Toyama die casting technology low-pressure die casting cost half
Aluminum die cast products are manufactured in a method of pouring molten aluminum at high temperature into a die and applying pressure for cooling and hardening. It has been a common practice to apply the pressure of 70 to 1000 MPa (mega pascal), but the company established a technology for production at a low pressure of 46 MPa based on the analysis of experiment results on the phenomena inside the die. The technology realized cutting the production cost by half as well as substantial reduction of production speed. Up until now, 80% of their aluminum die cast production lines have been shifted to the low-pressure method. This earned them a level ground for price competition with Chinese manufacturers.
Aishin Keikinzoku Co., Ltd. http://www.aisin-ak.co.jp/
Established in 1970 as a die cast molding manufacturer. In 1975, they started manufacture using extrusion method. The company has gained recognition as a manufacturer of high quality products, as substantiated by the Deming Prize awarded them in November 1983 for their high-level quality control. February 2002 marked the milestone of reaching a total production volume of 800,000 tons. Currently, they are supplying aluminum die cast parts for engine, transmission, etc. to Toyota, their leading stock holder, and other automobile makers.
The production method of aluminum die cast parts composing engine or transmission of cars is similar to that of Japanese fish-shaped pancake. That is to pour molten aluminum into a die and put pressure on it for cooling and hardening.
There used to be a “standard practice” observed in the aluminum die cast industry. It held that good products could not be made unless the pressure to be applied after pouring the material into the die were 70 to 100 MPa, which had been flatly practiced by all the manufactures for decades. They believed that any pressures lower than that might produce a line-shaped crack called “cold shut” on the product surface, generating defects inside the product that would cause the product to be rejected in the inspection. Mr. Ohsawa took up a challenge to defy that standard.
“The trigger was the Deming Prize (award system of Union of Japanese Scientists and Engineers) we received in 1983. Though our quality control was highly evaluated, it was pointed out that our
manufacturing did not live up to it.”
Against this background, the company set up its business visions for every five years and thus began a strategic challenge for enhancing their manufacturing capabilities. The “V 2000” planning that started in 1995 had an objective of “Half Cost” to reduce the cost of all production by half. The reason behind it was the competitors’ start of Chinese operations, so they needed to improve their cost competitiveness. Nevertheless, cutting the cost half is no easy task, requiring the comprehensive reviewing of production methods instead of implementing minor changes. Of the 20 new technologies proposed as the development theme, Mr. Ohsawa was put in charge of the “reduction of die casting pressure.”
“The reducing of the pressure has been already challenged by our predecessors. Yet, it hasn’t been changed at all because they all failed. Some in the industry community ridiculed me by sayiing things like’ it's just a waste of time,and you better think twice.’”
He could think of many advantages that come from reducing the pressure; 'the very expensive casting dies can last longer,’‘the pressuring equipment can be replaced by a smaller, more reasonable type,’ ‘it can effectively prevent the formation of burrs (redundant material pouring into joints), eliminating the removal operation of burrs,’ etc.
“First, I had to identify the reason why lower pressures can form cold shuts. What you cannot simulate on computer can be demonstrated by real materials on hand. Therefore, I had no choice but to do it through experimentation of real goods. What was finally clarified after repeated experiments was the fact that as aluminum was poured into a die, the temperature was dropping quicker than expected, forming what we call breaking chilled layer, or partially coagulated body which was blocking the flow of molten aluminum.”
Once the cause of a problem is pinpointed, a solution manifests itself. That is, to prevent the temperature of molten aluminum from dropping. The temperature was raised from 650°C to 670°C, the time from the start of pouring to the complete filling into the die was shortened from 10.7 to 5.4 seconds so as to fill it before the temperature drops, and also the pressure was set to half the traditional level, 46 MPa.
It was also a standard practice of die casting to pour the molten materials slowly so as not to generate bubbles, but it was speeded up double. For this purpose, the gas outlet was enlarged to facilitate the release of the air. It was possible because of the lower pressure method, and this is another breakthrough in the old-fashioned practice.
The realization of lower pressures revealed other merits than the aforementioned. The production speed was considerably accelerated, the splashing of molten aluminum under high pressures was diminished thus ensuring improved safety for operators, and, more than anything else, the production cost was literally reduced half.
“It was achieved not by my effort alone, but by all on the staff who seriously worked on halving the cost. We learned that in the conventional technology held as the industry’s standard, there are still small buds waiting to bloom. We were allowed to do anything we wanted in the development, but at the same time, not allowed to give it up (laughingly).”
They truly caused a revolution in the production law of aluminum die cast products.
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