Haimin Ding

A Modified Genetic Algorithm(GA) for Optimization of Process Planning

Computer-aided process planning (CAPP) is an important and complex in the computer integrated manufacturing system(CIMS). The expression methods of process knowledge based on manufacturing feature is established based on the analysis of characteristic of process knowledge. According to the constraints mong process knowledge, decision space of process planning based on process constraints is constructed which improved search efficiency of GA. In allusion to the uncertainty of decision of process planning, the multi-objective optimization function is established, and a GA is applied to optimization of process planning. Process planning is optimized using the reasonable coding strategy, fitness function, selection, crossover and mutation algorithm, etc. An case is offered to illustrate the process of optimization of process planing based on GA.

An Improved Ant Colony Optimization Approach for Optimization of Process Planning

Computer-aided process planning (CAPP) is an important interface between computer-aided design (CAD) and computer-aided manufacturing (CAM) in computer-integrated manufacturing environments (CIMs). In this paper, process planning problem is described based on a weighted graph, and an ant colony optimization (ACO) approach is improved to deal with it effectively. The weighted graph consists of nodes, directed arcs, and undirected arcs, which denote operations, precedence constraints among operation, and the possible visited path among operations, respectively. Ant colony goes through the necessary nodes on the graph to achieve the optimal solution with the objective of minimizing total production costs (TPCs). A pheromone updating strategy proposed in this paper is incorporated in the standard ACO, which includes Global Update Rule and Local Update Rule. A simple method by controlling the repeated number of the same process plans is designed to avoid the local convergence. A case has been carried out to study the influence of various parameters of ACO on the system performance. Extensive comparative experiments have been carried out to validate the feasibility and efficiency of the proposed approach.

Influence of carbon vacancies on the adsorption of Au on TiC(001): a first-principles study

In this work, it is found that the adsorption sites and geometries of Au clusters on TiC(001) surfaces containing carbon vacancies are significantly different from that without vacancies. In TiC(001) with carbon vacancies, the most preferential adsorption sites for Au are on top of vacancies sites, and then the sites neighboring the vacancies. The tendency for 3D Au clusters formation in TiC(001) with carbon vacancies is weaker and Au atoms are more likely to form rough 2D clusters. Furthermore, more charge is transferred from the substrate to Au and the polarization of electrons is stronger. In addition, the diffusion of Au on TiC(001) surface containing carbon vacancies is more difficult. The above affects can be helpful for improving the chemical activation of Au/TiC surfaces. Therefore, introducing carbon vacancies in the surfaces should be a very promising method to enhance the activation of Au/TiC systems.

First-principles study of doping and distribution of Si in TiC

In this work, first principles calculations have been performed to study the doping and distribution of Si atoms in TiC lattice. The results confirm that Si atoms prefer to occupy Ti sites and their segregation on the TiC crystal surface may occur. But in the presence of carbon vacancies on the surface, Si atoms tend to be chemically adsorbed around the vacancies rather than occupy the carbon sites. It is also shown that the diffusion of Si may be very difficult in stoichiometric TiC, in particular the diffusion from bulk to surface. However, the carbon vacancies can considerably decrease the energy barrier and enhance the diffusion of Si atoms.

Adsorption of boron and its relationship with morphologies of TiC

First-principle calculations were performed to study the adsorption of boron and its relationship with the morphologies of TiC. It is found that although the adsorption of boron on all the low-index TiC crystal planes is thermally favorable, it will be adsorbed more easily by C-terminated {111} and {011} planes, while less possible to be adsorbed by {001}. The study of the formation of B–B clusters indicates that the distribution of boron adatoms on C-terminated (111) and {011} planes will be more uniform, and the diffusion of the adatom further confirms the above results. According to the geometry relationship and growth rate of different crystal planes, it is deduced that the adsorption of boron on TiC will seriously impede the growth of {111} and {011} planes, which can make TiC grow into hexagonal platelets.

The influence of boron on the adsorption of Ti and C on TiC surfaces

The first-principles calculations have been performed to study the influence of boron on the adsorption of Ti and C on different TiC surfaces. It is found that boron can be adsorbed on both TiC (001) and (111) surfaces. When boron is present and carbon supply is high during the preparation of TiC, boron can bond with carbon atoms to form B-C clusters on (001) surface, but the formation of them is less favorable than that of Ti-C clusters. However, under the low carbon-supply condition, both B-B and Ti-Ti clusters can be formed, and, once being formed, B-B clusters are more stable than the Ti-Ti ones. On Ti-terminated (111) surfaces, boron adatoms are more likely to be moved to form B-B clusters. The study of the diffusion of the adatoms on the surfaces demonstrates that boron adatoms can be more easily migrated on (111) surfaces, which further confirms the above results.

Simulation study of influence of Al, Si and B on the growth of TiC

The influence of Al, Si and B on the growth of TiC is studied in this article. It is found that the adsorption of Al is more favorable on TiC {111} than that on {001}. Therefore, under the influence of it, the growth rate of {111} will be accelerated and result in the decreasing of the relative growth rate between {001} and {111}. Therefore, TiC will grow into truncated- octahedron. But when TiC is formed under the influence of Si and B, they will grow into hexagonal platelets due to the preferential adsorption of Si and B on {011} and {001}. Copyright©2011 VBRI press.