What Are Jigs and Fixtures? Differences, Uses, Advantages
Learn more about the uses of jigs and fixtures in manufacturing.
A jig is designed to guide a cutting tool and is normally used when manual operations like drilling or reaming are required. A fixture is a heavy-duty manufacturing aid used to secure and align raw materials in a CNC machine for example.
This article will describe the difference between jigs and fixture assembly aids as well as how jigs and fixtures work, where they are used, specific design considerations, and their various advantages.
Jigs are devices that guide and support the cutting or shaping tool in a manufacturing operation. For example, a jig can be used to guide a drill bit or reamer to precisely drill a hole. Jigs can be custom-made for specific operations, or they can be used for general-purpose applications across multiple operations and multiple parts. In many cases, jigs are an essential part of the manufacturing process, as they help to ensure that products are made to precise and repeatable specifications. It must be noted that due to the precision of CNC machines jigs are not required on these machines. A drilling jig is shown in Figure 1 below:
A drilling jig being used to make strong joints.
Image Credit: Shutterstock.com/kasarp studio
Fixtures are tools or devices that are used to hold, support, and position components during manufacturing processes such as: milling, turning, grinding, and fabrication. Fixtures are not designed to guide cutting tools. They help ensure accuracy and repeatability in manufacturing. Fixtures are custom-designed to fit the specific requirements of a component or product. They are especially useful for supporting complex shapes during machining. Fixtures allow manufacturers to produce high-quality products with repeatable results. A CNC fixture is shown in Figure 2 below:
A CNC fixture.
Image Credit: Shutterstock.com/Aumm graphixphoto
Fixtures and jigs are manufacturing aids used to help hold and position parts for subsequent operations. Jigs, however, are used to guide the cutting tool to help achieve precise results without the need for expensive, high-precision tools like CNC machines. Jigs are often lightweight, so they can be easily handled by technicians for maximum productivity. Fixtures on the other hand are used to hold and support raw materials and parts during manufacturing operations like CNC machining as well as in fabrication to align elements prior to welding.
Jigs are used to guide a cutting tool and are most often used for drilling, reaming, and tapping operations. The jig helps keep the raw material fixed in place so that it does not move or deflect during drilling, thereby allowing for precision holes without the need for expensive CNC machines.
Fixtures are devices that support and position workpieces during manufacturing processes such as: machining, grinding, fabrication, broaching, and milling. They are typically designed for a specific manufacturing process or component. Some fixtures are actuated so that they can clamp on to workpieces placed into the machine by robotic arms, for example. In fabrication, fixtures are used to precisely position weldments for improved productivity as well as to prevent the part from warping during welding.
Jigs and fixtures are both used to improve overall productivity and accuracy during manufacturing. If a part is to be machined on a 3-axis machine, for example, it would not be possible to machine a hole whose axis is angled with respect to the spindle axis due to the limitations of the machine. One option would be to machine the part on a 5-axis machine, but this would be costly, especially if only one feature requires the 5-axis capabilities. In this case, after machining the part can be removed from the fixture. A jig can then be used to allow a technician to drill the angled hole.
Jigs and fixtures are widely used due to the many advantages they offer as listed below:
- Increased Precision: Both jigs and fixtures improve overall precision. Jigs help remove the potential inaccuracies caused by human error, whereas fixtures help securely hold raw material during machining to prevent any inaccuracies caused by the material deflecting or moving during machining.
- Increased Productivity: Properly designed jigs and fixtures help reduce skill requirements for tasks that would otherwise require highly skilled personnel to achieve acceptable results. Essentially these manufacturing aids act as a force multiplier in terms of productivity.
- Reduced Cost: Jigs and fixtures help speed up tasks, and as such the overall labor cost per part is significantly reduced. For example, the raw material can be quickly aligned and set up in a well-designed custom fixture that would have otherwise taken much longer to set up with standard fixtures. Scrap rates are also reduced as the chances of failed parts are significantly reduced.
Before the increased popularity and accessibility of 3D printing technology, jigs and fixtures were machined from metal, wood, and plastic and were limited by the capabilities of the CNC machines. 3D printers can be utilized to produce jigs and fixtures that can be printed at significantly lower material and manufacturing costs when compared to CNC machining. In addition to this, 3D printed parts have fewer DFM (Design for Manufacturing) limitations when compared to machined parts, meaning that complex jigs and fixtures can be produced. It must be noted, however, that if extremely high-precision parts are to be produced, 3D-printed jigs and fixtures may not be the best option as they are not as precise as CNC-machined parts.
When designing jigs and fixtures, there are a number of best practices to be considered that will improve the overall function of these manufacturing aids. Some key design considerations are listed below:
- Orientation: Jigs and fixtures must be designed so that there is only one way to use them. For example, it must be impossible to place the raw material or component in the incorrect way.
- Multiple Operations: Where possible, jigs and fixtures must be designed so that multiple different operations can be performed using the same jig or fixture in a single setup without the need for additional human intervention.
- Location: Machining fixtures must be precisely aligned to ensure optimal accuracy. As such, it's important to constrain the fixture while being careful of over-constraining, which can introduce inaccuracies.
- Easy Handling: Jigs and fixtures must be designed to be very easy to handle. For example, it must be possible to manipulate the jig or fixture with one hand.
- Material Selection: The material used to make a jig or fixture must be carefully chosen. For example, if the jig or fixture is to be used for multiple parts it must be built from a durable material like hardened steel. Alternatively, materials like plastic or wood can be used.
When designing fixtures and jigs, it's important to consider the following when performing design calculations:
- Force Analysis: When it comes to fixtures specifically, there can be very high loads generated from cutting forces in CNC machining operations or from deformation caused by heating and cooling during welding. As such, the expected forces must be determined and incorporated into the design to ensure the fixture will not fail.
- Tolerances: It is important to calculate the potential tolerances expected. For example, if the raw material is to be squared prior to machining, the tolerances from this operation must be considered in light of the expected fixture tolerances.
This article presented jigs and fixtures, explained what they are, and discussed how their differences and how they are used in manufacturing. To learn more about jigs and figures, contact a Xometry representative.
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