Comparative Reliability Analysis of Milling Teeth Manufactured by Conventional Cutting Processes and Laser Cladding

This paper presents the estimation of the main reliability indices of two milling teeth types. The comparative analysis referred to milling teeth manufactured by conventional cutting processes, made of 41Cr4 (type I), and milling teeth manufactured by high-productivity welding loading processes, namely, laser cladding (type II). To analyze the distributions of the lifetime data specific to milling teeth types, the correlation coefficient value was considered. Goodness-of-fit analysis indicated that normal distribution was adopted in order to conduct parametric estimates of the reliability indices. Point estimations of the parameters and estimations with 95% confidence intervals of the components’ lifetimes were performed, applying the least squares estimation method. Compared to the type II milling teeth, lower values of the reliability function were estimated for the type I milling teeth. The type II milling teeth displayed higher values for the statistical parameters, with a mean of 6 h, while the mean of the failure of the type I milling teeth was 5.2 h. In addition, a more pronounced hazard rate for the type I milling teeth compared to the type II milling teeth was observed

Lifetime Analysis of Dies Manufactured by Conventional Processes and Reconditioned by Deposition Welding Operation

The refurbishment of dies by the deposition welding of wear areas is an efficient and economical process. The aim of this study was to conduct a comparative analysis of the lifetimes of different types of dies for the manufacturing of wagon wheels. The analyzed dies were manufactured by conventional processes (Type I) and reconditioned through a deposition welding procedure using a dedicated electrode (Type II). The Anderson–Darling test was conducted to analyze the goodness of fit of the lifetime data specific to the die types. The maximum likelihood estimation method (MLE) with a 95% confidence interval (CI) was applied in order to estimate the lifetime distribution parameters. It was found that the lifetimes of type II dies were longer than those of type I dies. The mean time to failure (MTTF) recorded for reconditioned dies was 426 min, while the mean time to failure of dies manufactured by conventional processes was approximatively 253 min. In addition, an accentuated hazard rate for type I dies compared to type II dies was observed. The results of this analysis emphasized the fact that dies can be restored to their initial operating capacity by successfully using deposition welding procedures that confer a high resistance to operational loads. At the same time, the use of these procedures allows for the sustainable development of resources and waste management

Reliability estimation of the milling machines teeth obtained by welding deposition process

Currently, governments and authorities worldwide allocate annually significant amounts of money in an attempt to maintain the existing road infrastructure functional and safe. In our country too there is this concern to rehabilitate a significant number of damaged road structures and to create new modern ones. The research presented in this paper focused on applying modern manufacturing technologies, loading by welding the milling teeth for stripped asphalt road structures in order to increase their reliability. It was thus estimated the reliability of classical teeth made from 41Cr4 and teeth manufactured through loading by welding with special filler materials in the active surfaces, which grants them self-protection systems from wear and locking in rotation and which equipped a Wirtgen 50 milling machine in operation on one of the national roads

Factors that influence the quality constant of the manufacturing process for asphalt milling knifes

The quality constant for mill knifes used to strip asphalt is significantly influenced by the quality of the reinforcement which, in its turn, is influenced by the thermic brazing process and by manufacturing the protection system at blockage through welding when it spins around its axis. It’s also influenced by the quality of the intelligent wear and blocking self-protection systems that in their turn are influenced by oxidation and diffusion processes of W and C that make simmered carbides from the reinforcement and brazed joints. Overheating during welding and brazing of the knife reinforcement and/or blockage self-protection reinforcement favours the oxidation of the W carbides leading to a fast degradation of the affected zones, even in exploitation. Exceeding optimum temperature during brazing of the reinforcement in the low chromium alloyed steel support leads to Zn evaporation in certain areas from the brazing material and lowers the brazed joint resistance to wear this causes the knife reinforcement to detach from the support. Taking into consideration the above mentioned facts it is recommended that the production stages of the mill knifes are done mechanized and/or automatic constantly monitoring the execution parameters