Understanding Melt and Mold Temperatures In Plastic Injection Moulding Process

Understanding Melt and Mold Temperatures in Plastic Injection Moulding Process 

Contrary to the popular belief that the properties of plastic resins are fixed as published on data sheets, the behavior of each material during the molding operation depends on several process operations and parameters. Many molders are of the opinion that an injection molding process only concerns the heating of the plastic into molten substances and running it till the final article is formed. Because of this, there is a general lack of understanding of important parameters like plastic melt and mold temperatures.

Melt Temperature
Mold and melt temperatures are paramount in determining the performance and characteristics of your end-use part. Melt temperature impacts properties such as the final molecular weight of the object, the viscosity of the molten plastic and impact resistance. This temperature is the actual temperature at which the plastic polymer leaves the nozzle into the mold. When molding, melt temperatures must be continually monitored as temperature fluctuations which may impact the resin characteristics can occur. The actual melt temperature of the injection molding process is subject to factors like the condition of the screw and barrel, the residence time and the amount of mechanical process carried on the raw material.

Mold Temperature 
Molding temperature plays its role in the final properties of the article. For instance, higher mold temperatures can impact the mold-in-stress, impact resistance, ability to handle fatigue and crack resistance. In semi-crystalline resins, the mold temperature will influence the degree of crystallinity achieved by the polymer. Consequently, the mold temperature can also be said to impact the wear, fatigue and creep resistance. Because of its effect on the crystallinity and structure, mold temperature can impact the stability of the object’s size and measurement in high temperature conditions.

Impact of improper melt and mold temperatures on Injection Molding 
In determining the melt temperatures, one must consider the nature of the resin being worked with, the final property desired in the molded article, the design of the screw and barrel and more. The effect of having an improper melt temperature is inconsistent and heterogenous melt temperatures during the process. Improper mold temperature may also cause jetting, warpage and sink marks on the project. 
In order to run an ideal injection molding process and achieve the desired properties in the final molded article, one must understand how melt and mold properties work. 

Generally, the mold temperature is the more important factor when dealing with injection molding. Optimal performance is attainable by using the right combination of low melt temperatures and high mold temperatures. This is because the increase mold temperature and lower melt temperature will control the volume of plastic in the cavity, creating a condensation layer that enhances the flow of the molten material. This causes better part weight, improved surface quality and tensile strength of the molded article.

Running at melt temperatures too high can result in increased injection molding times due to a longer cooling cycle, resin damage and overall energy consumption. Higher mold temperature will result in less flow resistance. However, this faster molten flow can cause higher pressure in the runner and result in some spillage. Due to the inexperience of most molders, most injection molding processes are run vice versa – higher melt temperatures and low molding temperatures. This is because most technicians do not understand how to strike a balance in process operations, using higher melt temperatures as the only means for reducing melt viscosity. 

Having a firm control over the mold temperature can reduce the cost of the injection molding process, improve the quality of the plastic article and prevent non-uniformity in the material shrinkage. As temperature control greatly impacts stress management, degree of crystallization, appearance, formability and physical properties of the product, it is very imperative to monitor the mold and melt parameters in any injection molding process to obtain optimal outcomes.

FirstPart Plastic Injection Molding Service in China 
FirstPart offers high quality injection molding service for all your plastic part projects in China. We also offer low-volume manufacturing that serve small quantities from 50 to 10000 parts and produce for mass production. Our grounded and detail-oriented approach is based on our years of experience in working with plastic injection molding and understanding the effects of production at various mold and melt temperatures. Our engineers are always available to advice on the best processes, materials and design optimization to ensure cost-savings and quick turnaround. Click here to request a free quote now and submit your design for a free evaluation and contact us on how to get started on your next project.