We present a method of discriminant diffusion maps analysis (DDMA) for evaluating tool wear during milling processes.As a dimensionality reduction technique,the DDMA method is used to fuse and reduce the original features extracted from both the time and frequency domains,by preserving the diffusion distances within the intrinsic feature space and coupling the features to a discriminant keel to refine the information from the high-dimensional feature space.The proposed DDMA method consists of three main steps:(1) signal processing and feature extraction;(2) intrinsic dimensionality estimation;(3) feature fusion implementation through feature space mapping with diffusion distance preservation.DDMA has been applied to current signals measured from the spindle in a machine center during a milling experiment to evaluate the tool wear status.Compared with the popular principle component analysis method,DDMA can better preserve the useful intrinsic information related to tool wear status.Thus,two important aspects are highlighted in this study:the benefits of the significantly lower dimension of the intrinsic features that are sensitive to tool wear,and the convenient availability of current signals in most industrial machine centers.