p/n 31-D107 Rev B

 

Material Usage, Build Speed, and Part Cost Optimization

 

3D Systems MultiJet (MJP) Printing is a robust and mature 3D printing technology with many unique values. MJP is well known for its world-class high precision and high-fidelity capability allowing parts to be printed true-to-CAD and with very good surface quality. The ProJet MJP 2500 has a broad material set with simple, automated, and low-cost material changeover. This includes a completely waste free changeover option and generally allows for quick, hands-free swapping of the materials based on daily job requirements. Each different material is optimized for specific uses cases based on customer needs. All the rigid and engineering materials can be used for drilling/taping/machining/pressing and achieve good surface finish, sharp corners, fine features, and create high fidelity true-to-CAD parts. The engineering materials M2G-CL (Armor) and M2G-DUR (ProFlex) maintain high quality, but were designed for the most aggressive engineering applications including high impact applications, complex snap fits, and living hinges. In this technology, the supports are automatically created regardless of part geometry and/or complexity, are removed quickly and easily by simply applying heat, and leave no residual surface marks or surface defects. The post processing is mainly hands-free and allows the creation of very small features and entrapped cavities for some of the most demanding applications. No two users are the same and each will leverage different aspects of this technology for their specific application. However, all users prefer fast print speeds and low costs per job. There are a number of different best practices to ensure maximum speed printing and minimal material cost.

 

Speed Optimization

MJP technology creates 3D printed parts using an industrial inkjet printhead. The build and support material are jetted during each pass of the printhead over the build plate. The ProJet 2500 has a printhead smaller than the total build size. The ProJet 2500 printhead has 880 individual jets (440 each for build and support) and are packed into an approximately 2.93 inch (7.45 cm) array at 150 jets per inch (approximately 1/3 the total width of the build area). To produce parts/jobs larger than the 2.75 inch width of the head, the printhead is translated and the end jets interlaced to make the larger jobs (~6” and/or 9” width jobs for the ProJet 2500). These lanes are shown in 3D Sprint by the lines on the build plate. 

The three imaging lanes in a ProJet 2500

 

Speed Optimization:  Part placement and z-height minimization

The standard layer thickness on MJP printers is about 1/800” or 32 microns (0.032 mm). Every layer that is printed requires multiple passes (a total of 6 passes per lane for the 2500). Therefore, on the 2500 a total of 12 passes are needed for a 2-lane job and a total of 18 passes are needed to make a single layer for 3 lane jobs. Therefore, to maximize the print speed, the parts should be placed in such a way to minimize the number of lanes printed. For example, on the 2500 one should try to place the parts into a single lane or two lanes if possible. Also, regardless of the number of lanes being printed in a job, one must also try and reduce the height of the job. There are a few tips one can try to reduce the height of the job to try and minimize print speed. 

 

Speed Optimization:  Part orientation

Often the simplest way is to rotate the part(s) by 90 degrees such that it (they) fit into one lane and have the shortest build height. 

Two lane & tall job, 18hr 26min

Single lane & tall job, 14hr 9min

Two Lane & short job, 7hr 52 min

Single Lane & short Job, 5hr 52min

 

When printing multiple parts, the fastest printing speed will be that which reduces the height and the total number of lanes to be printed.

90 degree rotation of parts reduce the printing time from 7hr 40 min to 2hr 5 min

 

 

For certain part geometries, another method of increasing printing speed is to rotate the tallest part to make it shorter and wider just before the point that the part would cross a lane and would result in a second lane. 

As placed two lane job, 16hr 16min

 

Rotated parts fit into two lanes with reduced job height, 9hr 31min

 

Speed Optimization:  Balancing height of parts in lanes

Another way to reduce job printing time is to move all the tallest parts to one of the lanes or orient the parts such that the tallest portion of the part resides in a single lane. Once the lane with the shorter part is complete, the printer software knows to revert and print only the single tallest lane and this will reduce the job time.   

Tallest section of part crosses two lanes, 16hr 58min

Tallest section of part is rotated into a single lane, 13hr 55min Orientation of tallest section into a single lane to reduce build time

 

Speed Optimization:  Operating at recommended ambient temperatures   

The wax support is solidified during the printing process. The build material also creates heat due to the curing process. Both processes require that the part is cooled as part of the printing process. To cool the part, there are eight part cooling fans, four on each side of the marking unit assembly. There is an adaptive cooling algorithm built into the printer that measures the inlet plenum temperature and will add cooling passes to insure that the parts will be cooled sufficiently even at higher ambient temperatures. The printer will run at full speed for ambient temperatures of about 24°C (75°F) and below.  The printer will add cooling passes for temperatures 25°C to 32°C (75°F to 90°F).  Above 32°C/90°F the ambient temperature must be reduced for the printer to operate.  Therefore, to achieve the fastest printing speeds, it is recommended to keep the printer is a well-ventilated room at 24°C/75°F or below. Other printer installation requirements should be followed according to the setup documentation. If needed, it may be advantageous to add a simple electrical fan to improve room thermals and air flow. It is also possible to purchase a small, floor mounted air conditioner to cool the ambient temperature.

Speed Optimization:  Final comments

Since each job starts by building a base support and the base support takes a fixed amount of time, it can often be quicker to print multiple parts in a single job. If parts can be added onto the build plate without adding to the height or number of printing lanes, these extra parts are printed without any increase in print time. It is interesting to consider the size requirements for a single day job. One typically would start the job at about 8 to 10am, depending on how much work was needed to prepare the part, printer, and send the job. Some additional time is needed for printer clean-up and post processing and an additional amount of time to actually take advantage of the part for its specific use. Considering that there is only about 8-10 working hours in a typical day, this dictates that a “single day” job needs to be no longer than about 6 hrs. The ProJet 2500 can print a 1” tall, 2-lane job in 6 hrs or a 1.5” single lane job. The parts could be as long as the build x-axis (11”) and as wide as one or two lane widths respectively (2.75” or 5.5”). Most other jobs will run overnight. Running a job overnight allows for an additional 15 or 18 hours for a total of about 24 or 30 hours printing time with still enough time in the 2^nd day to process and use the part. Most all practical jobs will be finished in one day or the next day.

Cost Optimization

Cost of the part or job is directly related to the amount of material that is used to print the job. Anything that can be done to reduce material usage will reduce the printing costs.

Cost Optimization:  Minimize the print time

 The ProJet 2500 printers perform an in-process maintenance periodically. This is done to keep the jets running within specifications and to insure reliable operation of the printer. Therefore, if one reduces the printing time using the methods already discussed, this can reduce the material used and therefore, reduce costs. The same is true for printing multiple parts in a single job. It can be most efficient in terms of speed, and least expensive in terms of cost per part to print as many parts as possible in a single build.

Cost Optimization:  Minimize the support overhangs through part orientation

Support needed for a job can sometimes be reduced by rotating the part. The simplest example often discussed is to place a box or bowel type part with the open side facing up vs. the open side facing down. If the open side is faced down, then the entire box or bowel needs to be filled with support material. Simply rotating the box or bowel by 180deg can greatly reduce the support needed. For a part that shaped like a box with a hollow section and vertical walls, this will greatly reduce the amount of support material required for the part. For a bowel shaped part, the round walls will require overhang support regardless of orientation and so one should check both orientations for the least amount of material used. Any orientation that reduces large overhangs should reduce the amount of material used and thus reduce the cost.    

Build:  0.156kg     Support 0.214k

Build:  0.163kg     Support 1.06kg

Rotation of parts in a job to reduce overhang support material

 

Cost Optimization:  Printing multiple parts per job

Like many 3D printing technologies, a MultiJet printer starts every job by building a base support that creates a flat surface for the part to be printed and allows for adhesion of the part to the plate. Also, the printer initiates a printhead purge prior to starting the job and in-process maintenance cycles are performed as the job is printing. Therefore, the cost and time for a part to be built can be reduced if multiple parts are printed in a single job. 

 

Cost Optimization: Using Shells and Infill

Using a shell and infill pattern as part of part creation is common in extrusion based rapid prototyping technologies and is also available for use with MultiJet Printing technology due to our melt away supports that can easily be removed from within a part. This capability can reduce cost and weight of printed parts, typically with no impact on the visual or dimensional accuracy of the part. The function works by creating a shell of any desired thickness and then adding an infill within the shell with a given density.

Step 1	Step 2	Step 3 (Bottom View)
Import your design into 3D Sprint.	Select Infill -> Offset, and input your desired wall thickness. The PRESET infill pattern is applied to the offset core that is created in this step.If you would like to change the pattern type, select Infill -> Lattice and apply the new pattern	Select Infill -> Vent Drain to add vent and drain holes to the part.  This allows removal of the internal support material, reducing weight and improving part quality.

 

The combination of the thin wall and sparse lattice structure results in a lightweight but rigid part.

Cut away view showing a thin shell filled with a 3-dimensional lattice structure.

The combination of the thin wall and sparse lattice structure results in a lightweight but rigid part.

 

The support material costs less than the build material and so using the shells and infill capability in 3D Sprint allows for a substantial cost reduction. The exact amount saved is dependent on the shell thickness and the percent acrylate in the infill pattern you chose. Parts printed using the ProJet MJP infill feature typically experience weight reduction of 40-70%, and cost reduction of 20-35%. 

Examples of cost and weight savings for two parts using the shells and infill capability in 3D Sprint.