Thermoplastic product design principles 1. Dimensions, precision and surface finish roughness <1> Dimensions and dimensions mainly meet the requirements of use and installation. At the same time, the processing and manufacturing of the mold, the performance of the equipment, and the fluidity of the plastic must be considered.
<2> There are many factors affecting precision, such as mold manufacturing precision, plastic composition and process conditions.
<3> The surface roughness is determined by the roughness of the surface of the mold. Therefore, the surface roughness of the mold is lower than that of the product. The surface of the mold should be polished and polished. The surface of the mold must be consistent with the surface finish of the core. < 0.2 um
There is no tolerance requirement on the plastic ring. The size is generally 8 grades in the standard. The tolerance can be marked for the hole size, and the dimensions of the shaft can be marked as negative. The center distance dimension can be brown plus or minus tolerance, and the matching part size is higher than the non-mating part size.
Second, the draft angle is due to the cooling shrinkage phenomenon of the plastic part in the cavity, so that the plastic part tightly embraces the core in the cavity and the protruding part in the cavity, so that the plastic part is difficult to take out, and the forced removal will lead to the plastic The surface of the piece is rubbed and pulled. In order to facilitate the demoulding, the inner and outer surfaces parallel to the direction of the demoulding (and the axis) must be considered in the design of the plastic part. The draft angle is designed to be sufficient, generally 1 - 130 `.
Generally, the core inclination is larger than the cavity, and the core length and the cavity depth are larger, the slope is not reduced.
Third, the wall thickness is determined according to the requirements of plastic parts (strength, stiffness) and the structural characteristics of the product and the requirements of the mold forming process. The wall thickness is too small, the strength and rigidity are insufficient, the plastic filling is difficult, the wall thickness is too large, the cooling time is increased, and the productivity is lowered. , generating bubbles, shrinkage holes, and the like.
It is required that the wall thickness be as uniform as possible, otherwise the internal stress will be generated due to the different cooling and solidification speeds, causing deformation and cracking of the plastic parts.
Fourth, the design principles of reinforced bars:
<1> The intermediate reinforcing ribs are lower than 0.5 mm above the outer wall, making the bearing surface easy to straighten.
<2> Local accumulation of plastics should be avoided or reduced.
<3> The ribs are arranged along the flow direction in the cavity.
5. The plastic part of the supporting surface generally does not use the whole plane as the supporting surface, but instead uses the frame and the bottom foot as the supporting surface.
Sixth, the fillet requires plastic parts to have corners (arc) transitions at the corners, because the sharp corners are easy to stress concentration.
The plastic parts have rounded corners, which are beneficial to the flow filling of plastics and the ejection of plastic parts. The appearance of plastic parts is good, which is beneficial to the strength and life of the mold.
Seven, hole (slot)
Three forming methods for the hole of plastic parts:
(1) The model is molded directly.
(2) Molded into a blind hole and drilled through.
(3) After the plastic parts are formed, drill holes. It is good to mold the shallow holes first.
1. Molded through holes require a smaller aperture ratio (length to aperture ratio). When the hole diameter is <1.5 mm, it is not suitable for molding the molded core because the core is easily bent and broken.
2. Depth of the pupil: h 〈 (3-5)d
d < 1.5, h 〈 3d
3. Shaped holes (grooves) If plastic parts are provided with side holes or grooves, the movable block or core-pulling mechanism "parallel shot principle" is required to determine whether the side holes (grooves) of the plastic parts are suitable for demolding.
The thermoplastic is soft and elastic, such as polyethylene, polypropylene, polyoxymethylene conductive products, and the inner hole and the outer image are forcibly demolded.
8. The thread in the threaded plastic part can be molded, or the cutting method can be usually folded or stressed. It should be formed by metal thread insert.
Nine, inserts In order to increase the strength and rigidity of the plastic product or a certain part, to meet the requirements of use, metal inserts are often placed in the plastic body.
Due to the decoration or some special needs, the surface of the plastic product often has a text pattern.
1, mark 2, embossed: such as handles, knobs, solid edges of handwheel products to increase friction, embossed lines should be made straight, in order to facilitate demolding.
3, pattern: embossed pattern, leather pattern, orange peel pattern, pattern wave pattern, dot grid pattern, diamond pattern.
Processing pattern method: EDM, photochemical abrasion, engraving cold extrusion.
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