AHSS lightweighting of truck components

The use of AHSS and UHSS (ultra-high strength steels) in automobiles keeps increasing with almost every new car introduction or model update. Some of this AHSS/UHSS use is to meet more stringent safety/crash standards. But weight reduction is probably the leading reason, and the automotive examples provide some guidelines as to truck lightweighting possibilities.

UHSS battery pack protection for electric trucks

To meet globally agreed-upon climate goals, all trucks — including big rigs doing long hauls — will eventually need to use either electric batteries, fuel cells, or hydrogen combustion. But before electric trucks become widely used, the trucking industry (in the USA, at least), needs to develop crash standards for battery packs.

Truck chassis frames and frame rails using UHSS

Top of mind for designers of truck frames is a material’s strength, stiffness, and fatigue properties — since truck chassis are constantly subjected to shock loads and twisting.

A traditional, baseline, Class 8 (USA) frame is a steel construction using 120 ksi (827 MPa) steel. Converting the truck’s frame to, for example, 160 ksi (1100 MPa) Docol^® cold-rolled 1100M martensitic steel allows truck OEMs to reduce gauge thickness and save 90 kg.

To realize additional weight reductions, truck designers are exploring tailoring the thickness of the steel across the length of the frame rail, to optimize the amount of AHSS strength where it’s needed. They could also run cost/benefit analyses for even stronger UHSS steels, for example Docol^® hot-rolled, cold-formed 1200M.

NACFE reports that one truck OEM recently stopped offering aluminum frame rails, probably due to their lack of durability. One participant in the NACFE survey reported “They (aluminum frame rails) don’t fatigue, they fail catastrophically.” (NACFE Confidence Report: Lightweighting 2021.)

The report goes on to note that aluminum’s lower modulus of elasticity (its stiffness) compared to steel makes aluminum sagging a common problem, ruling out aluminum frame rails for a range of weight-sensitive truckers, such as tanker trucks.

Making truck cross members more durable

While lightweight aluminum cross members are growing in popularity, many truck OEMs have the same concerns about aluminum cross members as they have about aluminum frames: namely, aluminum’s lack of long-term durability when it comes to stiffness, twisting, and fatigue. AHSS steels could prove to be the more durable and economical alternative for truck cross members.

Lightweighting truck cabins with AHSS

Even the most weight-sensitive trucking companies (bulk haulers) do not want to use shorter sleepers to save weight: retaining company drivers with a comfortable, “home away from home” is just too important.

On the other hand, when it comes to owner-operators, one fleet administrator put it this way, “Lightweighting is (freight efficiency) revenue…I only hire owner-operators with tractors that weight less than 16,000 lbs (7260 kg).”

Either way — using company drivers or owner-operators — it’s clear that keeping sleeper cabin weight in check is key, especially as sleepers continue to grow in size, such as the “condo or high rise” cabins.

The NACFE Report points out, “With the many innovations in steel, there is significant potential to reduce weight while maintaining a common supply chain.”

Cabin frame.

Increased safety using AHSS truck bumpers and underrun protection

Truck designers are noting that car OEMs and Tier 1 suppliers are starting to design and deploy ultra-high strength steels for bumper systems. UHSS grades such as press-hardening steels Docol^® PHS 1500 and PHS 2000 help create weight-saving, cost-effective bumpers with high crash protection performance.

Lightweighting compressed air tanks for truck brakes

Aluminum tanks can be up to 14 kg lighter than conventional mild steel tanks. But advanced high strength steels could match aluminum’s weight at significantly lower costs.

Combining truck air tanks with cross members

Volvo has built a proof of concept truck that combined an aluminum air tank integrated as a cross member. A similar idea could use Docol^® AHSS steel, which is not only more economical than aluminum — it also has the embedded CO₂ equivalence of recycled steel, even though it’s made largely from virgin iron ore.

Reducing forming costs for tractor roof fairings

Roof fairings help tractor-trailer be more aerodynamic and, in turn, more fuel efficient. But material conversions, to either aluminum or injection molded plastics, can simply be financially out of reach for the relatively low-volume Class 8 truck market.

NACFE reports, “A large injection mold tool for making those roof fairings can cost over US$1 million, and an aluminum body panel-stamping tool can be US$1.5 million.” More economical AHSS steel, formed by equipment the OEM probably already has, may be a better lightweighting approach for roof fairings.

Increasing 5th wheel durability with AHSS

Tractor fifth wheels traditionally are a heavy-duty component, designed for frequent hooking and unhooking of trailers. NACFE notes that aluminum may not be the best choice for 5th wheels when “… it’s common for the kingpin to hit off-center, causing damage to the (aluminum) throat or the ramps…They are (also) so expensive compared to stamped and cast steel models, (that) the overall take rate (acceptance rate) is very low.”

Potential AHSS steels for stamped tractor 5th wheels include Docol^® martensitic steel grades.

Cost-effective, lightweight truck wheels

Both steel and aluminum wheel producers have successfully reduced the weight of their products in recent years. By further increasing strength levels with steel grades that are readily cold-formed into stretched flange edges and have high hole expansion ratios, steel wheel manufacturers could achieve additional lightweighting at eye-catching prices.

Potential hot-rolled Docol^® AHSS grades for wheels include HR800CP, HR800HER, or 600FB.

Instrument panel structures

Aluminum has replaced some panel structures, but obviously at higher costs. “Replacing the replacement” with AHSS steel, such as cold-rolled Docol^® CR600DP sheets and precision tubes, could deliver a price competitive, lightweighting edge to truck OEMs.

Offering lightweight truck components at attractive prices

In addition to their strength/lightweighting potential and attractive pricing compared to aluminum and CFRPs, AHSS and UHSS steels can frequently be made with cold-forming equipment that truck OEMs already use — with relatively minor upgrades to tooling. And Docol^® AHSS/UHSS steels are also extremely CO₂ efficient, as already noted.

Ready to leverage the auto industry’s AHSS/UHSS lightweighting knowledge? Then please contact your local Docol^® representative. Your freight-efficient customers will thank you.