Design essentials of injection mold for front and rear shells of walking robot's right leg

Time：2020-12-01 15:06:28 / Popularity： / Source：

Product diagram of front and rear shells of right leg of walking robot is shown in Figure 1. Maximum size of product is 468.58 mm * 116.13 mm * 62.72 mm, average thickness of plastic part is 3.13 mm, plastic part material is PC, shrinkage rate is 1.006, weight of front and rear shell plastic parts is 291.5 grams and 256 grams respectively. Technical requirements for plastic parts are that there must be no defects such as peaking, underfilling of injection molding, flow lines, pores, warpage deformation, silver streaks, cold materials, jet lines, etc.

Figure 1 Product picture of front and rear shells of walking robot's right leg

It can be seen from Figure 1 that plastic part is shaped as a shell composed of irregular curved surfaces. Front and rear shells are positioned at peripheral stop and fixed with self-tapping screws. Front and rear shells each have a side through hole, which requires design of movable mold slider core. Due to long size of plastic parts, front and rear shells are both irregularly curved, so it is required that front and rear shells must not be deformed, curved surfaces of joints are in good agreement and gap is uniform.

Mold design cavity layout is 1+1. For front and rear shells that need to be assembled together, they are arranged in same set of molds. Due to same molding conditions and shrinkage, it is easy to control consistency of its size; on the other hand, because parting surface is a high and low curved surface, front and rear shells are arranged in same set of molds. It should be noted that mold cores of movable mold and fixed mold need to be designed and processed separately. When designing gating system, make parting surface as smooth as possible at joint of two mold cores, so that glue inlet position of runner is smooth, and molten plastic is easy to fill.
Due to large size of plastic part, mold base is a large straight non-standard mold base 6580, gate is a latent gate, mold is glued at two points at front mold. Size of mold is relatively large, therefore,mold core is fixed by a compression block. Material of plastic part is PC, which has poor fluidity, which makes it difficult to fill mold. When parting surface is processed, a margin of 0.02 is left as a venting groove, which is beneficial for quick filling.
PC material injection molding large-scale plastic parts, due to long plastic process, hot runner molding is often used. When non-hot runner injection molding is used, mold often needs to be heated to maintain mold temperature to avoid heat loss. Therefore, heat insulation boards are designed on mold panel and bottom plate to prevent mold heat from being transmitted to injection molding machine.
Two lateral parting and core-pulling mechanisms are driven by inclined guide posts and slide diagonally.
Ejection of plastic parts adopts ejector tube.

Plastic parts size inspection, in different injection molding factories, there are different inspection methods and standards, generally there is visual inspection, mainly to check appearance of defects and molding defects after injection molding, etc. Dimensional inspection mainly checks its size and geometric tolerances. For influence of assembly function, product sample inspection file of front and rear shells of walking robot's right leg is shown in Figure 3.

Figure 2 Diagram of front and rear shell molds of right leg of walking robot

Figure 3 Inspection report of front and rear shell size of right leg of walking robot

More mold design structure

1. product structure

It can be seen from figure above that main point of this set of mold lies in design of demoulding structure of outer part of three inclined columns. If according to conventional method, no matter which direction core pulling is carried out, there will be interference between slider and slider, what should be done?
We often talk about some more complicated mold structures such as "rotating core pulling" and "sliding core pulling twice", so why can't we do "rotating mold opening" or "slider twice rotation mold opening"? In fact, it is "rotating mold opening", which makes this trigeminal joint!

2. Mold structure

First determine a center of rotation and draw the first set of sliders.
injection molding factorie

Slider rotates to two sides, but before that, inner hole must be pulled out first.
mold design structure

Schematic diagram of a single slider:
mold design structure

Effect after rotating entire column:
mold design structure

When opening mold, group A rotates 35°, then group B rotates 15°. When closing mold, group B first, then group A. the two cannot move at the same time. Specific exercise steps are shown in following dynamic demonstration:

In fact, mold structure is not the only one, let's take a look at another mold release program.
mold design structure

Gud Mould Industry Co., Ltd