## 3 Quality Improvement
### Surface Finishing  
Due to layer-by-layer deposition, AM parts have low surface quality and need further post-processing. There are some reasons that contribute to the surface finish, namely powder/wire adhesion, stair-steps, and scanning strategy [104]. To address powder/wire adhesion, processing parameters such as scanning strategy and deposition orientation must be controlled. Since the fundamental of AM is layer-by-layer manufacturing, stair-step is an inseparable phenomenon that can be addressed by choosing a thinner layer. So, based on the achieved surface and desired quality, the post-processing is selected. Some methods, such as bead blasting, polishing, sanding, and abrasive flow machining, are the most widely used in AM processes. To compare post-processing for WDED with the other AM methods such as LPBF or powder-based DED, WDED needs more post-processing such as machining due to its lower surface quality by fabricating layer by layer via wire. The wire feeding approach may result in a coarser layer and larger stair-stepping effects, which make post-processing methods like abrasive flow machining (AFM) crucial to achieving acceptable surface quality. Contrary to WDED, powder-based AM offers better surface quality by using finer powder and setting-optimized processing parameters, but powder removal and residual stress relief are still vital. To post-process WDED samples, particularly those that are sensitive to thermal stress, EDM would be highly beneficial to fabricate the complex geometries, making it competitive for high-precision samples. Regarding heat treatment, WDED samples are intended to have higher residual stresses due to the larger, solid-state (using a wire) deposition structure, leading to deflection and distortion if not properly relieved. Heat treatment for WDED mostly accentuates stress relieving and microstructural refinement, with some methods, such as laser-based localized treatments, used to enhance specific regions. However, for powder-based methods, heat treatment is mostly utilized for homogenizing microstructures and increasing mechanical properties. Standards, namely ASTM F3001-14, guide Ti heat treatment in powder-based methods, whereas AMS 4999A uses DED-specific protocols, showing the various post-processing requirements between WDED and other AM methods. This paper provides information on different key post-processing methods such as machining, heat treatment, and surface finishing and their specific roles in improving the performance of WDED samples. Machining is essential for enhancing surface quality and achieving dimensional precision, which is a vital element for the fabrication of critical samples. For the aerospace industry, as with turbine blades or automotive components such as engine blocks, advanced machining techniques such as EDM or electrochemical discharge grinding (ECDG) are used. These techniques aid the removal of excess material by maintaining tight tolerances. By enhancing surface quality and removing defects from the additive process, machining significantly increases the structural integrity and performance of WDED parts. Heat treatment is crucial for changing the microstructure and to relieve residual stresses in WDED components, particularly for high-performance alloys such as titanium or stainless steel. In aerospace and biomedical industries, where fatigue resistance and strength are critical, heat treatments like annealing or quenching are used to enhance mechanical properties. For example, in biomedical implants, heat treatment can enhance the strength of titanium alloys. Surface finishing methods, such as polishing, bead blasting, or abrasive flow machining, play a key role in decreasing surface roughness, which is particularly important in applications like implants or precision automotive parts. A smoother surface not only enhances the aesthetic appearance but also improves the wear resistance, corrosion resistance, and overall functionality of the WDED part.