POSITIONERS USED

FOR WELDING

POSITIONERS  

A positioner is a Mechanical device which is used to hold the Job and move them according to their required

position to weld and do other operations. A fixture can be mounted on the positioner in order to hold and move

the Job in an effective manner to obtain advantageous quality welds. The job can be repositioned according to

the requirement of the process to be done on it. Rotation about an axis is possible using turn table, turning rolls,

head stock and tail stock arrangements, tilting is possible with the positioner having a tilting table and the

vertical movement is possible by using an elevating device which can move the component accordingly. The

movement and the positioning of the job can be classified into four different types with different variants under

each type. 

 

1.Rotation about one axis

Turning roll positioners

Headstock & Tailstock positioners

Turntable positioners

 

2.Tilting & rotating

Tilting rotating positioners

Drop center tilting positioner

3.Vertical movement

Powered elevation positioner

 

4.Special Positioner

Skyhook Positioner

TURNING ROLL POSITIONERS

Turning rolls are generally used for cylindrical shaped jobs which rotates about horizontal axis, non-cylindrical

jobs can also be mounted on rollers but it requires special roll fixtures according to the shape of the job used.

They can be used in manual, semi-automatic and fully automated welding machines in a flat position. They

basically consist of wheels, steel frame, drive train, drive motor and other controls. Generally in turning rollers

one will be a powered roll and the others will be an idle rollers. Longitudinal welds can also be performed by

attaching a manipulator or a carriage along with the setup. They have low initial cost as well as low maintenance

and repair cost. An example for turning roll positioner is shown below, 

Schematic representation of Turning Roll Positioner

HEADSTOCK AND TAILSTOCK POSITIONERS

It is a single axis positioning device in which the table is fixed along vertical direction and the rotation is along

horizontal direction. It gives easy access to all the parts of large work piece in flat welding. The head stock is

always connected to a power source which is responsible to rotate the object in the particular axis where in tail

stock it is not powered instead a free roller and a fixture or a support structure is fixed to hold the work piece and

rotate it along with the headstock. The alignment of the headstock and tail stock is very much essential because

misalignment may cause damage to the work piece or the welding equipment. Generally the concept of head

stock and tail stock resembles a common lathe machines used in the industries. An example for welding machine

with headstock and tailstock is shown below. The can be used to weld various components like truck and

machinery frames, large transformers tanks, structural girders, armored tank hulls, earth moving and farm

equipment components. An example for headstock and tail stock positioner is shown below.

 

Lathe Mounted Headstock Tailstock Positioner

TURN TABLE POSITIONERS

It is single axis rotating device which rotates the table along horizontal axis either in clockwise or anti-clockwise direction. The load carrying capacity and size varies with respect to the work piece mounted on the table. Their size can be varied from a range of 20kg’s to 500 tons. These turn tables can be attached with other positioners for various applications. Some of them are listed below

 

o Constant or variable speed drive

o Manual rotation of the table

o Indexing mechanism

o Tilting base

o Travelling carriage and rails

o Through hole in center of the table

o Digital tachometer 

These turn table can be widely used for various applications such as machine welding, scarfing and cutting, cladding, grinding, polishing, assembly and NDT. An example for turn table is shown below,

Turn Table Positioner

TILTING ROTATING POSITIONERS

Generally tilting rotating positioners are recommended only when a versatile in positioning of the work piece is required. The tilting mechanism can be constructed according to the limitations required by the user. These positioners can perform two functions

 1) Either the work piece can be fixed in a particular position so that the welding head moves along a

direction to weld. 

2) Or the welding head can be fixed and the positioner can be moved according to the weld.  

Tilting is carried out through gear mechanism which is mounted on the setup with a turn table on the top which allows the work piece to rotate in clockwise or anticlockwise direction. The base of the positioner is fixed with two legs which can allow to adjust the height of the positioner vertically in order to provide proper clearance to the table. The capacity rating of the positioner is based on

  The total load

  The location of Center of Gravity (CG) of the combined load

  

There are two dimensions used to locate the center of gravity of the  

1.The distance from the positioner table to the CG of the combined load. 

2.The distance from axis of rotation to the CG of the combined load referred to as Eccentricity (ECC).

 The mini positioner which are used for micro welding processes, heavy positioner with a load carrying capacity of maximum 1 ton and their tilting capacity varying from 90 degree to 180 degree including both horizontal and vertical position are shown below,

DROP CENTER TILTING POSITIONERS  

In this type of positioner the tilting mechanism is placed outside rather than beneath the table. And so the size of

the work piece is limited according to the distance between the vertical side members of the base. The offset

distance between both the tilting mechanism is called inherent overhang. The distance may vary according to

the positioner size. Its application is especially for a work piece which is supposed to travel along the direction

with a constant welding head. Example for drop center positioners are hemispherical components which

requires the movement of the work piece rather than the movement of the welding head. A schematic

representation for drop center tilting positioner mounted with a hemispherical work piece is shown below,

Schematic representation for Drop Center Tilting Positioner

POWERED ELEVATION POSITIONERS

Generally the height of the positioner is increased and lowered using a shop crane. But when powered elevation

positioner is used it can be avoided an instead it can be raised and lowered under power using a rack and pinion

or a screw jack mechanism. They are the most versatile among all the other processes but it is very expensive.

They are available with capacities up to 60 tons and the axis of rotation is along horizontal direction.

SKYHOOK POSITIONERS

The basic construction of the machine is, a long arm is attached to the headstock which rotates without any

restrictions and the turn table is attached at the end of the long arm. This type of machine provides unlimited

rotation along both the tilt and rotation axes. These kind of positioners are used only for specific application. A

schematic representation for a skyhook positioner is shown below,

Schematic representation for skyhook positioner

ADVANTAGES 

Reduces welder fatigue.

Increases welder safety.

Improves weld quality.

Increases productivity when compared to manual positioning of the parts.

Assists welders in maneuvering and welding large work pieces.

Ensures smooth welding table rotation.

Faster welding speeds especially for obtaining X-ray quality welds.

Arcraft Plasma Equipments (I) Pvt Ltd., 124, Diamond Industrial Estate, Ketkipada, Dahisar (East),

Mumbai- 400068.

INDIA.Ph : 00-91-22-28965890, 28965745, 28963247 Fax: 00-91-22-28966418