Posted on: Dec. 9th, 2020, | By WayKen Rapid Manufacturing
The success of custom machining will significantly depend on the process as a whole, and that is where tools and fixtures come along. Custom parts can be very challenging to work with because of the non-standard (special) features required for them. Sometimes, these special features significantly shoot up the price for fabricating a custom part. An excellent solution for this problem will be the utilization of the proper jigs and fixtures.
Jigs and fixtures are production devices used to accurately manufacture parts per specified requirements, especially for custom parts. The scope of jigs and fixtures in machining may include the bushings, sleeves, maskings, part holding support, location holders, and many more.
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Why are Jigs and Fixtures Important in Custom CNC Machining?
Careful selection of jigs and fixtures will significantly improve the economy of the fabrication process by allowing smooth operation, simplified production, and quick process transition. Tools and fixtures help compensate for the constraints of the CNC machine in working with a part. They are designed to provide secure mounting and maintain the part location's reliability during the machining process. Described below are the different roles of tooling and fixturing for custom machining:
1. Part Holding
One primary purpose of jigs and fixtures is to provide secure mounting of the part during the machining process. They are custom-designed to fit the particular part being machined. They provide custom part holding whenever a part may need to be held at a specific angle or to be clamped at a particular shape.
Reliable custom fixturing is crucial in preventing undesired inaccuracies caused by chatter and tool pull out. Some examples of fixtures used as part holding are vises, chuck, centers, milling fixtures, and various holding plates.
2. Parts Protection
One role of jigs and fixtures is they protect the work part while machining. They are a great help for maintaining the desired surface finish and maintaining proper runout.
Sleeve, bushing, and masking fixtures are commonly designed for custom parts where surface finish is controlled. This is done to protect the surface of the finished part from the metal chips/ swarf from different machining processes for the work part. Furthermore, customized machining centers are specifically designed to cater to custom parts with tight callouts on overall runout.
3. Location Control/ Fool Proofing
Jigs and Fixtures are very essential in maintaining dimensional and location accuracy. They ensure that the workpiece is held at the right location and orientation during the machining process. For these reasons, it makes fixtures a convenient way of incorporating fool proofing in a process to minimize errors due to human factors.
Fixtures control the location, orientation, and stability by constraining the degrees of freedom in the work part. This is done by using pins, clamps, planes, and fasteners in designing the needed fixture. Planes provide support for the part, clamps allow adjustable mounting while having the accessibility of being dismounted, and pins provide precise location control for specific features.
In custom parts machining, features like holes and slots are controlled at a specific location where it could be hard to machine because of some mounting constraints, and that is why fixtures are designed. Fixtures are the most reliable way of machining difficult part features.
4. Part Consistency
Fixtures make it possible to machine multiple custom parts while maintaining its quality. They make sure the quality is consistent from part to part. Examples of the feature controls that need consistency are flatness, parallelism, perpendicularity.
5. Set up Reduction
Fixtures are a great way of eliminating the tedious process of inspecting while loading a part. A fixture designed for a specific part makes the whole CNC process a plug and play operation. The operator's work will be just to load the work part because all the necessary location control and parts referencing are already managed within the fixture. Many CNC machining fabricators are doing this in their process to save precious setup time for other value-adding processes. Some examples of fixtures that lessens set up time are the SMED (single minute exchange of die) Fixtures, Milling Fixtures, soft jaws, hex milling fixtures, and many more.
Types of Fixtures in Milling and Turning
There is a broad spectrum of fixtures used in fabricating custom parts. Below are some of the general types of fixtures seen in custom machining:
1. Tombstone Fixture (For milling)
This fixture is also known as a pedestal type, fixture block, or tooling tower. Tombstone fixtures provide an easy solution for automating the machining process of multiple parts within one setup and loading. They typically have four sides, where parts can be attached or mounted.
2. Soft Jaws (for mill-turn/ turning)
Soft jaws are one of the most important fixtures for customized work holding. This fixture is machined to create an inverted version of a specific work part for efficient clamping. These fixtures are used to clamp a particular part of work with an odd shape -this makes it possible to clamp a custom part tightly and ensure a secure and snug fit while machining the part.
There are different mandrels, but the one used for fixtures is typically used to grip a work part to be machined. These mandrels have different ways of holding a work part; they can be either tapered or flanged. Tapered mandrels hold the part by being driven into a controlled hole and grip the work part by friction. On the other hand, the flanged mandrel has an integrated flange towards its end and is threaded at the opposite side. The work part is gripped between the flange and the nut on the thread.
4. Milling fixtures
These types of fixtures are custom built depending on the particular requirements and specifications for the part being machined. They firmly clamp and hold parts to the milling table in the controlled position while the table moves past the cutters. Milling fixtures are usually a combination of planes, pins, and clamps to firmly hold and locate the parts. Milling fixtures may cater to vertical and horizontal milling.