Tip : Choose A Surface Finish To Meet Your Function
The surface finish on your parts can have many different functions. The best course of action is to decide what you need from your parts. Is it physical? Does it also need to have visual appeal? Once you know what function you need, you can then start narrowing your focus on a particular surface finish. Another decision pertaining to the finish is tied to what class of mold you need based on production volume and what material the mold will be made from. Steel molds are harder than aluminum molds and offer more options for surface finish. Steel can be polished for a smoother surface finish, which can be a better option if your product requires painting or another secondary operation to enhance your product.
Some of the finish options available include:
- Gloss, matte, or satin polish
- Leathery texture
- Etched with a designed logo
- Prepared for painting or secondary graphics
- Blasted for a rough uniform texture
Surface finish has more function than just physical attributes and visual appeal. Strategic texture and finishes can blend and hide parting lines and make undercuts possible. Finishes can also allow trapped gasses to escape the injection mold, which improves the molding process efficiency.
Undercuts In Injection Molding: A Brief Overview
Undercut molding is an essential process for creating hooks, grooves, and other elements that have a direct effect on the functionality of your part. Resultingly, it becomes absolutely necessary to include undercuts when your injection molding design has these features.
So, what makes undercuts so important that you cant avoid them in some designs? Here are the 5 most common scenarios where undercut injection molding becomes necessary.
Bosses Aid In Assembly And Mounting
Bosses can be added to the part design for assembly, locating, or mounting of a part. Improper placement of a boss leads to uneven wall thickness and can have a negative impact on the aesthetics, shrinking, or strength of a part.
Don’t Miss: How To Clean Out Mold From An Air Conditioner
Achieve Undercuts Success With The Help Of Rapiddirect
The undercut plastic injection molding process comes with a series of complications and intricate requirements that only the right manufacturing partner can help you navigate. RapidDirect possesses state-of-the-art equipment and has the most experienced team to deal with all your requirements and successfully deliver you the results with utmost consistency and at the best price.
RapidDirect doesnt limit itself to simply providing you injection molding services as well. We can provide a detailed DFM analysis that can help you optimize your part design to minimize any complexities and help you recognize the overall best course of action for fast results.
So get started with RapidDirect now! Simply upload your design files, and then configure material requirements and project details.
Tip #: Avoid Undercuts In The Tooling
An undercut in the injection molding tool is when the opening and closing of the tool doesnt allow a feature to be formed. In this case, it will be best to use a lifter and slide to form the feature rather than complicated shapes. In molding, simpler is better. The lifter and slide can form difficult shapes and still allow the part to be removed from the injection mold.
You May Like: How Do You Get Tested For Mold
Get Frames To Make The Mold
The first step in our injection molding setup is to create a mold. We will use epoxy to create our mold. Epoxy is actually a two-part liquid. It is initially in liquid form, but it can then be poured into a mold or frame. It then solidifies and hardens.
You need to get a frame in which you can pour the epoxy to make your molds. You will need two frames for two molds. Moth these molds will clamp against each other. Each mold will make one section of your injection molded part. You can buy a frame for making your epoxy mold here.
You can always make your own frame, but that will add a significant amount of time to the whole process. If you really want to make your own frame, then make sure that the frames have a cavity for the epoxy to pour itself in and that they also have alignment pins so that the two frames line up correctly. The link we posted above is for a set of frames which have the alignment pins and the cavity.
Eliminate Undercuts That Arent Design Critical
Undercuts are features that prevent the injection-molded part from being ejected cleanly from the mold without any structural damage. Undercuts can come in a variety of forms holes, cavities, or areas where alignment is not perpendicular to the molds parting line. A product designers best bet is to avoid undercuts altogether. They always make the injection mold design more expensive, complicated, and labor-intensive than necessary.
Still, there are a few design tricks to handle undercuts. The simplest way to fix an undercut is to move the parting line of the mold such that it intersects with the undercut. However, this tip is only applicable for designs with undercuts on the outside of the mold.
Bumpoffs, or stripping undercuts, are an option if the feature and material are flexible enough to expand and deform over the mold during ejection. The bumpoff should be far away from the molds support structures and have a lead angle between 30 to 45 degrees.
As a last resort, side-actions or lifters can fix undercuts when the mold cannot be redesigned to avoid undercuts. Side action cores are perpendicular inserts that slide in and out of the mold as it opens and closes.These mechanisms drive up cost and complexity significantly. Even with these solutions, it would behoove designers to steer clear of undercuts altogether and eliminate undercuts during prototyping.
Recommended Reading: Can Mold Spread From One Condo To Another
Design Best Practices: Optimizing For Plastic Injection Molding
High quality, efficient tooling relies heavily on good part design, advanced skills in mold design, and the manufacturing of the tool. An injection mold is a high-precision tool that must be rugged enough to withstand hundreds of thousands of high-pressure molding cycles.
By optimizing your part design and focusing on consolidating many key features, you can reduce your overall investment costs significantly. Adhere to the most common best practices in designing your part for the plastic injection molding process and your product or part quality, consistency and reliability will meet your expectations.
Common Injection Molding Defects
Most defects in injection molding are related to either the flow of the melted material or its non-uniform cooling rate during solidification.
Here is a list of defects to keep in mind while designing a part for injection molding. In the next section, we’ll see how you can avoid each of them by following good design practices.
Warping
When certain sections cool faster than others, then the part can permanently bend due to internal stresses.Parts with non-constant wall thickness are most prone to warping.
Sink marks
When the interior of a part solidifies before its surface, a small recess in an otherwise flat surface may appear, called a sink mark.Parts with thick walls or poorly designed ribs are most prone to sinking.
Drag marks
As the plastic shrinks, it applies pressure on the mold. During ejection, the walls of the part will slide and scrape against the mold, which can result to drag marks.Parts with vertical walls are most prone to drag marks.
Knit lines
When 2 flows meet, small hair-like discolorations may develop. These knit lines affect the parts aesthetics, but also they generally decrease the strength of the part.Parts with abrupt geometry changes or holes are more prone to knit lines.
Short shots
Trapped air in the mold can inhibit the flow of the material during injection, resulting in an incomplete part. Good design can improve the flowability of the melted plastic.Parts with very thin walls or poorly designed ribs are more prone to short shots.
Don’t Miss: How To Remove Mold From Wood Beams In Basement
The Basics And Benefits Of Design For Manufacturing
Design for Manufacturing involves designing a product that optimizes manufacturing efficiencies for the equipment and/or process used in its production in order to realize the lowest possible unit costs at the highest possible quality. The most important reason for integrating DFM into manufacturing a plastic injection molded product is that 70% of its manufacturing costs can be determined by design decisions.
DFM requires choosing the right manufacturing process for a part or product investments in different technologies, using state of the art design principles , and selecting the right materials with the right properties to deliver the consistency and quality demanded by your customers and prospects.
DFM is an instrumental part of another customer demand: lowering manufacturing and assembly costs. A simple look at the way this is accomplished is presented below however, when a DFM plan is completed deskside, it should be an engineering document laser-focused on getting a just right balance of quality and costs.
Learn more about how DFM works into the comprehensive injection molding process in our guide: Injection Molding 101.
Tip #: Avoid The Temptation To Add Undercuts In The Tooling
An undercut in the injection molding tool is when the opening and closing of the tool doesnt allow a specific feature to be formed. Avoid the temptation to add an undercut to form the shape, and instead design a lifter and slide to form the feature. The lifter and slide may add a little extra cost to the mold, but it will be worth the investment to allow the part to be removed from the injection mold without extra force.
Read Also: How Does Vinegar Kill Mold
The Clamping And Ejection System
On the far side of an injection molding machine is the clamping system. The clamping system has a dual purpose: it keeps the 2 parts of the mold tightly shut during injection and it pushes the part out of the mold after it opens.
After the part is ejected, it falls onto a conveyor belt or a bucket for storage and the cycle starts over again.
Alignment of the different moving parts of the mold is never perfect though. This causes the creation of 2 common imperfections that are visible on almost every injection molded part:
- Parting lines which are visible on the side of a part where the 2 halves of the mold meet. They are caused by tiny misalignments and the slightly rounded edges of the mold.
– Ejector marks which are visible on the hidden B-side of the part. They are created because the ejector pins are slightly protruding above or indented below the surface of the mold.
The image below shows the mold used to manufacture both sides of the casing for a remote controller. Quick quiz: try to locate the core , the cavity , the runner system, the ejector pins, the side-action core and the air vents on this mold.
To Sum Up Adding Injection Angles To Your Design:
- Ensures smooth, uniform, unscratched finishes when required
- Reduces the possibilities of damage to parts due to friction during ejection
- Ensures the uniformity and integrity of other surface textures and finishes
- Reduces wear and tear on the molded part
- Reduces the chances of damaging the mold
- Minimizes warping to your geometry
- Reduces overall cooling time by eliminating or reducing the need for elaborate ejection setups
- Offer both direct and indirect reduction to overall production cost
Don’t Miss: What Are The Effects Of Black Mold Exposure
Designing Parts For Up & Down Molding Helps Control Cost
Designing a part that can be molded with a “straight pull” or “up & down” motion is a great way to keep the cost of the mold down. A straight pull mold is designed so that when the two halves of the mold separate from each other, there is no plastic blocking the path of the metal in the direction of the pull. Undercuts on the part cause this blockage of path and require an action in the mold . Action in the mold can have a major impact on the cost of a mold.
Tips For Properly Designing Plastic Injection Molded Parts
Every new product starts with a concept. A fresh idea to make a current product better, or to fill a void in the marketplace. Plastic injection molding is an excellent manufacturing process to create cost effective, but profitable products in a timely manner. If you have a fresh product idea, but dont know what to look for in development, these tips may help you understand the small details that need to be discussed with your molding partner.
You May Like: How To Get Rid Of Mold On Books
How Is Automation Used In Plastic Injection Molding
Just like many other industries, the world of plastics is continuously changing and growing. Companies are continually investing in automation to improve productivity and increase capacity and efficiency.
Plastic injection molding processes are fast, efficient, and precise when conducted by experienced technicians utilizing advanced automated machinery. Automation helps ensure each manufactured component will be identical to the validated design.Taking automation a step further, lights-out manufacturing describes processes, innovative machinery, and technology that is put into place within facilities to conduct tasks that would normally need constant oversight by on-site technicians. Essentially, an automated production facility can run lights-out or without substantial assistance from human labor, lights, heat, and other costly factors for a business. However, most highly automated facilities still require the supervision of highly skilled laborers and technicians. Lights-out manufacturing processes allow companies to keep facilities running 24 hours a day, seven days a week, with a scaled-back workforce or virtual technician oversight.
Engine & Power System Parts
Compared to the past, instead of metal, the manufacturers have shifted most of the engine accessories to plastic due to the widespread use of injection molding. Sensors, oil pans, cylinder head covers, and electrical kits can all be made out of plastics. The advantages of using plastic parts are light-weight and cost-saving. However, to consider the function and protection, the manufacturers often take fiber reinforced plastic as material for injection molding, which might need special design of screw.
You May Like: What Does Attic Mold Look Like
Dfm Guidelines For Reducing The Costs And Challenges Associated With Manufacturing A Plastic Component
Source: Computer-Aided Manufacturing, Second Edition, Tien-Chien Chang, Richard A Wysk, and Hsu-Pin Wang. Pages 596 to 598. Prentice Hall 1998
The Cardinal Rules Of Designing Injection Molded Plastic Parts
When designing injection molded plastic parts, here are some simple rules to follow that will help to ensure higher-quality parts that are easier to manufacture:
Maintain Uniform Wall ThicknessMaintaining uniform wall thickness is the single best design element you can incorporate in injection molded plastic parts. Uniform wall thickness promotes uniform filling patterns, uniform molded-in stress distributions, uniform shrinkage and ultimately, molded parts that are much less likely to warp out of shape compared to parts that have significantly varying wall thickness. This image shows the Nominal Wall Thickness Adviser plot from SOLIDWORKS Plastics 2015, which indicates areas that deviate significantly from the nominal wall thickness. You can then use this information to modify wall thicknesses and arrive at a final design with more uniform wall thickness. Hint: While most injection molded parts are thin-walled in nature, look for thick sections in your designs that can be cored-out to maintain the overall uniformity of the nominal wall thickness.
Folow Rib Design GuidelinesRibs are commonly used in plastic parts to provide structural integrity, prevent part warpage and aid in the integration ofinternal components. However, if ribs are not designed properly relative to the surfaces theyre attached to, problems such as sink marks, warpage and part failure can occur. The following rib design guidelines work well for most plastics materials:
Avoid Sharp Corners
Read Also: How To Clean Mold Off Washing Machine
Design Considerations For Injection Molding
There are many factors to consider for injection molding, but the part design and tool design are two of the most important.Getting them right could mean lower entry cost, high production quality, shorter cycle time, and quick assembly. Getting them wrong, on the other hand, can be very costly indeed.
Wall thickness
The thinner it is the easier the injection molding process. Parts with thin wall thickness cool faster, weigh less and use less plastic per part. This means shorter cycle times, resulting in more parts produced per hour and lower production cost.
On average, injection molded parts should have a wall thickness that ranges from 0.08 to 0.16 , but thin wall injection molding can go as thin as 0.02 . But wall thickness also depends on the material used. The recommended wall thickness of an ABS resin, for example, 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 0.0300.115, Polycarbonate at 0.040 0.150, Polyester at 0.025 0.125 and Polypropylene at 0.025 0.150.
Wall thickness must be consistent to reduce if not eliminate warping. If consistency is hard to achieve due to design limitations, the change in thickness should be done gradually. The use of a coring method will help eliminate such problems, while adding gussets will reduce warping.
Ribs
When adding ribs, follow the recommendations below.
Sharp vs curved corners
Draft angle
Bosses
The specifications below should be observed.
Undercuts