As a special engineering polymer, polyether ether ketone (PEEK) has been used widely due to its excellent mechanical properties, high thermal stability, and chemical resistance. Fused deposition modeling (FDM) is a promising process for fabricating PEEK parts. However, due to the semi-crystalline property and high melting point of PEEK, determining appropriate process parameters is important to reduce warpage deformation and improve the mechanical properties of PEEK. In this article, the influence of raster angle and infill density was determined by single factor experiment, which are the two most important parameters. The results showed that samples with 0°/90° raster angle and 50% infill density had the best comprehensive properties in terms of warpage deformation, tensile strength, and specific strength. Subsequently, based on the results above, the effects of printing speed, nozzle temperature, platform temperature, raster width, and layer thickness were analyzed by orthogonal experiment. The results indicated that platform temperature had the greatest impact on warpage deformation while printing speed and nozzle temperature were significant parameters on tensile strength. Through optimization, warpage deformation of the samples could be reduced to almost 0 and tensile strength could increase by 19.6% (from 40.56 to 48.50 MPa). This will support the development of FDM for PEEK.

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For molding equipment, the accurate measurement of tie-bar stress helps improve product quality and prolong the lifespan of the machine. In our previous work, the mathematical model between the ultrasonic time difference (UTD) and the tie-bar stress was established, and this model was shown to have high accuracy with the maximum of difference square being only 1.5678 (MPa)2. Nevertheless, when calculating the ultrasonic time difference using the cross-correlation function (CCF) method, it is necessary to manually divide the position of the echoes. This makes it impossible to automate the stress measurement and it is incompetent when dealing with massive data. In this paper, a non-intrusive (N-I) ultrasonic measurement method for tie-bar stress based on the minimum entropy blind deconvolution is firstly proposed. The results of simulation and verification experiments show that the proposed method has high precision, and the maximum relative error is only 2.4392%. Hence this method has been successfully applied in the tie-bar stress measurement in molding equipment. Compared with the CCF method, the accuracy is improved and the maximum relative error is reduced from 3.67% to 1.68% when the clamping force is small. In summary, the proposed method is comparable to the CCF method in accuracy, and has a higher resolution during echos disturbance. Moreover, this approach does not require human intervention and is helpful to realize the automation of the tie-bar stress measurement for the molding equipment.

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