Die Science: It’s a servo drive stamping world

The stamping industry is evolving; materials are getting lighter and stronger, part geometries and tolerances are getting more difficult to achieve, and customers expect part costs to go down.

Servo technology is one way that stampers can meet these daunting challenges.

Servo Drive Presses

Think of a servo drive press as a giant, linearly traveling robot. Unlike a typical crank drive press, which uses a flywheel to create the energy to move the ram up and down, servo drive presses use servomotors to control the ram motion of the press. This servo motion allows the stroke length, motion, and ram speed to be changed so that one press can be used for a variety of stamping operations.

A servo drive press allows you to adjust the stroke length of the press to accommodate different part geometries and feeding times, and this can be a big advantage. For example, if you are running a fairly small part 1 inch deep and 2 in. long, you will need a press with about a 4-in. stroke to allow the part to move up at least 1 in. and forward at least 2 in. If the only press you have offers a 12-in. stroke, then you are not performing any work for 8 in. of the stroke length, so you’re getting only one-third of the potential output of your process. Adjustable stroke length allows for a variety of different part sizes and shapes to be manufactured in a single servo drive press.

Ram motion and speed also can be altered to aid in deep-drawing applications, which are most successful with slower ram speeds. A slower forming speed reduces friction and heat generation, which is important when forming materials such as dual-phase and high-strength, low-alloy (HSLA) steel. In addition, the punch-to-metal contact speed can be reduced, allowing metal to flow into the drawing cavity. The ram also can be programmed to approach the bottom of the stroke in microinch jogs, which is advantageous for forming certain part geometries.

Because the ram of a servo drive press can stop at the bottom of the stroke and remain idle for a programmed amount of time, it is suitable for hot stamping operations. And because the ram can dwell at bottom dead center, the amount of springback in stamped parts is reduced.

Servo presses don’t use a flywheel, so they typically are much quieter than crank drive presses. They also are more expensive than comparable-tonnage crank drive presses, but the return on investment usually is well above the additional cost.

Some servo presses have a press cushion that enablesthe blank holder force to be changed during deep drawing. This allows high holding forces to be obtained at the beginning of the stroke for forming draw beads. After that, the pressure can be released so the material can flow freely into the cavity and over the drawing punch. This cushion also helps eliminate secondary drawing operations.

Servo Drive Feeders

Servo drive feeders are the most accurate and reliable type of feeders available. They help feed the material smoothly and accurately in the tool.

These feeders use servomotors to control the tension or grip on the material, as well as the feeding amount. They also can be programmed to accelerate and decelerate the strip as it feeds into the die, which prevents the strip from hitting and shocking pitch notch blocks.

Servo Drive Transfer Systems

Servo drive transfer systems allow simple adjustment of part transfer movement vertically, in and out of the die, and from die to die. They can accelerate and decelerate their motion to reduce the risk of part vibration and thus parts falling from the transfer unit or being mislocated. This motion adjustability allows a single transfer system to be used for multiple part sizes and shapes requiring different pitch lengths and lifts.

When a servo drive transfer system is used with a servo drive press, the output can be maximized so that little or no time is wasted from part to part. In some cases, parts per minute can be doubled or even tripled.

Other Applications

Servo drive technology isn’t used only in presses, feeders, and transfer units; it's also used in supplementary operations such as in-die tapping and welding. Tapping and welding speeds can be changed at will and easily programmed into the system.

Materials such as stainless steel often are difficult to tap. Slowing down the rotation speed of the tapping head often is the solution. The speed at which the tap reaches its destination also is adjustable.

Servo technology gives stampers more flexibility, greater output, higher part quality, and simple adjustment capability. It's definitely turning into a servo drive stamping world. Now all we need are servo-driven diemakers. We could program them to slow down and think about the decisions they are making and then speed them up when it's time to execute the task. LOL!