What Is Low Volume Plastic Injection Molding?

      In the world of plastic products, blow molding and injection molding are two major molding technologies, but their relationship is often misunderstood. Some people say that "blow molding is a type of injection molding", but in fact, the two are completely different! They are like a pair of "twin flowers". Although they belong to the field of plastic molding, they have their own advantages in principle, application and cost. This article will take you to explore the mysteries of these two processes in depth to help you find the most suitable solution.

Blow Molding

Core principle: Use compressed air to blow the softened plastic parison to fit the inner wall of the mold to form a hollow product.

Steps: Heat the plastic → Extrude the parison → Close the mold and blow air → Cool and shape → Demold and trim.

Key equipment: Blow molding machine, mold, air compressor.

Typical applications: Hollow products such as plastic bottles, fuel tanks, and medical device containers.

Injection Molding

Core principle: Inject molten plastic into a closed mold at high pressure, and form solid or complex structural parts after cooling.

Steps: molten plastic → high pressure injection → cooling and solidification → demoulding.

Key equipment: injection molding machine, precision mold.

Typical applications: solid or high-precision parts such as mobile phone cases, gears, and auto parts.

Blow molding relies on air molding and is suitable for "hollow"; injection molding relies on high-pressure filling and specializes in "solid".

Injection molds require extremely high precision (such as CNC processing), while blow molding molds are more flexible, but are prone to problems such as flash.

Material selection

Blow molding: commonly used soft plastics (such as HDPE, LDPE, PP), suitable for containers with high flexibility requirements.

Injection molding: compatible with hard plastics (such as ABS, PC, nylon), can add glass fiber to enhance performance.

Design freedom

Blow molding is limited to hollow structures, but can achieve complex curved surfaces (such as bottles with handles).

Injection molding can produce precision parts with details such as threads and bosses, and even multi-color one-piece molding.

Case highlights:

The "star product" of blow molding: carbonated beverage bottles (stretch blow molding technology improves pressure resistance).

The "masterpiece" of injection molding: foldable safety seats (complex structure + high-strength materials).

Initial investment

Blow molding molds are low cost (only one side mold is needed), and the machine price is more affordable.

Injection molds are expensive (precision machining), but suitable for mass production to dilute the cost.

Production cycle

Blow molding is fast for single-piece molding, but post-processing (such as trimming) may increase the time consumption.

Injection molding cycle is stable, and multi-cavity molds can produce dozens of parts at the same time, which is more efficient.

Economic recommendations:

Choose blow molding for small batches of hollow parts (such as customized containers);

Choose injection molding for complex solid parts (such as electronic component housings).

Blow molding technology:

Multi-layer coextrusion: Improve barrier properties (such as anti-oxidation layer of food packaging).

Biodegradable materials: Respond to environmental protection needs, such as PLA blow molding bottles. 

Injection molding technology:

Micro injection molding: Produce millimeter-level precision parts (such as medical catheters).

Smart mold: Integrated sensors monitor pressure and temperature in real time

  Comparison Items

  Blow molding

  Injection molding

  Applicable Products

 Hollow containers (bottles, barrels)

 Solid parts (gears, housings)

  Material Type

 Soft plastics (HDPE, PP)

 Hard plastic (ABS, PC)

  Mold Cost

 Low

 High

  Design complexity

 Medium (limited to hollow structures)

 High (supports fine details)

  Production batch

 Small and medium batches

 Large quantities

     In the field of plastic injection molding, the "tonnage" of an injection molding machine directly determines its capacity limit. Tonnage does not refer to the weight of the entire machine, but the size of its clamping force, measured in tons (T). This parameter represents the maximum closing force that the clamping system of the injection molding machine can exert, which is used to resist the huge expansion pressure generated when the molten plastic is injected into the mold. If the clamping force is insufficient, the mold will be stretched open, resulting in flash burrs; and excessive tonnage will cause energy waste and equipment loss.

The calculation of clamping force follows the core formula:

Clamping force (T) = product projection area (cm²) × mold pressure (kg/cm²) × safety factor / 1000

The mold pressure depends on the material properties:

Ordinary plastics (such as PP, PE): 250-350 kg/cm²

Engineering plastics (such as PC, nylon): 350-500 kg/cm²

The safety factor is usually 1.1-1.2.

Injection molding machines can be divided into four categories according to tonnage, which have significant differences in mechanical structure, application scenarios and technical requirements:

（1）Small machine (30-100 tons)

Structural features: mostly vertical or angular design, mainly fully electric drive, small footprint

Injection volume: usually ≤200 grams (based on PE)

Typical applications:

Electronic connectors (USB interface, SIM card tray)

Precision gears (clocks, micro motor parts)

Medical equipment (syringe needles, test tubes)

Advantages: high precision (repeat error ±0.01mm), energy saving (60% less power than hydraulic presses), no oil pollution

（2）Medium-sized machine (150-500 tons)

Mainstream machine: hydraulic or hydraulic-electric hybrid drive, horizontal structure

Injection volume: 300-2000 grams

Application scenarios:

Household appliance housing (rice cooker, vacuum cleaner housing)

Daily necessities (washbasin, chair, toy)

Automotive interior parts (dashboard frame, door handle)

Technical highlights: Can be equipped with multi-color injection molding system (such as P-type/L-type double shot) to achieve dual-material composite molding

（3）Large machine (600-1000 tons)

Structural features: two-plate clamping mechanism, enhanced rigidity and mold opening space

Injection volume: 2500-5000 grams

Typical products:

Logistics pallet (1200×800mm standard size)

Automobile bumper

Large trash can

Challenge: Need to cooperate with mold temperature control system to prevent shrinkage of thick-walled parts

（4）Ultra-large machine (>1000 tons)

Representative models: Haitian 1600T, Fuqiangxin 1900T three-color machine

Capacity indicators: up to 4000 tons, injection volume exceeds 20kg

Application areas:

Automobile instrument panel (one-piece molding)

Yacht deck parts

Large turnover box (volume>1000L)

Innovative design: horizontal two-color machine (H type) with overlapping mold technology, production capacity increased by 70%

Table: Comparison of injection molding machine tonnage and key parameters

     Injection molding is an important process for manufacturing a variety of plastic parts. Its flexibility enables it to produce a variety of products from thin to thick walls. However, there are certain limitations to the thickness of injection molding, and overly thick plastic parts may face a series of technical challenges during the production process. This article will explore the thickness range of injection molding, factors that affect thickness, possible technical challenges, and how to optimize the molding process.

     Plastic parts molded by injection molding can generally range in thickness from a few millimeters to several centimeters. For most plastic parts, a common thickness range is 1-10 mm. For thick-walled products, the injection molding process can mold greater thicknesses, even up to 30 mm or more, but this usually depends on the type of material used, the mold design, and the capabilities of the injection molding machine.

    In injection molding, the thickness of a part is affected by several factors. First, the fluidity of the plastic material is inversely proportional to its thickness. Thicker parts require the material to have better fluidity so that they can evenly fill the mold. Second, mold design is also crucial. The mold's cooling system, exhaust system, and runner design must all take into account the molding needs of thicker parts. Finally, the injection pressure and injection speed of the injection molding machine also need to be adjusted accordingly to ensure that thick-walled products can be molded smoothly.

     When the thickness of injection molded parts is too large, there are many technical challenges. First, thicker plastic parts require longer injection cycles because the plastic takes longer to fill the mold and cool to solidify. Second, thicker parts are prone to uneven shrinkage during the cooling process, which can cause warping, cracking, or dimensional instability of the parts. In order to ensure the quality of thick-walled injection molded products, the cooling system and mold design need to be optimized to ensure uniform cooling and solidification of the plastic.

     In order to solve the challenges faced by thick-wall injection molding, a series of optimization measures can be taken. First, choose plastic materials with higher fluidity so that they can flow more evenly in thicker wall thicknesses. Secondly, when designing the mold, the cooling system of the mold should be enhanced, and an effective flow channel and exhaust system should be designed to avoid the problem of uneven cooling of thick-walled products. In addition, by increasing the injection pressure and speed of the injection molding machine, combined with a reasonable temperature control system, the injection molding efficiency can be effectively improved and the molding quality of thick-walled parts can be guaranteed.

     Injection molding can handle a variety of plastic parts thicknesses, ranging from thin-walled to thick-walled products. Although thick-wall injection molding faces some technical challenges, these problems can be overcome through optimized material selection, precise mold design, and reasonable injection molding process control. As technology continues to develop, the application range of injection molding will become wider and wider, and manufacturers can produce high-quality plastic parts of various thicknesses to meet the needs of different industries.