Page 39 - MetalForming Magazine April 2023

Metal Matters
By Daniel J. Schaeffler, Ph.D.
Save Time, Money and Weight with Tailored Parts
Assembled products often contain features that do not contribute to their functionality but exist solely to assist with the manufacturing process. One example: the flanges used for joining adjacent parts. While the flanges add to the material purchase price and weight, typical design approaches require them to facilitate assembly, while ensur- ing that the part has targeted performance characteristics in different areas. Introducing the joining step earlier in the manufacturing sequence offers significant benefits, at least for certain product designs.
Another constraint in current design approaches: limiting sheet metal selection only to monolithic blanks—one grade, one thickness and one coating for an entire part. There are no constraints on the shape, so the blank can have straight sides or a developed perimeter. Depending on this shape, significant engineered scrap may result from the chosen nesting pattern.
Moving beyond monolithic blanks to tailored blanks adds new flexibility for body-structure engineers, allowing them to design subassemblies with the targeted strength, coating, thickness and deformation behavior in separate sections of the part.
Rationale for Tailored Parts
The earliest tailored parts came from laser welded tailored blanks (LWTB, also referred to as laser welded blanks or tailor welded blanks)—created by welding two or more sub- blanks together. Each sub-blank can differ in thickness, strength and coating.
A tailored part allocates the required material strength and thickness only where it’s required in the subassembly. In contrast, conventional design approaches to address areas needing additional thickness—for stiffness or crash perform- ance—entail stamping a primary part as well as a smaller reinforcement and then joining them together, usually with spot welds or rivets. Following this conventional approach requires manufacturers to have the resources, infrastructure
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 forming technical editor of the AHSS Application Guidelines available from WorldAutoSteel at AHSSinsights.org.
Danny Schaeffler
248/66-STEEL • www.EQSgroup.com
E-mail ds@eqsgroup.com or Danny@learning4m.com
and personnel to stamp at least twice as many parts, transport and hold the work-in-process inventory, and then join the parts. Further, joining two stamped parts worsens tolerance- stackup issues related to geometric dimensioning and tol- erancing. In contrast, using tailored parts will result in part consolidation, improving material utilization, reducing scrap, and requiring fewer plant resources and less labor.
Build quality also should improve. Joining formed parts, each with their own springback and tolerances, is more chal- lenging than joining flat blanks first and then stamping the tailored blank. Also expect improved product performance due to continuous sections rather than relying on fastened joints to transfer loads. Eliminating spot welds or rivets also can reduce noise, vibration and harshness. A continuous weld line used to fabricate tailored products means a more efficient load path and improved dimensional integrity.
Material Utilization
Improvements in material utilization may be the strongest factor promoting the use of tailored parts in engineered components. Some parts (such as the door opening panel shown in the accompanying figure) have large cutouts des- tined to become engineered scrap. For parts such as these, structural requirements necessitate using numerous rein- forcements, or making the part from a blank as thick as the thickest section.
In the case of the door opening panel shown, the rocker area closest to the road is at risk of exposure to road salt, and as such body structures must use galvanized steel throughout the entire blank, even though the roof line has minimal risk of corrosion. Converting this part to a LWTB allows for optimized nesting of the individual components, with material strength, thickness and corrosion protection deployed only where the end product benefits from those characteristics.
In addition, reduced width requirements of the sub- blanks can allow stampers to select from a larger array of material suppliers or to use master coils yielding slit mults. At the other extreme, blank dimensions larger than rolling- mill capabilities become feasible, allowing, for example, the stamping of inner side panels of tall SUVs and cargo vans.
Types of Tailored Parts
LWTBs represent just one type of parts where designers can specify material strength, thickness and corrosion pro- tection where these properties are most needed for part function, and remove weight that does not contribute to part performance. Other tailored parts include patchwork blanks, tailor welded and tailor rolled coils, tailor rolled
36 MetalForming/April 2023
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