I. Part Design Stage: Laying the foundation for success
This is the most crucial step. Good design is half the battle.

Uniform wall thickness

The wall thickness of the parts should be as uniform as possible.

The reason is that uneven wall thickness can lead to different cooling rates, causing shrinkage, depression, internal stress and even warping deformation. It is generally recommended that the wall thickness be between 1.5mm and 4mm, depending on the material and the size of the part.

Countermeasure: If thickness differences must exist, a gradual transition should be adopted to avoid sudden changes.

Demolding slope

Key point: Sufficient draft Angle must be designed on the surface perpendicular to the parting surface.

The reason is to facilitate the smooth ejection of parts from the mold and prevent surface scratches or whitening. Generally, the slope of the outer surface can be slightly smaller (such as 0.5°-1°), while the slope of the inner surface (core) needs to be larger (such as 1°-2°). When the surface etching lines or the structure is complex, the slope needs to be further increased.

The design of reinforcing ribs

Key point: Use reinforcing ribs to enhance rigidity rather than simply increasing the wall thickness.

The golden rule: The thickness of the reinforcing bars should not exceed 50% to 60% of the wall thickness they are attached to, and their height should not exceed three times the wall thickness. The root of the rib must have a rounded corner transition.

Rounded corner transition

Key point: Use rounded corners as much as possible at all corners and edge junctions.

The reason is that sharp corners are stress concentration points and are prone to cracking. Rounded corners can make the molten material flow more smoothly, reduce internal stress, and enhance the strength and service life of the mold.

Holes and screw columns

Holes: Blind holes and sharp corners should be avoided, and the depth of the hole should not exceed four times the diameter of the hole. Reinforcing edges should be added to the edge of the hole.

Screw column: The bottom needs to be reinforced in a crater-like shape and connected to the side wall with ribs to prevent shrinkage and ensure strength.

Consider the mold structure and parting line

When designing, always think about “How will this part come out of the mold?” . The position of the parting line will affect the appearance and subsequent processing. Lateral core-pulling and sliders will increase the complexity and cost of the mold. They should be avoided as much as possible or communicated with the mold supplier.

Ii. Material Selection: Matching Functionality and Cost
Clarify the usage requirements

Mechanical properties: Do you need toughness (such as ABS, PP) or rigidity (such as PS, PC)?

Temperature resistance: What is the maximum temperature of the working environment? For instance, PP can withstand temperatures of approximately 100℃, while PC can reach over 120℃.

Chemical resistance: Will it come into contact with oil, solvents, acids or alkalis?

Electrical performance: Is insulation required?

Appearance and certification: Is transparency, food grade (such as FDA), flame retardant (such as UL94 V-0) required?

Introduction to Common Materials

General-purpose plastics: PP (inexpensive, resistant to bending), ABS (good comprehensive performance, easy to spray), PS (high rigidity, brittle)

Engineering plastics: PC (high strength, transparent, impact-resistant), PA (nylon, wear-resistant, tough), POM (PTFE, high rigidity, low friction)

High-performance plastics: PEEK (high-temperature resistant, high-strength, expensive)

Iii. Mold Design and Manufacturing: The Core of Quality and Efficiency
Runner and gate design

Flow channel: The balanced flow channel ensures that the molten material can reach the end of each cavity simultaneously and evenly. The choice between cold runner (which will produce sprue material) and hot runner (which has no waste but the mold is expensive).

Gate: The location and type of the gate (side gate, point gate, hidden gate, etc.) directly affect the appearance, quality and ease of removal of the product. It should be set up in a thick-fleshed area and be conducive to exhaust and filling.

Cooling system

An efficient and uniform cooling system is the key to enhancing production efficiency and ensuring stable quality.

Reason: Uneven cooling can cause warping and deformation of parts and prolong the molding cycle. The cooling water channels should be as close as possible to the cavity surface and be evenly laid out.

Exhaust system

Key point: Exhaust channels must be set up at the end of the molten material flow and at positions prone to trapped gas.

The reason is that poor exhaust can lead to defects such as burning, material shortage and bubbles. The depth of the exhaust groove is usually 0.02-0.04mm and needs to be set according to the material properties.

“Ejection system”

The selection and layout of ejection methods such as ejector pins, ejector tubes (pipe ejection), and push plates. It is necessary to ensure that the ejection is smooth and powerful, and no obvious marks are left on the appearance surface.

Iv. Injection Molding Process Control: Transforming Design into Reality
Temperature

Barrel temperature: Ensure that the plastic is fully and evenly melted.

Mold temperature: It affects the appearance (gloss), internal stress, warpage and mechanical properties of the product. High mold temperatures usually improve surface quality and material properties, but they will prolong the cycle.

Pressure

Injection pressure: Propels the molten material to fill the cavity.

Holding pressure and time: This is the key to preventing shrinkage. Before the gate solidifies, the reduced material due to cooling shrinkage is replenished into the cavity by holding pressure. Insufficient holding pressure/time leads to shrinkage, while excessive pressure results in burrs and excessive internal stress.

Speed and Time

Injection speed: Affects the filling mode of the molten material and the appearance of the product (such as flow marks, weld lines). High-speed injection can reduce flow marks, but it is prone to jetting. Low-speed injection is beneficial for exhaust, but it may cause lag.

Cooling time: Determined by the thickest wall thickness. Ensure that the part has sufficient rigidity before ejecting.

Cycle time: The sum of all action times, which directly affects production efficiency.