Tag Archives: dry fibers

-Making a Preform – How Can I Count the Ways?

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Making a part by RTM or vacuum infusion has two basic steps – first a dry Preform is produced and then resin is infused into the Perform in a tool where the part is cured. Building a high quality Preform is essential to produce a high quality part, and the majority of part cost and time are associated with manufacturing the Preform. Dry fiber material is supplied on rolls, which are processed in three steps to make a Preform:

  • Material is cut from the roll (usually to specific ply shapes)
  • Plies are placed into a mold or forming tool with the part shape
  • Dry plies are consolidated (using heat and pressure) to assure they remain fixed in the proper position, hold their shape and to compact the Preform and reduce bulk before infusion.

Several different methods have been developed to create high quality Preforms suitable for structural parts:

Pick-and-Place (PNP) – Perhaps the most widely used approach, this consists of:

  • Ply patterns are cut on a CNC Table Cutter (same equipment used for prepreg pattern cutting)
  • Cut patterns are “picked up” from the Cutter table. Often plies from several material types used in a part are organized into a Kit, which is stored temporarily.
  • Plies are picked up from the Kit and transferred or “placed” into the forming tool. Placement of the plies (which are 2d flat objects) into a forming tool (usually a 3d contoured object) requires that the placement process also form the dry material without wrinkles, excessive skewing or other ply distortion.

Pick and place can be performed in one operation if the forming tool is able to accept the plies immediately after they are cut, and if the cutting equipment is adjacent on the shop floor. If Kits are used, plies are handled twice, and requires separate floor space for storage. “Picking” and “placing” can be performed manually but is increasingly being performed by machines.

Pick-and-place equipment

Pick-and-place equipment (see article and video)

Dry Automated Fiber Placement (DAFP) – This is an adaptation of prepreg AFP, using dry tapes instead of slit prepreg tapes:

  • Several suppliers now offer dry fiber tapes with suitable binders, designed to be used on current AFP machines to create dry Preforms. These dry tapes are analogous to slit prepreg tape, but with no resin. There is a small amount of binder powder on the tape surface to hold the dry tapes together with the application of heat and pressure.
  • Preforms are produced using many passes of narrow bands of dry tape that are consolidated as it is placed, just like AFP.
  • Resin is later infused into the preform using either vacuum pressure or higher pressure in a matched mold (RTM).
  • Conceptually DAFP is very similar to AFP, using the same basic equipment and design practices.
DAFP using AFP with dry fiber tapes (see NLR)

DAFP using AFP with dry fiber tapes (see link)

Automated Dry Material Placement (ADMP) – A newer approach is to cut and place ply patterns in one operation:

  • A moving machine head with a fabric supply roll dispenses the fabric and cuts the pattern shape as the material is dispensed. Cutting the ply edges is performed with multiple CNC controlled knives in the machine head.
  • The cut patterns that emerge from the machine head are placed directly on the forming tool as the head moves over the tool surface. This eliminates the “pick up” and “placement” handling in the PNP approach.
  • Conforming the fabric material to the 3d surface of the forming tool is also performed by the machine head using compliant mechanisms.

    Automated Dry Material Placement (ADMP) equipment (see link)

    Automated Dry Material Placement (ADMP) equipment (see link)

 

 

-Aerospace Looking to Dry Fiber/Infused Composites

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Most aerospace composite structures are produced today using prepreg and autoclave cure. Recently an increasing number and type of large and critical structures are being manufactured in a very different way – using Preforms assembled from dry fabrics and tapes and then infusing the epoxy resin into the Preform followed by cure. If the infusion is performed in a matched closed mold under high pressure, the process is called RTM. For many larger parts, infusion is performed using vacuum pressure only with single surface tools. This process has many different names reflecting slight differences in the infusion process including VARTM, CAPRI, VAP, RTI, RFI, BRI, SCRIMP and several others.

A wide range of aerospace parts are fully qualified and in production today made from dry fiber and vacuum infusion – a few examples are shown below. Some of these assemblies, such as flight control surfaces (flaps and ailerons) and fuselage frames are considered secondary or redundant components. Others such as the Aft Pressure Bulkheads of the A380 and 787 are primary structure – failure of these critical components would likely lead to loss of the aircraft. The A400 Cargo Door operates in an even more challenging environment – this flat and large door sees full cabin pressurization, and experiences significant bending  and tension loads during flight.

That these highly critical parts are made using these materials and processes speaks to the high degree of confidence that the aircraft OEM’s and regulatory authorities have in the reliability, performance and safety of the dry fiber/infusion approach.

787 Dry fiber/infused parts include (left to right) ailerons and flaps, fuselage frames and the aft pressure bulkhead (APB) of the fuselage

787 Dry fiber/infused parts include (left to right) ailerons and flaps, fuselage frames
and the aft pressure bulkhead (APB) of the fuselage

A380 Aft Pressure Bulkhead (APB) and A400 pressurized Cargo Door

A380 Aft Pressure Bulkhead (APB) and A400 pressurized Cargo Door

Arguably the most advanced use of dry fibers and infusion is in the wings of next generation airliners such as the Bombardier CSeries and Irkut MS21 aircraft shown below. These aircraft, serving 120 to 200 passengers, are the newest in commercial aviation and have leveraged the latest advances in composite materials, processes and production methods available today. The CSeries has passed ground structural tests and is expected to make its first flight mid 2013, with the MC21 to follow about a year later.

The Bombardier CSeries wing (left) and Irkut MS21 wing (right) both are made from dry fiber preforms and resin infusion

The Bombardier CSeries wing (left) and Irkut MS21 wing (right) both are made from dry fiber preforms and resin infusion

How about your company – is this technology being considered and for what applications? What are the benefits, tradeoffs, concerns and issues associated with the use of these processes? Let us know what you think.