Injection molding deformation is a very common molding problem, and there are many causes of deformation. Each reason requires targeted improvement methods to better solve problem. For example, only when a doctor knows patient's symptoms and what condition they are in can he give targeted medications to help patient resolve his illness.
Then causes of product deformation are as follows:
Uneven cooling effect of mold water channel: This will lead to uneven temperatures in various locations of mold, resulting in inconsistent shrinkage and deformation of product.
Mold release system does not come off smoothly: An unbalanced and unsmooth release system may cause product to deform during ejection and pulling processes.
Too little water entering mold: If amount of water entering mold is too small, it will cause high material flow stress and stress deformation.
Thickness of glue position of product is too different: Difference in thickness of glue position is too large, which will lead to differences in shrinkage and deformation.
These reasons require targeted solutions to allow injection molding production to proceed better. Improvement method can be dealt with from many aspects, from mold design, from injection molding process, from product design, etc. to take corresponding measures.

 

So what kind of measures are the most effective and have immediate results? Next, let’s discuss it with an example.
Material of this product is ABS. Mold adopts one mold and two cavities, with a large nozzle for latent glue feeding.

 

Mold adopts one mold and two cavities. V/P switching time of single-point large nozzle to cold runner is 2.37S, and product is filled to 99%. V/P switching pressure is 30.1 2MPa.

 

Let’s take a look at temperature distribution after injection molding is completed.

 

Difference between cooling water inlet and outlet temperatures is within 2℃, and there is no overload.
Its total deformation can be seen from results, and maximum deformation position reaches 2.8mm.

 

This is basically result after we see injection molding, but what is final cause? We need to analyze it from all aspects.
First, let’s take a look at deformation caused by cooling

 

Picture above shows deformation of product caused by uneven cooling of product. Analysis results show that maximum deformation of product due to uneven cooling is 0. 37mm.
Let’s take a look at deformation caused by uneven shrinkage

 

Picture above shows deformation of product due to uneven shrinkage. Analysis results show that maximum deformation of product due to uneven shrinkage is 2. 69mm.
Finally, look at deformation caused by molecular orientation

 

Picture above shows deformation of product due to molecular alignment. Analysis results show that maximum deformation of product due to molecular alignment is 0. 00mm.
From above mold flow analysis, it can be known that theoretical total deformation of product is 0.17~2.78mm. Maximum deformation of product due to uneven shrinkage is 2.69mm; maximum deformation of product due to uneven cooling is 0.37mm; maximum deformation of product due to molecular alignment is 0.00mm.
It can be seen that product deformation is mainly caused by uneven shrinkage in all directions of product. There are many factors that affect shrinkage of injection molded parts.
Uneven shrinkage in various areas of the product leads to deformation. Solution:
Modify product design (difference in wall thickness, whether melt flow is balanced, etc.)
Mold pouring system design
Mold cooling system (change cooling)
Injection molding process (adjustment of holding pressure curve, etc.)
Solution:
After finding reason, let’s start with injection molding process.
Higher pressure and flow rate will produce high shear rate, forming internal stress in plastic part. It produces high residual stress and is prone to warping, while smaller injection pressure can reduce molecular orientation tendency of plastic and reduce its internal stress. To reduce warpage, injection pressure is adjusted to the lowest possible range.
Summary: Last factor is impact of holding pressure and holding time on injection molding. Explain principle.
1. Holding pressure is too high, and flow residual stress solidified due to material replenishment is high. At the same time, compressive stress of plastic is also high, and stress is easy to release, causing warpage and deformation of product;
2. If holding pressure is too low, backflow will occur near gate, which will not only form flow residual shear stress, but also form a large difference in volume shrinkage, resulting in high residual tensile and compressive stress, causing product to warp and deform.
3. Holding time is short, and when screw retreats, backflow will occur near gate, resulting in large residual stress.
Therefore, holding pressure should be moderate, and holding time should be extended until gate solidifies, so that residual stress generated can be smaller.
I hope this content can help everyone. Mold flow analysis can analyze deep-seated reasons in a more detailed manner. The key to understand is analysis of various data and evaluation of results. How to master mold flow technology?