For decades, injection molded parts have added flare and ease to our lives. From medical devices to household items and fashionable wear, injection molding has ensured people from all income classes have access to its functional inventions. It’s no wonder the demand for injection-molded parts continues to soar in the United States. Products made from plastic materials such as polypropylene, ABS, and HDPE continue to top the charts on the demand scale.
So, as an intending polymer manufacturer, you should know how to optimize your injection molding process if you hope to maximize your return on investment. Polymer manufacturing can be a complicated process if you don’t know how to control your product quality. Luckily, product variations and defects can be avoided with the right skills and technology.
That’s why we compiled a list of injection molding controlling factors to consider and process control methods to adopt to achieve success even in your first project.
What is Process Control in Injection Molding?
Injection molding process control is the act of monitoring, optimizing, and controlling the injection molding parameters—temperature, speed, pressure, time, and position—in a production cycle to ensure the final products meet an established set of standards, which usually includes the client’s specifications and industry regulatory requirements.
To achieve the best results during a production run, adequate attention must be given to the process parameters, the efficiency of the production materials and tools, and the cost of producing injection-molded parts as they affect the overall product quality.
Is Injection Molding Process Control the same as Quality Control?
Injection molding process control and injection molding quality control are components of a quality management system. While process control focuses on optimizing the process parameters in each stage of the production run to ensure they meet an established set of standards during testing, quality control focuses on optimizing the output at the end of production.
Quality control is the process of testing final parts to identify, evaluate, and correct deviations and errors undetected by process control. The goal is to measure the accuracy of the final output and implement changes to meet the established quality standards.
5 Stages of the Injection Molding Process
1. Material Preparation
Preparing your material to be injected into the heating chamber (barrel) is an essential pre-injection molding phase in the injection molding process. In this stage, the raw metal or plastic materials are cut, blended, and treated before being loaded as pellets or granules in the hopper.
2. Clamping
The injection molding cycle officially starts when the mold closes. The clamping unit holds the mold halves in place during the injection and cooling phases. The clamping unit generates enough force to keep the mold closed while the molten material adequately fills the cavity.
3. Injection
The hopper then inserts the metal bits or plastic pellets into the heating chamber, (barrel) where they are melted and heated under high temperatures generated by electric heater bands. The injection time is completed when the material fills the cavity. The injection time depends on the shot volume (size of the material) and the injection pressure. The pressure and flow rate of injection are controlled by the hydraulic or electric system.
4. Cooling
The molten material is then inserted into a cooling unit or allowed to cool and solidify naturally. The cooling unit regulates its temperature through forced convection—in which fluid motion is generated by an air heating system, water pump, or suction device. The material takes on the desired shape and characteristics, based on the mold design. The mold is then opened after the estimated cooling time is achieved.
5. Ejection
The entire injection molding phase can last a few minutes, yet can be used to produce multiple parts simultaneously. The injection molding process comes to an end when the material becomes solid and the ejection system separates the finished component from the mold and pushes it out.
Factors Affecting the Injection Molding Process
- Temperature: The molding temperature affects the viscosity, material fluidity, deformation, color, and shrinkage of the final product, leading to lower strength and durability of the parts. Nozzle temperatures should always be lower than barrel temperatures. Without proper adjustments, poorly set temperatures can restrict the flow of the molten material throughout the mold, altering the mold design and incurring losses for the manufacturer.
- Time: The time for each stage in the injection molding cycle should be properly regulated and set according to shot volume and mold designs to prevent shrinkage. As a rule of thumb, thin-walled plastics should have a shorter injection time. Factors to consider here are the injection time, holding time, cooling time, and ejector delay time. Dents and other deformations could appear on the surface of your parts if you fail to anticipate the proper cooling time for each material.
- Pressure: The injection molding pressure of a production cycle should depend on the signals from the control panel. The processor converts the process parameters into readable signals for each action program on the control panel so the manufacturer can regulate the pressure. Inadequate pressure in the mold cavity affects the flow rate and leads to multiple defects in the final product. For instance, if the injection pressure or hold pressure is too high, it can lead to an overflow and flash issue.
- Speed: The speed of the injection molding cycle depends on the pressure. An injection molding speed can be low, medium, or high and can be applied to different materials or mold structures. However, once in motion, it is difficult to control. On the other hand, the melt speed can be adjusted during each stage of the production cycle to give the best results. If the injection speed or pressure throughout the molding process is too low, it could lead to flow lines on the surface of the parts.
- Position: This is the point where the molded part is moved from one tooling unit to another. Switching the position of each action should be based on the mold speed, structure, and weight of the material. Some of the position factors controlling the injection molding process are the injection position, clamp position, and ejector position.
- Material properties: The molecular composition of the material can influence its fill rate and increase the risk of shrinkage during the injection molding process. For instance, materials with low crystallinity, high transparency, and good fluidity will perform better under the injection molding process. Some plastics crack under stress, as such mixing additives with these materials can improve their crack resistance.
Guarantee A Successful Outcome with these 5 Injection Molding Process Control Methods
Every client wants assurance that you have the capabilities to make their project better. This includes ensuring no variation in quality and minimizing overhead costs. The best way to achieve this result is to integrate process control into your production cycle.
Most injection molding machines come with inbuilt control systems but specialized manufacturing firms employ custom technologies—sensors, AI-powered software, and systems—people, and methods to give their clients the best possible outcome. We highlighted a list of injection molding process control methods you can adopt to optimize your plastic or metal production in 2024.
1. Statistical Process Control (SPC)
Statistical process control involves using statistical techniques to monitor and control the quality of parts in an injection molding production process. This method allows you to determine measurement parameters, periods, and control units, and then apply them to the production process to collect quality data in real-time for further evaluation.
Usually, when the values generated from the analysis exceed the control limits, the manufacturer should expect variation in quality. SPC has made it easy to uncover hidden process behaviors and product variation through the control chart. With the data derived from your analysis, you can identify waste areas to minimize scrap volume and reduce the cost of production.
2. Continuous Process Control (CPC)
Control process control allows you to collect and review controlled variables and parameters of production output—including the weight, volume flow rate, temperature, and pressure—in a continuous time flow, using a sensor, and comparing the parameters to the required values to ascertain errors.
This method is ideal for producing large batches of molded parts without interruption over a long period. Its feedback control function allows you to optimize your production process by ensuring you take action before, during, or after you discover errors in the performance parameters.
3. Real-Time Process Monitoring
This form of process control generates and analyzes data simultaneously, making it easier for you to troubleshoot issues as they emerge without waiting till the end of the production run. This intelligent model for the injection molding process comprises initial process parameters and an online defect correction feature you can set up based on the product’s geometric approximation to evaluate the process before the injection molding trial begins.
4. Multivariate Analysis (MVA)
The multivariate analysis evaluates multiple variables—pressure, temperature, flow, and cooling—at the same time, providing quantifiable data about the relation between the different process parameters in the entire production cycle in real-time in a simple graphical format.
This method uses a host of techniques—data collection, multivariate modeling, reject control, and reporting—to detect quality in molded parts and provide in-depth information about the sources of errors or variables in the production run. Unlike the SPC, this method allows you to achieve parametric release as sources of errors can be understood, anticipated, and controlled in successive runs.
5. Cavity Pressure Measurement Method
This popular method of process monitoring involves installing cavity pressure sensors into the mold cavity or the injection molding machine where they can monitor molding conditions and provide information about the pressure curve of the molten polymer during the different stages of the production cycle, based on the set measuring point.
A new set of injection molding parameters can be established using the data generated to optimize product quality in future runs. The goal is to detect and correct deviations in target production through automated identification and integrated control of the injection molding machine.
How Does Using An Injection Molding Process Control System Boost ROI?
Using an injection molding process monitoring system allows you to boost your team’s efficiency and increase your profit returns. A process monitoring and control system streamlines production activities. In the hands of skilled and experienced manufacturers, an injection molding process control system synchronizes and automates production steps, minimizes material wastage, prevents machine damage and downtime, shortens production time, and reduces flow lines.
These systems come with extensive data logging and monitoring capabilities that allow you to generate and analyze records of real-time data so you can use them to influence future manufacturing and sales decisions. Some of the benefits of employing a process control system include improved employee productivity, lower overall injection molding cost, higher quantity and quality of final products, better client satisfaction, and industry recognition.
At PTI Tech, we ensure we customize our injection molding process to suit the production needs and target market of our clients by employing over 36 years of experience in polymer, metal, and tungsten injection molding while adhering to multiple industry quality standards. Our clients enjoy round-the-clock IT support, top-quality engineering and manufacturing solutions, and world-class industry advice.