Page 30 - MetalForming April 2013

Deep Drawing Replaces Hydroforming
DeHosse, “with a stationary form ring in the upper ram, the punch mounted stationary in the press bed and a float- ing cushion.”
Press specs: 36-in. left to right and front to back; adjustable force from 112 to 562 tons; adjustable stroke to 40 in.; ram speed to 912 in./min. on close and 95 in./min. during forming; cush- ion force adjustable from 28 to 280 tons, with a 16-in. stroke; 20-ton ejec- tion force; and ram-mounted knockout force to 30 tons.
Rather than design the press with an integral blankholder, each tool features its own blankholder. And while DeHosse says that the drawing process would function similarly whether the blankholder was mounted to the press or tool, there is one distinct advantage to having it in the tool.
“With the blankholder on the tool,” he says, “we can set a very low blank- holding force, since we’re using purely hydraulic valving to control the force, independent of the weight of the ram. If we hold these blanks too tightly, we’ll experience stress cracks and fractures
at the top of the draw. By reducing blankholding force, we promote better material flow throughout the draw- ing operation.”
Die work—new builds and maintenance—is per- formed by a local shop, AccuDie Inc., Meadow Lands, PA. “AccuDie func- tions as our external tool- room,” says DeHosse. “Our projects take priority; they’re in here three to four times per week picking up and dropping off. Of particular concern are the draw rings (of Ampco bronze); they see a lot of heat and oxidation from the stainless steel. That oxide buildup has to be removed and the rings pol- ished every 2000 to 3000 draws.”
Ram-stroke settings are controlled by digital linear transducers, “and the end-of- draw repeatability with the
At the new Greenerd hydraulic press, DeHosse forms 7-qt. stock pots; a 7.75-in. draw reduces a 17.75-in.-dia. blank to an 8.4-in. dia. pot. The press measures 36-in. left to right and front to back, and boasts an adjustable stroke to 40 in. and a 16-in. cushion stroke.
Triple-Action Press Technology—Why, Where and When
Submitted by Thomas M. Lavoie, applications engineering manager, Greenerd Press & Machine Co., Inc.; www.greenerd.com
Triple-action hydraulic presses feature several cylinders that can perform multiple operations during one setup, often the case when forming cookware as well as aerospace components and other products. The three actions include the main punch, cush- ion and blankholder platen. The presses can help to eliminate additional tooling requirements while enabling manufacturers to produce more uniform components, rather than having to manip- ulate the part several times with different tools.
A triple-action press also provides complete control over the various ram movements. The ability to set and manipulate param- eters will result in the most efficient cycle possible, for a better- finished part. Parameters can include draw speed, reverse ton- nage on the cushion, and when to actuate an eject function.
Depending on the application, the press can be custom- designed to meet specific requirements. Consider the examples below.
1) For some applications, including cookware, a triple-action press includes a main slide (where the tooling is mounted), a knockout/eject mounted on or above the main slide and a cush- ion/eject mounted below the press bed. This design proves use- ful for drawing a deep pan—the part draws over a punch but sticks in the upper tool when the main slide retracts. At that point, the knockout/eject can keep the part down on the punch or strip the part from the upper tool. Here, the cushion/eject is
used primarily to provide pressure on the material so it can be drawn without wrinkling or tearing.
By altering the press design and mounting the punch to the main slide, the cushion/eject will provide blankholding force dur- ing the downstroke of the main slide. The cushion/eject then would be used to push the part up and off of the lower tool or punch.
2) For other applications, a triple-action press includes a blankholder slide—which allows a higher-tonnage ram to run through the middle of the press—as well as a bed-mounted cushion/eject. The press can feature any combination of cylin- ders to provide power to form, punch, coin, draw, etc. in one setup, and finds use in the manufacture of jet-engine cowlings. The main slide serves as a blankholder platen, and applies adjustable tonnage to the material as the main ram (located in the middle of the main slide) descends to form the cowling. The cushion/eject can be used to push the part up and out of the lower tooling.
3) A triple-action press also can allow for a reverse draw to, for example, produce a “wave” form on the bottom of the part. In this case the main punch descends as the blankholder clinches the material. When the main ram reaches its full depth, it holds its position while the pressurized cushion/eject cylinder pushes back against the main ram. This action produces a small form or “wave” on the bottom of the drawn part. Here, the cushion is used on the downstroke to help draw the part and reverts to an eject to produce the form.
28 MetalForming/April 2013 www.metalformingmagazine.com