When we hear the term precision, you might think about a Swiss watch, a fighter jet, a robotic surgery arm. Across the board, precision is defined by accuracy.
What does accuracy mean in molding terms? Precision molding requires all of the factors that control the injection molding process to be at best-in-class levels. This includes the molding equipment, the mold, the resin, the process used to control the molding, and the people working on the project. Each of these important factors all have strict requirements and specifications that must be met to be able to produce molded products that can be called “precision”.
Resin: Where Challenges Arise
Let’s start with resin. In the injection molding process, resin is typically the largest variable and the one item that creates the most challenges. As advancements in resin technology have been made, allowing molded products to achieve new and enhanced functionality, this has created new challenges for the molder. Higher melt temperatures, cooling temperatures, and resins that flash in micro portions of an inch all can accelerate tool and equipment wear.
Resin itself has myriad limitations that affect the achievable level of precision in any given part configuration. Glass-filled materials that can withstand elevated temperatures tend to cause molded parts to warp or distort. All resins have limitations on dimensional accuracy and repeatability. Not every resin can maintain a tolerance of .001”, especially when these dimensions must meet a capability of 1.33 CpK or better.
Included in the resin topic are the requirements for proper handling, storage, drying and conditioning of the resin prior to molding. Normally, precision parts include a requirement for 100% virgin resin. Precision parts may include a requirement for narrow-spec material. All resins have a range of performance. Precision parts require a narrow performance range.
Eliminating Variability
To achieve a manufacturing process that can support molded products at a precision level, process variability must be eliminated as much as possible. You can’t afford unexpected surprises during serial production. The mold and the molding equipment should be standard and not change over time – this is a key way to prevent variability. The mold is made from tool steel, and its shape and size should not change over time, except for minor changes caused by wear, abrasion, or corrosion. The molding press should not change over time either, except for a few high-wear items.
Another important item to success is up-front planning. Injection molding is a process involving many people throughout many functions of the company, all working together to guarantee a positive result. The process starts with an in-depth planning process (APQP). This is a cross-functional process ensuring all functions in the organization have their needed issues addressed in the planning process. Part of this process is an MFA (manufacturing feasibility analysis). In the MFA process, the product drawing and specifications are reviewed in detail by a team of engineers who jointly determine if the product can be produced as specified or if changes/suggestions can be provided to the customer for review. The earlier the molder can get involved in the planning process, the greater the likelihood of a successful product launch.
At Chemtech Plastics, we begin every new project with a full computer simulation of the mold. This information serves as the starting point for the development of the master process. All of our mold standards are based on best-in-class expectations and requirements. Precision molds are typically an SPI/SPE 101 or 102 class mold. If ultra-tight tolerances are required, tool steel selection becomes very important.
The other main area of focus is the molding press and auxiliary equipment. The press and equipment should allow for a stable, repeatable, and accurate molding process. Variations caused by delays in press functions or wide tolerance ranges in the press’ operation cannot be tolerated. At Chemtech, we purchase electric and hybrid presses, some with planetary drives. Our Sodick press allows for very accurate shot control. These highly sophisticated molding cells require regular routine maintenance to stay at top performance levels.
Another big part of the equipment portion is the highly sophisticated process controller and hot runner controls. Injection molding today is no longer an art form – it is a science. The equipment technology has advanced to a level that allows a precision molder very accurate control of the molding process at a finite level.
Cooling is of great importance for temperature control of the mold and molding equipment. Having a water supply system capable of supplying turbulent flow at every press is a must. Ensuring adequate water flow in every cooling channel should be part of the master process development. The water supply should have the proper flow capabilities, and it must be clean and protected against plaque and buildup in the cooling channels. If not, maintaining proper mold cooling becomes more difficult.
How to Develop a Master Process
The development of the master process should be a statistical study conducted over time. A reliable master process starts with items like a short-shot study, gate freeze analysis, viscosity curve study, and results presented in an optimized master process with the largest possible processing window. When a molded product has a very narrow processing window, it is only a matter of time before a discrepant product is produced. The master process should become a “stake in the ground,” and if the process needs to be changed, the process should stop until the cause of the needed change is found and corrected. To produce precision parts, the process must be stable and repeatable. The main variable is either changes in the resin or changes in the equipment.
Precision Molding at Chemtech
At Chemtech Plastics, we believe the secret weapon to high precision is our people. We tell everybody who visits us, “Anyone can buy capital and equipment, brick and mortar, but you can’t buy a passionate, dedicated workforce.” Successful precision molding demands a passion for excellence. Our process starts with a group of tooling engineers who design and build precision molds for the highly trained process engineers to develop the master process, and then pass the parts off to the quantity engineers who inspect the parts and provide the final quality submission. There is a large support group required to support these technical experts.
Precision injection molding requires all elements of the process to be at best-in-class levels. Chemtech Plastics takes pride in our ability to meet these stringent requirements. We have been supplying precision injection molded components for over four decades. We’ve earned a reputation for supplying some of the industry’s most challenging applications. Whether it’s robotic surgery, safety-critical functions in your car, or your next most important component, Chemtech Plastics is your precision injection molding leader.
