3D Print Design – 3D Print Unit Testing and Tolerance

Welcome to the 3D printing design column “Designing for 3D Printing (DF3DP)”. DF3DP is a series of articles dedicated to 3D printing tips and tricks to follow when using any 3D printer. 3D printers will help you reduce production costs, printing time and materials, and we will show you how 3D printers follow your original The design is designed to assist with the completion of your parts.

Whenever you find that you spend a lot of time and the parts printed on the material do not meet your original design requirements, don’t worry, we will always be with you. You can help you solve the problem. 3D printing is an unattended manufacturing process, so once you send a pre-designed CAD model to the printer, you don’t need to make any changes. Parts can take hours or even days. If you need to print before the deadline, from a time or money perspective, using a corrected tolerance can effectively avoid the loss of reprinted parts. Since 3D printed parts use fused filament fabrication (FFF), the final molded 3D printed part size may be compressed, as 3D printers usually do not accurately print the size you originally set, so We need to consider tolerances before printing. In this article, I will guide you on how to ensure that the 3D print tolerance is correct to avoid waiting for the component to print out and then find the error.

The unit test comes in handy when printing 3D parts. Unit testing is traditionally a software term. The main purpose is to run a small piece of code separately, and then merge them into a complete script after the test is successful. We plan to do the same thing with 3D printing: quickly print the partial components and then integrate them into a larger design to verify or test their functionality and applicability before printing out the complete components.

3D Print Design — 3D Print Unit Testing and Tolerances

Designing a 3D printed microweight combat robot made with Markforged printer

For example, I am designing this 3D printed micro-weight combat robot prototype with its top sliding through a set of wedge-shaped boring grooves (one of which is circled below) onto the base. Since these two parts take 107 hours to print, I want to perform a 3D printing unit test before printing all the parts to ensure the correct size of the groove.

3D Print Design — 3D printing unit test and tolerances

The battle robots marked with red circles in the figure are on both sides of the chassis and it will be a groove, it will Locking two parts together

Designing a 3D printing unit test

A well-designed unit Testing should be quick and easy to prototype and easy to print (I usually focus on about half an hour to an hour of printing). I simulated a pair of micro-grooves and made replicas of different offsets, ranging from no offset on all sides of the wedge-shaped hoe to an offset of -0.2 mm. This means that each groove profile is thinner than the final product.

3D Print Design — 3D printing unit test and tolerances

The tolerance of each group of fingers is slightly different, I can test the mother on each of them Slider profile

I also marked the samples with different offsets so that I can recognize the different sizes of parts, as shown below:

3D Print Design - 3D Printing Unit Tests and Tolerances

This 3D printed unit test allows me to find out which size is best.

Testing 3D Print Unit Tests

One thing to remember is to print the direction of the unit test. In order to ensure that the final part of the printing accuracy can be tested as accurately as possible. Printing took only 1 hour and 15 minutes, much faster than printing the entire robotic chassis, and then found that my sliding-in grooves had poor tolerances.

3D Print Design — 3D printing unit test and tolerance

3D printing test of groove track

To test it I just slide the groove profile onto the different rails, starting with the largest face offset (-0.2 mm) and testing them one by one in my way until the end of the offset of 0.0 mm.

3D Print Design — 3D Print Unit Test and Tolerance

Test the 3D print unit test. It was finally found that the tolerance of -0.05 mm met my requirements.

-0.2mm offset profile is very loose – I don’t want the top of the robot to fall off easily. The male figures of -0.15 mm and -0.1 mm are decent, but not as comfortable as I want. The -0.05 mm offset is just right – it’s comfortable enough, it’s not easy to be beaten, I can slide it down with a little pressure. The final outline, the offset of 0.0 mm, is a bit too tight for my preference. Now I can enter a -0.05 offset value in the final design and I am sure it will slide as I want. There are also some features that actually lock the top, but the grooves that connect the two parts are my uncertain tolerances.

3D Print Design — 3D Print Unit Test and Tolerance

Add the final offset size to the 3D printed combat robot

Other applications for unit testing

Unit testing is very valuable for any type of tolerance, even if you just want to know about you The test results of the printer in some cases. For example, to understand hole tolerances on a given 3D printer, you might need the printer to provide the following:

3D Print Design - 3D Print Unit Test and Tolerance

(you A hole tolerance test like this can be used to ensure the accuracy of the printer and to determine the tolerance required for the bolt hole by comparing the hole size of the design with the actual measurement.)

Then, you can measure the hole size and compare the measured value to the dimension value in the CAD model, giving you a clear understanding of the required hole tolerance on each plane on the 3D printed part. You can then use this test result as a reference for future design work, and it can help with the checksum testing of many 3D printed parts.

In addition, with the Markforged 3D printer, you can take advantage of unit testing more: assuming you really need to print out the entire robot chassis, you must first make sure you have to use carbon fiber. You can make a 3D printed fit prototype for testing to test whether all components are suitable for your 3D printed parts (or other methods) before adding carbon fiber for printing. This reduces material waste and reduces costs, so you can test the final geometry and shape of fiber-filled parts before printing.

3D Print Design — 3D printing unit test and tolerance

(3D printing unit test for 3D printing camera lens hood. Used to confirm that it can be locked on the lens It takes 15 minutes for the ring to print, and the lens cover takes 4.5 hours to print.)

The true value of unit testing

So we can say that the entire chassis and top are printed, and I messed up the tolerances of the grooves. Then I need to print the entire part again, otherwise I will have to spend a few hours to delve into a very tiny geometry, and no one really wants to. 3D printed parts are sanded later to make them suitable for size, especially when they involve small geometries, which often leave scratches, poor surface roughness, and can accidentally damage component functionality or expose 3D printed parts. Internal structure. Obviously, two 3D printing of large parts is not as expensive as designing, then printing a small part and a large part. Here is a detailed table of robot printing, in case you are not sure if the 3D printing unit test is complete:

3D Print Design - 3D Printing Unit Tests and tolerances

Unit tests take only a fraction of the time and do not require post-processing.

Unit testing is critical for proofreading large 3D printed components, and it can help you reduce the chance of repeated prints due to print size issues. Post-processing of parts is a process that most people must go through in the later stages of 3D printing, whether it is grinding the surface, drilling or reducing the error. On 3D printers that are as reliable and accurate as MarkTwo, post-processing is no longer a step you must take. Unit testing ensures that your parts are printed to the maximum extent you want.