The process defects that are prone to occur in product dispensing include: unqualified glue point size, wire drawing, glue dipping, poor curing strength and easy to fall off, etc. To solve these problems, various technical process parameters should be studied as a whole to find a solution to the problem.
1. The size of the dispensing volume
According to work experience, the size of the glue point diameter should be half of the product spacing. This ensures that there is sufficient glue to bond the components and avoids excess glue. The amount of glue dispensing is determined by the length of time. In practice, the dispensing time should be selected according to the production situation (room temperature, viscosity of glue, etc.).
2. Dispensing pressure
The dispensing equipment provides a certain pressure to the needle tube (glue gun) to ensure the supply of glue. The pressure determines the amount of glue supplied and the speed of glue flow. If the pressure is too high, the glue will overflow and the amount of glue will be too much; if the pressure is too small, there will be discontinuous dispensing and leakage, which will lead to product defects. The pressure should be selected according to the properties of the glue and the temperature of the working environment. High ambient temperature will make the viscosity of the glue smaller and the fluidity better. At this time, the pressure value needs to be lowered, and vice versa.
3. Needle size
In practice, the inner diameter of the needle should be about 1/2 of the diameter of the dispensing point. During the dispensing process, the dispensing needle should be selected according to the size of the product. Different needles should be selected for products with huge differences in size, which can not only ensure the quality of glue points, but also improve production efficiency.
4. The distance between the needle and the working surface
Different dispensers use different needles, and some needles have a certain degree of stop. Before each work starts, the distance between the needle and the working surface should be calibrated, that is, the Z-axis height calibration.
5. The viscosity of the glue
The viscosity of glue directly affects the quality of dispensing. If the viscosity is high, the glue dots will become smaller, or even stringy; if the viscosity is low, the glue dots will become larger, which may bleed into the product. During the dispensing process, a reasonable pressure and dispensing speed should be selected for glues of different viscosities.
6. Glue temperature
Generally, epoxy resin glue should be stored in a refrigerator at 0-5°C, and taken out half an hour before use, so that the temperature of the glue is consistent with the working environment. The use temperature of the glue should be 23°C-25°C; the ambient temperature has a great influence on the viscosity of the glue, the viscosity increases when the temperature decreases, the flow rate of the glue decreases accordingly, and the phenomenon of stringing is more likely to occur. When other conditions are the same, a difference of 5°C in the ambient temperature will cause a 50% change in the size of the glue output, so the ambient temperature should be controlled. At the same time, the temperature of the environment should also be guaranteed. If the temperature is too high, the glue point will dry out and affect the adhesion.
7. Curing temperature curve
For the curing of glue, the general manufacturer has given the temperature curve. In practice, a higher temperature should be used for curing as much as possible, so that the glue has sufficient strength after curing.
8. Bubbles
The glue must not have air bubbles. A small air bubble will cause many products to have no glue; every time the rubber hose is replaced midway, the air at the connection should be emptied to prevent empty punching.
9. Fluids that require special settings
Instant glue: Use safety piston and Teflon-lined metal needle for water-based instant glue, use tapered needle for thick instant glue, and use PP needle for flexibility;
UV glue: use amber syringes, white pistons and oblique needles (can block ultraviolet rays). If you use other types of needles, please order needles that can block ultraviolet rays;
Light-curing glue: use a black opaque syringe to avoid light sensitivity;
Anaerobic adhesive: use 10CC syringe and white PE universal piston;
Sealants and pasty fluids: If the white piston rebounds seriously, please switch to a safety type with a slanted needle.
For the adjustment of various parameters, it should be adjusted from point to surface. The change of any parameter will affect other aspects. At the same time, the occurrence of defects may be caused by multiple aspects. Possible factors should be checked one by one.