I. Introduction
Ever wonder what technicians mean when they talk of injection molding cycle times? This is simply the time it takes to manufacture one set of plastic parts from the injection stage, the ejection and demolding of the plastic part from the mold.
However, many steps between these phases need to be optimized for process efficiency and to deliver quality parts for every cycle.
Thankfully, as experts in the injection molding industry with decades of experience optimizing injection molding cycle times, we have put this body of knowledge together just for you.
At the end of the few minutes, it will take you to read this, you will understand injection molding cycle times including influencing factors, innovations, common challenges and how to navigate it successfully.
If you are excited to know more then let’s dive right in.
II. Understanding Injection Molding Cycle Times
Injection molding cycle time refers to the time taken to produce a single set of plastic parts starting with closing the mold, through the injection phase to the ejection of the molded plastic. Each phase in this process is of critical importance to the overall quality and efficiency of injection molding. We’ve expanded each phase for a better understanding.
- Injection phase: The injection phase is a combination of precisely orchestrated activities including pouring the plastic pellets into the hopper of the injection machine where it is transported into the heating chambers. Once the pellets have been melted, the injection molding screw fills the mold using optimal pressure to ensure the mold cavity is adequately filled. Here it is important to carefully control the filling speed, temperature, and pressure for a flawless part manufacture.
- Cooling phase: At this stage, the molten plastic has adequately filled the mold cavity and is allowed to solidify in the mold under consistent and controlled temperature reduction. The cooling phase can result in defects such as warpage and sink marks if the temperature reduction is not well-regulated using adequate vents or external cooling mediums like air. However, this temperature control will depend on the material type, part geometry, and intricate details among other factors.
- Ejection phase: Once the part has cooled it is time to eject it from the mold. Ejection often relies on mold features like pins and plates to make the process more efficient. The rise in innovation and technological advances has provided even easier more efficient means like air blast automation using robotics for molded part ejection. It is important to carefully eject parts from the mold to avoid defects caused by part sticking.
- Mold closing phase: reuniting the mold halves is the last phase once the part has been successfully ejected. This allows for adequate positioning for the next cycle. The molds clamping unit helps secure these mold halves in place and features like mold pins help with correct mold alignment to facilitate efficient production and high part quality.
III. Factors Influencing Cycle Times
Several factors are often responsible for maintaining the efficiency of injection molding cycle times and a thorough understanding of these factors will be of immense help to an injection molding professional.
· Material Properties: This is the most critical factor when it comes to cycle times as it is the foundation on which other factors are laid. Hence choosing the right material will significantly help in getting consistently high part quality. Essentially, material properties such as viscosity, melting and cooling temperature are all vital to the cycle time. These properties determine the length of each cycle. For instance, high viscous material indicates a high melting point and longer cooling time which all add up to longer cycle times. Ultimately, these properties define the efficiency and part quality for each cycle.
· Part Design: Simpler part geometry makes for faster cooling time and hence, faster cycle time. More complex part designs often have more intricate details and require more injection molding requirements, resulting in longer cycle times. However, streamlining part design using principles such as Design for Manufacturability (DFM) helps simplify complex details of the design making the cycle time shorter. Consequently, this design principle helps make the injection molding process more efficient and cost-effective with higher part quality and reliable results.
· Mold Design: The mold is often very critical to the quality of injection molded parts and as such careful consideration is often given to the features that make it efficient. For instance, the type of runner and gate system determines the material flow within the mold designers take utmost care in designing these mold features. Likewise, the cooling system is another important element that requires the utmost care in injection mold design. This component determines the rate of cooling of the heated material and consequently controls the length of the cycle time. The cooling channels provided and the cooling medium utilized can significantly impact the cycle time and the quality of part output.
· Machine Performance: The capacity of the injection molding machine is another critical influencer of injection molding cycle time given that the machine is central to the whole injection process. For starters, the injection molding machine determines critical requirements like the clamping force for the mold, injection pressure, and feed rate. Thus, employing a suboptimal machine only retards the injection molding cycle time. Frankly, adequate machine maintenance and calibration are pivotal to ensuring optimal performance and a satisfactory cycle time. Also, upgrading injection molding machines to modern versions with advanced controls further helps to improve productivity and injection molding cycle times.
IV. Optimizing Each Phase of the Cycle
Achieving part quality with the design specification can be a handful. However, having the right information and knowing the parameters to optimize at every injection molding phase makes it easier to achieve. Here, we have highlighted the important considerations to fully optimize the injection process at every stage.
- Injection Phase: The critical requirement in the injection phase often includes the injection speed and pressure as this usually determines the mold fill rate and how molten materials behave in the mold. Hence, adjusting the injection speed and pressure based on the material type for the smooth flow of material within the mold is essential to shorten the cycle time. Additionally, the melting temperature is important to facilitate a faster filling of the mold resulting in a quicker cycle time and an increased part quality. Optimizing all these injection phase parameters guarantees adequate material flow while avoiding downtimes and delays in the injection molding process.
- Cooling Phase: Optimizing the cooling phase requires an efficient cooling system that incorporates uniform cooling to mitigate against internal stresses that often lead to deformations and other defects. Essentially, a strategy of cooling channels often does the trick. However, employing some advanced cooling systems might be necessary for situations where the mold design is complex with intricate details. This might also require some innovative cooling channel design to effectively control the temperature and minimize delays making the whole process more efficient.
- Ejection Phase: To ensure that parts are not stuck and are safely removed from the mold is pretty much the objective of optimizing the ejection phase. The reason is that sticking is one major reason for deformations in injection molding. Therefore, to achieve this objective, ejection parameters such as ejection speed must conform with part characteristics like shape, size, and material properties. Still, innovative mold design features like stripper plates and robotic ejection systems can immensely make the process even smoother, more efficient, and more reliable.
- Mold Closing Phase: While it may sound simple, closing the mold can be one of the most influential stages of the injection molding process if done efficiently. This can help speed up the cycle time and reduce delays between cycles once optimized. Fortunately, there are fast clamping machines that help to optimize this process, but more importantly, carrying out regular maintenance on mold clamping systems is critical for this phase. it will not only give longevity to the mold but also help maintain its peak performance levels.
V. Technological Innovations in Cycle Time Reduction
Advanced technology has been at the forefront of better and more efficient manufacturing and injection molding has not been an exemption. There is virtually a technological improvement to optimize every stage of the injection molding process including cooling, injection, and ejection.
- Advanced Cooling Techniques: There are conformal cooling channels which help to optimize cooling systems, especially for complex part designs with intricate details. This channel often adheres to the corners and outlines of the mold to facilitate uniform cooling throughout the mold. This ensures no part of the mold is exempted from the impact of coolant flow during the cooling phase. The result is a balanced heat dissipation resulting in a significantly shorter cycle time and a flawless plastic part.
- Automation and Robotics: This innovation has gained much popularity among manufacturers and industries including the injection molding sector considering the efficiency and speed it offers. Automation and robotics in the ejection phase help to swiftly remove parts from the mold significantly increasing the effectiveness of the process while reducing injection molding cycle times. It also reduces the probability of human errors which often account for a huge part of the defects experienced in the process.
- Simulation and Software Tools: Especially when there is the need to understand the flow of molten material in the mold, simulating this flow can be of great assistance for analysis. Thankfully, simulation and software tools come in handy for such needs helping mold designers optimize designs and detail injection molding parameters easily. Additionally, these tools can predict defective outcomes like warpage, trapped air, and flow lines from flow simulations saving manufacturers from potential material wastage, production time loss, and needless expenses. But that’s not all. These software tools can also inform of machine recalibration, failures, and scheduled maintenance which can save manufacturers the cost of unnecessary repairs and part replacement. In the end, part quality gets better and cycle time reduces on account of innovative tools like simulation and software tools.
VI. Case Studies
In the injection molding industries, several household names understand the need to optimize their processes and have successfully implemented strategies that have helped them reduce cycle times. For instance, Engel has successfully integrated automation into their processes to make them more efficient with faster cycle times. For Arburg, optimizing cooling techniques has increased their part quality while their investment in advanced machine technology has significantly shortened their cycle time. From these and many other top injection mold manufacturers, the emphasis is usually on investing in injection molding technologies and employee development to improve precision and part quality. Furthermore, consistent data-driven optimization and tool maintenance continues to yield huge benefits and is considered part of best practices injection mold manufacturers should adopt to enhance their molding cycle times.
VII. Common Challenges and Solutions
Injection molding like every other manufacturing industry has its fair share of challenges especially when it relates to optimizing processes for improving cycle times. But there are actionable steps that can help solve these challenges
- Cycle Time Variability: Variability in cycle times is often caused by several issues one of which is wrong material selection. This can be solved by critically considering material properties ensuring that it matches the injection molding objectives before selection. Other causes include mold design variability and unoptimized injection molding machines. Incidentally, maintaining a regular maintenance routine, ensuring recalibration of injection molding machines, and optimizing mold designs are great ways of overcoming these challenges.
- Balancing Speed and Quality: A balance between injection speed and part quality can seem difficult to achieve, however, it is not impossible. It requires painstakingly evaluating design details, process optimization, and material consideration. Additionally, including efficient cooling channels and conformal cooling are other ways of increasing production speed without sacrificing quality.
- Cost Considerations: The cost of an injection molding project is often a key indication of feasibility for manufacturers. Hence, evaluating the cost-to-benefit ratio of investing in production factors like robotics and automation can be eye-opening. This type of analysis should be at the forefront of any expenditure to see the short and long-term benefits, especially when it leads to shorter cycle times.
VIII. Conclusion
In a nutshell, you need to approach injection molding cycle time from a well-balanced standpoint given its complexity and the number of stages involved in an injection molding cycle.
Even though it is not as hard as finding a needle in a haystack, you still have to pay attention to many details, including material selection, maintenance routines, mold design parameters, and process considerations. These factors are spread across the injection, cooling, ejection, and mold closing stages of injection molding.
Moreover, you’ll be able to significantly shorten your injection molding cycle time once you can address these elements while also finding a balance between cost, quality, and efficiency.
Ultimately, the part quality should not suffer at the expense of reducing the cycle time.
