Thickness of plastic products (overall shell) is usually about 0.80-3.00. If it is too thick, it will easily shrink and generate air bubbles. If it is too thin, it will be difficult to fill full.
Larger products need to be thicker, smaller products need to be thinner, Generally, 1.0-2.0 is OK.
Adhesive position should be as uniform as possible. In the case of last resort, local area can be appropriately thicker or thinner, but it must be gradually changed and cannot be abruptly changed. It should be based on principle of non-shrinking and full adhesive.
Generally, it is difficult to injection when thickness of plastic is less than 0.3, but soft rubber and rubber can also be filled when thickness is 0.2-0.3.

Most plastic products have reinforcing ribs. Because reinforcing rib can greatly increase their overall strength without increasing overall thickness of product, they are particularly useful for large and stressed products, and they can also prevent product deformation.
Thickness of ribs is usually 0.5-0.7 times overall thickness. If it is greater than 0.7 times, it will easily shrink. When height of stiffener is large, it is necessary to make a slope of 0.5-1.5 (due to high resistance to demould), slope may not be used when height is short.

Plastic products are required to have a draft angle, except for shallow heights (such as a flat plate) and those with special requirements (but when side wall is large and mold slope is not available, row position is required).
Draft angle is usually 1-5 degrees, and it is usually about 2 degrees. It depends on size, height and shape of product. Principle is that mold can be smoothly ejected and function is not affected.
Slope of front mold of product is usually 0.5 degrees larger than slope of back mold, so that product can stay in back mold when mold is opened.
Usually shut-off, insertion, bumping and other places need to do slope, upper and lower gaps (that is difference between big-end size and small-end size) should be greater than 0.1 on one side.

In addition to special requirements for sharp edges, plastic products are usually rounded at edges to reduce stress concentration, facilitate plastic flow and demolding.
Minimum R is usually greater than 0.3, because too small R is difficult to achieve on mold.

From perspective of facilitating mold processing, it is best to make holes with regular and simple shapes, do not make complicated shaped holes as much as possible. Hole diameter should not be too small, hole depth and hole ratio should not be too large, since thin and long mold core is easy to break and deform.
Distance between hole and outer edge of product should be greater than 1.5 times hole diameter, distance between hole and hole should be greater than 2 times hole diameter, so that product has necessary strength.
Holes that are parallel to mold opening direction are usually molded with a core (can be inserted and extended) or punched and inserted. Holes that are not parallel to mold opening direction are usually made into sliders or lifters. On the premise of not affecting use and assembly of product, holes in side wall of product should be made into holes that can be formed through collision and insertion as far as possible.

 

Boss is usually used for shaft-hole fitting of two plastic products or assembly of self-tapping screws. When BOSS is not very high and it is ejected with a tube on mold, it does not need to be inclined.
When BOSS is very high, a cross rib (rib) is usually added on outer side. Cross rib usually has a slope of 1-2 degrees, and boss also has a slope depending on situation.
When BOSS and pillar (or another BOSS) fitting, fitting clearance is usually taken from assembly clearance of 0.05-0.10 on one side in order to fit position error generated during processing of each BOSS.
When BOSS is used for assembly of self-tapping screws, inner hole is 0.1-0.2 smaller than single side of diameter of self-tapping screws, so that screw can be tightened. For example, when using M3.0 self-tapping screws, inner hole of BOSS is usually Ф2.60-2.80.

When an existing metal or plastic parts is placed in a mold for re-molding, existing part is called an insert.
When plastic products are designed with inserts, it is necessary to consider that inserts must be able to be positioned completely, accurately and reliably in mold, also that inserts must be firmly connected to molding part. It is not easy to be secure when plastic is too thin.

Surface of plastic products can be smooth surface (polish on mold surface), fire pattern (cavity of mold cavity formed by copper discharge machining), etched surface (grained surface) of various patterns and carved surface.
When depth of texture surface is deep and number is large, resistance to mold release is large, and demolding slope should be increased accordingly.

Text on the surface of plastic products can be embossed or indented. It is easy to make corresponding concave cavity on mold for convex character, and it is difficult to make convex core on mold.

Precision of threads on plastic parts is usually not very high, and a special unthreading mechanism is required. For those with low accuracy requirements, structure can be simplified into a structure that can be forcibly demoulded.

Plastic products generally do not use entire surface as a support surface, but instead use separate bosses, bumps, and ribs as support. Because plastic products are difficult to achieve entire large absolute plane, they are easily deformed and warped.

(1) Ultrasonic wire bonding assembly method. Its characteristics are easy to do on mold, but a special ultrasonic machine is required in assembly process, cost is increased, and it cannot be disassembled. Cross section of ultrasound line is usually made into a triangle with a width of 0.30 and a height of 0.3, with a length of 5-10MM discontinued by 2MM;
(2) Self-tapping screw assembly method, which is easy to do on mold, but increases assembly process, cost increases, and disassembly is troublesome.
(3) Hook-snap assembly method, which is characterized by more complicated mold processing, but is easy to assemble, can be disassembled and used repeatedly.
There are many forms of hooks. To avoid local adhesive at hooks being too thick, it is also necessary to consider convenience of mold making at hooks. Hook must be properly fit and easy to assemble and disassemble. Mating surface is fitted, and other surfaces are properly spaced.

(4) BOSS shaft-hole assembly method. Its characterized are convenient mold processing, easy assembly and easy disassembly, but its disadvantage is that assembly is not very strong.

 

Mating contact surface of two plastic products is usually a tooth mouth. Depth of tooth mouth is usually about 0.8-2.5, a gap of about 0.1 is left on the side. When depth is deep, slope is 1-5 degrees, and 2 degrees is often taken. Do not make slope when shallow. Upper and lower mating surfaces of tooth mouth are usually fitted (ie, 0 clearance).

Beautiful plastic lines are usually made at mating surfaces of two plastic products. Width of beautiful lines is usually 0.2-1.0, depending on overall size of product.

Spraying, silk screen, bronzing, printing, electroplating, engraving, etching, polishing, adding colors are commonly used.

Stainless steel, copper alloy (brass, bronze, phosphor bronze, red copper), spring steel, spring, aluminum alloy, zinc alloy.

Electroplating, antirust oil, spray antirust paint.