Assembly relationship of plastic parts in the product will provide mold manufacturing with some information about requirements of plastic parts, such as clearance with other plastic parts, and connection method.

Mold engineer assembles 3D model according to connection mode and fit gap of each plastic part; analyzes whether there is interference between plastic parts. Using Pro/E to analyze interference between various plastic parts, steps are as follows:
Analysis ® Model Analysis ® Pairs Clearance (analyze gap or interference between two parts in a combination) ® [Select two parts or surfaces for analysis] ® Compute.
Another way to check interference of entire assembly:
Analysis ® Model Analysis ® Global Interference (analyze interference between parts in entire combination) ® [Select entire combination] ® Compute (get interference information between parts in entire combination).

Assembly gap between various plastic parts should be uniform. General gap (one side) of plastic parts is as follows:

(1). Fit gap between fixed parts is 0～0.1mm, as shown in Figure 3.3.1;

 

(2) Gap between surface and bottom shell is 0.05～0.1mm, as shown in Figure 3.3.2;
(3) Movable gap (unilateral) of regular buttons (diameter Ø£15) is 0.1～0.2mm; movable gap (unilateral) of regular buttons (diameter Ø>15) is 0.15～0.25mm; movable gap of irregular buttons is 0.3～ 0.35mm, as shown in Figure 3.3.3.

 

Analyze column position and buckle position of each plastic part, as shown in Figure 3.3.4 and Figure 3.3.5. Check post and buckle dimensions in assembled 3D model and 2D files of each plastic part, their position dimensions must be consistent. When size of column or buckle of plastic part is changed, size of matching plastic part should also be changed.

 

Since plastic wall at connection between root of column and plastic shell will suddenly thicken, some plastic parts have no instructions for reducing glue. At this time, mold must be added with steel (adding crater) to root of column to avoid sink marks on the surface of plastic part.
Common column size plus crater data are as follows:

 

Note:
1) Average glue thickness of above data is 2.5, as shown in Figure 3.3.6;
2) For screw column smaller than M2.6, there is no crater in principle, but thickness of bottom glue of suspension pin should be 1.2 to 1.4mm;
3) For screw column with crater, in principle, it should be equipped with an arrow foot to improve strength and facilitate flow of plastic.

 

Refers to condition of exposed parts of each plastic part after assembly; text, pattern, texture, shape and safety standard requirements on the surface of plastic part.

For characters and patterns directly molded on plastic parts, if customer does not require them, embossed characters and patterns can be used. When characters and patterns of plastic part are concave, mold is convex, mold production is relatively complicated.
There are usually three methods for making text and patterns on mold:
(1) Print text and patterns (also called chemical corrosion);
(2) Electrode processing mold, engraving electrode or CNC processing electrode;
(3) Engraving or CNC machining molds.
If electrodes are used to process characters and patterns, process requirements for characters and patterns on plastic parts are as follows:
(1) There are convex characters and patterns on plastic parts, height of protrusion should be 0.2～0.4mm, line width should not be less than 0.3mm, and distance between two lines should not be less than 0.4mm, as shown in Figure 3.4.1.

(2) There are concave characters or patterns on plastic parts. Depth of concave is 0.2～0.5mm. Generally, concave depth is 0.3mm; width of line is not less than 0.3mm, and distance between two lines is not less than 0.4mm. As shown in Figure 3.4.2.

 

In production of surface relief of plastic parts, engraving methods are commonly used to process molds. Since plastic 3D file will not have embossed shapes, size of embossed on 2D file is also inaccurate. Shape of embossed is based on the model. Therefore, mold design and manufacturing personnel should understand manufacturing process of engraving mold; production coordination and positioning of engraving mold should be determined in analysis.

Shape of plastic part should meet safety standard requirements of various types of products. There should be no sharp edges or sharp points on plastic parts; for inner and outer surfaces of corners, rounded corners can be added to avoid stress concentration, increase strength of plastic parts, and improve flow of plastic parts, as shown in Figure 3.4.3.
In 3D modeling of plastic parts, if there are wrinkles or small broken surfaces on the surface, determine plan to improve surface; or trim electrode during manufacturing to meet requirements of smooth surface, as shown in Figure 3.4.4.

 

Surface texture requirements of plastic parts are usually smooth or textured; textured surface has two types: sun pattern (also called chemical corrosion pattern) and fire pattern.
When surface of plastic part needs to be sprayed with oil or silk screen, surface of plastic part should be smooth or fine grained surface (Ra<6.3). If grain surface is too thick, it is easy to cause oil spillage. It is better to choose silk-screened surface at protruding or flat part of plastic part; surface after spraying will enlarge surface traces produced during molding.