What should be paid attention to when servo water jet cutting equipment processes the die cushion?

Key points for attention in machining the die cushion with servo water jet cutting equipment

Servo water jet cutting die elastic cushion (rubber/foam elastic material), the core should take into account the cutting edge accuracy, no burr/delamination, no damage to the elasticity of the elastic cushion, and at the same time adapt to the high-precision speed control and pressure control characteristics of servo water jet to avoid the problems such as displacement, slag sticking and incision collapse that are easy to occur in cutting elastic materials. The control should be carried out from five dimensions: preliminary preparation, equipment parameter debugging, cutting technology, auxiliary material adaptation and post-treatment.

First, preparation before processing: control the base material and equipment foundation.

Fixing the base material of the spring pad: the spring pad of the knife die is mostly made of elastic soft materials such as EVA, foam, rubber, etc. Before cutting, it needs to be fixed by vacuum adsorption platform and high-temperature double-sided adhesive tape (to avoid the material moving when the vacuum adsorption force is insufficient). When fixing, ensure that the base material is flat and wrinkle-free, and the edge is aligned with the positioning line of the platform to prevent cutting deviation; It is strictly forbidden to press only with heavy objects, which may lead to slippage of the substrate due to cutting vibration.

Inspection of equipment and consumables: check the pressure stability of the high-pressure pump of the servo water jet (no pressure fluctuation) and the positioning accuracy of the servo motor (zero return error ≤0.01mm), and ensure that the sand pipe (usually 0.8~1.2mm, suitable for thin material cutting with spring pad) is free from blockage and eccentric wear, and the deviation of the coaxiality between the sand pipe and the gem nozzle is ≤ 0.02 mm; Garnet sand with 80~120 meshes is selected (the sand grains are uniform and free from caking), and the sand material is dry and free from moisture, so as to avoid pipe plugging or excessive sand marks on the incision.

Drawing and positioning calibration: the CAD drawing of the die spring pad is imported into the water jet control system, and the actual cutting origin and the drawing origin are calibrated (three-axis positioning calibration is required for the servo water jet). When aligning the cutter, the cutter is lightly touched (to avoid the initial damage caused by the impact of high-pressure water on the substrate). Before batch processing, try to cut 1~2 pieces, and check the matching degree between the cut size and the die (the size of the spring pad should be 0.05~0.1mm smaller than the die slot to fit the assembly gap).

Second, debugging the core parameters: adapting the servo and water jet parameters of elastic materials.

Servo speed control, high-pressure water pressure and sand flow rate of servo water jet are the key points, so it is necessary to abandon the high parameters of metal cutting and adopt the principle of low impulse, high precision and slow feed, and refer to different spring pad material parameters (basic values can be fine-tuned according to thickness):

form

Material cutting thickness of spring pad (mm) High pressure water pressure (MPa) Servo cutting speed (mm/min) Sand material flow (g/min) Feed mode

EVA foam 1 ~ 5 180 ~ 220 800 ~ 1500 150 ~ 200 continuous feed

Rubber spring pad 1 ~ 5 200 ~ 250 600 ~ 1200 180 ~ 220 continuous feed.

High density foam 5 ~ 10 220 ~ 280 500 ~ 1000 200 ~ 250 segmented feed

Key debugging points:

The water pressure should not be too high (> ＞300MPa is easy to break the elastic material incision, leading to edge collapse and delamination), and if it is too low, the cutting will not be complete, and burrs and sticking edges will appear;

The servo speed should be uniform (the servo water jet turns on the constant speed mode) to avoid sudden acceleration/deceleration, and to prevent the elastic material from being partially stretched due to inertia, resulting in notch deformation;

The flow rate of sand should match the speed. When the speed is slow, the amount of sand should be reduced appropriately to avoid the accumulation of sand particles at the incision, which will cause the sand mark to be too deep and affect the flatness of the spring pad.

Third, cutting process control: avoiding the unique problems of elastic materials

Incision process design: most of the spring pads of the die are shaped like slots, rings and strips. When cutting, direct cutting of sharp corners is avoided (elastic materials are prone to stress concentration at sharp corners, leading to edge collapse), so it is necessary to change the sharp corners into small rounded corners of R0.2~R0.5mm (which will not affect the assembly of the die); When cutting the closed pattern, reserve a 0.5~1mm tool joint (to prevent the spring pad from falling off the platform due to high-pressure water impact after cutting, and then manually break it off without burr), and uniformly handle the tool joint after batch processing.

Tool path planning: Turn on the optimal path planning function of servo water jet, and follow the cutting sequence from inside to outside and from fine to coarse (cut small slots and special holes first, then cut the outer contour), so as to avoid the looseness and dislocation of the base material of spring pad caused by internal cutting after cutting the outer contour first; The same batch of spring pads adopt array cutting, which reduces the idle travel of equipment, improves efficiency and ensures the consistency of cutting parameters of each piece.

Angle of high-pressure water jet: keep the sand tube perpendicular to the substrate at 90 for cutting (the servo water jet calibrates the verticality of Z axis with a deviation of ≤ 0.01), and it is forbidden to cut obliquely, otherwise, it will lead to the notch inclination of the spring pad and fail to fit with the cutter die; When cutting thick materials (> 8 mm), the micro Z-axis floating mode can be turned on to compensate the slight deformation of elastic materials and ensure the vertical incision.

Layered cutting adaptation: If the elastic cushion is made of multi-layer composite materials (such as foam+rubber), it shall be cut in layers with low water pressure and slow speed to avoid interlayer separation caused by high-pressure water penetration. After cutting, the adhesion between layers shall be checked. If there is no degumming and delamination, it is qualified.

Fourth, auxiliary materials and equipment matching: improve cutting accuracy and efficiency.

Adaptation of platform and protection: When cutting elastic materials, the water jet platform needs to be paved with PVC pad/absorbent sponge to prevent high-pressure water from directly impacting the platform to cause pits, and at the same time absorb the sewage generated by cutting to avoid edge softening and deformation caused by sewage soaking the elastic pad; The platform shall be cleaned regularly, and there shall be no accumulation of sand and sundries, so as to ensure that the base material is flat and fit.

Cooling and sewage treatment: open the low-pressure cooling water channel of the equipment (to avoid excessive high-pressure water), and pump the sewage in time when cutting (to open the water absorption function of the platform) to prevent the elastic pad from contacting the sewage for a long time, which will lead to the decrease of elasticity and sticky material; When cutting rubber elastic cushion, a small amount of special release agent can be added to water to reduce rubber debris sticking to sand pipe and incision.

Replacement of sand tube and nozzle: Fine-diameter sand tube (0.8~1.2mm) is preferred for processing the spring pad of the cutter die, which is suitable for the fine incision requirements of the spring pad. When the sand tube is used for more than 8~10 hours or appears eccentric wear or blockage, it will be replaced in time, otherwise the incision will be widened and the sand mark will be overweight; Check the matching clearance between gem nozzle and sand pipe regularly. If the clearance is too large, it will easily lead to divergence of high-pressure water jet and decrease the cutting accuracy.

5. Post-processing: ensure the adaptability of the finished product of the spring pad.

Immediate cleaning and drying: after the cutting is completed, immediately use a high-pressure air gun (low-pressure mode, 0.2~0.4MPa) to blow off the sand particles and debris at the incision, so as to prevent the sand particles from being embedded in the gap of elastic material (which will affect the subsequent knife die assembly); Then place the spring pad in a ventilated and dry place to dry naturally (baking at high temperature is strictly prohibited, which will lead to the aging and loss of elasticity of the spring pad), and the drying time shall be more than or equal to 30 minutes, and subsequent testing shall be carried out after the surface is free of moisture.

Inspection and finishing of finished products: check the dimensional accuracy (tolerance ≤±0.05mm) of the elastic pad, the smoothness of the incision, no burr, edge collapse and too deep sand mark, and touch the edge of the incision with your hands without sticking your hands or sticking slag; If there is slight burr, use * * fine sandpaper (400~600 mesh) * * to lightly grind it, and it is forbidden to trim it with a sharp tool to prevent scratching the surface of the spring pad or causing dimensional deviation.

Specification for batch storage: The finished spring pads are stored according to specifications, stacked with flat pallets (stacking height ≤50cm to avoid deformation of spring pads caused by heavy pressure), and the storage environment is kept at normal temperature (20~25℃) and dry (humidity ≤60%), away from oil, high temperature and sharp objects to prevent the spring pads from aging, deformation and damage.

VI. Daily Maintenance and Safe Operation of Equipment

Equipment maintenance: after cutting, clean up the residual sand particles in the sand pipe and nozzle in time, and flush the high-pressure pipeline with clean water to prevent sand particles from caking and blocking the pipe; Regularly calibrate the three-axis accuracy and water pressure stability of the servo water jet, and check the sealing performance of the vacuum adsorption platform to ensure the subsequent processing accuracy.

Safe operation: wear goggles and non-slip gloves during operation to prevent high-pressure water jet splashing or sand particles from hurting people; When the equipment is running, it is forbidden to touch the cutting area or adjust the substrate by hand to prevent the hand from being hit by high-pressure water or scratched by the sand pipe; When the high-pressure pump is working, avoid frequent start and stop to prevent equipment pressure fluctuation.