Tag Archives: DAFP

-Pros and Cons of Automated Preform manufacturing methods

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In our last post we described three methods to automate dry fiber Preform manufacturing: Pick-and-Place, Dry Automated Fiber placement and Automated Dry Material Placement.

Pick-and-Place (PNP) – Ply patterns are cut on a Table Cutter, “picked up” and then transferred or “placed” into the mold.

Dry Automated Fiber Placement (DAFP) – Similar to prepreg AFP, where bands of narrow unidirectional tapes are placed into the mold, except that the tape is dry (not impregnated). A small amount of binder holds the tapes in place as they are placed under heat and pressure.

Automated Dry Material Placement (ADMP) – Fabric rolls are cut into Ply patterns and placed into the mold, all in one operation and one machine pass over the mold.

PNP, DAFP and ADMP preform manufacturing methods

PNP, DAFP and ADMP preform manufacturing methods

Each of these automation methods provides advantages and disadvantages, as presented below.

Preforming Methods – Pros and Cons

Preforming Methods – Pros and Cons

PNP has been used to produce preforms for some time, and directly mimics the way many prepreg, RTM and infused parts are made today. The industry is comfortable with designing, producing and inspecting CNC cut ply patterns, whether from prepreg or dry fabric forms. Flat pattern shapes of any complexity can be accommodated (internal windows, cutouts, etc.) Instead of manually placing plies in the mold, with PNP this operation is performed by a machine, therefore the complexity of the layup (mold contour, folded flanges, etc) is more limited. Both woven and noncrimp fabric (NCF) styles provide good mechanical properties as well as excellent permeability for complete resin wetout and infusion. A drawback to PNP is that more floor space is needed for both the Table Cutter and the PNP transfer mechanism. If cut plies are not laid directly in the mold (i.e. are stored in kits before layup), PNP requires more ply handling, which makes it more difficult to manage fabric distortion and placement accuracy.

The design practices, machinery and manufacturing approach with DAFP are very similar to prepreg AFP. This familiarity or aerospace “pedigree” makes DAFP attractive because it is a less disruptive process change where AFP equipment is already in use. Other benefits of DAFP include very good properties achieved with unidirectional fiber and the lowest material scrap rate, since each tow is dropped or added exactly as needed. This feature also means that complex patterns can be produced, though there remain limitations associated with minimum cut-and-add length and edge crenulation. The use of individual tapes allows DAFP to conform to complex shapes. The drawback of DAFP is similar to that of AFP – in practice, actual productivity (pounds deposited per hour, i.e. the floor-to-floor or C rate) is relatively low.  The time required to manually inspect every placed tape against the defined drawing often far exceeds the time the machine is actually placing material, and this is another factor in low throughput.

ADMP’s value proposition is that it can achieve very high productivity due to wider materials (than DAFP tow bands), multilayer materials (such as NCF) and pre-made layup schedules provided in the fabric form itself. For example, to produce a balanced, symmetric quasi-isotropic layup only requires 2 passes of an ADMP machine (using a four layer [0/45/-45/90] NCF fabric placed back-to-back) but requires 8 passes of an DAFP machine to produce a [0/45/-45/90]s layup from uni dry tape. Like PNP, the textile forms used in ADMP have very good through thickness infusion properties, but ADMP textile forms do not provide mechanical properties as high as unidirectional tape used in DAFP. The mold contours and ply pattern geometry suitable for ADMP is somewhat more limited than for other methods, and the method has yet to be proven for use in aerospace applications.

So there are many factors and tradeoffs to consider. Nor are PNP, DAFP and ADMP the only ways to automate the Preforming process. Other methods like stitching, 2D and 3D braiding, 3D weaving and others are also being used.  Ultimately the choice of Preforming method, when it comes to automation, depends on the specifics needs of the application and the customer.

-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)