March 11, 2008
This multi-source article offers readers advice on the criteria to consider when buying a press. The article examines application suitability, drives, and controls as well as other considerations such as tonnage, frame construction, speed, and horsepower.
Editor's Note: This article is Part IV of a series covering questions and answers for those who are in the market for a press or press system.Part I, speed; Part II, covers tonnage; Part III, materials; Part V, best for operation; Part VI, best for part; Part VII, automation; Part VIII, matching automation to press; and Part IX, selecting the right press for your application.
The following questions–and their answers, provided by industry equipment manufacturers and experts–are intended as a general guide to help you simplify the daunting task of selecting a press or press system.
4. What Else Do I Need to Look for in a Press to Meet Demands for Increased Part Accuracy?
Part Accuracy—Frame Accuracy."Part tolerance demands have become tighter, and zero defects are the norm. These demands have created the need for new press designs and very careful selection," Minster's Cattell said.
The more rigid the frame, the lower the deflection and vibration, and the more accurately the part can be made, press manufacturers said (see Frame Design sidebar in Part II).
"Most presses in the field today meet the industry standard for press bed deflection of 0.0018 inch per foot, with the full load spread over two-thirds of the bed area," Cattell said."This distance is measured in the right-to-left direction between the centerlines of tie rods–not the length of the bolster. The slide and crown are designed to meet the same standard.
"With new technology demands, the die designer often calls for a much lower total deflection with new press designs. A 0.001-inch-per-foot deflection is becoming the norm," Cattell said.
[Tip]Red Stag's Pfundtner said."The JIS [Japanese Industrial Standard] accuracy inspection standard should be used to analyze press accuracy. This is a knife edge on the centerline under maximum force to determine the elongation of the press to the outside edge of the bolster."
Part Accuracy—Slide Guides. To improve part accuracy, the press must have low bearing clearance, close tolerances, slide guide systems, and wide-spaced connections as well as high rigidity, AIDA's Boerger said.
Part Accuracy—Servo. A servo-mechanical press's controllable slide motion allows it to adapt the slide speed to the requirements of the forming process, which can improve part quality, Schuler's Kinzyk said.
Part Accuracy—Hydraulic. A hydraulic press's control over forces and motions empowers the press to enhance overall quality of a manufactured part, manufacturers said. Control of lateral slide movement caused by off-center or unbalanced loads helps achieve tight tolerances and improves part quality.
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