Plastic Rear Bumper Molding

Process Design And Analysis Of Plastic Rear Bumper Mold

The structural design of the plastic rear bumper mainly includes the following aspects: shape, thickness, de-molding angle, ribs, support surface, rounded corners, hole positions, and the like.

1. The shape of the part

When designing a part, details such as manufacturability and reliability of the part are carefully considered in advance. The partial protrusion of the part and the large cantilever structure tend to cause the part to deform after assembly, so it should be avoided during design. It can be solved by the following methods:

First, the two mounting points are integrated into one, the second is to widen the flange, and the third is to reinforce the back. For the boundary with the body requirements, the method of adding flanges can minimize the deformation of the parts, which is beneficial to the improvement of the matching precision, thus ensuring the quality of the whole vehicle.

2. Thickness of parts

During the cooling of the part, the curing or cooling rate is uneven, which will result in uneven shrinkage, which will cause stress inside the part, resulting in warpage and shrinkage. In order to avoid these defects, the bumper must have a uniform thickness.

The thickness of the car bumper is generally: (3 0.25) mm to (3.5 0.25) mm. When designing, the use of a sufficient thickness variation transition zone can achieve the purpose of avoiding the influence of the thickness variation of the surface quality of the part.

3. Release angle

The demolding angle is a problem that must be carefully considered in the design of plastic parts, and the angle of demolding should be greater than zero. Under the condition of satisfying greater than zero, the ease of demolding of the part is proportional to the size of the demolding angle. However, the draft angle is not as large as possible, and a large angle tends to cause uneven thickness of parts and lower manufacturing precision.

The draft angle is closely related to the depth of the part. Table 3 shows the minimum and maximum draft angle reference values. In general, the draft angle needs to be slightly larger than that of the non-skinned piece, and the specific size is also related to the depth of the skin. The depth of the skin of 0.025 requires a draft of 1°.

4. Reinforcement

For plastic parts, especially large parts, ribs must be added in some places, such as large curved surfaces, holes, or mounting points, to increase strength and rigidity. Because only a certain thickness is required, the shape, size, and certain strength of the workpiece cannot be guaranteed. For automotive exterior parts, the main surface is generally not reinforced. When the rib is used on the secondary surface, the root thickness is less than 1/2 of the thickness, while for the non-visible surface, the apparent quality requirement is not So strict. At some special times, due to structural constraints, the main surface needs to be placed behind the mounting points, etc., the mounting points should be as thin as possible or partially open to prevent surface shrinkage, and often add some small ribs to prevent installation.

5. Support surface

If the support surface of the part is the entire surface, a slight deformation will affect the appearance and the fit of the body. Therefore, in actual production, the flanges and the partially raised rims are often used to serve as the support surface.

6. Fillet

The rounded corner design of the bumper, on the basis of compliance with the regulations, must be in perfect shape with the shape of the whole vehicle. The fillet corresponds to or overlaps the position of the R corner inflection point. In general, the R angle of the bumper is generally between (3 and 0.5) mm. In the case of sharp corners, in order to ensure the firmness of the structure and the fluidity of the material, the R angle should be at least 0.5 mm. In order to avoid the stress concentration at the corners and thus improve the service life of the mold, when designing the plastic parts, it is generally necessary to adopt a circular arc transition, and the rounded corners of 0.5 to 1 mm should be designed at the joints. In addition, in order to reduce the stress and ensure a uniform wall thickness, some rounded corners are also used at the corners.

7. Hole

The shape of the mounting hole on the bumper should not be complicated and should be as simple as possible, generally designed as a through-hole. There must be a certain distance between the hole and the wall. The minimum distance between the hole and the boundary is 1 times the aperture.