Experienced injection molding technicians know: mold determines foundation, raw material determines properties, and process determines yield rate.
Vast majority of injection molding defects—shrinkage, flash, bubbles, burning, weld lines, warpage, and whitening—are not due to mold defects (over 90%), but rather to improper parameter ratios.
Many beginners adjust their machines by "blindly increasing pressure and temperature," relying on intuition for trial molding. This not only fails to solve problems but also easily introduces new defects, lengthens production cycles, and increases material waste.
Core process parameters of injection molding fall into only five categories: temperature, pressure, speed, time, and position. All machine adjustments are a delicate interplay of these five parameters.
Today, drawing on twenty years of hands-on workshop experience, we'll break down each parameter from scratch, explaining its underlying logic, standard value range, adjustment priority, and corresponding defect solutions. Beginners can get started immediately, while experienced technicians can use it to standardize and solidify processes.
In-depth Analysis of Five Core Parameters in Injection Molding
Quality, efficiency, and stability of injection molding are primarily determined by five core parameters. Properly setting and optimizing these five parameters is key to achieving high-quality injection molding.

Comprehensive Tips: Five parameters influence and restrict each other. It is necessary to conduct comprehensive debugging and optimization in combination with material properties, product structure, mold conditions and equipment performance. Through a cycle of trial molding, analysis, adjustment and verification, optimal process window can be found to achieve stable, efficient and high-quality injection molding production.

Temperature is prerequisite for all parameters. If temperature is incorrect, adjusting pressure and speed will be useless. Core function of temperature is to ensure uniform melting of plastic particles, achieving optimal fluidity, while preventing high-temperature decomposition and low-temperature agglomeration.
Injection molding temperature system is divided into four main sections: barrel segment temperature, nozzle temperature, mold temperature, and drying temperature. These four sections complement each other.
1. Barrel Segment Temperature (The Most Core Plasticization Temperature)
Barrel uses a four-segment gradient heating logic: feeding section → compression section → homogenization section → nozzle front section, strictly adhering to "higher at the front, lower at the back" principle to avoid feeding bridging and poor plasticization in the front section.
Material feeding section (rear section): Lowest temperature, only preheats raw material to prevent particles from melting and sticking to hopper opening, causing feeding failure or bridging blockage;
Compression section (middle section): Critical heating zone, where plastic begins to shear and melt, core of plasticization;
Homogenization section (front section): Highest temperature, ensures uniform melt flow, eliminates localized raw material and particles;
Nose front section: Connects to mold, temperature slightly lower to prevent drooling and cold material from entering cavity.
Standard Temperatures for Commonly Used Raw Materials (General Workshop Reference)
General Plastics: ABS 180-220℃, PP 190-230℃, PE 170-210℃, PS 180-210℃
Engineering Plastics: PC 250-300℃, PA6 220-260℃, PA66 240-280℃, POM 180-210℃, PBT 220-260℃
Machine Adjustment Tips:
For products with poor flowability, thin walls, and long flow paths, appropriately increase initial temperature to improve mold filling flowability.
Heat-sensitive raw materials (POM, PVC, flame-retardant ABS) must not be heated to high temperatures; excessively high temperatures will cause decomposition, yellowing, smoke generation, and product cracking.
Glass fiber materials require moderate heating to ensure uniform fusion between glass fiber and plastic, avoiding fiber floating and surface discoloration.
2 Nozzle Temperature
Optimal nozzle temperature is between temperature of barrel tip and mold temperature, 10-20℃ lower than barrel tip.
Overheating: During machine shutdown or material storage, molten material drips, causing drooling, cold slug spots, and black spots or granules on product surface.
Underheating: Molten material cools and solidifies at nozzle tip, causing blockages, material shortages, and short shots.
3 Mold Temperature (Determines Product Appearance and Internal Stress)
Mold temperature does not directly affect filling speed, but it determines product's gloss, smoothness, internal stress, and demolding effect, making it a key parameter for high-end products.
Low mold temperature (cooled by a chiller): Short molding cycle, high output; disadvantages include rapid melt cooling, leading to weld lines, high internal stress, and later warping. Suitable for ordinary daily necessities and products with no appearance requirements.
High mold temperature (heated by a mold temperature controller): Slow melt cooling, better mold filling and fusion, higher product gloss, less weld lines, dimensional stability, and lower internal stress; disadvantages include a longer cooling cycle and reduced output. Suitable for appearance parts, transparent parts, and precision structural parts.
Practical tip: Increase mold temperature for appearance parts, decrease mold temperature for mass production parts, and maintain a stable mold temperature for precision parts.
4 Raw material drying temperature
A critical temperature that is easily overlooked! When plastic raw materials absorb moisture, water vapor will vaporize at high temperatures, forming bubbles, silver streaks, shrinkage voids.
ABS: Drying at 70-80℃ for 2-4 hours; PC: Drying at 100-120℃ for 4-6 hours; PA/PA66: Drying at 90-110℃ for 3-5 hours; PBT: Drying at 120-140℃ for 3 hours

Pressure is driving force for melt flow. Four core pressures of an injection molding machine are injection pressure, holding pressure, back pressure, and clamping pressure. Each has its own function and must never be mixed or adjusted haphazardly.
1. Injection Pressure (Mold Filling Pressure)
Function: Overcomes resistance of mold runner and cavity, quickly filling mold cavity with melt.
Value Logic: Thin-walled products require high pressure, thick-walled products require low pressure; the larger flow length ratio, the higher pressure requirement.
Standard for regular products: 80-120 bar; Thin-walled, slender, and complex structures: 120-160 bar; Thick-walled, simple, large parts: 60-90 bar
Common Problems and Their Corresponding Causes:
Insufficient pressure: Inadequate mold filling, insufficient material, short shots, incomplete cavity filling;
Insufficient pressure: Excessive melt impact force, instantaneous mold expansion, resulting in flash, burrs, excessive internal stress in product, and demolding deformation.
2. Holding Pressure (Core of Shaping and Shrinkage Compensation)
80% of shrinkage and depression problems are due to improper holding pressure adjustment!
After mold filling, melt begins to cool and shrink, reducing its volume. Core function of holding pressure is to continuously replenish material into cavity, offsetting cooling shrinkage and fixing product dimensions.
Industry-standard values: 30%-70% of injection pressure. For thick-walled products and areas prone to shrinkage: use medium-high holding pressure (50%-70%) to ensure sufficient shrinkage compensation. For thin-walled products and products prone to flash: use low holding pressure (30%-40%) to prevent flash and sticking.
Practical precautions:
Excessive holding pressure: Stress concentration at gate, whitening, cracking, product demolding damage, and longer cycle time.
Insufficient holding pressure: Surface depressions, internal voids, smaller dimensions, and loose assembly.
3. Back pressure (crucial for plasticizing uniformity)
Back pressure is reverse pressure applied when screw retracts during material storage. It's easily overlooked by beginners but has a significant impact on product quality.
Core functions: Expressing melt, expelling air from raw material, eliminating bubbles and voids; Ensuring more thorough shearing of plastic, uniform melting, consistent color, and no patterns; Preventing excessively fast screw storage and uneven mixing.
Standard Values: Ordinary Plastics: 5-15 bar; Color Masterbatch, Transparent Parts, Precision Parts: 15-25 bar; Fiberglass Materials, Flame Retardant Materials: Should not be too high to prevent high-temperature shear burning and fiberglass breakage.
Defect Corresponding Factors:
Insufficient Back Pressure: Uneven plasticization, product color mixing, internal bubbles, surface mottling;
Insufficient Back Pressure: Slower material storage, abnormally high material temperature, raw material decomposition and yellowing, accelerated equipment wear.
4. Clamping Pressure (Clamping Force)
Function: Locks mold, resists cavity tension caused by injection and holding pressure, and prevents mold parting surface from opening.
Value Principle: Calculated based on product's projected area; err on the side of insufficient force, strictly prohibit low clamping force and high-pressure injection.
Insufficient Clamping Force: 100% flash, parting surface burrs, product roughness;
Excessive Clamping Force: Mold deformation under pressure, guide pillar wear, template tearing, shortened mold life.

Temperature and pressure determine foundation, speed adjusts appearance.
Vast majority of weld lines, jetting marks, air bubbles, scorching are related to excessively fast injection speeds and chaotic injection rhythms.
Speed is divided into: injection speed, material storage speed, mold opening and closing speed, and ejection speed. Among these, segmented injection speed is essence of machine tuning.
1 Segmented Injection Speed (Crucial)
Complete mold filling process is divided into four segments, which must follow a "slow-fast-slow-gradual" rhythm. Avoid maintaining high speed or low speed throughout the entire process.
Gate Entry Segment: Low Speed
Avoid high-speed impact of melt on mold wall, which can cause jetting marks, gate halos, and runner defects. Also prevent cold material from entering cavity.
Runner Cavity Main Body Segment: Medium-High Speed
Quickly fill cavity, shortening mold filling time and preventing premature cooling of melt, which can cause cold glue and weld lines.
Cavity End Welding Segment: Medium Speed
Ensure smooth melt fusion and reduce weld line depth.
Final Sealing Segment: Extremely Low Speed
Ventilate and stabilize pressure to prevent trapped air, scorching, flash at the end, and exceeding dimensional limits.
Practical Summary
1. High Speed: Used for long flow lines, thin walls, simple cavities to solve material shortages and cold glue issues.
2. Slow Speed: Used for exterior surfaces, gate locations, and end venting areas to solve air bubbles, jetting patterns, and scorching.
2 Material Storage Speed
Used in conjunction with back pressure; high back pressure with low speed, low back pressure with medium speed.
Too fast storage: Uneven mixing, poor venting, and air bubbles.
Too slow storage: Longer production cycle and reduced capacity.
3 Mold Opening/Closing and Ejection Speed
Unified Principle: Fast in, slow stop.
Mold Opening/Closing: Rapid operation, decelerating near mold closing/opening to prevent mold collisions, vibrations, and misalignment.
Ejection Speed: Low and uniform speed throughout; excessive speed will inevitably result in whitening, cracking, and product deformation.

All parameters require time to take effect. Time parameters are guarantee of stable mass production and mainly include: injection time, holding pressure time, cooling time, and delay time.
1 Injection Time
Match injection speed to ensure complete melt filling of mold.
Injection time too short: High-speed filling easily leads to air entrapment and flash.
Injection time too long: Lengthens production cycle and reduces efficiency.
2 Holding Pressure Time (Critical for Gate Sealing)
End point of holding pressure: Gate is completely cooled and solidified.
Insufficient holding pressure time: Gate is not sealed, melt backflows into cavity, resulting in product shrinkage and smaller dimensions.
Excessive holding pressure time: Stress concentration at gate, whitening and cracking, with no quality improvement, only wasted production capacity.
Simple judgment technique: Gradually increase holding pressure time until product size and weight no longer change; this is optimal holding pressure time.
3 Cooling Time (Highest Cycle Segment)
Cooling time determines production efficiency, accounting for more than 60% of the overall molding cycle.
Core Logic: Ensure product is fully set, without deformation or sticking to mold; avoid excessive cooling.
For thick-walled products and complex parts: extend cooling time to prevent demolding deformation and warping.
For thin-walled, simple parts: shorten cooling time to increase production speed.
Common Misconception: Many operators blindly extend cooling time to stabilize production, resulting in a direct halving of output, which is completely counterproductive.
4 Delay/Dwell Time
In-mold venting delay and injection delay are mainly used to solve problem of air trapped in deep cavities and dead corners, allowing time for air to escape from cavity and preventing burning and material shortage.

Position parameters are "switching thresholds" for all actions, controlling stroke positions of screw, mold plate, and ejector pins to achieve precise switching of segmented actions. This is dividing line between ordinary and refined machine adjustment.
Core Positions: Injection segment position, pressure holding switching position, material storage termination position, mold opening and closing position, ejection stroke.
1. Holding Pressure Switching Position (V/P Switching)
The most critical position parameter!
This refers to position where screw advances to switch from "Injection Pressure/Speed Mode" to "Holding Pressure Mode."
Switching too early: Cavity is not fully filled, leading to premature holding pressure, resulting in insufficient material and shrinkage.
Switching too late: Overfilling, excessive cavity pressure, resulting in flash, mold bulging, and excessive internal stress.
2. Injection Segment Position
Precisely defines speed switching points for gate segment, cavity segment, and end segment, addressing localized appearance defects.
For example: Air bubbles at the end of product; simply slow down at the end position without changing the overall parameters.
3. Material Storage Termination Position
Determines material storage margin for each injection, reserving a reasonable buffer to prevent insufficient injection and inaccurate metering, ensuring consistent product weight and quality across each mold.

1 Set Temperature First, Then Pressure, Next Speed, Finally Lock Time and Position.
New users must not mess up adjustment sequence. Temperature provides foundation for plasticization, pressure ensures full saturation, speed optimizes appearance, time and position stabilize mass production.
2 Defect-First Adjustment Principle
Shrinkage, voids, unstable dimensions → Prioritize adjusting holding pressure, cooling, and mold temperature.
Flash, burrs → Prioritize reducing pressure, speed, and increasing clamping force.
Air bubbles, burnt marks, air bubbles → Prioritize adjusting back pressure, injection speed, venting, and drying.
Obvious weld lines → Prioritize increasing temperature, adjusting injection speed, and increasing mold temperature.
Whitening, deformation → Prioritize adjusting cooling, ejection speed, and reducing internal stress.
3 Fine-Tuning Parameters, No Major Adjustments.
During mass production, drastic parameter changes are strictly prohibited. Adjust 5%-10% each time, observe for 20-30 molds to ensure stability, then solidify changes to avoid batch defects.

Injection molding processes do not have fixed, universal parameters. All high-quality processes are based on optimal combination of mold, raw materials, and product structure.
Truly experienced machine operators don't rely on rigid parameters, but on logic: understanding properties of raw materials, mastering mold venting, and flexibly combining five key parameters—temperature, pressure, speed, time, and position—according to product structure.
Standardized parameters are foundation, fine-tuning is core, and stable solidification is the key to mass production.