The printing consumables currently available for SLS technology include nylon powder, PS powder, PP powder, metal powder, ceramic powder, resin sand and coated sand. Because the materials are different, the specific sintering process is also different.
1. Sintering process of polymer powder materials
Take polymer powder material as an example. The sintering process of this material can be divided into three stages: pretreatment, powder layer sintering stacking and post-treatment:
①The pre-processing is mainly to use the design software to design the three-dimensional CAD model, and then input the static STL data into the powder laser sintering rapid prototyping system after conversion.
②The second stage is the powder layer laser sintering stacking: the device sets specific manufacturing parameters according to the structural characteristics of the prototype, and the device automatically completes the layer-by-layer powder sintering stacking process of the prototype. After the automatic sintering of all the laminates is completed, the manufactured prototype needs to be cooled to 40°C in the forming cylinder, and the prototype is taken out for post-processing.
②Post-processing: Because the strength of the manufactured model is very weak, it is necessary to infiltrate wax or resin for reinforcement during the entire post-processing process.
2. Indirect sintering process of metal parts
The indirect sintering process of metal parts is divided into three stages: the production of SLS prototype parts, the production of powder sintered parts, and the post-treatment of metal infiltration.
The production of SLS prototypes includes CAD modeling, layered slicing, laser sintering, and prototypes. The key to this stage is how to select reasonable powder ratios and processing parameters to achieve prototype production. The "brown parts" production process is the second sintering (800°C) and the third sintering (1080°C). The key to this stage is that the organic impurities in the burnt-out prototype obtain a metal structure with a relatively accurate shape and strength. body. The process of metal infiltration stage is secondary sintering (800°C)-tertiary sintering (1080°C)-metal infiltration-metal parts. The key to this stage is to select appropriate infiltration materials and processes to obtain denser metal parts.
3. Direct manufacturing process of metal parts by SLS process
The direct manufacturing process of the metal parts of the SLS process is: CAD model-layered slices-laser sintering (SLS)-RP prototype parts-metal parts.
4. Factors affecting model accuracy in SLS process
In the process of manufacturing prototype parts using SLS process, there are many factors that easily affect the accuracy of prototype parts, such as SLS equipment accuracy error, CAD model slicing error, scanning method, powder particles, ambient temperature, laser power, scanning speed, scanning distance, Single layer thickness etc. Among them, the sintering process parameters have a great influence on the accuracy and strength. In addition, uneven preheating can also lead to poor accuracy of prototypes.
①Laser power: With the increase of laser power, the size error increases in the positive direction, and the increasing trend in the thickness direction is larger than the size error in the width direction.
② Scanning speed: When the scanning speed increases, the size error decreases in the negative error direction, and the intensity decreases.
③Sintering distance: As the scanning distance increases, the size error decreases in the negative direction.
④Single layer thickness: As the thickness of the single layer increases, the strength decreases, and the dimensional error decreases in the direction of review.