Page 43 - MetalForming January/February 2022
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 Metal Matters By Daniel J. Schaeffler, Ph.D.
New Column Tackles Pressroom Challenges
Four years ago, I had the privilege of taking over Metal- Forming magazine’s The Science of Forming column, crafted for decades by Dr. Stuart Keeler, the father of the forming-limit diagram (FLD). His were big shoes to fill, and I have tried to do justice to the memory of Dr. Keeler and the great knowledge he shared over his long and storied career.
Dr. Keeler passionately brought science to the pressroom floor, and his articles reflected just that. Nearly every topic he discussed had its origin in a classic textbook or something observed in a laboratory. He had a knack for stating theoretical concepts in a manner understood by experienced practitioners.
Some of my writings attempt to cover similar topics. I also have incorporated concepts related to common issues observed while working with global metal producers and manufacturing companies, small and large. With the evolution of content, the MetalForming magazine editorial staff and I decided we should retire the Science of Forming moniker and create a new column—Metal Matters—which more accu- rately reflects the wider spectrum of topics now covered.
Several of my recent articles have spurred remarkable conversation among the readers. Among them: An article from 2018 titled “Golf Shots and Manufacturing Variability,” which notes that while every company has certain strengths which they play to their advantage, many do not fully grasp the nuances of the production and supply of different metal grades and how these affect stamping-process optimization. The article discussed how process-control differences at three metal-production mills leads to each supplying a prod- uct in full compliance with the ordered specification, however, the different property ranges impact stamping performance.
Also from 2018, an article titled “Sims Aren’t Everything” discussed how metal forming simulation has advanced tremendously during the last 20 years and saves days of hands-on trial-and-error work, helping stampers evaluate what-if scenarios associated with variables such as sheet metal grade and thickness, binder and addendum designs and blank shape. However, simulation results only are as
Dr. Danny Schaeffler, with 30 years of materials and applications experience, is president of Engineering Quality Solutions (EQS) and Chief Content Officer of 4M Partners. EQS provides product-applications assistance to materials and manufacturing compa- nies; 4M teaches fundamentals and practical details of material properties, forming technologies, process- es and troubleshooting needed to form high-quality components. Schaeffler is the Metallurgy and Form- ing Technical Editor of the AHSS Application Guide- lines available from WorldAutoSteel at AHSSinsights.org.
Danny Schaeffler
248/66-STEEL • www.EQSgroup.com
E-mail ds@eqsgroup.com or Danny@learning4m.com
good as the simplified estimates of reality used as inputs. For example, imported CAD files are accurate prior to tool construction, but sheet metal flow deviates from sim- ulation once a grinder changes the tool surface, especially at a draw bead. Simulations may assume a rigid tool, ram, bolster and press, but production stampings reflect a different reality. Tool recuts to address forming or dimensional issues remove mass from the tool, and therefore contribute to a loss of rigidity not considered in the simulation. These are just a few scenarios that require the need for additional
hands-on analysis of physical parts.
We’ve also discussed the FLD, noting in a five-part series
in 2019 that many stamping companies require a passing FLD as a go/no-go gate to proceed to the next stage of tooling buyoff. That series also covered strain analysis, the form- ing-limit curve (FLC), and the associated thinning-limit curve, where we highlighted the differences between the FLC and FLD and how the FLC provided by the sheet metal supplier can help stampers assess the robustness of a stamped part with an FLD. Importantly, these articles guide the prac- titioner on techniques to promote measurement accuracy, critical since incorrect measurements or their interpretation may lead to acceptance of a substandard tool and process, or result in unnecessary, costly and time-consuming tool work. Also included are the procedures for using an ultrasonic thickness gauge to obtain nearly all of the information pro- vided by a full circle-grid strain analysis.
Material-Selection Science
Selecting the right sheet metal alloy for a particular appli- cation has implications far beyond the stamping press. In my January 2020 column, “Material Selection: The Rest of the Story,” I describe how the development of higher-strength steels has led to equipment upgrades at steel mills and at metal forming and processing companies. In fact, even first responders need new equipment and modified extrication techniques to address the properties and characteristics of new alloys. Automotive-accident repair has even become more challenging since welding and flame straightening adds unwanted heat, resulting in degraded local properties in parts made from advanced steels. And, increased use of aluminum requires greater consideration of the higher scrap value, in terms of its minimization as well as its capture.
I followed up in February 2020 with an article titled “Getting More Than You Ordered,” discussing how sheet metal suppliers may choose to upgrade an ordered material to help improve their own production-scheduling efficiency. Steel mills cast and roll grades of similar thickness and width together to achieve a steady-state production environment, which maxi-
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