Modeling for Orientation Deviation of Workpiece and Analysis of Machining Accuracy

The machining accuracy of workpiece is influenced by its orientation deviation, which is caused by the fixture-workpiece error. Based on the spatial coordinate theory, the orientation deviation of workpiece is measured by using an on-machine verification system, which can take into account the errors resulting from fixture manufacturing, installation and adjustment, location and clamping of workpiece. According to the least square method, the model of orientation deviation is built to determine the relationship between the theoretical and actual coordinate systems. The influence of orientation deviation on machining accuracy is quantified, and it is shown that the orientation deviation only affects the dimensional precision and position precision, rather than shape precision. In the experiment, the compensation processing of realtime errors was conducted, and the perpendicularity and inclination errors of the tetragonal part were reduced by 38.46% and 47.06%, respectively.

Modeling and Compensation Technology for the Comprehensive Errors of Fixture System

Error modelling and compensating technology is an effective method to improve the processing precision.The position and orientation deviation of workpiece is caused by the fixing and manufacturing errors of the fixture.How to reduce the position and orientation deviation of workpiece has become a technical problem of improving the processing quality of workpiece.In order to increase machining accuracy,an implementation scheme of fixture system comprehensive errors（FSCE） compensation is proposed.A FSCE parameter model is established by analyzing the influence of contact points on the position and orientation of workpiece.Meanwhile,a parameter identification method for FSCE parameter model is presented by using the 3-2-1 deterministic positioning fixture,which determines the model parameters.Moreover,a FSCE compensation model is formulated to study the compensation value of the cutting position.By using RenishawOMP60 Probe and combining vertical machining centre（SKVH850） equipment with SKY2001 Open CNC System,on-machine verification system（OMVS） is built to measure FSCE successfully.The processing error can be reduced by analyzing the cutting position of the tool with the homogeneous transformation of space coordinate system.Finally,the compensation experiment of real time errors is conducted,and the cylindricality and perpendicularity errors of hole surface are reduced by 30.77% and 28.57%,respectively.This paper provides a new way of realizing the compensation of FCSE,which can improve the machining accuracy of workpiece largely.

Influence of the Substrate Orientation on the Isothermal Solidification during TLP Bonding Single Crystal Superalloys

Angle deviations between the two substrates during transient liquid phase （TLP） bonding single crystal superalloys cannot be avoided. In the present work, specimens have been prepared to investigate the influences of the various substrate orientations. It is found that the width of the non-isothermal solidification zone （NSZ） is linear with the square root of the isothermal solidification time. This suggests that the isothermal solidification process is B-diffusion controlled in different substrate orientation deviations. And also the width of the NSZ increases with increasing angle deviation, indicating that the isothermal solidification time needed in the TLP bonding increases with increasing orientation deviation between the two substrates.

Crystal plasticity behavior of single-crystal pure magnesium under plane-strain compression

A phenomenological crystal plasticity constitu- tive model for magnesium single crystal was presented. Four deformation mechanisms （including basal （a）, pris- matic （a）, pyramidal （c ＋ a） slip and tension twin） and their interactions were considered. Twin-induced lattice reorientation was also incorporated in the model. The proposed model was then applied to the simulation of plane-strain compression deformation for different orien- tations. Related material parameters were calibrated at first according to the classical channel-die tests. The predicted macro-and microscopic responses, along with the experi- mental results, show strong orientation-dependent proper- ties. It is also found in the simulation that basal slip in the twinned region is active even before the saturation of twin activity in a twin-favored case. Furthermore, the effect of an initial deviation angle on the mechanical responses was evaluated, which is proved to be also orientation-depen- dent. Basal slip is found to be easily activated due to a slight deviation, while a slight deviation in the twin-fa- vored case could result in a significant difference in the mechanical behavior after the reorientation. The effort on the study of magnesium single crystal in the present work contributes to further polycrystalline analysis.