What are the clamping methods of CNC milling machine fixtures?

Installation of workpiece

The CNC milling machine fixture is used to clamp the workpiece (and guide the tool). Its function is to position the workpiece to obtain the correct position relative to the machine tool and the tool and clamp the workpiece reliably.

The contents of workpiece clamping include:

·Positioning: Make the workpiece in the correct position relative to the machine tool and tool.

·Clamping: After the workpiece is positioned, the workpiece is fastened so that the position of the workpiece does not change during processing.

The relationship between positioning and clamping: there are two processes in the installation of the workpiece, first positioning and then clamping,

 Clamping method:

1. Use the correct method to clamp:

1) Method:

a) Put the workpiece directly on the machine table or in the machine tool accessories such as four-jaw chuck, machine vice, etc. According to one or several surfaces of the workpiece, use a scribe or an indicator to align the exact position of the workpiece before proceeding. Clamp;

b) First, carry out the scribing process of the processing surface position according to the processing requirements, and then align according to the scribed line marks to realize the clamping.

2) Features:

a) This kind of clamping method is labor-intensive, low in production efficiency, and requires workers to have a high technical level;

b) The positioning accuracy is low because the scribing process is often required to be added, so the production cost is increased;

c) It only needs to use machine tool accessories and tools with good versatility, so it can be suitable for processing various surfaces of various parts, especially suitable for single-piece and small-batch production.

2. Install with clamps:

1) The workpiece is mounted on the fixture. No alignment is required and can directly obtain the clamping method of the accurate processing position.

2) Features: It avoids wasted person-hours due to scribing and positioning, avoids the expansion of the dispersion range of machining errors of the processed workpiece, and is convenient for clamping.

1. The steps of clamping the workpiece by the alignment method:

1) Scribe first to mark the position of the slot;

2) Put the workpiece on the table of the vertical CNC milling machine, and align it according to the drawn line marks. After the alignment is completed, clamp the workpiece with a pressure plate or a vise.

3) Adjust the position of the milling cutter relative to the workpiece according to the position of the groove line marks, and then start processing after the adjustment.

4) In the process of processing, it is necessary to cut a particular stroke, measure the size, and then adjust the relative position of the milling cutter according to the measurement results until the requirements are met.

5) Repeat the above steps for each workpiece processed.

Therefore, this clamping method is not only labor-intensive and time-consuming but also has an extensive dispersion range of processing errors for processing a batch of workpieces.

2. Use clamps for clamping

The workpiece can be placed directly into the jig without scribing using the jig clamping method. The A-side of the workpiece is supported on the two support plates 2; the B side is supported on the two toothed top support nails 3; The pressing plate 8 clamps the workpiece to complete the clamping process of the workpiece. When the next workpiece is processed, the fixture's position on the machine tool does not change, and the workpiece can be loaded and unloaded only by loosening the nut 9.

(3) Classification of fixtures

It can be classified by application range, machine tool used, and clamping power source.

a) According to the different processes, the fixtures can be divided into machine tool fixtures, inspection fixtures, assembly fixtures, welding fixtures, etc.;

b) According to the different types of machine tools, machine tool fixtures can be divided into lathe fixtures, milling machine fixtures, drilling machine fixtures, etc.;

c) According to the different clamping power sources used, it can be divided into manual clamps, pneumatic clamps, etc.;

d) According to the scope of use, it is divided into general fixtures, fixtures, combined fixtures, available adjustable fixtures, and group fixtures.

The definitions and characteristics of various fixtures are shown in the table below.

Universal fixture Strong versatility, widely used in single-piece small batch production

The fixture is specially designed for a particular process, with a compact structure, convenient operation, high production efficiency, and easy guarantee of machining accuracy. It is suitable for batch and mass production of shaped products.

Combination Fixture A fixture assembled from a set of pre-manufactured standard components and assemblies.

Universal adjustable fixtures do not correspond to a specific processing object and have a wide range of applications. By adequately adjusting or replacing individual components on the fixture, one can use it to process various workpieces with similar shapes, sizes, and processing techniques.

The group fixture is specially designed for the group processing of a group of parts, with apparent processing objects and strong pertinence. It can be adapted to various processes and processing shapes and sizes through adjustment.

e) Traveling fixture: The traveling fixture is a fixture used on automatic or semi-automatic production lines. Although it is only suitable for a certain kind of workpiece, after the blank is mounted on the traveling fixture, it can use in various positions from the beginning of the production line to the end of the production line. Processing of different processes. According to this, the structure of the traveling jig also has the versatility to be applied to various processes.

(4) The composition and function of the fixture

Composition: positioning element, clamping device, coupling element, tool setting or guiding element, other devices, clamping body.

Fixture composition

1) Positioning element: used to determine the position of the workpiece in the fixture.

2) Clamping device: used to clamp the workpiece.

3) Tool setting, guide element: determine the position of the tool relative to the fixture positioning element.

4) Other devices: such as indexing elements, etc.

5) Connecting elements and connecting surfaces: used to determine the fixture's position on the machine tool spindle or table.

6) Clamp body: Connect various components and devices on the clamp into an organic whole.

Functions: (1) Ensure that various processing accuracy requirements are met stably and reliably; (2) Shorten processing hours and improve labor productivity; (3) Reduce production costs; (4) Reduce labor intensity of workers; workers for processing; (6) can expand the scope of machine tool technology.

Guarantee of dimensional accuracy

1. The tool setting block 5 is installed on the fixture. The tool setting feeler gauge 10 is inserted between the working face of the tool setting block and the cutting edge of the end mill to determine the position of the milling cutter relative to the fixture. At this time, the position of the milling machine table is horizontally accordingly. Position and vertically lift the table to achieve the correct position of the tool relative to the tool setting block.

2. Since the two working surfaces of the cutter block and the respective support surfaces of the corresponding fixture positioning support plate 2 and the toothed top support pin 3 have been guaranteed and dimensioned, the dimensions a and b of the milling groove are finally guaranteed, as shown in the following figure.

3. As for the position and size of the length of the slot, adjust the position of the travel stop of the longitudinal feed of the milling machine table according to this so that the end position of the longitudinal feed of the vertical milling machine table ensures that the distance between the milling cutter and the support pin 4 is equal to c. Since the workpiece is in contact with the working surface of the supporting nail 4 with its end face, the length and position of the milled groove finally meet the size requirements.

Guarantee of Fixture Accuracy

When processing a batch of workpieces, as long as it is within the allowable tool size wear limit, there is no need to adjust the tool position, no trial cutting is required, and the processing size requirements are directly guaranteed. This is the working principle of using the adjustment method to achieve dimensional accuracy when clamping the workpiece with a fixture.