Problem solving case09

Machine parts break
and workers are put at risk

A quick and reliable response is required, not just a supply of parts.

PROPOSER

Nagoya Branch Sales Representative

Our mission is to provide industrial equipment manufacturers with the right amount of parts for manufacturing and production equipment in a timely manner.
Ensuring adequate inventory is also important for rapid supply.

BEGINNING

At the factory of one of our customers, a home appliance manufacturer, an accident occurred in which a ball screw part of a vacuum molding machine exploded during operation, scattering the iron balls inside.

Even after replacing the ball screw parts, they would explode again soon after. To prevent this, they needed to make an immediate improvement and consulted us.

Although this vacuum forming machine was not delivered by our company, we worked closely with the vacuum forming machine manufacturer to quickly improve the ball screw.

OBSERVATION

Is the pressure greater than expected or
is there a design flaw?

An iron ball was placed inside a metal tube, and the metal tube that held the iron ball was made by joining semicircular rails. Therefore, when more pressure than expected was applied, the joint broke and the iron balls inside were scattered.

We decided to visit the site to find out why the ball screw was designed with this shape in the first place, and whether the customer was using the vacuum forming machine with pressure higher than expected.

In conclusion, the resin plate to be molded was thicker than the vacuum molding machine manufacturer had anticipated, and the mold needed to be pressed down with greater force, which resulted in more pressure being applied to the ball screw than had been anticipated.

This ball screw was designed to be able to adequately handle the pressure assumed, taking into account sliding properties and frictional resistance, but in reality, the pressure applied to it was greater than expected.

SOLUTION

I want to prevent this accident from happening again

We need to work with the vacuum forming machine manufacturer to improve the ball screw design as soon as possible.
We decided to change the metal tube, which had been divided into two parts, into a single seamless metal tube and add an oil refill function so that a constant amount of oil always flows through the tube.

With this improvement, the tube will not burst even if it is subjected to pressure stronger than the pressure currently used, and even after more than five years since delivery, there has not been a single accident without it bursting.

When we think of solving problems, we usually think of things like reducing the number of people required, increasing efficiency, and cutting costs, but surely eliminating dangerous situations like this one, which involve human lives, should be a top priority in preventing accidents?
When solving problems involving dangers where failure is not an option, it is important to carry out an accurate analysis of the causes of the risks. If this analysis is done incorrectly, a second or third accident will occur.

Factor analysis requires extensive experience and wide-ranging knowledge, but we will work with our partner companies to perform accurate factor analysis without mistakes.

As in this case, we will continue to respond promptly and courteously to any proposals for resolving issues, especially those related to risk avoidance and safety measures.