The Evolution of Automated Prepreg Layup Techniques: Early Developments to Modern Applications (ATL)

Introduction

The article examines the development of Automated Tape Laying (ATL) as a manufacturing process for layering material, known as prepreg tape, onto a mold surface in a specific direction to build up layers. The process is similar to additive manufacturing, or the reverse of machining, as material is added rather than removed. The development of these systems has a long history, starting with the use of carbon fiber in aerospace manufacturing in the 1960s. The article discusses the various developmental stages of ATL and explains why they function in their current form and why they may not be in high demand.

Jump to the right section

• Historical Developments of Automated Tape Laying: 1960-1980

• Automated Tape Laying Development from the 1980s to 1990s: Challenges and Advances

• Automated Tape Laying development from the 1990s till today

• ATL (Automated Tape Layering) Process for Prepreg Layup in Aerospace Manufacturing

Historical Developments of Automated Tape Laying: 1960-1980

Drawing of an ATL delivering slit tape over a curved surface [2]

1. In 1966, carbon fibers became commercially available, which led to early efforts to automate prepreg layup to improve productivity and quality

2. Automated tape laying (ATL) systems were developed in the late 1960s and were in use by the mid-1970s

3. In the 1970s, aerospace manufacturers and research institutions developed early ATL systems

4. In the 1970s, ATL layup speeds of 10-20 m/min were reported, with improved material utilization and reduced layup errors.

5. Materials were wasted 50-100% at the time of the 1980 manual layup, with a productivity estimate of 1 kg/h

6. For certain components, ATL was able to reduce material waste and layup time by 65% compared to manual layup

Automated Tape Laying Development from the 1980s to 1990s: Challenges and Advances

Typical gantry style tape laying machine [1]

1. In the early 1980s, ATL technology was changed to a generic process and layup speeds were increased to 60 m/min with new systems

2. ATL machines at that time were mostly Flat Tape Laminating Machines (FTLM), which could only apply tape to flat tools

3. Robot arms were used for layup applications but had speeds limited to 60 m/min and required high accuracy for offline programming

4. Many ATL systems became high-rail gantries that were stiff and heavy, with difficulties in delivering tape with defined compaction pressures and regular debulking cycles

5. By the end of the 1980s, increased layup capability led to issues with ply alignment due to uneven layup pressure and tape tension on the head

6. To prevent transverse movement of the ply and improve alignment, systems were developed with controlled tension and layup pressure

7. In 1995, the approach was extended to multiple layup elements operating independently from the layup head

8. The aim of using layup pressure control became mainly focused on reducing debulking operations,

9. Material outline and changing tack levels remained unresolved, and actual layup speeds remained unchanged at 10-20 m/min

10. Commercial aircraft adoption was slow during this period due to the high cost of ATL systems (estimated at $3.5M for basic systems) and high productivity requirements.

11. The end of the 1980s showed no significant improvement in productivity for an automated layup over manual forming, but automation was still desirable as it improved reliability, consistency, and reduced material waste

Drawing of an early composite components manufacturing system [2]

Automated Tape Laying development from the 1990s till today

Schematic of an ATL layup head [2]

1. Tape heating was introduced in the 1990s to improve laminate layup and control tack

2. The first thermoplastic layup used tape heating in 1991, and a hot-air heater was added to the ATL to enable tape attachment to complex contours

3. To keep plies aligned during layup on complex geometries, the layup roller diameter was decreased to 50 mm in order to improve dexterity.

4. There was no relationship between layup pressure and the number of plies during thermoset tape layup, while ply orientation and roller diameter were weakly related, although tack was not included in the study.

5. In order to lay up and consolidate thermoplastic materials directly, laser-assisted heating of thermoplastic tape was proposed, but AFP was adopted instead.

6. Today, ATL layups are in very limited usage in aerospace and renewable energy industries owing to their high initial capital expenditures, limited geometric complexity capabilities, and higher material wastage rates than AFPs.

ATL (Automated Tape Layering) Process for Prepreg Layup in Aerospace Manufacturing

Composite tape layer delivery head [1]

Automated Tape Laying (ATL) is a manufacturing process in which a continuous sheet of material, known as prepreg tape, is added to a mold surface in a specific direction to build up layers in different directions, resulting in a layup. The process can be thought of as a form of additive manufacturing, or inverse machining, as the material is added rather than removed through machining.

Picture of an ATL layup head with relevant functional groups labelled [2]

1. Prepreg tape is used in ATL, typically 75, 150, or 300 mm wide, and supplied on a cardboard core similar to prepreg used for a manual layup

2. ATL systems are mounted on horizontal gantries or vertical columns and are CNC systems that follow predefined paths accurately and reproducibly to eliminate layup errors

3. The tape is adhered to the mold or previous layers without any air voids using a flexible silicone roller or segmented laying shoes.

4. The layup speed is typically 0.83-1 m/s, with compaction of 445 N for 75 mm wide thermoset tape or 1000 N for 300 mm wide thermoset tape, and pressure of 0.1 MPa for thermoset material or 1.4-3.6 MPa for the thermoplastic material.

5. In order to improve alignment, and enable layup into curved geometries, tension is imparted on the plies and ply backing between the material supply and layup point.

6. Material can be heated during layup to control temperature, either in front of the layup head or on the layup system as it is passing through the ATL head

7. At the end of a ply course, the tape is cut using rotating or ultrasonic blades, and the remaining length is delivered to finish the ply course

8. The process is repeated until the ply is finished, or stopped by the program, user intervention, or an automated fault detection system.

Summary

In conclusion, the development of Automated Tape Laying (ATL) has evolved significantly since its inception in the 1960s. From its early beginnings as a process specifically developed for carbon fiber and aerospace manufacturing, the technology has undergone numerous changes and advances. In the 1980s and 1990s, challenges such as high layup speeds, difficulties in delivering tape with defined compaction pressures, and limited heating capabilities were addressed through the development of new systems and technologies. In the years since, ATL has been further refined and diversified, with a focus on increasing productivity and addressing specific layup issues. Despite the significant progress made in the field, ATL Today, they see very limited usage in aerospace and renewable energy industries owing to their high initial capital expenditures, limited geometric complexity capabilities, and higher material wastage rates than AFPs.

About Addcomposites

Addcomposites is the provider of the Automated Fiber Placement (AFP) ecosystem - including the Fiber Placement System (AFP-XS), 3D Simulation and Programming Software (AddPath), and Robotic Cells (AddCell). With the leasing program for the AFP system (AFPnext), composites manufacturers can work with thermosets, thermoplastics, dry fiber placement, or in combination with 3D Printers on a monthly basis.

Sources

1. Characterization of damage in Dry Automated Fiber Placement (DAFP) carbon/epoxy composites under tensile loading

2. The engineering aspects of automated prepreg layup: History, present and future