Work Holding Technology Pt. 1: Introduction to Work Holding

Introduction

Continual advancements in the fields of mechanization and automation have led to large strides forward for the manufacturing industry. Various products ranging in size from cars to small circuit components are today made through automated procedures in manufacturing facilities. These automated procedures help improve efficiency, save on labor costs and reduce the occurrences of defective products thereby improving company growth and product quality.

A common feature of automated processes is the need for the item being worked on to be held firmly as work is being done on it. This idea of securing a part so that work can be done on it is known as work holding. Work holding technology summaries a large group of devices used to secure the part and these devices are known as “work holders”.  Using work holders helps improve the economy of production by creating smooth operational processes and helping facilitate quick transitions from one work station to another. This leads to less skilled labor needed as the process of mounting parts for the next operation has been simplified and streamlined to be as easy as possible. In Figure 1 we can see the basic idea of what work holding entails.

basic workholding

Figure 1: Illustration of basic work holding

Work holders use many different methods to hold the parts securely. Currently available to the manufacturing industry there are hydraulic, electric, pneumatic and mechanical holders which are used depending on the application. Work holding devices are commonly referred to as jigs and fixtures. Jigs and fixtures are known to be used interchangeably when describing work holding tools. A fixture secures the workpiece and has to have the tool move relative to the workpiece while a jig properly positions the workpiece before being restricted.

Locating

The primary function of work holders as previously stated was to secure a part to allow manufacturing processes to be conducted on them. Work holders do this through locating and clamping. Establishing the position of the work piece in relation to the tool with accuracy and consistency is important to maintain a repeatable and reliable process. This is done with the help of locators and is known as the principle of locating.

An unsecured work piece has 12 degrees of freedom. Figure 2 shows these 12 degrees of freedom with 6 axial degrees of freedom and 6 radial degrees of freedom. The role of locators is to establish reliably the position of the work piece and eliminate the degrees of freedom so as to restrict movement. This also means that locators must be strong enough to withstand the forces it will experience as the work piece is being worked on. The clamps on the other hand provide needed pressure and friction to hold the part against the locators. Figure 3 shows the different kinds of locating that are possible to secure a work piece while a tool is in operation.

fig 1 degrees of freedom

Figure 2: Degrees of freedom present on an unsecured workpiece

Fig 2 degrees of freedom

Figure 3: Example of locating

We’ve covered why it’s necessary to restrain parts, and how they can move. In the next article we will reveal the most common ways to keep your component restricted from the 12 degrees of freedom.

 

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