How Aluminium Power Wheelchair Reduces Weight Without Compromising Strength

When it comes to the electric wheelchair users, each kilogram counts. A heavy chair cannot be easily transported, stored and maneuvered. But the weight must be lost without injury to safety or strength--a frame which is bent or cracked by weight is of no use. The aluminium power wheelchair resolves this dilemma. In Ningbo Baichen Medical Devices Co., Ltd., we have produced thousands of aluminium power wheelchairs through the high-technology engineering. Four methods through which aluminium saves on weight but still retains strength are given below.

High-Strength Aluminium Alloys (Not Pure Aluminium)

The general myth about aluminium is that it is a weak material. Practically, aerospace grade aluminium alloys are very strong in weight to weight ratio. Aluminium is soft, although alloyed with magnesium, silicon or zinc, it forms materials that are competitive with steel in particular strength.

The aluminium power wheelchairs we make are made of heat treated alloy, with a yield strength of about 240-260 Mpa - about 60-70 % that of mild steel but at only a third the density. This implies that an aluminium frame may be created by making the walls slightly thicker or the tube diameter larger to get the same stiffness as steel but a much lower weight. In design, we apply finite element analysis (FEA) to optimize the shape of tubes, so that we can apply the material only where the stress is the highest.

Optimized Tube Geometry and Gusseting

It is not only the material that makes a strength in a wheelchair frame but also the shape. An aluminium frame that is well designed contains larger diameter tubes than a similar steel frame to raise the moment of inertia (resistance to bending).

The aluminium power wheelchairs are designed with oversized oval and rectangular tubes which spread loads over broader areas. At cross-sections of tubes (including at the point of the backrest frame and seat rail) we insert forged aluminium gussets (strengthening brackets) which remove stress peaks. The larger diameter with thinner walls combined with strategic reinforcement come together to produce a frame that is rigid under a 120-150 kg user load without the weight penalty of steel. Computer modeling makes sure that we do not add material where we are not required.

Robotic Welding and Heat Treatment

The heat affected zone (HAZ) of any aluminium weld is its weakest part, and the strength of the alloy can reduce by 30-40% here. Bad welding makes a good design a hazardous one.

Robots in our factory incorporate robotic welding whereby the heat input and travel speed is accurately controlled to reduce the HAZ. Following the welding process, every frame is T6 heat treated (solution heat treated and artificially aged) to provide the alloy with strength throughout the entire structure. This post weld treatment is important most manufacturers who make lower quality frames do not do this and, in several months, the frames start to crack at the welds. We have 60 systems of frame processing to include our special heat treatment ovens to enable all aluminium wheelchairs to achieve their design strength.

Strategic Use of Steel Components at High-Stress Points

It is not necessarily the solution of an all aluminium frame. The cleverest constructions that are lightweight include mixed structures: aluminium is used in the main frame, steel in parts that have localized loads or abrasion.

Our power wheelchairs, which are aluminium, contain steel axle brackets (which are subjected to repeated wheel mounting and removal), anti-tip bars (which should not bend), and some pivot points. These steel components weigh under 1-2 kg in total but significantly enhance the life-span at its key points. The remainder of the frame side rails, backrest supports, footrest hangers, is aluminium. This composite solution provides the weight reduction of aluminium and the hardiness of steel where the strength is most needed.

Conclusion

Four engineering strategies (high strength alloys , optimum tube geometry with gusseting), robotic welding and T6 heat treatment, and location of steel in high stress areas, enable aluminium power wheelchairs to reduce weight without loss of strength. The product is a lightweight but strong enough to support years of daily use (typically 20-25 kg) chair.

We integrate these methods in Ningbo Baichen Medical Devices Co., Ltd., which occupies a 20,000 m2 plant, has 60 frame processing machines and 4 assembly lines. Get in touch with us and feel the power of lightweight aluminium.