TPT September 2018

AR T I C L E

Advanced Machine & Engineering/AMSAW

Why some material load tables are overloaded with cost By Christian Mayrhofer, manager R&D – Advanced Machine & Engineering/AMSAW

Modern CAD technology, such as SolidWorks, provides powerful tools to calculate and analyse mechanical structures. These programs make it easier to add and test materials that fortify structures in CAD software. The advantage of working in the virtual world is that you can test a variety of materials without adding more cost to the prototyping process. Within these CAD programs, features such as finite element analysis (FEA) can simulate the effects of shock load before the prototype product is even produced. This allows for early modifications in the design process at little to no cost, while ensuring the best strength-to-weight ratios at the lowest cost for the customer. Theory and analytical example An alternative way to approach this is by using the simplifying assumptions of strain energy and the principle of conservation of energy. One can presume that the potential energy before the impact, the kinetic energy right at the impact, and the stored elastic energy in a structure (spring) are equal. In the following formula, δ max is the maximum displacement of the spring; c is the spring rate; m is the falling mass; g is the acceleration of gravity; and h is the starting height:

Heavy material infeed systems in production sawing systems are often over-engineered in an attempt to avoid severe damage from dropped loads. The downfall? The potential for significant cost increases.

It is no easy task to move material stock that spans over 12m in length while weighing a few tons into a sawing system. For this process, it is common to use forklifts or gantry cranes to move the material onto a loading table or transfer mechanism. The danger any plant manager faces is the potential that an inexperienced crane or lift truck operator may accidentally drop heavy materials from a higher distance, damaging the material load table. This uncontrollable interaction may also put the rest of the material handling system at risk for severe abuse. A “poka-yoke” system is needed to guarantee high overall operations effectiveness (OOE).

Why material load tables are over-engineered

The formula for introducing displacement under a static loading condition δ st looks like:

Material load tables and transfer mechanisms are often over- engineered with excessive material in an attempt to avoid severe damage from dropped loads. Although the strength of the load table may be improved, this may increase the cost – a cost that gets passed on to the customer. Another approach to avoid increased costs when designing material handling systems is to use advanced engineering practices.

The same formula can be written in a different form when applying Hooke’s Law – F max is the maximum contact force and F st is the static force:

Figure 1: An example of severe material load table damage experienced from a heavy material drop

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SEPTEMBER 2018