For ordinary wire cutting machine, the wire speed is generally fixed. The adjustment of the feed rate is mainly the adjustment of the gap between the electrode wire and the workpiece. Feeding speed and erosion speed should be well coordinated during cutting and do not lag behind or track too tightly. The feed rate is adjusted mainly by adjusting the variable feed rate. Under a specific machining condition, there is only one corresponding optimal feed rate. At this time, the feeding speed of the molybdenum wire is exactly equal to the actual maximum erasing rate of the workpiece. . Under-tracking often results in open-circuit machining, virtually reducing productivity, and current instability, which can easily lead to broken wires. Over-tight tracking can easily lead to short-circuits and can also reduce the rate of material removal. Generally adjust the frequency conversion feed so that the processing current is about 0.85 times the short-circuit current (the current meter pointer is slightly shaken). It can guarantee the best working condition, that is, the frequency conversion feed speed is the most reasonable, the processing is most stable, and the cutting speed is the highest. The following table shows how to adjust the frequency conversion according to the feed state.
Table Adjust the frequency conversion method according to the feed state
Real-frequency status
Feed state
Working surface condition
Cutting speed
Electrode wire
Frequency adjustment
Tracking
Slow and steady
Brown
low
Slightly coke, fast aging
Should slow down the feed rate
Tracking
Suddenly
Uneven
Not clean
Easy to get deep marks
Faster
Easy to burn, silk
White spot scars
Should speed up the feed rate
Poor tracking
Slow and steady
Slightly brown, striped
low
Focus color
Should slightly increase the feed rate
Best tracking
Very stable
White, smooth
fast
White, slow aging
No need to adjust
Second, the application of electric spark wire cutting process equipment The form of workpiece clamping has a direct influence on the machining accuracy. It is common to use a platen screw to fix the workpiece on a universal fixture. In order to adapt to the needs of various shapes of workpiece processing, magnetic fixtures or special fixtures can also be used.1. The name, purpose and use of common fixtures
(1) Platen clamp It is mainly used for fixing flat-shaped workpieces, and is used in pairs for slightly larger workpieces. If there is a positioning reference surface on the fixture, the fixture positioning reference surface should be calibrated in parallel with the corresponding guide rail of the worktable beforehand with a stylus or dial indicator. This is convenient when processing a batch of workpieces because the cutting of the cutting cavity is easy. It is generally based on one side of the template. When the clamps are used in pairs, the heights of the two reference surfaces must be equal. Otherwise, the cut-out cavity is not perpendicular to the end surface of the workpiece, resulting in waste products. A V-shaped reference can be machined on the fixture to hold the shaft-like workpiece.
(2)Magnetic clamps use magnetic table or magnetic table holder to clamp the workpiece. It is mainly used to clamp steel workpieces. Because it absorbs the workpiece by magnetic force, it does not need the pressure plate and screws. The operation is quick and convenient. Press and change, as shown in Figure 1.
Figure 1 Magnetic fixture
2. Workpiece clamping general requirements (1) The reference surface of the workpiece should be clean without burrs. After the heat-treated workpiece, heat treatment residues and oxide scales should be removed in the threading holes and the stepped holes. (2) The fixture should have the necessary accuracy, be firmly fixed on the workbench, and the force should be even when tightening the screw. (3) The position of the workpiece clamp should be conducive to align the workpiece and be compatible with the stroke of the machine tool. The workpiece must not collide with the wire frame when the table is moved. (4) The clamping force on the workpiece must be uniform and the workpiece must not be deformed or tilted. (5) When a large number of parts are processed, it is best to use a special fixture to increase the production efficiency. (6) Small, precise, thin-walled workpieces should be fixed on an auxiliary fixture that is not easily deformed.3. Bracing method
There are mainly cantilever support methods, two-end support methods, bridge support methods, plate support methods, and multiple support methods. 4. Workpiece adjustment When the workpiece is clamped, adjustments must be made in conjunction with the alignment so that the positioning reference plane of the workpiece is kept parallel to the feed direction of the table or table of the machine tool to ensure the relative position accuracy between the cut surface and the reference plane. The commonly used methods of correction are:(1) Dial indicator method As shown in Fig. 2, the dial indicator is fixed on the silk frame with a magnetic watch stand, and the work table is moved back and forth. The position of the work piece is adjusted according to the indicator value on the dial indicator until the indicator of the dial indicator is biased. The pendulum range achieves the required accuracy.
Figure 2 Dial indicator alignment Figure 3 Line alignment
(2) Marking correction method As shown in Fig. 3, the workbench is reciprocally moved by using a reference line drawn on a normal work piece by a stroke fixed on the wire frame, and the deviation between the stylus and the reference line is visually observed to adjust the position of the work piece. This method is suitable for workpiece processing with low precision. 5. Wire position adjustment Before the wire cutting process, the electrode wire should be adjusted to the starting coordinate position of the cutting. The adjustment methods are as follows:(1) Visual inspection method As shown in Fig. 4, the cross reference line drawn at the threading hole is used to observe the relative position of the electrode wire and the reference line along the scribe direction, and the worktable is moved according to the deviation between the two. When coincident with the reference lines of the longitudinal and transverse directions respectively, the readings on the dials of the vertical and horizontal directions of the worktable determine the center position of the wire electrode.
Figure 4: Adjusting wire position by visual inspection
(2) Spark method As shown in Fig. 5, turn on the high frequency and the transport tube (Note: The voltage amplitude, pulse width and peak current must be minimized, and do not open the coolant). Move the table to bring the reference surface of the workpiece close to Electrode wire, in the moment of spark, note the relative coordinates of the table, and then calculate the center coordinates of the electrode wire according to the discharge gap. Although this method is simple and easy, it has poor positioning accuracy.
Figure 5 spark electrode wire position adjustment
1 - Workpiece 2 - Electrode Wire 3 - Spark
(3) Automatic alignment The general wire-cutting machine tools have the functions of automatic edge finding and automatic center finding. The method of operation varies from machine to machine.