Since its introduction in the 1990s, the use of hot stamping has been steadily gaining popularity across the automotive industry. As the technology develops, and its benefits increasingly justify the upfront investment costs, hot stamped parts are appearing not only on large premium cars, but also on small, mainstream and even low-cost cars. Martin Kahl investigates
Hot stamping is used to produce safety-critical structural parts, such as bumper beams, door and A- and B-pillar reinforcements, and roof and dash panel cross members. Its main attraction is that it offers the associated benefits of weight reduction and the production of higher strength parts. As a result, hot stamping is now widely regarded as a mainstream manufacturing technique.
“The question is how quickly OEMs not currently using many hot stamped parts will close the gap with the best in the industry,” says Jean-Luc Thirion, Head of Automotive Product Portfolio, Global Research and Development, ArcelorMittal.
“Hot stamping is a cost-effective technology enabling the production of high-strength complex parts without too many processing issues. Hot stamping technology, and Usibor, [ArcelorMittal’s proprietary 1500MPa steel grade developed specifically for hot stamping] enable weight-saving solutions at a notable cost, because even if the material and the technology is slightly more expensive than conventional products, the decrease of thickness of the material compensates for that.”
The rise of hot stamping in China
Although hot stamping started life in Europe, it is now being used in almost all major automotive markets. Demand for Usibor in the BRICS varies, says Thirion. “In China, you see the same cars as in Europe. India is a very local market with products adapted for the market.”
The cost-sensitive nature of the Indian market, along with lesser crash and emissions requirements, puts hot stamping lower down the priority list when it comes to investment. “In China, local brands are developing cars to Western standards. In India, the market is far behind. The interest for global standard products is quite low. The market will not develop at the same speed as China. India is much more price-driven than China.”
At a recent media briefing, ArcelorMittal said it expects its upcoming VAMA (Valin ArcelorMittal Automotive) joint venture factory in western China to account for up to 10% of China’s automotive steel production – thanks to growing demand for high grade automotive steel.
ArcelorMittal is forecasting an increase in automotive steel consumption in China from 14 million tonnes in 2012 to 17 million tonnes in 2014, 20 million in 2016, and 22 million in 2018. This demand is due to a growth in annual car sales, which the company expects to reach 31.5 million units in China by 2017.
In China, the demand for Usibor comes mainly from OEMs using it in global platform-based models. “Our objective is to develop the same solutions for China as for other markets,” says Thirion. The new VAMA plant will produce not only Usibor but also laser-welded blanks.
“VAMA is a huge investment,” says Philippe Aubron, Chief Marketing Officer for ArcelorMittal Automotive Europe. “The target is to produce up to 2.3 million tonnes of steel for automotive. That should represent roughly a 10% market share in China.”
The major hot stampers, including Gestamp, Benteler and Magna are increasing the number of their hot stamping lines in China, says Thirion. “In China, there are also local hot stampers who are using more of our coated Usibor, because it’s a good, cost-effective technology even for an emerging country like China.”
There are also some local stampers producing hot stamped parts in China, but Thirion does not expect domestic OEMs to invest in in-house hot stamping. “The classic Western hot stampers are there but there are also local hot stampers, which are not bad at all. We are quite confident that these local hot stampers and the global players will propose a lot of interesting hot stamped parts for the car industry in China. There are demanding objectives in terms of CO2 emissions and pollution in China, and that will force them to go in these directions.”
Along with the benefits of hot stamped high strength steel parts, OEMs and suppliers are being offered attractive solutions by suppliers of other materials, including aluminium and, to some extent, carbon fibre. Thirion admits that carbon fibre “is a very interesting material. The leaders in this market are making some very interesting parts. But the use of carbon fibre is slow and expensive, for the time being.”
But is it a real threat to steel? “We are working on third-generation AHSS – this is a new generation of Usibor up to 2000 MPa with which we will deliver additional weight-saving potential. Even if our competitors are catching up, we will increase the gap with new products and reduce the cost of weight saving,” says Thirion.
“There is also another solution, a very high grade martensite steel used in North America for roll-formed parts. Even if we think that hot stamping will be a mainstream solution, it’s not the only solution. And it will depend heavily on the target cost of the vehicles.”
Safety in South America
This year Latin NCAP crash test results have highlighted the gulf between safety standards of cars sold in Europe, North America and Japan, and those offered in regional markets like Latin America. The press coverage surrounding the disappointing results of these tests – several global OEMs scored zero points and zero stars – is spurring a new drive for safety, and Thirion is convinced that Latin NCAP standards will force local production to higher standards of safety.
“We need to propose the same solutions in South America as Europe and North America. For years, we have developed AHSS in South America. In 2012, we developed 15 new steels for South America, cloning them from European products. Now we know that demand for AHSS in Latin America will rapidly follow Europe and the US.”
Growing OEM investment
In addition to the growth of hot stamping at the classic outsourced suppliers of hot stamped parts, there is also growing investment by OEMs, including Fiat, BMW (at its Dingolfing plant), Volkswagen (at Kassel) and Volvo (at Olofstrom). In addition, “Some car makers are increasing their use of this technology in collaboration with major hot stampers. Some Asian car makers will also produce hot stamped parts in-house.”
Volkswagen, at the same time as investing heavily in hot stamping, is now focusing on the use of four core vehicle architectures, off which most of its group models will be built. That obviously offers great potential for high volumes of similar parts and economies of scale across many different models. And Thirion believes the industry will see the growth of hot stamping and the growth of vehicles architectures running hand in hand.
“The need for weight saving is such that OEMs need to customise their solutions to the market, to the specific high cost, and so on. Initially we saw the growth of Usibor mainly in the upper segments. But Usibor parts are increasingly used in smaller segments. Hot stamping is a mainstream solution because it’s a cost-effective solution.”
From small cars to heavy trucks, light trucks, and even medium and heavy commercial vehicles, Arcelor Mittal are planning heavy promotion of hot stamping, because it says that, compared to what is available, hot stamping is a very interesting weight-saving solution.
Such parts, says Thirion, would be structural safety parts. “Initially, hot stamped parts were used mostly in the upper parts of the vehicles, and the current trend is to go more and more into lower parts of the vehicle, where OEMs need corrosion protection. Our Usibor product has good results but we are developing new hot stamping grades with new coatings. It’s more niche market, but it enables customers to use hot stamping for parts and applications where they currently don’t. With the solutions that we are developing, we will also soon be able to use hot stamping for chassis parts.”
ArcelorMittal sees chassis parts as the next area of focus for hot stamping parts. These could come to market by 2015, a year that will see something of a renewal of ArcelorMittal’s hot stamping offering. “We are dedicating a lot of effort in R&D to the development of new coatings and new grades in order to make it possible to use hot stamping for applications like chassis parts where we need more deformability and maybe less strength. For chassis parts, the objective is to reach 1000 MPa in order to save weight on some parts. This really illustrates how there can be a variety of different strengths per application.”
In terms of specific parts, Thirion says the cradle will be a possible candidate. “We use hot stamping together with laser welded blanks, and we have developed a material called Ductibor which is used with Usibor. We use it for the B-pillar because we need 1500 MPa in the upper parts and deformability in the lower part, where we already have 500 MPa. We are trying to develop intermediate grades; we will have a 1000 MPa steel for chassis parts. You can imagine that intermediate value would be useful for side rails, for parts which need to absorb energy during a crash. So we will be developing hot stamping technology for everything we can, trying to customise the mechanical properties that the customer needs to exactly where they need them.”
As well as lower strengths of steel, ArcelorMittal has talked in the past about introducing a 2000 MPa steel, now expected to be launched in 2014 or 2015.
“Our future Usibor 2000 will replace 1500, but not for all parts. We do not plan to replace all Usibor 1500. Strength is not everything. Sometimes you cannot save weight anymore because of the stiffness. When you have reached the minimum thickness for the required stiffness, you cannot reduce it any further, so there is no need to use higher strengths.”
Bringing a higher grade strength steel to market has its challenges. “Developing such a product is complex. There are numerous trials by our competitors, but the availability is limited and some processing properties are restricted. Such a product can only be successful if customers can use it, weld it and form it.”
Production capacity
Despite the anticipated rise in the number of hot stamped parts, Thirion does not foresee any production capacity constraints. “The number of stamping lines across the world is increasing constantly. The steelmakers are developing new lines, and the stampers are investing more and more in hot stamping. The number of new hot stamping lines around the world is huge, and growing very fast, including in China and Korea.”
Notably, the use of new hot stamped parts in vehicles replaces existing parts, so growth is in line with replacement. “We will not substitute every chassis part, because there are some parts which are designed for stiffness and for some chassis parts we are not able to decrease the thickness even if we increased the strengths. But we think that at least one quarter of chassis parts could be lightened with such materials.”
Despite attractive material solutions being offered from other quarters, along with other ways of saving weight and increasing vehicle safety, Thirion is confident that hot stamping has a strong future. “We are developing new products to broaden the application of hot stamping, and increasing strengths in order to enable further weight saving.”
Ending on a bullish note, Thirion says, “We are convinced that hot stamping will remain the mainstream technology, at least for a quarter of all vehicles in the future.”
Martin Kahl is the Editor of Automotive World
