What is CNC Fixture

What is CNC Fixture

The function of fixture on the lapsing bed

The fixture is in the process of machine tool machinery manufacturing, used to fix processing products, so that it is fixed in the correct position, to accept processing or detection of machine tool additional device, referred to as fixture. In our actual production, the role of the fixture is to position the workpiece in order to make the workpiece get the correct position relative to the machine tool and the tool and to clamp the workpiece reliably. When processing industrial parts on machine tools, the fixture must be fixed to be processed workpiece. The workpiece is installed, is in the machine tool to determine the workpiece relative to the correct position of the tool. This process is called positioning. The workpiece clamping is to exert force on the workpiece so that the workpiece has been fixed in the specified position and will be reliable. This process is called clamping. The whole process, from positioning to clamping, is called clamping. The main function of iron bed fixture is to complete the workpiece clamping and fixing work. The workpiece clamping condition will directly affect the machining accuracy of the workpiece.

Modular fixture Modular fixture

The modular fixture is composed of a set of structures that have been standardized. The size of the machining center has been normalized. General components and composite components can, according to the workpiece machining needs of all kinds of functions of the fixture. A combined clamp has a slot, a modular fixture, and a modular hole fixture. A machine tool is a series hole modular fixture; A slot is a modular fixture and its assembly process. The basic characteristics of a modular fixture are to satisfy three conversions: standardization, seriation, and generalization. Combination of resistance, adjustable, flexible, emergency and economical efficiency, long service life, and can meet the requirements for product cycle is short, low cost in the process of; Is suitable for machining center applications. It has the following advantages:

(1) save the fixture design and manufacturing working hours; 

(2) to shorten the production preparation cycle; 

(3) save steel and reduce cost; 

(4) improve the coefficient of enterprise process equipment.

However, due to the modular fixture being made up of all kinds of universal standard components, reciprocal links between each element is more, and special fixture precision and rigidity are dwarfed, especially element link joint stiffness, which had a greater influence on the machining center for machining accuracy, usually adopts the modular fixture when the dimensional processing accuracy can reach IT8 ~ IT9 level, this makes the modular fixture in the range of application. First large investment, in addition, the use of modular fixtures (of course, taking the lease way will save investment), the overall look bulky, machine tool and chip removal of inconvenience. For a medium and small batch, sheet (such as new product trial production, etc.) or parts machining accuracy requirement is very strict, on the machining center processing, should choose as far as possible combination fixture and special fixture for the main products of the factory, the batch is bigger, and take turns to play processing, high accuracy requirement of key parts, on the machining center processing, selects the special fixture is very necessary. The special fixture is specially designed according to the structural characteristics of certain parts of the fixture, the features of reasonable structure, strong rigidity, stable and reliable clamping, convenient operation, improving the precision of installation and the clamping speed, etc. Choose the fixture and machining center after a number of workpiece machining sizes are stable. The compatibility is better and also can greatly improve productivity. However, the inherent only special fixture for the machining of the parts by special narrowness, is constantly updated variant and varieties of products does not match the situation, especially the special fixture design and the manufacturing cycle is long, cost of labor is higher, simple processing parts, apparently, not economic.

The key points of design

In order to improve the stability of the iron clamp installed on the machine and reduce the intermittent cutting that may cause loosening caused by vibration, the clamp concrete not only has enough firmness and strength, but the height and width ratio should also be appropriate, generally have H/B < 1 ~ 1.20, in order to reduce the jig center of gravity, make the machining workpiece near the surface of the work surface. Also, reasonably adjust the stiffener and ear. If jig, wide width overall, can set in the same side of the clamp two equidistant between iron bench t-slot ear seat: the heavy iron clamp, clamp concrete should also set up the hole for hoist or rings on both ends for handling such as P. In addition to machine aspects that should pay attention the overall design also needs to pay attention to the points:

1. the design of directional keys. Directional keys are fixture positioning keys installed in a fixture on the underside of the longitudinal slot, generally for two, on the same straight line. The farther the distance, the guidance accuracy is higher. With the screw fastening on the clamp concrete, directional keys by shaped groove cooperate with iron bed table fixture on the machine to confirm the correct position: what else can bear part of the cutting torque, at the same time can be mitigated Clamping bolt load, the jig itself is more stability, so the plane clamp and some special drill front bed is also often used. The kinds of directional keys are divided into rectangular and round two. Directional accuracy of heavy fixture unfavorable use the directional keys, but on the clip to the specific processing out a long, thin face, as is the base to find proper calibration fixture installation, location.

2. Design of knife setting device. The knife device is composed of the knife block and feeler. Its effect is used to determine the relative position of the fixtures and tools. The knife device structure depends on the shape of the machined surface. Common pin and screw fastening on the knife block on the clamp concrete, so the location of the design is easy to use feeler of the cutter and does not interfere with the workpiece loading and unloading. On the knife, the cutting tool needs to add a feeler gauge between the knife block in order to avoid direct contact with the knife block tool and damage to the blade or causing premature wear and tear on the knife block 4. Feeler types are divided into flat feelers and cylindrical feelers, two kinds, the thickness and diameter of about 4 ~ 6 mm, and h6 manufacturing tolerances. For knife block and feeler have been standardized. When used in the processing, the fixture on the assembly drawing should indicate the feeler size on the knife block work between the positioning device and the surface location. For the knife, the device should be installed easily on one end of the knife and cut into the workpiece.

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