What matters should be paid attention to when water jet cutting machine processes products such as die cushion?

When using water jet cutting machine to process the die cushion (usually elastic materials such as rubber and polyurethane), we should focus on three core dimensions: material property adaptation, machining accuracy control and safe operation of equipment, and at the same time give consideration to efficiency and finished product quality. The following are specific precautions, which are explained according to the operation process and key elements:

First, before processing: materials and equipment preparation stage

There are great differences in elasticity, density and wear resistance of the die spring pad (for example, the hardness of polyurethane spring pad is mostly 50-90 Shore A), so it is necessary to adjust the parameters before processing to avoid material deformation, delamination or incomplete cutting.

1. Confirmation and pretreatment of material characteristics

Clear material parameters: confirm the material (natural rubber/polyurethane/nitrile rubber), thickness (usually 1-5mm) and hardness of the spring pad, so as to avoid "sticking to the knife" (the material bounces back and fits the notch after cutting) or edge collapse of brittle materials (such as hard polyurethane) due to excessive toughness of the material.

Material fixing method:

Elastic material is easy to displace under the impact of high-pressure water jet, so it needs to be fixed by vacuum adsorption platform and elastic batten (to avoid crushing the surface with metal fixture), and the fixing force should be uniform-too tight will easily lead to tensile deformation of the material, and too loose will lead to deviation of cutting trajectory.

If the thickness of the spring pad is less than ＜2mm, it is recommended to pad a layer of high-density foam or acrylic board underneath (to assist adsorption and avoid direct impact of high-pressure water on the workbench).

2. Equipment and consumables adaptation

Pressure and flow adjustment of high-pressure pump:

Elastic materials do not need excessive pressure (to avoid excessive extrusion deformation of materials), and are usually set to 150-250MPa (300-400 MPa is commonly used in metal processing); The flow rate shall be matched with the nozzle diameter (usually 0.15-0.2mm nozzle) to ensure smooth and burr-free incision.

If machining holes and narrow seams (such as locating holes and avoidance grooves of the spring pad of the knife die), it is necessary to appropriately reduce the pressure (120-180MPa) to prevent high-pressure water from "penetrating" the edge of the material.

Abrasive selection (in case of sand-adding water knife):

When processing elastic materials, it is recommended to choose 80-120 mesh (fine-grained abrasive) as the abrasive (commonly used garnet sand) to avoid coarse notch and abrasive embedding on the surface of the material due to coarse particle size (such as 60 mesh); Abrasive flow rate is controlled at 150-200g/min, which is too high to cause material surface wear.

Calibration of nozzle and cutting head:

Check the perpendicularity of the nozzle (error ≤ 0.1). If the nozzle is inclined, the notch will be inclined (the tolerance in the thickness direction of the spring pad is out of tolerance). The height of the cutting head (the distance between the nozzle and the surface of the material) is set to 3-5 mm. If it is too close, it is easy to scratch the material, and if it is too far, the water jet will spread, which will widen the incision (reduce the accuracy).

Second, in processing: precision control and process optimization

The die spring pad requires high dimensional accuracy (for example, the tolerance of positioning hole is ±0.05mm, and the straightness of cut is ≤0.1mm/m), so it is necessary to avoid errors through fine-tuning parameters and real-time monitoring during processing.

1. Cutting path and speed optimization

Path planning principles:

Follow the principle of "first inside and then outside, first small and then big"-first process the positioning hole and special-shaped groove of the spring pad, and then cut the outer contour to avoid the internal processing deformation caused by the weakening of the external material fixing force;

For arcs and sharp corners (such as the avoidance angle of the die pad), it is necessary to reduce the cutting speed (the conventional linear speed is 50-80mm/min, and the arc/sharp corner is reduced to 20-40mm/min) to prevent the material from stretching due to inertia and "over-cutting" (the size of the sharp corner is too large).

Layered cutting (for thick materials):

If the thickness of the elastic cushion is greater than 3 mm, it is recommended to adopt layered cutting (the depth of each cutting is 1-1.5mm) to avoid the material delamination caused by excessive single cutting pressure (especially polyurethane elastic cushion, the interlayer adhesion is weak).

2. Real-time monitoring and exception handling

Observe the incision state:

The normal incision should be smooth without burr and "hanging edge" (edge bulge caused by material rebound), and should be adjusted in time if the following problems occur:

Rough cut: increase abrasive flow (50-100g/min) or reduce cutting speed;

Material rebound sticking: add a "tool withdrawal groove" (depth 0.5mm, width 1mm) at the end of the cutting path, or blow the incision with compressed air immediately after cutting;

Size deviation: check whether the vacuum adsorption leaks, re-fix the material and calibrate the position of the cutting head.

Avoid the problem of "flooding":

Elastic materials are easy to expand after absorbing water (for example, the water absorption rate of rubber is 0.5%-1%). When processing, it is necessary to open the drainage system of the workbench to discharge the sewage generated by cutting in time to avoid dimensional deviation caused by long-term soaking of the materials (it is recommended to air dry naturally for 1-2 hours before measuring the dimensions after processing).

Third, after processing: quality inspection and equipment maintenance

1. Finished product quality inspection

Detection of key dimensions: use calipers (accuracy 0.01mm) to detect the diameter and outline dimensions of positioning holes, and use micrometers to detect the thickness tolerance (within ±0.03mm);

Appearance and performance inspection: Observe whether there are abrasive indentations and scratches on the surface, and press the elastic pad by hand to confirm the elastic recovery (no permanent deformation) to avoid material aging caused by cutting overheating (the temperature of high-pressure water jet is usually ≤50℃, and if the temperature is too high, check the cooling system of high-pressure pump).

2. Equipment cleaning and maintenance

Nozzle and abrasive pipeline: after machining, disassemble the nozzle, blow off the residual abrasive inside with high-pressure air (to avoid the unstable cutting pressure caused by blockage), and clean the abrasive tank and pipeline regularly (every 50㎡ material is machined) to prevent the abrasive from caking;

Worktable and adsorption system: clean up the residual material debris on the surface of the workbench, check the tightness of the vacuum sucker (replace the aging sealing strip) to avoid air leakage during the next fixation;

Maintenance of high-pressure pump: regularly replace high-pressure oil (every 100 hours) and filter element (every 50 hours) according to equipment requirements to ensure stable pressure and prolong the life of pump body (the processing pressure of elastic material is low, but if the pressure fluctuation is greater than ＞10MPa, it will easily lead to the decrease of incision accuracy).

Fourth, the safety operation standard (the core can not be ignored)

The high-pressure water jet (> ＞100MPa) of the water jet cutting machine has strong penetrating power, so the safety regulations should be strictly observed during processing:

Personal protection: you must wear anti-impact glasses (to prevent abrasive splash) and non-slip gloves (to avoid scratching when handling the elastic pad), and it is forbidden to put your hand into the cutting area (even if the equipment is suspended, there may still be residual pressure in the high-pressure pipeline);

Inspection before starting the equipment: make sure that the pressure safety valve and emergency stop button of the high-pressure pump are normal, that there is enough abrasive in the abrasive tank (to avoid idling and damaging the pump body), and that the workbench fence is closed;

Emergency stop treatment: If there is any abnormality such as material displacement and nozzle rupture, immediately press the emergency stop button and deal with it after pressure relief (it is not allowed to disassemble the high-pressure pipeline directly, but wait for the pressure to drop to 0MPa).

summary

The core of machining the spring pad of knife die is "adapting to the characteristics of elastic material"-controlling deformation by reducing pressure, optimizing path and strengthening fixation, while giving consideration to accuracy and safety. The parameters of elastic pads made of different materials need to be flexibly adjusted (for example, polyurethane elastic pads focus on anti-delamination, and rubber elastic pads focus on anti-rebound), and the rationality of the parameters is verified by trial cutting before processing (processing 1-2 samples first) to ensure the consistency and stability of mass production.