Bottom case of cleaning robot is shown in Figure 1. Maximum external dimensions of product are 320.44 mm * 239.23 mm * 161.04 mm, average thickness of plastic part is 2.50 mm, plastic part material is ABS, shrinkage rate is 1.005, and plastic part weight is 327.93 grams. Technical requirements for plastic parts are that there shall be no defects such as peaks, underfilling, flow lines, pores, warpage deformation, silver lines, cold materials, and spray lines.

 

Figure 1 Product diagram of bottom shell of cleaning robot
As can be seen from Figure 1, plastic part is a closed shell with an approximate rectangular shape. There are three small functional structures on the edge of shell that need to be designed for slider core pulling. Slider core is designed, and shape of oblique cylinder also needs to be designed for slider core. Top surface of plastic part has local protrusions, 4 bosses and round holes. There are multiple reinforcing ribs on the edge and inside of plastic part.
Size of plastic part is large, mold structure is complex, and shape has multiple slider cores. Mold design cavity ranking is 1 cavity. Mold design ranking diagram is shown in Figure 2. Mold base is a non-standard mold base 6075, and two inclined positioning blocks are designed on the edge of mold base.

 

Figure 2 Mold Design Ranking Diagram

 

Figure 3 Slide block and its parting surface design

 

Figure 4 Cylinder-driven needle valve hot nozzle
In order to improve product quality, shorten injection molding cycle, and save plastic raw materials, a needle valve type hot runner system is used, which has better product quality than an open type hot runner system. On appearance of product, gate is flat and there is no protruding gate trace. Gate with a larger diameter can be used, which can speed up filling of cavity, further reduce injection pressure, and reduce deformation of product; therefore, gating system adopts a needle valve type hot nozzle for single point feeding, and needle valve is driven by a cylinder, as shown in Figure 5. A mold plate is added between fixed die base plate and A plate to install needle valve hot nozzle and cylinder. A Ø30 locating pin is designed between fixed die base plate and hot nozzle fixing plate. This locating pin bears a lot of force and cannot be too thin. The most common control methods of needle valve hot nozzles are air pressure control and hydraulic control. Because air pressure control uses air, it is clean and environmentally friendly, and has obvious advantages. Therefore, needle valve hot runner of cleaning robot bottom shell adopts air pressure control method. .
Due to thickness of cylinder and sufficient space required for movement of piston rod, cylinder block is sunk on the back of A plate, copper sleeve is designed on cylinder head to guide piston rod, lever fixing seat is fixed on the back of A plate, and positioning pin is used to prevent rotation. Rotation center of lever is fixed on lever fixing seat, one end is slotted to hold cup head of valve needle, and the other end is connected to piston rod. Ventilation at the bottom of piston can make piston rod lift up, lever swings, and valve pin is driven to press down, locking gate. After injection molding is completed, top of piston can be ventilated to lift valve needle.
All sliders are rear die sliders, sliders at inclined round holes at corners are sliders driven by oil cylinders, and oil cylinders are Japanese sun iron oil cylinders. The rest of sliders are all sliders driven by inclined guide posts. When designing inclined guide column, if slider is high, inclined guide column must act on lower part of tail of slider, see mold drawing (there is 1 higher slider), and design wear plate on slope of slider, for easy mold fly and adjustment.
Edge of plastic part has a whole ring of seal installation grooves, and there are many bone positions inside, so plastic part has a great tightening force on rear mold. Ejector system of mold is designed with two ejector elements, ejector pin and straight ejector. A travel switch is designed on ejector plate, which is convenient for monitoring timely reset of ejector system.
Cooling water design of mold is relatively sufficient. Both front mold and rear mold are designed with ponds and direct water transportation. A straight-through water transport is designed on slider to effectively ensure normal operation of injection molding.
There are many bone sites on the edge of plastic parts, and inserts are designed in fixed mold to facilitate exhaust of bone sites.

 

Figure 5 Structure of cylinder-driven needle valve hot nozzle