheet 1 fig. 3 shows a constructed unit where 1 and 2 are the main body members in which is machined the oil channels 9 and 10 to house the seals 7 and 8 to form the pressure chamber 3 is a strip to form the reactor jaws for the stressable jaws 5 and 6. 4 is an '0' seal to prevent loss of oil from between the assembly.

Sheet 2 fig. 1 shows another unit construction in which 1 is the Unit body, 2 and 3 are the reactor bars housing the pressure chambers 5 and 6.

Claims (14)

1. A self-aligning workplate comprising a series of metal sections or pads, each having the capability to attach itself to a workpiece placed upon it, and each housed in a channel or vice-like structure, which grip it in a rigid interference condition.

Associated with the channel is a means to spring it open so as to allow the sections free compound movement so as to make it possible for the sections to collectively assume the profile of the contacting surface of the workpiece before allowing the 'jaws' to close and regrip the sections.

2. A workplate as in Claim 1 in which the means to open the gripping channel takes the form of a sealed channel, closed at its ends, and abutting onto the inner face of the gripp;ng channel, that can be pressurised by hydraulically so as to enable it to force the walls of the gripping channel apart.

3. A workplate as in Claims 1 and 2 in which the pressurising means is a screwed hydraulic piston, manuaiiy operated, in a closed, circuit linkup with the sealed channel.

4. A workplate as in Claims 1 2 and 3 in which the closed circuit has an adjustable screwed piston linked in to control the degree of opening of the gripping channel.

5. A workplate as in Claim 1. in which the means to open the channel can be any conventional means.

6. A workplate as in Claims 1 to 5 in which the area of the section that is gripped is formed so as to allow a compound movement of the section when the channel is opened a minimal amount

7. A workplate as in Claims 1 to 6 in which the gripping channel has a lateral abuttment to retain the sections.

8. A workplate as in Claims 1 to 7 in which the sections have abuttments to prevent them from being lifted out of the channels when removing the workpiece.

9. A workplate as in Claims 1 to 8 in which the sections have a magnet built into its cotact face.

10. A workplate as in Claims 1 to 8 in which the sections have an adhesive contact face.

11. A workplate as in Claims 1 to 8 in which the sections have the properties of a suction pad and are flexibly linked to a vacuum pump.

12. A workplate as in Claims 1 to 1 1 in which a single sheet of a suitable resilient material perforated at hole spacings to suit the section positions is used as a swarf seal.

13. A workplate as in Claims 1 to 12 in which the sections are formed with a boss as the work support, around which is a recess to accommodate the swarf seal.

14. A workplate substantially as herein described with reference to the accompanying drawings.