Optimizing the molding cycle does not rely on aggressive operation, treating it like a high-speed race. The following are improper practices resulting from extreme speed and their associated risks.
Material shear degradation: Setting the injection speed to the maximum causes severe shear as the material passes through the gate. This leads to molecular chain scission, excessive internal stress in the part, and reduced toughness and impact resistance.
Jet flow formation: The material is injected into the cavity at an extremely high speed. The material that enters first cools down and fuses poorly with the subsequent material, resulting in cold slug marks and high internal stress.
Insufficient back pressure and excessively fast screw retraction: Inadequate venting of the melt in the front section of the barrel allows gas to become entrapped. This leads to unstable injection and charging, causing bubbles and silver streaks in the part.
Adiabatic compression: When the injection speed is too high, the gas inside the cavity has insufficient time to escape. The instantaneous gas temperature can surge to over a thousand degrees Celsius at peak injection pressure, causing localized material degradation and carbonization, and annealing of the mold steel.
Thermal fatigue of mold steel: An extremely short cycle time subjects the cavity surface to high-frequency thermal expansion and contraction. Thermal fatigue develops on the steel surface, producing micro-cracks (heat checking).
High-speed erosion: When fiber-reinforced material passes through the gate at an extremely high velocity, it scours the mold steel like high-velocity abrasive erosion. The gate becomes enlarged, leading to sealing difficulties and flash formation.
Water hammer effect: When the directional valve cuts off a high-speed oil flow within tens of milliseconds, the high-pressure hydraulic oil instantly transforms into a violent dynamic pressure surge (water hammer). This directly damages the valve seals and accelerates fatigue of high-pressure hose fittings.
Oil temperature surge: Frequent high-speed braking and reversing in the hydraulic system converts a large amount of kinetic energy into heat. The temperature rises sharply, oil viscosity decreases, and internal leakage in the pump and proportional valves worsens significantly.
Pump cavitation: When the motor responds with extreme acceleration during oil suction, if the oil viscosity is too high or the suction filter is clogged, a strong negative pressure develops at the pump inlet. Dissolved air comes out of solution, forming bubbles. These bubbles collapse under high pressure at the outlet, releasing shock waves that cause pitting erosion on the pump impeller or piston surfaces.
Tie-bar stress fatigue: During high-speed mold opening and closing, the immense centrifugal and deceleration inertia forces cause uneven loading on the four tie bars. At stress concentration areas such as thread undercuts, very high alternating stresses at high frequency induce microscopic fatigue cracks, eventually leading to fatigue fracture of the tie bar.
Toggle bushing galling: During high-frequency, high-speed mold clamping, the lubricant cannot form a continuous hydrodynamic lubrication film under the extremely high unit-area pressure. Local metal-to-metal dry rubbing occurs between the toggle link steel pins and the brass bushings, causing galling of the bushings and loss of clamping precision.
Machine frame deformation: The rapid braking of the moving platen transmits huge kinetic energy to the machine frame. Over time, microscopic stress relief and plastic deformation occur at the welded joints, deteriorating the parallelism between the stationary and moving platens and causing flash on the parts.
Aggressive ejection: With the ejector cushioning disabled, the ejector plate undergoes a slight displacement under immense acceleration during high-speed ejection. The ejector pins, which have a clearance of only a few micrometers, scrape unilaterally against the hole walls, causing scuffing and accumulation of metal debris. This eventually leads to ejector pin seizure or breakage.
Lifter side galling: During high-speed ejection of angled lifters, the drastic increase in ejection resistance and lateral force component overloads the bottom guide block. The oil film on the guide surface is instantly torn, causing seizure, which leads to bending deformation or fracture of the lifter at its base.
Slide inertial overshoot: With extremely fast mold opening, the slide possesses massive inertia at the moment it disengages from the angle pin. If the locating ball or spring damper cannot respond quickly enough, the slide is prone to rebounding out of position. During the subsequent mold closing, the angle pin collides with the slide, crushing the locking face.
Water line fitting fatigue: Water lines on the slide undergo high-speed, high-frequency, rapid reciprocating motion. The resulting high-frequency, high-amplitude bending stress creates fatigue stress concentrations at the root of the water fittings, eventually causing the fittings to crack and leak.
Electronic scale wear: Intense vibration caused by rapid braking during mold opening and closing acts directly on the potentiometer-type linear scale. The internal brush contact accelerates wear on the carbon-film track under high-frequency vibration, causing severe fluctuations in contact resistance and display jumping. This leads the controller to misjudge the position, resulting in failure of the low-pressure mold protection.
Guide pillar collision: Due to slight sagging of the mold half under its own weight, there is insufficient time for the guiding taper to correct alignment during extremely fast mold closing. This results in hard interference between the precision locating elements and the guide pillars, causing chipping of the locating block edges and galling of the guide pillars.
Servo DC bus overvoltage: The servo motor undergoes braking and reversal within milliseconds. The large inertia forces the motor into generator mode, pushing all the regenerated braking energy back into the drive DC bus. If the braking resistor cannot dissipate the heat adequately or fails to activate in time, the bus voltage spikes instantaneously, causing frequent drive alarms, protective shutdowns, and even component damage.
Screw drive keyway damage: At the instant of transition from high-pressure, ultra-high-speed injection to holding pressure, and the sudden restart of screw rotation, the motor applies an immense impact torque to the screw drive shaft. The keyway at the screw tail and the coupling undergo micro plastic deformation under the repeated torque shocks. The clearance gradually increases, eventually leading to tearing or shearing of the keyway.
