In response to concerns about global warming and depletion of subterranean resources such as petroleum oil, the automobile industry is rapidly shifting from gasoline-based cars to hybrid and electric cars. As a CO2 emissions-reduction measure, many countries are competing to make solar power or wind power generation fit for practical use as a source of energy. Weight-reduction techniques are one of the most important technological innovations amid this competition. The purpose of adopting weight-reduction techniques is to save energy consumption by reducing the weight of a moving body. For example, automobile body material made usually with steel is substituted with an aluminum alloy. The weight of bullet train cars is reduced by using aluminum alloy materials. The weight of an airplane is thus reduced by increasing the ratio of CFRP (Carbon Fiber Reinforced Plastics) composite.
Adopting weight-reduction technologies is becoming more important in the field of automation devices and mechanical devices for the same purpose. Change the metal stock with resin material to reduce the weight of a movable body, substitute the steel material of the device column portion with resin composite, concrete composite, or ceramic materials, and adopting a slim or hollow design for the component parts such as linear slide guides or changing the material of the linear guide are all examples of weight-reduction technologies in the automation industry.Weight-reduction techniques are of particularly necessary for fast-moving machines. In the aerospace industry, high-strength and high-reliability materials are extremely important, and there has been a shift towards using CFRP composite materials as a replacement for lightweight metals such as Duralumin. The same materials used for airplane bodies are adapted for F1 racing car bodies. The arm parts of electronic packing machines and conveyance robots are examples of their use in high-speed drive units.
To make a product lightweight by material substitution, the following technical requirements must be satisfied at the same time:
A typical example of material substitution is replacing metal-based materials with plastics. There are many cases where metal parts have been replaced with engineered plastics to reduce weight. Engineered plastics are a group of plastic materials that have excellent resistance properties against heat, dust, chemical, weather, and flames. Because they can maintain dimensional stability and mechanical properties even at a high temperature, they can be used in structural components. Engineering plastics may be referred to as EPs. The most common types of EPs include PC (polycarbonates) and ABS resin (acrylonitrile butadiene styrene copolymer).
For factory automation parts, EPs have been adopted for retainer parts used to change the direction of the ball screw bearings in the circulation zone. They also have been adopted for device parts that are frequently exposed to chemicals during processes such as etching and cleaning. They are also adopted for parts requiring high accuracy in areas where the temperature changes. Other examples of this application include exterior parts requiring lightweight properties, such as replacement lens bodies for digital cameras or high-end models of single-lens reflex cameras. Some automobiles have had their glass or body parts replaced with engineered plastics to improve fuel efficiency by reducing the vehicle weight. Reducing the weight of structural materials can speed up the processing equipment and transports since the acceleration increases for the same amount of energy.
Material Strength and Structures
For material substitution from a metal to a resin, designers must adopt a composite structure in order to reduce weight while maintaining the same strength of materials with the substituted material. CFRP consists of carbonizing the fiber and molding it to the structural member inside the resin. The fiber continuum and adhesive strength of the resin will make the material lightweight and shatter-proof.
Iron casting is adopted for columns in the body structure of machine tools. Structural materials used for machine tools need to have morphological stability, which means that the initial accuracy will not be degraded for a long period of over 10 years. Therefore, certain characteristics are required, such as the homogeneous stability of the material itself and non-existence of residual stress inside. The required characteristics are summarized here.Currently, the following materials are mainly adopted as structural members:
Each material has its own characteristics. Granite has the least specific weight. However, Young’s modulus is so small that it is susceptible to deformation. Adopt an appropriate material as the structural member to avoid deformation. Ceramics are the lightweight and strong materials. However, they are extremely difficult to work with. In addition, they are not meant for large-sized products. The exterior panel of a space shuttle is an example of using ceramics in tiles (see [Fig.1]). Resin concrete has superior vibration damping but with less structural strength.
Stay tuned next week for more ideas on weight reduction!