Injection Plastic Molding Product structure design knowledge

1. Thickness (glue)
The thickness of the diy plastic injection moulding product (the overall shell) is usually around 0.80-3.00, too thick and easy to shrink and create bubbles, too thin to get full of glue.
The thickness of a large product is a little thicker, and the smaller one is thinner. The average product is 1.0-2.0.
The glue position should be as uniform as possible. In the case of last resort, the local area may be appropriately thicker or thinner, but it needs to be gradual and not mutated. It should be based on the principle of not shrinking and filling the glue.
Generally, when the plastic part rubber thickness is less than 0.3, it is difficult to take the glue, but the soft rubber and the rubber can also be filled with glue when the thickness is 0.2-0.3.

2. Rib (bone)
Most of the Injection Plastic Molding products have reinforcing ribs. Because the ribs can greatly increase the overall strength without increasing the overall thickness of the product, it is especially useful for large and stressed products, and also prevents product deformation.
The thickness of the rib is usually 0.5-0.7 times the thickness of the whole glue, and if it is more than 0.7 times, it is easy to shrink. When the height of the rib is large, the slope of 0.5-1.5 is required (due to the large die resistance), and the slope is not made when the height is short.

3. Demoulding slope
Custom Plastic Injection Molding products are to be demoulded, but shallower (such as a flat plate) and except for special requirements (but when the side wall is large and there is no drafting, it needs to be done).
The draft angle is usually 1-5 degrees, usually about 2 degrees, depending on the size, height and shape of the product, so that the mold can be smoothly demolded without affecting the function.
The slope of the front mold of the product is usually 0.5 degree larger than the slope of the back mold, so that the product can remain in the back mold when the mold is opened.
Usually, the position of the pillow, the insertion, the piercing, and the like need to be sloped, and the difference between the upper and lower gaps (ie, the difference between the big end size and the small end size) is greater than 0.1 on one side.

4. Rounded corners (R angle)
Plastic Injection Molding Parts products are usually rounded at the edges except for the special requirements to specify sharp edges, in order to reduce stress concentration, facilitate plastic flow and easy demoulding.
The minimum R is usually greater than 0.3, which is difficult to achieve on a R mold that is too small.

5. Hole

From the point of view of Plastic Mold processing, the hole is preferably made into a circular hole with a simple shape. As far as possible, it is not necessary to make a complicated shaped hole. The hole diameter should not be too small, and the hole depth and the hole diameter ratio should not be too large, because it is thin and long. The mold core is easily broken and deformed.

The distance between the hole and the outer edge of the product is preferably greater than 1.5 times the aperture, and the distance between the hole and the hole is preferably greater than 2 times the aperture so that the product has the necessary strength.

The hole parallel to Plastic Molding opening direction is usually formed by a core (can be set, can be extended) or a punch-through, insert-through molding, and the hole which is not parallel to the mold opening direction is usually used for the position or the slanting top. Under the premise of not affecting the use and assembly of the product, the hole of the side wall of the product should be made into a hole that can be pierced and inserted through, if possible.

Injection Plastic Molding diy plastic injection moulding

6. Boss (BOSS)

The bosses are typically used in the form of shaft-hole configurations for two plastic part products, or for the assembly of self-tapping screws. When the BOSS is not very high and it is ejected on the mold by the cylinder, it does not need to be inclined.

When the BOSS is very high, it is usually added with a cross rib (rib) on the outer side. The cross rib usually has a slope of 1-2 degrees, and the BOSS also needs to be inclined.

When the BOSS is matched with the column (or another BOSS), the fitting clearance is usually taken from the assembly gap of 0.05-0.10 on one side, so as to be suitable for the position error generated during the processing of each BOSS.

When BOSS is used for the assembly of self-tapping screws, the inner hole is 0.1-0.2 smaller than the single side of the self-tapping screw so that the screw can be locked. When assembling with M3.0 self-tapping screws, the inner hole of BOSS is usually Ф 2.60-2.80.

7. Insert

When an existing metal piece or plastic part is reshaped in a mold, the existing part is called an insert.

When the plastic product is designed with inserts, it must be considered that the insert must be completely, accurately and reliably positioned in the mold, and the insert must be firmly connected to the molded part. When the rubber is too thin, it is not easy to be firm. Also consider not leaking glue.

8. Product surface

The surface of the plastic product may be a smooth surface (light saving on the surface of the mold), a fire pattern (formed by a copper electrical discharge machining of the mold cavity), an etched surface (a embossed surface) of various patterns, and an engraved surface.

When the depth of the grain is deep and the number is large, the die resistance is large, and the draft angle is correspondingly increased.

9. Text

The surface of the plastic product can be either convex or concave. It is easy to make the corresponding concave cavity on the mold. It is difficult to make the convex shape on the plastic mold.

10. Thread

The thread on the plastic part is usually not very high precision, and a special thread-removing mechanism is required. For the precision requirement, the structure can be simplified into a structure capable of forcibly releasing the injection plastic mold.

11. Support surface

Molds for Plastic Injection products usually do not use the entire surface as a support surface, but instead use bosses, bumps, and ribs to support them. Because plastic products are difficult to achieve the entire larger absolute plane, it is easy to deform and warp.

12. Assembly form of plastic products

(1) Ultrasonic wire bonding assembly method, which is characterized by easy on the mold, but requires a special ultrasonic machine in the assembly process, which increases the cost and cannot be disassembled. The cross section of the ultrasonic line is usually made into a triangle of 0.30 width and 0.3 height, and is interrupted by 2 mm in the length direction by a length of 5-10 MM;

(2) Self-tapping screw assembly method, which is characterized in that it is easy to be done on the mold, but the assembly process is increased, the cost is increased, and the disassembly is troublesome;

(3) The hook-and-buckle assembly method is characterized in that the mold processing is complicated, but the assembly is convenient, and it can be repeatedly disassembled and used repeatedly.

There are various forms of hooks. It is necessary to avoid that the local glue position is too thick at the hook, and it is also convenient to consider the mold at the hook. The hook should be suitable for the tightness of the fit, and the assembly and disassembly are convenient. The mating surface is suitable for the fit, and the other surfaces are appropriately left.

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

13. Tooth

The mating contact surfaces of the two plastic products are usually made with tooth openings. The depth of the tooth gap is usually about 0.8-2.5, and the left side has a gap of about 0.1. When the depth is deep, the slope is 1-5 degrees, often 2 degrees, depth. When it is shallow, it does not have a slope. The upper and lower mating faces of the teeth are usually fitted (ie, 0 gaps).

14. Aesthetic line

The mating surface of the two plastic products usually makes a beautiful line, and the width of the beautiful line is usually 0.2-1.0, depending on the overall size of the product.

15. Surface treatment methods for plastic products: commonly used are fuel injection, silk screen printing, hot stamping, printing, electroplating, engraving, etching, polishing, coloring, etc.

16. Commonly used metal materials

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

17. Common anti-rust methods for metal materials: electroplating, anti-rust oil, anti-rust paint.


Post time: Feb-18-2019