Abstract: The limitations of 1D tolerance analysis by dimensional chain and the advantages of 3D tolerance analysis were analyzed.3D dimension and tolerance analysis of the gap between air conditioning pipe of chassis and front sub-frame unit was carried out using 3DCS software.The unreasonable components that cause assembly interference were found out by comparative analysis of the main contribution factor.And then,the product structure and tolerance can be optimized,assembly process can be improved.It shows that the method can effectively carry out assembling tolerance stack-up analysis and evaluate the assemblability of product.

Key words: tolerance analysis, Geometric Dimensioning and Tolerancing(GD &, T), 3DCS software, chassis