This study addresses frequent issue of uneven filling, flash, or material shortages caused by directly replicating injection speeds across different machines for same product. It breaks down differences in speed control hardware, algorithm logic, external configurations between FANUC, Sumitomo, and Haitian injection machines, establishing a penetrating analysis model of "speed setting → dynamic response → filling effect." This model helps machine engineers master "speed compensation strategies based on equipment characteristics," solving problem of "setting speed but molding process being unstable."

 

Injection speed is "rhythm controller" of injection molding—it determines speed at which melt fills mold, timeliness of pressure transmission, and microstructure of final product. However, due to limitations in servo system precision, control algorithm design, and external configuration, three firing machines exhibit significant differences across the entire speed chain (setting → response → action), resulting in vastly different actual filling effects for same speed setpoint on different machines.
1. Speed Hardware: Inherent Differences Between Servo Systems and Screw Design
- FANUC (ROBOSHOT series): Employs a high-response servo motor (±0.1ms control precision) + a low compression ratio screw (e.g., CR23:1), coupled with real-time encoder feedback (1μm resolution). Its injection speed control precision reaches ±0.5mm/s, accurately tracking complex speed curves (e.g., stepped, exponential acceleration).
- Sumitomo (DE series): Standard configuration includes a medium-response servo valve (±0.5ms level) + a medium compression ratio screw (e.g., CR22:1), with a slightly shallower screw groove depth (compared to FANUC). Its advantage lies in more refined pressure-speed linkage adjustment, but due to a slightly slower servo response, injection speed fluctuations at high speeds (>300mm/s) can reach ±5mm/s.
- Haitian (MA series): Uses a standard asynchronous motor (±10ms response) + high compression ratio screw (e.g., CR24:1), with a relatively large screw diameter (commonly over 45mm). While it has strong load-bearing capacity, injection speed control accuracy is only ±10mm/s, and "creeping" (uneven speed) is prone to occur at low speeds (<100mm/s).
Key conflict: Hardware differences determine "speed-sensitive scenarios" for three machines—Fanuc needs to prevent high-speed fluctuations (e.g., injection speed deviation leading to material shortage when filling thin-walled parts), Sumitomo needs to compensate for high-speed lag (e.g., speed not increasing in time during end-filling), and Haitian needs to maintain low-speed consistency (e.g., speed creep leading to shrinkage when filling thick-walled parts).
2. Control logic: Differences in "precise-linked-coarse" mode of speed adjustment
- Fanuc: Uses "position-speed dual closed-loop" control. During injection phase, system prioritizes tracking position curve and simultaneously corrects injection speed in real time via an encoder (e.g., when injection speed is set to 200mm/s, system dynamically adjusts motor speed to ensure that actual injection speed fluctuation is <±1%). Typical application: When filling thin ribs in mid-frame of mobile phones, it can precisely maintain a uniform speed of 200mm/s, avoiding weld lines caused by speed fluctuations.
- Sumitomo: Based on a "speed-pressure gradient" algorithm. Injection phase proceeds according to preset speed segments (e.g., 3 segments: 100% filling → 80% holding pressure), and pressure dynamically compensates for speed changes (e.g., pressure automatically increases by 10% in high-speed segment). Its advantage lies in avoiding flash or underfill when filling complex structures through speed-pressure linkage. For example, when filling deep cavities, Sumitomo reduces injection speed at the end (from 300mm/s to 150mm/s) and simultaneously increases pressure (from 10MPa to 12MPa), balancing filling and flash risks.
- Haitian: Simplified to a coarse-tuned "speed-time" logic. Injection phase proceeds at a constant speed, with time set empirically (e.g., total injection time 200ms). This logic relies on "speed coverage." For example, if injection speed is set at 250mm/s, actual speed may only be 230mm/s due to slow motor response, requiring extended injection time to compensate for insufficient filling.
Key conflict: For same product's "filling target" (e.g., no flash, no missing material), three injection machines need to achieve this through different logics—Fanuc relies on dual closed-loop precise speed control, Sumitomo relies on speed-pressure linkage speed adjustment, and Haitian relies on time to compensate for speed differences.
3. External configuration: Differences in "speed constraints" between mold and material
- Fanuc: Standard configuration includes high-precision mold positioning rings (tolerance ±0.02mm), ensuring a tight fit between mold and injection machine, resulting in low melt flow resistance (friction coefficient <0.1). Engineers routinely polish mold runners (once every 5000 mold cycles) to reduce impact of flow resistance on injection speed.
- Sumitomo: Slightly large mold interface tolerance (±0.05mm), leading to accumulation of plastic residue on runner surface after long-term production (friction coefficient increases to 0.15), resulting in an actual injection speed 5%~8% lower than set value. Regular runner cleaning (once every 3000 mold runs) is required to maintain low friction.
- Haitian: Poor compatibility of mold temperature controller interfaces (common pressure drop causes actual mold temperature to be 2℃~3℃ lower than set value), resulting in decreased material flowability (e.g., ABS viscosity increases from 150Pa·s to 200Pa·s), requiring an additional increase in injection speed (e.g., from 200mm/s to 220mm/s) to compensate for flow resistance.
Key Conflict: External configurations amplify discrepancy between "set injection speed" and "actual filling speed"—Fanuc needs to prevent mold contamination, Sumitomo needs to combat residue accumulation, and Haitian needs to compensate for increase in material viscosity.

 

Background and Known Conditions
- Product: PC/ABS automotive instrument panel for a certain model (size 400×200×100mm, average wall thickness 3mm, multi-slider + fan-shaped gate injection);
- Material: PC/ABS alloy (melt flow index 18g/10min, recommended injection speed 200~250mm/s);
- Objective: All three injection machines must achieve "no weld lines, no shrinkage cavities, and surface gloss ≥80°".
Case 1: FANUC → Sumitomo: "High-Speed Lag Trap" of Frequent Weld Lines
FANUC Initial Parameters (Stable Production):
- Injection Speed: 220mm/s (3 stages: 100% filling → 80% holding pressure);
- Screw Speed: 80rpm;
- Result: 1200 molds produced continuously, smooth surface without weld lines, gloss ≥82° achieved.
Issues with directly copying to Sumitomo DE-80:
- After producing 600 molds, a noticeable weld line appeared in the center of instrument panel (0.4mm width, gloss reduced to 70°);
- Actual injection rate fluctuated (210~230mm/s, FANUC remained stable within ±1%).
Engineer Analysis and Adjustments:
Sumitomo's servo response was slow (±0.5ms vs. FANUC ±0.1ms). Original 220mm/s setting caused lag in high-speed section (end-fill), leading to melt front cooling and enhanced weld lines. Therefore, end-fill rate was increased from 220mm/s to 240mm/s (to cover lag losses), and Sumitomo's "speed gradient compensation" function was enabled, increasing speed by 5% during end-fill stage (total speed 252mm/s).
Simultaneously, residue accumulation occurred in Sumitomo runner (friction coefficient 0.15), resulting in 10% higher actual flow resistance than FANUC. Therefore, runner was cleaned periodically (reduced to once every 2000 molds), and injection speed setting was corrected to 235 mm/s (to compensate for resistance).
After adjustment, 1200 molds were produced, with weld line width < 0.1 mm and gloss level of 81° meeting the standard.
Case 2: FANUC → Haitian: "Speed Creep and Material Constraint" Trap of Frequent Cavities
FANUC initial parameters (same stable parameters as above).
Problems of directly copying to Haitian MA3000:
- Cavities (0.3 mm~0.4 mm in diameter) appear in thick-walled areas of product (such as at the root of reinforcing ribs);
- Actual injection speed is only 200 mm/s (FANUC is stable at 220 mm/s), and viscosity of PC/ABS increases due to low mold temperature, resulting in incomplete filling.
Engineer Analysis and Adjustments:
Haitian's motor response was slow (±10ms vs. Fanuc ±0.1ms). Original 220mm/s setting resulted in only 200mm/s due to creeping during low-speed phase (initial filling). Therefore, injection speed was increased to 240mm/s (to compensate for creeping losses).
Simultaneously, Haitian's mold temperature was insufficient (actual 55℃ vs. set 60℃), causing an increase in PC/ABS viscosity (from 150Pa·s to 200Pa·s). An additional increase in injection speed (from 240mm/s to 260mm/s) was needed to compensate for flow resistance.
Furthermore, Haitian's "speed-time" logic relied on injection time for shrinkage compensation; original injection time of 250ms was insufficient. Therefore, injection time was extended to 300ms (to ensure full melt filling).
After adjustments, 1200 molds were produced, shrinkage cavities disappeared, and surface gloss of 80° met standard.

 

Core Conclusions
Essence of speed parameter failure across machine tools is:
- Speed characteristics determine sensitive scenarios: Fanuc is susceptible to high-speed fluctuations (±1% affects thin-walled parts), Sumitomo is susceptible to high-speed lag (gradient compensation is required), and Haitian is susceptible to low-speed creep (increasing setpoint and extending time is required);
- Control logic determines adjustment direction: Dual closed-loop control requires precise tracking of speed curve, linkage control requires matching speed-pressure, and coarse-tuning logic requires time compensation for speed differences;
- External configuration amplifies deviations: "Small problems" such as mold contamination, runner residue, and mold temperature/viscosity can directly lead to speed failure.
Core Competency Requirements for Machine Adjustment Engineers:
1. Speed Sensitive Area Identification: Ability to quickly identify speed-sensitive areas of machine (e.g., FANUC's high-speed stability, Sumitomo's high-speed lag, Haitian's low-speed consistency);
2. End-to-End Resistance Calculation: Thoroughly investigate each step from "motor response → screw and groove → flow channel friction → material viscosity," quantifying compensation values (e.g., a 10% increase in flow channel friction results in a 10% increase in injection speed);
3. Proficiency in Verification Tools: Mastery of tools such as high-speed cameras (for observing melt front velocity), screw tachometers (for measuring actual injection speed), and melt flow rate meters (for monitoring material viscosity), enabling three-dimensional verification from "setting to response to filling."