Source | Interior and exterior design of automobiles
1 Foaming
Foaming is the key component of the seat, foaming provides the shape and contour of the seat, the characteristics of foaming affect the comfort and H-point of the ride, and the foaming mold directly affects whether the quality of the foam product can meet our design requirements, understanding the foaming mold manufacturing process and manufacturing quality will help the design of the foam structure.
2 Foaming molds
According to the requirements of the design of foam parts and the foaming production process, the mold used to manufacture and produce foam parts is called foam mold. According to the mold structure, it can be divided into two-piece and three-piece type, according to the manufacturing method of the parting surface, it can be divided into epoxy parting surface mold and EDM parting surface mold, according to the manufacturing material of the mold cavity, the foaming mold can be divided into epoxy mold and aluminum alloy mold.
Two-piece mould (upper and lower moulds)
Three-piece mould (upper and lower mould and core)
The design and manufacturing process of foaming mold is divided into the following main steps:
Design collation and analysis of input information
The input information includes the vehicle model, seat configuration, development schedule, project budget, development basis (3D, 2D, prototype), etc.
The processing of data (master model, aluminum mold, inspection plate), the main model is an enlarged model with comprehensive shrinkage, and the aluminum mold is generally used. Aluminum mold is a forming mold with comprehensive shrinkage - shrinkage of aluminum alloy material.
The inspection plate is a gauge used to inspect the size of the foam product.
Output the technical and process requirements of mold development
Sand turning mold production and inspection: sand turning mold is made on the basis of the main model to prepare for the aluminum alloy sand turning model, it will determine including cavity angle, parting surface, installation size, water pipe distribution, wall thickness and other mold structure, for the final structure of the mold in the future to provide a guarantee, its quality will directly affect the quality of sand casting.
Sand turning and casting: On the basis of the sand turning mold, the sand box is used for modeling to prepare for pouring aluminum alloy, and this process is sand turning. After the sand turning is completed, the liquid aluminum alloy that reaches the pouring standard after various process control is poured into the sand box, and the process of cooling and forming is casting, and the sand turning and casting directly affect the intrinsic quality of the mold and the quality of the mold post-processing in the future.
Machining, assembly and inspection of aluminum molds: including processing and inspection of cavities, peripheral dimensions, parting surfaces and assembly of parts (positioning devices, cylinders, pipe joints, etc.).
Mold trial verification: After the mold base installation, parts positioning, automatic exhaust cylinder installation, process parameter preparation and other related preparations, the online trial production will begin, and the size and performance test will be carried out after maturation.
After the mold is completed, according to a certain trajectory, a certain flow rate and a certain pouring time to the mold to inject, and control the temperature of the raw materials, the temperature and pressure of the mold, the raw materials react at a certain temperature, the molding time is about a few minutes, after the foam out of the mold, the bubble is broken, otherwise the foam is easy to shrink and crack, and finally matured, the process takes a few hours, and we get our final product.
When designing the foaming mold, first confirm the structure of the mold, whether it is a two-piece, three-piece, or a variety of configurations; secondly, the parting surface should be selected, whether it is epoxy or EDM, and the mold manufacturing process and foaming process should be determined according to the appearance and function of the product, and the distribution of the parting surface should be determined; and then for the fixation and positioning of the parts, the skeleton positioning datum should be selected and the tolerance should be controlled.
It is also necessary to consider the shrinkage rate, the comprehensive shrinkage rate is also mentioned above, and there are many influencing factors, such as the shrinkage of polyurethane foam raw materials, the shrinkage of aluminum alloy materials in the casting process, the influence of the shape and position of the parts in the foam, the influence of the foam size, shape and structure, and the shrinkage rate obtained by the above various shrinkage factors, which is called the comprehensive shrinkage rate.
Design factors that affect the manufacturing quality of foam molds:
Data design directly affects the quality of foaming molds, so before the data is released, it needs to go through strict review to ensure that the data meets the requirements of STO modeling and other design inputs such as H-point, skeleton, body environment and function, etc., while meeting the requirements of mold making, here are some foam design requirements, as shown in the following table:
3 Hardness and density of foaming
The density and hardness of the foam are important parameters of foaming, the density affects the durability of the foam, and the hardness is an important factor in the foam not to deform when it is loaded. The hardness and density of the foam directly affect the comfort of the seat.
In the case of maximum allowable load, higher density will bring better durability, but too high density will lead to high hardness, which will affect the riding comfort of occupants. At the same time, higher density will also increase the cost of foaming, and high-density foam means that more foam raw materials are injected into the mold, so it is particularly important to control the density of foaming. The density is too low, and the physical properties of the foam cannot meet the requirements of ride comfort.
Foam hardness is expressed by indentation load deflection (ILD). It is used to determine the load required to compress the foam thickness of the seat to 50%. ILD mainly depends on the foaming composition and foam thickness. ILD is used to determine the amount of foam depression when the human body loads the foam, and is an important indicator to measure the occupant comfort.
To measure the ILD value, it is necessary to have a fixture that matches the foamed B-side (usually the seat frame support surface) to eliminate the error caused by non-foaming deformation during measurement, such as the foaming B-side vacating. The uneven force on the supporting surface of the foaming B surface leads to a large amount of local compression. When measuring the ILD value, the position that the occupants are in contact with when riding normally (the diameter of the test pressure plate is φ203mm) should be simulated, and the test method is shown in the figure below.
A device for measuring ILD values
The performance requirements for seat foams are shown in the table below
The foam performance is mainly reflected in the bump and peristaltic test, to verify the fatigue life of the seat frame, foam and cover, at a frequency of 100 times/min, the vibration test of the seat cushion 100 000 times and the backrest 50 000 times, the test sample should have no abnormal conditions, no cracks in the seat frame, no deformation of the foam, no damage to the fabric and padding, and the maximum change of H point is within the rated range.
4 Summary
The foaming of the seat occupies a very important position in the seat, including the riding comfort and durability of the seat, the protection and energy absorption of the occupants during the collision, and the sound absorption performance in the NVH of the vehicle interior are closely related to the foaming, so the design of the foam is particularly important.
We still have a long way to go, and we need to rely on the joint efforts of the automakers to take our country's automobile manufacturing process to the next level.