In this study, we developed a new vertical thermal gradient rig that uses methane-oxygen fuel. We conducted thermal gradient testing on a thermal barrier coating system, with a flame temperature of 1,900℃. Our results showed that the maximum surface temperature reached 1,065℃, while the temperature difference between the surface temperature and the temperature of the middle substrate (ΔT) was 70oC. Using the same torch as in this study, our finding suggest that the total flow rate of the flame should be above 12.4 LPM, and the gun distance should be less than 8 cm, to simulate a surface temperature of 1,300℃, while keeping the substrate temperature below 1,000℃. This will ensure that the flame is wide enough to cover the entire surface area of the thermal barrier coating.

Hybrid additive manufacturing (AM) refers to a combination of two metal AM techniques: material deposition by powder bed fusion (PBF) and additional building by directed energy deposition (DED). This study focused on different characteristics in accordance with relative deposition directions of PBF and DED during hybrid AM production. Characteristics of the sample fabricated by hybrid AM (i.e., hybrid sample) were compared with those of the sample fabricated by PBF or DED. Ferrite was dominant in the microstructure of PBF deposits with very fine retained austenite observed locally. In contrast, lath martensite and retained austenite were formed uniformly in the microstructure of DED deposits. Different microstructures in the two processes were attributed to differences of cooling rate. In DED deposits, microhardness was significantly decreased owing to a high retained austenite fraction. However, in the hybrid sample, microhardness was rapidly increased in the HAZ owing to aging heat treatment for long-term deposition. Principal wear mechanisms of PBF and DED samples were oxidative wear and plastic deformation, respectively.

Generally, cutting force models use a sin function method to calculate chip thickness. In slot end milling, the error from a sin function method is much bigger than other machining because a tool rotation angle in cutting is much larger. Thus in this paper, a new method to calculate chip thickness was suggested and evaluated. In a new method, tool position data according to tool rotation are checked and stored so that it is possible correct chip thickness is calculated. Cutting force waveforms simulated from a sin function method and a new method and measured waveforms from experiments were compared and error percentages were obtained. Finally, a new method had good results for simulating cutting force in slot end milling.

Runout causes severe differences among cutting force waveforms due to changes of rotational radii. Thus a runout model must be included in a cutting force model to simulate cutting force accurately. In this paper, a runout modeling method and a measurement method using a dialgauge were developed, which were easy to apply. To calculate runout parameters, a computer program algorithm which obtained runout parameters from measurement values was developed.
Cutting force waveforms simulated from cutting force model considering runout effect and measured from experiments had good agreements for their wave size and order.