Surface Treatment of Additively Manufactured Polyetheretherketone (PEEK) by Centrifugal Disc Finishing Process: Identification of the Key Parameters

Abstract

Polyetheretherketone is a promising material for implants due to its good mechanical properties and excellent biocompatibility. Its accessibility to a wide range of applications is facilitated by the ability to process it with an easy-to-use manufacturing process such as fused filament fabrication. The elimination of disadvantages associated with the manufacturing process, such as a poor surface quality, is a main challenge to deal with. As part of the mass finishing process, centrifugal disc finishing has demonstrated good results in surface optimization, making it a promising candidate for the post-processing of additively manufactured parts. The objective of this study is to identify the key parameters of the centrifugal disc finishing process on the waviness of additively manufactured PEEK specimens, which has not been investigated previously. The waviness of the specimen was investigated by means of confocal laser scanning microscopy (CLSM), while weight loss was additionally tracked. Six parameters were investigated: type, amount and speed of media, use of compound, amount of water and time. Type of media, time and speed were found to significantly influence waviness reduction and weight loss. Surface electron microscopy images demonstrated the additional effects of deburring and corner rounding. Results on previous studies with specimens made of metal showed similar results. Further investigation is required to optimize waviness reduction and polish parts in a second post-processing step.

Keywords: 3D printing; PEEK; additive manufacturing; centrifugal disc finishing; fused deposition modeling; fused filament fabrication; high-performance polymers; mass finishing; post-processing of 3D printed parts; surface treatment.

Figure A1

Schematic section view of sedimentation box. Foam formation as polymer media used without compound.

Figure 1

Illustration of specimen geometry and building direction (BD) on the left; the black rectangle shows the area of waviness measurement with unfiltered 3D height profile on the right.

Figure 2

Illustration of CDFP. Reduction of staircase effect by time. Two different abrasive media (Nr.2) of different materials and different shapes. Ceramic media has prism shape, polymer media has pyramid shape. Water interaction between the machine (Nr.1) and the sedimentation box (Nr.3) shown with arrows.

Figure 3

CLSM measurement filtered for different profiles; unfiltered primary profile (blue) represents actual measured data, including the waviness (red), roughness (black) and form (green) of the measured surface data.

Figure 4

Absolute waviness of specimen (in S_a) before and after centrifugal disc finishing (left). Exponential correlation of waviness reduction and weight loss (right).

Figure 5

CLSM images of same area of each specimen before (left) and after (right) post-processing. The image was captured using a laser scanning microscope for specimens of Treatments D1 to D14. The results demonstrate varying waviness of surfaces.

Figure 5

CLSM images of same area of each specimen before (left) and after (right) post-processing. The image was captured using a laser scanning microscope for specimens of Treatments D1 to D14. The results demonstrate varying waviness of surfaces.

Figure 6

SEM images of specimen before and after grinding. Top middle shows the initial state after manufacturing and cleaning. Left is after post-processing with polymer-based media (Treatment D2); right shows after post-processing with ceramic media (Treatment D14).