Rubber Molding Process

Rubber Injection Molding Process / Rubber Compression Molding Process / Rubber Transfer Molding Process

All of Qualiform’s rubber molding processes take place right here in the U.S.A. All our rubber molded products are American-made and designed to your unique specifications. Qualiform Rubber Molding delivers fast, reliable manufacturing of high-quality rubber products and rubber compound development at a competitive price.  We are proud to be the number one choice of OEMs across all industries including appliance, healthcare, electrical, industrial, medical, plumbing, sports, recreation, transportation, EMI shielding, sound management, vibration management, chemical, and aerospace industries.

Customers choose our rubber molding process for responsiveness, reliability, competitive pricing, and fast turnaround.  Pricing is maintained through attentive monitoring of raw material costs and environmental initiatives with repurposed rubber saved from landfills. We offer 3-shift/24-hour production for the shortest runs and quickest turnaround.

Factors Affecting Rubber Tolerances
Not sure which rubber materials and methods are best for you project? Contact Qualiform today to receive expert material recommendations.

Rubber Injection Molding

Injection Molding Process / Advantages of Injection Molding / Disadvantages of Injection Molding

Rubber injection molding is an ideal process to produce precision rubber molded components and rubber-to-metal bonded products. The rubber injection molding process is a rubber molding process based off a process that was intended for molding plastics. The difference in the processes is that rubber is cured under significantly more pressure per square inch of molds cavity surface. Rubber injection molding began in the mid-1960s.

This rubber molding process is selected for rubber parts that require high volumes, tight tolerances, over-molding or precision applications. Rubber injection molding delivers speed and precision not found in other rubber manufacturing processes.  It is an optimal manufacturing process for products specified with rubber compounds that have quicker rubber cure times. Efficiency is gained by a higher level of automation, strict control over flash and reduced waste from scrap parts.

Rubber Injection Molding Process Description

Rubber injection molding successfully alters the plastics process by heating the rubber and placing it under significantly more pressure per square inch of cavity surface in molding.  Through various innovations, injection molding has become one of the most efficient ways to create molded rubber products in many cases.

The process of injection and injection-transfer molding starts with efficient material preparation. To begin, the material is mixed in bulk and then stripped immediately into continuous approx. 1.25″ wide & .375″ strips. The strips of uncured rubber stock are then fed from a hopper into the rubber molding injection equipment via a conveyance channel.

A large auger type screw moves the stock into a barrel that holds a specific amount of rubber stock.  As it turns and moves through the channel into the injection unit, the material is heated.  As the rubber stock is heated, it plasticizes to a target temperature.  The plasticized rubber material is then injected into a heated mold cavity held under high-pressure.  A runner and gate system is used similarly to the plastic injection molding process.  The temperature and pressure activate the cure of the rubber compound, vulcanizing it.  Once the rubber reaches and required level of cure, it is allowed to cool and reach a solid state within the mold. The molds open and parts are removed or ejected ready for the next cycle.

injection molded rubber grommets
Custom Injection Molding
rubber injection molding

Advantages of the Rubber Injection Molding

  • A highly efficient process
  • Can be fully automated with automatic material feeding
  • Provide high precision rubber molded products
  • Superior process for consistency and repeatability
  • Allows for molding of complex geometry
  • Ideal over-molding of inserts, overmolded components and rubber to metal bonding
  • Eliminate preforms and preform labor cost
  • Flashless molding / flashless tooling / eliminating secondary trimming
  • Rapid cavity filling
  • Reduced cycle time
  • Minimal material waste

Disadvantages of Rubber Injection Molding

  • Higher start-up/shutdown costs
  • Suited for high volume applications
  • Not all elastomers are suitable
custom injection molded edpm suspension

Injection Molded Applications:

  • Rubber boots
  • Rubber gaskets
  • Rubber seals
  • Rubber grommets
  • Colored rubber products
  • Rubber bumpers
  • Rubber grips
  • Rubber diaphragms
  • Rubber bellows
  • Rubber shock absorbers
  • Rubber to metal bonding products
  • Complex rubber products
  • Vibration control parts / vibration isolation parts
  • Chemical or corrosion resistant parts
  • Abrasion-resistant parts
  • Custom rubber parts

Compression Molding

Compression Molding Process / Advantages of Compression Molding / Disadvantages of Compression Molding

Rubber compression molding is an ideal process for low to medium volume production of rubber products.  This rubber molding process can produce a diverse range of precision rubber molded components.  Allowing for the affordable production of large, intricate products. It is often used to produce environmental seal products such as rubber o-rings, seals and gaskets.

The Rubber Compression Molding Process

Compression molding is a process that involves taking a rubber compound or mixed raw material and creating “pre-forms” in the basic shape of the end product.

This rubber molding process uses a preformed piece of uncured rubber that is placed in an open mold cavity.  The mold is preheated to an elevated temperature.  As the mold closes, the material is compressed and flows to fill the rubber mold cavity.  A combination of high-pressure and elevated temperatures activates the curing of the rubber compound, aka vulcanization.  The optimal level of cure is achieved, the part hardens and cools then the mold is opened and part removed.  The cycle repeats with the next rubber preform inserted into the rubber mold.

Custom Rubber Manufacturers
butyl rubber molding

The Benefits of the Compression Molding Process

  • Economical process
  • Low-cost tooling compared to rubber injection molding
  • Maximized cavity count
  • Ideal for large parts that require a long cure time
  • Can process most elastomers and cure systems

Disadvantages of Compression Molding

  • Longer cycle times
  • Mid-range precision and consistency
  • Labor intensive

Applications of compression molding range from simple drive belts to complex large diameter diaphragms.

Compression Molded Applications:

  • Rubber Air Guage
  • Bumper for Suspension
  • Hospital Bed Tires
  • Commercial Washing Machine Seals
  • Rubber Seals

Transfer Molding

Transfer Molding Process / Advantages of Transfer Molding / Disadvantages of Transfer Molding

The transfer molding process can be used to produce both solid rubber parts and parts that require bonding rubber to a metal or non-metallic component. Examples of parts manufactured with transfer molding include vibration isolators and shock absorbers.

The Rubber Transfer Molding Process

Similar to compression molding, transfer molding requires raw material preparation into pellets and/or pre-forms.  Rather than placing the preform in the mold cavity, the preformed material is placed in a “pot” located between the top plate and a plunger.  In the pot, the material is compressed by the heated plunger and forced (transferred) through sprues into the cavity below.  The plunger is kept in place until the preform takes on the shape of the mold and the cure is reached, vulcanized.  The part is allowed to harden, cool, then is ejected. The cull pad, any cured rubber left in the pot, is removed, mold cavities are cleaned and the next molding cycle begins.

When used for rubber to metal bonding, the transfer molding process requires the components are loaded into a heated mold either by hand or using a loading fixture.  Material is loaded into the well pot of the transfer mold.  The mold closes and the heated rubber is then transferred through the runner and gate sprues into the mold cavities.  Under pressure and elevated temperatures, the rubber cures/vulcanizes and parts are removed.

The rubber transfer mold consists of a piston, well pot, sprue plate, cavity plate, and a base plate with a knock-out system used to eject the parts after molding.

Transfer Molding
colored neoprene transfer molded rubber parts

The Benefits of the Transfer Molding Process

  • Economical process with high cavity count per mold per cycle
  • Cost effective tooling
  • Allows for rubber to metal bonding
  • Allows for rubber overmolding
  • Tighter dimensional tolerances than compression molding
  • Ideal for large parts that require a long cure time
  • Can process most elastomers and cure systems

Disadvantages of Rubber Transfer Molding

  • Longer cycle times
  • Mid-range precision and consistency
  • Labor intensive
  • Increased flash and waste

Transfer molding is an ideal process to not only produce precision molded rubber products, but also products that require rubber bonded to metal surfaces.

Transfer Molded Applications:

  • Antenna Whip Assemble
  • Automotive Rubber Bumpers
  • Combine Parts
  • Latches
  • Custom Dental Grips