Let’s discuss one of the potential pitfall of designing for the process of injection molding. Melting plastic pellets and molding them into a part seems like a rather simple endeavor; however, it’s sometimes anything but. There are many factors to consider, and this month, we are going to talk about one of the more common: sink marks.

What is Sink?

 A sink mark is a local surface depression or void that typically occurs in moldings with thicker sections. They are also common in locations above ribs, bosses, or internal fillets. As the plastic cools at different rates in the mold, the surface hardens but leaves the thicker areas in the center still molten. As the thicker areas cool, they contract and leave depressions in the surface of the part; sometimes the part may even warp completely.

How to Avoid Sink?

  1. Core out the solid sections of your part to reduce thick areas.
  2.              * If you require the strength of a solid part, try using cross hatched rib patterns inside of the cored out area to increase strength and avoid sink marks

  3. As a rule of thumb,  make sure that all bosses and locating & support ribs are no more than 60% of the thickness of your nominal wall.
  4.  
      * Click here for a quide to recommend wall thickness by resin

Have any further questions about sink or enhancing your Injection Molding project?  Call your Sales Manager at 770-901-3200 to discuss your project today!

When working with metal, whether it’s cutting a tool or machining a final part, some features are too small to produce using traditional machining methods. For these applications, a process called electrical discharge machining (EDM) is used. EDM is also referred to as spark machining, spark eroding, burning, die sinking or wire erosion.

What is EDM?

Electrical discharge machining (EDM) is a metal working process in which controlled sparking is used to erode away a work piece. The EDM system consists of an electrode and the part (work piece). Material is removed from the work piece by a series of rapidly recurring current discharges between the two electrodes, separated by a dielectric liquid and subjected to an electric voltage. It is one of the most accurate manufacturing processes available for creating complex or simple shapes and geometries within parts and assemblies.

When is EDM used?

EDM is primarily used for hard metals or those that would be very difficult to machine with traditional techniques. EDM typically works with materials that are electrically conductive and can cut intricate contours or cavities in pre-hardened steel without the need for heat treatment to soften and re-harden them. This process is most widely used by the mold making tool and die industries, but is becoming a more common method of producing prototype and production parts where quantities are relatively low. EDM manufacturing is a very desirable manufacturing process when low counts or high accuracy is required.

Some of the advantages of EDM include machining of:

  • Complex shapes that would otherwise be difficult to produce with conventional cutting tools
  • Extremely hard material to very close tolerances
  • Very small work pieces where conventional cutting tools may damage the part from excess cutting tool pressure
  • Delicate sections and weak materials – can be machined without any distortion since there is no direct contact between tool and work piece

Some of the disadvantages of EDM include:

  • The slow rate of material removal
  • The additional time and cost used for creating electrodes for ram/sinker EDM
  • Reproducing sharp corners on the work piece is difficult due to electrode wear
  • Specific power consumption is very high

Have questions about EDM and how it can help you?  Call your Sales Manager at 770-901-3200 to discuss your project today!

Injection molding is the manufacturing process that is responsible for producing most of the plastic parts that you and I come in contact with each day. While the process is capable of producing a vast range of designs, it can take some time and therefore does not lend itself well to changes down the line. It is for this reason that Quickparts has created a new injection molding concept called Proto-duction tooling.

What is Proto-duction Tooling all about?

We at Quickparts have perfected the process of building “Proto-duction” tooling, also known as “Prototype-to-Production” tooling. It uses production steel multi-cavity tooling, with the 1st cavity serving as the prototype tool. After the 1st cavity is constructed, sampled, adjusted, and approved, then the remaining cavities are built to match this prototype cavity. The result is a production multi-cavity, steel injection mold tool, created in half the time of the traditional 2-step process (building a stand-alone prototype tool, then a multi-cavity production tool).

What are the benefits?

One of the great benefits of proto-duction is that the construction timeline is reduced, since the typical ‘prototype’ tooling phase goes hand-in-hand with the construction of the production tool. Additionally, the overall tooling cost will also be reduced, since the stand-alone prototype tooling is avoided. Finally, it is important to note that financial risk is now reduced because you wouldn’t order the construction of the remaining production cavities until the prototype cavity is approved.

Proto-duction tooling is a cost effective way to produce prototype and production tooling. There are no geometry limits, no volume limits, and no manufacturing limits on your part. Any commercially available material can be used in the production of the part and any surface finish can be applied.

Please call a friendly Quickparts Sales Manager at 770-901-3200 to discuss your upcoming project and discover how Proto-duction tooling can benefit your design.

 

A common design feature seen in injection molded parts is the use of lettering and logos. Designers use this feature for many reasons; to illustrate a brand identity, convey important end user instructions, aid in assembly, or display a part number or legal warning. The injection molding process allows lettering and other surface decorations to be easily incorporated into plastic parts. Once the lettering has been incorporated into the mold, each part will display the feature with few or no extra steps. This can save a significant amount of money by eliminating the expense of adhesive or painted labels.

Recessed vs Standoff Lettering & Logos

When applying lettering or logos to a mold, you will need to indicate whether you want your lettering to appear as recessed into the part or raised off of the part (also known as stand-off). This decision determines how your mold will need to be cut. For economic reasons, lettering is generally engraved into the mold which appears as raised letters on the parts. This enables the mold to be polished which provides a better finish on the surface of the parts. Engraving into the mold also extends the life of the mold since you do not have raised small features that wear faster than others. 

The Rules of Lettering & Logos

Engraved lettering or logos in the mold, if not done properly, can cause imperfections in the final part such as streaks, tear drops or flow marks around the features. These defects are usually caused by improper material flow into the letters. The following rules will help you to avoid these problems in your molded parts:

Rule of Thumb #1: Apply a radius to all sharp corners of the lettering. Deep, sharp lettering can lead to defects from air trapping in the mold.

Rule of Thumb #2: Limit the depth or height of lettering into or out of the part surface to approximately 0.010”. Letters and logos raised higher than 0.010” are unnecessary as they seldom wear out during the life of the part.

Rule of Thumb #3: Don’t forget to draft your features. The letter or logo sidewalls should have a draft angle of at least 3o to ensure proper fill.

Injection molding is the most common manufacturing method for producing plastic parts in the world. The purpose of these parts can range from a picture frame that is never touched to a gear that is used in a moving assembly every day. Many times, the stiffness of a part must increase due to the load applied to the part design. When designing strength into an injection molded part, considerations must be made to accommodate for the manufacturing process. This is where ribs and gussets come into the design.

Ribs are thin wall protrusions that extend perpendicularly from a wall or plane. Gussets are triangular shaped ribs that support a main wall. Ribs and gussets add strength and rigidity to primary walls without the dangers and high costs caused by excessive wall thickness.

If a wall is too thick, sinking and warpage may occur on the part, resulting in a rejected design. Ribs solve this problem by providing additional support for thin walls, and are in fact, more effective structurally than just a thick wall. Along with being stronger, ribs also require less material than thick walls making them the economical choice as well.

Ribs increase the durability and quality of your part while reducing material cost, but if used incorrectly, can have negative effects on the aesthetics of your molded part. The area where the rib intersects with the main wall will experience a thicker plastic section. If the rib is too thick it will cause a sink mark in the main wall due to inconsistent cooling rates. To avoid this there are several rules to follow when using ribs in your design:

Feel free to call me at 770-901-3200 to discuss your upcoming project and how ribs may benefit your design. Click Here to request a FREE molding sample that shows rib and gusset usage.

Just a reminder:

The Chinese New Year is the longest and most important of all Chinese holidays. This 2-week holiday falls on different dates each year between January 21 and February 20. During this holiday, the working people of China take leave from working so that they can celebrate the New Year with family. Quickparts Chinese manufacturing facilities will be closed during this period to honor these traditions.

By definition, an injection molding gate is an orifice through which the molten plastic is injected into the mold. The type and size of the gate plays a very significant role in the process of injection molding.

Gate Types

There are two types of gates available for injection molding; manually trimmed and automatically trimmed gates. Manually trimmed gates require an operator to separate the parts from the runners manually after each cycle. Manually trimmed gates are chosen for several reasons:

•  The gate is too bulky to be automatically sheared by the machine

•  Shear-sensitive materials such as PVC cannot be exposed to high shear rates

•  Flow distribution for certain designs that require simultaneous flow distribution across a wide front   Automatically trimmed gates incorporate features in the tool to break or shear the gates when the tool opens to eject the part. Automatically trimmed gates are used for several reasons:

•  Avoiding gate removal as a secondary operation, reducing cost

•  Maintaining consistent cycle times for all parts

•  Minimizing gate scars on parts

Common Gate Designs

The largest factor to consider when choosing the proper gate type for your application is the gate design. There are many different gate designs available based on the size and shape of your part.

Below are three of the most popular gate designs used by Quickparts’ customers:

The Edge Gate is the most common gate design. As the name indicates, this gate is located on the edge of the part and is best suited for flat parts. Edge gates are ideal for medium and thick sections and can be used on multicavity two plate tools. This gate will leave a scar at the parting line.

The Sub Gate is the only automatically trimmed gate on the list. Ejector pins will be necessary for automatic trimming of this gate. Sub gates are quite common and have several variations, such as a banana gate or tunnel gate. The sub gate allows you to gate away from the parting line, giving you more flexibility to place the gate at an optimum location on the part. This gate leaves a pin sized scar on the part.

The Hot Tip Gate is the most common of all hot runner gates. Hot tip gates are typically located at the top of the part rather than on the parting line and are ideal for round or conical shapes where uniform flow is necessary. This gate leaves a small raised nub on the surface of the part. Hot tip gates are only used with hot runner molding systems. This means that, unlike cold runner systems, the plastic is injected into the mold through a heated nozzle and then cooled to the proper thickness and shape in the mold.

The Direct or Sprue Gate is a manually trimmed gate that is used for single cavity molds of large cylindrical parts that require symmetrical filling. Direct gates are the easiest to design and have low cost and maintenance requirements. Direct gated parts are typically lower stressed and provide high strength. This gate leaves a large scar on the part at the point of contact.

Each injection mold design must have a gate, or an opening that allows the molten plastic to be injected into the cavity of the mold.  Gate design and location can have a drastic affect on your part that could result in incorrect parts and/or significant cost increase to fix your tools.The Affects of Gate LocationGate design and location are crucial to creating a successful part.  The type of gate and the location can have affects on the part including:

  • Part packing
  • Gate removal or vestige
  • Cosmetic appearance of the part
  • Part dimensions and warping

As you can see, using the incorrect gate can spell disaster, or at the least a mold rework, which can quickly and sharply increase manufacturing costs.Recommended Gate LocationsTo avoid problems from your gate location, here are 7 tips on choosing the proper gate location(s):

  1. Place gates at the heaviest cross section to allow for part packing and minimize voids & sink.
  2. Minimize obstructions in the flow path by placing gates away from cores & pins.
  3. Be sure that stress from the gate is in an area that will not affect part function or aesthetics.
    1. If you are using a plastic with a high shrink grade, the part may shrink near the gate causing “gate pucker” if there is high molded-in stress at the gate.
  4. Be sure to allow for easy manual or automatic degating.
  5. Gate should minimize flow path length to avoid cosmetic flow marks.
  6. In some cases, it may be necessary to add a second gate to properly fill the parts.
  7. If filling problems occur with thin walled parts, add flow channels or make wall thickness adjustments to correct the flow.

Gates vary in size and shape depending upon the type of plastic being molded and the size of the part.  Large parts will require larger gates to provide a bigger flow of resin to shorten the mold time.  Small gates have a better appearance but take longer time to mold or may need to have a higher pressure to fill correctly.

Have you ever wanted to create the look of a different material on a plastic part? Plastic parts not only benefit from designs that are pleasing to the eye, but they also benefit from the way a part feels when handled. Depending on the application, you may want your part to be as smooth as glass or possess a rough feel to indicate strength and durability. One way to injection mold a part with a unique look and/or feel is through the use of mold texturing.

What is Texturing?

Texturing is a process used to apply patterns to a mold surface. This process allows flexibility in creating the final appearance of your parts. Texturing is an integral piece in overall product development and should be considered during the design process to achieve the desired results. Texture can be a functional component of design as well. Imperfect parts can be camouflaged by the right texture. Is the part designed for frequent handling? Texture can be used to hide finger prints and improve the grip for the end user. Texture can also be used to reduce part wear from friction.

What Textures Are Available?

Quickparts has the ability to produce a wide variety of textures such as:

•  Natural/Exotic

•  Matte Finishes

•  Multi-Gloss Patterns

•  Fusions

•  Graphics

•  Leather Grains/Hides

•  Woodgrain, Slate, & Cobblestone

•  Geometric & Linens

•  Images or Logos Incorporated into the Pattern   

How Do I Design for Texture?

When applying a texture to your part, you need to adjust your CAD drawing to accommodate for this surface variance. If you are designing for texture on a surface that is perpendicular or angled away from the mold opening then no draft changes are necessary. If your texture is on a parallel surface with the mold opening, however, increased draft is necessary to prevent scraping and drag marks that could occur during part ejection.

Rule of Thumb:

Different textures have different impacts on the molded part. The rule of thumb when designing for texture is to have 1.5 degrees of draft for each 0.001” of texture finish depth.

Designing plastic parts is a complex task involving many factors that address a list of requirements of the application. “How is the part to be used?” “How does it fit to other parts in the assembly?” “What loads will it experience in use?” In addition to functional and structural issues, processing issues play a large role in the design of an injection molded plastic part. How the molten plastic enters, fills, and cools within the cavity to form the part largely drives what form the features in that part must take.

Using our 8 years of injection molding manufacturing experience, Quickparts has created several resources to assist you in designing for this process. The Basics of Injection Molding Design is a guide outlining the basic rules to designing parts for injection molding that will make your parts stronger and easier to manufacture.

Design for Manufacturing Analysis is a free service offered with injection molding quotes where a report is generated by a Quickparts Production Engineer who reviews the feasibility of your part for manufacturing.  Click here for a sample report.

Injection Molding Glossary contains commonly used injection molding terms and their definitions.

These resources are free of charge and are all available in the Quickparts Learning Center.

The Game Gripper is a hand-held instrument used to convert the Motorola Droid keyboard into one of the best performing gaming handsets on the market. The device fits over the phone and comes with custom buttons that align to the keyboard perfectly, dramatically enhancing the gaming experience while using the Droid handset.

Hyrum Fairbanks, the device inventor, spotted a need in the market for the device when he found the keyboard very clumsy and tough to use for gaming. “The Droid has some of the best games available on the market, but the keyboard was a limiting factor in how much the user enjoyed playing the games. My product made the phone great for gaming, I just needed a company to help me make them economically. Quickparts helped me make the design and material changes I needed to bring the costs down and bring it to market.”

In addition to the Motorola Droid, Game Gripper is in the process of releasing several other models that will allow users of other popular phones on the market to enjoy similar gaming benefits.