Machine setup is a core step in injection molding production, directly determining product quality, production efficiency, and cost.

Core Objective: Fast, Economical, and High-Quality – To stably produce products that meet quality standards with the fastest molding cycle, lowest raw material and energy consumption, lowest equipment wear and tear.
Scope of Application: Daily machine setup operations for injection molding workshop personnel, trial molding process debugging for new products, and process optimization for re-production of existing products.
Preparation: Preparing before setting up machine directly impacts subsequent setup efficiency. Many people skip this step and start machine immediately, ultimately wasting more time.
Document Preparation: Machine setup "instruction manual" must be complete.
Whether it's a new or old product, five types of documents must be prepared in advance; missing even one can lead to problems.
1. Production Process Data: Historical qualified parameters (temperature, pressure, speed, time, etc.) for existing products are the most direct reference; for new products, initial process suggestions from technical department are required.
2. Standard Product Samples: Clearly define product's appearance, dimensions, and performance standards. This allows for easy comparison during machine setup, avoiding judgment based on intuition.
3. Material Performance Data: Includes key parameters such as raw material's melt temperature range, density, shrinkage rate, and moisture absorption rate. For example, PE's melt temperature is 160-180℃, while PC requires 260-280℃. Incorrect temperature settings can directly lead to raw material decomposition or failure to melt.
4. Product Weight and Structural Drawings: Product weight determines amount of melt. Structural drawings show wall thickness, gate location, and presence of inserts. These are basis for setting injection stroke and holding pressure time.
5. Mold Structure Data: Mold's gate type (point gate/side gate), cooling channel distribution, and presence of slides/ejector pins are clearly stated in mold drawings. For example, for molds with slides, mold opening speed cannot be too fast, otherwise slides will be damaged.
Additional steps for resuming production of old products: Enter historical qualified parameters into injection molding machine control system, simultaneously adjust mold and equipment to initial state corresponding to parameters (e.g., mold temperature controller temperature setting, barrel temperature preheating).

 

After all documents are prepared, equipment, mold, and raw materials must be inspected item by item to ensure everything is ready before starting machine. Otherwise, problems such as raw material decomposition and mold damage may occur:
1. Raw Material Inspection
Confirm that raw material grade matches order. Moisture-absorbing raw materials (such as PA, PC, ABS) must be dried according to requirements—for example, PC should be dried at 120℃ for 4-6 hours. A moisture content exceeding 0.02% will cause silver streaks and bubbles in product. Check for lumps and impurities in raw materials. Lumped raw materials must be crushed before use to avoid clogging hopper.
2. Mold Inspection
Clean cavity, runner, gate of residual material and oil. Wipe with a clean cotton cloth to prevent black spots and scratches on product. Check ejector pins, slides, guide pillars for smooth operation and apply lubricant. Test open and close mold 2-3 times to ensure there is no jamming or abnormal noise. Connect cooling water pipes, open valves to check for leaks and ensure smooth water flow—blockage in cooling water system can lead to uneven cooling, deformation, and shrinkage of product.
3. Equipment Inspection
Clean barrel: If raw material used in previous batch is different from this batch, use a transition material (such as PE) to clean barrel to prevent mixing of different raw materials from affecting product performance.
Preheat barrel: Set barrel temperature according to raw material performance data, and preheat in sections (feed section < melting section < nozzle section). Wait 30 minutes for temperature to stabilize before starting machine—melting before temperature is reached will result in uneven plasticization of raw material.
Check safety devices (emergency stop button, safety door) for proper functioning to ensure production safety.

Machine setup involves two scenarios. Resuming production of old products is simple and quick, while trial production of new products requires a step-by-step exploration. We will explain each step clearly.
(I) Reproduction of Existing Products: Directly "Copy the Work" for Rapid Mass Production
1. Input historically qualified process parameters into injection molding machine control system, including barrel temperature, injection pressure/speed, holding time, cooling time, mold opening and closing speed, etc.
2. Manually produce 3-5 samples after starting machine to check appearance (no missing glue, flash, shrinkage) and whether dimensions meet sample requirements.
3. Send samples for QC inspection. After passing inspection, switch to semi-automatic/fully automatic mode to begin mass production. During production, conduct random checks every 30 minutes to ensure process stability.
(II) New Product Trial Production: From "Basic Parameters" to "Optimal Parameters," Step by Step
Since new products lack historical data, following these 6 steps can save you 90% of trouble:
1. First Step: Set Basic Process Parameters to Get Product "Produced" First
Core of this step is to "take middle value," avoiding extreme parameters at the beginning that could lead to product scrap or mold damage:
Barrel Temperature: Set according to middle value of recommended temperature in raw material instructions. For example, if recommended temperature for PP is 170-200℃, set it to 185℃ initially. Control temperature gradient between different material sections at 20-30℃. Nozzle temperature should be 5-10℃ lower than melt section to prevent drooling.
Molten Stroke & Injection Stroke: Calculate based on product weight—Molten Stroke = (Product Weight + Gate/Runner Weight) ÷ Raw Material Density ÷ Barrel Cross-sectional Area. Injection stroke should be 5-10mm shorter than melt stroke to allow for shrinkage compensation.
Injection Pressure & Speed: Initially set to medium pressure (50-80 MPa) and medium speed (30-60 mm/s). Too low pressure will result in insufficient filler, while too high pressure will cause flash. Too high a speed will cause melt fracture, while too low a speed will cause premature cooling of material.
Holding Pressure Time: Determined by gate type—6-8 seconds for spot gates, 8-10 seconds for side gates/direct gates. Set holding pressure to 60%-80% of injection pressure to avoid damaging mold due to excessive pressure.
Cooling Time: Initially set to 15-20 seconds to ensure complete product solidification and prevent deformation after demolding.
2. Second Step: Manual Test Production, Defect Correction, Start with High-Quality Samples
Switch to manual mode and produce 5-10 samples. Adjust parameters based on common defects until product's appearance and dimensions meet standards:

Adjustment Principle: Make small adjustments, changing only one parameter at a time to avoid changing multiple parameters simultaneously and failing to identify root cause of problem.
3. Third Step: Switch to Semi-Automatic Operation to Optimize Molding Cycle and Achieve Faster Molding
Once product quality meets standards, core objective becomes shortening molding cycle (molding cycle = mold opening/closing time + injection time + melt time + cooling time). A shorter cycle results in higher production efficiency.
Mold Opening/Closing Time Optimization: With a 110g injection molding machine and a two-platen mold, mold opening and closing times should each be controlled to approximately 2 seconds. If mold has a sliding block, sliding block movement time should be set separately, speed should be slowed down to prevent collisions between sliding block and ejector pins.
Injection Time Optimization: Decrease injection time by 0.5 seconds per injection, for example, from 5 seconds to 4.5 seconds, then to 4 seconds, until defects such as insufficient glue or shrinkage occur. Immediately revert to previous acceptable time—this is the shortest injection time.
Melting Time Optimization: While avoiding color mixing and air bubbles, minimize back pressure and accelerate melting speed—too much back pressure results in slow melting and can easily lead to material decomposition; too little back pressure results in uneven material mixing.
Cooling Time Optimization: Decrease cooling time by 1 second per trial run, comparing each run with a standard sample until product just sets without deforming. This time is optimal cooling time—for example, reducing it from 20 seconds to 15 seconds while maintaining product quality saves 5 seconds of cycle time.
After optimization, record all parameters to create a standard process card for new product, facilitating subsequent re-production.

 

Many machine tuners only treat symptoms without understanding underlying principles, leading to difficulties with complex products. Following seven factors are fundamental to determining process parameters:

Plastic shrinks after cooling; if shrinkage rate is not controlled properly, product dimensions will exceed specifications. There are four key factors affecting shrinkage rate:
1. Plastic type is fundamental: Crystalline plastics (PE, PP, POM) have high shrinkage rates (1%-3%), while amorphous plastics (PMMA, PC, ABS) have low shrinkage rates (0.5%-1%). For example, PE products of same thickness will have much larger dimensional deviations after shrinkage than PC products.
2. Part characteristics have a significant impact: Thicker product walls cool more slowly, resulting in a higher shrinkage rate. Addition of metal inserts restricts shrinkage of plastic around inserts, reducing shrinkage rate.
3. Inlet design is crucial: Direct inlets and large-section inlets allow more time for plastic to compensate for shrinkage, resulting in a lower shrinkage rate but stronger directionality (larger shrinkage along material flow direction). Wide and short inlets have weaker directional shrinkage, suitable for products requiring high dimensional uniformity.
4. Adjustable Molding Conditions: Higher mold temperature leads to slower plastic cooling and greater shrinkage; higher holding pressure and longer holding time result in more thorough shrinkage compensation and lower shrinkage. For example, the most direct way to address product shrinkage is to extend holding time.
High-Precision Product Mold Design Techniques: Design with a smaller shrinkage rate for outer diameter and a larger shrinkage rate for inner diameter. After trial molding, adjust mold based on actual shrinkage to avoid large dimensional deviations in a single molding.

Flowability refers to "consistency" of molten plastic. Plastics with good flowability flow easily like water to fill mold, while those with poor flowability flow like honey, requiring greater pressure to fill.
1. Common Plastic Flowability Classified into 3 Categories
Good Flowability: PA, PE, PS, PP – Suitable for thin-walled products (such as disposable lunch boxes), requiring less pressure for molding.
Medium Flowability: ABS, AS, PMMA, POM, PMMA, POM – Suitable for medium-thickness products (such as toy shells).
Poor Flowability: PC, rigid PVC, polysulfone – suitable for thick-walled products (such as appliance housings), requiring increased temperature and pressure during molding.
2. Three Ways to Adjust Flowability
Temperature Adjustment: For plastics like PS, PP, and PA, increasing temperature significantly improves flowability; however, PE and POM are not sensitive to temperature, and effect of increasing temperature is poor, so adjusting pressure is better.
Pressure Adjustment: The higher injection pressure, the greater shear force on plastic, and the better flowability – especially for PE and POM, increasing pressure is more effective than increasing temperature.
Mold Adjustment: Making runner and gate coarser, polishing mold cavity smoothly reduces flow resistance of plastic, which is equivalent to indirectly improving flowability.

When plastics cool, those with orderly molecular arrangement are called crystalline, while those with disordered arrangement are called amorphous. Molding requirements for the two are vastly different:
1. How to Distinguish: Crystalline plastics (PE, PP, POM) are usually opaque or translucent, while amorphous plastics (PMMA, PC) are usually transparent.
2. Key Points for Molding Crystalline Plastics
Requires an injection molding machine with strong plasticizing capacity: Crystalline plastics require more heat to reach their melting point, and smaller machines are prone to uneven plasticizing.
Mold cooling must be sufficient: Crystallization process releases a large amount of heat; insufficient cooling will lead to uneven crystallinity in product, resulting in deformation and cracking.
Mold temperature control is crucial: Higher mold temperature results in higher crystallinity, leading to better product hardness and heat resistance; lower mold temperature results in lower crystallinity, leading to better toughness and higher transparency—for example, when making transparent PP lunch boxes, mold temperature must be lowered to reduce crystallization.

Some plastics (such as rigid PVC and POM) are sensitive to high temperatures and prolonged heating. Excessive temperature or prolonged exposure to heat in barrel will cause discoloration, decomposition, and production of pungent gases; this is heat sensitivity.
1. Prohibitions for Molding Heat-Sensitive Plastics
Temperature must not exceed upper limit: For example, rigid PVC will decompose at temperatures exceeding 180℃, releasing hydrogen chloride, which corrodes mold and equipment.
1. Must-Clean Barrel: After production, barrel must be thoroughly cleaned of heat-sensitive plastic with a transition material such as PE. Otherwise, residual material will decompose upon next startup.
2. Molding Techniques: Use a screw-type injection molding machine to avoid strong shearing force of a plunger-type machine.
Make gate and runner slightly coarser to reduce shear heat generated during plastic flow.
Add stabilizers to raw materials to reduce heat sensitivity.

Plastics like PC, PA, and ABS decompose under high temperature and pressure with even a small amount of moisture, resulting in silver streaks and bubbles in product. This is due to hydrolytic susceptibility.
The only solution is to thoroughly dry plastic before molding and use it as soon as possible after drying to prevent re-absorbing moisture—for example, after drying, PC should be stored in a moisture-proof box; otherwise, it will absorb moisture within half an hour.

1. Stress Cracking: Product has "hidden stress" inside after molding, causing it to crack easily when broken or upon contact with solvents.
Solutions: Thoroughly dry raw material; increase mold temperature and slow down cooling; anneal product after demolding (e.g., bake PA products at 80℃ for 2 hours) to eliminate internal stress.
2. Melt Fracture: Ripples appear on product surface, resembling orange peel, affecting appearance.
Solutions: Enlarge gate and runner; reduce injection speed; increase material temperature to allow for smoother plastic flow.

Different plastics have different heat absorption and dissipation capacities. Cooling rate directly affects cycle time and product deformation:
1. Plastics with high specific heat capacity (e.g., PC): Plasticization requires more heat, necessitating machines with strong plasticizing capabilities; slow cooling rate, thick-walled products require extended cooling time, otherwise deformation will occur.
2. Plastics with low specific heat capacity (such as PE): They plasticize and cool quickly, making them suitable for high-speed mass production.
3. Mold temperature control techniques: Thick-walled products require slow cooling, while thin-walled products can be cooled quickly; mold cooling water channels should be evenly distributed to avoid uneven cooling of product.