Modern metal stamping presses are versatile systems. They can perform a variety of operations on a single machine, including bending, blanking, piercing, coining, four slide forming, piercing, notching, flanging and many others.
The types of metal-stamping presses used however, depend on the nature of the stamping work to be done. Metal stamping presses can be categorised according to the drive mechanism, like mechanical, hydraulic, and servo. They can also be classified by press frame construction. Whether it is gap-frame, c-frame, or straight side, they are based on certain important characteristics of the press.
Go Faster With Mechanical Press
Most mechanical presses use flywheel drives, driven by motors, to store energy that is then transferred to ram motion. Because flywheels expend energy with each down stroke of the ram, they slow down. The motor then restores the energy to the flywheel in time for the beginning of the next stamping-press cycle.
Mechanical presses are known for their speed. With this capability, many operators use mechanical presses for high-volume metal stamping applications where parts are flat and do not have high depth. While this may seem like a limitation, compared to its hydraulic press counterparts, speeds of above 1,000 strokes/min make up for this. Finally, the stroke range of mechanical presses is typically short.
More Control With Hydraulic Presses
Hydraulic presses differ from mechanical drives by depending on the pressure of hydraulic fluid in cylinders to provide force to the ram. These presses, by controlling the pressure, allow the pressing force to be controlled (up to the full force if need be, throughout the motion of the ram) as the part is formed.
Force is an important consideration for hydraulic presses because force control in the vertical motion, ie: throughout the stroke length, can affect the effects of forming. It is said that hydraulic presses are relatively easier to maintain due to better hydraulic system designs and they incur lower energy costs for users.
Mechanical + Hydraulic Presses = Servo Presses?
A relative newcomer in the world of stamping are the servo presses. These presses use servo drives, a control device that outputs electrical signals to a servomotor to induce motion, while providing adjustments for deviation from the set state.
These presses arguably combine the advantages of mechanical and hydraulic presses as they have the capability to control the press’ stroke length and velocity.
According to Schuler, a press technology solutions provider, the advantages of these presses are higher efficiency, better component quality, better flexibility due to adaptable slide movements, superior energy efficiency compared to conventional presses, and maximum process reliability.
Stamping The Dynamic Way
Schuler has its own ServoDirect technology. The use of dynamic torque motors permits the straightforward and rapid programming of different movement profiles in one press cycle.
Oscillating stroke mode permits user-programmable slide stroke heights. The reversing movement of the torque motor means that the eccentric drive of the slide has an oscillating motion and alternates between moving forward in one stroke and backward in the next stroke. Energy accumulators can be used as an option in order to reduce the connected load.
For frame construction, stamping presses generally conform to two basic designs: gap-frame or straight side. Gap-frame presses, also known as c-frame presses because of their shape, are connected from bottom to top at one location, behind the work area. These presses feature lower capacities and typically perform as stand-alone machines, often manually fed.
Straight side presses are supported on each side of their rectangular footprint, and given their robust construction, they are less susceptible to deflection arising from off-centre loading than gap-frame presses.
Such deflections can occur when stresses drive the ram out of its normal, parallel condition. Due to their beefed-up framework, straight side presses offer high capacities and often operate in press lines, either teamed with other straight side presses or outfitted with ancillary equipment.
Energy Efficiency
Metal stamp presses have improved rapidly in features and functionality. One of those improvements that manufacturers like to shout about usually involves energy efficiency.
For example, the Evolution series of press brakes from Ermaksan is touted as an energy efficient machine that uses energy only while it is bending. It is a fast operating press brake using servo motors and efficient pumps that are quieter than most presses at 63 db and is TÜV-SÜD certified.
It can achieve an accuracy of between +/- 0,01 mm. Other improved features include longer system and pump lifespan due to better quality components and smart running technology. These press brakes are also said to use 65 percent less energy than a standard press brake, with no oil change needed for five years.
Automated Stamping
Automation of stamp pressing has also become the norm, as the competition for ever increasing productivity and speed escalates throughout the industry. New processes such as hot stamping have also made automation necessary. For example, special care must be taken when unloading the part from the press due to high temperatures inside the die after hot stamping. Manual operations are either inefficient or impossible.
One possible solution can be found in ABB robots, where multiple IRB 6650S and IRB 7600 robots are dedicated to load the oven, depending on press rates. By means of a battery of destacking tables and destacking robots, up to three or four parts run through the oven and are loaded into the press.
Another example is the Fanuc stamping press to press transfer system. The system incorporates various Fanuc technology, including six axes articulation robots, visions sensors and cameras.
A Fanuc R-2000iA can be used to destack blanks utilising modular tooling suction cups and double blank analysers while a different R-2000iA equipped with a Fanuc robotics 2D camera, locates and picks up a blank from a gauge table and loads the part into the draw press. Inter press robots transfer parts down the press line through the final press and onto a conveyor belt.
Looking Ahead
Metal stamping has undergone a period of change resulting in something that is radically different from the traditional way of stamping. A process that requires no physical force, electrohydraulic forming is a method of stamping, which the action of an electrical discharge on water is transmitted to the workpiece.
When that happens, the workpiece is deformed and takes on the shape of an evacuated die. Deformation is due to ‘shock waves’ in the rapid evaporation of fluid.
Metal stamping operations are the mainstay of any manufacturing line. With customers demanding higher precision, shorter timelines and greater product variation, improved flexibility and shorter time-to-markets are needed. Press manufacturers have responded, and press technology has evolved to serve these diverse needs.
Did You know?
Sheet-metal stamping started playing a prominent role in the early 20th century, especially in the production of motor-vehicle bodies. By the 1970s, other variants have emerged, one of them is hot stamping, also popular with automotive manufacturers. The technology was developed to make metal parts stronger yet lighter.
