please don’t limite your design when you design a plastic part, because it Increases your design options and requirements and still keep costs down, and plastic is easy in producing complex shapes. you know, when we design a metal product, there are many many design limitations
if we put several metal stampings or castings fastened together, the additional assembly cost will be generated, but a single injection molded part incorporating the features of the total assembly will meet your requirement. Even we need multiple assemblies, snap-together features of the plastic parts can eliminate any fasteners.
In today’s market, time is a very important facter, especially for a new product development, Injection molded parts just can shorten the time to the market place, because they are easily processed into complex shapes with high quality, but it would be impossible for metal parts.
Injection molding is a complex process with countless variables despite its widespread use in different industries. Many factors can impact the final result, so you must start with an excellent design to help manage the manufacturing process and ensure quality output while minimizing resource consumption and production errors.
There are several positive ways that a good design can impact the injection molding process. In this article, we will explore some of the most crucial product design best practices for manufacturers.
The cost per part of the process can be significantly reduced with a good mold design. For example, designing a mold for longevity, reducing undercuts, material selection, and designing a family or multi-cavity mold can help reduce cost. In addition, a high-quality mold, designed accurately and with suitable materials, can last for a very long time while increasing production speed and further driving down costs.
The goal of injection molding is to manufacture many products with minimal variation between each piece within tight timeframes. Of course, many variables are intrinsic to the injection molding process, leading to discrepancies between each piece. Still, a well-designed mold can help increase the repeatability of the process. Plus, once a mold is designed and put in place, it lasts for a very long time, delivering significant return on investment (ROI) while fostering additional benefits like improved production speed and productivity.
The design, material choices, and other factors can increase the time and parts per cycle of the injection molding process. Reducing the length of each cycle means more parts per hour, allowing you to produce a large number of parts more quickly. Therefore, the more parts made per hour, the more productive the process.
Note that this can also affect the cost – higher productivity can drive prices down yet further, particularly when coupled with improved mold quality and reduced production errors.
BETTER VISUAL RESULT
A poor design can lead to many visual defects in the final part. For example, warping, sink marks, drag marks, and knit lines can all impact the visual appeal of the manufactured part. A good injection mold design will take all of these factors into consideration, ensuring that the final product looks great.
Visual appearance is more than “mere aesthetics” – your customers will undoubtedly notice, mainly if their customers complain. Lines and marks mar the surface, leading to an inferior appearance despite using high-quality materials.
It’s essential to consider the durability of both the mold and the parts. The material and design of the mold itself can affect the number of parts that can be successfully manufactured from the mold before a replacement mold is required. The design of the mold can also impact the durability of the produced parts, reducing breakage. Less breakage and more outstanding part durability mean reduced production costs but also less tangible benefits, such as brand recognition.
Common Problem Areas in plastic parts
Warping is a common problem in injection molding, but there are ways to mitigate the impact of warping on the final product. The three main factors that contribute to warping are cooling rate, cavity pressure, and fill rate. Throughout the entire injection molding process, many things are happening to the material on a molecular level. Therefore, understanding the process steps can help facilitate a design that reduces the warping that occurs in the final product.
Different materials have different shrink rates. The material used can significantly increase the chances of warping. The temperature will also affect shrink rate and impact warping, so you must control it properly.
2. SINK MARKS
A part with walls that are too thick or improperly designed ribs is especially susceptible to sink marks. A sink mark is caused by the interior of a part solidifying before the surface is completely solid. This will lead to a small indent on a surface that should be flat.
Ideally, the maximum thickness at the base of ribs or bosses should be less than 60% of the thickness of the perpendicular face wall.
3. DRAG MARKS
When the plastic shrinks, it will apply pressure on the surface of the mold. When the part ejects from the mold, it can scrape against the side of the mold, leading to unsightly drag marks. Incorporating proper draft angles into the design will minimize the chance of receiving drag marks during the ejection process.
4. KNIT LINES
Knit lines are hair-like discolorations that can occur when two flows of resin meet. Knit lines not only look bad, but they can also cause the part to weaken. Parts with sharp angles or holes are more likely to develop knit lines. A good design will reduce the chance of knit lines by taking this problem into account. Some resins are less likely to cause knit lines, and thicker walls can slow cooling, making knit lines less likely to form.
5. SHORT SHOTS
A short shot occurs when the mold cavity is not filled, leaving a void or thin area in the final product. This is usually due to trapped air causing the improper flow of material. A poor design can greatly contribute to the likelihood of short shots. Conversely, a good design works to prevent this issue.
Wider channels or gates will improve the flow of material.
The speed or pressure can be increased to improve material flow.
If the material cools too rapidly, short shots are more likely to occur. Increasing the temperature of the mold can prevent rapid cooling of the material.
Vents can be incorporated into the mold, allowing trapped air to escape and preventing short shots.
Let’s first take a look at three significant considerations to keep in mind throughout the design process.
1. DESIGN FOR MANUFACTURING
In the injection molding industry, this is commonly known as DFM, and it is one of the first things you need to consider when beginning your design process.
“Design for manufacturing” basically means that you keep the many factors involved in the manufacturing process in mind as you are designing your part. Your technical specifications need to align well with the capabilities of the manufacturing process and should also consider the capabilities of the specific manufacturer you will be working with. Each manufacturer utilizes different materials and equipment, and the design of your part should take this into account. We recommend finding your manufacturer before beginning the design phase. Using a cooperative approach, you can ensure that your design is adaptive to what your manufacturer can do, rather than the other way around.
When designing a product, it can be easy to focus exclusively on how to make the product. However, this product will likely be purchased by a consumer somewhere, meaning you have another critical thing to consider: how will the product be used? Think about where and how the product will be used. Will it come into contact with water or any corrosive materials? How often will it be used? How many uses can the product withstand before it breaks?
Factoring in the eventual use of the product will inform your design process, making sure you don’t end up with an excellent design for a product that doesn’t work as intended. It will also help ensure that you’re able to deliver a product that meets or even exceeds expectations in terms of usability and durability, both of which help bolster brand image in the minds of your customers.
Assembly isn’t a necessity if your part consists of just a single piece. However, designing a part that will eventually fit together with other parts becomes very important. Therefore, it would be best if you considered how easy the final combination would be to assemble. Even if your cost per part is meager, a difficult assembly process will increase your overall costs, as well as the time to full completion.
The biggest challenge in injection molding is the process of designing a mold. There are almost no limits to your creativity (see the MOMA section on plastics here), but you can do the designs in clever and less clever way from a manufacturing point of view. Plastic manufacturers highlight this aspect as the most crucial part of injection molding. There will be no successful plastic part designs for injection molding if there is no perfect mold from where it is formed. The biggest factors to designing a mold are part and tool design. Getting these factors right means faster production, better quality and reduced costs while having them wrong could substantially affect these production aspects in a negative manner. Here are other factors you need to consider with injection molding during the product development and prototyping.
1. Wall thickness
Thin walls are advisable in plastic manufacturing for shorter cycle times and being able to produce more plastic part designs in shorter production lead time. Thinner walls also makes the cooling process faster. Ideal wall thickness from 0.08″ (2mm) to 0.16″ (4mm), but thin wall injection molding can go as thin as 0.02″ (0.5mm).
However, wall thickness also depends on the type of plastic material being used. Here are the recommended wall thickness for various plastic materials; ABS resin is between 0.045 and 0.140 inches, Acrylic is at 0.025 –0.150, Liquid crystal polymer at 0.030 -0.120, Nylon at 0.030–0.115, Polycarbonate at 0.040 – 0.150, Polyester at 0.025 –0.125 and Polypropylene at 0.025– 0.150.
Adding ribs helps increase the bending stiffness due to the increased moment of inertia. This is a suggested option instead of adding thickness to the wall. Here are recommendations with ribs in plastic production;
Rib’s thickness should not be more than 60% of the nominal thickness value.
Height should be three times lower than the wall thickness.
Draft angle is at 25 degrees.
The ribs position must be perpendicular to the axis where the bending occurs.
Corners of the attachment points must be rounded instead of having them pointed.
Bosses are layers wherein fasteners are attached and threaded inserts are located. Recommended specifications for bosses are the following;
Bosses’ wall thickness should not be more than 60% of the main wall.
Base radius should be at least 25% thickness of the main wall.
Bosses should be supported by ribs connecting to walls adjacent from their position or gussets at the bottom the mold design.
Ribs should be used to isolate bosses in corners of the design.
thanks for sharing your idea about plastic product design
our company focus on plastic product design, any question please feel free to leave a message here :-)
plastic product design has it’s special requirements
plastic product design is quite different with metal product design
Just because of the particularity of plastic molding
in my opinion,Plastic parts are still widely used in all walks of life
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about plastic product design, I want to say every designer needs to learn some professional injection molding knowledge
I agree your opinion
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But I found that the products with aluminum alloy shell in our local market are very popular
our products still need plastic parts.
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Very energetic blog, I love it, actually plastic product has a lot of unique advantages
Plastic product has many advantages
I agree with you at all! thanks!
sometimes it depends on industrial desiner’s ideal!
you are a real plastic product designer
A good industrial designer really need very broad knowledge
Only designers have injection molding experience or kowledge, he will know these design options
you have this conclusion, no doubt it just because of plastic forming method,
but plastic product design is still not easy, because Too many things need to be considered
But the metal forming has its advantages, you didn’t write them out
plastic product design is not easy, designer should have injection molding Knowledge
but an excellent designer should have very rich experience and knowledge in the industry when designing a Plastic product
for plastic product design, Your blog summed up well
Yes！This is clearly right.This is also the advantage of plastic products。Easy to get and easy to handle
as a product designer, I agree your point at all, but sometimes, our customers always complains that plastic part looks very cheap, maybe because they don’t really understand plastic part design…. too much need to explain
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Please write more details about this topic, also I have some experience in plastic product design, I will send them to you or share here
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