Varunee Premanond

Tribological behaviour of thin film coatings against high strength steels

The non-coated ball (SKD11; hardness 60 ± 2 HRC), balls coated with TiC-CVD, TiAlN-PVD, TiCN-CVD, TiCN-PVD and ball treated by VC-TD (thermal diffusion) have been evaluated in sliding contact against the disk which was made from automobile structural steel grade SAPH 440 and high strength steel grade SPFH 590. It was found that non-coated ball showed maximum specific wear rate and TiCN-CVD coated ball exhibited minimum specific wear rate. The effectiveness of hard thin film coated tool in metal stamping process is also investigated by performing U-bending experiment. In the case of non-coated tool, the result showed that adhesion of workpiece material on a die face was detected after 49 strokes for SPFH 590 steel. Whereas no adhesion was found on the tool coated with TiCN-CVD after 500 strokes. In order to understand the phenomenon, scratch tests were done on each type of coated tool to characterise the adhesion strength.

Notice of Retraction The study reduction of spring-back in U bending die process

Bending process is an important process in the sheet metal forming in many industries. The main problem of the bending process is spring-back phenomenon after removing the punch. This research aims to reduce spring-back value of sheet metal in U bending process. The conventional U bending and corner setting technique were designed for experiments. The corner setting technique has reduced the thickness in bending area to 5, 10, 15 and 20 percent of the original sheet thickness. Clearance between punch and die of both processes was equal to same thickness. The spring-back value was investigated by commercial program code DEFORM 2D which able to analyze the stress and force in bending area. Electrolytic zinc coated carbon steel grade JIS; SECC, JIS; 440 and JIS; 590 having the thickness of 1 mm were employed as the workpiece material for all experiments. The result of three materials in conventional U bending die shows larger spring back than the corner setting technique. Moreover, the corner setting technique reduces spring back value in bending process but requires high bending force. Corner setting technique at 15% and 20% shows spring go of all parts. The FEM simulation results explain the spring-go phenomenon on the stress analysis. Comparisons between experimental and finite element method results were also performed.

Characteristics of Fluoride Based Conversion Coating Film on Al-Alloy for Metal Forming Applications

During the process of cold forming of aluminum, the high pressure which is introduced on the die can result in high adhesion between the aluminum and the die surface. Therefore, it is necessary for the aluminum billet to be coated with a lubricant prior to forming, to reduce adhesion and to ease the flow of material in the die. There are several popular types of lubricant systems used in cold forging of aluminum. For severe deformation, conversion coating in conjunction with soap lubricant are commonly used. The conversion coatings include soap phosphates (PO4-soap), as well as soap aluminum fluoride (AlF-soap). Therefore, this work studied the performance of the AlF-soap system and compared it to the conventional PO4-soap system as tested on AA6063 aluminum. Ring compression tests and ball on disc tests were conducted to explore friction conditions and the thinning of the lubricant under several forming conditions. It was found that the quantity of metal soap layer of AlF-soap used affected the friction coefficient and the lubricant thinning under forming operation. The suitable coating weight of metal soap layer of AlF-soap for this experiment was found to be 2 g/m2. The friction coefficient of the PO4-soap system was 16.26% lower than the AlF-soap system. However, the amount of thinning of the AlF-soap film after ring compression tests was lower than that of PO4-soap film.

Residual Stress Measurement for Coated Film on Cold Work Tool Steel

This paper aims to evaluate residual stress of coated film on cold work tool steel grade SKD11 (JIS) substrate. Four types of film coating were deposited on hardened SKD11 steel. Mechanical property of film coatings was examined by nano-indentation. The thickness of the films was analyzed by scanning electron microscopy (SEM). Residual stress of coated film was investigated by using curvature technique based on the Stoney equation. The results of them were compared and correlated to the bond strength of the films from scratch testing. The influences of residual stress on bond strength of the films were thoroughly discussed in details.

Effect of Bending Direction on Springback of High Strength Steel Sheet

Anisotropic behaviors of high strength steel grade SPFH590 and HPFC780 used extensively in automotive industry are explored. V-bending tests were carried out on various bending direction. It was found that the investigated material showed little differences in the resistance to deformation and resistance to thinning from all directions. Thereafter, negligible effect of the bending direction on the degree of springback was detected. Large bend radius caused high level of springback. However, the increasing rate of springback is decreased with larger radius.

Wear Behavior of the CVD and PVD Coated Piercing Punch

The purpose of this work is to investigate the effectiveness of PVD and CVD process of TiCN film coating on SKH51 JIS tool steel on reducing wear in piercing operation. Both processes of PVD and CVD were carried out under commercial conditions. It was found that the amount of wear found for TiCN-PVD coated punch is lower than that of CVD coated punch. Adhesive strength of film coated by CVD technique is found lower which is related to photograph taken from SEM show major adhesive wear.

The Effect of Tool Surface Treatment on Friction in Hot Forging Process

This work considers the influences of various types of die surface treatment, lubricants and temperature on friction for hot forging process of brass. Well-known ring compression test were carried out to evaluate friction coefficient for various conditions. Tool material was hot work tool steel H13 and workpiece material was brass C3771. Tool surface condition selected were normal hardening, treated by hard chrome, plasma nitriding and vacuum nitriding. Tests were conducted with and without lubricants at elevated temperature between 400–600°C. The results of experiments without lubricant show that friction coefficient is reduced when using die with treated surface regardless of working temperature. The influences of surface treated on die are not significant when forming under lubricated condition. In other word, lubricant has minor effect to reduce friction when the treated tools are employed. However, graphite in water was found to be almost compatible lubricant to graphite in oil when forming by tool which is treated by vacuum nitriding. The hardness and roughness of tool surfaces are found no relevance to friction coefficient in this work.Copyright