**6. Analysis of machine for manufacture of structural composite pre-forms**

Lace braiding technology has been demonstrated in the manufacture of intricate and decorative fabrics for more than a century. If lace braiding machines are suitable for handling large high strength yarns such as aramid and even carbon fiber prepregs, it was thought that the structures might be suitable for use as planar and 3-D space trusses. An evaluation of a modern lace braiding machine is performed on the typical execution to determine if braided composite strength-to-weight ratio could be improved by utilizing a lace braiding technology. A modern lace braiding machine incorporating a computer controllable electro-mechanical yarn interlacing system was purchased to test the proposition that it might be used to more efficiently orient and interlace yarns to create a truss-like pre-form in either a flat or cylindrical form [17]. **Figure 8** is an example of a CAD model for a proposed composite tube manufactured with a lace braiding machine.

**Figure 9** shows the initial lace fabric preform made with a modern lace braiding machine during the evaluation and research phase of this work. The small white yarns are cotton. **Figure 10** shows a flat lace manufactured on a modern lace braiding machine made from larger twisted yarns.

**Table 1** denotes a list of advantages of the modern lace and braiding machine.

**Figure 8.** CAD model of lace braided composite tube.

stiffness and breaking strength exceeded the capacity of the carriers and clutches. Furthermore, these yarns would not break if the machine had payout and tension problems. This would result in excessive clutch failure and machine down time. Constant clutch replacement is time consuming. After repeated adjustments to the machine, it was determined that the machine would not operate consistently with large, high strength yarn without the machine shutting down and/or breaking plastic clutches. Solving this problem will require a more robust machine design of the clutches and improved carrier payout necessary for braiding. In the process of evaluating the lace braiding machine, several other structural deficiencies were noted. Despite these inherent limitations, the feasibility of using lace braiding technology was "proved in concept" when a more robust machine can be designed and built. To do this, some open structure lace patterns have been designed and produced using the light-weight yarns that the machine could process. Composite preforms using lace-like patterns possible with lace braiding have been made on a conventional Maypole braiding machine and evaluated for strength and stiffness to further promote the structural lattice concept [17].

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**Figure 10.** Machine braided lace.

• Control of individual bobbins

• Precision fiber placement

• Bobbin carriers are easily removed

**General advantages of modern lace braiding machines**

• Cylindrical and flat fabrics produced from the same machine

• Open structure amenable to truss formation is possible

**Table 1.** Advantages of lace braiding machine technology.

• Small driver plates leads to increase in number of total yarns for given machine size

• Yarn crossovers are stabilized by a 360-degree twist around the adjacent yarn

**Figure 9.** Initial preforms evaluated for composite reinforcement.

**Table 2** denotes a list of problems encountered with the modern lace braiding machine during the evaluation of this study and comparison to conventional Maypole braiding machines.

**Figure 2** shown previously is an initial attempt to make a lace from high performance yarns (1100 denier). In this attempt, we discovered that the yarn carrier mechanisms supplied with the machine are not well suited for using larger yarns. Large and thus stiffer yarns are needed for producing lace pre-forms suitable for structural composite applications.

When large, high strength yarns (<2400 denier) such as Kevlar®, Vectran®, and carbon fiber were used, the clutches would quickly fail because tension developed in the yarns due the yarn

**Figure 10.** Machine braided lace.

#### **General advantages of modern lace braiding machines**


**Table 2** denotes a list of problems encountered with the modern lace braiding machine during the evaluation of this study and comparison to conventional Maypole braiding machines.

**Figure 2** shown previously is an initial attempt to make a lace from high performance yarns (1100 denier). In this attempt, we discovered that the yarn carrier mechanisms supplied with the machine are not well suited for using larger yarns. Large and thus stiffer yarns are needed

When large, high strength yarns (<2400 denier) such as Kevlar®, Vectran®, and carbon fiber were used, the clutches would quickly fail because tension developed in the yarns due the yarn

for producing lace pre-forms suitable for structural composite applications.

**Figure 8.** CAD model of lace braided composite tube.

68 Engineered Fabrics

**Figure 9.** Initial preforms evaluated for composite reinforcement.


**Table 1.** Advantages of lace braiding machine technology.

stiffness and breaking strength exceeded the capacity of the carriers and clutches. Furthermore, these yarns would not break if the machine had payout and tension problems. This would result in excessive clutch failure and machine down time. Constant clutch replacement is time consuming. After repeated adjustments to the machine, it was determined that the machine would not operate consistently with large, high strength yarn without the machine shutting down and/or breaking plastic clutches. Solving this problem will require a more robust machine design of the clutches and improved carrier payout necessary for braiding. In the process of evaluating the lace braiding machine, several other structural deficiencies were noted.

Despite these inherent limitations, the feasibility of using lace braiding technology was "proved in concept" when a more robust machine can be designed and built. To do this, some open structure lace patterns have been designed and produced using the light-weight yarns that the machine could process. Composite preforms using lace-like patterns possible with lace braiding have been made on a conventional Maypole braiding machine and evaluated for strength and stiffness to further promote the structural lattice concept [17].


**Table 2.** Problems encountered with lace braiding machine evaluated.

### **6.1. Other important issues: twisting of yarns, beat-up mechanism, and machine design**

The carriers used in lace braiding are free to rotate about the plate. Motion about this additional degree of freedom will be exacerbated at high speeds as inertial effects increase and may potentially cause problems. The freedom of the carrier to rotate during braiding can cause excessive buildup of twist in the yarn. **Figure 11** illustrates an example of this phenomenon due to carrier rotation. Twist build up in the yarns can be alleviated by pre-twist that counteracts the twist occurring in the opposite direction, however requires additional processing and reduces yarn stiffness. Careful consideration of the bobbin movements required by the yarn paths in each pattern can reveal the amount and direction of pre-twist required to eliminate the buildup. Alternatively, a rotating terminal eyelet can be employed to reduce yarn twist,

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The braiding formation process can cause severe damage to yarns. The violent action of the beatup knife mechanism damages fibers. **Figure 12** illustrates an accumulation of broken fibers resulting from the formation process of lace braiding machines. Minimizing abrasion is

Lace braiding technology has been introduced and a brief historical context provided. A description of how the components function has been presented. The lace braiding machine components and their functionality were described to demonstrate how the machine works as well as to assess the limitations for producing structural scale composite preforms. Based on the experiments that were made on the modern lace braiding machine, the machine deficiencies for manufacturing composites (listed in **Table 2**) are discussed. Suggestions for remedies in the machine design and operation are presented to enable future progress to be built upon addressing the current limitations while further advancing the future of lace technology in new areas such as space and aerospace. Complete re-design and construction of a machine suitable for composite preforms were considered beyond the scope of the research and left

especially important if high performance brittle fibers are to be utilized.

**Figure 12.** Accumulation of broken fibers at fell point due to beatup knife abrasion.

else other means are required.

**7. Conclusion**

for future work.

**Figure 11.** Buildup of excessive twist in yarn.

**Figure 12.** Accumulation of broken fibers at fell point due to beatup knife abrasion.

due to carrier rotation. Twist build up in the yarns can be alleviated by pre-twist that counteracts the twist occurring in the opposite direction, however requires additional processing and reduces yarn stiffness. Careful consideration of the bobbin movements required by the yarn paths in each pattern can reveal the amount and direction of pre-twist required to eliminate the buildup. Alternatively, a rotating terminal eyelet can be employed to reduce yarn twist, else other means are required.

The braiding formation process can cause severe damage to yarns. The violent action of the beatup knife mechanism damages fibers. **Figure 12** illustrates an accumulation of broken fibers resulting from the formation process of lace braiding machines. Minimizing abrasion is especially important if high performance brittle fibers are to be utilized.
