Thermoplastic Molding

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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.

Resin Injection Molding

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Molding With Plastic Resin

Resin injection molding is the manufacturing process of molding raw plastic pellet into usable parts.   Thermoplastic resin is the most common type of plastic used in the polymer molding process.  The resin, or plastic pellets, is used by injection molders to make parts for a wide variety of industries.

 

Custom injection molding is the process used by custom molders to make parts that are designed by others, typically engineers in the Automotive, Aerospace, Consumer Electronics, or Medical field.  Injection molding is also used for the Furniture, Construction, and Toy industries, although precision molding is required for the former mentioned industries requiring a high level of quality with tight tolerances.

 

Each resin has a melt temperature when it becomes pliable, which allows it to flow through an injection molding press, into a barrel and screw, where it is injected with pressure into a steel mold forming the desired parts.  After forming, the mold ejects the parts and closes again to prepare for another cycle.

 

Characteristics of Thermoplastic Resins

 

Thermoplastic resins have a unique ability to be strong and durable, yet also lightweight which makes is a desirable material for several functional parts. They can be reinforced with glass filled polymers, or they can have a rubber like appearance, and several variations in between.  They can be made into virtually any color, size or shape.  This flexibility is the main reason that plastic resins are the material of choice for supplying various industries with necessary functional parts.  Some examples:

 

  • Polycarbonate
  • Polyethylene (low or high density)
  • Polyethylene Terephthalate (PET)
  • Polypropylene (Acetal)
  • Polyphenylene Ether (PPE)

 

The experienced molder has all procedures in place to provide full traceability throughout the resin injection molding process up to and including shipment of quality parts that meet or exceed customer specifications, along with proper documentation.  Contact Michiana Global Mold today to see how we can help you with your injection molding needs.

 

 

Precision Parts Manufacturing

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Industries That Require Precision Parts Manufacturing

Precision Parts Manufacturing supplies several industries with critical components.  Aerospace, Automotive, Military / Ordnance, Medical and Consumer Electronics are just a few of the areas where a precision parts molder is a valuable supplier.

The majority of molded critical components are made by the precision injection molding process, using thermoplastic resins.  Engineering Resins are a group of thermoplastic materials that combine great strength with light weight to be a desirable material in a wide range of conditions, and still be economical.

Precision Molding Process

The quality of a final critical component from the precision parts manufacturing process depends on several parameters.  Three factors that greatly impact the quality of a precision part are the manufacturing parameters, the material characteristics, and the mold design.

Manufacturing Parameters

When a precision injection molder is presented with a part print, they must determine the best size press to run the parts in taking the press attributes including tonnage, and clamping pressure into consideration.  They must also consider the type of tool to build, and the molding conditions that would yield the most optimum processing conditions.

Auxiliary equipment must also be considered.   When a precision molder can use automation such as sprue pickers and conveyors, they can maintain a consistent process and reliably produce quality accepted parts.

Determining the optimal parameters for the molding process is necessary to ensure consistency and reliable product quality.

Material Characteristics

When choosing the best material for an application, engineers must consider all characteristics of several different thermoplastic resins to choose the most appropriate resin that will meet the strength and durability demands of the functionality of the part.

It is also important to maintain a strong relationship with your resin suppliers.  Most polymer supply companies have material experts on hand ready and willing to assist with new information, suggestions and/or simulations.

Mold Design

A quality precision injection molded part requires a quality precision injection mold.  A flawless mold is the key to reliably and consistently producing parts to customers’ specification.

In most cases, the injection molder will design the mold based on the part print received by the customer.  Molds for manufacturing precision parts can be complex and require the skills of a journeyman mold maker.  It is helpful to have journeyman mold makers in-house that will lead the tool design and communicate with the customer’s engineers during the design phase.

CAD software and mold flow analysis is used, which is an indispensable tool for any plastic injection molded part.  Mold flow analysis is an indispensable component of any plastic injection molding design project.

Quality Procedures of Precision Parts Molders

Precision Injection Molding for demanding industries requires the molder to follow necessary quality procedures.  Meeting ISO9001:2008, and compliant to TS/ISO16949, and AS9100 standards and practicing them daily is necessary for success with precision parts manufacturing.