Even with advanced cutting tools, it may be challenging to produce machined parts with high accuracy and precision if there is no workholding method. Workholding fixtures help to hold parts firmly during machining. From milling vises to jigs and fixtures, many workholding options are available.
However, the type of materials you are working on and the number of parts you want to produce are factors that play a role in determining the most practicable method to adopt. This article discusses the different workholding solutions available, their positioning, and factors you need to consider before choosing a workholding method.
What Is A Workholding In Machining?
A workholding is any tool or device that prevents a workpiece from moving from its original position during a machining process. In more detail, a workholding device performs two basic tasks: locating and clamping.
Locating helps to align the workpiece to the cutting tool. On the other hand, clamping holds the workpiece firmly enough to withstand the force of cutting while preventing the workholding fixture and the part from deformation.
In addition, in the CNC machining process, a CNC fixture firmly holds a workpiece while a CNC jig directs the cutter’s movement. Though a machining workholding does not perform any cutting operation, they are valuable and are the most important non-cutting tools.
Why Should You Choose A Strong Workholding Method?
Choosing a strong CNC workholding method is as important as choosing the right cutting tool for your part. Workholding devices, when used correctly, enable the CNC machine to operate at its full capability to produce high-quality parts. A strong workholding method is important because of the following:
Increased Part Immobility
For high accuracy and precision, the entire cutting operation needs to be stable and immobile. The CNC machine, cutting device, workpiece, and the workholding method employed all contribute to the rigidity of the machining process. Even a slight movement during the machining operation can lead to mistakes that may require you to remake the parts. With a strong workholding method, you can minimize the time and expenses associated with machining.
Secure it Against the Forces of Machining
Machining generates some forces that can affect the position of the workpiece and the subsequent accuracy of the process. As a result, the workpiece prevents movement of the workpiece by securing it in place. This is very important, especially when machining designs with sharp internal corners or when working with CNC techniques such as milling and turning that generate high torque.
Safety
The safety of the operator and the workpiece depends on how strong the workholding method is. Although the CNC machine will contain the workpiece, this may not always be the case. When the workholding device is not strong enough, the workpiece or fragments of the cutting tool can fly off, so the workpiece must remain stationary to guarantee the safety of the employees.
Examples Of Workholding Solutions You Can Use In Part Manufacturing
The following are examples of workholding fixtures you can use to hold your workpiece during cutting operations.
Milling Vise
This is the most popular workholding solution. The most common milling vise used is the machinist vise. A machinist vise uses its jaws to keep a part immobile as the cutter rotates through it.
You can clamp the part between the fixed and movable jaws. Because these vises are commonly made of soft materials, they may not work with all engineering materials.
However, you can use any milling vise to hold down plastics, steel, aluminum, and other material. Furthermore, the shape and thickness of the material affects their use. When using milling vises, set them up appropriately to produce precise parts.
Plates and Clamps
Plates and clamps are both used for CNC mill fixturing. The simplest workholding device is a clamp customizable to meet a particular part’s needs and suitable for working with metals of all types, including aluminum, cast iron, brass, and steel.
A clamp is a form of a lever that works like all levers do. A part of it holds down the surface of the workpiece. Because plates and clamps are made of steel which can be further hardened, they are highly resistant to wear, and you can reuse them.
Soft Jaws
Soft Jaws are made with soft metals like aluminum. They can hold parts with complex shapes, and you can reuse them if the parts are of the same design. But, because soft jaws are not highly resistant to wear, they may not be useful when handling large numbers of parts. In this case, you may go with hard jaws.
Although soft jaws are helpful in CNC machining operations, making them may be challenging. Workholding tools do not increase a company’s profits directly. So, the process of manufacturing them should consider cost-effectiveness.
Step Clamps
With step clamps, one can access a part’s surface while working on it. This reduces its interference with the cutting tool. Step clamps grip a part down by pressing against its sides. Additionally, this device works well with both manual milling and CNC machining.
Step clamps provide a firm way of securing a workpiece. However, they have a few drawbacks. Not only does it require reconfiguration before each use, but the time to set it up is also relatively long.
Fixture Plates
Fixture plates use numerous threaded holes to clamp down parts while working on them. Typically, screws that fit into these holes serve as protection, and they may be removed when you are ready to use a particular hole.
Fixture plates are popular because they can hold down most materials, including large, complex, and unusually shaped parts. Also, maintenance costs are low, and they can handle specialized tasks.
Positioning For Workholding Devices
There are two main components of a workholding method: the workholding device and the tool used to position it. The following are some tools you can use to set up workholding devices:
T-slots
A T-slot is a workholding device with a T-shaped cut-out used to secure workpieces on a machine bed. It is the most common device used to set up and position workholding solutions. They are reliable and simple to use. However, with T-slots, it may be challenging to reposition the workholding fixture. The accumulation of debris and dirt also limits its use.
Fixture Sub-plates
Fixture sub-plates provide flat and stable surfaces to position workholding devices during machining operations. Fixture sub-plates come in different shapes and are made using different materials. These plates are easy to use, and you can place them vertically or horizontally for precise positioning.
Tooling Plates
It is similar to the fixture sub-plates. Tooling plates have holes that position the workholding devices accurately. This accurate positioning enables a part to meet the machining tolerances.
Modular Fixturing
A modular fixture may be the best option to save on cost. These devices perfectly hold workholding devices, and you can use them multiple times. Modular fixturing systems can come with grid pattern holes or T-slots. Systems with grid holes are stronger with better positioning.
Trunnion Fixtures
Trunnion fixtures are ideal for automated applications such as CNC machining. The device can be set up in minutes and uses locator pins to position workholding devices quickly. With trunnion fixtures, one can be sure of batch-to-batch consistency.
Tombstones
Using tombstones with more compact devices is advisable instead of bulky ones such as milling vises. Tombstones are a reliable and efficient positioning tool for CNC machining operations. More importantly, most tombstones have hole plugs already fitted in the grid. This makes cleaning fast and minimizes chip build-up.
Tooling Column
Tooling columns are made with either aluminum or cast iron. For this reason, they are highly wear-resistant, and you can use them multiple times. Tooling columns are becoming popular because they provide surfaces to fix and position workholding devices and workpieces.
Considerations For CNC Workholding Setup
Setting up a CNC workholding solution depends on material type, point of contact, and other factors. This section talks about the factors and what you can do when setting up the workholding solution.
Material Type
The material you are working on significantly affects how strong your workholding device will be. There are many engineering materials with different textures. As a rule of thumb, the harder your material, the stronger the force needed to hold it down. For example, because milling vises are made of soft materials, they are better suitable for soft materials such as plastics and aluminum. On the other hand, hard jaws can work with both hard and soft materials.
Size and Shape of the Material
This is another key factor you can use to narrow down workholding options. An irregularly shaped part may need special attention. For instance, milling a large part with complex shapes and geometries will require more robust fixturing that can withstand the force of the milling operation. Furthermore, you may use a simple clamp device if the part is small with a flat surface.
Point of Contact
You also need to consider the contact point of the workholding device and the workpiece. Do you want your device to hold down the sides or surface of your workpiece? Must the surface be easily accessible during machining operation? These are some of the questions you need to ask yourself to choose the ideal workholding solution for your part.
Number of Parts
Your choice of workholding solution should depend on the number of parts you want to make. Workholding devices used for small-scale production are different from large scale because they wear out with time. While it is possible to pause and change them during the machining process, this may be time-consuming. So, considering the number of parts you want to produce will help narrow down options when choosing the right workholdings for your project.
From prototyping to complete production runs, the success of any operation depends on the workholding solution used. For this reason, selecting the ideal tool for your project is essential. The ideal workholding solution must not only be durable and reusable to reduce cost. They must also be easy to set up to save time and boost productivity.
The whole process of setting up the right workholding may be challenging. It is advisable to work with manufacturing experts. At companies like WayKen, a professional team can offer outstanding custom manufacturing services and strong workholding solutions.
From ideas to parts production, engineers can help with every step of manufacturing to produce high-quality parts and shorten the time your product gets to market.
Conclusion
A good workholding setup can streamline quick production runs while guaranteeing that all batch parts adhere to specifications. You should know there is no standard solution for choosing the best project method. You may consider the versatility of the workholding device. This is because manufacturing aims to reduce costs while producing high-quality parts.
FAQs
What are the characteristics of a good workholding device?
A good workholding device should not only hold and position the workpiece relative to the cutting tool, but it must also resist the force associated with the machining operation.
Is there any difference between soft and hard jaws?
The main difference is the material used to manufacture them. Hard jaws are made from hardened steel. On the other hand, soft jaws are from softer metals such as aluminum or cast iron.
What are workholding jigs and fixtures?
Jigs and fixtures do not perform the same function. A fixture holds down the part. Jigs not only hold the parts, but they also direct the cutter.
