Injection molding is a broad term used to describe one of the most important processes in the manufacturing industry. It’s a process that requires a mold, typically made of metal with a cavity in the shape of the desired part. Molten plastic is injected into the mold and ejected. The process repeats to produce thousands of identical parts. It’s safe to assume that every large-volume plastic part on the market has come from an injection molding machine because the benefits of using injection molding for production are numerous. These benefits include low cost per part, short cycle times, extensive materials, and compatible, in-tolerance parts.

There was a total of 16 measurements recorded for each cycle. The research continued for four years. Thousands of machine cycles were run and recorded on chart paper to be individually analyzed. Test bars and plaques of various thicknesses were molded and measured. Machine adjustments were made to cause dimensional variations and cause part defects, such as: voids, sink marks, burn marks, and flash. In nearly every case, the defect could be directly attributed to one or more of the four basic plastic processing variables.

Once injection molding is chosen for a specific application, the next step is often whether to use insert molding, overmolding or just stick with plain injection molding. When trying to weigh the advantages of the processes, it is important to accurately define the product application. Each of these processes has specific use cases that are suited to different product types. It can be difficult to gauge which process will best suit your particular product, so it’s good to get expert advice early on. Contact a Xometry representative to leverage decades of vast manufacturing expertise. We will help steer your design decisions in the right direction so that you can choose between insert molding vs. overmolding or just injection molding.Â

In early 1963, Don Paulson, a professor at the General Motors Institute, began a different approach in his research on the causes of mold part variations. The basic premise was plastic processing had to follow the same laws of physics, as all other processes, and that the molding process was simply a four-step sequence of energy inputs and removals.

Overmolding is essentially a type of insert molding. However, overmolding vs. insert molding is, as the name suggests, plastic is molded over another molded part. The first component is made inside an injection mold, and it is then placed into a second mold to add the over-molded material. This technique combines multiple plastics for either practical or aesthetic purposes. For example, one might use different durometer plastics to mold a softer plastic over a more rigid one to make a part easier to grip. Using multiple colored plastics in an overmolded part can also distinguish the product from other brands. Overmolding is regularly used on the handles of tools like screwdrivers, power drills, or toothbrushes.

Over the years, numerous companies and researchers set out to determine which machine controls to use to eliminate each specific part problem. An example was an Eastman Kodak research project in 1962 to establish how to control specific dimensions in their Instamatic film cartridge. In a design of experiments project, and after six months of molding and measuring, the report concluded that the dimensions were being affected by:  barrel zone temperatures, screw RPM, injection pressures, holding time, fill time, and back pressure. In the conclusion, the author states, “all of the above machine settings had an effect on part dimensions and further study would be required”.

Various sub-processes add further capabilities to this already versatile technology. This article will specifically explore insert molding vs. overmolding and the advantages of each.

This is the third post relating to Paulson injection molding courses and the application of Scientific Molding Packing pressure and gate seal- If you’ve followed our sequence of machine control settings, you’ve learned about fill rate control and the velocity to...

For decades, the idea that specific machine control settings would directly correlate to specific part problems and their solutions seemed ingrained in the industry. However, that was wrong.

A molding machine was then instrumented to ensure that each molding cycle could be examined to check for unintended machine or plastic variations. These instruments measured and recorded the machine timers, barrel temperatures, screw travel, screw RPM, back pressure, injection pressures, and clamp force.  In the mold, three pressure transducers and thermocouples measured the plastic pressures and the mold temperatures. They also measured fill times.

Despite the many benefits of insert molding, a few disadvantages need to be considered before choosing to use this sub-process. Â

This blog post continues the Paulson Training series on learning injection molding as a science - Scientific Injection Molding. From the plastic's point of view there are only 4 basic variables in the injection molding process - plastic pressure in the cavity, melt...

Insert molding can also eliminate the need for fasteners by including the necessary metal parts in the mold, thus firmly securing the parts into a single bonded component.

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Injection molding, which includes the sub-processes insert molding and overmolding, is a versatile and low-cost manufacturing production process that is used in the large majority of consumer products. Injection molding often results in the lowest cost per part when compared to other manufacturing techniques like CNC machining and even 3D printing.Â

More and more molders are turning to what has become known as "scientific molding" in an effort to systematize their injection molding processes, make them more controllable and make them easily repeatable. As we mention on this site and in many published articles...

One of the most common applications for insert molding is the creation of metal attachment features for fasteners. Fasteners enable assemblies to be securely assembled and disassembled without product damage. Heat-set threaded inserts are molded into plastic to reduce the risks of thread damage during installation.

By Donald C. Paulson (As published in Plastics Business Magazine)   More and more we hear the term Scientific Molding used to describe the ideal injection molding process. But what does it mean exactly? Opinions vary widely. Allow me, as a long-time researcher...

It is very important to understand the Velocity to Pressure (VPT) setpoint in order to set up a robust scientific molding process. Not very many years ago, injection molding machines commonly used a hydraulic injection pressure setting and an injection timer to fill...

Despite the many benefits of overmolding, a few disadvantages need to be considered before deciding to use this process. Â

There are various sub-processes within injection molding that add further capabilities to this already versatile technology. This article will explore insert molding vs overmolding and the advantages of each.

Was browsing through a forum at the Plastics Today website and ran across a thread that brought back memories. Today, Decoupled Molding™" and Scientific Molding are commonplace. But when did these concepts REALLY begin to be used in the injection molding...

Each of these molding steps 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. These three equations applied to the molding process required only four measurements during each molding cycle. Those four measurements are the melt temperature, the fill time, cavity pressure, and the mold temperature.

Insert molding is a subset of injection molding techniques similar to overmolding where metal components are placed into a mold cavity before the actual plastic injection. The insert is precisely positioned inside the mold either manually or by a robotic arm. The mold then closes, and plastic is molded over the insert, creating a single part.

In the November 2012 issue of Plastics Technology magazine, there was an excellent article by Kip Doyle in their "Know How" column (John Bozzelli took a well deserved month off). The title of the article was The Top 10 Reasons Why Molders Fail at Implementing...

The injection molding process for plastic was developed more than 100 years ago. A dynamic growth in all processing methods occurred after World War II. As plastics achieved wider use, it was apparent that production personnel had to learn how to solve part quality and consistency problems. The method used was to determine which of the 20 or so machine controls would solve each type of part problems, e.g. dimensions, weld lines, voids, sink marks, warp, etc. But there seemed to be little or no correlation between machine control settings and most of the molded part problems.

First, the research was proof that plastic processing follows the same physical laws as all other materials, and secondly, the properties and characteristics of the molded parts are determined by the four basic plastic variables.

For decades, the idea that specific machine control settings would directly correlate to specific part problems and their solutions seemed ingrained in the industry. However, that was wrong.

In the past, the training of competent molding personnel has required years of experience on the production floor. This new understanding of molding as a science based technology allows personnel to learn injection molding from the plastic’s point of view and understand the actual causes of part defects. Molders must still learn machine setup, the operation of each machine control and the effects of each machine control on the plastic. The raw material must still be monitored, and the machines must be maintained, but the decisions on best control settings, best cycles and how to solve molded part problems will be science-based. Experience has shown that learning plastic processing from the plastic’s point of view is far faster and more effective than the traditional method.

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