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SHI Xiaohua, DONG Yuehu, HAN Bing, LI Mingyang. Solving the Problem of Incomplete Cleaning in the Subframe Manufacturing Industry with TRIZ
Abstract. In the cleaning process of the subframe after processing, due to the complex internal structure of the subframe, impurities such as aluminum scraps and oil stains in the cavity are not easy to be cleaned. Nowadays, cleaning liquid is used to clean the subframe, and two problems of incomplete cleaning in the cleaning system and incomplete drying in the subsequent drying system are exited, that is, liquid droplets will remain in the cavity and blind hole of the subframe. In this paper some tools such as function analysis and Su-Field model of TRIZ will be applied to analyze and solve the problem, and the existing cleaning and drying device will be improved. In this way, the cleaning of aluminum scraps and oil stains of the subframe will be realized, and in final, drying of the internal and external of the subframe will be ensured.
Key words: TRIZ, aluminum alloy subframe, thorough cleaning, drying.
1. BACKGROUND
The aluminum alloy subframe is located in the automobile chassis, which is an important part of the front and rear axles. And it has the effect of blocking vibration and noise. In addition, it can reduce the vibration and noise in the cockpit and create a more comfortable environment for drivers and passengers.
The manufacture of subframe belongs to the automobile manufacturing industry. In recent years, the alloy subframe is more and more popular with customers because of its lighter weight while meeting the strength requirements [1-4]. The manufacturing process of the subframe includes casting molding, machining drilling and cleaning. However, due to the need to process a lot of fixed mounting holes on the subframe [5-8], the cleaning process in its processing is important, and its main purposes are:
(1) to make the remaining impurities such as cutting liquid and oil stains on the surface and inner cavity of the subframe cleaned;
(2) to clean the remaining impurities such as sand and aluminum scraps in the cavity of the subframe.
Most of today 's subframe cleaning devices adopt pipeline structure, which can to complete the step-by-step cleaning work automatically and without manual intervention. One of the structures of the current subframe cleaning and drying device is shown in the following figure [9]. It is mainly composed of multiple single-function manipulators, which are distributed to complete the functions of subframe transportation, cleaning and drying.
feeding area Cleaning area drying zone
Figure 1. Subframe Cleaning Drying Device Schematic Diagram
The lifting manipulator in the cleaning area drives the rotating clamping manipulator, and the subframe on the feeding table is immersed in the cleaning pond for rotating cleaning. At the same time, the stirring wheel rotates reversely in the cleaning pond. In the drying area, compressed air
provided by the air compressor blows the subframe to dry. The heat source is installed in the drying area, and it provides heat to the heat dissipation plate to assist in drying the subframe.
These existing cleaning devices can largely complete the removal of aluminum scraps and oil in the subframe. However, for some reasons, there will be the following two problems in the practical application:
(1) incomplete cleaning: the internal structure of the aluminum alloy subframe is complex, and the scraps in the cavity are not easy to be removed;
(2) incomplete drying: in the drying stage, due to the complex structure of the subframe, there are liquid droplets in the cavity and blind hole.
The second problem which is called "incomplete drying" and described in the previous section, is actually a derivative problem caused by the selection of the cleaning method of the subframe. The feasibility analysis of several existing methods that can move impurities such as aluminum scraps is carried out as shown in Table 1.
Table 1 Methods can Move Impurities
Principles Solutions
Advection Using high pressure gas, the aluminum scraps in the cavity of the subframe are blown out in a specific direction.
Gel The jelly-like material is used to remove the aluminum scraps in the cavity.
Ultrasound The sound wave causes the aluminum scraps to fall off in the subframe cavity.
Electric Field The charge in the aluminum scraps is rearranged, and the aluminum scraps are discharged from the inner cavity under the action of the electric field.
Though these methods will not produce the derivative problem with residual liquid, these methods will produce other difficult problems in the process of removing aluminum scraps. The method 'advection' is difficult to control the direction of the gas, and it cannot completely remove the aluminum scraps. For the method 'gel', the jelly-like material which is sticky will reside in the subframe, and it is difficult to clean. For the method 'ultrasound', its noise is very large. The method 'electric field' is difficult to achieve, and electric will affect other parts of the cleaning device. So, these methods are not be considered in the next content, and the method with cleaning liquid will still be as the common cleaning method.
It can be seen that some existing common methods have certain difficulties in solving problems. Therefore, TRIZ will be used to analyze and solve the two problems through the following contents and propose an improved device.
2. PROBLEM ANALYSIS
2.1 Brief Introduction of TRIZ
TRIZ is a structured innovation method, which was originally created by the former Soviet Union inventor Genrich.S. Altshuller after studying a large number of patent documents. After a century of development, TRIZ theory has become an independent discipline of innovative methods. It can provide systematic tools for basic knowledge base, problem raising, analysis, solution, evaluation and improvement. Therefore, TRIZ can help scholar to avoid making a compromise solution limited by limited knowledge domain [10]. Compared with other methods, TRIZ can also propose a large number of innovative solutions to solve practical problems.
2.2 Function Analysis
Firstly, Function analysis can be carried out. In the cleaning process, the subframe is regarded as a super system, impurities such as aluminum scraps are regarded as products, and the mechanical arm and the stirring wheel and cleaning liquid are components. And the functional model
diagram composed of them is shown in Figure 2. The lifting manipulator drives the rotating manipulator to submerge the aluminum alloy subframe in the cleaning solution. In addition, a stirring wheel is arranged in the cleaning tank, so that the cleaning liquid flows and the aluminum scraps attached to the subframe are taken away.
By analyzing the model diagram in the cleaning process of the subframe, the following main problems can be obtained: (1) The effect of cleaning liquid on moving aluminum scraps is insufficient. (2) The role of the subframe support cleaning liquid is excessive.
The first of these problems will lead to incomplete cleaning, and the specific reasons include the stirring wheel cannot make the cleaning liquid move effectively and the aluminum scraps in the cleaning liquid will be disordered and reenter the subframe. The second problem is a derivative problem, which will lead to incomplete drying of the subframe, so the next contents will mainly analyze and solve these two problems.
Lifting Manipulator
Remove
Clamping Rotating Manipulator
Rotate
Revolution Axis Drive Driving Motor
Drive , r Support L
Mixing Wheel Support Cleansing Pond
Remove\
Cleaning Liquid
-1-
Remove
^ ^^ I Remove
^^^Support w
^.AAA_ Furnace WW Aluminum Scraps Adhere
Figure 2. Function Model
'Support
3. PROBLEM SOLVING
3.1 Prime Problem- Incomplete Cleaning (1) Trimming
Based on the above analysis, the cleaning liquid cannot be provided sufficient power to achieve the cleaning function by the mixing wheel. So, the function of the mixing wheel is insufficient. This is the fundamental problem need to be solved. Here trimming can be used to solve this problem. As is known, function carrier can be trimmed if another component performs its useful function. Here the "mixing wheel" can be trimmed, and the model will be shown in Figure 3.
Supporting Platform
Lifting Mechanical Arm
Remove,, Clamping Rotating Manipulator
Remove
High Pressure Piping
upport
■ ^
Auxiliary Frame
\_!_A
Remove
Rub
Remove
connect High Pressure
Pump
Remove
Support
Cleaning Liquid
Remove _v_
Furnace
Support
Support Cleansing
Pond
Aluminum Scraps
Figure 3. Function Model after Trimming
In the model, some function disadvantages are clearly presented, the corresponding cleaning function is replaced by the high-pressure nozzle. And the high-pressure nozzle is installed on the feeding manipulator. In this way, the cleaning liquid can be removed to everywhere of the subframe directionally. Thus, the cleaning process is more efficient. At the same time, a support device is added to realize the transfer and support of the subframe from the cleaning zone to the drying zone.
(2) Effects Database
The above cleaning process can remove as much aluminum scraps as possible. However, the cleaning liquid in the cleaning pond is mixed with aluminum scraps, it will cause the aluminum scraps to reattach to the subframe. So, the Effects Database can be used to solve this problem, and two effects of ' Centrifugal Force ' and ' filter ' were found, they are as shown in Figure 4.
1) Centrifugal Force
Through the centrifugal force generated by the stirring wheel stirring, the aluminum scraps flow to the periphery of the cleaning liquid tank under the action of centrifugal force.
2) Filter
By adding a filter screen in the cleaning liquid output pipeline, the aluminum scraps are filtered and the aluminum scraps in the cleaning liquid are separated.
Figure 4. Two Effects of 'CentrifugalForce' and 'filter'
In the actual device, by comparing the two methods of 'centrifugal force' and 'filter', it is found that the second scheme is relatively simple and cost-effective, because the whole device only needs to add a filter component. In addition, there is no effect of centrifugal force. In the process of recycling the whole cleaning solution, the impurities such as disordered aluminum scraps in the original cleaning solution are also easier to be removed. Then a filter screen can be added at the outlet of the pipe to separate the aluminum scraps in the cleaning liquid.
3.2 Derivative Problem- Incomplete Drying
Firstly, the functional model diagram of the system with drying function in the device is analyzed, as shown in Figure 5. The lifting manipulator drives the clamping rotating manipulator to drive the subframe into the drying device. This part includes air compressor, heat source and heat dissipation device. The high-pressure air produced by the air compressor can blow out the cleaning liquid in the complex inner cavity of the subframe. The heat source and heat dissipation device can heat the subframe and high-pressure air to vaporize the cleaning liquid droplets.
Figure 5. Function Model for the Drying System
By analyzing the functional model diagram, the main problem in the model that the heating function of the heat source and the heat dissipation device is insufficient in heating the subframe and heating the high-pressure air is found.
(1) Technical Contradiction
In order to solve the problem that the heat source and heat dissipation device mentioned above in the existing device have insufficient effect on improving the temperature of the subframe and high-pressure air, the use of a higher-power heater or a heat dissipation device that provides a larger heat source area can be considered. This method can increase the temperature of the high-pressure air and the subframe in a short time, so that the liquefaction effect is better. But this will produce a technical contradiction in the meanwhile.
IF: using a larger power heater
THEN: 'productivity' will be improved
BUT: 'power' will be deteriorated
Here two Inventive Principles can be used according to the Contradiction Matrix, and the corresponding solutions are shown in Table 2.
Table 1 Methods can Remove Impurities
Inventive Principle Solutions
No.10: Preliminary action Before the subframe is dried, it is rotated or shaken first, and some water droplets are thrown off.
No.21: Skipping Reduce the duration of the subframe in the high-power drying area.
The solution is to shake the subframe before heating and drying, to shake off some liquid after experiments.
(2) Physical Contradiction
There is also a physical contradiction in the system about the heating time. It can be described as: the heating time needs to be long, because the subframe needs to be completely dry. However, the heating time also needs to be short, because the process time needs to be as short as possible, to reduce process time and save costs. Here Separation in Space can be used to solve the problem, the solution is shown as Figure 6.
Auxiliary Frame 1
Auxiliary Frame 2
Drying Zone 1
Drying Zone 2
Figure 6. Solution of Two Drying Zones
In space, two drying zones are set in the upper and lower positions, and then a cleaned subframe can enter the upper drying zone 1, another subframe can enter the lower drying zone 2. Compared with the existing single pipeline equipment, the general drying time is greatly shortened. In this way, each subframe can stay twice the required time in the drying area, that is, there is sufficient time to heat and meet the process time requirements.
(3) Su-Field Model
Through the above analysis, the su-field model diagram shown in Figure 7 can be obtained. Cleaning liquid and compressed air are substances, and the thermal field is the field. Under the action of thermal field, the effect of compressed air on the cleaning liquid is insufficient.
Figure 7. Su-Field Model
Now this Su-Field Model can be solved by S2.1.2: A new field ' vacuum field ' can be introduced. In this way, under the combined action of the two fields of the thermal field and the vacuum field, the compressed air can better remove the cleaning liquid. And the new su-field model is shown in the Fig. 8.
Figure 8. New Su-field Model
(4) Trimming
The heat source and heat dissipation device with insufficient function are trimmed in the functional model diagram. The air compressor, heat source and heat dissipation device are replaced by a movable compressed air heater. And it is integrated into a multi-degree-of-freedom manipulator to blow high-temperature and high-pressure gas into the inner cavity to increase efficiency. And the model diagram after trimming is shown in Fig. 9. In this way, all parts inside and outside the subframe can be blown to by hot high-pressure air, and it can ensure that the residual cleaning liquid is dried and distributed. A mechanical arm carrying the compressed air heater can make the heating effect completely sufficient. The high temperature compressed air is provided with sufficient power and can heat inside and outside the subframe sufficiently.
Figure 9. Function Model for the Drying System after Trimming
4. SOLUTIONS
The final solution can be obtained through the above solution.
(1) the Prime Problem - Incomplete Cleaning:
1) Multi-degree-of-freedom feeding spray integrated manipulator can be used. The multifunctional manipulator integrates the functions of the feeding manipulator and the high-pressure spray nozzle. It can not only move the aluminum alloy subframe to be cleaned from the feeding platform to the transfer frame, but also carry a high-pressure spray nozzle to spray the cleaning liquid into the sub-frame cavity. In this way, the impurities in the subframe can be removed more efficiently.
2) The use of a filter can make efforts. The filter can remove the aluminum scraps mixed in the cleaning solution in time. This will not cause the problem of being brought back into the inner cavity of the subframe.
(2) the Derivative Problem - Incomplete Drying
1) Pre-shake before drying is used. Before drying treatment, the excess liquid droplets in the subframe are removed by shaking. In this way, the cleaning liquid remaining in the subframe will be reduced a lot, and the drying effect will be better.
2) Double drying areas are set. Two subframes to be dried can enter different drying zones, and the waiting time can be improved, and the drying efficiency can be improved.
3) Multi-degree-of-freedom cutting manipulator with compressed air heater makes efforts. The mechanical arm can drive the high-pressure gas nozzle to the residual cleaning liquid inside and outside the subframe. High-temperature and high-pressure air is blown to the cleaning solution more efficiently. And this process has a directional effect and higher efficiency.
According to the solutions, the improved subframe cleaning device is shown as the Fig. 10: The feeding spray manipulator can realize the functions of feeding grasping and directional cleaning. The cross-layer transport device can make the two subframes interlaced for cleaning and drying processes, reducing the total time of the processes; The Multi-degree-of-freedom manipulator with compressed air heater can realize the drying of the subframe and the function of cutting and grasping.
Figure 10. Improved Subframe Cleaning Device
It is found that there are no impurities such as aluminum scraps in the cleaned subframe and there is no residual liquid in the subframe after using the improved cleaning equipment. At the same time, the overall processing time is shortened by half, and the processing efficiency is improved.
5. SUMMARY
In this paper, an improved subframe cleaning and drying device is proposed by TRIZ, which can better improve the cleaning and processing effect, and can also improve the processing efficiency to a certain extent.
In the future, the existing method of cleaning the subframe can also be optimized. For example, the cleaning method without liquid cleaning solution can be used, or the cleaning solution which can disappear in an easier way can be considered. In this way, there will be no longer need to dry processing of such derivative problems. And in this case, the overall subframe cleaning equipment will be more simplified.
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