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acleveland - Custom Tips for Injection Molding

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Design engineers don’t have to be fluid dynamics experts to injection mold plastic parts without a hitch. Pitfalls associated with flow dynamics can still be averted through the use of simple designs and by following general guidelines. The following rules will help engineers avoid problems when designing injection-molded plastic parts:

Rule 1: Keep Wall Thickness Consistent
Plastic part walls must be uniform in thickness. This is the most basic design parameter, and strict adherence to it will eliminate many manufacturing problems. Parts with uniform walls will not warp, will fill properly and will fit together because variable shrinkage is minimized. Wall thickness variations should not exceed 10% in high mold shrinkage plastics. In fact, even this slight disparity can introduce processing and quality problems.

Rule 2: Provide for Proper Gate Location
If varying wall thickness cannot be avoided, then designers should provide for proper gate location. If this is not supplied, then attaining uniform pack of the molded part will be nearly impossible. The most effective gate location is when the melt enters at the thickest part of the cavity and then flows to the narrower areas.

Rule 3: Determine Optimal Wall Thickness
Theoretically, there is no maximum wall thickness for injection-molded parts. But designers are more concerned with determining the minimum wall thickness because thinner is almost always less expensive. Two factors contribute to this: first, thinner parts require less raw plastic material, and second, they cool faster. To determine the most suitable wall thickness, engineers should first consider product requirements. Generally, strength dictates the wall thickness. Engineers can also rely on a finite analysis to select the optimal wall thickness.

Rule 4: Radius Corners Generously
During injection molding, the molten plastic has to navigate turns or corners. Rounded corners will ease plastic flow, so engineers should generously radius the corners of all parts. In contrast, sharp inside corners result in molded-in stress—particularly during the cooling process when the top of the part tries to shrink and the material pulls against the corners.

If the inside and outside radii of a part are each equal to half of the nominal wall thickness, a uniform wall around the corner can be achieved. Both sides of the corner will display equal amounts of shrinkage, and sink marks will be avoided entirely. Moreover, the first rule of plastic design—uniform wall thickness—will be obeyed. As the plastic goes around a well-proportioned corner, it will not be subjected to area increases and abrupt changes in direction. Cavity packing pressure stays consistent. This leads to a strong, dimensionally stable corner that will resist post-mold warpage.
Rule 5: Select Suitable Draft Angles
From a cost and manufacturability viewpoint, the ideal draft angle is the largest angle that will not lessen the customer’s satisfaction with the product. The minimum allowable draft angle is harder to quantify. Plastic material suppliers and molders are the authority on what is the lowest acceptable draft. In most instances, 1° per side will be sufficient, but between 2° and 5° per side would be preferable. If the design is not compatible with 1°, then allow for 0.5° on each side. Even a small draft angle, such as 0.25°, is preferable to none at all.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

We got a great response to last month’s money saving tips post. For this month, we wanted to provide you with 3 easy steps to ensure the success of your next tooling project.

Step 1: Get a Design for Manufacturability (DFM) Analysis

Most tool shops have the ability to provide some form of Design for Manufacturability (DFM) analysis, which can range from very basic to very detailed. No matter the level of detail, giving your mold maker the opportunity to review your designs ahead of time can go a long way in strengthening the customer-supplier relationship. Knowing everyone’s expectations in advance will streamline the tool build and lead to better molded parts.

>> Get a Complimentary DFM Analysis 

Step 2: Send Your Mold Maker a Rapid Prototype of Your Design

Any engineer knows that getting it right the first time is a rare phenomenon. Even after thorough DFM feedback and countless hours of CAD review, you never really know what you’re going to get until you hold the part in your hand. Do some research on which rapid prototype process suits your application the best, make sure the design is right, and then send a few sample parts to the mold making facility of your choice. Although they have surely seen thousands of parts, each design is unique, and seeing a rapid prototype part could change their perspective on the best way to mold the part. 

Step 3: Take Time to Thoroughly Review T1 Samples

After the DFM and rapid prototype phase, you can finally rest easy once the tooling is on order. The next challenge will arise when your molded T1 samples arrive. Although the race to get your product to market weighs heavily, it is extremely important to spend some time evaluating the initial parts off of the mold. Hastily signing off on your samples in order to produce thousands can be a disaster if the samples have not been properly evaluated. Along with fit and function testing, it’s a great idea to request hard data from your mold maker in the form of a first article inspection report.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200

Injection Molding Design Guide

Download Our Free Design Guide!

If you’ve ever wondered if draft angles were a must, we’ve got the answer for you!

The justification for draft angles comes from the nature of the injection molding process, and the ever present issue of mold shrinkage. Injection molding is a high-pressure process. These high pressures force the plastic into intimate contact with all surfaces of a mold’s cores and cavities. This high-pressure packing of the cavities makes it difficult to get the part out of the mold, or “eject” the part.

Draft facilitates the removal of the part from the mold and is very important in injection molding where the molds are straight pull only (no side actions).

The guidelines associated with the number of degrees of draft required will vary with geometry and other part characteristics (e.g. surface texture requirements), but in general the more the better. Draft is your friend when building molds.

Here are some rough guidelines to follow:

  • We ask for at least 0.5 degrees on all “vertical” faces
  • 2 degrees works very well in most situations
  • 3 degrees is minimum for a shutoff (metal sliding on metal). Without this, the
    mold would lock up and be unable to open
  • 5 or more degrees is required for heavy texture

Remember, draft is your friend when designing molds.

To discuss draft for your next project or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

Have you ever wondered how these items were made??

Injection Molding Design Tips - Overmolding - Screwdrivers
The answer is overmolding. The overmolding process involves the use of two separate materials to form one cohesive component. The most common type of overmolding is insert molding. Insert overmolding is an injection molding process where one material (usually elastomeric) is molded “over” a secondary “substrate” material (usually a rigid plastic or object).

Overmolding can add immeasurable value to product design by enhancing the end users experience in terms of comfort, ergonomics, and ease of use. In order to achieve this level of manufacturing there are two important concepts that must be understood for success to take place:

1) Know your materials

The materials used need to be compatible so that your designs attain a high level of molecular adhesion. Know what the melt temperature is of your substrate and overmold. If the melt temperature is lower on your substrate than your overmold material, then you are in for a big problem! Also, if you are using color, make sure your color concentrate is compatible with your other materials and won’t degrade their properties. Using the right materials could make or break your designs.

2) Understand your designs

When designing, you need to consider how much or how little you want your substrate and overmold to stick. Don’t count on the material alone to create the adhesion that you want. To ensure that the components “mesh” well with one another, use mechanical interlocks such as these:

Injection Molding Design Tips - Overmolding

Knowing the proper rules for overmolding can yield a very successful and aesthetically pleasing product. To discuss overmolding options for your next project or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

How do you select the right injection molding material? This is a very difficult question. Making the decision even harder is the fact that there are over 300,000 different types of material available, and that number grows by 750 more every year.

Injection Molding SampleSome people think the best thing to do is just select the latest and greatest material that has the best properties and can take super high heats. They might think that their requirements will never exceed these properties and their part will be fantastic. This is almost never the case. When selecting resins, it is a good idea to contact your local representative whether it is for Sabic, Bayer, or DuPont. Let them know what your product is for, the conditions that it will be exposed to, and the colors that you would like it in, and they will certainly point you in the right direction. Most of the time, simple resins like: PP, ABS, PC, or PC/ABS will be more than sufficient for your needs. If you have an out of the norm requirement, resin makers can blend additives into the resins to meet your requirements. 

So how do you select the right material? Ask for help first or go to the resin manufacturer’s website, you will be amazed. Remember, it does not have to be the most expensive resin to be a quality material.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

Quickparts | Injection Molding SampleDesigning plastic parts is a complex task involving many factors that address a list of requirements of the application. In addition to functional and structural issues, processing issues play a large role in the design of an injection molded part. Adhering to some basic rules will result in a part that, in addition to being easier to manufacture and assemble, will typically be much stronger in service.

Quickparts has created an injection molded sample to illustrate the different design basics and things to keep in mind when designing for injection molding.

>> Click Here to Request a Sample!

What do a leather wallet and a ketchup bottle cap have in common? You got it…they both implement the living hinge to bring the object to life through movement.

When speaking in terms of manufacturing, a living hinge is a thin flexible web of material that holds two rigid plastic pieces together. The living hinge concept has been around for years, but in terms of plastics, its full potential wasn’t realized until the inception of polypropylene in the late 1950’s.

So, what is the secret behind the “living” part of it?

It’s all in the design…

Injection Molding | Living Hinge Diagram | Quickparts.com
The key details to a successful living hinge include:

  • Hinge thickness
  • Radius
  • Recessed notch above the hinge feature

The hinge thickness controls the overall stiffness of the hinge; each application has its own requirements so make sure you find your part’s ideal thickness. Also, because the hinge plastic is so thin, it may be susceptible to tearing at the edges, so giving just the ends of the hinge extra thickness while adding radii will increase its tear resistance.

The overall radius applied will help to orient the plastic molecules flowing through the hinge, ensuring that the hinge bends along a straight line. This molecular orientation gives the hinge its strength and long life. Another way to ensure proper material flow and hinge operation is to choose a gate location that will place weld lines away from the living hinge feature.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

One of the most common questions we are asked is “How much draft do I need for the texture that I want?”

The general rule of thumb is that you allow for 1.5 degrees of draft for each .001″ of texture finish depth. However, there are other considerations that must be taken into account due to the many new resins and polymers, molding improvements, and various other factors that come into play in modern plastic molding. Examples of situations that require additional draft are thin wall part design and high pressure molding.

Some important considerations to keep in mind are:

  • Is the vertical wall in question an inside or outside wall? If it is an inside wall, the part will shrink onto it during molding, so you will need more draft in order to apply a texture, or apply the texture at a lighter depth.
  • Certain plastics have very little shrinkage and will therefore not shrink away from outside walls as easily as other plastics. Thermosets, Ryanite, Glass Filled Nylon, Glass Filled Polypropylene, ABS, Polycarbonate, etc. will usually require more draft in order to mold parts without scuff or drag marks.
  • If the core is very simple, and there is nothing on the core to hold the part in place during ejection, the part will tend to hang onto the cavity, creating scuff marks. The part may require more draft, or perhaps texture could be applied to the core side. This helps hold the part onto the core during ejection. This method has been used very successfully to solve this sort of problem.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

As plastic product designs become more complex, Design for Manufacturing (DFM) plays an instrumental role in successfully launching new products on time and under budget.  Our DFM service allows customers to take advantage of the vast manufacturing experience and knowledge of the dedicated Quickparts manufacturing team.  This service (valued at $300) is offered free of charge to customers working with Quickparts on injection molding projects.  A comprehensive DFM report is available which includes process flow details, expectations for the build, and final DFM recommendations.

Quickparts is a business that has been providing custom-designed plastic and metal parts to product development companies since 2000. Many companies, from the multi-billion dollar operations to the two-man design shops, have utilized the benefits of using Quickparts.

You can find a sample report and learn more about Design for Manufacturing in the Learning Center at www.quickparts.com.

If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

FREE Injection Mold SampleI hope the end of the year is treating you well. We have had a few conversations with customers recently regarding shut off angles, and I wanted to get one final post out to everyone this year to briefly discuss the subject.

A shut off angle is where two parts of the mold shut against each other to prevent plastic from passing through. This term applies where one part of the mold closes against another to form a slot or hole, or it is sometimes used to refer to the interface where a slide shuts against a core or cavity. Sometimes, the shutoff surfaces are parallel to the direction that the mold opens. When this happens, draft has to be added to avoid grinding the parts of the mold against each other. A 3 – 5 degree draft is ideal for these shutoff areas and will ensure the life of the mold. Without this amount of draft the mold will get damaged, and may potentially even “lock up” and not open. Even with hardened steel, lack of draft in this area will ruin the mold.

Understandably, many customers do not understand why we ask for this draft, but without it, every time the mold opens and closes, the steel will wear out in this area in a very short time. When this happens, repairs can be costly.

If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200. Thanks, and Happy Holidays.