In-depth analysis of injection volume of injection molding machine: the trade-off between theory and practice

In the world of injection molding, the injection volume of injection molding machines is an important parameter, which directly determines whether plastic products that meet the needs can be successfully produced.Whether it is a novice in the field of injection molding or an experienced practitioner, it is essential to clearly grasp the theoretical injection volume and actual effective injection volume of the machine.
1. Exploring the theoretical injection volume: the potential value at the beginning of the design
The theoretical injection volume of an injection molding machine is essentially determined by factors such as screw diameter, stroke, and density of plastic materials.Usually, equipment manufacturers will clearly mark this value in the product manual.Taking a common small and medium-sized injection molding machine as an example, if the screw diameter is 40mm and the stroke is 200mm, for general plastics with a density of about 0.95g/cm3, the volume of plastic that the screw can push during the stroke is calculated according to the cylindrical volume formula. Combined with the material density, the theoretical injection volume can be calculated to be approximately 240g.This value represents the maximum amount of plastic that an injection molding machine can emit in a single shot in an ideal state, and it is an important benchmark for measuring the injection molding capacity of the machine.
2. Focus on the actual effective injection volume: the true force in production
However, the actual production environment is complex and changeable, and the actual effective injection volume of the injection molding machine often deviates from the theoretical value.Many factors restrict the actual injection volume, such as the melting characteristics of the plastic, the degree of wear of the screw, and the pressure loss of the injection system.During the melting process, if the plastic fails to reach a uniform state and the fluidity is poor, it will be difficult to be completely squeezed out of the front end of the screw, resulting in a decrease in the actual injection volume.At the same time, the gap between the front end of the screw and the inner wall of the barrel for long-term use will gradually increase due to wear and tear. During injection, part of the plastic will return to the gap, causing material loss, and the actual injection volume will be reduced.Under normal circumstances, the actual effective injection volume may only be 80%-90% of the theoretical injection volume, which means that the above-mentioned machine with a theoretical injection volume of 240g may actually only stably emit 192g-216g of plastic.
3. Adapt to the weight of the product: accurate matching of the injection volume
When producing plastic products at hand, it is critical to accurately judge whether the injection volume of the injection molding machine can meet the weight requirements of the product.Assuming that a plastic container weighing about 150g is to be produced, it seems feasible on the surface for an injection molding machine with a theoretical injection volume of 240g.However, according to best practice recommendations, the actual weight of a mold product should be controlled within 70% of the theoretical injection volume of the machine, that is, within 168g, so as to ensure the stability of the injection molding process and reliable product quality.If the weight of the product exceeds this range, it may cause problems such as insufficient filling and uneven product density, which will affect the appearance and performance of the product; and if the injection volume far exceeds the product demand, it will cause material waste and prolong the production cycle.Therefore, before the start of the project, it is necessary to carefully calculate the adaptability of the injection volume of the injection molding machine in combination with factors such as product weight and mold cavity quantity, and make adjustments to the mold design or injection molding machine selection if necessary.
The precise control of the injection volume of the injection molding machine runs through all aspects of product research and development, mold design, and production and operation.Only by thoroughly understanding the difference between theoretical and actual injection volume, and carefully matching the weight of the product and the injection capacity of the machine, can we efficiently produce high-quality plastic products in the process of injection molding production and maximize the benefits of the enterprise.