Fiat LP-7N035 Two-Stage Molding Method for Adhesion Between Hard and Soft Materials

The “Fiat LP-7N035 Two-Stage Molding Method for Material Bonding - Adhesion between Hard and Soft Materials” standard, developed by Fiat Chrysler Automobiles (FCA) (now Stellantis), an Italian-American automotive company, describes the requirements and test methods for parts produced by top molding or two-component injection molding where two different thermoplastics are permanently bonded together in a single process. This standard is commonly used in the following areas:

• Soft-touch handles and buttons (hard plastic + thermoplastic elastomers / thermoplastic polyurethane)
• Sealing elements integrated into rigid housings
• Interior trim pieces with different textures or colors
• Multi-material automotive components requiring strong adhesion without the need for additional adhesives.

The main aspects covered by this standard are:

• Material compatibility between two polymers.
• Adhesion strength (peel, tensile, shear)
• Temperature cycle, humidity and aging resistance.
• Visual and dimensional requirements
• Chemical resistance
• Process parameters for reliable bonding.

Fiat uses a range of LP-7xxxx specifications for various plastic material and process requirements. The Fiat LP-7N035 standard, in particular, focuses on multi-material injection molding technology, which is becoming increasingly important for modern vehicle interiors and lightweight components. This type of specification is primarily used by suppliers to verify materials and manufacturing processes during part approval.

In short, the Fiat LP-7N035 standard is an automotive material testing specification used to evaluate the adhesion between rigid and flexible materials in multi-material molded components within an engineering system. This standard specifically focuses on two-stage molding assemblies where rigid thermoplastics are chemically or mechanically bonded to flexible elastomeric materials.

This standard generally applies to interior and exterior automotive parts that combine the following materials:

• A rigid structural substrate
• Soft-touch or sealing layer
• Thermoplastic elastomers (TPE)
• Polypropylene (PP)
• Acrylonitrile butadiene styrene (ABS)
• Thermoplastic polyurethane (TPU)
• Other molded polymer systems

The primary purpose of the Fiat LP-7N035 standard is to verify that bonded materials maintain adequate adhesion throughout the vehicle's service life. In modern automotive manufacturing, many components are produced using die-casting technologies for the following improvements:

• Ergonomics
• View
• Sealing performance
• Vibration damping
• User comfort

Poor adhesion between hard and soft layers can lead to the following:

• Layer separation
• Peeling
• Security risks
• Noise generation
• Cosmetic flaws
• Water inlet

Therefore, the Fiat LP-7N035 standard specifies controlled procedures for evaluating adhesion integrity under mechanical stress and exposure to environmental influences.

This standard generally applies to the following:

• Two-stage injection molding parts
• Soft-touch interior upholstery
• Arms
• Buttons and switches
• Instrument panel components
• Door trim elements
• Seals integrated into plastic carriers
• Decorative automotive components

The described test method evaluates whether the elastomer layer remains securely bonded to the rigid substrate after manufacturing and aging. This method generally follows these steps:

• Preparation of molded samples
• Conditioning of samples under specified environmental conditions.
• Application of mechanical separation forces
• Measuring adhesion strength or observing failure modes.

The assessment includes the following:

• Peel test
• Pulling separation
• Manual delamination examination
• Adhesion and cohesion failure analysis

A successful outcome normally requires the following:

• Minimum bond strength values
• No visible separation.
• Controlled failure within the soft material, not at the interface.

The Fiat LP-7N035 standard is generally used for the following combinations:

• Polypropylene (PP) + Thermoplastic elastomers (TPE)
• Acrylonitrile butadiene styrene (ABS) + Thermoplastic polyurethane (TPU)
• Polyamide (PA, nylon) + elastomer systems
• Polycarbonate (PC) / Acrylonitrile butadiene styrene (ABS) + soft-touch coatings
• Thermoplastic vulcanizates (TPV)

These combinations are frequently found in modern automotive interiors where tactile feel and durability are important.

Bonded materials used in the automotive industry must withstand harsh operating conditions. Fiat LP-7N035 standard tests therefore include exposure to the following:

• heat aging
• Gender
• Thermal cycle
• Exposure to UV rays
• Chemical substances
• Low temperature conditioning

These conditions simulate real vehicle environments and ensure long-term reliability.

Without a standardized adhesion test, components may appear acceptable when new but may fail during vehicle use. In this respect, the Fiat LP-7N035 standard is considered important for the following reasons:

• Prevents separation and peeling: Many vehicle parts combine a hard plastic substrate with a soft elastomer layer for comfort, grip, sealing, or aesthetics. If the bond between these materials is weak, the soft layer can:
  • Peelable from the bottom layer.
  • It can be separated from the edges and corners.
  • Bubbles or raised areas may form.
  • It may lose its functional characteristics.

This standard confirms that the bond is strong enough to withstand these failures.

• Ensures long-term durability: Automotive components are exposed to harsh environmental conditions, including:
  • High summer temperatures
  • Freezing winter temperatures
  • Humidity and condensation
  • UV radiation
  • Cleaning chemicals
  • Repeated mechanical loading

This standard helps ensure that material adhesion remains effective for the lifetime of the vehicle, rather than degrading after exposure to environmental factors.

• It maintains safety and functionality: Some molded components have functional roles. For example,
  • Door handles
  • Control buttons
  • Keys
  • Sealing elements
  • Handles and arms

A connection failure can affect user operation, component reliability, and perceived vehicle quality. This standard helps ensure these components continue to function as designed.

• It preserves the interior appearance: Interior upholstery is a key factor in customer satisfaction. Poor adhesion can lead to:
  • Visible peeling
  • Surface defects
  • Gaps between materials
  • Premature wear

Tests conducted according to this standard help maintain a high-quality appearance throughout the vehicle's lifespan.

• Supports lightweight vehicle design: Modern vehicles are increasingly using polymer-based multi-material components to reduce weight and improve fuel efficiency. Because these designs rely heavily on material bonding rather than mechanical fasteners, adhesion performance becomes critical. This standard enables lightweight bonded assemblies to replace heavier, conventional structures without sacrificing durability.

Consequently, the Fiat LP-7N035 standard is necessary because it verifies the strength and durability of bonds between hard and soft materials used in automotive components.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its customers, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services in accordance with the Fiat LP-7N035 standard.