Sensors - A220

Sensors
Document Type	Article
Document Identifier	220
Themes	Thermal management Materials deposition and consolidation management Residual stress and dimensional control management
Relevant Class	Equipment
Tags	Debulking Equipment Fibre-bed compaction Fluid flow Gas flow Pressurized Resin flow Thermal transformation
Factory Cells	Deposition Forming Thermal transformation
Prerequisites	Equipment

Introduction

Sensors are devices that are can detect and respond to physical changes in it's environment. They are an essential component of automation, monitoring and control systems of a large number of composites manufacturing processes as well as for use in mechanical testing and structural health monitoring in service.

Scope

This page provides an overview and typical applications of sensors that are used in the composites industry.

Significance

Sensors are integral to the manufacturing, testing, and health monitoring of composite parts, offering precise process control, quality assurance, and real-time structural evaluation. Process parameters play a crucial role in determining the final product quality, making it essential to measure and monitor these parameters using specialized sensors for effective control systems. The demand for sensors has grown significantly with the increasing adoption of automation in composite manufacturing processes. Beyond manufacturing, sensors are also utilized for mechanical testing of composite parts and for monitoring the development of defects during their service life.

Prerequisites

Recommended documents to review before, or in parallel with this document:

• Equipment

Overview

Depending on the specific process, there are different sensors used to measure process parameters in a composites manufacturing process. Some sensors are also used to characterize equipment behaviour that can provide valuable information when designing the actual manufacturing process. Some common types of sensors used in composites manufacturing include:

• Temperature sensors: Temperature sensors are used to measure the temperature of a tool-part configuration or the equipment processing environment during a manufacturing process. These sensors can both be local sensors that measure temperature locally (like thermocouples) as well as full field sensors that can measure temperature across a wider area (like thermal cameras). Again, temperature sensors can be either contact type sensors where the sensor is in full contact with the object to be measured (like thermocouples, thermistors) or non-contact type which are not in direct contact with the object to be measured (like thermal cameras).

Link to main Temperature Sensors page

• Pressure sensors: Pressure sensors are used to measure the operating pressure during manufacturing processes like autoclave cure, compression molding and resin transfer molding (RTM). They can be used in different stages of the manufacturing process, starting from material deposition management (checking for leaks in vacuum bags) to monitoring and controlling equipment operating pressure during thermal transformation (measuring autoclave pressure during curing).

Link to main Pressure Sensors page

• Flow sensors: Flow sensors are used to monitor the flow of liquids or gases in a variety of applications in composites manufacturing processes.
  • Liquid flow sensors: Liquid flow sensors can be used to monitor and control the flow of resin in processes like resin transfer molding (RTM) and vacuum assisted resin infusion (VARI) .
  • Gas flow sensors: Gas flow sensors like anemometers are often used to measure and characterize the airflow in processing equipment like autoclaves. The airflow analysis inside autoclaves are a crucial part of designing cure processes for highly reliable autoclave-based composite manufacturing processes .

Link to main Flow Sensors page

• Strain Sensors: Strain sensors are used widely during manufacturing and mechanical testing of composites parts. Fibre optic strain sensors like Fibre Bragg Gratings (FBGs) are used to measure strains for a number of applications like mechanical testing, conditioning monitoring as well as structural health monitoring . These sensors are typically very small in size and can be embedded into composite structures either during or after manufacturing.

Link to main Strain Sensors page

• Cure sensors: Cure sensors are used in manufacturing processes to monitor the progress of cure in real time to enable precise process control for consistent quality. They typically work by monitoring the change in properties of the resin as it cures. For example, dielectric sensors work on the principle of detecting the change in the resin's electrical properties during curing .

Link to main Cure Sensors page

Applications

Typical applications of sensors in composites manufacturing setups include:

• Use of thermocouples in monitoring and controlling temperature of curing parts during autoclave cure
• Use of pressure gauges to check for detection of leaks in vacuum bags
• Use of anemometers to measure the airflow in a particular location inside an autoclave
• Use of strain gauges in measuring strain distribution in composite samples during mechanical testing
• Use of dielectric cure sensors to monitor and reduce cycle times during cure

Explore this area further

• Sensors - A220
  • Temperature Sensors - A221
    • Thermocouple - A227

References

About	Help

Engineered materials (designed to have specific properties) made from two or more constituent materials with different physical or chemical properties. The constituents remain separate and distinct on a macroscopic level within the finished structure.

For polymer matrix composites (PMCs), resin refers to the matrix; the continuous material phase that binds the reinforcement together, maintains shape, and transfers load. Resins are divided into two main groups: thermosets and thermoplastics.

Resin transfer moulding (RTM) involves loading a preform into a two (or more) piece, matched tool, closing it, and injecting resin under pressure (~15-100 psi, or ~1-7 bar).

Well suited to small to medium sized parts, limited to large sizes due to injection pressure loads and tool cost.

A central processing theme in the manufacturing cycle. It includes the steps primarily involved in moving material into the correct position on the tool or with combining fibre, resin and other constituents in-situ on tools.

Vacuum assisted resin infusion (VARI) - also known as vacuum assisted resin transfer moulding (VARTM), vacuum infusion process (VIP) or often just resin infusion. VARI is a liquid composite moulding (LCM) closed mould process with a single side tool and vacuum bag where the resin is drawn through the preform using vacuum.

The continuous material phase that binds the reinforcement together, maintains shape, transfers load, protects the reinforcement from environment and damage, and provides the composite support in compression.

Desirable characteristics:

• Moisture/chemical resistance
• Low density
• Processability