Design considerations for the thickness of the plastic product

Consideration of product meat thickness, influence on manufacturing and production, influence on product performance and methods of reinforcement and prevention of deformation

The selection of product meat thickness, structural requirements, cost, appearance and touch, the mold capacity is not easy to open the product, such as sag, warping deformation, etc. Control the molding cycle, quality and cost considerations, the molding cycle time increases with the increase of meat thickness, but it is relatively Thick products are easy to warp. Thin and uniform products have better quality. Generally, the method of reducing meat thickness is used to control the impact on manufacturing. Generally speaking, reducing meat thickness requires increasing pressure to fill the mold cavity. , sometimes, the shear heat of the material will make the plastic flow more easily, reducing the injection pressure.

Many different factors affecting injection pressure are covered in the design guide. We have divided this list into four key impact areas. In the part design category, the most important factor affecting injection pressure is wall thickness. Wall thickness and pressure are inversely proportional. As the wall thickness decreases, the required injection pressure increases. As the wall thickness increases, the injection pressure decreases. What problems do you find if the wall thickness is too thin? Flash, short shot, burning, etc.

The relationship between meat thickness and flow length

First, let's look at the part thickness and maximum flow length for this resin. We saw that the plastic would flow about 7 inches at the lowest pressure shown. However, if we applied the highest pressure, we could push the plastic up to 17 inches. Since our flow length is only 5-6 inches, we should need lower pressure to fill the part.

Changes in meat thickness, sudden changes in meat thickness will change the filling mode, plastic will be filled in thicker places, and many problems may occur, including short shots, uneven volume shrinkage, and warping deformation

Another part design effect on injection pressure is surface area. Locations that touch more mold area have more cooling and greater resistance to the flow of plastic. This results in higher pressures required to fill the part than parts with less surface contact area. What applications might you see this effect of stress on? (Any type of speaker grill pattern, vent effect or surface mesh pattern)

Other meat thickness variation problems When the plastic area in contact with the mold surface increases, the injection pressure also increases, and the problem of surface defects may follow

More cooling and drag vs. less cooling vs. lower drag Another part design impact on injection pressure is surface area. Because more area is in contact with the mold, there is more cooling and more resistance as the plastic flows. This results in higher pressures required to fill the part than parts with less surface contact area. What applications might you see this effect of stress on? (Any type of speaker grill pattern, vent effect or surface mesh pattern)

The influence of meat thickness and molding pressure

Based on the injection pressure and melt temperature range in which the part can be molded. Want to have as wide a process window as possible so you don't have a lot of problems molding the part.

The relationship between meat thickness and packing pressure Thin shell molding will limit packing pressure. The longer the flow length, the smaller the packing pressure. When filling small feature areas, over packing pressure must be avoided

Relationship between meat thickness and cooling time

Cooling time ~ (thickest wall thickness) The thermal diffusivity of the melt gave me a quick idea of how important wall thickness is in determining cooling time. The basic formula for calculating part wall cooling time is shown here. One thing to note here is that the cooling time is proportional to the square of the thickest wall section. The width or length of the wall section doesn't really matter, the thicker the thickness between the core and cavity surface, the longer it will take to cool. What happens if you have isolated thick areas in your part and you try to eject the part too early? (Sinking or uneven shrinkage causes warpage)

Relationship between meat thickness and warpage

You can't really do much with the properties of the plastic resin other than changing to a different resin. However, you can control some factors that affect part shrinkage. These include melt and mold temperatures, which reduce shrinkage as temperature decreases. Injection rate has some effect, but not major.

The effect of low crystallinity and high crystallinity meat thickness on warpage deformation

High shrinkage, high cooling rate, low crystallinity, low cooling rate, high crystallinity are in the warped part, that is, the volume shrinkage is not uniform. In this case, the cooling from the core to the cavity may be uniform. However, the thickness of the part will vary, resulting in different shrinkage rates between parts of the part. This difference in shrinkage causes stress differences between sections and can lead to part warping. This is especially true for semi-crystalline resins, as more crystallization occurs in thicker parts where the plastic stays longer. The flakes cooled faster and didn't have time to crystallize significantly. Compared to molding the part with an amorphous resin, this situation increases the thickness of the product where the difference in shrinkage between the two parts is not uniform.

Reinforcing and preventing deformation of the rib design, the rounded corners that meet the surfaces change the thickness and shape

Rib design: Reinforcing ribs (Rib) can increase the strength and rigidity of the product, prevent deformation caused by residual stress, and also improve the fluidity of the plastic. Use circular arcs to avoid large-section rib designs.

Surface-to-surface fillet: The place where the surface meets the surface is where the stress is concentrated, especially the sharp intersection angle, which is more likely to cause stress concentration. If the surfaces are connected by a certain arc, the phenomenon of stress concentration can be reduced, and at the same time, the plastic can have good fluidity during molding, which is more helpful for product demoulding.

Change of meat thickness and change of shape: Change of meat thickness or change of the shape of the molded product can prevent the side wall or edge from being twisted and deformed, and increase the strength and rigidity of the molded product. Proper position adjustment can sometimes improve the flow of the plastic