New Injection Molding Tech Boosts Lightweight Composite Strength

In modern engineering, composite materials are playing an increasingly vital role. From aerospace to automotive industries, and from sports equipment to medical devices, composites are gradually replacing traditional metal materials due to their unique advantages, including high strength-to-weight ratios, excellent corrosion resistance, and design flexibility. As environmental awareness grows and energy efficiency becomes increasingly important, lightweight design has emerged as a key driver across industries. Against this backdrop, a new composite manufacturing technology called "injection molding sandwich" has emerged and quickly captured widespread attention in the industry.

This article provides an in-depth analysis of injection molding "sandwich" technology, covering technical principles, process flows, advantages, application cases, material selection and performance, as well as future development trends. We will examine a case study of a motorcycle seat base jointly developed by Engel and KTM Technologies to explore the technology's practical potential and value. From an expert perspective, we will analyze the challenges and opportunities facing this technology and envision its future prospects in composite manufacturing.

Composite materials combine two or more different materials through physical or chemical methods to achieve performance characteristics unattainable by single materials. Common composite manufacturing techniques include:

• Hand Lay-up: A traditional method suitable for small-batch, complex-shaped components, but suffers from low efficiency, inconsistent quality, and high operator skill requirements.
• Compression Molding: Uses pre-impregnated or short fiber materials cured under high temperature and pressure, ideal for mass production but with high mold costs.
• Filament Winding: Winds resin-impregnated fibers around a mandrel, suitable for rotational parts like pipes and pressure vessels.
• Pultrusion: Pulls resin-impregnated fibers through a die to create profiles like beams and columns.
• Resin Transfer Molding (RTM): Injects resin into a mold containing reinforcement materials, enabling automated production of complex shapes.

Despite significant achievements, these methods face challenges:

• Low Production Efficiency: Traditional methods often have long cycles and low automation, limiting mass production capabilities.
• High Costs: Expensive raw materials combined with energy-intensive processes result in elevated production costs.
• Recycling Difficulties: Technical and economic barriers complicate recycling efforts, leading to environmental concerns.
• Performance Inconsistency: Material quality, processing conditions, and environmental factors can cause performance variations.

Injection molding "sandwich" technology represents an innovative composite manufacturing process that combines thin reinforcement layers (such as unidirectional tapes or fabrics) with thermoplastic matrices to form a sandwich structure. Unlike traditional methods, this approach eliminates preheating by directly placing reinforcements into the mold before injecting thermoplastic material for rapid, efficient forming.

Key characteristics include:

• Lightweight Design: Optimized material distribution reduces weight while maintaining performance.
• High Stiffness: The sandwich structure significantly enhances load-bearing capacity.
• Space Efficiency: Thin-walled designs minimize installation space requirements.
• Cost Reduction: Eliminates preheating, uses standard equipment, and shortens cycle times.
• Recyclability: Thermoplastic materials enable easier end-of-life recycling.

Compared to conventional methods, this technology offers:

• High Efficiency: Automated injection molding enables mass production with short cycles.
• Cost Effectiveness: Reduced energy consumption and material waste lower production costs.
• Design Flexibility: Accommodates complex geometries and multiple material combinations.
• Environmental Benefits: Thermoplastics support circular economy principles.

Limitations include:

• Material Restrictions: Primarily limited to thermoplastics rather than thermosets.
• Lower Reinforcement Content: Flow requirements constrain reinforcement percentages.
• Interfacial Bonding Challenges: Requires careful optimization of matrix-reinforcement adhesion.

The core innovation lies in the sandwich structure's mechanical behavior:

• High Bending Stiffness: Faces bear primary stresses while cores prevent buckling.
• Shear Resistance: Cores effectively transfer shear loads between faces.
• Impact Absorption: Cores dissipate energy to protect structural integrity.

The manufacturing sequence involves:

1. Reinforcement Preparation: Cutting and positioning UD tapes or fabrics (typically polypropylene-based).
2. Mold Preparation: Specialized molds maintain reinforcement alignment during injection.
3. Material Placement: Positioning reinforcements in both mold halves without preheating.
4. Injection Molding: Injecting molten thermoplastic to penetrate reinforcements.
5. Cooling and Demolding: Solidifying components before extraction.

Key controls include:

• Injection pressure and speed
• Melt and mold temperatures
• Cooling rate optimization

Advanced control methods like closed-loop systems and expert algorithms ensure quality consistency.

Weight reduction strategies combine:

• Low-density material selection
• Sandwich structural optimization
• Topology-driven design minimization

The synergistic face-core interaction delivers exceptional rigidity through:

• Face-dominated load bearing
• Core-supported stability
• Integrated structural response

Compact designs enable:

• Reduced part thicknesses
• Multifunctional component integration
• Improved packaging efficiency

Economic benefits stem from:

• Eliminated preheating steps
• Rapid cycle times
• High material utilization
• Automated processing

Mono-material constructions (e.g., PP-PP systems) facilitate:

• Mechanical recycling
• Re-melting and reforming
• Sustainable lifecycle management

KTM Technologies partnered with Engel to redesign motorcycle seat bases, reducing thickness from 9mm to 2.5mm while maintaining rigidity, creating space for electronic components.

The sandwich structure combines:

• UD-reinforced PP faces
• Expanded PP (EPP) core

Achieved 66% space savings and 26% weight reduction at equivalent stiffness.

Automated injection molding with closed-loop parameter control ensured quality consistency.

• UD Tapes: Unidirectional strength for linear loading
• Fabrics: Multidirectional reinforcement for complex stresses

• Polypropylene (PP): Balanced processability and chemical resistance
• Polyamide (PA): Enhanced strength and thermal performance

Tailored formulations balance mechanical properties, thermal behavior, chemical resistance, and cost.

Potential growth sectors include:

• Automotive: Interior/exterior components and structural elements
• Aerospace: Cabin interiors and airframe structures
• Sports Equipment: High-performance gear requiring durability and lightness

Future directions encompass:

• Smart Manufacturing: AI-driven process optimization and quality control
• Sustainability: Enhanced recyclability and reduced environmental impact
• Performance Enhancement: Novel material developments for extreme conditions

While facing material cost and process control hurdles, the technology benefits from:

• Growing lightweighting demands
• Continuous technical innovation
• Supportive regulatory policies

This innovative approach delivers unparalleled advantages in lightweighting, stiffness, space efficiency, cost reduction, and sustainability. With expanding applications across industries and ongoing technological advancements, injection molding sandwich technology is poised to redefine composite manufacturing, offering sustainable solutions that meet evolving engineering demands while addressing global environmental challenges.