The linear motion guideway (LM guide) is one of the key parts of precision motion and positioning, and it requires high straightness, form accuracy, stiffness, and surface quality. LM guides are actively used in manufacturing facilities for automobiles, aerospace, optics, semiconductors, robots, displays, and portable communication equipment. At present, most of LM guides are based on rolling contact, using either balls or rollers. Roller LM guides have been in high demand in recent years in various industrial fields that require high rigidity. In this study, the friction characteristics of ball and roller LM guides with the same rail width were compared, and friction behavior was analyzed. An experimental setup consisting of a driving unit, specimen, force sensor, and signal acquisition unit was constructed, and signals were collected under various conditions. Three lubrication conditions were used: no lubrication (dry surface), ISO-VG 32, and 68, and a wide feed-rate range from 1 to 100 mm/s was selected. The experimental results showed that the ball LM guide and the roller LM guide had significantly different friction characteristics, which were analyzed from the aspect of Stribeck curve components. In conclusion, friction behavior differed according to lubrication conditions in the no-payload state of the ball and roller LM guides, and the effect of lubrication conditions on friction behavior was shown.

In this paper, a microfluidic co-culture system comprising an embedded polydimethylsiloxane (PDMS) microstencil was fabricated. The fabricated co-culture system has two micro-channels separated with a PDMS microstencil membrane. Master molds for microchannels and stencil membranes were fabricated by photolithography, then used for casting of PDMS devices. The stencil membrane was 10 thick, with holes 10-μm large in diameter. The fabricated system co-cultured two types of cells (HepG2, NIH-3T3 Cells) successfully for seven days. The viability and stability of the cells were verified through LIVE/DEAD® staining and analysis. Additionally, albumin secretion of HepG2 cells was measured for seven days, using an HSA ELISA kit. The measured data were analyzed, to compare the activity of HepG2 cells. Results confirmed that cells can be co-cultured in the fabricated microfluidic system.

Reduction of welding residual stress is very important in the railway industry, but calculating its distribution in structures is difficult because welding residual stress formation is influenced by various parameters. In this study, we developed a finite element model for simulating the repair welding process to recover a surface damaged rail, and conducted a series of parametric studies while varying the cooling rate and the duration of post weld heat treatment (PWHT) to find the best conditions for reducing welding residual stress level. This paper presents a three-dimensional model of the repair welding process considering the phase transformation effect implemented by the ABAQUS user subroutine, and the results of parametric studies with various cooling rates and PWHT durations. We found that heat treatment significantly reduced the residual stress on the upper rail by about 170 ㎫.