Page 18 - MetalForming April 2012

Rebuild
or Retrofit
Slower cycle times and inconsistent part runs can be byproducts of older presses. To reduce cycle times and improve part quality, metalformers can upgrade their presses using servo-quality proportional valves and high-performance PLCs.
Today’s metalformers face shorter lead times, tighter tolerances and stricter quality guidelines, all while minimizing their internal pro- duction costs. Operating within these guidelines can be challenging when using hydraulic presses purchased as recently as 10 to 15 years ago, which likely employ outdated technology. That’s why many metalformers are con- sidering press rebuilds or retrofits as a way to upgrade older presses with new advancements in press technology.
There are numerous reasons to con- sider a press rebuild or retrofit. Slower cycle times and inconsistent part runs can be byproducts of older presses. At the heart of older press technology will likely be a control panel with limited functionality compared to today’s pro- grammable-logic controllers (PLCs). Older operator interfaces have mono- chromatic keypad displays, and provide a slow update time for viewing critical data. These controllers do not offer a way to automate press runs, requiring oper-
Tim Wilson is a design engineer with Greenerd Press & Machine Co., Nashua, NH: 603/889-4101; www.greenerd.com.
ators to manually enter instructions with each job setup. Manual setup increases cycle time and the likelihood of errors.
Presses more than 10 yr. old may include a manual proximity switch to signal positioning on reversal, a critical process for producing accurate parts. This manual switch is only as accurate as your hand is steady, and parts may eventually fall out of tolerance. In addi- tion, many older presses were designed with small proportional directional valves that provide a slow pressing speed into the part, in order to achieve an accurate reversal position. With today’s servo-quality proportional directional valves, metalformers can achieve positional accuracy and very high flows, due to the rapid response time of the valves.
Aging pumps, motors and even hydraulic fluids are not as efficient by today’s standards. In addition, due to enhancements and new options, older power units may not be as economical as new equipment. And, as shops grow and add larger presses, the amount of power needed increases.
Last but not least, metalformers must address safety and update their older
presses as needed. Upgrading to ANSI B11.2-1995 (R2010) and adding light cur- tains allows a press to be run by an aux- iliary piece of equipment such as a feed- er or foot switch, to reduce cycle time.
Pressing Ahead
Today’s hydraulic presses are faster and more reliable than ever. In the last decade, the technology has experi- enced constant upgrade. PLCs and other electronically based controls have improved speed and flexibility.
To reduce cycle times and improve part quality, better valves and high- performance PLCs provide faster speeds and excellent positional accu- racies. Servo-quality proportional valves offer fast response times, even in larger-size valves that can handle the required flow and faster cycle times. Proportional valves offer an improved level of control over older servo valves, without the sensitivity to contamina- tion that can lead to maintenance issues. And, today’s PLCs have scan times fast enough to achieve ±0.001-in. positional accuracy with a D08-size valve, and provide monitoring of the linear transducer to achieve the rever-
BY TIM WILSON
16 MetalForming/April 2012
www.metalformingmagazine.com
That Aging Hydraulic Press?