Having worked in product structure and mold design for many years, I've encountered quite a few difficult structures, but this three-way joint is definitely a "tough nut to crack" recently. I recently found drawings for this product online, which reportedly stumped many experts. Out of curiosity, I sent them to foremen in our factory. Even senior mold design master, who has been working in industry for over ten years, frowned when he first received drawings, studied mold parting and demolding, saying it was difficult to do and required a different approach.
Today, let's skip formalities. From perspective of a product structure engineer, I will discuss mold design approach for this product in detail, thoroughly breaking down this common industry problem so that colleagues can directly refer to it when encountering similar structures.

Structure of three-way connector is shown in diagram below.

 

Let's look at product itself. This three-way connector isn't a typical straight tee; it has a three-dimensional, branching, irregular structure. Core challenge lies in undercut demolding of three outer angled pillars, which is also the most technically demanding part of the entire mold.

 

Consider this: three angled pillars don't face same direction but are distributed at multiple angles, creating a very compact spatial arrangement. There's no single, straight direction for core pulling. Conventional side-angled core pulling and split-slider solutions are completely ineffective on this product. No matter which direction you pull core from first, movement of sliders immediately causes spatial interference. This can range from minor damage to product's appearance and structure to serious damage to mold mechanism, even rendering the entire mold unusable—a very high risk.

 

We often discuss complex structures like rotary core pulling and two-stage core pulling with sliders. When faced with such a deadlock, we must break free from fixed mindset of traditional core pulling and not focus solely on pulling in one direction.
For this three-pronged joint, final core solution was a step-by-step rotary mold opening, relying on the sliders to rotate in stages to avoid interference, thus completely resolving interference problem. This was the key to overcoming this challenge.

In mold design, the first step is always to find correct reference point, and this product is no exception. We first precisely located core rotation center of mold based on distribution angles of three inclined pillars. Layout and movement trajectory of all sliders are planned around this center. This is foundation for ensuring rotational accuracy, preventing offset, and avoiding mold jamming; not a single step can be wrong.
Determine a rotation center and draw the first set of sliders.

 

A common pitfall for many in industry is immediately moving sliders, which is absolutely unacceptable. This mold opening sequence has strict requirements: before sliders rotate and open, core (insert) of product's inner hole must be completely removed. If inner insert isn't fully removed before rotating slider, it will not only scratch product's internal structure but also jam slider, causing it to seize up and directly damage mold mechanism. This sequence must not be reversed.

 

Looking at a single slider, its structural design perfectly matches rotation trajectory, with no unnecessary sharp corners or jamming. Rotation process is smooth, without any stuttering or resistance. The overall effect after rotation perfectly conforms to product's shape, resulting in a high degree of product integrity after demolding.

 

2. Slider Rotation in Steps: Two Groups Moving in tandem, Simultaneous Movement Strictly Prohibited
Only after inner insert is fully removed can slider rotate for demolding. The key here is "step-by-step rotation." We divide slider into two groups, A and B, whose movements are completely staggered and absolutely cannot move simultaneously. This is a crucial detail to avoid interference.

 

Specific motion logic is clear: During mold opening, slider A rotates 35° around rotation center first. Once slider A is fully rotated and clears space, slider B then rotates 15°. During mold closing, sequence is reversed: slider B must close first, and only after it has returned to its original position should slider A close. This process is done step by step, ensuring no slider collisions or interference occur.
Specific motion steps are demonstrated in following dynamic demonstration:

 

3. Not Unique Structure: Alternative Demolding Schemes for Reference
There is no single, absolute standard answer to mold design. For this three-pronged joint, we have also developed alternative demolding schemes. Approach differs from step-by-step rotation mold opening, but it still revolves around core principle of "avoiding interference," adapting to different mold processing conditions and production needs. When encountering similar structures, you can flexibly adjust design scheme based on your factory's processing capabilities and cost budget.

 

Accompanying dynamic demonstration provides a clearer view of the entire mold's motion flow: inner core insert is pulled first → slider A rotates 35° → slider B rotates 15° → product is smoothly ejected and demolded, then mold closes in reverse order. Each step is seamlessly connected without any interference.
Dynamic demonstration of motion steps is shown in image below.

 

In fact, many mold challenges for irregularly shaped structural parts are not solved by building up complex mechanisms, but by thinking outside box and identifying core bottlenecks. For products with multi-directional inclined pillars and prone to interference, step-by-step rotational mold opening approach is highly applicable. Colleagues encountering tee joints, multi-fork irregular joints, and similar products can refer to this design logic.