A new energy vehicle manufacturer experienced batch short-shot issues when producing PP+30%GF thin-walled bumpers (wall thickness 1.8mm, flow ratio 120:1, total length 420mm). Short shots resulted in material shortages at bumper ends (2-5mm short in length), making assembly with the side skirts impossible. Customer had to stop production for 8 hours waiting for materials, resulting in direct losses exceeding 500,000 yuan. Traditional processes, by increasing injection pressure (from 100MPa to 140MPa), only improve situation by 15%, and lead to severe flash (a 300% increase in overflow). A solution needs to be restructured from perspective of coupling machine characteristics with melt flow depth.

 

Essence of short-shot injection is that cavity is not completely filled due to insufficient pressure, flow rate attenuation, or temperature gradients during filling process. However, pressure transmission accuracy, flow rate stability, temperature field uniformity of different brands of electric injection molding machines directly affect "energy supply," "flow resistance," and "filling integrity" of melt front. Today, using this bumper as an example, we will deeply analyze "short-shot genes" of three mainstream electric injection molding machines, moving from "filling gaps" to "flow control," allowing melt front to "completely complete its journey."

1.1 Microscopic Chains Formed by Short-Shot Formation
When PP+GF melt fills mold cavity, leading edge must overcome three resistances:
- Viscous Resistance: Internal friction of melt flowing in runner (PP+GF viscosity 2500 Pa·s @ 230℃). Surface area to volume ratio of runner is 6.8:1, resulting in significant frictional losses;
- Pressure Decrease: Pressure loss of melt from gate to the end of cavity is calculated using formula ΔP = ρgh + ηLv²/d². Actual measurement shows ΔP = 45 MPa (initial pressure 120 MPa → end pressure 75 MPa);
- Temperature Gradient: Viscosity increase due to melt cooling follows an exponential relationship (Arrhenius equation). For every 10℃ decrease in temperature, viscosity increases 2.3 times. As the end temperature drops from 230℃ to 185℃, viscosity increases from 1200 Pa·s to 3500 Pa·s.
Core contradiction arising from short-shot injection: High-precision pressure/flow rate control of electric injection unit conflicts with "flow energy requirements" of thin-walled parts with long flow paths and high-viscosity materials, causing melt front to "exhaust its energy" en route.
1.2 Individualized Performance and Underlying Mechanisms of Short-Shot Injection on Three Electric Injection Units
FANUC ROBOSHOT S-2000i/800 (Electric Injection Molding Machine): "Progressive Material Shortage"
- On-site Observation: Bumper gradually tapers from gate end (A side) to the end (B side), with a 3-5mm material shortage at the end. Wall thickness decreases from 1.8mm to 1.2mm, and surface of material shortage area is smooth without weld lines;
- Machine Characteristics Correlation: Servo motor has high linearity in pressure rise rate (50MPa/s±2%), but melt flow rate decreases with increasing flow rate (from 200mm/s to 80mm/s, a decrease rate of 60%), and end pressure is only 60MPa (filling requirement pressure needs to be >80MPa);
- Material Behavior: PP+GF experiences shear heat generation during long flow (ΔT=15℃, center temperature 245℃→surface temperature 185℃), but dissipates heat quickly (thermal conductivity 0.18W/m·K), increases end crystallinity (from 35% to 55%), and increases shrinkage by 0.8%.
- GF Influence: Glass fibers undergo orientation reorganization during long flow, aligning along flow direction (orientation factor increases from 0.6 to 0.8), increasing flow resistance by 30% and coefficient of friction from 0.08 to 0.12.
Sumitomo DE-1200 (Electric Injection Molding Machine): "Intermittent Flow Interruption"
- On-site phenomena: "Bamboo-like" texture appears on bumper surface, with material flow interruptions occurring every 50mm. Material shortage locations are randomly distributed, with a shortage length of 1-3mm.
- Machine characteristics: Pressure-holding switching valve has a response delay of 0.12 seconds (set switching point at 95% injection speed). During actual switching, melt temperature has already dropped by 4℃, viscosity has increased by 50%, and flow rate has plummeted from 180mm/s to 120mm/s, creating a "flow gap."
- Material behavior: PP+GF has a high elastic recovery rate (6.5%). Sudden changes in flow rate cause melt to "retreat," creating voids. Void rate increases from 0.5% to 3%.
- Thermal management: Mold cooling channel layout is unreasonable, resulting in localized overcooling (surface temperature 15℃). Melt solidifies instantly upon contact, blocking flow path.
Haitian Mars 2000E (Electric Injection Molding Machine): "Overall Underfill"
- On-site phenomena: Bumper is underfilled overall, with a 2-3mm material shortage at the end, but no obvious trace is visible, and shortage area is uniform;
- Machine characteristics: Servo motor speed fluctuates by ±2rpm, melt flow rate is unstable (±8mm/s), filling pressure fluctuates by ±10MPa throughout, and end pressure is insufficient;
- Material behavior: Uneven dispersion of PP+GF glass fiber, with locally enriched areas (length 50-80mm) having higher viscosity (Δη=500Pa·s), increasing flow resistance and forming "flow obstacles";
- GF distribution: Uneven distribution of glass fiber length (1.2-3.5mm), with long fibers (>2.5mm) forming a network structure in flow channel, hindering melt flow.

2.1 FANUC: A Precise but Rigid "Pressure Transmitter"
Core Contradiction: "Supply-demand mismatch" between linear pressure curve and nonlinear decay of melt flow rate.
- Data Insights: Pressure decays with process distance >50% (initial 120MPa → final 55MPa), while filling pressure needs to be maintained >80MPa to overcome high viscosity at the end;
- Process Trap: "Uniform injection" strategy is adopted, with melt flow rate uniformly decreasing from 200mm/s to 80mm/s without considering pressure decay compensation, resulting in insufficient energy at the end;
- Control Logic: FANUC's servo system uses PID control, which has a fast response speed (±0.1 seconds) but lacks "foresight," failing to predict pressure loss in long processes;
- GF Orientation: High orientation increases melt "rigidity," reduces fluidity, and further exacerbates pressure loss.
Short-shot formation mechanism: Rapid pressure decay + monotonous decrease in flow rate → "energy depletion" of melt front → gradual material shortage.
2.2 Sumitomo: A stable but sluggish "switching executor"
Core contradiction: Valve response delay and "rhythm mismatch" of melt pulse flow.
- Data insight: During switching, melt temperature drops by 4℃, viscosity increases by 50%, and flow rate drops sharply from 180mm/s to 120mm/s, forming a "flow gap" lasting 0.3 seconds;
- Control logic: Sumitomo uses a "pressure-speed" dual closed-loop control, but there is a control dead zone at switching point, causing sudden changes in pressure/speed;
- Material behavior: Elastic recovery of PP+GF causes melt "re-moistening," resulting in localized filling interruptions with a retraction distance of approximately 10-15mm;
- Mold design: R-angle at flow channel bend is too small (R=0.5mm), causing melt flow obstruction and exacerbating flow interruption phenomenon.
Short-shot formation mechanism: Switching delay + sudden flow rate changes → melt front "stops and starts" → intermittent flow interruption.
2.3 Haitian: Intelligent but fluctuating "flow regulator"
Core contradiction: "Inherent conflict" between speed fluctuation and overall pressure stability.
- Data insights: Speed fluctuation ±2rpm → flow rate fluctuation ±8mm/s → pressure fluctuation ±10MPa, end-point pressure fluctuation range 45-75MPa, average 65MPa (requirement 80MPa);
- Control logic: Haitian uses "intelligent PID" control, which can adaptively adjust, but its response to high-frequency fluctuations (>1Hz) is insufficient;
- GF dispersion: Unreasonable screw mixing section design, uneven glass fiber dispersion, forming local high-viscosity areas, increasing flow resistance by 25%;
- Thermal stability: High heat dissipation efficiency of electric stage, but local areas cool too quickly, causing premature melt solidification.
Short-shot formation mechanism: Flow rate fluctuation → unstable pressure → insufficient filling throughout process → overall underfill.

 

3.1 FANUC: Building a Dual Engine of "Pressure Compensation - Flow Rate Optimization"
Process Optimization: Dynamic Pressure Gradient Control
- Segmented Injection Strategy:
- Initial Injection (0-3 seconds): Pressure 140MPa, Flow Rate 200mm/s (Rapidly fills front end, establishing initial pressure gradient);
- Intermediate Injection (3-8 seconds): Pressure 120MPa, Flow Rate 150mm/s (Maintains mid-section pressure, compensating for initial attenuation);
- End Injection (8-12 seconds): Pressure 100MPa, Flow Rate 100mm/s (Focuses on compensating for end pressure loss, ensuring complete filling);
- Holding Pressure Stage: Employs a "gradual decrease" holding pressure, reducing from 80MPa to 40MPa at a rate of -1.5MPa/ms to avoid sudden pressure changes;
- GF Orientation Control: Adjusted screw compression ratio (from 2.3:1 to 2.6:1), increased mixing section length (from 3D to 5D), reduced glass fiber breakage (length restored from 1.5mm to 2.5mm), and reduced flow resistance by 15%;
- Mold Heating Optimization: Added an 8mm heating rod (60W power, temperature control accuracy ±1℃) at the end of runner, increasing end temperature from 185℃ to 220℃, reducing viscosity from 3500Pa·s to 1800Pa·s, and lowering flow resistance by 48%;
- Effect Verification: Gradual material shortage disappeared, end wall thickness restored from 1.2mm to 1.7mm, filling integrity improved from 85% to 98%, and flash was controlled within 0.05mm.
Fine-tuning of parameters:
- Optimized flow channel taper (increased from 1° to 2°), reducing pressure loss from 50% to 35% and increasing terminal pressure from 55MPa to 75MPa;
- Adjusted injection speed profile, employing an "S"-shaped acceleration to reduce initial impact, reducing flow rate fluctuation from ±10mm/s to ±3mm/s.
3.2 Sumitomo: Building a "Switching-Flow" Collaborative System
Hardware Upgrade: High-Response Servo Valve + Buffer Control
- Servo Valve Replacement: Original valve assembly with a response time of 0.12 seconds was replaced with a high-precision servo valve with a response time of 0.02 seconds (response frequency increased from 80Hz to 500Hz), reducing switching timing deviation from 0.12 seconds to 0.02 seconds;
- Software Buffer Settings: Deceleration begins 0.5 seconds before switching point, and acceleration gradually increases within 0.3 seconds after switch, avoiding sudden viscosity changes caused by a rapid drop in melt temperature;
- Process Curve Optimization: A "gradual descent" injection curve is adopted, reducing flow rate fluctuation from ±15mm/s to ±3mm/s, eliminating pulsating flow;
- Mold Improvement: Radius (R) at runner bend is increased (from R0.5mm to R1.5mm), reducing flow resistance by 30% and eliminating local stagnation;
- Effect Verification: Intermittent flow interruptions disappear, surface bamboo-like texture is eliminated, dimensional stability is improved, and material shortage rate decreases from 35% to 0.8%.
Control Strategy Upgrade:
- Enable "Predictive Control," which predicts switching points based on historical data and adjusts pressure/speed in advance;
- Add real-time monitoring of melt temperature; automatically adjust injection parameters when temperature deviation > 2℃.
3.3 Haitian: Establishing Intelligent Balance of "Flow Rate-Pressure"
Servo System Deep Calibration + Material Dispersion Optimization
- Precise Rotation Speed Calibration: Servo motor parameters were optimized using FANUC SERVO GUIDE software, reducing rotational speed fluctuation from ±2 rpm to ±0.6 rpm and flow rate stability from ±8 mm/s to ±1.5 mm/s;
- Improved Glass Fiber Dispersion: Screw back pressure was adjusted (from 3 MPa to 5 MPa), and number of kneading blocks in mixing section was increased (from 4 pairs to 6 pairs), improving glass fiber length distribution uniformity by 60% and reducing flow resistance by 25%;
- Mold Temperature Control: Micro-heating elements were installed throughout flow channel (temperature control accuracy ±0.5℃), reducing melt temperature fluctuation from ±6℃ to ±1.5℃, ensuring viscosity stability;
- Process Parameter Optimization: A "fast at the beginning, slow at the end" flow rate strategy was adopted, with a front-end flow rate of 200 mm/s and a back-end flow rate of 100 mm/s, and pressure gradually decreasing from 130 MPa to 70 MPa;
- Performance Verification: Overall underfill decreased from 2-3mm to 0.5mm; CT scans showed an improvement in fill integrity from 92% to 99.2%; and dimensional accuracy improved to ±0.05mm.
Intelligent Monitoring System:
- Establishes real-time monitoring of melt flow status, automatically alarming and adjusting when flow rate fluctuations > ±2mm/s;
- Detects pressure curve anomalies, triggering a compensation mechanism when pressure decay rate > 30%.

4.1 Four-Step Location Method for Short-Shot Diagnosis
Step 1: Morphological Analysis to Determine Type of Short Shot
- Progressive Short Shot: Gradually tapering from gate to the end → Focus on checking pressure decay and flow rate curves; Detection method: Use a coordinate measuring machine to obtain wall thickness distribution and plot a "thickness-distance" curve. A slope > 0.05 mm/mm indicates progressive short shot;
- Intermittent Flow Interruption: Regular bamboo-like patterns on the surface → Focus on checking switching timing and flow rate fluctuations; Detection method: Record melt front with a high-speed camera and observe for periodic interruptions;
- Overall Short Shot: Uniform short shot → Focus on checking flow rate stability and pressure uniformity; *Detection method: Multi-point pressure sensor monitoring; pressure fluctuation > ±5 MPa indicates a target.
Step 2: Data Acquisition and Quantification of Problem Severity
- Pressure Testing: Embed 6 pressure sensors in mold (2 each at gate, middle section, and end) and record pressure curve throughout process; Target: Pressure decay < 30%, end pressure > 80 MPa;
- Temperature Testing: Record melt temperature distribution using an infrared thermal imager and calculate temperature difference; Target: Temperature difference < 5℃, end temperature > 210℃;
- Flow Testing: Observe flow path using a fluorescent tracer and calculate flow velocity distribution; *Target: Flow velocity fluctuation < ±3 mm/s, filling time difference < 0.2 seconds.
Step 3: Machine Characteristic Matching and Root Cause Identification
- FANUC: Check pressure decay rate and GF orientation; Verification: Change screws with different compression ratios and observe changes in pressure decay;
- Sumitomo: Check switching response and flow velocity fluctuation; Verification: Manually control switching timing and observe flow stability;
- Haitian: Check rotational speed stability and glass fiber dispersion; *Verification: Adjust back pressure and observe GF distribution uniformity.
Step 4: Verify closed loop to ensure long-term stability
- Process monitoring: 5 pieces are randomly sampled every hour, and wall thickness is measured using an ultrasonic thickness gauge to monitor filling integrity; Standard: Wall thickness deviation < ±0.1mm, material shortage rate < 0.5%;
- Statistical analysis: After 24 hours of continuous production, a control chart is created to confirm that short-shot rate is consistently < 0.5%; Tool: X-R control chart, with upper and lower limits set at ±0.1mm;
- Parameter solidification: Optimal parameters are written into machine process card, establishing standardized operating instructions.
4.2 Technical Accumulation: "Electric Stage Short-Injection Genetic Archive"
FANUC S-2000i Electric Stage Short-Injection Control Key Points
- Core Cause: Rapid pressure decay + GF orientation leading to increased flow resistance;
- Solution Keywords: Dynamic pressure gradient control, GF protection, end heating;
- Verification Indicators: Fill integrity > 98%, end wall thickness > 1.7mm;
- Preventive Measures: For long-flow products, use segmented injection with pressure decreasing from high to low.
Sumitomo DE-1200 Electric Stage Short-Injection Control Key Points
- Core Cause: Switching delay + sudden flow rate changes causing intermittent flow interruptions;
- Solution Keywords: High-response servo valve, buffer control, mold flow channel optimization;
- Verification Indicators: No bamboo-like surface texture, dimensional fluctuation < ±0.05mm;
- Preventive Measures: Decelerate 0.5 seconds before switching point, accelerate 0.3 seconds after switching.
Key Points for Short-Shot Control on Haitian Mars 2000E Electric Stage
- Core Cause: Speed fluctuations + uneven GF dispersion leading to overall under-filling;
- Solution Keywords: Precise speed calibration, optimized material dispersion, constant temperature throughout;
- Verification Indicators: Fill integrity > 99%, wall thickness uniformity > 95%;
- Preventive Measures: Regularly check servo motor parameters to ensure stable speed.

5.1 Mindset Upgrade: From "Pressure Compensation" to "Flow Control"
Short-shot problem of thin-walled parts cannot be solved simply by "increasing pressure." It is an "energy game" between machine characteristics and melt flow behavior. Learn to replace "experience-based parameter tuning" with "flow field analysis": observe energy loss through pressure sensors, observe flow status using high-speed cameras, and combine this with machine characteristic databases (such as FANUC pressure decay curves and Sumitomo switching response times) to accurately match solutions—this is modern injection molding "flow control" mindset.
Practical Implications:
- Don't blindly increase pressure: Excessive pressure leads to flash, while insufficient pressure at the end is main cause of short shots;
- Pay attention to flow rate profile: A flat flow rate profile ensures more complete filling than a high flow rate;
- Temperature control is key: End-stage heating is more effective than overall temperature increase, and precise control is more energy-efficient than large-scale heating.
5.2 Industry Implications: A New Paradigm for Short-Shot Control
- Material Innovation Direction: Developing low-viscosity PP (1800 Pa·s) + chopped glass fiber (1.2 mm length) to reduce flow resistance at source; Case Study: A material manufacturer developed PP + 20% GF, reducing viscosity by 30% and short-shot rate from 25% to 8%;
- Equipment Collaboration Strategy: Linking electric injection stage with mold temperature controllers and hot runner systems to achieve a real-time closed loop of "temperature-pressure-flow rate"; Case Study: Haitian collaborated with a mold temperature controller manufacturer to develop an intelligent temperature control system, reducing short-shot rate by 60%;
- Process Standardization: Establishing "Electric Injection Stage Thin-Wall Part Short-Shot Control SOP," clearly defining injection curves, pressure gradients, and speed ranges; Value: New employee training time reduced from 2 weeks to 3 days, and process consistency improved by 80%.

 

After cross-motorized injection molding adjustments for this bumper:
- Short-shot defect rate dropped from 35% to 0.4%, customer downtime losses were reduced to zero, and monthly cost savings exceeded 500,000 RMB;
- Production efficiency increased by 40% (no need for post-processing material replenishment), and annual capacity increased by 150,000 pieces;
- Technology output: Compilation of "Short-Shot Control Guide for Thin-Wall Parts of Electric Injection Molding Machines," covering 12+ models, and promoted for application by 5 OEMs.
Essence of short-shot molding is an energy balance battle between machine, material, and flow. When you can accurately identify "short-shot genes" of each motorized injection molding machine and, through coordinated control of pressure, flow rate, and temperature, you can ensure melt front runs "energetically" throughout the entire process—this is not only a victory for technology but also a leap from "passive firefighting" to "proactive prevention" in manufacturing industry.
Next time you adjust short-shot injection of an electric injection molding machine, don't rush to increase pressure—first observe machine characteristics, then control flow rhythm; completeness naturally lies in details.
Key to Success (Short-Filling Issues on Electric Presses, Thin-Walled Parts Version):
Short-filling issues aren't caused by low pressure; machine characteristics are root cause.
Fanuc uses gradient pressure control, heating and temperature compensation reduce resistance.
Sumitomo requires buffering during switching; valve assembly upgrades eliminate fluctuations.
Haitian requires speed calibration; glass fiber dispersion ensures even filling.
Observe form to determine solution; measure data to verify effect.
Remember to verify closed-loop system; ensure complete filling without material shortages!