Call: 503-943-2781
Search
Close this search box.
RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

Table of Contents

General Recommendations

Introduction

When using HP Multi Jet Fusion (MJF) technology, there are general recommendations to follow to optimize the printing process, keep the printer in top condition, and obtain the desired results.

General Considerations

General considerations to keep in mind are as follows:

Equipment
  • The operating temperature of the equipment should be between 20°C and 30°C to prevent thermal fluctuations. Going beyond these limits could have adverse effects on part quality.
  • The printer’s operating relative humidity (RH) should be between 30% and 70% for optimal system usage and performance.
    Depending on the material, a different operating relative humidity might be necessary for processing. For example, HP 3D
    HR PA 12 requires relative humidity levels between 50% and 70%. To verify specified environmental conditions, check the
    material data sheet.
  • Power line quality is important. If it is suspected that the power installation at the site will suffer from variability or alterations, it is recommended to install an uninterrupted power supply (UPS) system.
  • The set-up altitude should be based on the location of the facility and the printer. A wrong selection could directly affect the cooling system and pressure parameters.
  • Read the User Guide to master the key aspects related to cleaning, maintenance, and calibration practices.
  • Make sure that the glasses that cover both fusing lamps and the thermal camera are clean.
  • Temperature camera calibration: This calibration is used to compensate for small misplacements of the top temperature camera sensor. This calibration is only needed for new installations and after thermal camera replacements.
  • Fusing lamps calibration: This calibration is used to correct irradiance deviations and obtain the true statuses of the lamps. It is highly recommended to perform this calibration under 40% to 60% relative humidity and to double check the printer’s RH readings with an external humidity sensor. This calibration is only needed after a fusing lamp
    replacement or intensive cleaning of burn spots.
  • Some problems may be caused by printhead issues, so it is important to make sure that the printheads are correctly maintained and aligned, and that nozzles are in good condition.
  • Even if the printer is perfectly clean and calibrated, it may be necessary to fine-tune the energy provided by the lamps. To do this, the operator can modify the irradiance of the lamps depending on an assessment after printing some control parts. Each print profile requires a specified fusing lamp irradiance. The fusing lamp irradiance value can be checked on the front panel before printing
Printing Profiles and Materials

HP Multi Jet Fusion technology allows for the use of different powdered materials, such as HP 3D HR PA 11 (“HP PA 11”), HP 3D HR PA 12 (“HP PA 12”), and HP 3D HR PA 12 Glass Beads (“HP PA 12 GB”). 

Some materials like HP PA 11 and HP PA 12 can be printed using different print profiles, which are tested sets of parameters
aimed toward maximizing specific final properties such as dimensional accuracy, mechanical strength, or part appearance.

There is a relationship—maintained across different current materials—between the energy received by the parts during the
printing process and the general consequence of their mechanical properties and appearance, as shown in Figure 1:

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

Thus, the hotter the part, the greater the sintering of the powder, leading to denser parts with stronger properties. However, excessive heat can result in adjacent powder sticking to the surface of the parts (thermal bleeding) and contraction-related artifacts such as sinks.

On the colder side of the spectrum, these effects are minimized, thus improving the overall look of the parts at the expense of mechanical performance and localized non-homogeneous shrinkage.

Print profiles are placed on the scale as a guideline, but their exact position would be determined by their fine-tuning potentiality. Fine-tuning is required to center these print profiles at the optimum levels according to the specific application.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
  • Extremely high-packing density jobs, non-recommended powder mix ratios, and poor system maintenance may lead to some part quality issues.
  • It is recommended to use balanced print profiles (HP PA 11, HP PA 12, and HP PA 12 GB), which require two passes per layer, for a compromise between look and feel, dimensional accuracy, and mechanical properties. The compromise in dimensional accuracy in HP PA 11 occurs mainly in the Z-direction with respect to HP PA 12.
RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
  • It is recommended to use mechanical print profiles (HP PA 11 and HP PA 12), which also require two passes per layer, to
    achieve the best elongation at breakpoints and impact resistance results while maintaining tensile strength, which is not
    affected with respect to balanced print profiles.
RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
  • Fast print profiles (HP PA 11 and HP PA 12) are recommended for reducing time and cost as they use half the number of printing passes as Balanced or Mechanical modes and require a lower volume of fluid agents. In both cases, tensile strength remains comparable to their respective Balanced modes but elongation at breakpoints is lowered, especially in the Z-direction. This trade-off is less pronounced for HP PA 11 than for HP PA 12, since the overall mechanical performance is higher for all HP PA 11 print profiles. Furthermore, the Fast print profile for HP PA 11 generally yields linear accuracy comparable to that of Balanced HP PA 11 but shows reduced warpage.
  • The cosmetic print profile is only available for HP PA 12 and aims to reduce the occurrence of geometric artifacts such as sinks on the tops of parts. It requires two passes per layer.

To highlight the differences between the current print profiles and materials, the behavior of their general characteristics is approximated, as shown in Figure 3:

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

Tuning for Accuracy

Introduction

There are several recommendations that must be evaluated during the printing process to maximize accuracy.

Optimizing Dimensional Accuracy

To maximize accuracy, the system needs to operate at voxel level with adequate energy delivered to properly fuse the intended sections layer by layer. To achieve this, it is recommended to bear the following in mind:

Printing Profiles and Materials

• In general, Balanced print profiles are recommended for optimizing dimensional accuracy. Fast modes (HP 3D HR PA 11 [“HP PA 11”] and HP 3D HR PA 12 [“HP PA 12”]) can be considered lower-cost alternatives, keeping in mind their associated mechanical trade-off.
• In the case of HP PA 11, it is also better to use the Balanced print profile, which is dimensionally similar to HP PA 12 on the XY-plane but has a higher trade-off with respect to the Z-axis.
• When warpage is the main concern, it is recommended to switch from Balanced (HP PA 11) to Fast (HP PA 11).
• With thin and long parts where flatness is critical, consider using HP PA 12 or HP 3D HR PA 12 Glass Beads (“HP PA 12 GB”), since HP PA 11 presents higher warpage potential. If HP PA 11 is the material of choice, then it is recommended to use the Fast print profile.

Build Platform Placement and Printing Process

• Orient each part by placing its critical features on the horizontal XY-plane as this will provide the highest resolution.
• Place small features such as pins, holes, and thin walls upside-down on the XY-plane to improve their look, feel, and strength. This also applies to raised texts, which should be printed on the XY-plane for maximum resolution.
• Embossed text, however, results in increased clarity when printed facing upwards.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

• The recommended minimum distance between parts is 5 mm, and the ideal distance between parts and the build volume margins is between 10 mm and 20 mm.
• It is recommended to leave enough space between dense parts, or those with a wall thickness greater than 15 mm. This distance should be more than 10 mm.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

 • It is recommended to place the parts with the highest dimensional requirements, especially on the Z-axis, as centered and as low on the printing platform as possible.

• It is recommended to distribute the parts as homogeneously as possible on the XY-plane to facilitate similar energy absorption across the printing bed

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

• As well as in the XY-plane, it is recommended to place the parts in the bucket to prevent drastic changes in the printed areas per layer in the Z-direction.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

• A good compromise between throughput and part quality is a packing density range between 8% and 12%. However, this value can be revisited depending on application requirements.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Warpage Concerns

• When warpage is the main concern—especially for large, thin, flat parts—it is recommended to place the parts parallel to the XY-plane.
• Long parts should be placed along the Y-axis to reduce the thermal gradient even further, as this is the printing direction of the carriage.
• When printing parts prone to warpage, it is recommended to place them as centered and as low on the platform as possible. This allows them to cool more slowly, reducing the probability of warpage.
• It is recommended to print short jobs in order to minimize the Z-height—number of layers—which allows for faster printing and cooling stages.
• It is recommended to avoid fast cooling for parts prone to warpage.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

Dense Parts

Dense parts are those with a substantial mass concentrated in a reduced volume, thus resulting in fewer cavities and walls no thicker than 15 mm to 20 mm.
• Favorable orientation is critical for parts that do not have a homogeneously distributed mass. It is recommended to print them at an angle and not along clear array patterns in order to facilitate heat distribution during printing.
• Make sure that the parts are appropriately separated (> 10-15 mm) and that the packing density does not go beyond the recommended range.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

• High packing density print jobs with dense parts may result in powder deterioration and eventually impact the powder recyclability and, thus, the cost.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

The recommendations are summarized in the following flowchart, which can be used as a guide for maximizing the dimensional
accuracy of HP MJF–printed parts:

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

Dimensional Accuracy Examples

Honeycomb Plate

The following example involves the printing of a honeycomb plate to maximize dimensional accuracy. This part is very similar to a big, flat plane, and therefore the object is moderately susceptible to experience warpage. However, thanks to its light honeycomb design, this deformation is not expected to be as severe as on a fully dense plate.

To maximize the accuracy and circularity of positioning holes, it is recommended to orient the part so that these features are contained on the XY-plane. This orientation minimizes the height of the part, which is compatible with the recommendations for reducing warpage and bowing.

To preserve the flatness of a part, center it as much as possible on the platform, place it in the lowest quarter, and use Slow Cooling (50% longer than the standard recommendation).

Keep in mind that placing a part flat can induce capillarity on its top face, so angle the part slightly to prevent it if this is more critical than obtaining maximum accuracy of its holes. This trade-off is reduced for HP PA 12 GB and HP PA 11 parts in Fast and Balanced print profiles, which result in similar accuracies with reduced capillarity and abraded tops.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

As shown in the figure above, in a collective scenario where several plates of this type are required, the following are recommended:
• Print short buckets (using different Build Units).
• Center the parts as much as possible.
• Make sure that a similar number of parts are being printed at each level. In the example there are either two parts or none.
• Shuffle the parts so that they do not line up along the same XY-coordinates. This allows the printing load to be shared across more printheads, extending their lifespans.
• Use extended Natural Cooling.

Phone Case

The following example involves a phone case that does not require a great deal of accuracy but can potentially show warpage and bowing if not correctly oriented. This is a flat and thin part that can be considered small, and it is a good candidate for orienting perpendicularly to the XY-plane, laying on its side parallel to the Y-axis.

In this orientation, each layer is printed very quickly while the height is still short enough for the build to maintain thermal homogeneity. To minimize warpage the parts must be placed as centrally as possible, jobs should be short, and Fast Cooling should be avoided.

However, these recommendations apply mainly to HP PA 12, HP PA 12 GB, and the Fast print profile of HP PA 11, as these configurations are not significantly affected by the bowing effect if parts are printed far from the walls. Figure 7. A honeycomb plate (left) oriented to maximize dimensional accuracy and minimize warpage. Critical features such as the positioning holes are contained on the XY-plane (middle). Right: A bucket with 10 plates in the same orientation.

Mechanical and Balanced modes for HP PA 11 can exhibit incidences of bowing, so it is worth considering an alternative orientation. In these cases, this part should be placed flat on the XY-plane as is the case for bigger objects. The rest of the guidelines, such as using extended Natural Cooling and printing short jobs, still apply.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

Best Practices for Aesthetics

Introduction

To maximize the look and feel of parts when 3D printing, it is important to consider the orientation and positioning of the parts in the build platform as well as the specific print profile and material used. It also is advisable to avoid situations wherein these elements are exposed to excessive or non-homogeneous heat during the printing process.

Optimizing Look and Feel

Printing Profiles and Materials

• If available for the intended material, consider using the Cosmetic print profile to maximize part look and feel.
• Consider also using HP 3D HR PA 11 (“HP PA 11”) in Fast or Balanced print profiles as it results in far fewer part quality defects. HP 3D HR PA 12 Glass Beads (“HP PA 12 GB”) also reduces the likelihood of imperfections, but the improvement with respect to HP 3D HR PA 12 (HP PA 12) is less pronounced than with HP PA 11.
• When the focus is on the appearance of the part, do not use Mechanical or non-tuned Balanced print profiles.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Build Platform Placement and Printing Process

• Place small features such as pins, holes, and thin walls upside-down on the XY-plane to improve their look, feel, and strength. This also applies to raised texts, which should be printed on the XY-plane for maximum resolution.
• Embossed text, however, results in increased clarity when printed facing upwards.
• It is recommended to avoid upward-facing angles that are smaller than 20° between big, flat areas and the XY-plane.
• Downward-facing surfaces are typically exempt from stair-stepping if they are oriented using angles greater than 5° to 10°.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

• The recommended minimum distance between parts is 5 mm, and the ideal distance between parts and the build volume margins is between 10 mm and 20 mm.

• It is recommended to leave enough space between dense parts, or those with wall thicknesses greater than 15 mm. Normally, this distance separation should be greater than 10 mm.

• Avoid placing dense parts close to the walls of the build chamber as these artifacts mainly affect the last printed layer. Thus, it is recommended to rotate the part so that the top layers have reduced cross-section, avoiding flat areas as much as possible.

• It is recommended to distribute the parts as homogeneously as possible on the XY-plane to facilitate similar energy absorption across the printing bed.

• Place parts in the bucket to prevent drastic changes in the printed areas per layer in the Z-direction.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 5. The printed area per layer distribution (right column) is used as an indicator of homogeneity in the Z-direction to prevent major differences in the energy absorption of parts. a) An example of a non-recommended job configuration displaying non-homogeneity in the three dimensions. b) A job that is homogeneous on the XY-plane but with a distinct and potentially problematic gap along the Z-axis. c) The gap along the Z-axis is smoother after rotating the cubes in order to prevent exposing large areas to the last layers to be printed. d) Using automatic packing, the printed area distribution is smoothened even further, minimizing adverse thermal effects. This is a recommended configuration

• Parts prone to displaying sinks or bubbles should be positioned farther away from other parts (approximately >10 mm), especially for objects directly above them (in the Z-direction). Positioning them in the top quarter of the bucket may help to reduce these effects.

• A good compromise between throughput and part quality is a packing density range between 8% and 12%. However, this value can be reassessed depending on application requirements. 

The advice provided in this section is summarized in the flowchart (Figure 6), which can be used as a guide to maximize the look and feel of printed parts.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 6. Flowchart for an appropriate process-parameter selection based on the geometry and functionality of a part in order to maximize its look and feel

Aesthetic Example

To further illustrate the recommendations provided for cosmetic parts, below is an example involving a toy sailboat:

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 7. An example of part orientation focusing on maximizing the look and feel of a toy sailboat (a). b-d) Initial orientation stage wherein the part has a large area parallel to the XY-plane, increasing the effect of the artifacts. Fifty parts were placed, allowing rotation around the Z-axis. The area-per-layer distribution fluctuates and ends abruptly. e-g) A boat rotated 25° around its own axis in order to prevent artifacts and excessive layer-stepping. The collective area distribution with 50 boats is smoother than in the previous scenario

Since the most visible area of the object is the inside of the boat, it is clear that the part needs to be placed facing downward to provide a better finish in that section.

A first approach would be to leave it flat, but the printed area distribution of this orientation (especially in the collective case with 50 parts) ends sharply after a maximum peak, which should be avoided in order to minimize surface artifacts such as capillarity, abraded tops, and sinks.

Consequently, the boat should always be angled more than 20° in order to minimize the visibility of the individual layers. This rotation can be performed around a different axis or a combination of them. The rotation axis along the boat’s length is chosen to minimize the required Z-dimension printing and smooth the printed area distributed across the many layers.

In terms of the position of the parts in the build chamber, it is best to look for the center of the platform, but there is no significant difference in the result between orienting the parts along the printing axis (X) or re-coating axis (Y). Thus, in the collective scenarios where 50 boats are printed in the same job, rotations around the Z-axis are allowed, which can increase packing density (depending on the geometry of the parts) and, more importantly, helps the required droplets to be shared across the build platform. This homogeneous distribution of the printing load is critical to prevent the over-stress of a small set of dies while leaving others idle for long periods of time.

The orientation advice for this part can be used for HP PA 12, HP PA 12 GB, and HP PA 11. However, since HP PA 11 and HP PA 12 GB typically result in reduced capillarity, a flat orientation could be applied in situations where the accuracy of some features on the XY-plane (like the hole for the sail) are critical or the height of the job is restricted.

Natural Cooling is recommended for all materials, since a faster cooling rate can lead to deviations on the flat areas with respect to their nominal shapes.

Tuning for Mechanical Properties

Introduction

Selecting the proper printing and cooling profile, printing part material, or placing the part in a specific orientation in the build platform are a few ways to maximize the mechanical properties of a 3D-printed part.

Maximizing Mechanical Properties

There are several considerations that must be evaluated before printing a part in order to increase its mechanical performance:

Printing Profiles and Materials

• Mechanical and Balanced are the print profiles that yield the best mechanical properties for both HP 3D HR PA 11 (“HP PA 11”) and HP 3D HR PA 12 (“HP PA 12”) materials, with the former exhibiting better results.

• HP PA 11 provides higher elongation and impact resistance1 than HP PA 12, while HP 3D HR PA 12 Glass Beads (“HP PA 12 GB”) results in higher tensile moduli while reducing elongation and tensile strength.2

• Using Cosmetic (HP PA 12) or Fast (HP PA 11 and HP PA 12) print profiles is not recommended for applications with high mechanical requirements.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 1. Recommended distance between dense parts
Build Platform Placement and Printing Process

• The recommended minimum distance between parts is 5 mm, and the ideal distance between parts and the build volume margins is 10 mm to 20 mm.

• It is recommended to leave enough space between dense parts, or those with wall thicknesses larger than 15 mm. Normally, this distance should be more than 10 mm.

• In cases where many parts with the same shape are tightly packed with parallel main surfaces, treat them as dense parts and increase the distance between them.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 2. Left: Many parts arranged in a configuration that can result in excess heat. Right: Alternative configuration that increases heat homogeneity and facilitates dissipation, resulting in better results overall

• It is recommended to distribute the parts as homogeneously as possible on the XY-plane to facilitate similar energy absorption across the printing bed.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

• As well as in the XY-plane, it is recommended to place the parts in the bucket to prevent drastic changes in the printed
areas per layer in the Z-direction.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 4. The printed area per layer distribution (right column) is used as an indicator of homogeneity in the Z-direction to prevent major differences in the energy absorption of parts a) An example of a non-recommended job configuration displaying non-homogeneity in the three dimensions b) A job that is homogeneous on the XY-plane but with a distinct and potentially problematic gap along the Z-axis c) The gap along the Z-axis is smoother after rotating the cubes in order to avoid exposing large areas to the last layers to be printed d) Using automatic packing, the printed area distribution is smoothed even further, minimizing adverse thermal effects. This is a recommended configuration d-i d-ii d-iii 0
RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer

• When optimizing mechanical properties, a good compromise between throughput and part quality is a packing density range between 8% and 10%.

• Using a low packing density improves the heat management between parts, which increases positive results through homogeneity.

• It is recommended to print short jobs in order to minimize the Z-height—number of layers—which allows for faster printing and cooling stages, and to increase the elongation at breakpoints and impact resistance of parts.

• Fast Cooling has a similar beneficial effect on elongation at breakpoints and impact resistance, but it should not be used for parts prone to warpage. This is especially critical for HP PA 11, which is more prone to warpage.

Mechanical Examples

Below is an example of a part orientation for a part that requires increased elongation and impact resistance in its thinner features:

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 5. Left: A mechanical part with high elongation requirements on its thinner features Right: A short bucket containing 20 iterations of the same part

As mentioned previously, process factors such as print profiles, cooling profiles, and job heights are key factors in achieving better mechanical properties.

Thus, to obtain high elongation and impact resistance values, it is recommended to use a Mechanical print profile, to cool the parts as fast as possible, and to print shorter jobs (minimizing Z-height) with low packing densities. 

The choice of Mechanical print profiles for both HP PA 11 and in HP PA 12 entails a trade-off in dimensional accuracy. However, this is not an issue for the present application. Similarly, Fast Cooling would most likely induce warpage on thinner features, but their flatness in this case is not as relevant as their elongation, which would be boosted with faster cooling.

In terms of materials, the Mechanical print profile for HP PA 11 would result in higher elongation than its HP PA 12 counterpart, even without using Fast Cooling. HP PA 12 GB would not be a good choice of material for this application since it typically results in stiffer parts that tend to snap rather than bend.

Primary Post-Processing Recommendations

Introduction

Post-processing is the final stage in the end-to-end process for HP Multi Jet Fusion technology. It is a crucial stage in the manufacturing cycle. Finding a suitable post-processing workflow can significantly impact the look and feel of the final part, as well as its mechanical properties.

Post-processing encompasses two key stages: primary and secondary post-processing. Primary post-processing refers to cleaning processes that are required for Multi Jet Fusion printed parts. Secondary post-processing, on the other hand, refers to processes that may affect the mechanical properties of the part, provide cosmetic enhancements, or reduce surface roughness, for example.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 1. E2E HP Jet Fusion 3D Printing workflow

Given the nature of HP Multi Jet Fusion technology, which injects fusing and detailing agents onto a powder-based material, primary post-processing is a mandatory stage for all parts printed with HP Jet Fusion 3D Printing Solutions. As the part is printed, it is encapsulated in unfused material, which needs to be removed to obtain the desired raw printed part.

It is important to consider this post-processing stage when designing the part. By adding drain holes, lattice structures, or a chain in duct parts, cleaning the printed parts need not be a complex task. For specific tips and recommendations on how to design parts to facilitate cleaning, see Design for Cleaning.

Secondary post-processing is an optional step and depends on the specific requirements of the application where the final part will be used. The techniques included in this post-processing stage can be classified as providing cosmetic attributes (for example, dyeing and painting), or reducing surface roughness (for example, vibratory tumbling or chemical polishing); however, this is not a strict classification, as some techniques such as painting or electroplating can provide both attributes.

Primary Post-Processing – Cleaning

This stage involves removing excess unfused material from the surface of the printed part. If this excess is not removed correctly, it will not only affect the part’s overall look and feel, but also alter the dimensional accuracy of the part.

After a job is finished, parts are “uncaked” or unpacked, either automatically or manually, in the processing station or in the printer depending on the specific HP Jet Fusion 3D Printing Solution, and unfused material is reclaimed in the system for recycling. When unpacking, printed parts must be left with a significant layer of unfused material, as it has been exposed to varying levels of fusing and detailing agents, as well as high levels of energy, altering its properties. Any unfused material left after material reclaim should not be recycled.

The layer of remaining unfused material can be removed by using different techniques:

• Bead blasting

• Air blasting (in combination with bead blasting)

• Water jet blasting (also known as water jetting)

The basic operating principle for the three techniques is identical, although the media used to expel the excess material changes. They all use pressure to dislodge the unfused material from the surface of the part so that the fused material is visible. Bead blasting and air blasting are dry techniques, whereas water-jet blasting is a wet technique.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 2. Part after unpacking, uncleaned (left); Part after cleaning (right)
Bead Blasting

Bead blasting involves propelling an abrasive or blast media, usually in bead or sphere form, at high pressure against the surface of the part using compressed air. As well as dislodging the unfused material from the surface, the bead dimples the surface without affect its dimensional stability, providing a more uniform, “satin” finish.

The unpacked parts are placed in the blasting chamber. An air compressor pushes air into a pressurized hopper, where it is mixed with the blast media, and the air-blast media mix is projected into the blasting chamber onto the unpacked parts via a blast gun or nozzle.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 3. Functional diagram of a bead blaster

Bead blasting can be performed manually or automatically depending on the specific requirements of the part to be cleaned.

In automatic bead blasting, the parts are placed in the blasting chamber and usually moved, using a turntable, tumbler, track or conveyor, so the parts are exposed to the fixed or mobile blast nozzles. In manual blasting, an operator is responsible for controlling both the delivery of the blast media using a foot pedal and the distance from the blast nozzle to the part.

Automatic bead blasting allows multiple parts to be processed simultaneously, achieving a consistent finish on all parts. Often additional parts such as small filler balls are added to the chamber to ensure a uniform finish on all parts.

Manual bead blasting is more suited to fragile parts that require careful processing to avoid damage. However, the process is more time-intensive than automatic blasting for high production volumes, and is also susceptible to greater error as parts can be burnt more easily if they are placed too close to the blast nozzle.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 4. Automatic bead blaster

Both systems require a compressed air installation that offers a minimum air pressure of 3 bars, however more pressure may be required for better results. There are numerous solutions on the market that offer manual and automatic bead blasting, and standard equipment specifications usually satisfy the requirements for cleaning HP Multi Jet Fusion printed parts.

Regardless of whether an automatic or manual system is used, there are five key factors to consider in bead blasting:

• Blast media

• Air pressure

• Nozzle diameter

• Distance to part

• Time required

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 5. Made for HP Jet Fusion blasting equipment

Blast Media

The size and the type of beads result in different surface finishes. There are several materials that can be used as blast media: glass, stainless steel and other metals, for example. For parts printed with HP Multi Jet Fusion technology, pure glass beads with a diameter of 70–110 µm are recommended, since they do not affect the dimensional accuracy of the part. Stainless steel beads of a similar diameter may also be used, as they provide a darkened, more uniform surface and result in a greater abrasion of the surface. Although their cost is higher, stainless steel beads are suited to high production volumes, as they are hardwearing, and cleaning the filters and the machine afterwards is easier.

The beads may be single-use or reusable depending on the blaster configuration; however, they must be replaced at least 6 to 8 hours in high production lines, for a blast media load of 12 kg, or 3 to 4 hours for a blast media load of 5 kg, to avoid the risk of polyamide contamination.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 6. Printed part cleaned with glass beads (left); part cleaned with metal media (right)

Air Pressure

This is a determining factor in bead blasting. If the pressure is too low, the process will be ineffective and more time will be required to clean the surface. If the pressure is too high, the bead may break and cause damage to the part’s surface. Nonetheless, generally speaking, increasing the pressure decreases the cleaning time.

For automatic bead blasting, the air pressure should be set at around 4–7 bar. This value should be adjusted according to the time required, the geometry of the part, and the quality of the abrasive media.

For manual bead blasting, the air pressure should be lower, around 3–5 bar, with the recommended value for non-fragile parts being 5 bar, and 4 or 3 bar for fragile parts. A lower pressure is recommended for manual bead blasting compared to automatic bead blasting, as other factors such as operator experience and blasting angle can affect the outcome.

Nozzle Diameter

The diameter of the nozzle should be taken into consideration when determining the air pressure. The abovementioned values for air pressure are based on the use of a 10 cm-diameter nozzle. If the diameter of the nozzle is less than that, the pressure value should be adjusted proportionally.

Distance to Part

The distance from the blast nozzle to the part determines the effect that the blast media have on the part’s surface. It is also one of the factors that can give rise to incidents during the cleaning process. For automatic bead blasting, the distance is controlled by the equipment configuration (around 15–20 cm), while for manual bead blasting this can be manually controlled, and a closer distance of 10–15 cm is recommended.

To avoid damaging parts by insufficient distance, a printed cage can be used to group small parts or parts with fragile features.

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 7. Cage printed with small parts inside

Time Required
As mentioned before, manual bead blasting is more time-intensive, and depends on the operator’s experience and judgment on
whether the part is clean enough or not. The time required also depends on the geometry, size and complexity of the part. On average,
20 to 40 seconds is required to clean a part of medium size and complexity with no thin surfaces or fine detail. For fragile parts where
less pressure is used, the value might be greater.
For automatic bead blasting, the time required is calculated based on the condition of the media. If the media is new, less time will be
required compared to bead blasting done with reused media. On average, the process takes around 10 to 20 minutes.
It should be noted, however, that the overall look and feel of the part can be improved with less pressure and longer blasting time.

Air Blasting

Air blasting involves propelling a stream of compressed air onto the part’s surface. It is usually used in conjunction with bead blasting to remove any remaining powder material and blast media dust that may have been left on the surface without affecting the dimensional or mechanical properties of the part.

The operating principle of air blasting is similar to bead blasting: an air compressor feeds air into a pressure vessel, and a trigger mechanism releases the jet of compressed air from the pressure vessel onto the surface of the part via a blast nozzle.

Air blasting requires a compressed air installation that provides a minimum air pressure of 3 bar, although greater pressure may be required for better results.

Since compressed air has a lower impact force on the surface compared to blast media, air blasting does not provide uniformity on the powder removal process and is not recommended as the sole solution for cleaning parts. It should be used only after the part has been bead-blasted.

Nonetheless, air blasting may not be necessary if the part has been blasted using a blaster that contains a deionizer. The deionizer electrically discharges the parts, meaning that any dust falls from the surface.

Some bead-blasting solutions also offer air blasting functions, in which case the same machine may be used for both processes, however ensure that the machine does not contain any abrasive media before proceeding to air-blast the parts.

Similar to bead blasting, the key factors that influence the outcome of the process are air pressure, nozzle diameter, distance to part, and time required. The values for these factors are similar to manual bead blasting. To summarize, the air pressure range should be between 3 to 5 bar, adapted according to the nozzle diameter; an optimal distance of 15 cm should be left between the part and the blast nozzle; and an average time of 10 seconds per part will be required, depending on the complexity and size of the part, as well as the operator’s experience.

Water Jet Blasting

Water jet blasting or water blasting involves jetting a fluid mixture of compressed air and water via blast nozzles onto the part surface to remove powder. It can also be used for initial surface finishing by including a suspended solid (or blast media) in the fluid mixture. 

The technique has usually a higher cost than bead blasting, but it provides several key advantages. It is ideal for cleaning complex geometries or ducts automatically, since the blast nozzles have different orientations, allowing the fluid to penetrate hard-to-reach areas. It also can reduce slightly the surface roughness with minimal additional processing time, much faster than using traditional vibratory system for the same initial roughness reduction.

It ensures a dust-free environment, as no subsequent processing is required to remove blast media dust. In general, the fluid can process several kg of powder before becoming saturated, moment in which the supplies would need to be replaced.

The key factors for achieving the best results with water jet blasting are similar to bead blasting:

• fluid composition

• air pressure

• nozzle diameter / distance to part

• time required

RapidMade|Dialing in an HP Jet Fusion (MJF) 3D Printer
Figure 8. Water jet blasting equipment
Fluid Composition

One of the key factors in water jet blasting is the fluid used as the medium. Different fluid compositions can be used according to the solution; for example, pre-treated water without any blast media, or a water-soluble detergent in which an abrasive ceramic or an abrasive ferrous metal is suspended, providing an initial surface finish.

Air Pressure

The pressure value is dependent on the part geometry and the presence of fine detail, but it is usually lower than the one used in bead blasting.

Nozzle Diameter / Distance to Part

Since water jet blasting is usually an automated solution that is performed in a sealed chamber with several nozzles pointing different directions, both the nozzle diameter and the distance to part is controlled by the equipment’s configuration.

Time Required

As with bead and air blasting processes, the time depends on the complexity and geometry of the part. For parts of medium size and complexity with no thin surfaces or fine detail, an average of 30 minutes or less is required for a full cleaning job.

©Copyright 2019 HP Development Company, L.P. The information contained herein is subject to change without notice.
The information contained herein is provided for information purposes only. The only terms and conditions governing the sale of HP 3D printer solutions are
those set forth in a written sales agreement. The only warranties for HP products and services are set forth in the express warranty statements accompanying
such products and services. Nothing herein should be construed as constituting an additional warranty or additional binding terms and conditions. HP shall not
be liable for technical or editorial errors or omissions contained herein and the information herein is subject to change without notice.