Factors affecting placement rate of SMT equipment
SMT placement equipment is mainly purchased with consideration of placement accuracy and placement speed In actual use, in order to effectively improve product quality, reduce production costs and improve production efficiency, how to improve and maintain the placement rate of SMT equipment is the main problem faced by users
1. Meaning of placement rate
The so-called placement rate refers to the ratio between the actual number of equipment placed and the number of suction cups in a certain period of time, that is, placement rate=* 100% of the number of suction cups. The total number of discarded parts refers to the number of suction cup errors, identification errors, standing times, missing counts, etc., Identification errors fall into two categories: equipment specification and size errors and poor optical identification of equipment. Whether it is a small machine, a medium-sized machine, a large machine, or a medium speed machine or a high-speed machine, the placement machine is mainly composed of equipment storage and transportation device, XY workbench, placement head and control system. The chip mounter is the core and key component of the chip mounter. The placement head is generally divided into fixed head and rotary head. The fixed head is generally arranged in multiple heads,
From 2 to 8, it can be selected simultaneously or separately. The rotating head is divided into horizontal plane rotation and vertical plane rotation
A. The unit draws in the suction nozzle to switch the suction height
B. Rotation (± 90 ）
C. Optical identification of equipment
D. Equipment attitude detection: 2 rotation (± 90 ）
E. Installation unit/nozzle height switch
F. 3. Rotating (Î 180 – Î) nozzle origin detection defect removal
G. Nozzle conversion
H. Nozzle number detection is based on the data picked up from the mounter
In the whole placement process, only from the perspective of equipment, by correctly setting the nozzle pickup height and the position of the nozzle center relative to the feeder, according to the production information collected by the equipment, the main factor affecting the placement rate of equipment is the pickup position, which accounts for more than 80% of the entire factor. The reason for this is: on the one hand, the device storage and transportation device on the feeder; on the other hand, about 60% of the film of the two feeders and about 40% of the film of the suction nozzle are caused by the pollution of the suction nozzle.
2. The influence of feeder mainly focuses on abnormal feeding.
The feeder has several drive modes, such as motor drive, mechanical drive, and cylinder drive Here, taking the mechanical drive as an example, the influence of the feeder on the drive is explained. The smt placement rate is:
1. The drive part is mechanically worn. The cam spindle drives the feed mechanism to quickly knock the impact arm of the feeder, and the ratchet drive component connected to it through the connecting rod advances the weaving by one pitch. At the same time, the plastic take-up tray is driven to remove the plastic cover on the weaving, and the suction nozzle drops to complete the suction action. However, because the feeder enters the feeder at a high speed, the pawl of the feeder is seriously worn after a long time of use, resulting in the pawl being unable to drive the plastic belt of the drum to peel normally, making the suction nozzle unable to complete the work of picking up parts. Before installing the braid, carefully check the feeder. The worn ratchet feeder shall be repaired immediately, and those that cannot be repaired shall be replaced in time.
2. The structural parts of the feeder are deformed due to long-term use or improper operation by the operator, and the moving mechanisms such as the cover plate of the press belt, thimble and spring are deformed and rusted, which may cause the device to be deflected, erected or unable to hold the device. This shall be checked regularly and problems shall be solved in time to avoid a large number of wasted parts. At the same time, the common feeder shall be correctly and firmly installed on the feeder platform, especially on the equipment without feeder height detection, otherwise the feeder or equipment may be damaged.
3. Generally speaking, it is easy to ignore the maintenance of the feeder due to poor lubrication, but regular cleaning, cleaning and lubrication are essential tasks.
Third, the influence of suction nozzle
The suction nozzle is another important factor affecting the placement rate, which may be caused by internal and external reasons.
1. The internal cause is insufficient vacuum negative pressure Before the suction nozzle picks up the parts, the mechanical valve on the placement head will automatically switch, and the air blowing will be converted into actual suction, which will produce a certain negative pressure When the parts are sucked in, the negative pressure sensor and the machine are normal when the detection value is within a certain range, otherwise the suction is poor Generally, the negative pressure from the picking position to the nozzle installation position should be at least 400mmHg or more When installing large components, the negative pressure should be greater than 70mmHg Therefore, the screening program in the vacuum pump should be cleaned regularly to ensure sufficient negative pressure; At the same time, check the working state of the negative pressure detection sensor regularly On the other hand, due to the pollution and blockage of the surrounding environment or impure air source, the screening program on the head and on the suction nozzle turn black Therefore, the screening program should be replaced regularly Generally, the screening program on the nozzle should be replaced at least once every half a month, and the screening program smt head should be replaced at least once every half a year to ensure smooth airflow
The above is the explanation given by the editor of pcb circuit board company.
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