Category Archives: plastic injection mold design

Plastic Injection Mold Design Considerations

mgmold1Injection mold designers and engineers have numerous considerations when planning out the best approach for the mold design of plastic components.  Plastic injection molding is used in various industries such as automotive, electronics, medical and defense, to name just a few.  When the same part is required in a high volume, engineers choose injection molding to mass produce required components with consistent quality.

Mold Design Derived from Part Design

 Every injection molder knows that in order to manufacture a quality part, to specification, you must begin with a quality tool.  Injection mold builders today utilize technology such as CAD (Computer Aided Design) and Mold Flow Analysis software to provide an accurate three-dimensional image of the desired plastic part before even cutting steel.  These tools provide advanced product and quality planning procedures, and assist the mold builder and the injection molder to work together in producing the part to specification.

Critical Elements of the Part Design

Careful evaluation of all critical dimensions is extremely important when designing a tool.   Some parts are designed with thin walls that can succumb to underfill, or a hole that must be within strict tolerances per customer specifications. Knowing up front where the critical dimensions, and required strict tolerances lie is of the utmost importance when designing a tool.  Some tolerances can be as tight as + or – .001 of an inch, the width of a human hair!  When carving steel from a mold to meet these tight tolerances, it is important to get it right the first time.

Mold Design is Influenced by the Molding Environment

A mold designer must know what specific type of press the mold will run in and the properties of that press such as whether it has a vertical or horizontal clamping system.  A vertical press requires shuttle molds with multiple B halves, and is typically used in over-molding, also referred to as insert molding,  which is molding plastic around an object typically made of either plastic or steel.

The most common type of injection molding press has a horizontal clamping system where both halves of the mold open and close on a horizontal mounting system,  and parts fall into a bin below the mold when it opens and ejects them.

Most injection molding presses have water fittings and lines to run through the mold for instant cooling to aid in the setting of plastic, reducing cycle time.  The placement of fittings for cooling systems, electrical connectors and wiring is an important consideration for mold designer to ensure that the mold will fit and work properly in the press.

Michiana Global Mold is an ISO9001:2015 Registered injection mold designing and building company.  We have been supplying custom precision injection molds to various industries including automotive, medical, electronics and defense for over 52 years.  Contact us today to see how we can assist you with your plastic injection mold designs.  

 

Plastic Injection Mold Designs Requiring Cam Action and Lifters

Engineers have many factors to consider when it comes to plastic injection mold designs, including cam action and the ejection system.    Once a mold designer has evaluated all geometric tolerances on the part print, they will typically create a CAD (Computer Aided Design) drawing of the part to aid in the design of the tool.  While reviewing part requirements and the tooling necessary to mold the part, it will become apparent if any Cam Action, or specialized ejection system is necessary.

What is Cam Action

Cam action refers to the mechanics necessary to create an undercut feature, a hole in a part would be an example.   Cam action occurs on sliding plates that would slide in when the plastic is molding around it to create the feature such as a hole, then it must slide back out in order for the part to eject properly.  If the pins or mechanics that molded the feature like a hole did not slide out of the way, the part would be lodged on that pin and would not fall out.  A cam device will pull the side-action mold surface out of the way to allow ejection from the mold.

cam-action-1-minPictured is an example of cam action; the sliding plates have barrel like rods attached to move in during the molding process creating holes in the part.  They slide back out when finished for proper ejection.

cam-action-2-minThis photo shows cams in a closed position, while molding the hollow geometrical shape of the part.

Lifters and the Ejection System

The ejection system is what pushes the part out of the mold after a fully formed plastic part has been molded.  In some instances, some help might be required for proper ejection.  This is where lifters would be included as a mechanism in the ejector system.  A lifter is an angled feature that is part of the ejector plate system, and is activated upon ejection.

The ejection system has several considerations during the injection mold design.  The ejection pattern and stroke of the press must correspond with the mold design.  Proper location of ejection pics is crucial to properly eject the mold without damaging the finished part.  In some instances, lifters are the only option to ensure proper ejection.

lifter-example-iso-view-cut-away-1An example of lifters assisting with ejection

 

Michiana Global Mold is an ISO9001:2015 Registered injection mold designing and building company.  We have been supplying custom precision injection molds to various industries including automotive, medical, electronics and defense for over 52 years.  Contact us today to see how we can assist you with your plastic injection mold designs.  

 

Injection Mold Types: Hot runner molds

 

 

Hot runner molds is a generally effective method of mold making that has less scrap (sometimes the process has no scrap) due to keeping the plastic is kept above the melting temperature. Because it is more effective, it tends to be a bit more expensive than other types of molds, particularly cold runner molds. The overall savings makes up for the cost if you have large quantities to produce or if you need quick production.

 

Components and Process

All hot runner mold systems include two plates to complete the process quickly. It is composed of the manifold and drops. The purpose of the manifold is to convey the plastic to an area above the cavity.

Running perpendicular to the manifold are the drops, which move the plastic from the manifold to the part. Systems have some variations based on the method of heating the plastic.

 

Things to Consider

In addition to reducing the waste, hot runner molds have a quicker cycle time. Robotics are common in many molding processes, but you will not need as many for a hot running system. Large parts are typically best when made with hot runner molds because these molds can better accommodate the size.

However, if you have a more limited budget or fewer parts, you can save on the cost by using a cold runner system. If color is important and you are likely to need to change it frequently, hot runner systems will not be able to make the change easily.