Even if advanced cutting tools are used, it may be difficult to produce high-precision and high accuracy parts without workholding. The workholding helps to firmly fix the parts during the processing. From milling vises to jigs and fixtures, there are many workholding to choose from.
Your CNC machining process depends on your workpiece fixture settings. The CNC workpiece fixing method can firmly fix your parts in place and reduce the stiffness. You can also call a workholding a fixture. Good CNC fixture setting is the key to locate the next part to be machined. Fixture is also important for safety!
This article introduces what is a workholding, the importance of a powerful CNC workholding, and six things you need to know before selecting a workholding.
What Is A Workholding In Machining?
The workholding is any tool or device that prevents the workpiece from moving from its original position during processing. More specifically, the workholding performs two basic tasks: positioning and clamping.
The Importance Of A Strong CNC Workholding Method
Increase the fixity of parts
In order to obtain high precision and high precision, the entire cutting operation needs to be stable and immobile. CNC machine tools, cutting equipment, workpieces and the workholding adopted all contribute to the rigidity of the processing process. Even slight movements during machining operations can cause errors and may require you to remake the part. With workholding, you can minimize the time and costs associated with processing.
Protect It From The Forces Of Machining
The machining will produce some forces, which will affect the position of the workpiece and the subsequent machining accuracy. As a result, the workpiece is prevented from moving by holding it in place. This is very important, especially when machining designs with sharp internal angles, or when using CNC technologies such as milling and turning that generate high torque.
Keep Safe
The safety of the operator and the workpiece depends on the strength of the workholding. Although CNC machine tools will contain workpieces. This may not always be the case. When the workholding is not strong enough, the workpiece or tool fragments may fly out. Therefore, the workpiece must be kept still to ensure the safety of employees.
Six Things You Need To Know Before Choosing Workholding Devices
Learn the following six points about theworkholding, and you will find the best workpiece fixture for any project.
1. Part size
The two most important factors for good fixture setup are stability and accessibility. Both are directly related to fixtures of appropriate size and need to find a balance between them. Fixtures can be large and provide rigid fixation, but increase the chance of limited access to the workpiece and vice versa.
If a part is too small for your fixture, consider stacking multiple parts.
If a part is too large for your fixture, and if you have modular parts, consider upgrading, or add custom parts if possible.
2. Part shape and condition
The selection of a workpiece fixture that fits the shape of your part actually depends on whether it is circular or prismatic (with planes). If the part is prismatic, a vise is usually used. If the part is circular, you need to grasp the outer diameter or inner diameter of the part. This may require collet collets, lathe collets or V-blocks if it needs to enter the milling machine, etc.
Knowing whether raw materials, castings or parts of finished products are used will also indicate what the workpiece fixture must contain. For example, a round bar from a rolling mill may have an outside diameter tolerance of ±. 005 “, but if it is a cast part, the dimension may be ±. 02” – either better or worse. If a part has been machined, then the size is not a variable, but a known controlled value.
3. Number of axles
Prismatic parts usually require multiple machining axes. This introduces a different set of workholding considerations. For multi axis machining, especially 5-axis machining, the workpiece needs to be fixed in a way that provides clearance for movement, without generating interference areas that will eventually lead to machine collapse. The most common interference area occurs between the worktable and the spindle housing of the machine. This is generally due to the need to have a wide angle of attack on the workpiece from the spindle to the workbench.
The use of things such as riser chucks to lift the workpiece provides a processing channel and allows the use of shorter tools, resulting in better cutting parameters, faster feed rates and greater depth of cut. When machining multiple faces of large workpieces in one fixture, the shape and position tolerances will also be improved. Similarly, the quick change workholding component can be directly installed on the bottom of the workpiece to be clamped without any side restrictions.
4. Production and mixing level
The frequency and complexity of part conversion should affect the speed at which you need to clamp the workpiece. In general, the higher the part combination and/or production level, the more conversions. Carefully consider how long it takes for a workpiece fixture to position and clamp.
We found that we usually do not see customers asking for changes until the setup cost reaches a critical point, usually 20% to 25% of the total cost of manufacturing parts, that is, hour/day and minute/fixture. The waiting time is very long, and the efficiency will be greatly reduced. In any case, the zero point workholding solution can maintain impeccable accuracy and strength, while allowing extreme modularity and rapid fixture/part replacement.
5. The degree of interaction between the operator and the workholding
How automatic are your loading, unloading and clamping? Or, what investment do you plan to make in workshop automation, and will it be used for machining? If any automation is in progress, workholding is a key consideration. If not, you still need to know who will handle the work fixture, how many people, and the level of experience to make the right choice.
When we think of automation, we usually think of robots or assembly lines, but when it comes to workholding, the focus is mainly on the ability to repeatedly and accurately clamp and release parts or fixtures, usually with the help of pneumatic or hydraulic. Three levels of automation need to be considered in workholding.
fully automatic. All loading/unloading of parts and/or fixtures is done automatically, including clamping of the system.
Some manual/automatic. A mixture of manual loading and automatic clamping.
Fully manual. All settings and clamping are done manually.
6. Options And Accessories
If you are working on a very specific job or have unique requirements, you may have to look beyond the core fixture system for options and add ons. In some cases, this can completely determine your choice.
In another case, heavy or complex parts are often difficult to handle. The guide pin and locking options help ensure that the part is secured in a controlled and accurate manner, preventing mis installation and damage. This greatly reduces the risk of damage to the workpiece fixture or the material itself.