In our plastic mold design industry, there are many types of mold structures. For general mold designers, ordinary sliders and lifter structures are familiar to everyone, they can design them. However, for some more special and typical mold structures, there will be a feeling of inability to start. Today I will explain to you key points of design of screw thread mold structure. I hope that mold design enthusiasts and partners who want to know more about screw thread core structure will be inspired:

 

Plastic product threads are divided into two types: external thread and internal thread. For external threads with low precision, Huff blocks are generally used for molding, while internal threads mostly require thread unloading devices. Here is a brief introduction to internal thread demoulding method and introduction of gear calls:
1. According to action mode:
①Thread core rotates and push plate pushes product away;
②Thread core rotates and retreats at the same time, and product naturally detaches.

 

2. Divided by driving mode: There are generally two types of extraction molds: one is that cylinder drives rack to move, the other is motor drives chain to move. Following picture shows cylinder drives rack to twitch:

 

Following picture shows motor driving chain twitch:

 

3.Twitching principle of thread mold: tooth distance of braces and braces must be same as that of product, and braces have a guiding effect. Cylinder drives rack 1 to move-rack 1 drives gears 2 and 3 to rotate-gear 3 drives gear 4 to rotate-gear 4 and screw are positioned to rotate together, as shown in the following figure:

 

4. When designing a thread mold, you must know pitch. Definition of pitch is vertical movement distance of screw when it rotates one circle, as shown in following figure:

 

5. Pitch of glue position of product and pitch of screw must be same, otherwise product is easy to drag.

 

6. How to call gears and racks: Hu Bo can call gears and racks externally. According to product layout in our mold, we can determine indexing circle required by our gears, and then gear modules are same. You can call up gear as shown below:

 

7. How to call rack: Rules for using Hu Bo's external rack are also to follow formula (modulus X number of teeth = index circle diameter)
8. If you want to design a thread mold, you must understand relationship between rack and pinion. Following figure shows relationship between rack and pinion, relationship between each gear:

 

9. Calculation of number of exit turns required for product and calculation of length of rack: Number of turns of tooth is 5, so screw exit requires at least 5 turns. Screw retreats 6 turns. Then you can calculate rack twitching distance according to previous page:

 

 

In some consumer products, in order to meet needs of product functions, some buckles and undercuts are often designed on the product. Some products not only have undercuts on outside and inside, but also have some special undercuts and deep reinforcing ribs inside product. Front mold cavity is also very deep. External structure of product is complex and there are many undercuts. How do we design mold structure when encountering such a product? Today I will share with you a set of car cover mold structure, hoping to give you some inspiration.

 

Product glue feeding method:
There are many ways to feed product, including bottoming, diving, direct gating, horn feeding, dispensing, etc. This product has strict appearance requirements and high efficiency requirements. This set of molds uses a large nozzle to directly feed glue, as shown in the figure below.

 

Through slope analysis, it can be seen that there are deep ribs in the front mold of product and an 80mm deep column. In order to prevent product from sticking to front mold, column position of front mold should be designed as a front mold insert. Because front mold ribs are very deep, considering design of ejector structure in the front mold, this product has a round shape, there are undercuts throughout product, some undercut directions are not exactly same, as shown in figure below.

 

Analysis of front mold structure:
Because product has a deep cavity in the front mold, there are deep bone and column positions inside product. Column position is designed as a front mold insert, and deep cavity is designed as a front mold insert. In order to prevent product from sticking to front mold, we use button mechanism to design ejection mechanism on the front mold when mold is opened, as shown in  figure below.

 

Product has five undercuts in rear mold, only one of which is normal ejection position, and other four positions are oblique. Because first position is very long, cylinder core pulling structure design is adopted here, as shown in figure below.

 

Product is in second position of rear mold and fifth position of slider is same. When designing, pay attention: second position is next to first position. Due to limited space, second slider’s bead is only designed with a single-sided guide. Since thickness of A plate is very thick, inclined guide posts of two small inclined sliders are fixed with pressure blocks, as shown in figure below.

 

Third part of product is an oblique slider in back mold. When designing this slider, please pay attention to: slider has a long core-pulling stroke. This slider uses a cylinder core-pulling structure, but there is a long core inside slider, which needs to be inlaid separately, as shown in following figure:

 

Fifth part of product is an oblique slider in rear mold. When designing this slider, please pay attention to: slider has a long core-pulling stroke. This slider uses a cylinder core-pulling structure, but there is a long core inside slider, which needs to be assembled separately. Connection method of oil cylinder, connection of oil cylinder and slider insert are as shown in figure below.