Jig and Fixture Design

Image Sources: Siemens Digital Industries Software

Jigs and fixtures are manufacturing tools that are used to produce identical and interchangeable components. These work-holding and tool-guiding devices are designed for use in the machining and assembly of parts.

What is a Jig?

A jig is a device used in securing a workpiece and machine part on a workstation. It is secured to the computer numerical controlled (CNC) machine tools such as a lathe cutting tool, which dictates the location and motion. That means, in a way, it guides such machining tools. Jigs are unique such that when they move, the tool becomes stationary.

What is a Fixture?

A fixture or CNC fixture is another popular CNC machining tool regarded as an agent of stability, support, and positioning. Like the jig, it works to secure, support, or mount a workpiece on a CNC machine.

Jigs vs. Fixtures: What's the Difference?

The jig and fixture can be two very confusing tools. Both tools are similar, and they promote productivity and efficiency. However, they function differently. Below are some highlighted differences between jigs and fixtures.

Main Function

The major jig and fixture differences are in their main functions. A jig guides the cutter to work at a predefined location on a workpiece. It also supports and locates the part. The fixture, however, only secures, supports, and locates the workpiece. It does not guide the machine part.  

Complexity

When comparing a jig and fixture, the machinist agrees that jigs are easier to use. Fixtures require machinists to have some skills before performing an operation.

Weight

Another property to look at is the weight in which jigs are lighter than fixtures. Fixtures are heavier because they have to withstand the huge cutting force and vibration.

Whether Fitted to The Machine

Jigs can be held or fixed on the table depending on the type of work they are used for. Also, jigs do not require additional devices when used in heavy work, although they might need to be clamped. Fixtures, however, require clamping and accessories for better functioning.

Design

Jigs are more complex than fixtures in terms of their construction.

Whether they come in contact with the tool

Fixtures don’t need to come in contact with a machine part since their design is to fit the part. However, a jig must come in contact with the tool to set the angle and position accurately.

Advantages of Jigs and Fixtures

In manufacturing operations, it's important to meet the higher demands of customers. This means producing quality products as fast and efficiently as possible. Jigs and fixtures help make manufacturing processes more efficient and precise.

By utilizing jigs and fixtures in machining processes, manufacturers benefit from:

• increased production

• decreased manufacturing costs

• improved product consistency

• improved assembly line safety

• a reduction in non-productive hours

• reasonable automation capabilities

• interchangeability and accuracy

Types of Jigs

Jigs are common devices in CNC machining, and they come in different and various types. Below are the common types of jigs used in machining operations.

• Template Jigs
  These jigs are simple and ideal due to their accuracy. They also have tremendous speed. However, machinists use them more for accuracy than speed. Template jigs are used in many ways. For example, you can fit them over, or into the workpiece. However, they are not usually clamped.

• Angle-Plate Jigs
  Angle plate jigs are ideal for holding parts prepared for drilling at angles to their mounting locators.

• Plate Jigs
  Plate jigs are like template jigs with the same ways of use. However, unlike template jigs, they have built-in clamps to hold the workpiece.

Types of Fixtures

Most machinists are not familiar with fixture classification. No wonder they have a problem with selecting the right one for their operation. The fixtures illustrated below are based on three things: machining operations uses and power sources.

The list will be summarized.

• Fixture Tools Based on the CNC Machining Operation:

  • Turning Fixtures.

  • Milling Fixtures.

  • Drilling Fixtures.

  • Boring Fixtures.

  • Grinding Fixtures.

• Fixture Tools Based on their Uses:

  • Universal Fixtures.

  • Special Fixtures.

  • Assembled Fixtures.

  • Modular Fixtures.

  • Combination Fixtures.

• Fixture Tools Based on their Power Source:

  • Manual fixture.

  • Pneumatic fixture.

  • Hydraulic fixture.

  • Electric fixture.

  • Magnetic fixture.

  • Vacuum fixture.

Tips for designing a Jig or Vibration Test Fixture

There are two key important factors that need to be considered for designing a good vibration test fixture:

• The vibration test fixture must be designed to be as light as possible in order not to significantly reduce the testing capacity of the vibration test machine

• The vibration test fixture must be designed to be as stiff as possible to allow the resonance to lie far beyond the upper limit of the test frequency range

From the material perspective, there are 2 types of materials used for vibration test fixtures:

• Aluminium

• Magnesium

Steel is not commonly used for vibration test fixtures due to its weight and light-damping value. The most common material used is aluminium, since it is much lighter and has better damping characteristics than steel. If we have enough budget, then we can also try to use magnesium.

Is there any tool that can help us to design vibration test fixture? The answer is YES, if you have the capability to perform Finite Element Model (FEM) simulation, then this will be very useful for predicting the dynamic characteristic of your vibration test fixture. Of course, the more complex design you have, it will need more modelling skill on your simulation.

Most of FEM software may offer below type of simulations:

• Normal Mode

• Frequency Domain Response

• Time Domain Response

For designing vibration test fixture, performing normal mode simulation should be good enough, since we will be able to obtain the resonance frequencies and the mode shape at each resonance.

By having the mode shape, we should be able to understand better on how to increase the stiffness or reduce the mass which are not contributing to the structure stiffness. Unless it is not possible to push the resonance out from the test frequency range, then we may want to use the Frequency Response Simulation. Running frequency response simulation will be much more challenging compare to normal mode since the accuracy of the result will not be depending only on mass and stiffness, but also the damping properties that we put into the simulation.

---

How can we help you?

Interested in our vibration testing fixture design?
Send us your inquiry via the Fixture Design Form and we will be pleased to help you.