Tag Archives: Dry Preforms

-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.

-We go dry

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Dry Composites is an initiative by Danobat Composites to share the latest advancements in automation using dry composite material. This online community aims to connect companies, research centers, academics and experts interested in the use of dry composite material to develop structural parts in aerospace.

What do we mean by Dry Composites? There are two distinct methods of making composite structures. The first involves impregnating the fibres in a dedicated off-line machine to make a pre-impregnated material, called pre-preg. This is then transported to a factory that makes structures where it is laid up by machines or manually.

The second, more direct route is to take dry fibres, usually in some textile format and after assembly into a pre-form, infuse them with liquid resin. The infusion process is known by a number of trade names and acronyms such as RTM, VARTM etc.

The pre-preg route involves an extra process and hence cost, but it does result in structures with good consistent properties. Recently, the performance of structures made by infusing Dry Preforms has improved and is now claimed by some, to match that of more conventional pre-preg materials. Working with dry fibers, fabrics and textiles enables thicker layers to be used, saving time and labour costs, plus aiding in the creation of more complex, one-piece structures.

However whereas the pre-preg manufacturing industry is well served by automation with dedicated machine tools, the lay-up of dry fabrics has not received the same attention. Danobat Composites has pioneered the development of Automatic Tape Laying using woven and NCF fabrics. This has improved laminate quality, repeatability and reduced the cost of composite structures by significantly cutting manufacturing labour and material costs. Moreover, it is worth mentioning that the use of dry materials can give rise to out of autoclave curing processes acquiring required properties in primary structural aerospace parts.

Today, manufacturers face the challenge of doing more with less, the aerospace industry needs to adapt quickly to new material and process developments to remain competitive. In doing so, the ultimate goal of a disruptive automation technology is to introduce new processes that may deliver better high efficiencies and control at less cost. This requires broad support from an ecosystem of R&D, manufacturing, engineering teams and material developers.

Dry Composites is an open space for those interested in learning more about how automation using dry composite material can be applied to the aerospace industry. From sharing industry news, information, data and technical solutions about dry composite solutions to interviews and perspectives from expert sources. Our target audience includes decision makers, R&D engineers, global suppliers of advanced materials, software and automation companies.

If you are interested in learning more about advancements in the use of dry material in the aerospace industry, follow us on Twitter @drycomposites and join the LinkedIn Group Dry Composites.

Stay tuned for more!