Fixture

What Are Fixtures

A tool fixture, or shortened to fixture, is a work holding device used across the manufacturing industry. Fixtures not only provide support but to securely locate a work piece in a specific orientation, ascertaining that all components produced using the fixture will retain interchangeability and conformity. 

Using a tool fixture can facilitate the economy of production by enabling smooth workflow and quick transition from component to component. It does not require highly skilled workers to operate one of these as the mounting of work pieces are greatly simplified. At the same time, conformity is also enhanced across a production run. 
 

How Do Fixtures and Jigs Differ

Jigs, although often mentioned complementary with fixtures, are not the same as fixtures. The most fundamental difference is that a jig is a type of tool used to hold and support the work piece, but in addition to this, it also controls the motion or location of the tool as well. Fixtures on the other hand only acts as a support to hold the work piece in place as it does not guide the tool in any way. Jigs, however, does guide the tools, meaning that they are able to instruct tools as to where to go.
 

Purpose of Fixtures

The main function of a fixture is to serve as a secure mounting place for the work piece, allowing stability during operation and enhanced precision, accuracy, reliability and interchangeability in the finished parts. The quick setup also reduces working time, making transition from part to part a smooth and easy process. 

Fixtures also simplify a process, reducing the need of skilled workers to perform the operation and allowing the transferring of expertise of the tool maker to the unskilled workers. Moreover, fixtures can ensure the safety of the operator by reducing the effort and focus needed to keep the work piece intact in a certain position.

From the economic point of view, a fixture's most valuable function is to reduce labor costs. Without a fixture, human interventions are required to undertake a machining process, thereby incurring more overhead costs. Using a fixture can eliminate the need of skilled operators without compromising the quality and efficiency of a process.
 

Types of Fixtures

Fixtures can be divided into two main categories: the milling fixtures and drilling fixtures.

Milling applications tend to involve larger projects where many chips with varying force are produced with large and straight cuts. Using a fixture robust and sturdy enough to support and locate these heavy duty milling operations becomes very critical, coupled with a strong clamp that’s able to hold the work pieces in place securely. Positive stops are recommended over friction for securing the work piece because of the vibration of the machine. For high volume automated processes, milling fixtures are typically complemented by hydraulic or pneumatic clamps. 

Another type of is the drilling fixtures which can be used in a wide array of procedures than milling fixtures. Although jigs are often the more preferred option for drilling operation, fixtures can also be used nonetheless. The two core components of drilling fixtures are the bushing and hole. The holes are to allow drill bits to go through the work piece without damaging the drill or the fixture, or to guide the drill bit to the designated point of the work piece. These holes are normally designed into drilling fixtures. Bushings on the other hand are bearing sleeves which are inserted into these holes to guide the drill bits and protect the holes.
 

Construction of Fixture

Economically speaking, fixtures are designed in such a way that cost can be minimized by taking into account the implementation expense of the fixture. Most fixtures are composed of a solid part which is fastened to the floor or on the machine tool, as well as one or more movable jaws referred to as the clamps. The clamps, which can be operated by various mechanical means, enable work pieces to be placed or removed easily and securely. Many of these clamps also have adjustable jaws, allowing the clamping of different sized or irregularly shaped objects for different applications.

Fixtures are also required to be designed in such ways that motion or pressure of the machining operation (i.e., feed) is guided towards the solid component of the fixture directly. This reduces the chance that the fixture will fail, or interrupt the operation in any way which will lead to the damaging of infrastructure or operators.

Fixtures that are designed for general purpose, such as those used by DIYists and hobbyists in workshops, have simpler design yet retain the same benefits of those specialty fixtures. Some examples include the vises that are seen mounted on benchtops in workshops, adjustable clamps, and so on. Just like those specially-designed fixtures, general-purpose fixtures also perform the two most fundamental tasks: locate and support. 

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