Lightweight Design of Forged Steel and

Aluminum Chassis Components

Michael Muckelbauer, CDP Bharat Forge GmbH, Ennepetal, Germany

Tobias Frenzel, Bharat Forge Aluminiumtechnik GmbH & Co. KG, Brand-

Erbisdorf, Germany

Shyam Takale, Bharat Forge Ltd., Pune, India

1 Introduction

More than ever, the lightweight design of chassis components is of great importance. With the

main focus on better ride quality, safety, handling characteristics and reduction of fuel con-

sumption, the reduction of unsprung mass is what engineers aim for when they develop a new

chassis component. Forged steel and aluminum parts are superior in durability, strength and

reliability. Their excellent material properties help save weight and satisfy the tightest packag-

ing requirements.

The Bharat Forge Group is the largest forging company in the world. Their core products are

chassis and engine components for trucks and passenger cars and several other applications for

the non-automotive industry.

Fig. 1-1 Product segments of the Bharat Forge Group

The plants in India, China, Germany, Sweden, Scotland and the United States of America (Fig.

1-2) develop, forge and machine (Fig. 1-3) and assemble forged steel and aluminum parts.

Their superior engineering capabilities make them a strong partner especially for the automo-

bile industry where short lead times are very critical.

Lightweight Design of Forged Steel and Aluminum Chassis Components

Fig. 1-2 Forging Plant Locations of the Bharat Forge Group

Fig. 1-3 Machining of Truck Knuckles at Bharat Forge Daun, Germany

In order to fulfill the requirement of being a full service supplier, it is important to have capa-

bilities in design and simulation of products, such as linear and non-linear FEA, shape optimi-

zation, and forging simulation and testing with resonance-frequency and servo-hydraulic test

rigs. When the engineering capabilities and the efficient material development approach are

combined, the need for optimum lightweight designs can be satisfied. This presentation will

show some examples.

As far as cost reduction, the focus is on automation and the use of forging simulation. The si-

mulation of the forging process with standard simulation packages is more or less state of the

art in the forging industry. What makes the difference is the way the simulation packages are

implemented. For highest efficiency, computer clusters have to be used. The simulation is used

mainly to reduce consumption weight, optimize die life and ensure a robust process (right-the

first-time production). The latter goal has an additional benefit for the customer as well. It

means that the samples are produced under mass production conditions, which is important for

the tests on test rigs or on the track.

2 Design of Forged Chassis Components

In order to optimize product development and process design, it is highly beneficial to work

hand in hand with supplier and customer. If the supplier is integrated in the product develop-

ment process in an early stage, the process restrictions can be considered in an optimized man-

ner. Nowadays, suppliers of chassis components, such as knuckles or control arms are impor-

tant partners in the simultaneous engineering process. Starting with critical hard points of the

product, package data, load cases and other restrictions or information, the supplier can design

the products with focus on function, lightweight and economical production (Fig. 2-1). This

speeds up the process significantly, by eliminating the interface between customer and supplier

during the optimization cycles. The data exchange is much less frequent, so development time

is reduced. Linear and non-linear FEA-systems such as Pro/MECHANICA and ABAQUS are

used in this process.

Fig. 2-1 Engineering process for a Forged Chassis Part

Lightweight Design of Forged Steel and Aluminum Chassis Components

The process engineering in a state-of-the-art-forging company includes optimization with non-

linear FEA as well. This enables overall development cost to be reduced and the customer gets

a product out of mass production process conditions. The process changes that were necessary

in the past are not needed any more. By offering product tests on test rigs based on resonance

or servo-hydraulic methods, the “full service” criteria is ensured.

Nowadays, the product design is often optimized by use of software tools such as shape optimi-

zation (Fig. 2-2). This software gives an idea, of how a structure should be built. Due to restric-

tions of the forging process the designer has to make a model that incorporates some of the

ideas and fulfils the requirements of the forming technology.

Fig. 2-2: Topology Optimization of a control arm

3 Material Development

The Bharat Forge Group has forging facilities for steel and aluminum. The lightest design, of

course, can be achieved with aluminum parts. For parts, where this material is not suitable, such

as truck knuckles or in very tight packages, steel is the better choice. Choosing steel does not

mean that lightweight design is not possible. Because of the excellent material properties,

forged steel does have a big weight advantage against other processes; especially with steels

such as cdpSO38 and cdpSO40, developed to avoid heat treatment of truck knuckles in the first

place. Today these steel grades are available for all kinds of parts. Table 1 shows a comparison

between several materials.

Table 1 Comparison of several materials in % (forged steel and cast iron)

With cdpSO40, tests have been performed to get an idea of the improvement of fatigue. For

that purpose a part was produced with standard micro-alloy steel and cdpSO40. The results are

shown is Fig. 3-1, which is a comparison of the S/N-curves of both steels. The improvement in

terms of product lifetime can be calculated as a factor of three /1/. This means that, this material

can be used to reduce even more weight or to have an option for very highly stressed compo-

nents.

Fig. 3-1 Newly developed micro-alloyed steels (BY)

However, if the lightest part design is required, light metals are the first choice. Here we find

the same advantages of forgings against other technologies. The material properties allow

lightweight designs, needing more space in the package compared to steel parts. A comparison

of different aluminum processes is shown in Table 2.

To be cost-competitive, forging companies have to work in several fields. Most of the time the

cost of raw material is what makes forgings quite expensive. One approach to reduce that cost

Lightweight Design of Forged Steel and Aluminum Chassis Components

with a newly developed process is adforge by Bharat Forge Aluminiumtechnik. With material

properties almost as excellent as with regular forgings, this process allows a significant reduc-

tion of manufacturing costs while the freedom in design is much better.

Table 2 Comparison of several materials (forged and casted aluminum)

In order to provide the complete service required by their customers, the Bharat Forge Group

has installed test rig capacity in most of its plants, as shown in Fig. (Germany and India). These

test rigs are also used to test the developed materials for fatigue behavior. At CDP BF two test

rigs are available for testing chassis parts for passenger cars and trucks as well as crank shafts.

Both test rigs are using the resonance test methods, which have a big advantage in speed and

cost. BFL has installed several shakers and some servo-hydraulic equipment that is used for

crankshafts and truck chassis front axle beams.

Fig. 4 Test rigs in Ennepetal, Germany (left) and Pune, India (right)

4 Process Improvements

To ensure cost-competitiveness, there are several tasks to accomplish for a forging company.

One is to reduce the consumption of raw material, as this is the main cost driver in this technol-

ogy. Another important goal is to reduce necessary changes during or after the production of

prototypes. To achieve this, the usage of forging simulation is state of the art in most of the

forging companies around the world. With a wide range of functions, the commercial software

packages allow to simulate the process and find possibilities for improvement.

The Bharat Forge Group is using the software Forge2008 (Transvalor, France) in all of its

plants over the globe. This software allows predicting forging defects. Then the design can be

revised and the simulation can be run again. Under fill problems can be seen, which has to be

avoided of course, although a minimum of material consumption is wanted. Another important

feature is the die stress analysis, which gives the designer the possibility to check for stresses

and improve die life by taking the necessary actions. The die stress analysis can even be per-

formed as a coupled analysis with deformable dies. With this option the material flow is simu-

lated by taking into consideration the deformation of the dies caused by the high pressure in the

metal forming process.

The main advantages for the customer is a reduction of production (meaning product) cost, a

robust process and a right-first-time process, beneficial for the tests of prototypes on test rigs or

cars. The overall development time can be reduced by this technology and resources are saved.

Fig. 4-1 Die stress analysis of a passenger car chassis part

Several more features are included, while the most important one for the Bharat Forge Group

with its complex products is the possibility to reduce computation time with computer clusters.

Fig. 4-2 shows the two clusters installed at CDP BHARAT FORGE in Ennepetal, Germany.

More clusters are installed in Brand-Erbisdorf, Germany and in India, Sweden, China and the

USA. Compared to a regular desktop computer a 9-node-cluster can reduce the computation

time by a factor of 8. This is very important, since the regular (single processor units) simula-

tion time of a chassis parts is about 100-200 hrs (CPU time only). The reason for that is that the

Lightweight Design of Forged Steel and Aluminum Chassis Components

multi-stage processes, where one stage takes 10-20 hrs, have to be simulated completely over

and over again, when changes have been incorporated.

The coupled analysis, needed to achieve the highest precision of the simulations, require even

more time. Only one stage, takes more than 20 hrs on a cluster, giving an idea of how much

time would be consumed on a single-processor unit. However, the memory requirement is often

too high for a single computer, which makes a cluster mandatory for highly complex parts and

processes.

Other simulations with a high demand of computation power are forming processes with incre-

mental material flow, like reducer rolling or new processes, which the research departments are

working on, to make the forging process more cost-competitive.

Fig. 4-2 Two Forge2008 (Transvalor) clusters at CDP BHARAT FORGE in Ennepetal

Further improvements are in the field of automation. All plants have automated more and more

processes over the past years and are still in the process of installing more such devices for the

coming years. Fig. 4-3 shows a fully automated truck knuckle forging line. For parts like these

the handling is a challenge because of the billet weight being between 40-60 kg. The lower part

of the picture shows a portion of a fully automated line for passenger car aluminum parts.

Fig. 4-3 Fully automated truck knuckle forging line at CDP BF (above) and robot in front of

knuckle press line at BF AT (below)

Literature

1. Arndt, J.; Roller, M.; Witt, M.: Einsatz von hochfesten AFP-Stählen für massivumgeformte

Pkw-Fahrwerkskomponenten. Schmiede-Journal September 2005, S. 20-21.