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Henry Stier

Considerations For Unattended Turning

There is a trend toward unattended machining, and turning presents its own special situations that should be accounted for in the early planning stage.

In any turning operation, one of the main problems is chip formation. If not broken up, long stringy chips can damage either the part or machine. Thus, some method of assuring proper chip formation is essential. Proved chipbreaker inserts or high pressure fluid methods are two chip control techniques currently employed.

Another problem is the possibility of a tool breaking and going undetected to damage either the workpiece and/or the machine. For this reason, a broken tool detector or limiting tool life to a satisfactory risk level and incorporating backup tooling should be considered at the planning stage. When switching tools, it is necessary to either have preset tooling within acceptable tolerance levels or a method of automatically picking up the appropriate tool offset so the machine control unit can make the proper compensation. Another possibility is having an automatic gaging cycle of the first part after tool change and a compensating feedback to the machine control. If this is done, some provision must be made for setting aside the out-of-tolerance part.

Most turned parts have a relatively short machining cycle. If this is the case, an unmanned operation during lunch breaks or other extended times requires a sufficient holding capacity for both blanks and finished parts. When changing from one part to another, even within a family, there is often a need for considerable flexibility in both the chucking and handling system. Thus handling, gaging, transport, and storage facilities become important considerations when planning a successful unattended turning operation. Attempting to rig satisfactory solutions after installation can lead to both frustration and a poor performance level.

Several options are available for automatic loading and unloading turning equipment. Stand-alone robots are one, but usually the fastest and most satisfactory approach is a dedicated robot arm as part of the machine itself. Depending on part size and weight, loading and unloading times of four to twelve seconds are quite common with this latter approach.

The particular storage racks or magazines for blanks and finished parts will determine the size and form of workpieces that can be handled by a particular CNC unattended lathe operation. Usually two completely different systems are necessary for chucking and shaft work. The capacity of such a storage and handling system must be relatively large for long periods of unattended operation. A universal arrangement to cover a greater range of part sizes and shapes will usually require more floor space.

The 100 percent quality level of parts produced without operator standby usually can be assured only by automatic 100 percent gaging of the parts. If coupled with a printout, it can be a powerful productivity and quality assurance tool for increasing all aspects of your production operations.

There definitely is a trend toward more automatic and unattended machining. But turning presents its own set of unique situations that are usually quite different from those of machining centers. Thus, they should be approached individually to arrive at productive installations.

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