DMX Research

Our innovative research team is continually experimenting with new combinations of metals and metallic alloys that improve PVD coatings and enhance properties such as adhesion, hardness, durability, and internal stress and tribological characteristics.

For these purposes DMX has invested in high performance equipment for characterization.

Labs equipments Labs news

[DM2340F] The complex issue of cold stamping of Advanced High Strength Steels

25-02-2012 12:11

INTRODUCTION

Automotive industry is still searching for new materials to meet their constant challenge of stronger and lower-mass vehicles.

Advanced High Strength Steels (AHSS) represent an effective answer to these problems. They offer both higher mechanical behavior (higher fatigue and impact resistance) and lightening effect.

However, this increase in steel mechanical properties comes in parallel with the need of more complex and precise parts.

In case of cold stamping applications, the technical problems encountered as a result can be:

  1. Surface damages (scratch) and wear on the formed parts
  2. Insufficient operating life time of dies (see figure 1)
  3. Higher spring back phenomena than those obtained with lower strength steels (creating an increase of friction between steel parts and tools)
    Example of premature wear phenomenon observed on a forming die

    Figure 1: Example of premature wear phenomenon observed on a forming die.

In order to offset these drawbacks, the solution is to implement a new and more efficient PVD coating on dies surfaces.

Thanks to a preliminary study, the requested coatings properties could be identified considering the thermal and mechanical constraints of this application.

Those elements are detailed on figure 2.

Mechanical and thermal constraints of stamping operations

Figure 2: Mechanical and thermal constraints of stamping operations.

DM2330F PROPERTIES

Considering preceding information, the coating elaborated by DMX Research for this application is a rather thick layer, with a thickness of up to 10µm, consisting of a specific multilayer structure.

The structure of this coating is presented on figure 3.

DM2340F structure

Figure 3: DM2340F structure : scheme of the layer stacks (a), magnified view of a calotest zone (b).


The multilayer period (= thickness of two elemental consecutive layers) of this coating has specially been studied in order to improve the fatigue resistance of the coating.

A tribological layer with higher properties than those of the staked layers has also been added on top of this coating system.

The hardness value of this coating is 4200HV.

The maximal service temperature is about 1100°C.

A friction coefficient of 0.25 has been recorded against steel (pure sliding test, 23°C, 20%<RH<40%).

TESTING CONDITIONS AND RESULTS

The component concerned by this test corresponds to the center pillar outer as illustrated on figure 4.

Illustration of the center pillar outer

Figure 4: Illustration of the center pillar outer.


Testing conditions of the stamping tests performed are:

  • Steel (Mechanical Strength): HLE (980MPa)
  • Thickness of the parts: 3 mm
  • Lubrification: No added lubricant
  • Dies treatment:
    1. TOYOTA process (diffusion process of vanadium carbide in salt bath with high temperatures)
    2. TiAIN multilayer (PVD)
    3. DM2340F

Figure 5 compares the lifetime obtained for the three tested dies.

Quantity of components stamped as a function of the coating applied on the die

Figure 5: Quantity of components stamped as a function of the coating applied on the die.

CONCLUSIONS

The DM2340F coating involves no deformation of the tested die contrary to high temperatures treatments (Thermal diffusion process or thermal CVD).

The DM2340F coating increases by 100% the life time of the die, in comparison with a TIALN PVD.

nanoindenteur

CSM Indentation Tester

The high precision CSM nanoindentation instrument (TTX-NHT) is used for mechanical properties characterization of thin films, coatings and substrates.
Properties such as hardness and elastic modulus can be determined on almost any type of material: soft, hard, brittle or ductile.

Revetest Scratch Testeur CSM

CSM Scratch Tester

The CSM Revetest Scratch Tester is a dedicated instrument for characterizing the surface mechanical properties of thin films and coatings, e.g. adhesion, fracture and deformation. The scratch tester’s ability to characterize the film-substrate system and to quantify parameters such as friction and adhesive strength, using a variety of complementary methods, makes it an invaluable tool for research, development and quality control.

Tribometre Standard CSM

CSM standard Tribometer

The CSM standard tribometer is used for the determination and study of friction and wear behavior of almost every solid material combination, with varying time, contact pressure, velocity, temperature, humidity, lubricants, etc.

Fisherscope XULM

Fischerscope XULM

The FISCHERSCOPE is an X-Ray spectrometer for quantitative materials analysis. Using X-Ray fluorescence principle, it is widely used for coating thickness measurement and is also well suited for element identification.

Calotest CSM

CSM calotest

The CSM calotest is widely used for analyzing coatings with thicknesses of between 0.1 and 50 µm. The simple ball-cratering method is a fast and accurate means of checking the thickness of any coating, whether a single or multilayered stack.