August 8, 2007
In a perfect world, all tooling and dies would create perfectly balanced loads across the bed of a press. Unfortunately, we do not live in a perfect world and many manufacturers are required to design production systems that require off-center loading in their presses. The reality is that symmetrical loading is sometimes inefficient, and sometimes impractical to achieve, and usually no matter what type of structural measures are taken, off-center loads can be problematic.
There are a variety of reasons for off -center loading. The most obvious is the geometry of the part being formed is not conducive to an even load. However, the trend to improve production efficiency and reduce costs is spurring an increase in off-center applications as manufacturers consolidate multiple dies or processes into single machines.
By answering the following questions, you can easily determine the right press solution for your application:
The answers to these questions will determine which type of press is ideal for the job.
Manufacturers that are looking for a multiple purpose machine to run multiple processes with varying load configurations are going to experience Dynamic Loading. This type of off-center loading is best accommodated by an Active Leveling System. These presses are equipped with a multi-axis high-speed motion controller, linear transducers to monitor ram position and sophisticated proportional hydraulics. The motion controller provides closed loop servo control of each individual press cylinder to maintain bed to ram parallelism.
Active Leveling control is offered in either 2 or 4 axis depending on the specific application. Two axis control provides parallelism from left to right or front to rear, while four axis control provides control of both left to right and front to rear.
In dedicated applications, the tooling and loading are known at the time of press design and compensation for the off-center loading is engineered into the structure and hydraulic design. To further define dedicated loading, we can subdivide into selective and non-selective applications.
In applications such as progressive die applications, multiple dies or stations are present in the press at the same time and are actuated simultaneously during each cycle of the press. This is referred to as Dedicated Non-Selective Loading. The press can be designed to handle the specific off-center load through hydraulic and/or structural modifications. This type of system usually results in lower upfront costs but results in a press system that is dedicated to and limited to the specific application.
Selective off-center loading is ideal for manufacturers that want to consolidate multiple processes into a single press system whereby 2, 3, 4 or more dies are always present in a press but only one die set is loaded and actuated per cycle. By utilizing traditional on/off valving and structural balancing, the press manufacturer can electronically shift the press force to center over different locations on the press bed. The operator then "selects"a specific die to be "active"during a given cycle. In addition to decreasing or eliminating die set up- time, selective off-center loading is an effective solution to save floor space by displacing multiple presses.
Whether the end user's application requires dedicated off-center loading, or a more advanced active level control, emerging technologies in the field of hydraulics are being implemented to ensure part quality, reduce die wear and reduce complex setup time. This technology is transforming what was once considered an obstacle into a reliable method for meeting our customers' off-center loading needs.
STAMPING Journal® is the only industrial publication dedicated solely to serving the needs of the metal stamping market. In 1987 the American Metal Stamping Association broadened its horizons and renamed itself and its publication, known then as Metal Stamping. Print subscriptions are free to qualified stamping professionals in North America.