All the latest news from the industry weekly compiled by the editorial team for you free of charge.
This eMail is already registered.
An unexpected error occured.
Please accept our Terms of Use.
Registration successful.

DIE & MOULD Mould-filling simulation

Mar 28, 2019

Instead of engaging in slow, expensive prototype iterations and test cycles to satisfy manufacturing requirements, designers, mould - makers, and manufacturing professionals can leverage mould-filling simulation software to optimise parts for manufacturability, refine tooling to improve quality, and shorten cycle times to reduce manufacturing costs.

In nearly all types of product development—from consumer electronics and automobiles to children’s toys and medical devices — the use of components made from plastic materials has steadily increased.

However, anyone involved in the production of plastic components knows that making plastic parts is more challenging and complicated than designing in metal. More than 80% of the plastic parts used in products today have to be injection-moulded — the process of injecting liquefied plastic materials into a mould, cooling/solidification of the material, and ejection of the moulded part. In many ways, injection moulding is as much an art as a science.

Successfully producing injection-moulded parts that are free of manufacturing defects requires a complex mix of time, temperature, pressure, material, and variations in tooling or part design. Designers, mould-makers, & manufacturing professionals must balance all of these variables to make quality parts.

  • Does the part geometry meet draft and wall thickness requirements?

  • How long should the injection/cooling/ejection cycle be? What’s the optimal temperature for the material, cooling channels, and mould?

  • What’s the right filling/packing pressure and best material to use for a particular part?

  • And, will the use of special inserts, side actions, additional injection gates, special secondary operations, or unique cooling channel designs improve part quality or shorten cycle times?

The traditional approach for answering these questions and producing quality parts is inefficient, expensive, and disjointed, resulting in slow, costly design iterations and test cycles that can actually compromise the rationale for using plastics and put a manufacturer at a competitive disadvantage. Part designers often rely on iterations with the mould-maker and the mould-maker’s expertise to evaluate the manufacturability of a part, and balancing industrial design and manufacturing considerations takes time. Although mould-makers draw upon their experience and expertise to develop moulds, they still need to create prototype moulds to validate mould performance, typically after completing trial-and-error iterations that add time and cost to the process. Charged with optimising production run cycles, manufacturing professionals frequently need to iterate with designers and mould-makers. Unfortunately, improving part quality at this stage is often difficult and generally only resolved through mould rework. With moulds ranging in cost from $10,000 to more than $1 million, mould rework is a costly and time-consuming proposition.

Complicating the process further is the fact that in today’s global economy, designers, mould-makers, and manufacturing professionals often are located around the world and speak different languages. For example, internationally scattered injection-moulding operations—such as having a designer in USA, a mould-maker in China, and a manufacturer in Mexico — are much more common than in the past. The time and language barriers inherent to these arrangements make resolution of injection-moulding challenges even more difficult. What’s really needed is a common, accurate mould injection simulation platform that cuts across barriers and allows designers, mouldmakers, and manufacturing professionals to collaborate more efficiently and effectively in a virtual simulation environment, without resorting to costly prototype mould cycles.

Injection moulding challenges

Every professional involved in the development and production of injection-moulded parts and tooling—from the original designer to the mould-maker to production personnel—face unique challenges. Each has their own point of view, focus, and specific types of issues. Designers care about the design aesthetics—the look and feel of a part. Mould-makers contend with quality considerations and want to make sure that their tool produces acceptable parts. Manufacturing personnel want to make sure that production runs as smoothly and efficiently as possible. Despite having different perspectives and roles, everyone involved in the injection-moulding process will benefit from having access to a plastics simulation environment.

Designers face manufacturability concerns

While a designer initially concentrates on design requirements—including form, fit, and function—he/she increasingly needs to assess whether a particular design is manufacturable, especially for injection-moulded plastics parts. The most beautiful and elegant possible design has no business value if the geometry cannot be manufactured at volume and then assembled and sold at a profit. Even though designers have access to tools for checking draft angles and wall thicknesses, they typically rely on their mould-maker’s recommendations and the results of iterative testing conducted with prototype moulds to minimise a range of potential manufacturing issues—tests that add time and cost to the process.

What can happen?

The potential for encountering quality issues on injection-moulded parts is great, and because these issues need to be resolved before moving to production, so is the probability of unplanned iterations and modifications to both part and tooling designs. Manufacturing defects occur for a variety of reasons related to the mix of variables that influence injection-mould performance. For instance, part warpage, also called “potatochipping” because of the wavy appearance of the part, happens when a part deforms after it is ejected from the mould. When a mould does not fill completely, air traps, sink marks, and flow marks can appear on the part. Did the designer allow for shrinkage of the part? Are the parting or weld lines (where different parts of the mould come together) in the preferred location?

Collaboration demands communication

Because designers need to eliminate a wide range of manufacturing defects from injection-moulded parts, as well as work with manufacturing partners to optimise production, they need to collaborate effectively with their tooling & manufacturing colleagues to make changes related to manufacturability without overly compromising the industrial design of a part. Language and time barriers can complicate this task, and designers need to understand the costs and delays associated with multiple design iterations with both the mould-maker and production personnel. However, because designers can’t predict the future, they tend to over-rely on the expertise of their mould-making and manufacturing partners, resulting in unanticipated iterations that create additional delays and unforeseen costs.

Pressure to cut costs

To compete successfully, mould-makers are increasingly under pressure to develop tooling that produces quality injection-moulded parts as quickly and affordably as possible. Of course, experienced mould-makers have broad knowledge regarding part manufacturability and the impact of changing the variables related to injection-moulding production, particularly with simple part geometries. Nevertheless, as designers strive to imbue products with innovation and sophistication, even the most experienced mould-makers need to create a series of prototype moulds and shoot many samples until they find the precise mix of injection-moulding variables that will produce clean, blemish-free parts.

How many prototype moulds are necessary?

Although veteran mould-makers take pride in their ability to gauge the manufacturability of specific part geometries, and know things like the minimum thickness of ribs to support ejection from a mould, predicting the exact number of prototype moulds required for configuring the injection moulding process, or the time and cost involved, is not as clear-cut. In addition to needing to validate that the final mould design will perform well, producing high-quality samples before ramping up to fullscale production, mould-makers usually need to conduct other trial-and-error prototype studies in order to reach the final mould design and specific injection recipe. For example, optimising injection gate diameters, locating gates in the most advantageous locations, improving cooling channel performance, or using special secondary operations generally requires additional time and iterations.

Balancing design & quality sensitivities

Mould-makers face the same communication and collaboration challenges as designers of injection-moulded parts. They need to be able to explain why the original part design geometry has to be changed due to manufacturability issues. This is why prototype mould cycles are so entrenched in the injection-mould tooling enterprise, because they serve to justify why design changes are necessary by demonstrating the defects and quality issues associated with strictly adhering to the initial design. Designers want to know the reasons why the part design that they laboured over needs to be altered, especially when such changes negatively impinge upon the design aesthetic. Mould-makers want to make quality parts, designers want to manufacture their designs, and prototype mould cycles are often the only way to reconcile the two.

Pressure to reduce cycle times

Once manufacturing personnel receive the final mould from the mould-maker, they too need to evaluate the tool from a production standpoint to determine if there are other modifications that can be made to reduce cycle times without opening the door to additional manufacturing issues. When you are shooting 500,000 to one million parts at a time, saving one, two, or three seconds in cooling time per part can result in dramatic time and cost savings. However, just like mould-makers, manufacturing personnel are blind to what’s actually going on inside the mould and have to rely on samples and tests to confirm that the tool will produce quality parts or discover that the mould requires additional rework.

Is mould rework required to speed production?

The first question manufacturing professionals need to answer is: Will this mould, material, and injection recipe produce quality parts or not? It’s critical for production personnel to verify mould performance because if they don’t, they may end up shooting a million bad parts. Similar to the prototyping performed by mould-makers, manufacturing personnel need to run samples to confirm that there are no structural weaknesses in the parts, no undesirable deformation in large-sized parts, and no poorly reproduced areas on parts with features having high aspect ratios. They can use the same trial-and-error approach to try to speed production, but ultimately have to determine if speeding up production will save more money than the cost of mould rework.

Optimising injection-moulded tooling

In their attempts to optimise production cycle times for specific injection moulds, production personnel may try different recipes, changing the length of cooling time in the mould, or raising or lowering injection pressure during filling and packing. They may also adjust temperatures in the mould cooling system as part of their efforts to shorten cycle times. Yet, just like designers and mould-makers, what they really need is access to a common mould-filling simulation environment that provides them with a view of what’s happening inside the mould and insights into the effects of changing these variables without having to shoot a part. This common platform can also improve collaboration with the designer and mould-maker regardless of language and time barriers.

Manufacturers can gain a substantial competitive advantage by leveraging SOLIDWORKS plastics simulation technology to shorten injection-moulded part and tooling development cycles, while simultaneously improving the quality of injection-moulded parts.

Courtesy: Solidworks, Dassault Systemes

Image Gallery

  • Mould-makers want to make quality parts, designers want to manufacture their designs, and prototype mould cycles are often the only way to reconcile the two

Companies related to this article
Related articles