The Technique of Losing Weight: Part Two

Strength and Shape Design Considerations

After looking at ways to use different plastics instead of metal in last week’s post, we will examine shape and material in this week’s post. Weight reduction is a design task assigned to many engineers, there are a variety of methods and we intend to help you with those decisions with these tips and ideas as well as configurable factory automation components. Be sure to check out our application library called inCAD Library that house hundreds of designs using MISUMI components! Get inspired!

The equipment structure of an automation device consists of the following two elements:

Expand the above two elements into more detailed subjects to understand the overall design objective. Keep this overall objective in mind, and check the advantages and disadvantages of the similar structure designed in the past. This way, you can minimize the risk of failure when designing lightweight and high-strength structures.

The designer of an automation device needs to check a considerable number of elements including those listed on the right side of the above figure. Therefore, the best way of minimizing the workload is to make improvements on the design of a certain type of the automation device and apply the accumulated knowledge to the similar design. The strong bend-resistance achieved by the hollow architecture is described by a technical term “second moment of area”.  The strength can be described by the following terms depending on what it refers to.Bamboo trees have large “stiffness” because of their hollow cylinder with nodes. In addition, they also have high “toughness” for their tissue structure being more densely distributed as they become closer to the epidermis. Since they excel in both stiffness and toughness, we can conclude that bamboo trees are the lightweight yet a strong structural member.

The second moment of area (written as an alphabet “I”) is a technical term that refers to bending resistance for the bending force applied to bar-shaped structural members. This second moment of the area can be modified by the cross-section shape of structural members. Therefore, it is possible to design a lightweight and highly strong structure by adopting the optimal cross-section shape.

Losing Weight via Aluminum Alloy

In recent years, using aluminum materials in place of steel or iron is becoming more common. The specific weight of aluminum is only 35% of steel (7.9). Therefore, 65% weight reduction is possible. While being more lightweight compared to steel, aluminum alloys are susceptible to deformation since Young’s modulus is approximately one-third of the steel’s. Thus, they are not the good choice of structural members requiring accuracy and strength. Because aluminum alloys are suited to continuously manufacture products in complex shape by extrusion, they are chosen as the base materials of aluminum frames for covers and bands. In this case, adopt the cross-section shape with the greater secondary factor for the frames to make the structural member lightweight and strong (see [Fig.1]). Aluminum is also adopted as structural frames of a worktable for prototype production line or jigs for small-lot production such as for trial or research purposes (see [Fig.2]). Aluminum alloys must go through welding process if you use them as large-sized structural members. Friction Stir Welding Method (patented in the U.K.) is a frontier technology of welding work. This method is adopted for manufacturing bullet train cars and high-speed vessels (see [Fig.3]). In the production facility of an automation device, aluminum materials are used for precision surface plates assembled to lightweight and high-precision tables. In this case, apply hard anodic oxide coating to improve abrasion resistance on the surface and increase the surface hardness before use.

This concludes our two part series on Weight Reduction. This is just one of the many ideas that need to be considered in designing and improving factory automation equipment. In case you missed last week’s post, click here! We hope you are inspired by MISUMI in your designs and keep using our parts!

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