Reducing defects, improving ROI with direct-drive motors

The type of motor used in a servomechanical press—traditional geared, chain drive system, or direct drive—can dramatically affect the final product.

Mechanical servo metal stamping presses use high-torque brushless motors to produce complicated stampings at fast speeds. But the type of motors used—traditional geared, chain drive system, or direct drive—can dramatically affect the final product.

Modern stamping machines are highly sophisticated devices and can be a large capital investment. They give metal formers the ability to create precise, often complex forms while meeting the need for high throughput and production. But that high throughput and production can pose a challenge: A higher production volume means it’s more difficult to inspect every piece and spot defects.

For nonappearance parts such as metal cans or automotive components, the finish on the product is secondary to its function. But for finished parts such as decorative metal trim on appliances, control panels, and door covers, the stamping press needs to produce parts free from any errors.

In a progressive die press system, the mechanical limitations of a traditional motor and gearbox system create vibration, which affects the final finish on the product. Traditional applications use oversized servos and gearboxes to match the inertia of large rolls. This is costly to maintain, limits index times and throughput, and has a low power density, and accuracy can suffer.

Using a direct-drive motor in next-generation stamping presses can increase speed and stroke optimization while requiring fewer parts and producing much less vibration throughout the process.

Fewer Parts, Less Vibration with Direct Drive

Direct-drive motors allow machine builders to use small motors with a high-resolution feedback design that couples directly to the load. This eliminates the need for mechanical transmission, such as the use of a gearbox, which is what typically introduces vibration into the production process. This creates a quiet and dynamic operation with a very long system lifetime.

A direct-drive motor also can protect the system against excessive reaction torque. It can reduce system inertia by removing the gearbox and related transmission elements, Again, this helps to minimize vibration and disruptions which could cause imperfections in appearance parts—and accelerates production.

Improved Performance

Reducing vibration in the stamping process is the principal reason for selecting a direct-drive motor, but there are other complementary advantages: reliability, size, power, speed, and ROI.

Direct-drive motors allow machine builders to use small motors with a high-resolution feedback design that couples directly to the load. This eliminates the need for mechanical transmission, such as the use of a gearbox, which is what typically introduces vibration into the production process.

Eliminating the gears, pulleys, seals, bearings, and other components means that there are fewer parts to maintain and repair. Directly coupling to the load also improves positional, speed and dynamic accuracy. No hysteresis, backlash, or lost motion occurs in any direction. Any tuning or maintenance to correct for this in a standard mechanical transmission system is eliminated, making it less costly to maintain and repair over time.

Smaller Motor, Same Power

However, a smaller motor doesn’t necessarily mean less power. A direct-drive cartridge motor can provide up to 510 Nm of continuous torque with speeds up to 2,500 RPM and overall power of 11,700 W. This can meet the needs of most medium-speed and high-torque applications, sometimes providing up to 50% more torque density than conventional servomotors. It also dramatically increases the power density of the system. With fewer components, the motor delivers as much power in a reduced size, allowing for a smaller overall machine.

The power and related torque density of direct-drive cartridge motors allow them to achieve higher accelerations compared to similar servomotors. Coupled with the lack of vibration from removal of the transmission system, this can significantly reduce index times and increase throughput because the machines can produce more with less worry about defects.

Reduced maintenance, more power, better throughput, less unscheduled downtime—all of these add up to significantly enhance the profitability of an application. Direct-drive technology allows for a longer usable life with fewer defects and greater production, and direct-drive motors may be able to deliver a better ROI in metal stamping presses than other motor types. There are fewer parts to install and maintain, lowering labor and parts cost for an economical, time-intensive machine.