21 february 2019
Case: impeller 3D-printing
Intas Power Systems (IPS) contacted Additive Solutions for manufacturing a stainless alloy impeller for experimental high pressure liquid pump.

For impeller manufacture using classical production method, a high-precision expensive 4 or 5 axis NC milling machine is required. It is possible to manufacture using casting, but it is expensive and takes much time, since it is necessary first to make a mold. Therefore, 3D metal printing was chosen.

In the photo below, you can see impeller already mounted on the shaft, before and after sandblasting and little grinding. Printed product required only a little post-processing in a sandblasting chamber to remove unevenness after printing and processing on a grinding machine, that is, a minimum of finishing operations.
Balancing

This was followed by the most difficult procedure - balancing the impeller. Since the revolutions in the pump working area are 6,000 to 10,000 revolutions per minute, beats are not permissible. Balancing revealed a slight imbalance in the rate of 0.23-0.7 grams per blade. Moreover, this parameter is close to a similar product made on 4, 5-axis coordinate processing centers with NC. Balancing was done by drilling from impeller end side in the area near the hole under the shaft. The impeller is balanced to the point of zero beats.

Test

Assembled pump tests showed whole working capacity of the printed impeller - operational parameters are equal to the impeller made on NC milling machine from a monolith blank. During load tests the impeller withstood both operating revolutions and increased to 14,500 revolutions per minute without blades breaking and warping for several operating days on stand. After test hours the impeller was examined. No signs of cavitation damage were noted. Tests were carried out in different modes, pumping various liquids with different viscosity and density. Working-off with pumping aggressive liquids (water with salt and soda high concentration) showed no signs of aggressive influence on the alloy itself.
Conclusions about 3D metal printing:

1. It is very convenient for R&AD: good solution for parts and structures prototypes manufacture.

2. Suitable if you need fast production of a small experimental products batch.

3. According to the final results, the product is close to that made on a NC milling machine.

4. Experimental batches and piece products. 3D metal printing is even more profitable than powder casting (cheaper, faster) because of absence of intermediate stage - the need to make a mold.

5. 3D printing loses in manufacturing costs only high-precision milling 4, 5 coordinate machines, if the customer has any. But on a 3D printer it is possible to manufacture parts with voids and channels of complex shapes, which are not possible to do on a milling machine.

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