by Cliff White
Factors to consider to ensure you have the right one for your shop
Selecting a positioner for a specific part or family of parts is based on more than weight capacity. Sequence of operations, welding process, accessibility and safety are other items to consider that may drive the size and design of the positioner you need.
A positioner manipulates a part into a correct position for various operations. Tilt/rotate, head and tailstocks, floor turntables and turning rolls are all types of positioners that can be used depending on the part size, project constraints and process requirements.
Sequence of operations
Consider the positions and the number of orientations required to present the part in the proper orientation to perform jobs. Consider how the part is fastened to the table and even the fixture design that allows the operator to perform the operations essential to a specific part. Understanding final expectations and process limitations may be the most critical information in determining the correct positioner for each application. Some positioners may offer unique advantages in some areas with downfalls in others. These possible advantages and disadvantages must be deliberated and understood to ensure the best choice for the final positioner design.
The welding process can also drive the final positioner choice and the fixture design. Open arc processes such as MIG and TIG may require less precise joint placement, due to the ability of the welder to perform some less critical welds out of position, while submerged arc welding (SAW) requires all joints to be properly positioned due to larger weld puddles and the need to keep the weld puddle fully submerged under a pile of loose granular flux. Welding may not be the only process that must be considered. Grinding, machining, final assembly, painting and blasting are several processes that can be performed on a positioner and will affect the final selection. Any reduced handling or time between operations can improve efficiencies and increase quality during the manufacturing process.
How the operator, robot or manipulator accesses the required areas of the part is critical for each process. Interference with the positioner, the fixturing or even the component itsself must be analyzed to ensure sufficient clearances. Although off the shelf positioners may suffice for simple projects, many jobs require specially engineered products to meet specific needs. How and where the part is held is directly related to where and what specifically needs to be accomplished. Proper fixturing and part attachment to the positioner will avoid interference and quality issues.
Safety is another factor. Manipulating the part to a safe position so the operator can easily reach the required areas eliminates the need for ladders and stands. Ergonomic working positions provide safer working conditions and happier operators, greatly reducing manufacturing accidents and injuries while increasing cycle times and quality. Accounting for the correct swing clearances and possible interference points reduces the chance of collision with the floor or other objects, which can cause damage to the part or machine as well as being hazardous to surrounding personnel.
A basic tilt-rotate type positioner provides powered tilt and rotation to manipulate the workpiece. This design offers a range of capacities: high tilt and rotational torques for overhung and eccentric loads, and large swing clearances for manipulating parts into the desired position. Disadvantages can be high table flat heights and larger machines required for excessive over hung loads due to the part being supported only by one end. Power elevating models can be used to lower work heights, but due to machine design, may still remain out of the workers reach.
Head and tailstock positioners support the part from both ends. This allows a machine to split the load and reduce the effects of a large over-hung load, reducing the machine capacity required. The part remains parallel to the floor keeping the work height as low as possible. Power elevating models can lower the work height even further while still allowing the part to be lifted and rotated for additional processes. However, this design offers limited positions as the part must remain attached to both the head and tailstock (parallel to the floor) allowing the part to be only rolled, with no tilt functionality available.
Floor turntables include a powered rotating table that remains parallel to the floor. It offers a low working height, large table diameter capabilities and reduced cost due to limited mechanical components. However, it has limited part mobility; with no tilt or elevation capabilities, the load can be rotated only with the main work plate and part remaining parallel to the floor.
Turning rolls are used primarily for round vessels in the flat position. Elevating and tilting models can be used for special applications as well as false rings for rotating square parts. However they’re designed for concentric parts. With friction between the wheels and the workpiece providing the rotating power, large eccentric loads may slip, requiring a more rigid connection as in a head and tailstock positioner.
Special engineered products and positioner options are almost always utilized in the final positioner design. Through-holes, special tables and PLC controls are just a few solutions that can be used in the design of a special positioner application. Several features of standard positioners can be used together to make specialty positioners such as Skyhooks and Drop centres. These machines are a combination of several axes and components that provide arrangements of tilt and rotation in one machine.
Follow these steps to determine which positioner will work for your operation. SMT
Cliff White is weld products manager with Koike Aronson Inc./Ransome