Injection Mold Design for Engineering Resins

Thermoplastic engineering resins are the most common type of plastic resins used in the injection molding process.  With many different types of plastic resins each with their own unique properties, it takes great care and consideration to properly design and construct a mold for use with thermoplastic resins.   These highly useful polymer resins have varying properties of elasticity, resistance to temperature, corrosives, shrinkage and right down to the exterior finish such as a matte or a glossy finish.  

Shrink rate is a very important property of thermoplastic engineering resins used in injection molding, as the cavities must be carved out to accommodate to this shrink rate.  If shrink rate is not accounted for properly, a part may shrink too much after cooling and deviate from customer requirements. Knowing the cooling and shrink rate of the polymer resin used for any molding process is of the utmost important to the journeymen mold makers constructing the tool.  

Cooling rate is also important for the part to become completely solidified prior to ejection.  Cooling rate must be configured into the injection molding cycle time, to ensure proper cooling and ejection without damaging the part.  

Each polymer resin will have a MSD sheet, Material Safety Data sheet along with material specifications clearly defined in each numbered lot of all thermoplastic resins.  If working with a new material, a mold designer may prefer to use Mold Flow Analysis, for a computer simulated demonstration of how the plastic material will melt, flow and fill.   Predicting the flow of thermoplastic resins prior to cutting steel is vital for accurate geometrical tolerances in the final product.  

Even with a material spec sheet which is necessary, nothing helps a skilled mold designer more than experience.  Skilled mold design engineers are very familiar with the various properties of engineering resins allowing for precise mold construction with even the most specialty of molding resins.  

Michiana Global Mold is an experienced mold design and construction company, with vast experience with various thermoplastic resins used in injection molding.  We employ highly skilled journeymen mold makers and expert design engineers to satisfy even the most demanding of customer requirements.  We tackle the complex mold designs that other companies shy away from.  For complex, precision molds that must meet tight tolerances, contact Michiana Global Mold today for superior mold design and mold making services.

Contact Michiana Global Mold today to speak with one of our skilled mold designers and learn how we can assist you with your next injection mold making project.  We are an ISO9001:2015 Registered mold making company with vast experience constructing custom, precision injection molds using various thermoplastic engineering resins.  

Injection Molds for Various Thermoplastic Resins

Thermoplastic resin is the most common type of polymer used in the injection molding process. There are several different types of thermoplastic resins with varying properties, including shrink rate, resistance to high temperatures, resistance to corrosives, elasticity, adhesion, finish such as polished or matte, and fatigue strength.  

These are all very important considerations when designing an injection mold to manufacture parts molded from thermoplastic resins.  Shrink rate is extremely important, as the cavities in the tool would have to be adjusted for such shrink rate.  Cooling rate is also very important to consider during mold design, and is important for ejection.  The part must be completely set and solid prior to ejecting from the mold.

When designing a tool for injection molding with thermoplastic resin, mold flow analysis may be helpful or even necessary to identify any critical areas in the part design.  Mold flow analysis is a computer aided simulation that shows clearly how the material will flow, based on its own individual properties.

By predicting these critical areas ahead of time, the mold designer can adjust for tight tolerances, problem areas for material flow and fill, and to identify the optimum location for gating.  This is a valuable tool when designing precision molds for critical components, and is a useful tool to avoid costly mistakes and improving lead times.

While mold flow analysis can be a valuable tool, the best knowledge of how particular thermoplastic resins flow comes from experience.  Experienced mold designers are well aware of the specific properties of different polymers, using that knowledge to design the tool properly to mold the part to print.  

Michiana Global Mold has more than 500 years of combined experience designing and building injection molds for various industries.  We utilize advanced technology combined with skilled journeyman moldmakers and vast resources to construct quality tools for injection molding of thermoplastic resins.  

Contact Michiana Global Mold today to speak with one of our skilled and experienced mold designers to learn how we can assist you with your injection mold requirement.  We are an ISO9001:2015 Registered mold making company with vast experience constructing custom, precision injection molds for various industries.

Thermoplastic Molding

Injection Molding with Thermoplastic Resins
Thermoplastic molding refers to the process of injection molding thermoplastic resins.  Thermoplastics is a type of polymer that melts and becomes pliable when reaching a certain temperature, allowing it to be molded into various forms.  This type of polymer can also be ground up and reused after hardening, as opposed to thermoset polymers, which cannot be melted and used again.  The third type of polymer is elastomer, which can also be thermoplastic, in which case this type of material is referred to as thermoplastic elastomers.  Thermoplastic resins are the most common type of material used in the injection molding process.
The Molding Process
The equipment required for thermoplastic molding is the same: a press, a steel mold, and plastic resin.  The resin is poured into a hopper on top of the press, and is then drawn into the press where it is heated in a barrel and injected into a steel mold where cavities carved out by journeyman mold makers form the molten plastic into the shape desired.  The steel mold is usually equipped with water lines running through it to cool the parts before the mold opens and parts are ejected.  Each time the mold opens, molds parts, and ejects them is called a cycle.  The typical injection molding cycle is measured in seconds.  Decreasing the cycle time can lead to improvements in efficiency and the bottom line, as long as it does not jeopardize the functionality of the part.
The Mold
The mold is the steel frame that contains the carved out cavities to actually form the part.  Every injection molding job requires a steel mold to form the molten material into a usable functional part.  There are different types of molds for different applications, but the most common is a class A hardened steel mold, capable of producing hundreds of thousands or millions of parts without wearing out. 
For the typical thermoplastic molding process, a steel mold will run in a horizontal molding press, meaning the mold will open and close on a horizontal plane.  In this case, when the mold opens and ejects the parts, the runner is also ejected.  The runner is the residual molten plastic that hardened in the channel getting the plastic to the cavity in the mold.  This is true of a cold runner mold, which is the most common injection mold.  A hot runner mold, in contrast, injects plastic directly into the cavity from a nozzle, and therefore has no runner.  A hot runner mold can assist with automation, but it is more costly than the more common cold runner mold. 
Equipment Required for Automation
While the necessary equipment is the same, a molder can invest in auxiliary equipment to automate the process and run parts without an operator, and sometimes even in a ‘lights out’ environment.  A vacuum conveying system sucks the plastic resin while in pellet form from a drum or gaylord into the hopper on the press.  As long as enough resin material is in the drum the conveying system will automatically supply a steady stream of thermoplastic resin into the press.  There are ways to regulate the amount of pellets drawn into the hopper at a time.  Some molders even have ways to measure the moisture content of material, and dry it accordingly before it enters the press.  Some molders use a moisture analyzer when required. 
Sprue Pickers Assist with Automation
When a cold runner mold is used in a horizontal press, the runner will eject with the parts and either drop to a bin below, or be grabbed by a robotic arm called a sprue picker.  A sprue is another term for a runner.  Sprue pickers assist in the automation process because it separates the parts from the runners, allowing the parts to collect in a tub by themselves and not need to be sorted or separated from the runners. 
Process Monitoring Adds Consistency and Reliability
A Process Monitoring System should be utilized for automated molding as it will monitor, as the name implies, the process as it is happening.  If something began to run out of spec, such as temperature or pressure, an alarm would sound to alert a technician.  These monitoring systems also function as material resource planning software, allowing the user to input specific job information and schedule production. 
These are some of the ways a molder can automate the injection molding process. If precision parts manufacturing is required, automation could assist to provide to a consistent and reliable process. 

Contact Michiana Global Mold today to see how we can reduce costs on your plastic part requirements.