WHITE PAPER INCREASE SPEED TO MARKET AND LOWER COST BY 3D PRINTING FIXTURES BY AARON LATZKE, CO-FOUNDER OF SIVA CYCLE, ON BEHALF OF FATHOM FATHOM is driven by advanced technologies that enhance our customers product development process. We leverage our expertise in 3D printing and additive manufacturing to help our customers innovate faster and more efficiently. Our product portfolio includes professional 3D printers and additive manufacturing systems. Our services focus on prototype fabrication and low volume production by way of advanced manufacturing techniques. This complete offering is supported by a dynamic in-house team focused on industrial design and mechanical engineering. We strive to be our customers preferred partner by providing best-in-class equipment, services, and support.
INCREASE SPEED TO MARKET AND LOWER COST BY 3D PRINTING FIXTURES Fixtures for assembly, quality assurance (QA), and alignment are critical parts for the mass production of a product. Traditional methods for fabricating fixturing can slow the time to market with long lead-times and slow iterations while adding cost to project budgets. 3D printing and additive manufacturing offer faster, lower-cost options for establishing production lines, which equate to increased iterations within given time and budget constraints, as well as a more efficient design process overall. THE CASE STUDY Recently, Siva Cycle went through the process of designing and implementing a QA fixture for our production process (Figure 2). As huge fans of 3D printing and its capabilities, we naturally turned to our 3D printer to tackle the job (FDM-based Mojo by Stratasys). Our first step, as in all design processes, was to ask, What does it need to do? This particular fixture would be testing the functionality of our electronics assembly, which required physical testing of the plugs and receptacles and electrical testing of the circuit components. The physicality of checking the plugs and receptacles meant the fixture had to be rigid and durable to handle repeated pushing and pulling on the work piece. The electrical testing required access to small test points on the PCB that meant precise positioning of the PCB and test probe. The fixture also needed to last without breaking, given its production setting use. Our production run was for 10k parts and we were testing 100% of the parts off the line, so it needed to last at least 10k cycles; something to think about in any setting, but an item of particular interest given the FDM material. Figure 1: 3D Printed Electronics Test Fixture In Development (FDM). Also See Figure 8. Figure 2: 3D Printed Electronics Test Fixture Utilizing Off-The-Shelf Components Including a Linear Slide and Pogo Pins (FDM). Lastly, the fixture had to be quick to use by the operator to keep cycle times and testing costs low. The electronic assembly needed to be placed, tested, and removed quickly, which required the operator to understand the work environment so he or she could move naturally and efficiently. Once we had our needs in place, the next step was determining how to make the fixture. We had already decided to use our 3D printer for its design freedom and quick iteration 2
cycles. With an FDM printer, we had a variety of material choices to complete the job. After considering our design needs and available choices, we chose a PC/ABS blend due to its robustness and durability, not to mention its economy. When designing the fixture, we kept in mind the build characteristics of the FDM printer and oriented certain features to take advantage of the anisotropic strength characteristics of the printed product. Snap features and flexures were oriented along build lines in such a way that the stress was oriented along the filament lines (Figure 3). High-precision features for aligning the PCB and electrical probes were placed in the x-y build plane where the printer is most accurate (Figure 4). Beyond the base structure, we augmented the fixture with electronic and mechanical features to obtain the functionality we needed. Pogo pins were used for the electronic probe to contact the test pads on the PCB. Shafts were used to make hinges, and then linear slides used when the hinge method proved inadequate (Figure 2). Blind nuts were used where thread strength was required, nestled in their own hex cutouts, easily printed into the part. Where that type of holding power was not required, we directly tapped the 3D printed plastic as you would any machined part with a standard cutting tap v. When it was all said and done, we ended up building three iterations before settling on our final design (Figure 5). We were able to design-print-test in quick succession and work through the problems in a way that simply wouldn t have otherwise been possible given our budget and resources. Quoting the fixture through a local machine shop in ABS plastic (the same material as used on our 3D printer), the fixture would have cost us $1678.63 with a 2-3 week leadtime. Printing the same fixture on a 3D printer took just under 28 hours (including support removal) and material cost was $80.43. Keep in mind this is for just one iteration; we went through three iterations before settling on the final design. Figure 3: Material Strength Varies Greatly With Build Stacking. Figure 4: The X-Y Plane Offers Greater Precision For FDM Printers. Extrapolating this process out, it would ve taken 6-9 weeks and more than $5,000 to complete the design using a traditional machine shop. Thanks to 3D printing, the same process took less than 1 week and cost less than $250 total. Figure 5: Final 3D Printed Electronics Test Fixture for Siva Cycle Production (FDM). 3
FIXTURES ARE KEY TO A SUCCESSFUL PRODUCTION RUN The Truths: Poor Assembly Fixtures = Poorly Assembled Parts Inadequate QA Fixtures = Parts and Assemblies Not Produced to Spec Proper design and iteration of certain fixtures define the product within the manufacturing process. This often requires multiple iterations to work through different fixture designs and ensure a proper production process. LEAD-TIME, FEATURE COMPLEXITY, PRECISION, & COST (TRADITIONAL METHODS) Traditionally, fixturing is made through standard machining operations like milling, turning, EDM, and other methods for low-volume fabrication. These come with trade-offs in respect to cost of lead-time, feature complexity, and precision. Lead-Time vs. Cost: Priority comes at a premium and therefore costs more to gain the attention of the machine shop. Feature Complexity vs. Cost: More features mean more time on the machine, which means a higher cost. Precision vs. Cost: Precision requires better equipment, slower feeds, and more passes, which translates to more time and higher costs. Feature Complexity vs. Precision: This relationship has a particularly strong impact on traditional manufacturing. If the feature complexity calls for machining options on more than one work surface, the machinist must hold the part in multiple orientations to complete the part. If the desired features cannot be fabricated within one part because of machining constraints, the feature set must be split into two or more parts that will be assembled together. This increases cost by adding parts to the BOM while also hindering precision due to the stacking of tolerances and assembly error. Figure 6: Example of a 3D Printed Production Electronics Test Fixture (FDM). More Desirable Than Traditional Method of CNC Machining. Figure 7: Additional Example of 3D Printed Production Assembly Fixture (FDM). 4
THE BOTTOM LINE: TIME From the project s perspective, extended lead-times become more than just a planning issue when the length of the iteration cycle increases the product s time to market. The opportunity cost of a delayed product shipment quickly outweighs the project cost, and each week of delay to the product s launch results in real dollars lost in the company s bottom line. SOLUTIONS AVAILABLE TODAY Today, there are services and technologies that address the issues of lead-time, feature complexity, and precision. 3D printing can offer great improvements in bringing products to market. Addressing lead-time concerns, 3D printing typically delivers parts in 1-2 days, with most 3D printing service experts hanging their hat on turning jobs overnight; FATHOM i and Stratasys Direct ii offer 1-2 days as a standard option. Figure 8: 3D Printed Production Electronics Test Fixture (FDM). Some businesses, such as Shapeways iii, find a niche in the market by providing reduced pricing for those who do not mind waiting two weeks for parts. However, a quick view of the Shapeways website shows that their target market isn t the product design engineer, but rather the DIYer making arts and crafts. This reinforces the notion that the product design world has a need for speed, making quick iterations key to project completion. In regards to feature complexity, 3D printing offers designers the ability to literally print their heart s content. Concerns about whether a design can be machined go out the window. All focus turns to functionality. The unlimited design freedom allows for geometries that were once considered unmakeable. Parts can be made lighter and more ergonomic. 3D printing also allows consolidation of parts; a design that would require several parts if being machined now becomes one or two 3D-printed parts with highly complex feature sets. Precision is a constant throughout the 3D print, and stack-up tolerance concerns are diminished. Time and money are saved by paring down the design process. Focus is on what the fixture has to do, not how to make it. 5
The top brands of 3D printers on the market build parts with tolerances that rival standard machining practices, with tolerances ranging from.001 -.010 depending on technology and geometry. Typically, there is a trade-off between precision and time of build, which means that higher precision parts are more expensive. While this mirrors what we find from machining, what sets 3D printing apart is the level of precision combined with the feature complexity. Instead of splitting parts into multiple sections to be machined, 3D printing can be used to produce a fixture assembly that has high precision with minimal assembly time and cost. TIP COMBINE FORCES FOR STRENGTH As amazing as 3D printing is, it does have its limitations. Strength of printed materials can be an issue, as can the durability. At Siva Cycle, we fortify our 3D- printed fixtures with machined or off-the-shelf parts so that a strong and durable fixture is made. For example, Helicoils iv are used where screws must be inserted repeatedly, linear slides are used where linear motion is needed, and machined plates are used where structural strength is needed. We use the 3D printer to quickly build and create the bulk of the structure that is then fleshed out with off-the-shelf components or custom machined parts where necessary. CONCLUSION In closing, 3D printing can drive valuable savings when making fixtures, an integral part of the production process. By enabling more complex feature sets with shorter lead-times and lower costs, companies can ensure they bring their products to market as fast as possible without compromising quality. i http://www.studiofathom.com/ ii http://www.stratasysdirect.com/ iii http://www.shapeways.com/ iv http://www.helicoil.in/ v A note on tapping FDM parts, we found roll taps, which are normally used when tapping holes in plastic, to become clogged and produce poor results. Standard cutting taps work best. 6