FAQ

Principles for Selecting and Applying Injection Molding Machines

1. How to choose the right injection molding machine?

Selecting an injection molding machine requires comprehensive consideration of various factors, including product size and weight, type of plastic material, mold structure and weight, production capacity, cycle time, and finished product precision requirements. For example, if the product size is large or requires higher injection pressure, a model with larger clamping force and injection capacity is needed. If the product has precise structures and demands dimensional stability, an all-electric machine can be considered. Future expandability and automation integration should also be evaluated.

2. What is clamping force? How to determine the required clamping force?

Clamping force is the force that prevents the mold from being forced open when high-pressure molten plastic is injected. If the clamping force is insufficient, defects such as flash may occur. The general estimation formula is: Clamping Force (Ton) = Molded Area × Forming Pressure × Safety Factor. Forming pressure varies depending on the material and product structure, typically between 300–800 kg/cm². A practical rule of thumb is that each cm² of projected mold area requires 3–5 tons of clamping force, with an additional 10–20% safety margin.

3. How to decide between hydraulic and electric injection molding machines?

Hydraulic machines provide high injection pressure and cost competitiveness, suitable for heavy-duty, large products, or applications without extremely high precision. Electric injection molding machines offer energy savings, oil-free operation, low noise, precise control, and high-speed operation. They are ideal for high stability, repeatability, and cleanliness requirements, such as optical, medical, and electronic components. Hybrid machines, combining hydraulic power with servo control, are an option when both precision and injection force are needed.

4. Which products are suitable for multi-color or multi-component injection molding machines?

Multi-color (or multi-component) injection machines can inject two or more materials or colors into the same mold simultaneously. Typical applications include dual-color buttons, two-material toothbrushes, automotive lamp covers, and kitchenware. These machines enhance product design flexibility, reduce assembly processes and labor, and improve efficiency. However, they require highly precise mold design, synchronization, and stable control systems. Choosing a machine with dual injection units and synchronized control capability is recommended.

5. How to select the injection capacity of an injection molding machine?

Injection capacity (shot size) should be evaluated based on the product volume plus the sprue, runner, and cold slug well. Typically, the optimal shot size is 1.3 to 2 times the product weight. If too small, it may cause short shots or machine overload; if too large, the material may remain too long in the barrel, leading to degradation or carbonization. Proper evaluation ensures production stability, reduces defects, and optimizes energy efficiency.

6. What should be considered when purchasing a used injection molding machine?

Before purchasing a used machine, thoroughly inspect its operating condition and component wear, including screw, barrel, clamping unit, electrical control system, and hydraulic parts for signs of wear or aging. A mold trial should be conducted to observe stability. It is also important to verify whether the brand still provides technical service and spare parts; otherwise, long-term maintenance could become problematic. Buying refurbished or manufacturer-certified machines can reduce risks if the budget is limited.

7. How should SMEs choose their first injection molding machine?

For startups, it is recommended to begin with a general hydraulic machine that offers stability, easy maintenance, and versatility. Initially, focusing on a limited number of product molds helps reduce risks. Basic automation (such as robotic arms or automatic loaders) can be introduced gradually. Choosing a brand with local service support ensures uninterrupted maintenance and technical assistance, enhancing operational reliability.

8. Which industries commonly use injection molding technology?

Injection molding is widely applied in industries such as automotive parts, household appliance housings, consumer electronics, medical disposables, food packaging, daily necessities, construction fittings, toys, and tools. Industries with high demands for dimensional consistency, cost control, and mass production particularly benefit from injection molding’s efficiency and stability, making it one of the essential processes in modern manufacturing.

9. What are the differences between servo energy-saving systems and traditional hydraulics?

Traditional hydraulic machines use fixed motors and pumps to maintain constant pressure, resulting in high energy consumption, heat generation, and limited control accuracy. Servo-driven systems use servo motors to drive pumps, supplying oil only as needed. When idle, no energy is consumed, reducing energy use by 30–70% on average. Additionally, servo systems generate less noise and heat, extending oil life and component durability, while allowing precise control of injection speed and position, improving product consistency.

10. Should mold design be considered when purchasing an injection molding machine?

Absolutely. Mold dimensions, weight, opening stroke, ejection stroke, cooling channel design, and mold mounting method must match the machine specifications. If the mold is too large or the opening stroke insufficient, installation or product removal may be problematic. If the ejection system does not align, additional modifications may be required. Ideally, mold and machine design should be coordinated simultaneously, or closely with the machine supplier, to ensure production efficiency and product quality.

Common Injection Molding Problems and Solutions

11. Why does short shot occur (incomplete filling of the cavity)?

A short shot occurs when molten plastic fails to completely fill the cavity, resulting in incomplete parts. Common causes include insufficient injection pressure, low injection speed, low melt temperature, low mold temperature, inadequate mold venting, or excessive moisture in the material. Solutions include increasing injection pressure and speed, raising barrel and mold temperatures, improving mold venting, and ensuring materials are properly dried.

12. How to solve flash (burrs) on molded parts?

Flash occurs when molten plastic leaks out of the mold parting line due to poor sealing. Causes include insufficient clamping force, poor mold fit, mold wear, or excessive injection pressure/speed. Solutions include increasing clamping force, lowering injection pressure/speed, checking mold wear and alignment, and polishing or repairing worn parts.

13. Why do molded products crack or become brittle?

Cracks usually occur on the surface or stress-concentrated areas. Causes include insufficient drying of hygroscopic materials (leading to voids from moisture evaporation), excessive melt temperature, uneven cooling, short holding time, or poor mold design. Solutions include confirming proper drying conditions (e.g., PA/PC requires 80–120°C for 4+ hours), adjusting molding parameters and cooling, and reviewing part and mold design if the issue persists.

14. How to eliminate silver streaks in molded products?

Silver streaks (splay) are caused by moisture or gas not being removed from the resin, appearing as silvery lines. Solutions include thoroughly drying the material, adjusting barrel heating for better gas release, increasing injection speed for faster filling, and ensuring mold vents are well-designed and clean.

15. Why do black spots or impurities appear in molded products?

Black spots are usually caused by carbonized material in the barrel or contaminants in recycled resin. Solutions include regular purging, avoiding excessive melt temperature or long residence times, and using clean, stable raw materials. In severe cases, screws and barrels must be disassembled for cleaning or purged with special cleaning resin.

16. What is a weld line and how to improve it?

A weld line forms when two or more flow fronts meet and fail to fuse properly, leaving a visible line or weak spot. Causes include poor mold venting or improper gate design. Solutions include raising mold and melt temperatures, increasing injection speed/pressure, changing gate location or flow path, and improving vent design.

17. How to deal with gate whitening?

Gate whitening occurs due to rapid cooling or stress during ejection. Solutions include adjusting injection speed and holding pressure, optimizing mold opening and ejection speed, switching to a resin with better flow/lubricity, or redesigning the gate (e.g., using a submarine gate).

18. Why does sticking or mold seizure occur?

Sticking occurs when parts fail to release properly due to insufficient draft angle, rough mold surface, excessive injection pressure, or inadequate cooling. Solutions include increasing draft angle, polishing the mold, optimizing cooling and mold temperature, ensuring proper ejection system function, and applying mold release agents if necessary.

19. How to shorten the injection molding cycle effectively?

Cycle time optimization focuses on filling, packing, cooling, opening, and ejection. Cooling efficiency is critical. Solutions include optimized cooling channel design, high thermal conductivity mold steel, cooling additives, and automation such as robotic part removal. Proper parameter setting ensures stable quality while reducing cycle time.

20. How to determine if defects are caused by the mold or the machine?

If multiple molds show the same defect on one machine, the issue likely lies with the machine (e.g., injection pressure, temperature control, or clamping system). If the defect disappears after changing molds, the problem is mold-related. Systematic analysis and mold trials help quickly identify the root cause and improve troubleshooting efficiency.

Basic and Advanced Knowledge of Injection Molding

21. What is injection molding?

Injection molding is a process in which thermoplastic materials are heated and melted, then injected into a metal mold under high pressure. After cooling and solidification, the molded part is ejected. This technology is suitable for mass production of complex and precise plastic products and is widely applied in automotive, electronics, medical, packaging, and consumer goods industries. Advantages include high efficiency, good repeatability, high material utilization, and strong automation potential.

22. What are common plastic resins used in injection molding?

Common resins include PP (polypropylene), PE (polyethylene), PS (polystyrene), ABS, PC (polycarbonate), PA (nylon), POM, and PMMA (acrylic). Material selection depends on mechanical strength, transparency, heat resistance, toughness, and cost, while also considering drying and processing conditions.

23. What are the main components of an injection molding machine?

An injection molding machine consists of four major systems: 1) Injection unit: hopper, screw, barrel, and heaters for melting and injecting resin. 2) Clamping unit: mold opening/closing, clamping, and ejection. 3) Power system: hydraulic, servo, or electric drive for movement. 4) Control system: HMI and PLC for setting and monitoring temperature, pressure, time, etc.

24. What is cycle time?

Cycle time is the total time required to complete one injection molding cycle, including mold closing, injection, packing, cooling, mold opening, and ejection. Optimizing cycle time improves productivity and reduces costs, depending mainly on cooling efficiency, mold design, automation, and machine responsiveness.

25. Why is drying necessary before injection molding?

Some plastics (such as PA, PC, PET, ABS) are hygroscopic. If not dried properly, moisture causes bubbles, splay, brittleness, or reduced strength. Dryers remove moisture before molding to ensure stable quality. Drying temperature and time must follow material specifications to avoid degradation.

26. What daily maintenance does an injection molding machine require?

Routine maintenance ensures stable operation and longer service life. Tasks include checking oil level and quality, cleaning filters, ensuring cooling water flow, inspecting screw and barrel wear, lubricating moving parts, and calibrating sensors and gauges. Maintenance logs should be recorded for tracking and planning.

27. What is the packing (holding) stage and why is it important?

The packing stage begins after injection, when pressure is maintained to compensate for shrinkage during cooling, ensuring complete cavity filling and product appearance. Holding pressure and time must be set according to part design and resin type. Excessive pressure may cause flash, while insufficient pressure can lead to sink marks or voids.

28. What is the function of the ejection system?

The ejection system removes molded parts from the mold. Common types include hydraulic, mechanical, and pneumatic ejection. Design considerations include ejection force, stroke, and timing, ensuring precise coordination with mold slides and guides. A good ejection design prevents deformation and sticking, improving efficiency and yield.

29. What is a hot runner system and how does it differ from a cold runner?

A hot runner system keeps plastic molten through heated channels, delivering it directly into the cavities without sprues or waste. Compared to cold runners, hot runners reduce material waste, eliminate gate trimming, and shorten cycle time. However, they require higher initial cost and precise temperature control, making them common in multi-cavity, high-volume production.

30. How to avoid defects caused by uneven mold cooling?

Uneven cooling causes warpage, uneven shrinkage, or sink marks. Solutions include designing uniform and dense cooling channels, using high thermal conductivity mold steel (such as BeCu), ensuring stable coolant flow and temperature, and eliminating dead zones. A mold temperature controller may also be used to stabilize mold temperature and improve consistency.

Production and Performance Optimization Guidelines

31. How to control production costs in injection molding?

Production costs can be controlled by improving yield, reducing scrap rate, shortening cycle time, selecting energy-saving machines, and introducing automation and data monitoring. For example, robotic arms and conveyors can reduce labor and errors, while regular maintenance prevents downtime losses. Using stable raw materials also reduces waste from quality issues.

32. How does automation help in injection molding production?

Automation greatly improves efficiency and quality consistency. Common systems include robotic arms, in-mold labeling (IML), automatic stacking and packaging, and automatic material feeding and drying systems. These reduce manual labor, minimize risk, and enhance productivity, leading factories toward smart manufacturing.

33. What is mold life and what factors affect it?

Mold life refers to the number of cycles a mold can produce. It depends on mold steel, maintenance, part design, and molding conditions. High-strength steels (e.g., H13, S136) with surface treatments (nitriding, chrome plating) extend life. Excessive pressure or poor cooling shortens life. Regular maintenance and lubrication are essential to maximize durability.

34. How can MES systems improve injection molding management?

MES (Manufacturing Execution Systems) monitor real-time production data, work orders, and quality information, enabling transparency and digital management. MES can connect to machines to record molding parameters, track production history, and support quality analysis. This is useful for implementing standards like ISO or IATF.

35. What defects are caused by unstable temperature control?

Unstable temperatures can cause dimensional errors, splay, warpage, brittleness, black spots, or visible weld lines. Stable barrel temperatures maintain resin viscosity, while stable mold temperatures improve filling and cooling. Multi-zone temperature control and mold temperature controllers are recommended, along with regular sensor calibration.

36. How to improve product consistency in injection molding?

Consistency depends on stable molding conditions and precise machine control. Solutions include fixing process parameters, ensuring raw material uniformity and proper drying, and maintaining stable melt temperatures. Machines with high repeatability, such as all-electric or servo-driven models, should be used. Mold maintenance is also crucial to avoid contamination or ejector pin issues that affect dimensions.

37. What is a balanced runner system and why is it important?

A balanced runner ensures that molten resin flows evenly into each cavity in multi-cavity molds. If unbalanced, short shots, warpage, or dimensional variations may occur. Moldflow simulations can optimize gate location and runner size, improving consistency and mold life.

38. What are the differences between multi-cavity and single-cavity molds?

Multi-cavity molds produce multiple parts per cycle, increasing productivity and cost efficiency for large-scale production. However, they require precise balance in runners, cooling, and mold temperature. Single-cavity molds are simpler, more flexible for small-batch or varied production, and cheaper to maintain. The choice depends on production scale, costs, and flexibility needs.

39. How to choose the right screw design?

Screw design (L/D ratio, compression ratio, mixing section) affects melting, mixing, and homogenization. Heat-sensitive plastics (e.g., PVC) require low-shear screws, while glass-fiber reinforced resins need wear-resistant screws. Selecting the right screw design ensures stable feeding and product consistency.

40. How to solve warpage deformation in molded parts?

Warpage results from uneven shrinkage, asymmetric cooling, or residual stress. Solutions include adjusting mold temperature and cooling time for uniform cooling, optimizing wall thickness and rib design, increasing packing pressure and time, and checking ejection balance. Mold modifications or moldflow simulations may also be needed for optimization.

Advanced Applications and Trends in Injection Molding

41. What is micro injection molding?

Micro injection molding is a precision molding technology for producing extremely small plastic parts weighing only a few milligrams. It is commonly used in medical devices, MEMS components, and electronic connectors. This process requires ultra-precise machine control, advanced mold-making, and specialized material flow properties, often with high-resolution injection units and precise temperature control.

42. What are the features of LIM (Liquid Injection Molding) for silicone?

LIM is a process where two-part liquid silicone rubber is mixed and directly injected into a mold. It offers high transparency, softness, heat resistance, and biocompatibility, making it suitable for medical devices, baby products, seals, and wearables. It requires dedicated machines, a cold mold/hot runner system, static mixers, and mold release coatings for efficient production.

43. How to implement production traceability and quality tracking?

By connecting sensors and MES systems to injection machines, molding parameters such as pressure, temperature, cycle time, and mold ID can be recorded in real time. These data can be tagged to product batches or serial numbers, enabling traceability. If quality issues arise, manufacturers can quickly trace back production data and use SPC (statistical process control) for analysis and improvement.

44. Can eco-friendly materials be used in injection molding?

Yes. Biodegradable plastics (PLA, PBS), recycled resins (rPET, rPP), and eco-composites are increasingly used. When molding with eco-materials, attention must be paid to thermal stability, drying, and flowability to avoid degradation or short shots. Molds and machine settings may also need adjustments for material differences.

45. What are low-carbon injection molding technologies?

Low-carbon molding strategies include: 1) using servo energy-saving systems and all-electric machines, 2) hot runner molds to reduce waste, 3) shortening cycle time to lower energy use, 4) process monitoring and AI optimization, and 5) using recyclable or bio-based plastics. These measures reduce carbon footprint and support ESG and carbon accounting goals.

46. How can injection molding factories implement ESG management?

ESG practices in molding include: environmental—energy-saving equipment, solar power, recycling, carbon tracking; social—workplace safety, training, supply chain cooperation; governance—transparent decision-making and compliance systems. Certifications such as ISO 14001 and ISO 45001 support sustainable competitiveness.

47. What is high-speed injection molding and what products suit it?

High-speed injection molding involves extremely fast injection and short cycle times, suitable for thin-wall products such as food containers, cups, and disposable packaging. Machines require fast response injection units, strong servo systems, and rigid clamping structures, combined with advanced mold cooling and automation.

48. What is In-Mold Labeling (IML)?

IML inserts pre-printed plastic film into the mold, where it fuses with the molten resin during injection. This enhances product appearance, improves label durability, and reduces secondary processing. IML is widely used in food packaging, cleaning product bottles, and cosmetic containers.

49. How do injection machines integrate with automation systems?

Injection machines can be integrated with robots, conveyors, stacking, packaging, and AGVs via IO or communication protocols (e.g., OPC UA, MODBUS). Effective integration increases automation, reduces human errors, and improves production efficiency and quality.

50. What smart injection solutions does Jon Wai provide?

Jon Wai provides intelligent injection molding machines and integrated solutions, including: energy-saving hybrid and all-electric models, high-speed and multi-color molding machines, smart monitoring and predictive maintenance systems, MES/ERP integration platforms, and customized automation planning to help customers improve productivity, reduce costs, and achieve smart manufacturing.