IMH’s tool and die capabilities extend to compression mold tooling for various manufacturing applications. We design, build, and maintain compression molds to support your production requirements, ensuring precise fit and long service life. Our experienced toolmakers understand the unique demands of compression molding for thermoset plastics, rubber, composites, and other materials that require heat and pressure to cure or form.

Compression molding remains a cost-effective manufacturing process for many applications, particularly for large parts, thick-walled components, and materials that don’t flow well in injection molding. IMH provides complete tooling support to keep your compression molding operations running efficiently.

What is Compression Molding?

Compression molding is a manufacturing process where material is placed directly into an open, heated mold cavity. The mold closes under pressure, forcing the material to conform to the cavity shape while heat cures or sets the material. Unlike injection molding where material flows through runners and gates, compression molding places material directly in the cavity, minimizing material waste and allowing the production of larger parts.

The process works well for thermoset plastics (phenolic, melamine, epoxy), rubber compounds, Sheet Molding Compound (SMC), Bulk Molding Compound (BMC), and composite materials. Parts range from electrical components and automotive parts to large industrial housings and panels. Compression molding excels at producing parts with excellent surface finish on both sides, uniform wall thickness, and minimal internal stress.

Compression Mold Design & Engineering

IMH’s engineering team designs compression molds optimized for your material, part geometry, and production requirements. We consider material flow characteristics, cure times, parting line location, ejection methods, and venting requirements during the design phase. Our goal is tooling that produces consistent parts while minimizing cycle time and maintenance needs.

Our design services include:

  • Part design review and material selection guidance
  • Mold cavity and core design for optimal material distribution
  • Parting line optimization to minimize flash and facilitate ejection
  • Venting design for air and volatile evacuation
  • Loading system design (hand load, preform, or automatic)
  • Ejection system design appropriate for material and geometry
  • Temperature control design for consistent cure cycles
  • Multiple cavity layouts for increased production
  • Detailed assembly drawings and specifications

We design molds from simple single-cavity hand load tools through sophisticated multi-cavity molds with automated loading systems and in-mold deflashing.

Compression Mold Manufacturing

IMH manufactures compression molds using precision CNC machining, wire EDM, and traditional toolmaking techniques. Our capabilities allow us to build molds ranging from prototype tools for product development through high-volume production molds.

Our manufacturing capabilities include:

  • CNC machining centers for mold bases, cavities, and cores
  • Wire EDM for intricate cavity details and tight clearances
  • CNC turning for cylindrical components and ejector systems
  • Surface grinding for precise parting line surfaces
  • Heat treatment coordination for optimal tool steel performance
  • Polishing and finishing for superior surface quality
  • Chrome plating coordination for wear resistance (when required)
  • Assembly and tryout capabilities

We select appropriate tool steels based on production volume, material abrasiveness, and operating temperature. For high-volume production or abrasive materials, we specify premium tool steels with appropriate heat treatment and surface treatments to maximize mold life.

Compression Mold Types

Positive Molds
Also called flash molds, positive molds allow excess material to escape as thin flash at the parting line. This is the most common compression mold design and works well for many materials. The flash must be removed in a secondary operation, but the mold design is simpler and more forgiving of charge weight variations. IMH designs positive molds with proper land width and clearance to control flash thickness while ensuring complete cavity fill.

Semi-Positive Molds
Semi-positive molds restrict material flow at the parting line while allowing some flash escape. This design provides better dimensional control than fully positive molds while remaining relatively forgiving. The restricted flash land creates back pressure that improves part density and surface finish. We use semi-positive designs when parts require better dimensional control than simple flash molds provide.

Fully Positive Molds
Fully positive molds (also called trapped molds or flashless molds) contain all material within the cavity with no flash escape. The male and female mold halves telescope together, trapping material completely. This design requires precise charge weight control but eliminates secondary deflashing operations. IMH designs fully positive molds with proper clearances and venting to prevent trapped air issues while maintaining flashless operation.

Transfer Molds
Transfer molding is a variation where material is placed in a pot and transferred into the cavity under pressure while the mold remains closed. This allows better control of delicate inserts and produces parts with less flash than conventional compression molding. IMH designs transfer molds for applications requiring precise insert placement or complex cavity configurations.

Materials & Applications

Thermoset Plastics
Phenolic, melamine, urea, epoxy, and polyester resins that cure under heat and pressure. Used for electrical components, handles, housings, and structural parts requiring heat resistance and dimensional stability. IMH builds molds accommodating the exothermic curing reactions and shrinkage characteristics of thermoset materials.

Rubber Compounds
Natural and synthetic rubber for seals, gaskets, grommets, vibration isolators, and other elastomeric parts. Rubber compression molds require special considerations for vulcanization times, vent design, and surface finish. We design molds with proper venting to prevent blisters and porosity while ensuring complete cure.

Sheet Molding Compound (SMC)
Glass fiber reinforced polyester or vinyl ester used for large body panels, electrical enclosures, and structural components. SMC compression molds must accommodate the material’s flow characteristics and fiber orientation effects. IMH builds large SMC molds with proper venting, material flow control, and structural integrity for high molding pressures.

Bulk Molding Compound (BMC)
Similar to SMC but with shorter fibers and used for smaller, more intricate parts. BMC flows better than SMC, allowing more complex geometries. We design BMC molds considering material flow patterns, fiber length effects, and surface finish requirements.

Composites
Carbon fiber, fiberglass, and other reinforced materials for aerospace, automotive, and industrial applications. Compression molds for composites must provide uniform pressure distribution and precise temperature control. IMH designs molds for both dry fiber with resin infusion and prepreg composite materials.

Special Features & Capabilities

Insert Molding
Compression molds can encapsulate metal inserts, fasteners, electrical contacts, and other components. IMH designs insert retention features that hold components securely during molding while preventing material flash around inserts. Our designs accommodate thermal expansion differences between inserts and mold materials.

Multiple Cavities
For higher production volumes, we design multi-cavity compression molds that produce multiple parts per cycle. Cavity layout considers material loading, venting, and ejection requirements. We ensure uniform pressure distribution across all cavities for consistent part quality.

In-Mold Deflashing
For positive and semi-positive molds, we can incorporate deflashing features that trim flash during mold opening. This eliminates or reduces secondary deflashing operations. IMH designs in-mold trimming systems appropriate for your material and part geometry.

Temperature Control
Compression molds require precise temperature control for consistent cure cycles. We design heating systems using cartridge heaters, strip heaters, or hot oil circulation depending on mold size and temperature uniformity requirements. Temperature control channels ensure even heating throughout the mold cavity.

Ejection Systems
Ejecting cured parts without damage requires appropriate ejection design. IMH designs ejector pin systems, air ejection, stripper plates, or combination systems based on part geometry and material. We ensure ejection forces are distributed to prevent part distortion or surface damage.

Mold Maintenance & Repair

Compression molds require regular maintenance to maintain part quality and production efficiency. IMH provides comprehensive maintenance services including:

  • Mold cleaning and inspection
  • Cavity and core polishing or refinishing
  • Parting line surface restoration
  • Vent cleaning and re-cutting
  • Ejector system inspection and replacement
  • Heating element testing and replacement
  • Guide pin and bushing replacement
  • Chrome plating repair (if applicable)
  • Documentation of mold condition and recommendations

Regular maintenance prevents common issues like flash buildup, poor surface finish, and incomplete cures. We create maintenance schedules based on your production volume and material characteristics.

Mold Repair Services

Cavity Damage Repair
Scratches, gouges, or wear in cavity surfaces affect part appearance and can cause sticking. IMH repairs damaged cavities through welding, machining, and refinishing. We match original surface finishes and restore proper dimensions.

Parting Line Repair
Damaged parting lines cause excessive flash and poor part quality. We repair parting line surfaces through grinding, milling, or EDM to restore proper metal-to-metal contact. Proper parting line fit is critical for flash control and part consistency.

Venting Restoration
Blocked or inadequate venting causes trapped air, blisters, and incomplete fill. We clean existing vents and add new venting as needed. Proper vent design and maintenance are critical for thermoset and rubber molding quality.

Component Replacement
Worn or damaged ejector pins, guide pins, springs, and other mold components affect operation and part quality. IMH manufactures replacement components from original drawings or reverse engineers damaged parts. We stock common components for rapid turnaround.

Industries We Serve

Electrical & Electronics
Circuit breaker housings, electrical insulators, switch components, and terminal blocks from thermoset materials requiring high dielectric strength and arc resistance.

Automotive
Under-hood components, body panels, structural parts, and interior components using SMC, BMC, and thermoset materials for heat resistance and dimensional stability.

Aerospace
Composite components, interior panels, and structural parts requiring high strength-to-weight ratios and precise tolerances.

Industrial
Electrical enclosures, pump housings, valve components, and equipment parts requiring chemical resistance, heat resistance, or electrical insulation.

Appliance
Handles, knobs, housings, and structural components using thermoset plastics for heat resistance and durability.

Infrastructure
Electrical utility components, metering housings, and outdoor equipment requiring weather resistance and electrical properties.

Quality Control

Every compression mold IMH manufactures undergoes thorough quality inspection:

  • Dimensional verification of cavity and core features
  • Parting line surface inspection and fit verification
  • Vent depth and placement verification
  • Ejection system operation testing
  • Temperature distribution verification
  • Sample molding under production conditions
  • First article inspection of molded parts
  • Documentation package with assembly drawings and operating procedures

Our ISO 9001:2015 certification ensures consistent processes and continuous improvement throughout every project.

Why Choose IMH for Compression Molds

Experienced Toolmakers
Our team understands the unique requirements of compression molding across various materials. We apply decades of combined experience to design and build molds that produce quality parts consistently.

Complete Manufacturing Capabilities
From design through manufacturing and maintenance, everything happens at IMH. This integration ensures quality control, faster turnaround, and responsive support throughout your mold’s service life.

Material Expertise
We understand how different materials behave during compression molding and design molds accordingly. Whether you’re molding thermosets, rubber, composites, or other materials, we optimize tooling for your specific application.

Responsive Service
When production issues arise, IMH responds quickly with repair and troubleshooting support. Our complete capabilities allow us to address mold problems efficiently without relying on outside services.

Getting Started

Ready to discuss your compression molding tooling needs? Contact IMH with:

  • Part drawings or CAD files
  • Material specification and grade
  • Annual production volume
  • Quality and surface finish requirements
  • Cure time and temperature parameters
  • Existing mold documentation (if repair/modification)

Our engineering team will review your application and provide a detailed quote including design recommendations, manufacturing timeline, and pricing. Whether you need new compression molds for product development or support for existing tooling, IMH delivers the expertise and quality your production demands.

Looking for compression molding tooling expertise? Request A Conversation