Scientific Molding

What is Scientific Molding?

Scientific molding is a process in which the fill, pack, and hold stages are treated separately to minimize fluctuations while improving overall product consistency. Separating these stages is also known as decoupled injection molding. Molders who use scientific injection molding equipment, software, and practices can, according to scientific molding educator John Bozzelli, “reduce cycle times, increase machine efficiency, and ultimately make more money.”

What’s the difference between traditional molding and scientific molding?

In the traditional method of injection molding, the mold is filled with a single shot under constant pressure to pack the cavity. In scientific molding, the cavity is filled to around 90–97 percent at a certain velocity. In the next phase, the machine switches from speed control to pressure control, where the cavity is filled or “packed out” to complete the process.

The scientific method allows for greater shot-to-shot consistency and improved control over the specifications of the part. On the other hand, large variations in part dimensions often occur cycle-to-cycle with the traditional injection molding method.

A scientific injection molding approach is especially important in the production of complex parts and components, where even the slightest variation in molding variables can have a significant impact on the process or the finished product. That said, the goal of scientific injection molding incorporates two key strategies:

• Develop a process that produces repeatable results with minimal variation
• Optimize the dimensional or mechanical characteristics of a molded part

Factors in Science-Based Molding

Another aspect of the traditional molding process involves machine-based control. It was once believed there were 20 or more machine-based settings that could impact various problems with the molded product (dimensions, voids, warping, and other quality issues). Research aimed to find connections between issues with the parts and the settings of the machine.

Over many years, when it was found that machine settings had little or no correlation to part quality, research shifted from the traditional machine-control method to a science-based approach. The “plastics point of view” became the revolutionary perspective of modern research based on the laws of science instead of injection machine settings. Donald C. Paulson pioneered this scientific approach by developing a plastics research laboratory at the General Motors Institute in the mid-to-late 1960s.

Injection Molding Processing Stages

Mr. Paulson focused on the four injection molding plastic processing stages best known to control the properties of the molded part: heat, pressure, flow, and cooling. Each of these, Paulson hypothesized, “would be governed by the laws of physics. First, the laws of heat transfer; second, the Poiseuille fluid flow law; and third, the equation of state for plastic.”

Measuring and recording the machine and plastic variations for each of the four cycles over four years led Paulson and his team of researchers to make a couple of industry-changing conclusions:

• Physical laws that apply to other materials also apply to plastic processing
• The four plastic variables determine the characteristics and properties of molded parts

The scientific approach to molding doesn’t change the molder’s need to understand machine setup or how machine controls affect plastic output and part quality. However, it does help the molder make better decisions about what the control settings and cycle times should be, as well as solve part issues if and when they occur.

Steps in Scientific Molding and the Role of Advanced Process Control

At its core, scientific molding focuses on decoupling the essential steps in the molding process. This decoupling ensures precision, accuracy, and control over each phase of the injection molding cycle. With advancements in technology, especially the introduction of the RJG eDart® system, molders can now achieve higher levels of control and consistency.

By using equipment and software measurement tools, such as the RJG eDart system, the variables of each cycle within the mold are continuously monitored. This real-time monitoring is dictated by the unchanging physical laws governing plastics. These laws, related to heat, pressure, flow, and cooling, are carefully controlled under the supervision of specially trained engineers, ensuring every component meets the highest standards.

• Initial Shot: The cavity is filled to approximately 98% of its capacity, with velocity as the key control parameter.
• Fill and Pack: The cavity is filled further, reaching its full capacity. The material is then compressed or “packed out” within the cavity, maintaining constant pressure. With RJG’s eDart systems, machine control is based on the plastic pressure inside the mold. This shift toward plastic pressure control, rather than only relying on machine parameters, offers a more robust process window.
• Cool and Stabilize: As the molded part cools, it stabilizes. Only after reaching the desired stability is the part ejected, preparing the machine for the next metered shot.

This decoupled approach, further improved by technologies like RJG’s eDart, allows molders better control over part dimensions. More importantly, it ensures consistent quality from one cycle to the next, commonly called shot-to-shot consistency in the industry. With such advanced process controls, Rosti can guarantee remarkably consistent product quality to its customers.

Advantages of Scientific Molding

It’s not hard to picture a world without scientific molding principles: product variations caused by wide fluctuations in temperature, pressure, and viscosity; increased cycle times; decreased machine efficiency; higher costs; more rejects; and lower quality parts for customers.

As stated in our post on the advantages of scientific molding, “Scientific molding practices are essential to achieving outcomes that deliver faster cycles, higher volume, and a more efficient injection molding process.” In addition, “quality control issues can be avoided by having automated containment control and traceability for specific applications.”

The technology behind scientific molding gives manufacturers the ability to operate more efficiently while also creating opportunities for a global competitive advantage. It also provides OEMs and customers with higher-quality parts and fewer rejects at lower costs.

The principles and technologies involved with scientific molding solve the problem of how to get injection molding machines to make good parts every single time.

The Role of Technology in Scientific Molding

The potential of scientific molding truly unfolds when paired with the latest advancements in injection molding technology. While it is a practice rooted in the laws of physics, its effectiveness greatly depends on technological innovations, particularly in the areas of engineering, equipment, and software.

A prime example of this synergy is Rosti’s adoption of the RJG eDart system for advanced process control. This system, which focuses on controlling and monitoring the plastic pressure inside the mold, has been pivotal in transforming how injection molders approach their process. It’s no longer just about machine setup or generic quality control; it’s about using state-of-the-art technology to ensure the highest quality while also achieving cost savings.

From the initial machine setup to the intricate details of quality control and everything in between, technology, like the RJG eDart system, highlights the importance of continuous innovation. Such advancements have made it possible for molders to not only meet but exceed the demanding expectations of their customers. In this context, technology isn’t just an enabler; it’s a game-changer for the overall success of the injection molding process. Let’s dive into this further below.

The Role of Mold Flow Simulation Software in Scientific Molding

Scientific molding principles follow a data-driven approach. And data makes it possible to improve and achieve repeatable results. For example, Rosti utilizes mold flow simulation software by SOLIDWORKS®. As a front-end design validation tool for plastic injection molders, it provides predictive insight into plastic component design. Some key benefits of using SOLIDWORKS software technology include:

• A shorter product development cycle and an overall reduced time to market through predictive insight into component design early on.
• Greater insight into plastic part geometry that would otherwise be too difficult or expensive to predict.
• The ability to identify potential problem areas up front relating to sink marks, weld lines, short shots, and other part defects and blemishes.

In short, SOLIDWORKS helps injection manufacturers get the part design right the very first time. By doing this, they can eliminate costly mold rework, improve part quality, and reduce time to market.

The Role of RJG in Scientific Molding

While renowned for its consulting and training services – offering flagship courses like decoupled molding, high-performance molding, and Master Molder 1 & II certification – RJG’s eDart system has proven revolutionary in the molding process at Rosti.

Rosti’s adoption of the RJG eDart process control system has been transformative. Designed to empower molders with critical information, the eDart system is adept at reducing scrap, ensuring process stability, and delivering repeatable, superior-quality outputs.

Rosti’s ambitions have always been to maintain high press utilization rates. Such goals demanded an agile fleet of presses and a relentless commitment to the principles of scientific molding. The eDart system, with its advanced in-mold pressure sensors, enhanced Rosti’s molding operations, providing unprecedented control and flexibility.

The journey began in September of 2009 when Rosti, facing unique challenges, integrated the eDart system into two of our presses. This integration proved so beneficial that the technology quickly expanded. By 2010, Rosti committed to a two-year initiative to ensure that every press was equipped with the eDart system. This pursuit of excellence made our commitment to closed-loop process control not just a strategy but a defining element of our culture.

One of the pivotal outcomes, as Kurt Behrendt, Rosti’s director of engineering, pointed out, was the “transformational change in managing part consistency across various material lots.” This was achieved by the eDart system’s proficiency in monitoring and controlling in-mold plastic pressure fluctuations. The result? Unparalleled consistency in the products Rosti molded.

Key advantages of integrating RJG’s eDart system into our scientific molding process include:

• Historical data recording for every molding shot, providing unmatched insights.
• Real-time production monitoring, ensuring timely interventions when needed.
• Significant improvements in quality assurance, resulting in more consistent, top-quality parts.
• Drastic reductions in scrap and processing time, driving operational efficiency.

In the world of scientific molding, the integration of mold flow simulation software, process control systems, and technologies like eDart form the backbone of a strong automation strategy. Our deep dive into automation support is up next.

How Automation Supports Scientific Molding

We’ve discussed the science of molding in terms of the laws of physics, process steps, and the role of technology in design, engineering, and process control. But scientific molding doesn’t stop there—not by a long shot. It also involves and benefits from automation and a highly skilled workforce.

In this section, we’ll discuss the impact of automation on scientific molding, and in the next, the importance of specially-trained engineers and technicians.

The invention and implementation of automated tools and robotics have positively impacted virtually every industry. And the injection molding industry is no exception. Make no mistake, the more a plastic injection molder is able to automate its operations, the more it can grow its business and gain a global competitive advantage.

The ultimate mark of a scientific molding operation is a fully-automatic production facility, like the one Rosti pioneered beginning in 2011 at its Bunsen Drive facility. A fully-automatic facility is sometimes also called a “lights-out” facility. The manufacturing process at Rosti’s Bunsen Drive facility is so unique the company was awarded U.S. Patent No. 8,827,674 B1 for the process: A specialized injection molding factory system and associated facility comprising machines on the first floor with the resin supply placed on a mezzanine level.

What does it mean to operate lights-out?

Four years ago, we published an article about how a lights-out manufacturing facility has revolutionized injection molding. In it, we described the lights-out process as follows:

“Lights-out manufacturing describes the process in which factories and production facilities are equipped with innovative and automated machinery to perform tasks that would normally require a human to be present. Essentially, the production facility can run “lights-out” – or without substantial assistance from human labor, lights, heat, and other costly business factors. Lights-out manufacturing processes also allow companies to keep facilities running 24 hours a day, 7 days a week without needing multiple workforce shifts.”

In this article, we also noted that “Not only has it allowed businesses to improve in the areas of cost and turnaround time, it has also enabled plastic part producers to lower the likelihood of defects and increase the overall quality of products made.” We pointed out several ways a lights-out facility has improved injection molding, such as:

1. U.S. manufacturers can achieve a globally competitive advantage.
2. Large orders can be completed quickly without the higher costs of adding more shifts.
3. Quality control, delivery, and cost containment requirements can be met.
4. It requires a highly trained and dedicated workforce to manage and maintain state-of-the-art automation equipment and processes.

Yes, scientific molding includes technologies such as mold fill simulation software, RJG eDart process control, advanced material handling systems, part conveyance systems, robotics, and a fully automated, lights-out facility.

Even so, these ever-evolving technologies and lights-out methodologies don’t allow a business to operate completely hands-free. In fact, without knowledgeable and highly trained personnel, none of this would be possible.

Rosti’s blend of experienced veterans and highly motivated young professionals is essential to its automation-focused and growth-oriented global business model. Next, we’ll look into the important role that specially trained engineers and technicians play in scientific molding.

The Crucial Role of Specialized Engineers and Technicians in Scientific Molding

While understanding the intricacies of physics and technology isn’t required to recognize the transformative impact of scientific molding on the injection molding process, it’s absolutely essential to have specialized engineers and technicians at the helm. Their expertise ensures that science-backed injection molding systems are operated with precision and efficiency.

Rosti’s Comprehensive Approach to Molding Education and Training

Rosti places a high value on molding expertise. The company’s strategic hiring and training reflect an unwavering commitment to fostering excellence, including:

• Internship Pipeline: Every summer, Rosti welcomes between two to four interns. This proactive approach ensures a steady stream of potential talent, preparing for expected staffing needs.
• Targeted Recruitment: Rosti specifically hires engineers from educational institutions where students are exposed to both theoretical and hands-on scientific molding training. This ensures new hires are familiar with the industry’s nuances from day one.
• Continuous In-plant Training: By partnering with industry experts like RJG, Rosti’s staff receive regular training on advanced concepts such as decoupled II and III molding principles, pressure sensor specifications, interpreting eDart system outputs, and much more.
• Four-level Curriculum: To further strengthen its commitment to excellence, Rosti has created a comprehensive four-stage curriculum. This program is carefully designed to develop a molding beginner into someone ready to take the RJG Master Molder course. The combination of on-site training and valuable mentoring from in-house Master Molders sets Rosti up to cultivate its next generation of team members.

Understanding Decoupled II and Decoupled III Molding

Decoupled II Molding:
This process involves filling the mold to a specific position. Next, the packing and holding phases are combined, where the second-stage pressure is used to fully pack out the mold, continuing until the gate is sealed.

Decoupled III Molding:
In this method, the mold is first filled to a certain position. A secondary filling stage or machine packing then packs the mold up to a set cavity pressure. Once reached, the process is maintained, holding until the gate seal is established.

RJG’s eDart process control system is designed to support decoupled molding processes. It helps molders monitor critical data, control variables in real time, and ensure consistency shot-to-shot. By integrating technologies like in-mold pressure sensors, the eDart system provides the insights and controls needed for the precise, step-by-step procedures of decoupled molding.

Rosti Engineers Involved Throughout Entire Process Window

Rosti engineers are directly involved throughout the entire scientific molding process. It starts early in the design specification phase, with engineers working to design both the part to be molded and the tool to be used in the process. From there, the engineer is able to specify how to incorporate pressure sensors in all new molds.

Once the sensors are in place, the tool is ready for testing under the guidance and observation of engineers. Testing is conducted to identify any variables and the parameters needed for consistent and optimal production.

With input from Rosti’s senior process technicians, our engineers approve the selection of decoupled II or decoupled III processes for each mold and confirm this process template for PPAP (Production Part Approval Process) and ongoing production. Once production is ramped up, engineers continue to monitor readings and outputs to maintain and optimize the process for the best possible results.

Where does design for manufacturing fit into the scientific molding process?

Design for manufacturing is a top priority for reducing costs in scientific molding. The first company to commercialize design for manufacture and assembly (DFMA), Boothroyd Dewhurst, Inc., found that 80% of the cost of a new product is directly related to its design.

According to John Gilligan, President of Boothroyd Dewhurst, Inc., “The use of DFMA to help choose the right structures, materials, processes, and labor has become critical given that companies get few second chances in today’s global markets.”

Therefore, the best time for a tool-maker or injection molder to get involved in the design process is early in the development cycle. Doing so will help fully understand customer objectives and avoid unexpected surprises.

In Rosti’s comprehensive guide to design for manufacturing in plastic injection molding, we’ve laid out a four-part approach to design optimization. They are as follows:

Design for Manufacturing

Design for Manufacturing (DFM) refers to the process of designing or engineering a product to reduce manufacturing costs, allowing potential problems to be addressed in the design phase, which is the least expensive time to resolve them.

Design for Functionality

Throughout the plastic part design process, it’s crucial to maintain focus on the functional requirements of the part. Experienced design engineers should recommend modifications that will help ensure the part meets its requirements—including what elements it will be exposed to, what chemical or corrosive materials it must withstand, functional cosmetic attributes, and more.

Design for Assembly

Design for Assembly (DFA) is a process where products are designed with ease of assembly in mind, with the ultimate goal of reducing assembly time and costs. Reducing the number of parts in an assembly is usually where the biggest cost advantages of DFA are realized.

Design for Sustainability

Design for sustainability focuses on designing parts with print measurement intent in mind—maintaining tolerances through proper measurement on an ongoing basis.

Why Does Material Selection Play Such an Integral Role in Scientific Molding?

According to Kip Doyle, author of an article on the Top 10 Reasons Why Molders Fail at Scientific Molding, many molders can’t get past a “machine-focused” approach and mold from the plastic’s “point of view.” He cites that many articles have been written on the four main plastic variables (plastic temperature, plastic flow, plastic pressure, and plastic cooling rate and time), and a scientific molder must understand this approach and the process optimized from the perspective of the plastic.

Aligning with your injection molding partner to choose the best resin early in the design for manufacturability process is crucial to a part’s production success. A good place to start is having a general understanding of the two main types of resins—amorphous and semi-crystalline.

Polymers are composed of structures defined by crystallinity—that is, how the molecules of the polymer are packed together.

Crystalline structures are, in most cases, very ordered, which gives the material strength and rigidity. Amorphous polymers are the opposite. Sometimes, the distinction between the two is not clear-cut. With most polymers, there’s a mix of both crystalline and amorphous structures. How the polymer is processed determines the exact proportion of each.

In our post on Preparing for Injection Molding Resin Selection, we break down the differences in polymers further.

When considering the intended end use of your injection molded part, understanding these key characteristics is essential to selecting the best resin.

Part Appearance and Geometry

A part’s overall appearance and geometry have a significant impact on molding capability and the type of resin that should be used. Part design—including size, shape, and wall thickness—can make a part prone to defects, while features like snaps, undercuts, bosses, ribs, and more can complicate the molding process.

It’s critical that injection molders use the latest technology to run simulations to optimize mold design specifications and resin selection before a project is finalized for production—this is where SolidWorks Premium plastics flow simulation provides predictive insights early on.

Part Strength and Flexibility

Material selection also plays an important role in the strength and flexibility of your molded part. Addressing specific needs early in the design process can help you avoid costly changes later on. Balancing characteristics like stiffness, durability, toughness, and others is key to achieving optimal part functionality.

Using Additives

When material performance can’t be achieved with available resins, custom blends of materials can be created to enhance the properties of different resins. Reinforcing materials with additives can give parts more strength and add stiffness that may cut down on warping and shrinkage. Additives like glass or carbon fibers can be used to improve part performance and boost flow, ejection, and dispersion.

High Heat Materials

We mentioned the important role of design in the injection molding process, and this is especially relevant when high-temperature materials are used to boost a part’s strength, stability, and other features essential to its specific application. Traditional molding techniques are not always effective with high-temperature and specialty resins.

Some characteristics of high-heat and specialty resins are unique and may perform differently from one application to another. To maximize both design and material advantages, experienced design engineers and injection molders need to consider a number of factors. In this post, we outline a few basic and advanced tips you should keep in mind when designing parts for injection molding using high-heat or specialty resins.

Calculating Plastic Residence Time

Plastic residence time is how long plastic or resin is exposed to heat during the manufacturing process.

Taking the time to calculate the specific plastic residence time for your manufacturing process will improve your material’s performance and the overall quality of your final product.

Understanding the residence time of material in the first stage of the screw can help you determine the optimal time and temperature for your production needs.

What Does Plastic Residence Time Affect?

If plastic residence time is too long, it can affect part quality in several ways:

• General weakness in produced parts
• Color variation
• Degradation not visible to the eye
• An overall compromised product

However, it can also affect machine performance, causing inconsistency in melt quality and shot weight, as well as melt temperature.

No matter how many formulas or calculations are available, plastic residence time should be individually calculated by each manufacturer to determine the ratio that works best for their specific product.

Using scientific molding practices, Rosti uses recorded data to assess quality control and make any necessary tooling adjustments, thereby improving overall part quality and avoiding the negative impact of poorly calculated plastic residence time.

Learn more about the importance of calculating plastic residence time here.

Plastic variables require an understanding of the material’s nature and its preferred molding conditions. When a material’s key characteristics, behavior, and response to processing are understood, scientific molders can optimize the molding process to produce the most consistent parts possible.

What Attributes of Scientific Molding are Used in Part Design and Tool Optimization?

Creating tools for prototype and production components represents one of the most time-consuming and expensive parts of new product development. To reduce manufacturing lead times and costs, prototyping and manufacturing processes have quickly advanced through the development of scientific molding techniques.

Scientific molding uses data to develop a process that produces repeatable results with little to no variation. Through resin expertise and testing, both the dimensional and mechanical characteristics of a molded part can be optimized. Often achieved through the use of mold fill simulation and process control systems, predictive insight, process validation, and complete process documentation are essential to producing demanding parts.

Part Optimization

Design engineers should rely on previous experience and expertise to optimize part design for unique applications. Elements of scientific molding related to part design may include using the latest software and technology, such as computer-aided engineering, mold flow, and prototype development to validate how the part will perform in its end use.

Design considerations can include:

• Radius, draft angle, sink marks, wall thickness, etc.
• Gate location
• Weld line locations
• Environmental / end-use factors
• Part appearance

Injection molders should understand how to avoid designing a part, building the tooling, and starting the molding process only to find that the design does not work in production. Prototype tooling is a great way to validate and optimize critical mold and scientific molding variables.

Tool Optimization

Scientific molding practices can also be used to optimize tool design or to improve poorly designed tools. It is essential for injection molds to be evaluated for their performance in producing consistent, defect-free parts. Engineers should examine every aspect of a mold’s mechanical functionality using the appropriate material settings.

Testing can then be performed to check for any imbalances among cavities. Once this analysis is complete, a gate seal study can be conducted to gather data on where the gates fully seal at what points in the mold cavities. Recording findings and making recommendations for adjustments in the process or tooling are essential steps to correcting potential defects.

The Impact of Quality Control in Scientific Molding

Quality control is fundamental in refining and perfecting the scientific molding process. The ability to leverage and analyze recorded data means that adjustments can be made proactively, enhancing the overall quality of the molded parts. Once these quality benchmarks are met, scientific molding principles significantly streamline the manufacturing workflow. This increased efficiency is so substantial that there is a reduced need for operator intervention and machine oversight.

Leading-edge molders are now adopting groundbreaking “lights-out manufacturing” strategies. In these setups, advanced automated equipment carries out operations that traditionally required human intervention, showcasing the potential of technology in modern manufacturing.

The continuous advancements in scientific molding empower manufacturers with technology-driven processes, giving them a strong competitive edge on a global scale.

Additionally, RJG provides molders with the ability to monitor essential parameters in real-time. By offering insights into critical variables, it allows manufacturers to maintain consistent quality, reduce scrap, and stabilize their molding processes. This system also helps monitor in-mold plastic pressure variations, ensuring that products are consistent in quality across various production runs.

RJG’s in-mold pressure sensors offer an additional layer of monitoring and control. Measuring and managing the pressures within the mold is a critical factor in achieving consistent and high-quality parts.

Its ability to record historical processing data on every shot means that injection molders have a wealth of information at their disposal to analyze and improve their processes. This data-driven approach enables a proactive response to any quality inconsistencies, leading to more predictable and reliable outcomes.

How Has Scientific Molding Transformed Injection Molding?

The advances in scientific molding practices have impacted the plastics industry at a high level. Not only has it allowed businesses to improve in cost and turnaround time, but it has also enabled plastic part manufacturers to reduce the likelihood of defects and increase overall product quality. Other examples include:

Competitive Advantage

When designing and producing complex injection molded parts, there’s a significant advantage to partnering with a company that uses state-of-the-art processes and is also easily accessible geographically. Many companies are recognizing the benefits of having their manufacturing partners nearby. The ability to react quickly and make important changes on a short timeline is an important factor that often comes up in selecting a manufacturer. When production facilities adopt advanced manufacturing processes, including lights-out functions, it shows their partners that they are working and producing parts as efficiently as possible.

Faster Turnaround with Lower Cost

When manufacturing processes are set up and monitored in a smart, data-driven way, companies see their production capacities increase and orders are completed much faster. While not suitable for every job, automated molding is best for jobs that run at medium and high volumes, about 2,000 hours per year or more.

Additionally, the capacity, speed, and labor efficiencies created by scientific molding practices can be passed on to the customer—ultimately lowering overall product costs. When managed appropriately, the process also improves OEM production flexibility.

Highly Trained Workforce

When we talk about automation, lights-out manufacturing, and other scientific molding services offered by an injection molder, much of the emphasis is on the positive aspects of reducing human labor. While the process can create a more streamlined approach to production and may allow for fewer people to be involved, not all projects can be run solely by technology. State-of-the-art technology and processes require a highly trained and dedicated workforce that can make smart decisions and maintain equipment.

Protection for Intellectual Property

When product manufacturers rely on innovation and speed to market to stay competitive, offshoring aspects of production can expose designs to patent infringement, counterfeiting, and more. Working with a reputable and knowledgeable partner that keeps everything from design, development, and production under one roof will ensure the manufacturer protects and retains all intellectual property, as well as knowledge acquired throughout the process.

Is It More Expensive to Use an Injection Molder That Implements Scientific Molding Processes?

You can save money by partnering with a molder who uses scientific molding processes to intelligently design molds and validate parts. When molds are smartly designed, less material is used, and defects are reduced—both of which directly lower costs.

Additionally, working with an injection molder who can identify opportunities for improvement during a design for manufacturing analysis can result in significant savings. Identifying issues early on—such as radius, draft angle, wall thickness, gate location, and other moldable features—will eliminate financial and cosmetic issues down the road. In fact, up to 80 percent of manufacturing costs can be determined by design decisions.