Browsing Posts published by acleveland

Last month’s design tips discussed how draft angles are specific to each part that is built.  This month we will look at some standard injection mold resins and some of the properties that they possess.

When deciding which molding resin to use, one must consider the mechanical properties, molding properties, and cost of the resin selected for the given application.  Application-specific requirements will always drive the need for particular material properties, like tensile strength and elasticity.  Successful plastic part design is based on an understanding of processing related issues during manufacturing, such as mold filling, likelihood of flash, part ejection and the potential for warp and sink.  The table below lists some commonly used resins, along with brand names, and a high-level summary of their material properties and moldability characteristics.

Standard Injection Molding Resins

Please keep in mind that this is a concentrated view of how to select the right resin for your plastic part.  All major material representatives have application specialists that can help you with your selection.  We strongly urge you to discuss your project with one of these specialists prior to making your mold.

We hope this gives you some ideas for your next molding project.  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.

Draft angles are needed so that a plastic part can be released from the mold without distortion or damage. The high pressures of injection molding force the plastic to touch all the surfaces of a mold’s cores and cavities. The cavity becomes so tightly packed that it is often difficult to remove the part. Sometimes, shrinkage will actually make it easier to take the part out of the mold, but in other cases, shrinkage will cause the part to stick to the mold’s cores. These natural occurrences call for draft angles.

No single draft angle is suitable for all parts. Each individual part requires a unique specification. Large parts call for more draft than small parts. Thin-walled parts that undergo high-pressure injection molding need more draft than parts that are subjected to lower-pressure molding. When calculating appropriate draft angles, the plastic material’s shrinkage and physical properties are also considerations. Sizeable draft angles and smooth polish should be used for parts molded in strong, stiff, abrasive, and gluey materials. Smaller draft angles can be utilized on soft, malleable, and slippery plastics.

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.

I hope this gives you some ideas for your next molding project. If you have any questions regarding this or any other injection molding information, please feel free to contact me at (770) 901-3200.

Injection Molding SampleWe learned last month that selecting the optimal gate size and location is vital in the creation of any molded part. However, that is just half the story. Just as pivotal to the success of the design is the type of gate that is used.

There are actually four main types of gates that are frequently used when molding parts. Edge gates are often popular since they are fairly simple and cost effective, but may not always be the best choice. Here is a brief description of some gating options that will help you customize your design and really take your part to the next level.

Edge Gate • Suitable for medium and thick sections
• Used on multi-cavity two plate tools 
• Gate located on the parting line and the part fills from the side, top or bottom
DOWNSIDE: leaves “vestige” at gate location which should be trimmed with a secondary process
Submarine Gate • Used in two-plate mold construction
• As parts and runners are ejected, the gate is sheared at the part
• Tunnel can be located either in the moving mold half or in the fixed half
• Sub-gate is often located into the side of an ejector pin on the non-visible side of the part when appearance is important
Sprue Gate • Recommended for single cavity molds or for parts requiring symmetrical filling
• Suitable for thick sections where holding pressure is more effective
• A short sprue is favored, enabling rapid mold filling and low-pressure losses.
• A cold slug well should be included opposite the gate.
DOWNSIDE:  a gate mark is left on the part surface after the runner (or sprue) is trimmed off.

We hope this gives you some ideas for your next molding project. 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.

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.