- Structural design of plastic products
- Glue thickness (glue position) :
The thickness of the glue for plastic products (the overall shell) is usually around 0.80 to 3.00. If it is too thick, it is prone to shrinkage and the formation of bubbles. If it is too thin, it is difficult to fill the glue thoroughly. For large products, a thicker glue should be chosen, while for small products, a thinner one should be taken. Generally, 1.0 to 2.0 is more common for most products. Moreover, the glue application should be as uniform as possible. In cases where it is absolutely necessary, the local areas can be a bit thicker or thinner, but it should gradually increase without sudden changes. The principle should be to avoid shrinkage and ensure full glue application. Generally, when the plastic glue thickness is less than 0.3, it is difficult for the glue to apply, but for soft rubber and rubber, full glue application can be achieved when the glue thickness is between 0.2 and 0.3.
2 Strengthening tendons (bone position) :
Most plastic products have reinforcing ribs. This is because reinforcing ribs can significantly enhance the overall strength of the product without increasing its overall thickness, which is particularly useful for large and stressed products. At the same time, they can also prevent the product from deforming. The thickness of the reinforcing ribs is usually 0.5 to 0.7 times the overall thickness of the rubber. If it exceeds 0.7 times, it is prone to shrinkage. When the height of the reinforcing ribs is relatively large, a slope of 0.5 to 1 should be made (due to the high demolding resistance), while a slope is not necessary when the height is relatively low.
3 Demolding slope
All plastic products need to have a draft Angle, except for those with a relatively shallow height (such as a flat plate) and those with special requirements (but when the side wall is large and there is no draft Angle, a row position needs to be made). The draft Angle is usually 1 to 5 degrees, often around 2 degrees. The specific Angle should be determined based on the size, height and shape of the product, with the principle of smooth demolding and no impact on the usage function. The slope of the front die of the product is usually 0.5 degrees larger than that of the rear die, so that the product can remain in the rear die when the mold is opened. Generally, the pillow position, insertion, collision and other places all need to be beveled, and the upper and lower break difference (i.e., the difference between the large end size and the small end size) on one side should be greater than 0.1.
4 Rounded corners (R corners)
Except for the areas where sharp edges are specified by special requirements, plastic products usually have rounded corners at the edges to reduce stress concentration, facilitate the flow of plastic and make demolding easier. The minimum R is usually greater than 0.3, as it is difficult to achieve such a small R on the mold.
5 Kong
From the perspective of facilitating mold processing, it is best to make the holes into regular and simple round holes. Complex and irregular holes should be avoided as much as possible. The hole diameter should not be too small, and the ratio of hole depth to hole diameter should not be too large, because the thin and long mold core is prone to breakage and deformation. The distance between the holes and the outer edge of the product should preferably be greater than 1.5 times the hole diameter, and the distance between holes should preferably be greater than 2 times the hole diameter, so that the product has the necessary strength.
Holes parallel to the mold opening direction on the mold are usually formed by the core (which can be inlaid or extended) or by bumping through or inserting through. Holes not parallel to the mold opening direction usually need to be made in a row position or at an inclined top. Under the premise of not affecting the use and assembly of the product, holes on the product side wall should also be made as much as possible to be formed by bumping through or inserting through when possible.https://solidcomould.com/product/armrest-8/
6 BOSS
Bosses are typically used for the shaft-hole fit of two plastic products or for the assembly of self-tapping screws. When the BOSS is not very high and is pushed out of the mold with a sprue, it does not need to be used as a slope. When the BOSS is very tall, a cross rib (rib) is usually added to its outside. This cross rib usually needs to be made at a slope of 1-2 degrees, and the BOSS also needs to be made at a slope depending on the situation. When the BOSS fits with the column (or another BOSS), the fit clearance is usually taken as an assembly clearance of 0.05-0.10 on one side to accommodate the positional errors generated during the processing of each BOSS.
When BOSS is used for the assembly of self-tapping screws, its inner hole should be 0.1-0.2 smaller than the single side of the self-tapping screw diameter to ensure that the screw can be tightened. When assembling with M3.0 self-tapping screws, the inner hole of BOSS is usually made with a diameter of 2.60-2.80.
7 Insert
When an existing metal or plastic part is placed in a mold for re-molding, the existing component is called an insert. When plastic products are designed with inserts, it is necessary to consider that the inserts must be completely, accurately and reliably positioned in the mold, and also to ensure that the inserts are firmly connected to the formed part. If the rubber coating is too thin, it will not be easy to be firmly connected. It is also necessary to consider that there should be no glue leakage.
8 Product surface texture:
The surface of plastic products can be smooth (the surface of the mold is polished), fire-patterned (the cavity of the mold is formed by copper electrical discharge machining), etched surfaces (sun-patterned surfaces) with various patterns, and engraved surfaces. When the depth and quantity of the texture are large, the demolding resistance is high, and the demolding slope should be correspondingly increased.
9 Text
The characters on the surface of plastic products can be either raised or recessed. It is easy to make corresponding concave cavities for raised characters on the mold, but it is more difficult to make a raised core for recessed characters on the mold.
10 Thread
The threads on plastic parts usually do not have very high precision and require a special thread removal mechanism. For those with lower precision requirements, their structure can be simplified to a structure that can be forcibly demolded.
11 Support surface
Plastic products usually do not use the entire surface as the support surface, but instead use individual protrusions, points and ribs for support. Because plastic products are difficult to achieve a large absolute plane, they are prone to deformation and warping.
twelve Assembly forms of plastic products:
The ultrasonic line joining assembly method is characterized by being easy to achieve on molds, but it requires specialized ultrasonic machines during the assembly process, which increases costs and cannot be disassembled.
The cross-section of the ultrasonic line is usually made into a triangle with a width of 0.30 and a height of 0.3, and is interrupted by 2MM in the length direction at intervals of 5-10MM.
- Self-tapping screw assembly method, its characteristic is that it is easy to achieve on the mold, but it increases the assembly process, raises the cost and is troublesome to disassemble.
- The hook-latch assembly method is characterized by relatively complex mold processing, but it is convenient to assemble and can be disassembled repeatedly for multiple uses. There are various forms of hooks. It is necessary to avoid the local rubber position at the hook being too thick and also consider the convenience of mold making at the hook. The hook should have a proper fit of tightness, be easy to install and disassemble, and its mating surface should be in close contact, with appropriate gaps left on other surfaces.
- The BOSS shaft-hole assembly method is characterized by convenient mold processing, easy assembly and convenient disassembly. However, its disadvantage is that the assembly is not very firm.
13 Tooth mouth
The contact surface between two plastic products is usually made with a tooth, and the depth of the tooth is typically around 0.8 to 2.5. A gap of about 0.1 is left on the side. When the depth is deep, a slope of 1 to 5 degrees is made, often 2 degrees. When the depth is shallow, no slope is required. The upper and lower mating surfaces of the tooth mouth are usually in fit (i.e., zero clearance).
fourteen Aesthetic line
At the mating surfaces of two plastic products, aesthetic lines are usually made. The width of the aesthetic lines is often taken as 0.2 to 1.0, depending on the overall size of the product.
15 Surface treatment methods for plastic products:
Commonly used methods include oil spraying, silk-screen printing, hot stamping, printing, electroplating, engraving, etching, polishing, and color addition, etc.
16 The commonly used metal materials include:
Stainless steel, copper alloys (brass, bronze, phosphor bronze, red copper), spring steel, springs, aluminum alloys, zinc alloys.
17 Common rust prevention methods for metal materials include electroplating, applying anti-rust oil, and spraying anti-rust paint.
