Making A Flexible Machine Tool More Flexible

This tool allows five different cutting operations, including turning and milling. The inserts for turning are positioned such that they don't interfere with the milling inserts when the tool is used for milling.

Cutting tools that can perform more than one operation offer the possibility to tap the full potential that multitasking machines offer.

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Anyone with the resources and the inclination can buy a machine tool. But not everyone can wring out the same amount of production from the same machine. Multitasking machines loaded with multiple turrets and/or spindles offer a great deal of production potential, as they can often completely machine a part on its own. Granted, these machines are more costly than their straightforward lathe and milling machine brethren. However, it's clear that shops battling just-in-time delivery schedules and shrinking batch sizes recognize the money-making potential of such machines, as their sales increase every year. It's the classic case of biting the bullet and choosing equipment that initially is more expensive, but offers greater payback down the road.

But the multitasking machine can't do it alone. The choices made in combining various machining elements and strategies into an efficient process ultimately separate the great shops from the average Joes. CAM programming continues to be a challenge for multitasking machines, which isn't surprising considering it involves simultaneous machining operations and orchestrated movement of a number of machine components.

Tooling can also play a make-or-break role. It's logical to think that a multitasking machine designed with flexibility in mind would use tooling that was also flexible. Such tooling would provide the capability to perform a variety of different machining operations with just one tool. A universal spindle interface that can accommodate both turning and milling operations can also augment process versatility. There are a few reasons for this.

First, space can be saved—turret space, to be more specific. The multiple turrets and spindles located within a multitasking machine not only limit space within the machining zone, but also place limits on tool magazine capacity. A single tool that offers five different cutting operations, for example, could free up four tool pockets. Those extra pockets could then be used to hold different tools for parts that require many machining operations or sister tooling to allow extended, unattended operation.

Second, cycle times can be quicker through the elimination of non-value-adding tool change time. A multitasking tool might just require spindle indexing to bring a different turning insert into position, for example.

Third, a universal, modular spindle interface that is effective for milling, turning and drilling operations allows for one common tooling platform for the shop's entire operation. This concept of standardization falls in line with the strategies of lean manufacturing.

During a recent visit to its international headquarters in Sandviken, Sweden, Sandvik Coromant (Fair Lawn, New Jersey) demonstrated the value that a multitasking tool platform, such as its Coroplex line, can provide for multitasking machines. The visit included a tour through the production facility for its mining and construction division, which heeds the advice of its sister tooling company by using robot-tended cells that combine multitasking machines with multitasking tools to produce various mining drill bit components (see sidebar on page 77).

Tooling Versatility

There are a few different approaches in terms of multitasking tool design. One is the combination of turning and milling inserts on a single tool body. That one tool could perform shoulder milling, turn-milling or circular interpolation, for example, as well as face and longitudinal turning, profiling or internal turning. To combine turning and milling capability on one tool requires a design in which the turning inserts don't contact the workpiece while the tool is milling. To avoid this, the milling inserts are located just ahead of the turning inserts axially and radially so that the turning inserts are not in cut when the tool is milling.

Another technique combines two turning inserts located on opposite sides of a tool body. The tool can perform a rough turning operation, then be indexed 180 degrees in the spindle to allow finish turning.

Yet another concept uses a modular mini-turret unit that can combine four different cutting modules to allow four turning operations on one tool. This would enable a single tool to rough turn, finish turn, cut a groove and turn a thread, for example. The combination of cutting modules is user-selectable, and it would depend on the type of part and the required machining operations.

Maintaining tool center line accuracy is especially important for multitasking machines to make sure that the tool is precisely positioned to perform a turning operation. This is where it is helpful to have a modular, universal spindle/tool interface. Such an interface is effective for multitasking machines, as their spindle(s) could be called on to mill or lock into position for a turning operation.

Programming And Tooling

One of the issues that tooling companies sometimes face when introducing new tool designs is the lag in terms of CAM software support of new tools. Often, though, programming is not made more difficult because of the new tool. To change from a milling operation to a turning operation for tools that can perform both just requires the spindle to precisely index to bring the turning insert is in proper position. There's no programming difference if that tool is used for milling, as the tool essentially is a milling cutter that happens to have turning inserts on board.

CAM Considerations For Multitasking Machines

Multitasking machines come in a variety of configurations, but each type will typically perform multiple cutting operations simultaneously. Proper synchronization of turret and spindle is vital to achieve the full benefits of these multiple operations. This job, in addition to collision avoidance, falls to the CAM programmer.

CAM system requirements vary depending on the particular multitasking machine configuration. Simon Lee, marketing director for Pathtrace Systems (Southfield, Michigan), offers some programming advice for a few common configurations to help programmers get the most out of these flexible machines.

Subspindles—Subspindle machines perform an operation in which the subspindle moves to the main spindle to pick off the part, and then it becomes the clamping spindle for subsequent machining operations. If the material is barstock, then a parting-off operation will have to be incorporated in the pick-off. It is more efficient if the pick-off is executed while the spindles continue to rotate, which means the speed of each spindle must be identical to allow unclamping and clamping while rotating. The CAM system should be able to support this process in addition to automated spindle docking, component part-off and subspindle retract commands.

Multiple turrets—As the number of turrets on a machine increases, so does the level of programming complexity. A common configuration uses two turrets, which allows balanced and mirror cutting cycles. For these operations, both turrets will be machining simultaneously on opposing sides of a workpiece. The CAM software must synchronize turrets and also perform highly accurate cycle time calculation. It is an added benefit if the CAM software provides separate instruction lists for each turret. These allow editing of synchronization points and related machining instructions. APKT Insert Software that provides side-by-side view of instruction browsers for each turret helps in lining up the synchronization points to reduce machine idle time and also in preventing turret and spindle collision.

B-axis machining—Machines with a B-axis spindle might mill parts held in either of two spindles. For maximum process efficiency, the CAM software should allow the B-axis spindle to be used for prismatic milling and drilling operations, as well as independent freeform or surface machining.

The potential for collisions between turrets, spindles and B-axis spindles can be minimized through process simulation and synchronization calculations. A collision noticed during the simulation stage allows the programmer to rectify the problem before machining. A timeline view of all machining instructions Milling inserts incorporating both spindles and turrets is also helpful.

 Multitasking Application

Sandvik's mining and construction division at Sandviken, Sweden, began using multitasking machines to produce steel mining drills in 2001. By using cells of multitasking machines tended by robots, rather than a series of dedicated machines, the company was able to bring production from low-wage Mexico to Sweden.

The operation in Mexico used seven machines to perform eight different operations and required 50 workers. Component leadtime was 20 days. In Sweden, automated multitasking cells that complete all necessary turning, milling and drilling operations reduced the leadtime to 5 days using only 12 workers.

The latest multitasking cell, shown below, uses a robot to tend three Nakamura STS 40 machines. These machines have magazines that hold 40 tools—30 of these are permanently positioned in the magazine and ten are changed according to the component being machined. Sandvik's Capto modular spindle/tool interface is also used, because it works for both turning and milling operations. For some turning operations, the machines use multitasking tools with two inserts for roughing and finishing.

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