Page 18 - MetalForming-Jan-2018-issue

Tooling by Design
By Peter Ulintz
Four Things Die Setters Need to Know for Safe and Accurate Setups
There are four areas with which die-setters must be intimately familiar in order to ensure safe and accurate setup of stamping dies: press capacity, coil-feed-line capacity, feed accu- racy and coil payout. Here’s what you need to know about each.
Press Capacity
Every mechanical power press is designed and manufactured to operate within the capacity limits set forth by the press manufacturer. Capacity limits dictate which dies can safely run in the press. Gener- ally, these will include press ton- nage, press energy, stroke length, shut height, bed size, off-center loading limits and stroking speed.
Fig. 1—Concentrated loads reduce press force capacity
let decoiler may perform the uncoil- ing function. A powered straight- ener, pull-through straightener or a straightener-feeder combination can perform straightening to remove coil set. Coil feeding, which moves material into the die in pre- cise lengths at a predetermined rate, can be performed by air feeds, mechanical roll feeds or servo-dri- ven roll feeds. Other coil-handling products and added equipment fea- tures enhance material loading, threading and removal procedures. These may include loading cars or ramps, turnstiles, cropping shears, threading tables and threader-peel- er systems.
Three basic types of coil-straight- ening equipment are available: tradi- tional spread-center straighteners (sometimes called flatteners), precision close-center straighteners and preci- sion roller levelers. It is critical that the die setter understand the capability and limitations for each machine type.
Coil straightening is accomplished by bending and unbending the incom- ing coil material around several sets of rolls that alternately stretch and com- press the sheetmetal’s upper and lower surfaces. Each bend works the material past its yield point until both surfaces end up having the same surface length. The number of rolls in a straightener correlates to the number of yielding strains (bends) it can produce, which in turn determines the extent of possible shape correction. The die setter must properly set and adjust the roll depths for each coil width/thickness/strength combination to assure the best results and to prevent damage to the straight- ening equipment.
Feed Accuracy
Setting the feed system properly, including the pilot-release function,
Die Too Small for Press
The tonnage rating of a press is the maximum load that a press can with- stand under normal operating condi- tions without causing damage to its structure or drivetrain. Keep in mind, this rating assumes that the die length spans across at least two-thirds of the press slide. When the die covers less than two-thirds of the slide length, the maximum allowed tonnage is reduced substantially in order to prevent dam- age to the slide caused by concentrated
Peter Ulintz has worked in the metal stamping and tool and die industry since 1978. His back- ground includes tool and die making, tool engi- neering, process design, engineering manage- ment and advanced product development. As an educator and technical
presenter, Peter speaks at PMA national seminars, regional roundtables, international conferences, and college and university programs. He also pro- vides onsite training and consultations to the met- alforming industry.
Peter Ulintz
Technical Director, PMA pulintz@pma.org
loads applied between the pitman con- nections (see Fig. 1).
Tonnage ratings for mechanical presses are specified at a small distance above the bottom of the press stroke, usually between 1⁄32 in. and 1⁄2 in. above bottom dead-center. When a mechan- ical press must work higher up in the press stroke, as is the case for deep drawing, less tonnage is available due to the reduced mechanical advantage of the pitman connections (Fig. 2).
Deep drawing consumes significant- ly more press energy than conventional stamping, especially when working at slower speeds. When considering force and energy requirements for deep drawing, the attributes of a hydraulic press should also be considered. Hydraulic presses provide maximum force throughout the entire stroke dis- tance and can provide higher forming- energy levels than a mechanical press of equivalent force rating.
Coil-Feed-Line Capacity
Uncoiling, straightening and feeding are the three basic functions performed by a coil-feed line. A reel, cradle or pal-
16 MetalForming/January 2018
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