The following report and data are courtesy of Ohio State University Graduate Student, Eren Billur, from the Center for Precision Forming (CPF) as it appeared in FMA Publication, The Stamping Journal.

Die materials and wear in stamping AHSS, Part III

Research results and recommended die materials and lubrications

Many cast-iron and steel grades are used for manufacturing dies in the stamping industry. The cost of these materials varies considerably, but with appropriate surface treatments, coatings, and lubricants, a cost-effective die material can outperform the expensive ones.

Die material selection requires a systematic evaluation of tool materials, coatings, and heat treatments, with cost considered as a parameter. Having a proper knowledge of surface treatments and coatings can save money in stamping die manufacturing.

Comparative Studies

Several studies rank tool materials and coatings using a widely accepted standard test.^{1, 2} However, they do not give quantitative information regarding tool life under practical stamping conditions. There are a number of publications on comparative die wear studies, yet not many of them use advanced high-strength steel (AHSS) as sheet material. Figure 1 provides a summary of ranking results.³

Benchmark Studies

Benchmark studies give a numeric comparison of tool life (number of good parts stamped) for a given tool material and coating. Forming tests were conducted until galling and scratches were visible on the sheet metal.

The first study was a channel forming test using uncoated DP600. Figure 2 shows the results of this study.

A similar study was performed with uncoated DP980 material using the part seen in Figure 3. The forming tests were conducted up to52,000 stampings, and results are shown in the figure.4  As a benchmark, forming of a B-pillar inner also showed that conventional tool materials fail from heavy galling after making a few hundred stampings in AHSS. Figure 4 shows how the tool life of D2 changes with three different coatings.5

Guidelines and Recommendations

For the forming of AHSS with 500-to 800-MPa tensile strength, several tool steel companies, industrial experts, and research facilities recommend the following tool materials, treatments, and coatings.^6,7

• Hardened Carmo
• D2 + TD
• D2 + PVD CrN
• D2 + CVD TiC
• Vanadis 4E + PVD CrN
• Vanadis 4E + CVD TiC
• Vanadis 6 + PVD CrN
• Vanadis 6 + CVD TiC
• Hardened Vancron 40

FEA Prediction of Die Wear

The wear coefficient can be used to simulate wear progression using the pressure distribution and sliding distances are not constant throughout a stamping die, inserts may be used to reduce wear at critical locations in the dies. At this point, simulations can be useful for the proper design of die inserts. Figure 5 shows how simulations can be used to determine the locations of mild and severe die wear.

When the wear coefficient and surface hardness of tools and sheet used to estimate how many successful parts can be stamped before galling and scratches become visible. With these parameters, we can estimate tool life, and insert design can be improved.

The original version of this article from the May 2010 version of The Stamping Journal is available at http://nsmwww.eng.ohio-state.edu/May10R_DUpdate_628-9.pdf 

The following article is courtesy of American Machinist

The powerful, and heavily armored, troop carrier called the MRAP (for “mine-resistant ambush protected” vehicle) won’t win any prizes for style, though the people who ride in it don’t mind a bit. That’s because thanks to a V-shaped hull that deflects the force of explosions beneath it, and its outer shell of thick steel plate, it has brought U.S. soldiers and Marines an unmatched level of protection against explosives and small arms fire. Once the effectiveness of these vehicles in saving lives and preventing injuries became obvious, the U.S. Dept. of Defense rushed to increase the number of them available for deployment to combat zones. In May 2007, Secretary of Defense Robert Gates declared that the acquisition of MRAPs was the DoD’s highest priority.

Among the companies charged with supplying these vehicles is Navistar Defense. Navistar and its suppliers had to move quickly to fill the DoD’s order. The work of developing new components for this evolving family of vehicles had to be done rapidly and it had to be done right. Navistar Defense supplier Inteva, a manufacturer of door systems, was tasked with producing a new door-assist module for the Navistar Defense MaxxPro MRAP, as well as the heavier MaxxPro Plus and MaxxPro Dash models. The module assures that the vehicle’s 2,000-lb armored door with its air-assisted hydraulics opens in case of an accident or emergency. It also prevents the door from accidentally closing on a person.

As a partner in this vital work Inteva chose 3-Dimensional Services Group, a firm that specializes in design, engineering and analysis, in-house tool construction, and complete build of prototype first-off parts and low-to-medium volume production runs. Its use of advanced process methods, manufacturing technologies and staff talents means that prototype parts—not just models—are typically provided up to 70% faster than conventionally equipped prototype shops are able to offer.

The door-assist module is a complex part and 3-Dimensional Services was tasked with creating 63 components in all. These included the base plate, two latching components designed to be mounted to the body inside the door skin, hinges which are, similarly, covered by the door skin, side rods, and slider blocks.

An array of production processes
To create this complex part an array of production processes were required. Forming was used to produce the angle supports for slide system. Welding, both manual and robotic, was employed: manual welding for the module’s handles, levers, and angle supports, while the main base plate and close out brackets were robotically welded. Plastic injection molding, using tough, metal-like Delrin (Polyoxymethylene) as well as Sanaprene thermal plastic elastomer was used to make the wedges and handle covers.

Laser cutting and CNC machining were primary operations used on nearly all of the module’s metal components. Materials included A36 stainless, high strength/low alloy steel and, for the hinges, CNC 1045 steel. Fortunately, 3-Dimensional Services was able to bring both a high degree of staff expertise and a virtual arsenal of equipment to bear in each of these areas.

“Our lasers—both 3- and 5-axis—can cut through thick armor plate or slice through thin sheet metal, all with amazingly tight tolerances,” notes Mike Brabandt, Senior Sales Engineer for 3-Dimensional Services Group. The 3-axis laser cutting systems excel in speed, accuracy and flexibility, while the 5-axis systems are ideal for cutting complex contours and shapes, and 3-Dimensional has designed, developed and produced needed laser systems in house, including an ultra high-speed unit with cutting speeds up to 50,000 mm per minute.

In terms of machining 3-Dimensional Services has over 40 CNC machining centers along with 75 knee mills and lathes, and the ability to machine steels hardened to 60 Rockwell at feed rates of up to 20,000 mm per minute, as well as machine and finish grind with machining centers that provide a 40,000-rpm spindle with 30,000-mm per minute feed rate. Thus, neither machining capacity nor machining expertise was an issue when it came to processing the metal components for the door-assist module.

Seven-day turnaround
Capabilities like these allowed 3-Dimensional Services to complete the prototype in a mere seven days. Four design iterations followed, and all were successfully performed over the course of a single month thanks in large measure to the size and capabilities of 3-Dimensional Service design and engineering department, which boasts over 30 high-speed CAD terminals and employs nearly all major CAD/CAM packages, including CATIA, Delcam, Mastercam, Unigraphics, SolidWorks and ProE.

The final design of the MRAP door modules called for components to be zinc yellow chromate-plated for superior corrosion resistance, and for the module to be CARC (chemical agent resistant coating) painted. CARC, which is typically used on today’s U.S. military vehicles, is a polyurethane paint that provides superior durability, extends service life for military vehicles and equipment, provides surfaces with superior resistance to chemical warfare agent penetration, and greatly simplifies decontamination.

3-Dimensional Services moved swiftly to commence limited-run production of the approved door-assist module design, making 300 to 400 per month for an eventual total of 2500 units. According to Mike Brabandt, successfully completing a demanding prototyping challenge is always a professionally rewarding experience, but in the case of the MRAP door-assist module it was something more.

“We know how important these modules, and the vehicles they’re a part of, are for the safety of our troops, so we’re gratified that we were able to work closely with Inteva to make this happen.”

The 3-Dimensional Services Group, consisting of 3-Dimensional Services, Urgent Plastic Services, and Urgent Design & Manufacturing, provides rapid prototyping services that encompass virtually all relevant processes, including injection molding and casting, stamping, machining, robotic and manual welding, laser cutting and welding, waterjet, hydroforming, tube bending, vibration welding, casting and pattern fabrication, RIM tooling, SLA, LOM and SLS rapid prototyping, and assembly.

Senator Sherrod Brown made the announcment.

To create a numerical simulation model, that covers all the complex conditions involved in crash situation, Volvo 3P uses the Altair software RADIOSS. In the need to study several aspects such as elasto-plastic behavior, hardening, strain rate dependency, triaxial behavior and failure, Volvo 3P relies on the modeling capabilities of RADIOSS. Several tests for material property identification were accomplished to obtain data about the material's behavior up to the rupture in case of torsion, tension and compression (hardening, strain rate effect, stress state influence). The achieved data were used to validate the numeric model in RADIOSS and enabled the Volvo 3P engineers to set up the right material laws for simulation.

"We are pleased to see Volvo 3P Cab Engineering engineers expanding the usability of RADIOSS in their development tasks," said Mauro Guglielminotti, managing director, Altair, France. "Having the ability to better predict crash results is a highly competitive advantage and will lead to better and safer products, a reduced number of prototypes and savings of time and money. Including special validated material laws is the right answer to the calculation needs at Volvo 3P Cab Engineering."

About RADIOSS

RADIOSS is a next-generation finite element solver for linear and non-linear simulations. It can be used to simulate structures, fluids, fluid-structure interaction, sheet metal stamping, and mechanical systems. This robust, multidisciplinary solution allows manufacturers to maximize durability, noise and vibration performance, crashworthiness, safety, and manufacturability of designs to bring innovative products to market faster.

About AB Volvo

The Volvo Group is a customer-oriented organization that is distinguished by transport solutions that strengthen the customer's long-term competitiveness. The Volvo Group has its roots in Sweden, France, Japan and the US and has about 100,000 employees. Production is carried out in 19 countries, while sales take place in about 180 markets. Volvo's business areas are Volvo Trucks, Renault Trucks, Mack Trucks, Nissan Diesel, Buses, Construction Equipment, Volvo Penta, Volvo Aero and Financial Services. There are a number of business units that support the business area's operations. The largest are Volvo 3P, Volvo Powertrain, Volvo Parts, Volvo Logistics, Volvo Technology and Volvo IT. The Group's structure creates conditions for working closely together with customers. The Volvo Group's strategy is based on customer's requirements and focused on profitable growth, product renewal and internal efficiency.  (Original Article in PR Newswire)

 

"The prediction of the behavior of single components can be very complex, as recently shown by the prediction of crash behavior for ductile cast-iron brackets," said Jerome Lagrut, senior analyst, Volvo 3P Cab Engineering. "Since the brackets are the critical link between chassis and the driver's cab, they are key components for the crash behavior and the occupant safety. Certain crashworthiness requirements, such as regulations and severe internal requirements must be covered. After the identification of the material behavior via tests, we have been able to implement these laws in a simulation model for further investigations. The crash simulations on complete vehicles in RADIOSS showed very good correlations with physical tests and we are very pleased with the outcome of our development efforts," he continued.