Structural Design of Automotive auxiliary handle

                      FENG Bo, Zhou Bin

 

          (Zhuzhou Times New Material Technology Co., Ltd., Zhuzhou, Hunan 412007)

 

  Abstract: The automobile auxiliary handle retrofit design feasibility study. Molding process for the causes of defects in a position to increase strength pore size, the establishment of auxiliary handle the finite element model, the division of labor conditions discuss various loads on the auxiliary handle the impact, compared before and after the retrofit auxiliary handle intensity variations. Design studies show that the modification does not affect the strength of the premise, effectively reduces the defects generated from process to process, but also reduces the use of materials.

 

    Keywords: Auxiliary handle; gas-assisted molding; finite element analysis; structural design

 

    CLC: U463. 82 Document code: A Article ID :1005-5770 QOIl) 10-0056-03 Structure Analysis Study on Automobile GAM Handle FENG Bo, ZHOU Bin Zhuzhou New Times Material Technology Co., Ltd., Zhuzhou 412007, China)

 

    Abstract: Feasibility of automobile handle retrofit program was researched. Dimensions of holes on the intensity position were mcreased because of process defects. The FEA model of handle was created. Various load cases influence on handle were studied. The handles before and after modification was compared . Re-search showed that the retrofit design method can effectively reduce defects by the process, costs, and hadlittle influence on the impact strength. Keywords: Handle; GAM; FEA; Structure Design

 

    Car roof auxiliary handle for automotive interior materials common one, mostly installed in the vehicle passenger seat and rear seats of the upper part of the window, usually fixed to the body by screws on both ends of the buckle cover to ensure beautiful, while some Some limousine auxiliary handle fixed to the body through the tension spring on. Auxiliary handle in addition to protect occupant safety, but also can add hooks or lighting and other small structures, to achieve functional diversification.

 

    Auxiliary handle is plastic products, commonly used material for polyethylene or polypropylene, low-pressure molding method molding, extrusion molding, injection molding, etc. thesis auxiliary handle with gas-assisted injection molding. Gas-assisted injection molding process is the 1990s before they get the practical application of a practical new technology injection molding, the process is first injected with a syringe full of a certain amount or all of the plastic melt mold cavity re-injected after compression inert gas, the use of gas to promote the melt complete mold filling, fill the gap left after the plastic shrink when the parts to cool before the gas is discharged from the airways [1-2].

 

    Because of this molding technology makes certain characteristics of the finished product, there are some flaws auxiliary handle, impact of product aesthetics and reliability, and by changing the product mix to avoid these pitfalls, it is also to some extent affect its reliability.

 

    Papers in some small batch auxiliary handle for the study, due to molding technology for its defects resulting structural improvements, and this improvement feasibility study aimed at reducing costs while maintaining product quality.

 

A structural modification program

 

    Thesis auxiliary handle gas-assisted molding method using small batch, we found workpiece surface defects exist in the air intake on the side of one end of the melt solidification shrinkage of shallow pits (area A in Figure 1 position). This is due to the inlet side is too thick, resulting in large differences in the melt solidification rate, appear shallow pit, such defects seriously affect the product is beautiful, and even affect the product performance and quality, the need for retrofit design.

 

    Initial retrofit solution is the screw holes extend around the square hole BC, thereby reducing the wall parts at both ends, reducing the amount of solidification shrinkage. Figure 1 shows a modification of the structure before and after the auxiliary handle.

 

    Expanding the square hole, the wall thickness is reduced and the reduced strength, in order to investigate changes in the size of the square hole strength of the auxiliary handle, the article analyzed using the finite element method, the CAD design engineers reasonable suggestions.

 

Two finite element strength calculation

 

    Auxiliary handle both ends of the screws on the body through the human hand handle Central, so the auxiliary handle the mechanical model can be simplified clamped ends, Central withstand external loads the rod.

 

    Based on the above analysis of the mechanical model created in Hypermesh9.0 grid model, import abaqus6. 10 in perfect pre-processing and solving calculations.

 

2.1 grid model

 

    Ends of the auxiliary handle is bound by location, consider the Saint-Venant principle, the boundary conditions can not be directly applied to the handle body, so the finite element model is required to create the screw structure.

 

    Since the auxiliary handle many small and irregular structures with hexahedral element meshing has some difficulties, so use quadratic tetrahedral element mesh. This means high accuracy, can simulate arbitrary geometry, the calculation conditions permit modeling is more convenient. The number of pre-modified unit 45867, modified rear unit number 44431.

 

    In Hypermesh the handle attached to the screws and auxiliary material properties after import abaqus.

 

2.2 Finite Element Model

 

    Screw the auxiliary handle fixed to the vehicle body, the clamping nut and handle does not occur relative sliding surfaces, does not involve contact problems, the auxiliary handle screws and analyzed as a whole. According to the model of stress analysis, constraint nut plane node six degrees of freedom, is about to screw fully constrained.

 

    Auxiliary handle the load received by the central distribution of pressure from the hand in a certain bearing surface. Selected on the handle 10 cm long area to establish coupling load is applied.

 

    So that the auxiliary handle mounted in the XZ plane, the finite element model shown in Figure 2.

 

Auxiliary handle body material is polypropylene, the elastic modulus of 2 000MPa, Poisson's ratio of 0.35. Steel screw 45, an elastic modulus of 210 GPa, Poisson's ratio is 0.3.

 

2.3 Calculation condition and results of

 

    Auxiliary handle three types of strength checking discuss working conditions ridicule:

 

    Horizontal-load along the y, axis negative direction. This condition assumes that the tension of passengers to the auxiliary handle in the horizontal direction along the vehicle body.

 

    Vertical-load along the Z-axis direction. This condition assumes that the auxiliary handle to pull passengers along the vertical direction of the vehicle body.

 

    Degree - Load and Z axis 30. Angle downward. Setting this condition is due to the body can not long hold along the horizontal or vertical direction auxiliary handle, will be at an angle with the vertical direction to relieve fatigue.

 

    Before and after the retrofit auxiliary handle model presented calculations, first study the various types of working conditions on the handle structure of the trend, and then discuss the situation after remodeling handle intensity variations.

 

2.4 Analysis

 

    Figure 3 shows the structure prior to modification of the three load cases the principal stress contours.

 

    Principal stress contours shown auxiliary handle the maximum principal stress is distributed in the holes near the results of this analysis does not represent holes at the weakest intensity, but because of the contour and the coupling nut between 900 flat tip angle, thus creating stress concentration inaccurate. If you want to get the exact position of principal stress the need to establish sub-model for detailed analysis, but from the contours of view, the impact of stress concentration at the screw has not spread to key parts - Auxiliary handle sidewalls article will therefore screw at the case of inaccurate stress is negligible (hereinafter modified auxiliary handle after doing the same principal stress contours analytical processing).

 

    From the main stress contours can be seen, the main impact of the horizontal force auxiliary handle wide face section, if the level of tension is too large, it will lead to the middle or near the end of the handle position pulled off. The principal impact of the vertical direction tension auxiliary handle narrow face part if plumb tension is too large, easy to handle Central pulled off. Also from the numerical analysis of the principal stress, the vertical direction, the impact force of the auxiliary handle with respect to the horizontal force to be large, and this is due to the vertical force acting on the handle due to the greater pressure. Degree from the condition of the principal stress contours can be seen, when the load angle and the vertical direction, the same tension of the first two conditions including the combined effect of the auxiliary handle in the middle position is still weak.

 

    Through the above analysis, we can determine the external loads on the auxiliary handle BC holes relative to the side walls of the central small. Based on this analysis result, the auxiliary handle of the enlarged end portion BC retrofit solutions hole is reasonable.

 

    After the modified auxiliary handle modeling analysis submitted, from the main stress contours obtained as shown in Figure 4.

 

    From the main stress contours can be seen, the auxiliary handle in the working conditions, the stress distribution trend Horizontal pre-modified coincide with the maximum principal stress distribution in the middle handle; the remaining two conditions sidewall thickness calculating the auxiliary handle impact of changes in the larger, the maximum principal stress concentrated in the auxiliary handle ends. Modified stress distribution around the changes in trends also indicate: Before remodeling design, in order to lose weight and remove the ends of the material needs to be carefully considered this practice, when necessary, to make CAE analysis.

 

    Auxiliary handle for retrofit design, in order to quantitatively examine the auxiliary handle after modification still meet the strength requirements, now modified key parts before and after the auxiliary handle comparative analysis of the intensity (for example in Table 1).

 

    By comparison, after modification of the auxiliary handle wall strength becomes weak a little, but did not exceed the tensile strength of 96 MPa, to meet strength requirements.

 

    Auxiliary handle after remodeling into trial production, thinning of the wall, the melt solidification rate difference is small, making the area appear pits and other defects significantly reduced, to ensure product beautiful, improve product quality and reliability.

 

    After modification trial sample and measuring quality, because of the increased size of the hole, the mass ratio of each single product be reduced by modification of 3.92%, to a certain extent after the production, reduce costs.

 

3 Conclusions

 

    1) In the course of the auxiliary handle design, CAE analysis results for the design of the program has provided a guarantee reliability and shorten the product development cycle, improve the work efficiency.

 

    2) modification of the BC post-secondary handle hole expanded slightly changed handle sidewall strength is weak, but did not exceed the tensile strength, to meet the strength requirements, retrofit design and reasonable.

 

    3) after modification auxiliary handle can effectively reduce the defects and decrease in mass piece 3.92%, reducing production costs.