Fri Apr 21 00:09:16 CST 2023
The basic knowledge of moulds is about the basic composition of moulds, the influence of shapes on products, the introduction of mould models and other knowledge content.
1. The basic components of a mould
(1) front mould (female mould) (fixed mould), (2) back mould (male mould) (moving mould), (3) insert (insert), (4) line position (slider), (5) slant top, (6) ejector, (7) gate (water inlet)
2. The influence of the shape of the moulded product on the product
Wall thickness and geometry affect the shrinkage rate of the mould and the size of the release slope.
3. Influence of the inlet on the shrinkage of the produc
If the size of the inlet is large, the shrinkage is small, if it is small, the shrinkage is large, if the material flow is parallel, the shrinkage is large, if it is vertical, the shrinkage is large. Shrinkage in vertical direction
4. The effect of too large wall thickness and too small wall thickness of the mould
Excessive wall thickness: (1) increases cost
(2) Extend the forming time and reduce the production efficiency
(3) Difficult to control quality, prone to bubbles, shrinkage, dents, etc.
Too small wall thickness: (1) High resistance to the flow of plastic in the mould. If the shape is complex, it will be difficult to form.
(2) Poor strength
If the wall thickness of the plastic part is not uniform, then the forming process will shrink unevenly, causing not only bubbles, dents and deformation but also large internal stresses.
Avoid sharp corners at the junction of wall thickness and wall thickness, and avoid excessive ribbing.
5. Rounded corners (R-position)
Rounded corners (R-position) increase strength and prevent deformation or cracking of the moulded part.
(1) In order to ensure the strength and rigidity of the product without making the wall of the part thicker, reinforcement can be placed at appropriate parts of the part to prevent deformation and, in some cases, to improve the flow of the plastic during forming.
(2) The thickness of the reinforcement should not exceed 50% of the part, usually around 20%.
(3) The reinforcement should be lower than the flat surface of the part.
(1) The perimeter of the hole is susceptible to fusion marks, which reduce the strength of the part.
(2) The edge of the hole can be strengthened by a tab.
(3) The depth of the blind hole should not exceed four times the diameter of the hole.
(4) Special attention should be paid to the strength of the screw hole and the size of the hole diameter. If the diameter of the hole is too large, the screw will slip, if the diameter of the hole is too small, it will not be able to enter the screw or burst the screw column.
(5) The hole column is too long (high) should pay attention to the mold exhaust poor
(6) The depth of the hole diameter is best not to exceed 8 times the diameter of the hole
(7) With a step hole, the cores are fixed on both sides of the fixed and moving moulds, it is difficult to ensure concentricity, and in the joint of the two cores is easy to produce burrs, so the core of either side (aperture) should be increased by more than 0.5 MM, guided by the other end of the molding
8. Mould inserts, rows and sloping topsThe inserts, rows and beveled tops of the moulds are usually set in the moving moulds, and if the inserts are not tightly fitted, there will be burrs.