September 2017 Archives

General description

While production methods are diversifying from mass production to high-mix low-volume production and one-piece flow production, the cleaning processes in the precision machining lines also need to be adjusted accordingly.This volume describes the precautions for switching the cleaning method from the existing lot-by-lot process to that designed for high-mix low-volume production or one-piece flow production.

Explanation

To automate the cleaning process for high-mix low-volume production or one-piece flow production, the following specifications are required for the equipment:

Requirements-1. The equipment must be designed in the specifications (appropriate size, capacity, etc.) eliminating inefficiency.

・For the mass-production batch manufacturing system using large machine tools, the batch processing by a large washing machine was also adopted for the cleaning process (Fig.1). For the high-mix low-volume production, the washing machine should be smaller and adjusted for smaller lots (Fig.2).
・For the one-piece flow production and the cellular manufacturing system, the goods are processed in synchronization with the previous process and the subsequent process (in the same pitch.) Therefore, such tasks must be performed in the optimum environment and the equipment should be designed in the specifications (appropriate size, capacity, etc.) eliminating inefficiency.In other words, small machine tools instead of the large-sized ones are used in these methods; the machining work itself will also be different.This means that the cleaning process should be adjusted accordingly, such as adopting a small washer, so that the machine operators can clean the products whenever they have done with the other tasks.

Requirements-2. Appropriate cleaning solution and conditions must be selected to work better with smaller lots.

・Since various types of solvents are included in the machining fluids, such as cutting fluid and grinding lubricant, insufficient cleaning conditions or drying conditions may result in dry stains or cause the products to corrode after reacting with the materials.The cleaning conditions designed for large washers will not work. When adopting a simplified cleaning method, it is necessary to select preliminary cleaning solution and cleaning conditions once again.

General description

To stabilize the cleaning quality using automation technologies, it is essential to select an appropriate cleaning basket and a proper structure for the cleaning fixtures. They should be designed exclusively for respective usage upon understanding the characteristics (e.g. shapes, strength, and materials) of the workpieces to be cleaned and satisfying the quality requirements.

Explanation

(1) Cleaning and quality problems

- The required cleaning quality has become higher than before due to the trend of making the parts and units more compact and integrated, in addition to complying with the upgraded label requirements.
- The quality problems related to cleaning include the following: (1) Degraded adhesion strength, (2) Reliability problems related to surface alteration/corrosion by attachment of foreign materials, (3) Aesthetic quality problems due to external defects.

(2) Cleaning basket structure for stable cleaning quality

- One of the important measures to stabilize the cleaning quality is to adopt an appropriate cleaning basket structure.
- The following five requirements must be met for the cleaning basket structure to be appropriate:

1. To prevent leaving the residual cleaning solution in the area where the cleaning basket contacts the workpiece, it is important to design the cleaning basket so that it contacts the workpiece at multiple points without touching the whole surface (Fig.1).
2. To prevent the quality deterioration of the workpiece during cleaning, be sure to avoid the important surface of the workpiece to be in contact with the basket.
3. Oscillation by ultrasound may cause the workpiece to chip if the workpiece is in contact with the cleaning basket and/or the cleaning fixtures. Therefore, the R-shape design is recommended for the corner area and the contact point of the cleaning basket and fixtures (Fig.2).
4. For ultrasonic cleaning, a mesh should be selected for improving the circulation and drainage of the cleaning solution on both the bottom and side faces of the cleaning basket, as well as for minimizing the degradation of cleaning energy distribution efficiency.
5. The cleaning basket and fixtures should be made of materials that will not be corroded by the cleaning solution and that will not react with the workpiece.

General description

Ultrasonic cleaning equipment is used for most cases of precision cleaning. It is important to detect where the ultrasonic cleaning energy is generated and to design and produce the cleaning basket so that the workpiece can be cleaned at the optimal position.

Explanation

(1)How to detect positions where ultrasonic cleaning energy is generated

・To improve the ultrasonic cleaning effect, the workpiece must be placed at an optimal position in the cleaning basket.
・Therefore, it is important to detect how the ultrasonic cleaning energy is being generated in the cleaning tank of the ultrasonic cleaning equipment you will use.
・Fig.1 illustrates how to detect ultrasonic cleaning energy being generated in the cleaning tank.
・Using a commercially available aluminum kitchen foil, the intensity of ultrasonic energy can be relatively determined by the conditions and positions of deformation and fracture of the aluminum foil. (Fig.2)
・Fig.2 illustrates how to prepare the aluminum foil designed for detecting cleaning energy.A frame made with a rust-free stainless steel wire is used for setting the aluminum foil sheet in place.

(2)Relationship between intensity distribution of ultrasonic cleaning energy and cleaning conditions

・For ultrasonic cleaning energy, the amplitude (distance) of vibration energy is determined by the characteristics of the ultrasonic oscillators.
・The cleaning energy is distributed based on the amplitude of vibration energy and the oscillation intensity pattern.
・Therefore, to be able to stabilize the cleaning quality of workpieces in the cleaning basket, the optimal cleaning conditions (swaying motion and distance) delivering consistent cleaning energy to the workpieces must be selected by swaying the cleaning basket for the same distance as the amplitude of the vibration energy.

General description

Ultrasonic cleaning equipment is used for most cases of precision cleaning. To optimize the cleaning performance, it is important to design the cleaning basket so that the workpiece will be positioned at the location that receives the largest cleaning energy.

Explanation

(1)Cleaning energy of ultrasonic cleaning

- In most cases, an ultrasonic cleaning device is used for precision cleaning.
- For the most part, the cleaning energy in this ultrasonic cleaning is determined by the number of ultrasonic oscillators that are installed at the bottom of the cleaning tank as well as their capabilities.
- How to optimize the cleaning energy of this ultrasonic cleaning equipment is up to the production engineer's skills and abilities.
- The cleaning energy is generated in ultrasonic cleaning equipment's cleaning tank as shown in Fig.1.

(2)Cleaning posture and position of workpiece

- To optimize the cleaning energy that occurs in the cleaning tank as shown in Fig.1, the cleaning posture (workpiece direction) and the cleaning position must be appropriately selected.
- The optimal cleaning posture means that the workpiece is placed a direction in which the cleaning energy works effectively for contaminants on the workpiece and that the cleaning solution can be easily washed off.
- The optimal cleaning position is where the maximum cleaning energy works on the workpiece to be cleaned. To improve the effect of ultrasonic cleaning, it is important to design the cleaning basket so that it can set the workpiece in the best position. (Fig.2)

General description

It is difficult to remove liquid contaminants that are trapped in gaps.This volume describes the pre-treatment method for cleaning residual liquid contaminants in the gaps.

Explanation

(1)Example of contaminants that are difficult to remove

・If you clean small components by stacking them or clean LCD components with two pieces of glass substrate glued together, the capillary action causes foreign particles, chemical liquid, or cleaning solution that were present in the process to enter into the products from the gaps. These contaminants are difficult to remove.
・If you dry the product with liquid contaminants left in the gaps, the product may turn out to be defective since it leaves stains on it.
・If you blow the contaminants using an air gun, the liquid ends up being transferred to the surrounding area or being splashed onto another item to leave stains.
・As you see, the residual contaminants in gaps may be often difficult to be isolated in the subsequent cleaning process.

(2)How to remove residual liquid from narrow gaps

・The strong air-blow method does not usually remove the liquid contaminants trapped in gaps completely. (Fig.1)
・On the other hand, a suction method using strong airflow (removal by suction) can eliminate liquid contaminants trapped in gaps effectively when appropriate conditions and hardware are selected.In addition, this method hardly causes a secondary harm. (Fig.2)
・To use the removal by suction, it is important to select an appropriate positional relationship (distance, direction, and so on) for the suction nozzle and the workpiece to be cleaned.
・It is also necessary to adopt a mechanism to trap the liquid contaminants that have passed the suction nozzle.