The basic knowledge of mold is to describe the basic structure of mold, the influence of shape on the product, and the introduction of mold model.
1. The basic composition of the mold
(1) Front mold (female mold) (fixed mold), (2) rear mold (male mold) (moving mold), (3) insert (insert), (4) row position (slider), (5) ) Inclined top, (6) thimble, (7) gate (water inlet)
2. The influence of the shape of the mold product on the product
Wall thickness and geometry will affect the shrinkage of molding and the size of the draft
3. The influence of the water inlet on the shrinkage rate of the product
Larger size of the water inlet means smaller shrinkage, smaller size means larger shrinkage, parallel flow direction means larger shrinkage, vertical direction shrinks
4. The mold wall thickness is too large and the wall thickness is too small
Excessive wall thickness: (1) Increase cost
(2) Extend the forming time and reduce the production efficiency
(3) Quality is difficult to control, bubbles, shrinkage holes, dents, etc. are easy to appear
The wall thickness is too small: (1) The resistance of the plastic flowing in the mold is large. If the shape is more complicated, it will be difficult to form
(2) The strength is poor
If the wall thickness of the plastic part is uneven, it will shrink unevenly after the forming process, not only causing bubbles, depressions, and deformation, but also large internal stress.
Avoid sharp corners at the junction of wall thickness and thin wall, and excessive convergence. The thickness should be gradually reduced along the direction of plastic flow.
5. Fillet (R position)
Set the rounded corners (R position) to increase the strength, so that the plastic parts will not be deformed or cracked
6. Reinforcing ribs
(1) In order to ensure the strength and rigidity of the product without making the wall thickness of the plastic part thick, reinforcing ribs can be set at the appropriate part of the plastic part to prevent deformation. In some cases, it can also improve the flow of plastic during forming.
(2) The thickness of the stiffener should not exceed 50% of the plastic part, usually about 20%
(3) The stiffener should be lower than the plane of the plastic part
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(1) The periphery of the hole is prone to weld marks, which reduces the strength of the plastic part. Note: The distance between the hole and the hole, and the distance between the hole and the plastic part should generally be more than twice the hole
(2) The edge of the hole can be strengthened by the boss
(3) The depth of the blind hole should not exceed 4 times the diameter of the hole
(4) Pay special attention to the strength of the screw hole and the size of the hole diameter. If the hole diameter is too large, it will slip into the screw. If the hole diameter is too small, the screw cannot be inserted or the screw column will burst.
(5) If the hole column is too long (high), pay attention to poor mold exhaust
(6) The depth of the aperture should preferably not exceed 8 times the aperture
(7) For holes with steps, the cores are fixed on both sides of the fixed and movable molds. It is difficult to ensure concentricity, and it is easy to produce burrs at the junction of the two cores. Therefore, either side of the core (aperture ) Increased by 0.5MM or more, formed by the guide at the other end
8. Mould insert, row position, inclined top
Mold inserts, row positions and inclined tops are usually inlaid on the movable mold of the mold. If the fitting is not tight, there will be burrs.