Turning centers

Turning centers have multifunctional capabilities and multi-axis capabilities. This means that you might have a C-axis, Y-axis and driven tools on the turret to be able to perform not only turning but also milling, drilling and tapping operations.

Turning centers machine configuration

There are several machine options to consider, depending on the type of component being produced. Careful consideration ensures an optimal and secure machining process.

The development of driven tool holders has lead to turning centers becoming truly multifunctional machines.

The two traditional types of turret, shank and VDI, were developed when turning centers only carried out turning and center-line drilling operations. Shank and VDI are suitable for traditional turning centers.

CBI (Coromant Capto® Bolt interface) is well adapted for multi-functional turning centers. This interface has more room inside the turret for the driven tool holder bearings, providing best stability and shortest gauge lengths. CBI is unique to each machine tool builder, which means that machine adapted clamping units (MACUs) are needed that suit the specific machine model.

CDI (Coromant Capto® Disc interface) is a standardized turret interface that fits multiple machine brands and models. It is mainly European machine builders who supply CDI as a replacement to VDI.

Different configurations of MACUs allow the turret to be configured to each production environment, mixing the right combination of external, internal, static and driven. Double clamping units are often used to increase the number of tool positions.

Driven tools allow milling and drilling operations with C-axis control required on the main spindle. 2-axis operations can be carried out, such as keyway slots or holes on the center line. To be able to mill pockets or drill off center line, a Y-axis option is needed.

For drilling operations, it is best to use driven tool holders with internal coolant supply and high-pressure coolant to provide the best chip evacuation and process security.

A Y-axis makes it possible to use driven tools for 3-axis milling and drilling off center line. Most features requiring milling operations benefit from Y-axis. Double turning positions can be added, increasing the number of tools for sister tooling or increasing the variety of holders, reducing the need to change tool-holder styles.

Y-axis

Half turret indexing allows double turning positions to be used, increasing the number of tools. This option is not required if a Y-axis is available; therefore, it is generally selected on turning centers without driven tools.

Half turret

Sub-spindle/lower revolver

Machining from both sides is often required for completing a part. Sub-spindles are often used in combination with a bar feed. With this combination, unmanned production of completed parts is possible.

For higher volume production, the lower revolver can halve the cycle time compared to a single revolver. A lower revolver enables tandem turning and permits machining operations on the sub-spindle at the same time as the main spindle, offering lower cycle time. Typical applications are long, slender components like shafts and components machined on both sides using the sub-spindles.

The drawbacks of the lower revolver are reduced component diameter and increased programming and set-up time, making it suitable mainly for turning centers bought for specific components.

When pre-measuring the tools outside the machine, it is important to have an optimized zero position for each clamping position. The tool holder offset function allows for a pre-measured tool to be put in any clamping unit and cut correctly from the first component produced, saving measuring time and reducing scrap components.

High-pressure pump

Most machines offer a high-pressure coolant capability around 70 bar (1015 psi).

Read more about coolant aspects

Automation

Future machine and tooling requirements are driven by the common challenges of globalization, skills shortage, shorter product life cycles and a continual demand to reduce production costs. Over the last two decades, the macro trends show us that the primary focus for manufacturing companies is that of reducing the number of manufacturing steps and total manufacturing time (TMT). This has allowed for more automated processes, still in a cell environment, with reduced manual intervention.

Machines, tools and CAM will continue to evolve new functionality and will help manufacturing take steps in the future to adapt to common challenges.

In terms of automation development, turning centers are behind machining centers, but we predict that evolution and revolutions will take place in the following areas in the future:

• Higher coolant pressures to provide chip control – Coromant Capto® is already prepared to handle up to 200 bars (2900 psi)
• Automatic tool changing, using robots or a gantry
• Standardization to increase efficiency and communication
• Turret interface – as with machining centers where common spindle interfaces allow for tool rationalization, a new ISO interface is needed to allow for common clamping units
• Product data – the common tool definition defined in ISO13399 provides us with the manufacturing language of the future to describe tool data

Quick change in turning centers

Turning centers have fast tool indexing but typically have a lower utilization than machining centers due to the tool change and set-up time. Use quick change holders to reduce the measuring, set-up and tool change time and instead allow for extra machining time.

Read more about quick change solutions

Automatic tool change in turning centers

Each machine has a maximum turret swing diameter. All external tool projections need to be within this diameter to allow the turret to rotate without collision. Turning cutting units have a common length and offset dimension for each Coromant Capto® size.

The clamping units for each machine turret interface are designed so that standard cutting units fit within the turret swing diameter. When using driven tool holders, it is also advised to keep the tool as short as possible, not only to fit within the swing diameter but also to increase stability.

The bearings on a driven tool holder are much closer together than on a machining center. The short gauge line reduces vibration, ensuring increased productivity with increased security. For external tools that exceed the standard cutting unit length, the turret swing diameter can often be a limitation.

For applications requiring tool penetration, Coromant Capto® short tools are available to provide the shortest gauge line and fit within the turret clearance. Coromant Capto® short tools do not have gripper grooves and are for manual tool change only.

Examples of Coromant Capto® tools, with and without gripper grooves