If the mold temperature is set too low during injection molding, the plastic melt cools too quickly as it flows through the mold cavity. This results in uneven shrinkage between the inner and outer layers of the part, generating significant internal stress on the surface and ultimately leading to cracking.

Excessively high injection speed generates high shear stress as the plastic melt flows rapidly into the mold cavity. This stress accumulates within the part and, upon release after demolding, can easily cause cracking.

Excessive holding pressure applied for too long subjects the part to high internal pressure, over-compressing the plastic. After demolding when the pressure disappears, uneven elastic recovery forces within the part can lead to cracking.

Low-quality plastic raw materials, containing impurities or excessive moisture, can compromise the part's integrity. Impurities disrupt the molecular structure, while moisture vaporizes at high temperatures, creating bubbles that weaken the part and make it prone to cracking.

Excessively high screw rotation speed in the injection molding machine subjects the plastic to excessive shear and friction in the barrel. This can break polymer chains, degrade plastic properties, and increase the risk of part cracking.

An undersized gate in the mold creates high resistance for the plastic melt flow, generating significant shear heat and shear stress. This stress is transferred into the part, potentially causing cracks.

Insufficient cooling time means the part's internal temperature is still too high and its strength is low during demolding. The part may deform or crack under the force of ejection.

Insufficient draft angle on the mold creates high friction between the part and mold surface during ejection. This friction generates tensile stress on the part's surface, leading to cracking if it exceeds the material's tensile strength.

High surface roughness of the mold increases friction, which can scratch or mar the part surface during demolding. These surface imperfections become stress concentration points, initiating cracks.

Poor flowability of the plastic material makes it difficult to fill the mold cavity completely, leading to defects like short shots or weld lines. These defects act as stress concentration points, weakening the part and making it prone to cracking.

Non-uniform wall thickness in an injection-molded part causes uneven cooling rates—thicker sections cool slower and shrink more, thinner sections cool faster and shrink less. This differential shrinkage creates internal stress, resulting in cracking.

Insufficient back pressure during plasticizing leads to inconsistent plastication in the barrel. Unmelted pellets within the part reduce its overall strength and make it prone to cracking.

Poor mold venting traps air in the cavity as the melt flows, forming bubbles. These bubbles create internal stress concentration points, compromising part quality and potentially causing cracks.

A nozzle temperature set too low reduces the fluidity of the plastic melt entering the mold, potentially causing cold slugs. These cold slugs affect molding quality and can lead to cracking.

Improper post-processing of the molded part, such as rapid cooling or heating, can induce thermal stress. Cracking occurs when this thermal stress exceeds the material's tolerance.

An improper plastic formulation, including unsuitable types or amounts of additives, can alter plastic properties, reducing its strength and toughness and increasing cracking susceptibility.

Non-uniform temperature distribution in the injection machine barrel (some zones too hot or too cold) leads to inconsistent plasticization, affecting part performance and potentially causing cracks.

Poorly designed ejection mechanisms (improper placement or number of ejector pins) apply uneven force during demolding, creating localized stress concentration that can crack the part.

Physical impact during transport or storage can create surface cracks on the part. Over time, these cracks can propagate, eventually causing failure.

High ambient humidity affects hygroscopic plastics, causing them to absorb moisture. This alters material properties, reduces strength, and can lead to cracking.

Inaccurate screw metering leads to inconsistent shot sizes, resulting in unstable part dimensions and properties, which increases the likelihood of cracking.

Poorly designed mold cooling channels cause uneven cooling rates across the mold. This leads to non-uniform part cooling, generating internal stress and potential cracking.

A plastic material with a high coefficient of thermal expansion undergoes significant dimensional changes with temperature. When this expansion/contraction is constrained, internal stress develops, potentially causing cracking.

Unstable hydraulic system pressure in the injection machine causes fluctuations in injection and holding pressure. This compromises molding quality and increases the chance of cracking.

A poorly designed mold parting line can subject the part to squeezing and deformation during mold clamping, generating internal stress and potential cracking.

Sharp corners, notches, or other stress concentrators in the part's design focus stress when load is applied. Stress at these points can easily exceed the material's strength limit, causing cracking.

Inadequate drying of plastic pellets leaves residual moisture. During molding, this moisture vaporizes, forming bubbles and voids that weaken the part and can cause cracking.

Improper fit between mold inserts and the main body can create gaps or protrusions on the part surface. These become stress concentration points, prone to initiating cracks.

Insufficient injection shot volume fails to fill the mold cavity completely, resulting in a short shot. The unfilled area has low strength and is prone to cracking.

Plastic material aging, from prolonged storage or use, degrades performance through molecular chain scission. This reduces strength and toughness, increasing cracking susceptibility.

Mold heating system malfunctions cause unstable mold temperature, disrupting the molding process, generating internal stress, and potentially causing cracks.

Applying excessive assembly force during part installation can deform the part and create stress concentrations. Cracking occurs if this exceeds the material's capacity.

Non-uniform mixing of plastic raw materials leads to inconsistent properties within the part. Under load, this can cause localized stress concentration and cracking.

Sticky or sluggish movement of mold sliders or lifters creates additional pulling force during demolding, damaging the part and potentially causing cracks.

Severe wear on the injection machine screw tip affects plasticization and injection performance, leading to unstable part quality and increased risk of cracking.

Improper surface treatment of the part, such as overly aggressive sanding or chemical processing, can damage the surface structure, reduce strength, and initiate cracks.

Excessively long cooling time in the mold can over-cool the part, making it brittle. It then becomes prone to cracking during demolding or subsequent handling.

Insufficient plasticizing time prevents complete melting and homogenization of the plastic. Unmelted particles within the part reduce its strength and can cause cracking.

Oil, grease, or debris on the mold surface affects release and part surface quality, creating defects that act as stress concentration points and can initiate cracks.

Low precision in the injection machine's pressure control leads to inaccurate injection and holding pressures. This compromises molding quality and increases cracking risk.

Significant variation in the shrinkage rate of the plastic material causes different areas of the part to shrink inconsistently during cooling. This differential shrinkage generates internal stress, leading to cracking.

Poor gate location causes uneven flow direction and speed of the melt within the cavity. This can create weld lines and internal stress, potentially leading to cracking.

Exposure to certain chemicals during use can react with the plastic, altering its properties, reducing strength, and causing cracking.

Residual old material in the injection machine barrel mixes unevenly with new material, compromising part quality and potentially causing cracking.

Ejector pins with too small a diameter apply high pressure during ejection, which can create marks and stress concentration points on the part surface, initiating cracks.

Excessively high material flowability can cause defects like flash and flow marks during injection. These defects affect appearance and strength, increasing cracking risk.

Excessive clearance between the screw and barrel reduces plastication efficiency. Unmelted plastic within the part lowers its strength and can cause cracking.

Clogged mold cooling lines reduce cooling efficiency, leading to uneven part cooling, internal stress, and potential cracking.

Inadequate structural design strength means the part cannot withstand the stresses encountered during normal use or under expected loads, making it prone to cracking.