Jigs and fixtures by Xometry – 3DPMN

Jigs and fixtures are often made with custom parts from Xometry. Both of these devices help engineers and manufacturers to make better products.

A jig is a device that helps support, hold and locate a workpiece by guiding the tools that are needed to execute a manufacturing operation. Well-made jigs can have a major impact on the repeatability and accuracy of a manufacturing process. Jigs are used in uni-dimensional processes like drilling, tapping and reaming. Jigs also can have installed components, like bushings, which can come into contact with the cutting tool. An example is a drill bushing, which keeps drills in the right position and at the right angle to perform their work. 3D printing jigs is common practice due to the process ability to create conformal shapes and off-angle features without expensive tooling and setups.

Unlike jigs, which help to guide tools, fixtures help to hold workpieces in position so that they can be machined accurately. Examples include blocks of raw materials fixed inside machines and vices or clamps that hold workpieces in place. Most manufacturing facilities use fixtures to enable automation to increase production speed. For example, Xometry builds automotive fixtures for BMW that are used for aligning a vehicles front end during assembly. This helps BMW to manufacture their vehicles more efficiently and reduce operational error though repeatable work holding and installation solutions. BMW uses 3D printing services, urethane casting and CNC machining services to produce custom fixture assemblies.

Jigs and fixtures are both used to increase the productive time of mass production processes. But there are key differences between the two. Jigs always help guide a tool, while fixtures hold and locate the work, but do not guide tools. Fixtures are usually heavier and are bolted directly to the machine table, while jigs are usually lighter and are not affixed directly to the table. Jigs are also generally more complex to design and more expensive to produce than fixtures.

Both jigs and fixtures can be made with CNC Machining or 3D Printing, though it is more common to see 3D printed jigs since they are lighter. 3D printing can be a great choice with parts with complex geometries since they can often be expensive or challenging to machine. 3D printed jigs can be significantly cheaper than machined ones, so its worth getting a quote in 3D printing as part of your process.

Designing a fixture or jig begins with the application in mind as well as the quantities needed. There are three main processes used when making jigs or fixtures.

1. CNC machining is great for producing low to medium complexity shapes that require high stiffness, extreme environments and precision tolerances. Delrin (Acetal), Garolite, PTFE and PEEK are the most common polymers used for machining jigs and fixtures. In metal, typically Aluminum 6061-T6 is the most common, which can be enhanced by finishes like metal plating, color anodizing and chemical conversion coatings. CNC milling is the best approach for quality check fixtures, due to its ability to achieve precision tolerances and surface finishes.

2. Additive manufacturing or 3D printing can produce low to very high complexity shapes with ease. Fused Deposition Modeling (FDM) is heavily used in making fixtures because of a build area up to three feet and the ability to make lightweight parts using sparse infill. Handheld jigs, such as surgical drill guides, may utilize processes like Carbon DLS or Stereolithography due to a good combination of precision and durable parts. PolyJet 3D printing is useful for laser marking fixtures because of its ability to produce soft-touch, non-marking holders using multi-material 3D printing, similar to a rubber overmold.

3. Urethane casting combines the design freedom of 3D printing with high-wear, urethane-based materials. Urethane casting can produce low volume production parts that can be color-matched, hit a specific durometer and are non-marring for holding finished products and ornamental pieces. Cast urethane parts are often flexible or rubber-like but can also be highly stiff depending on the material used.

Each jig or fixture is custom, and specifically designed for its application. There is no right way to make or combine parts together but there are best practices that will help guide your thought process. The tips below aid in design best practices for fixtures and jigs.

1. Make a mockup if you do not have the part yet. 3D printing is by far the best means to get a rapid prototype of a part to be fixtured. Even before the design process, a physical model to reference can be a powerful tool to inspire a design approach. 3D printed parts can also be robust enough to trail fixture or jig setups, including drilling, part marking and running automated inspection like CMM.

2. Limit your touchpoints in the design to those which critically support the object as well as indicate or index its orientation. This will reduce the complexity of the jig or fixture and save headaches when the digital design meets realitywhere minor deviations may occur from manufacturing.

3. Give clearances to corners and bends when designing conformal jigs and fixtures. Many manufacturing processes may have small radii in sharp internal corners. Instead of risking an interfering fit, it is best to design generous pockets or clearances around those features. For fixturing bent tubing or sheet metal components, it is best to design for the maximum condition of the curve or avoid touchpoints in that area altogether. This is due to deviations from the CAD which can often occur in the bent or formed locations.

4. Split up large parts to reduce manufacturing costs and increase the flexibility in the design. For example, you can build a 30 fixture, but it may be 2-3X less expensive to build smaller components only where the touchpoints are requiredespecially if the fixture will be mounted to a threaded plate.

5. Make the parts lightweight by using ultralight or sparse infills with FDM, or by designing features like pockets, ribs and holes to reduce the material used. This is particularly useful for jigs, where it is very common they will be handheld. Lighter parts will reduce fatigue over time and can be easier to store between uses.

6. Mix materials and processes to get a specific function out of the jig or fixture. It is not uncommon to see 3D printed components cover the highly custom contours of a jig or fixture while other features are generated using precision milling or other processes. Each process has its strengths and trade-offs, and with manufacturing as a service models (MaaS) like Xometry there are very few restrictions to what process and materials can be used.

7. Use COTS frequently to reduce costs on standardized components like handles and clamps. COTS stands for commercial off the shelf and is a catch-all term for anything you can buy without needing to custom design it (screws, pins, handles, rails, etc.). COTS components are almost always cheaper than custom manufactured pieces, often by orders of magnitude in costs. The custom components machined, cast or additively manufactured should be specific to the application need. Adding threaded inserts or tapped holes to the custom components prepares them for custom COTS integrations.

8. Prepare for benchtop adjustments by incorporating adjustable features. For example, metal shims between screw-mounted components are extremely common to compensate for tolerance deviations in assemblies. Using slots for table top-mounted fixtures allows minor adjustments to be made without heavy rework. Spring-powered pogo pins, whether custom or off-the-shelf, are also useful for giving firm mounting while allowing for small deviations between parts.

With online machine shops and online 3D printing services available today, it has never been easier to produce single and low volume custom jig and fixtures. Xometry has the benefit of providing the most common services and materials used for producing custom guides and work holding solutions with short lead times and low costs. Xometry can even build custom assemblies on-demand as it does for BMWs automotive line. Getting started is easy by uploading the 3D models for the jig or fixture to Xometrys Instant Quoting Engine.

This article was published in collaboration with Xometry.

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Jigs and fixtures by Xometry - 3DPMN

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