Wuxi Little Swan Company Limited, one of the world’s largest washing machine manufacturers, operated by Midea Group, specializes in the development, production and sale of washing machines and clothing dryers. Little Swan has established a strategy to provide leading products in an efficiency-driven global operation.
As China’s consumer market is becoming increasingly mature, consumers do not regard price as the decisive factor in the selection of durable consumer goods such as washing machines. Manufacturers are no longer concentrating exclusively on price competition; instead, market differentiation has replaced pricing as a leading factor. Manufacturers of name-brand washing machines now focus on the positioning of their products and set quality requirements that correspond to their brand positioning.
Clean, healthy and environmentally friendly are the main product characteristics of washing machines. The associated quality requirements include improved cleaning performance, reduced wear, pollution prevention, reduced water and energy consumption, reduced noise and others. The continuous improvement of these requirements is one of the biggest challenges faced by the manufacturers.
Over the past few years, China has changed its birth regulations and implemented the two-child policy. Two-child families are considered the most important target market for washing machine manufacturers. For them, silence is one of the most impor - tant requirements, as parents do not want themselves or their babies to be disturbed by washing machine noises. This is also reflected in statistical data. According to the Nielsen 2013 research on requirements for washing machines in China, 51 percent of all interviewed consumers regard vibrational noise as one of the biggest problems that washing machine manufacturers must solve.
The vibrational noise that consumers complain about is reflected mainly in the body, but the actual vibration energy comes from the rotating component, the drum. The eccentricity of the rotating drum produces centrifugal force, resulting in forced vibration of the drum. The vibration frequency is the same as the rotational speed. Due to the damping provided by shock absorbers, the amplitude of this forced vibration is very small. However, when the rotational speed is close to the integral frequency of the body structure, the amplitude of the forced vibration increases, causing a lot of energy to be consumed by the vibration of the body. This results not only in the noise problem, but also in material fatigue of the body and a reduction in the reliability of the machine.
Three classic methods can solve this problem.
Adjusting the exciting frequency (limiting the speed of rotation) can avoid the integral frequency of the body structure. However, this method affects the basic cleaning and dewatering functions of washing machines, so it is not a desirable method.
Adjusting the body rigidity or changing the connecting device to change the body rigidity produces the vibration and noise reduction results, but requires mold and process changes that increase the manufacturing costs.
Adjusting the damping by adding or adjusting shock absorbers can limit the vibration amplitude at the time of resonance. The cost of this method is low, but it does not really eliminate resonance, so the noise reduction result is limited.
Most manufacturers use a combination of the second and third methods. However, each method, whether combined or not, requires setting up conditions and analyzing test data to obtain the resonant frequency and to verify it after each proposed improvement plan. For the research and development (R&D) team of a washing machine manufacturer, improving the test and analysis efficiency for rapid iteration is the key to solving this technical problem.
In 2013, Little Swan recognized that the market needed to change and immediately set up a pioneer technology team at the research institute. This technical team has been used to solve key problems, such as the reduction of vibrational noise. One of the most important initiatives was the introduction of Simcenter Testlab™ software, part of the Simcenter™ portfolio, from product lifecycle management (PLM) provider Siemens Digital Industries Software. Utilizing the powerful test and data processing capabilities of this solution, the team set up a standard test and a complete optimization design process, especially for the vibration noise of washing machines.
This process played a critical role in the development of a new washing machine model.
In the pre-development process of this model, the R&D team quickly identified a resonance range in the right side plate by using the hammering method and the Simcenter Testlab signature tool, when the rotating speed was above 1,200 rpm. After identifying the problem, the R&D team had to consider the routes through which the barrel vibration transfers to the body and determine the contribution of the various routes to the body side plate vibration at different rotating speeds.
In a drum washing machine, the drum is connected to the body by the following components: left hanging spring, right hanging spring, left front shock absorber, left back shock absorber, right front shock absorber and right back shock absorber. The six points at which such components are connected with the body are named as coupling points, and the body right side center is named as the target point. A transfer path is formed from each degree of freedom of each coupling point to the target point.
With Simcenter Testlab transfer path analysis (TPA), the Little Swan team quantified the contribution of each transfer route to the body right side vibration. The analysis showed that the contributions of the hanging points of the suspension springs are always the greatest at different rotational speeds, so the team concluded that reinforcing the connecting structures of the springs could effectively increase the body rigidity and achieve the best vibration noise reduction results..
At the same time, only the connecting structure of the suspending spring required reinforcement and the entire body did not need to be altered, so that the effects of the changes on the process were limited.
The analysis of the problem enabled the Little Swan R&D team to focus on improving the reinforcement of the springs and quickly develop several preliminary design plans. At this stage, the ease-of-use of the Simcenter solution – from operation of the data acquisition equipment to the user interface of the analysis software – makes it much easier to compare plans. The excitation forces and transmission functions are compared at different rotational speeds and different coupling points. By using the report creation template, engineers can quickly generate reports after completing the test and then compare the vibration and noise reduction results of different design plans.
The body vibration was reduced to by 50 percent compared to the original design, and the body radiated noise was reduced by three decibels. This was the direct result of improving the spring reinforcing element. The new washing machine was well received in the marketplace. Both the total number of complaints and the number of noise-related complaints for this product are much lower than the industry average.
“With the new trend of consumption, the core competitiveness of washing machines lies in precisely grasping consumer requirements,” notes Gu Chaolin, chief engineer of Performance Development, R&D, Little Swan. “’Quiet,’ ‘durable,’ ‘stable’ and ‘energy-efficient’ are the technical targets that are continuously pursued by Little Swan. In this process, the Simcenter Testlab solution from Siemens Digital Industries Software plays an important role.”