7 tips on HP MJF 3D printing

HP MJF 3D printing, prints a little differently to other printers. It’s most similar to SLS printing but with reduced costs. It can print a variety of materials including TPU, PA11, and PA12, with more materials on its way. One main issue is that to print a different material the whole printer needs cleaning out and resetting. This process can take up to 12 hours to complete.

As with all 3D printers optimizing your print can take time, with trial and error. This means a lot of time and material is wasted.PA materials can be as expensive as $2 per gram! This can get very expensive, and even more so with color printers. Colour printers not only use powder and fusing agents, but also Ink and printer heads. Colour printers not only have a 3D part builder but also have a full-color printer built-in. This is where the HP MJF printer sets itself apart.

To try to achieve a lower cost per parts a few easy steps can be taken. However, to achieve this you need to follow a few rules.

Tip 1 – Print your object at an angle

Printing your object at a slight angle produces a much better finish and part quality. If printed flat sometimes the roller can pick up parts and move them. In this case, the print will fail and the part quality will be very poor and weak.

Tip 2 – Printing powder ratio’s

Powder ratio is a very important one in terms of cost per part. With fresh powder costs being so high, keeping a lower cost per part requires you to use a higher used power %. A ratio of 20% fresh to 80% used is the cheapest option. This option though is not also the best, in terms of part quality.

Tip 3 – % packing density

The higher the packing density the cheaper parts will be. This is because parts can be moved together into a smaller space, therefore, reducing the amount of powder that is used. The higher the build the higher the cost. Aiming for a packing density of 8%-10% is optimal for part quality and strength. Packing densities of 12%-15% though make the cost per part a lot lower.

Tip 4 – space between parts

Space between parts and the edges of the print area can also affect the cost per part and the part quality. It is recommended that parts are placed 5mm apart. Any closer than that and it can have a detrimental effect on the color and strength of the parts. Having parts too close together can cause leaking of color onto a neighboring part.

The closer parts are together can also affect cooling. The closer the parts are together the more uneven the powder is around the part due to excess fusing agents. Having a consistent layer of powder around the part means that the part will cool evenly all the way around. The results in a more consistent strength, and reduces weak points.

Tip 5 – Cost per part

As it costs money to turn the printer on, warm it up, lay down pre powder layers and more, the more parts you can fit into one print the cheaper the cost per part will be. The second point is that the fewer powder layers the printer has to lay down, the less power that will be used, and so the cheaper the cost. This is managed by optimizing the spaces between parts and optimizing the packing density. This can be the difference between printing 1 item and it costing $400 per part, all the way to printing 40of the same parts and it costs $30 per part.

Tip 6 -Cooling time

Like most things, the quicker the cooling the more brittle an object will be. The printer has 3 cooling settings. Auto cool, where the printer determines the cooling time based on the amount printed. Quick cooling, where the parts are not allowed to stand for a long time. The last is manual cooling, where the person can choose the length of time the objects are cooled. The latter option is the best one as it allows you to let the objects cool over a 24 hour period. This time creates an optimal part.

Tip 7 – part strength

Part strength is not only determined by the model design itself, but also the printing and cooling techniques. Printing wise, a higher distance between parts and an angled orientation is best. The as we mentioned before the longer the part is left to cool the better.


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