Generally speaking, to determine whether a product can be mold-opened, one should follow this line of thinking:
Product appearance and requirements → structure → gate → demoulding
Why is it like this?
Next, I will take a product as an example to illustrate that changes in thinking caused by various factors during entire design process lead to excessive changes in mold design results.

 

 

 

 

After getting this product, let's take a look at its main information. In picture, red circles are all undercuts. Product is a decorative strip, appearance part. Except for necessary mold structure, it is not allowed to damage appearance.

 

In picture above, many small undercuts in this part of product have same ejection direction. Therefore, consider making them on a slider.

 

 

Small side holes on left and right sides are undercuts, and parting surfaces on both sides shown by draft analysis are just on exterior surface. In order to maximize beautiful appearance, left and right sides should be considered as integral sliders for entire sides. Parting cannot follow position shown in draft analysis, it should be wrapped at the bottom of product, at red line in figure below.

 

Reason why package is here is because if mold is produced for a long time, mold is worn out, or mold is not matched properly. Parting surface is prone to burrs, and product parting is moved inside. If burrs are generated here, it will have no effect on quality of entire product. This is an invisible position.

 

Next, look at undercuts on both sides of picture. This is the most troublesome position of this mold. There are undercuts at two places AB, which is nothing more than an inner sliding block or an lifter.
To talk about practice of this position, it is necessary to talk about it with gate, because there is an influence between two. Choice of gate for this product is better in two places, as shown in arrow below.

 

For inside, since there is no undercut in middle position, it can be used as a latent gate or horn gate without increasing difficulty of mold. Moreover, inside can greatly reduce mold eccentricity. Therefore, it is more appropriate to choose gate inside.
Because gate is inside, lifter here can leave more space. Just add a set of thimble plates to front mold, which is a more reasonable choice.

 

Looking at above picture, part of front mold slanting top is under two outer sliders. If large sliders on left and right sides are used as rear mold sliders, front mold lifter and the rear mold slider will shift in mold opening direction. After mold is fully opened, lifter stays on front mold and separates from back mold. When clamping mold, lifter of front mold must be synchronized with parting surface to return to position, otherwise mold will crash.
Therefore, overall large sliders on both sides of product must be made into a front mold with an oblique spring or an lifter to ensure synchronization.
At this point, I have basically clarified my thoughts. Left and right sides are springs, and middle position is front mold lifter.
Because lifter is driven by thimble plate, inclined spring is driven by its own hook and spring. Because driving forces of two are different, it is difficult to ensure complete synchronization. If inclined spring moves first when mold is opened, it will inevitably pull sealing surface of lifter and inclined spring.
How can we guarantee complete synchronization?
Only when two rely on same driving force can they ensure complete synchronization.
Therefore, oblique bullets on left and right sides should be on front mold thimble plate, so as to ensure that two are completely synchronized. Then, this oblique bomb has become an lifter. As a result, mold became like this.

 

Oblique bombs on left and right sides have become lifters, but they are not completely lifters. Top is pulled by hook. Top of inclined bomb is fitted with a spring.
But a new question arises, what drive does thimble plate rely on?
Considering spring drive, there is a hook on inclined spring, then spring on the top of inclined spring can be cancelled, and spring can be directly installed on front mold back pin. As shown below.

 

In order to ensure that mold can be fully activated when mold is opened, so that stress point does not act on oblique spring I-shaped, we add elastic glue to bottom of front mold thimble plate, so that neither spring failure nor hook gap is worried. Risk is minimized and mold requirements we need are met.
Every time you get a new product, you should proceed according to this idea. This should be idea that a qualified mold designer should have, or a mind map, to maximize focus.