Keywords: circumferential uniform narrow slot clamp rapid positioning
Foreword: When the groove width of machined parts is less than or equal to 1mm, it is difficult to process with ordinary mechanical equipment. The smaller the cutting tool is, the more difficult it is to process, and even the processing is impossible; in this case, the electricity in special processing must be used. Spark wire cutting or other machining equipment processing can solve the processing of narrow groove parts. On the other hand, processing on narrow-groove, on-line, circular-cutting machine tools has traditionally been regarded as one of the more difficult processes. As a result, the idea of ​​developing auxiliary jigs has sprouted, and the technical problems of processing batch products on an on-line cutting machine have been solved through the use of good results. .
Not long ago, a company commissioned us to process a batch of ring products. In the production and processing of this part, beneficial trials have been made on narrow grooves with a groove width of only 0.2 mm and uniform circumferential distribution, and good results have been achieved. The basic dimensions of the part: φ48mm × 75mm, the material is 45 steel (as shown in Figure 1).
figure 1
First, the technical analysis of the ring
(1) High precision of shape accuracy
(2) The perpendicularity of the hole of φ48 with respect to the end face is 0.02;
(3) The two holes of φ16 and φ27 require a coaxiality of 0.025;
(4) The centrality of the axis of the 12 slots with respect to the central axis requires 0.02.
(5) higher requirements for positioning size
Six of the 12 slots have a round hole length of 50 mm and another six bars having a length of 35 mm. They are separated by a length and a short and uniformly distributed over the center circle, allowing the upper groove width to have a deviation of 0.02 and the lower deviation to be zero.
The processing requirements for the notch are: to ensure that the tolerance of width 0.2mm, length is 50mm and 35mm, the surface roughness is Ra3.2μm, and 12 grooves are required to be evenly distributed to the center circle, in order to ensure the accuracy requirements, this procedure is In terms of both the processing of the workpiece and the installation of the fixture, there are considerable difficulties. Therefore, it is necessary to carry out careful analysis and formulate the corresponding processing process.
The conventional machining process of the workpiece is: (1) Firstly, six uniformly-distributed lines are drawn on the workpiece, and then the workpiece is scribed with the naked eye. There is an error in finding the right line with the naked eye, which cannot guarantee the quality of the processing, and often produces waste products, causing great losses to the enterprise. The feature is that it is difficult to ensure the consistency of dimensional tolerances and form-position tolerances during processing, and the accuracy of the clamping positions, and the processing efficiency is too low. With this type of process, only one machine per class can cut only 2-3 pieces. (2) If the indexing head is used, the maximum length of the X-axis and Y-axis of the active DK7725e wire-cutting machine table is only 250mm. It is difficult to mount the clamps due to its large volume. At the same time, the entire machining process requires Operators have a high level of technology, careful concentration, and no errors in processing. The adjustment of the machine tool, the choice of electrical parameters, the choice of cutting fluid usage, and the high labor intensity and low production efficiency. Through the analysis of parts drawings, and considering high technical requirements and large processing volumes, in order to maintain a good cooperative relationship with enterprises and solve difficulties for enterprises, we tried to design a set of efficient, simple and practical fixtures with similar indexing heads to complete the Product processing tasks.
Second, fixture design principle
The design mainly considers the basic requirements of wire cutting and the dimensional accuracy requirements of the part: it can guarantee the processing requirements of the workpiece; it can increase the labor productivity; it is simple to manufacture and easy to maintain; the cost for fixture production is lower.
The principle of the fixture is relatively simple, it is the use of the flange on the same circumference of the six equally small blind holes and the vertical plate seat in the same diameter in a small round hole in the spring, the spring drag a steel ball, the use of spring The elastic force (the elastic force can be adjusted according to the elasticity), each time the flange is rotated, the steel ball just falls in the small hole, and the rotation is quickly positioned, and the indexing is rotated like the dividing head. The vertical plate seat of the fixture is tightly connected with the flange plate to ensure the rotation accuracy.
Third, the structure of the fixture
The fixture is as shown in the figure: It mainly consists of three components such as a riser seat, a flange plate and a three-jaw chuck. Its characteristic is that it can be easily fixed and loaded and unloaded to ensure fast positioning. It can rotate freely and accurately to ensure the uniformity of 12 lines. The size of the clamp just fits the size of our DK7725e WEDM machine table and it is very convenient to use. .
1. Chuck 2. Vertical plate base 3. Flange 4. Steel ball 5. Spring 6. Adjusting screw
7. Sturdy nut 8. One-way thrust ball bearing 9 copper sliding sleeve 10. Chuck bolt
Figure 2 Assembly drawing
Fourth, fixture production and assembly
The main features of the fixture are: using the protruding part of the steel ball for positioning to control the rapid indexing and positioning of the flange.
1, the main component requirements
1 Chuck: The K1180 three-jaw self-centering chuck (with both claw and reverse claws) can be used to hold workpieces with different rings or other shafts.
2 Upright base: It is made of A3 steel material. The part plays a supporting role. The two plates of the bottom plate and the upright plate are connected to each other through 90° by welding. The bottom surface and the other side are completed by milling and grinding. To reach 0.015-0.02, the surface roughness reaches Ra1.6 
m; fixture center height of 90mm has a φ35 hole, used to fix the copper sliding sleeve and its interference fit clearance to reach H7/P6, φ35 hole relative to the side panel perpendicularity requirement is 0.025, surface roughness reaches Ra1.6 
m, milling can be completed (see Figure 2-1)
Figure 2-1 riser seat
Figure 2-2 Flange
3 Flange: 45 steel is used for the material. The φ55 circle and φ30 positioning mandrel of this piece are turned and formed once. The coaxiality error must be strictly controlled within 0.025mm and the roundness error must be controlled. The flange front φ55 length 3mm step and the chuck with the tolerance of 0.01-0.02mm; rear end φ30 is a sliding part, must be local heat quenching and tempering, the surface hardness of HRC40-45, size to H7 requirements, surface roughness For Ra1.6 
m; in the rear of the flange with the central axis as a benchmark, there are six positioning holes with uniform R3 depth 1.5 drilled on the φ47 circle, and the threads of the nut and the mandrel are fixed to each other on the vertical plate seat, and the requirements are reached vertically. 0.015 (see Figure 2-2).
4 steel ball: Use φ6mm steel ball to play a positioning role.
5 Spring: Cylindrical helical compression spring is selected, spring wire diameter is 0.8mm, outer ring diameter is 6mm, and the end structure has YI type that is tightly and flattened to ensure that the supporting end face is perpendicular to the axis of the spring, so that the spring will not be skewed when pressed. .
6 Adjustment screw: Use M8×1 flat head screw to adjust the spring force.
7 Fastening nut: Use M16×1 hex nut for clamping action.
8 One-way thrust ball bearings: Type 8203 rolling bearing (8224GB301-64) is used for sliding action.
9 Sleeve: The material is made of brass, which acts as a slide. The hole of φ35 and φ30 requires the coaxiality of 0.02, which can be completed by turning; the clearance of φ30 and the flange mandrel must reach 0.01-0.02; Blue disk rotation is flexible.
10 Chuck bolts: Use M6 hexagon bolts for fastening.
Fixture assembly drawing
2, the assembly process
Complete machining of clamps on the milling machine → Assembly of three-jaw self-centering chucks and flanges → Fitting of upright seats and copper sliding sleeves → Positioning of seats and steel balls Flexible adjustment assembly → Mandrels for flanges Sliding sleeve assembly with upright seat plate → Flange mandrel and one-way thrust ball bearing clamping clearance adjustment.
For the accuracy of the spindle rotation, when assembling the inner ring of the sliding sleeve and the main shaft of the flange plate and assembling the outer ring of the sliding sleeve and the vertical plate seat hole, a method of directional assembly is often adopted. Directional assembly is a method of artificially controlling the radial runout error of each assembly so that the errors cancel each other instead of accumulating to improve assembly accuracy.
1, the fixture work process:
(1) Fixture installation and adjustment Fix the fixture to the middle position of the online cutting machine table. Use the dial gauge to calibrate the base plane of the stand and parallel to the X axis and Y axis of the machine tool. Use screws to fasten the fixture. Workbench. (2) Place the workpiece in a three-jaw chuck (using reverse jaws) to clamp the workpiece so that the end face of the workpiece contacts the side of the chuck. (3) Before processing, the first piece needs to be positioned using the automatic centering function on the machine so that after the molybdenum wire is at the center of the workpiece, it can be cut and processed according to the program. After the first part is machined, the coordinate values ​​of X-axis and Y-axis of the machine tool are locked, and it is no longer necessary to correct the machine to continue machining. (4) According to the processing technology of the ring, considering that the length and shape of the groove processed by the workpiece are inconsistent, there are two methods for the operation of the flange: First, the one-by-one processing method means that each line is cut, the flange plate According to the direction of the positioning holes need to be rotated one by one to gradually process. After this method cuts a line, it is necessary to change the processing program to continue processing. The second is that the skipping processing method refers to that when the first line is cut, the flange plate must be rotated one more positioning hole (ie, rotated twice) in order of orientation before it can be processed by the same program until the program is finished. When the second program is processed after the first program is completed, the same procedure can be used to continue processing the second program.
Flange rotation direction processing path (as shown in the figure): When using the gradual processing method path from A → B → C → D → E → F.
When using the skipping method path (dotted part of the path), such as processing the first program from A → C → E; processing the second program from F → B → D.
Machining path schematic
2, the fixture should pay attention to the process problems:
(1) Sliding fit clearance between the mandrel of the flange and the sliding sleeve The gap must be controlled between H7/h6, and the flange can rotate freely and freely. If the clearance between the mandrel and the sliding sleeve is too small, there will be difficulty in rotating the flange; if the clearance is too large, the radial runout error of the mandrel will be large, which will affect the precision requirements of workpiece machining. (2) The gap size of the steel ball positioning hole and the ball in the upright seat must be controlled within 0.05-0.1mm to ensure the flexibility of the steel ball and the spring. (3) The fixture is designed according to the rotary type positioning fixture and is positioned by elastic elements. Therefore, the center hole pitch and depth dimension of the six uniform holes on the flange plate must be controlled to be consistent, thereby reducing manufacturing positioning errors. Otherwise, the contact gap is too large, affecting the positioning accuracy.
Fifth, the use of effects
1. The manufacturing process of the fixture is simple and uncomplicated, the cost is low, and the potential of the machine tool can be fully utilized to achieve the purpose of multiple uses of one machine.
2. Tried and machined the workpiece to achieve a H8 grade dimension after machining in a narrow groove, with a surface roughness value of Ra=1.2 to 3.2. 
m, the straightness of the groove width is also good. After inspection, the dimensions of the drawing are fully met. Thousands of pieces are continuously processed without waste, which improves the economic efficiency of the enterprise.
3. After the use of this fixture, the processing efficiency is rapidly increased. At present, there are about 15 machining tools in one class, and the efficiency is increased by nearly four times, which reduces the labor intensity of the operator. This fixture has been used for more than one year and its performance is very stable.
Sixth, concluding remarks
The production of fixtures is a comprehensive science. It requires us to clearly design the task, analyze the parts drawing, master the machining process specification of the workpiece, understand the role, shape, structural characteristics, materials and technical requirements of the workpiece; the surface, requirements, margin, positioning reference, clamping Surface and other aspects of the information. Practice has proved that only by constantly summing up experience, collecting design materials, mastering design, and rationally designing the fixture's structural scheme, properly arranging manufacturing and assembly processes. Even if the conditions are limited, we can produce a clip with a reasonable structure, reliable positioning, and economical and practical use. The design and application of the fixture greatly facilitates the processing of round or shaft parts. The structure is simple and the operation is convenient. It can reduce costs, improve work efficiency, ensure quality, and has good promotion and application value.
references:
1. New Principles of Machine Tool Fixture Design Mechanical Industry Press 1997
2. "Mechanical Worker-Cold Working" magazine Institute of Mechanical Industry Information, 2003
CNC Bending Shearing Machine,CNC Machine,Machine Machinery,CNC Cutting Bending Machine
ST Machinery Co.,Ltd , https://www.stpipemill.com