It is important to clarify the behavior of the hot forging lubricants in order to prolong the die life. Here, we introduce methods of observing the behavior of spray solidification on the die and the behavior of a sliding interface in ironing directly by a tribometer with high-speed camera and observation examples. In order to form an uneven lubricating film, it is necessary to ensure that the spray particles are quickly solidified and not flow on the die. On the other hand, at the case of sliding interface, it was observed that the lubricant melts due to heat, boils with bubbles, eventually disappearing, resulting in cohesion. When the lubricant film is thick, the change is suppressed and low friction is maintained.
In micro/meso (between macro and micro)-scale metal forming, the contribution of friction between the tool and material on the material deformation is higher than that in macro-scale metal forming. The friction between tool and material in this scale is essentially nonuniform and nonconstant during forming. The interfacial phenomena including the friction force and adhesion were studied by the following method: direct measurement of friction force during forming, the atomistic calculation of ceramics/aluminum interface during forming, and the contact potential difference (CPD) measurement of tool surface after forming. The CPD measured on the tool surface can be compared with the electronic state calculated on adhered surface.
The seizure resistance in ironing of stainless steel and aluminum alloy cups was improved by using a TiCN-based cermet die having fine lubricant pockets on surface made by shot-peening and polishing. The seizure resistance for a die having lubricant pockets of an appropriate surface shape became higher than that for a polished surface having very fine surface roughness. The friction was reduced by the liquid lubricant being squeezed out from the pockets during ironing, then the lubricant film became thick due to much amount of remaining lubricant in ironed cups. The TiCN-based cermet die having fine lubricant pockets was applied to forward extrusion of aluminum alloy billet. The seizure resistance for the die having lubricant pockets was improved. It was found that the use of the TiCN-based cermet die having lubricant pockets is effective in preventing seizure in ironing of stainless steel and aluminum alloy cups and forward extrusion of aluminum alloy billet.
Towards the fabrication of functional die surface for dry forming systems, the present paper gives a brief overview of a characterization of tribological behavior in dry forming operation. As a basic properties in dry sliding friction, instability due to the three-body plowing by wear debris at the contact interface are focused. As an approach to stabilize under the dry sliding friction,the present paper introduces the application of surface texturing of diamond like carbon films. Stable tribological properties with low friction are demonstrated with the textured DLC coated surface, owing to the prevention of plowing by less entrapment of wear debris at the interface. Applicability of the textured DLC surface in sheet bending process is also demonstrated by in-situ observation of interface between dies and work materials.
The realization of a “smart factory” using manufacturing machines and Internet of Things (IoT) is desirable at manufacturing sites. Smart factories require intelligent machine tools. Monitoring, analytical, and guidance and control technologies are required for realization of intelligent machine tools. To meet the required machining accuracy for a product, the cutting condition is monitored, and information such as tool wear is detected and analyzed using the three technologies previously mentioned. Adjustments can then be made to the cutting conditions, the tool diameter correction amount, and the tool itself. In this study, an attempt was made to detect the tool wear state by monitoring the cutting process with an on-machine measurement system using the acoustic emission (AE) method. So, the cutting resistance, surface roughness, and abrasion of tool edge were measured during end milling of stainless steel (SUS 304). In addition, the relationship between the measured parameters and the AE signal was investigated. As a result, although the change in the AE signal amplitude was minor with respect to the change in the tool wear, when the tool wear width increased, many AE signal waveforms including the frequency component of 70kHz were observed. Furthermore, in the machining state where chips are adhered to the workpiece, an AE signal waveform including a frequency component of 350 to 1000kHz was observed.