**2.2 Control and quality of the produced UD prepreg**

For the *in situ* consolidated LATP/LAFP process first main is the quality of the raw material, which can vary greatly from supplier to supplier and for each material matrix. As mentioned earlier in the production of thermoplastic tape can often occur defects of the tape itself (especially porosity) which requires a different temperature, greater consolidation, and melting time during the LATP/LAFP process. Therefore, the raw material must be tested. What is meant by quality control of raw material in this process? It is an examination of purchased raw material:

	- degree of crystallinity of raw material,
	- void content of raw material,
	- content of resin/fiber of raw material,
	- surface roughness of raw material,
	- microphotography (surface and cross-section) of raw material.

The thermoplastic tapes are typically not as consistent as thermoset materials, the uneven resin application can produce regions of resin richness, which can be both helpful and detrimental. In order to see a homogeneous distribution of the resin in the raw material, microphotographs of the procured raw materials are made with the help of an optical microscope (**Figure 3**).

The following figure shows some optical images from more raw materials UD thermoplastic prepreg:

In LATP/LAFP process, the **surface roughness** of the raw material has the biggest impact. Complete intimate contact is achieved if all the unevenness is the same

**Figure 3.** *Microscope images of some raw material (UD thermoplastic prepreg).*

*Unidirectional Carbon Fiber Reinforced Thermoplastic Tape in Automated Tape Placement… DOI: http://dx.doi.org/10.5772/intechopen.101110*

size, that is if all the unevenness is pressed to the same order [19]. The **presence of voids** in the starting material requires a longer heating time and greater pressure during the process of laying a thermoplastic strip with a laser. It is, therefore, necessary to know the percentage of voids on the tape that will be used in the process.

The **resin content** in the thermoplastic band has a great influence on the mechanical properties of the finish, but it also has an effect on the percentage of crystallinity and the heat balance for the LAFP/LATP process.

Determining the crystallinity of the raw material for the LATP / LAFP process is important to determine the temperature of the tool and to compare it with the crystallinity of the final product.

## **2.3 Selection of process parameters in LATP/LAFP**

In general, the LATP/LAFP process using laser heating involves many parameters that affect the results of the process. To obtain quality parts, the combined effect of the main process parameters must be studied and analyzed. **Table 2** and **Figure 4** show the factors that affect the output of the automated fiber/tape laying process by using a laser heater. In the same table is entered a part where it is said which factor how much they influenced the final product and at what.

The association of semicrystalline thermoplastic tapes with the LATP/LAFP process has been analyzed in many literatures [6, 7]. Many studies have been done to determine the temperature distribution near the connection zone in order to determine the optimal angle of incidence of the laser beam to achieve a good interface between the layers [10–38]. Recent studies show that automated thermoplastic laminating processes with a velocity even greater than 200 mm/s produce composite


*(@) has a high impact on the final product for voids.*

*(#) has a high impact on the final product for the degree of crystallinity.*

*(\$) has a high impact for (Tt) and (Ts)*

#### **Table 2***.*

*Parameters that affect the quality of the final product of the process.*

#### **Figure 4.**

*Factors affecting the automated application process of laser heating.*

flat slabs with properties close to those of the resulting flat slabs when consolidated in an autoclave [13–17].
