This blog is the third in our series on statistical process control (SPC). In the previous blogs, we discussed the basics of statistical techniques and process capability indexes. In this blog, we will be focusing on control charts and their core benefits in the manufacturing landscape.
The control chart is a very helpful tool in identifying unwanted variation in a production process. The goal of statistical control is to identify process variation and to determine which variation is beyond our control. While some variations are inherent to the process, others are special or assignable. These deviations are outside of the “normal” variation that we typically see in a process. It can be identified using statistical tools to be reduced or eliminated from the normal process.
To understand control charts, let’s first discuss variation. In a perfect world, there would be no variation. Whenever we turn on a machine, it would produce the exact same part every time. However, we don’t live in a perfect world - machines fail, internal parts abrade, molding tools wear out, temperatures change, and materials subtly change from one production badge to the other. There are several inputs to a given production process that must work together to produce parts that meet customer requirements. By measuring key characteristics of the finished part, we can evaluate the manufacturing process. Using control charts, we can identify inherent variations from special variations (e.g. an injection mold wearing off or an improper machine setting). By eliminating these unique discrepancies, we can return the process to “normal”.
The two types of control charts that are regularly used at GMN Plastics are individual charts and x-bar R charts. As seen in the below example, both these charts feature two elements – 1) a center line which is the mean (average) for the particular data set being studied, and 2) upper and lower control limits which are statistically calculated from the same data set. Measurement data for key characteristics are collected and entered at regular intervals over time.
The control limits, calculated statistically, represent plus/minus three standard deviations from the average (mean). These lines represent the threshold at which the process output is considered to be statistically “unlikely”. In other words, the control limits represent the division of the natural variation of a process from the “unlikely” variation, occurring due to special or assignable causes, that can be eliminated from the process. Data points that appear outside of these control limits or unusual data runs (data increasing or decreasing over six or more successive measurements) should be investigated to determine and eliminate the source of the assignable variation.
One of the biggest advantages of identifying and addressing variations early in the production cycle is to prevent problems before any out-of-specification parts are produced. It maximizes machine and material efficiency, which in turn lowers production cost and time. The various statistical tools employed by the process engineers at GMN Plastics continue to play a pivotal role in meeting customer demands and consistently building high-quality parts.
This blog is the second in our series on statistical process control (SPC). In the previous blog (read here), we learned about the fundamentals of statistical tools and techniques. In this blog, we will be focusing on one of the most commonly employed statistical tools in the manufacturing industry – process capability indexes (Cpk).
Process capability index is an indicator of how the production process is performing with regards to key process control parameters and customer specifications. Besides the obvious reason of satisfying customer requirements, there is another reason to develop and use capability indexes. They can be critical predictors of future performance and a robust method of measuring the ability of production processes to produce high-quality parts consistently.
The letter “C” in SPC stands for control. But, what are we controlling? Statistical analysis of a production process is all about controlling and reducing variation in the process. It aims at identifying and separating the natural causes of variation, that are inherent to the process, from the special or assignable causes that can be controlled, adjusted, and/or eliminated. Process capability is the ability of a process to produce a product that is both accurate and precise. The accuracy and precision of a set of measurements can be illustrated as follows:
Cpk takes into account both the accuracy and the precision of the measurement around the average. Statistical software takes measurement data and shows the process capability as a single number that represents the process’ ability to provide both – an accurate and precise product. At GMN Plastics, we aim for a Cpk of 1.33 or greater for most of our customers. The core benefits of creating a process that delivers high-level capability include optimizing manufacturing time and materials, reducing scraps and re-work, and equipping the production system to create more products in the least amount of time possible.
Ultimately, process capability is all about creating products that meet customer specifications with a minimum variation over time. Stay tuned to learn more about control charts in our next blog. Until then, check out our other blog on Qualification process: Four parts to ensure part consistency.
As customer needs become more nuanced, it is incumbent on us, as injection molders, to continually innovate and improve our processes to meet their evolving demands. The tools of statistical process control (SPC) are critical in understanding process capabilities, identifying unwanted variations, and refining manufacturing processes. Overall, it enables us to efficiently and consistently meet our customer’s sophisticated needs for quality, lead time, tolerances, delivery, and cost.
Primarily developed by Walter Shewhart at the Bell Labs in 1920s, statistical techniques have been around for decades. Competitive companies worldwide have implemented a wide array of statistical tools to help reduce costs by mitigating scraps, re-work costs, and variances in production processes. These tools range from simple graphing to more complex analysis including Pareto analysis, histograms, capability analysis, fishbone charts, and control charts.
In recent times, advanced statistical software has made “data crunching” easy and efficient. At GMN Plastics, it provides us with a quick overview of how our injection molding processes are performing by analyzing data from internal product characteristics and/or customer-driven product features. This data can be viewed in several forms - as a line graph (Individuals data charting), or by stratifying data into a histogram (including process capability indexes), or a control chart (typically x-bar/R). These tools allow us to understand process conditions and provide actionable data to our engineers in the event of an unforeseen production issue or bottleneck.
We, at GMN Plastics, work with a broad spectrum of part sizes, shapes, forms, and complexities every day. When manufacturing a wide array of components for diverse customers and industries, it is critical to identify machine capabilities and production processes. Being able to make prompt decisions based on statistical data, developed during both initial qualification and in-process production, gives us flexibility in production and allows us to develop sound process controls.
In our upcoming blogs, we will discuss two of the most commonly used statistical tools at GMN Plastics – capability indexes (Cpk) and control charts. Until then, stay tuned and visit our website to learn about our plastic manufacturing capabilities.
There are several factors that dictate the type of mold or tool that is best suited for producing complex injection molded plastic parts. Understanding the requirements for part design, material type, and product life cycles are essential to evaluating and selecting the optimal mold type. In order to define standards for injection mold construction and corresponding life expectancy, the Society of the Plastics Industry (SPI), now known as the Plastics Industry Association, has established the following mold classifications -
1) Class 101 - This class of tooling offers the highest quality molds compared to its counterparts. When production exceeds one million cycles, Class 101 is chosen for its ability to support high volumes. Designed for extreme durability, the mold base is made with heat-treated stainless steel that is hardened to a minimum of 280 BHN. Other molding surfaces, including the cavities and cores, also offer very high wear resistance and can withstand resistance from abrasive additives in the plastics.
2) Class 102 - Supporting medium to high production volumes (ranging from 500,000 to 1 million parts), Class 102 molds work best for abrasive materials and/or parts requiring tight tolerances. Similar to Class 101, the mold base and surfaces under this classification are also made with heat-treated tool steel to effectively combat premature wear and tear.
3) Class 103 - Class 103 tooling is typically made with P20 steel and is commonly used for low to medium volume programs, ranging between 250,000 and 500,000 cycles. While only some tools are heat-treated for wear resistance, the mold base is made with a minimum hardness of 165 BHN. Since the base is softer as compared to Class 101 or 102, these tools aren’t recommended for fabricating parts with stringent tolerances. Striking a balance between quality, performance, and cost, Class 103 molds usually fall within the average price range.
4) Class 104 - Moving a degree lower, Class 104 tools are good for manufacturing parts with non-abrasive materials. With the mold base and cavities constructed of either mild steel, aluminum, or alloys, this classification supports low-cost projects and low-volume production, not exceeding 100,000 cycles.
5) Class 105 - Known as prototype tooling, Class 105 is suited only for quick-turn prototypes or volumes under 500 cycles. The molds are made with extremely fragile materials including soft aluminum, epoxy, cast materials, or any other alloys suitable to produce minimum quantities. These tools exhibit accelerated wear and tear, low strength, and minimal durability.
While GMN Plastics utilizes class 101 through 103 for the majority of its production, it usually steers clear of Class 104 and 105 tooling. Utilizing the above SPI mold classification to determine the correct mold type for your project is crucial to ensure process repeatability, minimize production downtime, and reduce defects and scrap rate. With extensive experience and technical know-how, the engineering team at GMN Plastics can help guide you through the unique parameters for each classification to select the best mold type to meet your quality, production, and cost objectives. To learn more about our tooling and tool room services, visit our website here.
A US-based customer of GMN was designing an electrical connection between two plastic housings for an outdoor application. In order to establish the connection, it was vital to achieve a permanent, air-tight seal between the two housings. Given the nature of the design, even the slightest ingress of moisture or foreign particles would hinder the optimal performance and durability of the product. Hence, shielding the seal from dust and water was critical. Additionally, the seal also needed protection from extreme temperatures and flames.
Originally, the customer utilized a bead of silicone (silicone rubber paste) on the edges of the two housings that hardened over time to form a seal. However, this approach presented several manufacturing challenges and shortcomings. Dispensing a uniform layer of silicone rubber was not only cumbersome, but also inconsistent, leading to an uneven bond line. As the paste became rigid upon drying, it formed a seal that was susceptible to breaking under stress, thereby producing cracks and weakening the bond strength. The drying and curing of the silicone rubber paste also spiked up the processing time, creating a bottleneck on the assembly line.
The customer approached GMN to achieve a better form-fitting solution to prevent moisture ingress. After learning about the environmental conditions that the seal was required to withstand, GMN proposed a custom-fit Roger’s BISCO® silicone foam gasket. From the extensive range of BISCO® silicones available in the market, GMN narrowed it down to HT-800 family to strike the right balance between seal-ability and compressibility. As a Preferred Converter of Rogers Corporation, GMN delivered a high-performance solution with accelerated lead time and competitive pricing.
Roger’s BISCO® silicone, with its high flame resistance, seamlessly fit the needs of the project. In addition to excellent viscoelasticity, it provided high dimensional stability and sealing capability. Contrary to the previous solution, BISCO® silicone foam does not break under stress or pressure. It allowed for quick and easy application, eliminating the extra processing time associated with bead of silicone.
Although, selecting the right material wasn’t enough. Creating a custom shaped gasket to fit the exact configurations of the housings was equally important. Since the customer had initially planned to utilize silicone paste, they did not have the dimensions of the housings readily available. Based on the customer’s sketch and 3D file of the housings, GMN developed a CAD file for the laser tool to fabricate the gasket. By flowing into every nook and cranny of the surface area, the gasket flawlessly married the two housings together to achieve an enhanced seal.
With the help of GMN’s dedicated rapid prototyping team and equipment, we then created two distinct prototypes of custom BISCO® silicone foam HT-800 gaskets in two different thicknesses and durometers. It enabled the customer to test compression and seal strength of the two different gaskets and choose the most optimal solution.
GMN’s ability to determine and source the right material and create a tailored-fit gasket allowed the customer to meet the functional requirements of the project without compromising on the aesthetics. Given our extensive experience and technical expertise with die-cut components, customers can truly rely on GMN to efficiently provide quick design fixes and improvements.
GMN is welcoming the new year with exciting changes! Effective today, we are rebranding Elite Plastics to GMN Plastics. In addition to unifying the company’s different brands (GMN Aerospace and GMN Automotive), the new name and logo will continue to put the focus on our plastic services, while also reflecting the full extent of the vertically-integrated capabilities and solutions that GMN can provide.
This rebranding initiative has allowed us to reflect on all the successes we have celebrated as “Elite Plastics”, and everything we aspire to achieve as “GMN Plastics”. We hope to embark upon a new journey in the growth of our plastics capabilities and services under the new brand name, GMN Plastics.
To learn more about the rebranding, read our press release here.
What makes plastic decoration at GMN unique? Along with dedicated engineers to support your projects from concept to creation, state-of-the-art equipment, a robust quality system, and complementary capabilities to plastic injection molding like value-added assembly, GMN provides all the decorating options for plastics under a single roof.
To determine the most appropriate plastic decoration technique for any application, there are multiple factors that go into consideration, including the plastic type, environmental requirements (exposure to fluctuating temperatures, humidity, and moisture), component dimensions, cosmetic requirements, regulatory requirements, and production volume. In this blog, we will be skimming over all the plastic decorating options available at GMN to understand their core advantages and pitfalls.
1) Pad printing - In this printing process, the image is engraved on a plate which is then coated with ink and transferred to the desired surface via a silicone pad.
- Same set-up for multi-color
- Can accommodate fine artwork and detailed graphics
- Difficult to print on heavy textures or surface finishes
- Cannot pad print on swooping or curved surfaces
- Cannot use metallic inks
- Size restrictions
2) Screen printing - In this method, the artwork is transferred on to the plastic surface using a mesh screen and a squeegee.
- Quick set-up time
- Can accommodate larger artwork
- Ideal for high-volume production
- Can only be performed on flat surfaces
- Needs different screens for different colors
- Longer curing times
- Challenging to achieve finely detailed graphics
3) Hot stamping - This dry printing technique utilizes heat and pressure to transfer colored foil onto the plastic surface.
- No ink-mixing or curing of part required
- Can accommodate metallic colors
- Ribbon can be expensive due to the minimum order of quantity (MOQ)
- Raised surfaces only
- Size restrictions
4) Laser etching - As the name indicates, this technique employs a laser beam to etch a design on the plastic surface which would have otherwise been difficult to mark mechanically.
- Details are permanently etched into the surface of the part
- Ideal for products with barcodes, lot numbers, backlighting, or intricate artwork
- Longer cycle times depending on size and detail of the image
- Size restrictions
5) Spray painting - Often used in conjunction with laser etching, spray painting utilizes either an automated robotic spray or manual hand-spray method to apply the ink on the desired parts.
- Can hide flaws on the plastic surface
- Can utilize the manual method for low-volume to mid-volume production and utilize the automated method for high-volume production
- Can accommodate multiple colors and materials
- Detailed masking may be required, making the process labor intensive
- Requires a clean environment
- Requires longer lead time
6) In-mold decoration (IMD) - This advanced technique allows for the printing of highly durable and complex three-dimensional shapes.
- Can achieve compound curves and complex 3D forms
- Well suited for designs incorporating small windows or backlighting
- Offers versatile decoration options
- Ideal for high-wear applications
- Development phase can be long depending on the design
- Automation can be expensive
There are typically a variety of pieces and processes involved in making a complete part. As a result, customers sometimes require several different suppliers to make each specific component of the assembly. Even smaller products can have a long list of components and suppliers. During the manufacturing process, costs can vary greatly and the time it takes for products to be completed depends on a range of factors, one of them being how long the supply chain is. In general, a shorter supply channel means your products will get to market quicker, with fewer costs. A great way to shorten your supply chain can be to partner with suppliers that offer value-added processes, or can provide multiple different services or aspects of production.
Value-add can be defined as a process where the value of an article is increased at each stage of its manufacturing, bringing an enhanced benefit and cost savings to the customer.
As a value-added supplier, GM Nameplate’s (GMN) plastics division in Beaverton, OR created a video that demonstrates the value-added assembly process of a medical part. In this video, you can see the stages that these molded parts go through to reach the completed subassembly. Similar to most projects at GMN’s plastics division, the process begins with injection molding. Once that part is molded, it can be decorated, depending on what the customer wants. Offering different decorating options, such as screen printing or hot stamping, after a part is formed is an example of a value-added benefit.
In the video, an operator can be seen placing 17 brass inserts in different bosses of the molded part. To make sure the inserts are properly installed every time, the operator places the molded part in a poka-yoke (Japanese term for “mistake-proofing”) fixture. The molded part will only fit in the fixture one way, so the operator installs the inserts into the correct bosses. These inserts are then heat staked, where a heating element makes contact with each brass insert. The insert then transfers heat to the boss, melting the plastic around the screw. This enables the screw to be removed without stripping the plastic.
Next, the video shows the part being placed in another fixture where a three-camera vision system verifies all the inserts were properly installed. This vision system also has a poka-yoke fixture to ensure consistent verification. Once the vision system notifies the operator that all inserts were properly installed, the part moves to the next value-add station. We see the molded part moved to an assembly fixture where a blue latch-spring component (which is also injection molded by GMN) is assembled to the main plastic enclosure. After this, an operator installs gasketing to the perimeter of the part. Finally, the part is inspected and then packaged for shipment.
From beginning to end, multiple different components and processes were used to make this part, all under one roof. This added value allows customers a cost savings as well as a streamlined supply chain, as several components were completed by one manufacturer, instead of multiple vendors for each individual operation. GMN takes a holistic approach to building your device, and the breadth and depth of our internal capabilities bring increased control, predictability, and reduced costs to your supply chain.
To watch this process in action, click play on the video below.
When you look at or feel a plastic component, you would usually assume that it’s made of one type of plastic. However, some plastic products are actually made using two different types of resin, sometimes more. You are probably familiar with this application which can be seen in plastic toothbrushes that have a rubberized grip. The main body of the toothbrush is made of a rigid plastic, while the grip is made of a rubberized plastic. Even though there are two different types of plastic present, both were formed at the same time using two-shot molding.
GM Nameplate’s (GMN) plastics division in Beaverton, OR recently created a video that demonstrates this two-shot molding process. The process is called two-shot molding because there are two different resins being injected by two separate barrels. There is a primary barrel, which injects the first resin, forming a rigid substrate in most cases. The secondary barrel then injects a different resin on top of or surrounding the region of the first substrate.
Depending on the size and intricacy of the part, you can design the tool to make several parts in each cycle. In the video, we see that two parts are completed during each cycle. On the left side, the rigid substrate is injected by the primary barrel and forms the backbone of the two components. The tool then rotates 180 degrees, and the rubberized plastic is injected onto those two pieces by the secondary barrel. While this is being done, two more rigid substrates are made at the same time again by the primary barrel on the left side. After the pieces are injected by the secondary barrel, an end-of-arm tool picks up the completed parts, and then the tool rotates 180 degrees once more, ready to start a new cycle.
Two-shot molding is ideal for higher volume projects, as more engineering is used in designing the two-shot molding tool. The tooling used for two-shot molding is intricate because it must inject two different plastic resins simultaneously, but only in certain features of the part. Two-shot molding is a much more efficient process for high-volume projects compared to conventional over-molding, where you use two separate tools to manufacture parts with different resins. Due to this efficient output, two-shot molding is frequently used in the automotive and medical industries.
Click on the video below to see the two-shot molding process for yourself!
Due to our ongoing commitment to the medical device industry and growing demand, GM Nameplate’s (GMN) Beaverton, OR Division attained ISO 13485:2003 certification. The Beaverton, OR Division, GMN’s dedicated plastics facility, received this certification after auditing and approval by the Orion Registrar on May 9, 2017. This ISO standard is in regard to the quality management system requirements specific to medical device manufacturers. GMN’s Beaverton, OR Division is the third GMN division to obtain this quality certification.
What does this standard mean for GMN customers?
Meeting the strict standards of ISO 13485 assures that GMN can continue to support existing and future customers in the medical industry. ISO 13485 demonstrates that GMN meets regulatory standards and legal requirements to operate in the medical device industry, reduces risk effectively, and has systems in place to consistently yield safe and effective medical device components.
With little room for error in the medical industry, GMN has continually worked to uphold a quality system that meets the highest quality standards in order to produce best-in-class solutions. This certification validates the strength and sustainability of our processes which differentiates us from competitors.
Dedication to quality
For decades, GMN has shown commitment to the medical device industry and a dedication to creating quality products. Compliance with ISO 13485 ensures that the medical device components and sub-assemblies produced by GMN will meet or exceed thoroughly planned specifications every time, without exception.
As a company that supports multiple regulated industries, such as medical, we are committed to ensuring that our Quality Management System is robust and flexible enough to meet the variety of challenges presented by our wide range of customers and industries. With this new recognition, GMN’s Beaverton, OR Division shows its ability to handle increasingly stringent and diverse customer requirements. In addition, the ISO 13485 compliments ISO 9001, another quality standard that GMN has long been in compliance with, which reflects our continual efforts to broaden our quality system to better align with the current Good Manufacturing Practices.