Structural design principles of product development:
a. The structural design shall be reasonable: the assembly clearance shall be reasonable, and the clearance shall be reserved for all plug-in structures; sufficient strength and rigidity (safety gauge test) shall be ensured, and the reasonable safety factor shall be properly designed.
b. In the structural design of plastic parts, the manufacturability of mould should be considered comprehensively, and the manufacture of mould should be simplified as much as possible.
c. The structure of plastic parts should consider its plasticity, that is, the injection production efficiency of parts should be high, and the rejection rate of injection molding should be minimized.
d. Consider ease of assembly (especially not conflict with assembly).
e. As far as possible, the structure of plastic parts adopts standard and mature structure, so-called modular design.
f. Can be general / public, try to use existing parts, do not open new mold.
g. Consideration of cost
The general summary of the common problems in the structure points for attention, in the hope of common improvement.
1. About the draft angle of plastic parts:
Generally speaking, for any side of the molding product, there must be a certain amount of demoulding slope, so that the product can smoothly get out of the mold. The angle of demoulding is generally 0.5 to 1 degree. Pay attention to the following points when selecting the demoulding slope:
a. If the surface of the plastic part is smooth, the dimensional accuracy is high and the shrinkage is small, a small demoulding slope, such as 0.5 °, shall be selected.
b. For the higher and larger size, the smaller demoulding slope shall be taken according to the actual calculation, such as the rib plate of the large barrel of the double barrel washing machine, and the calculated value shall be 0.15 ° ~ 0.2 °.
c. If the shrinkage of plastic parts is large, a larger slope value shall be selected.
d. When the wall thickness of the plastic part is thick, the forming shrinkage will increase, and the angle of demoulding should be larger.
e. The demoulding slope of transparent parts shall be increased to avoid scratches. Generally, the demoulding angle of PS material shall not be less than 2.5 ° ~ 3 °, and that of ABS and PC material shall not be less than 1.5 ° ~ 2 °.
f. For the side wall of plastic parts with appearance treatment such as dermatoglyphics and sandblasting, the demoulding slope of 2 ° ~ 5 ° shall be taken according to the specific situation, depending on the specific dermatoglyphic depth. The deeper the dermatoglyphic depth is, the larger the angle of demoulding is.
g. When the structure is designed to be inserted in pairs, the inclination of the insertion surface is generally 1 ° - 3 °.
2. About the determination of the wall thickness of plastic parts and the treatment of the wall thickness:
It is very important to determine the wall thickness of plastic parts reasonably. The wall thickness of the plastic part first depends on the use requirements of the plastic part: including the strength, quality cost, electrical performance, dimensional stability, assembly and other requirements of the part. Generally, the wall thickness has experience value, which can be determined by reference to similar values (for example, the wall thickness of an iron is 2mm, and that of a vacuum cleaner is about 2.5mm). The points for attention are as follows:
a. The wall thickness of the plastic part shall be as uniform as possible to avoid too thin, too thick and sudden change of wall thickness. If the wall thickness of the plastic part must be changed, gradual change or arc transition shall be adopted, otherwise the forming process problems such as deformation of the plastic part due to uneven shrinkage, affecting the strength of the plastic part, and affecting the fluidity during injection molding may be caused;
b. The wall thickness of plastic parts is generally within 1-5mm. The most commonly used value is 2-3mm;
