Application Of 3D In Print In Powder Flow

Rapid prototyping and 3D printing, it relates to the "print" is often perplexing, strict component specifications, method is to add the powder layer by layer, and then selectively fusing together. The control characteristics of powder, the processing efficiency and quality are crucial to the final product. The powder flow and compaction of powder layer is formed in the decisive factor of raw materials, bulk density differences will lead to inconsistent, inhomogeneous, low tensile strength and poor surface roughness.

When the powder thin layer is applied in a uniform manner when rapid prototyping (AM) is very sensitive to the powder, it requires raw materials have high consistency and repeatability. The particle size is usually used as a key quality attributes (CQA), but not enough to test the standard as raw material. In fact, whether it is Holzer flow meter, or Hausner Ratio, any single parameter testing are not sufficient to fully characterize the powder characteristics. This paper uses four case studies to demonstrate the limitations of a single parameter, and how to use several kinds of metal powder in the application of AM on the rheological property of fluid in the process to construct the characteristic. In the first study, a group of powder significantly reduced permeability and special flow can increase significantly, and clearly show the inter layer uniformity adverse association. The second study investigated the effect of metal powder production method and the supplier, and reveals the characteristics why not rely solely on shear properties to identify the impact of the process. At the same time, the evaluation of additives on AM can affect the processing of polymer blends. The results show that even the small amount of the additives, can also have a great effect to raw material permeability and basic flow. The study revealed that in the use of recycled metal powder production parts, how to use the rheological measurement results to determine the optimal allocation of new materials and renewable materials mixing ratio. These case studies show the modern powder rheometer detection and processing properties of AM powder directly related to subtle changes, and the traditional characterization methods are unable to do this.

AM will affect the industry outlook depends on the development of high-speed, precision machinery, and find and continuous supply of raw material powder can accurately meet the requirements of these machines. More and more emphasis to the powder itself, and how to wisdom and reliable method to optimize. Characterization of powder in support of this process and can play an important role in property testing technology reliable measurement and AM performance is directly related to the. What determines the performance of powder properties can bring a consistent, repeatable, optimization can help to achieve a new formulation, but not in the sample testing process, and produce significant economic and time cost for suitability evaluation, and contribute to the reduction of the final product irregular phenomenon.

A case study of 1 different batches of raw materials: quantitative difference

Strict tolerance AM machine operation, means that the differences between the batches may lead to significant differences between the various characteristics of the product and the quality of the final. Before entering the unit operation, for each batch of screening methods helps to ensure consistent performance. However, many of the traditional powder characterization technique could not identify a variety of subtle changes and important.

This study evaluated three kinds of stainless steel powder samples of the same supplier, they behave differently in AM process. Metal powder and metal powder A B's performance is acceptable, but the metal powder C often cause blockage and bad deposition, and lead to unqualified products. The size distribution of the three samples is almost identical to the test results, the angle of repose and Holzer flow meter is also very close to the.

The use of powder rheometer test highlights a number of differences between samples, these differences are related to the characteristics observed in the operation of the. The basic flow of energy (BFE) to quantify the forced flow in non gravity (dynamic) in the implementation of powder displacement energy required, such as powder in the screw conveyor or mixing machine in the flow, namely under the constraint conditions of powder flow resistance. It is through the sample in the leaves from the top of the container through the bottom of the test, when measured. Special flow (SE) is used for the blade upward movement to evaluate powder flow resistance in unconstrained) environment, and normalized according to the weight of the powder. In this case, SE clearly distinguish the metal powder C, the higher SE values showed higher mechanical bite and friction, indicating the presence of congestion and other flow problems (Figure 1).

Fig. 1 Variation between different batches of SE

Metal powder C also appeared significantly higher than the voltage drop of A and B, showed that the permeability decreased significantly. The permeability has great influence on various operations need to move the powder, especially in rely on gravity to push, even more so. Therefore, when the AM application requirements of powder deposition, low permeability layer may lead to the uniformity of poor, leading to the final product defects.

Case study 2: the influence of different suppliers and manufacturing methods

Rapid prototyping of raw materials can be produced by different methods, each production method can be obtained with similar particle size and particle size distribution of the powder, each manufacturer has its own level and acceptance criteria. However, a method of manufacturing a powder may change the acceptance test has not been determined, but can lead to other characteristics of the performance differences in AM process. The use of powder rheometer were evaluated on three kinds of raw material powder, shear box test to determine the differences caused by the manufacturing method of change, which illustrates the potential impact of customers can not control variables, and that deal with raw materials for regular assessment of acute.

Case 3: the effect of additives on the properties of raw materials

Adding additive in the raw material to improve the functionality of the final product. However, these additives can also affect the performance characteristics of raw material and in a given unit operation in. If we can quantify the impact characteristics of the mixture of different additives, will be able to achieve the optimization of the mixture itself and the process, so you can keep the advantage of additives, and without sacrificing processing performance.

In selective laser sintering (SLS) process, selection of three kinds of Polyoxymethylene (POM) samples, two of which contain different additives (pigments and liquidity additives). We observed three types of recipe from the hopper into the sintering machine when the flow performance is different, which leads to the difference of the final product performance and quality, to a variety of traditional powder testing technology to determine the difference of each sample, so the use of powder were carried out further tests.

With liquidity additive samples generated from BFE was higher than that of the other two samples, which leaves powder rheometer needs more energy through the sample. In this case, the BFE value is high, that loose material stacking is more dense, it also shows that adding additives can make the material flow to free flow. This sample is still low consolidation stress the highest drop value, showed the decrease of permeability, and further enhance the bulk density of samples. However, with the increase of consolidation stress, the pressure drop of all three samples were increased, compared with flow additive samples, pure POM sample and the sample containing pigment change degree is much higher (Figure 2).

Figure 2 additive influence on permeability of POM (for pressure drop)

Case 4: the difference between the new material and recycled materials in the process on the performance of the

AM process will consume a large amount of powder, but not all raw materials will become a part of the finished part. The use of raw materials to provide great potential for greatly reducing the cost of raw materials and the overall level of waste. However, before being reused, should further evaluate the powder used by the AM machine and the degree of influence, and whether can be reused without affecting the quality of the finished parts.

The test results of new materials and recycled powder showed significantly increased basic flow regeneration powder (Figure 3), which indicates that the free flow of recycled powder is lower than that of new material, therefore, the process performance is unlikely as well. From the AM powder recovery machine may contain splashes from the molten pool, including larger particles, or particles may also be subject to pollution. Therefore, to decide on the regeneration through experiments, powder screening can make it flow to reach an acceptable level, but eventually found that screening has little effect.

Figure 3 application of powder rheology on the use of recycled materials to optimize

summary

The case study shows that the modern powder rheometer has the ability to detect subtle changes in powder performance and process performance is directly related to the AM. Therefore, can use powder rheology to provide support for the success of the optimization and the life cycle management of AM powder. It also reveals why need to use multiple methods to complete the selected powder material conforms to a given process.

The material properties of the fluidity of the powder is not a natural, it can be understood as the powder material in specific equipment to the expected flow ability. Success requires processing technology of powder material and process, very good, the same kind of powder material good performance and poor performance in the case of another which is not uncommon in some unit operation, this implies the need for a variety of characterization methods, from a variety of characterization methods and combining with the results of the process, create the parameter design of a spatial process characteristics corresponding to the acceptable.