Emil Evin

Optimizing of Electric Discharge Texturing Parameters of Rolls of the Rolling Mill of Steel Sheets

The producers of components require that cuts of steel sheets for superficial parts of cars would have guaranteed surface microgeometry, minimum defects, homogenous surface over the full width and length of the belt, mat appearance, good adhesion of the Zn layer. Microgeometry of the surface of galvanized sheets for superficial parts of cars is one of the decisive factors affecting the appearance of the surface after painting and stampability of steel sheets. Requirements for microgeometry are mainly focused on the roughness parameters Ra [μm] (roughness), Pc [cm-1] (number of peaks) or Wa [μm] (undulation roughness). This paper presents the study results of the influence of selected parameters of electric discharge texturing of rolls of the rolling mill on the Ra roughness parameter and number of peaks. Reliability of the process of electric discharge texturing of work rolls was assessed according to Cpm and Cp reliability indices. Dependencies on electric discharge texturing were depicted to predict Raand Pc qualitative indices of roughness.

Tribological Properties of Coatings for Sheet Metal Stamping Dies

The conventional and innovative surface technologies are applied to sheet metal stamping dies in order to produce a composite material with properties unattainable in either the base or surface material. To select proper materials for forming dies the systematic evaluation of dies materials, their heat treatment and coatings are required. This paper deals with evaluation of plasma sprayed coatings Cr2O3, Al2O3 and WC12Co by pressure plate-ring test (tester T 05) and deep drawing process. Friction coefficients and seizure of these coatings were studied under dry and wet friction conditions. For different types of die rings (with and without ceramic coatings) the punching forces were measured during deep-drawing process. The results show that the main advantage of application of plasma sprayed coatings on the die contact surfaces under wet friction conditions compare to dies made of the tool steel may be the increase of seizure resistance of stamped part surface. The more significant difference in the friction coefficient values was not observed.

Local Tribological Characteristics of Steel Sheets for Microforming

The die radius represents the important local part of drawing die due to transferring contact loading under deep drawing. Within the experiments local contact pressure on die radius was researched using numerical simulation of strip drawn test and micro deep-drawing. Experimental research of strip drawn test was done using coatings with different alloying – under alloyed, optimal and slightly pre alloyed. Alloying level was evaluated by phase composition and % Fe in coating. Presented coatings were created on IF steel sheet DX54D. Experimental results of strip drawn test were used to verify strip-drawn test numerical simulation. Based on numerical simulation results, contact pressure on drawing die radius at deep drawing of cups Ø 50 mm and Ø 15 mm were observed.

LASER WELDING IMPACT ON DEFORMATION PROPERTIES OF STEELS WHEN USED FOR CAR BODY PARTS

The energy absorption at crash, usually described by stiffness and crashworthiness, is the key request for the car-body components, considering the material they were made from. The modified 3-point bending test with fixed ends has been developed in our department to assess materials for the carbody parts. The force and punch path are measured and used to calculate stiffness and crashworthiness. Experiments were performed on high strength low alloyed steel H220PD, dual phase steel DP 600 and austenitic stainless steels AISI 304 for base material and specimens welded by solid state fiber laser YLS-5000. Based on the experiments and analysis, the austenitic stainless steel is better to use for car body components of frontal deformation zones. Otherwise, the passenger’s compartment is better protected by applying dual phase steel for car body parts when side impact occurs.

ANALYSIS OF COATED STEEL SHEETS’ RESISTANCE TO CORROSION AFTER PLASTIC DEFORMATION

The automotive industry is influenced by customers’ requests, including safety and lifetime improvement, weight and emissions decreasing. The paper presents corrosion resistance improvement of car-body components by steel sheets coated with Zn-Al-Mg coating. Specimens coated with GI and Zn-Al-Mg coatings have been deformed by stretching (Erichsen test) and 3-point bending tests to 90 and 180. After deformation they have been tested in aggressive corrosion atmosphere of salt spray in corrosion chamber. Reached results showed better corrosion resistance of Zn-Al-Mg coatings when compared to standard Zn coating GI.

Laser-beam welding impact on the deformation properties of stainless steels when used for automotive applications

Abstract Materials other than standard and advanced high strength steels are remarkable for the thin-walled structures of the car-body in recent years in order to safety enhancement, weight and emission reduction, corrosion resistance improvement. Thus, there are presented in the paper the deformation properties of laser welded austenitic AISI 304 and ferritic AISI 430 stainless steels compared to these one measured for the high strength low alloyed steel H220PD. The properties were researched by tensile test and 3-point bending test with fixed ends on specimens made of basic material and laser welded one. The specimens were welded by solid state fiber laser YLS-5000 in longitudinal direction (the load direction). The deformation properties such as strength, stiffness and deformation work were evaluated and compared. The strength and stiffness were calculated from tensile test results and the deformation work was calculated from both, tensile test and 3-point bending test results. There has been found only minor effect of laser welding to the deformation properties for high strength low alloyed steel H220PD and austenitic stainless steel AISI 304. Otherwise, the laser welding strongly influenced the deformation work of the ferritic stainless steel AISI 430 as well as the elongation at tensile test.

Evaluation of Limit Deformations of Zn Coated High Strength Steel

The paper presents the evaluation of limit deformations by the tensile test of notched specimens to measure the left side of forming limit curve. The notch radii R5, R10, R17.5 and R25 were machined on the specimens of 40 mm in width. The limit deformations have been assessed for Zn coated high strength steel TRIP with thickness 0.76 mm. Two types of deformation grid were electrochemically etched on the specimens: circles with diameter of 2 mm and the pattern of dots with diameter 0.5 mm and spacing 1 mm. The tensile test of notched specimens has been also numerically simulated. The experimentally measured limit curves have been compared to the mathematic Swift-Hill model.

Morphology Characteristics of Coatings for Forming Applications

The contribution focuses to study of selected properties of thin coatings deposited on tool steel. Used samples were prepared by PVD method. Samples were evaluated using the scanning electron microscopy. Characteristics of surface morphology Ra, Rz Rt, RSm and RPc were established according to standard STN EN ISO 4287. The coatings TiN, TiCN, Supral and Exxtral Plus have been deposited on tool steel substrate having a thickness of 16 mm. The morphology characteristics were compared to the surface morphology of the reference material tool steel X155CrVMo12.1.

Selection of Materials for the Body Deformation Zones

Deformation characteristics are analyzed for stress components deformation zones to move and bend. To verify the appropriateness of the proposed model were experimentally determined strength and deformation characteristics of deep-drawing steel DX 57 D, microalloyed steel HSLA , high-strength multi-phase steels DP 600 and TRIP, anti-corrosive austenitic steels A304 2B and ferritic A 430 2B by three-point bending. The analysis of the results obtained Cause and Effect matrix shows that for front impact deformation zones are more suitable austenitic steels respectively TWIP and for zones flanking the passenger compartment (cab) are preferable DP and TRIP steels.