Watch a comparison of the semi-dry process and a conventional process.
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On the engine machining line, parts cast at the materials plant go through a variety of machining processes such as surface milling and drilling, which consume an enormous amount of energy and resources.
With the introduction of the semi-dry process, which substantially reduces waste and power consumption, Mazda has realized machining processes with a 'low environmental impact.'
In conventional machining processes, a huge amount of water-based coolant is used to cool and lubricate cutting tools and remove and collect the swarf (waste metal). A pump is also required to discharge the coolant and this consumes a significant amount of power. A further problem is disposal of all the waste coolant. Reducing the amount of coolant is a huge challenge and an important issue for environmentally-friendly operations.
The semi-dry process minimizes the amount of coolant required for machining processes. It also substantially reduces the amount of contaminated waste liquid generated on machining lines, and improves quality.
Key technologies employed to realize coolant-free machining are described below:
- (1) Cooling (ensuring accuracy)
- (2) Cutting tool lubrication
- (3) Swarf removal
(1) Cooling (technology that ensures accurate machining)
This technology ensures accurate machining without the use of coolant to control temperatures. In one machining process, a drill guide bushing is used to align two holes for drilling with an accuracy of ±3.5 microns. Since the coefficients of thermal expansion of the iron jig and aluminum work piece are different, conventional machining cannot ensure the required accuracy without using a coolant to control the temperature.
To overcome this problem, Mazda developed an autonomous adjustment mechanism which ensures the relative positions of the work piece and jig do not change even upon thermal expansion.
The system also achieves greater accuracy by:
- 1) matching the coefficients of thermal expansion by using an aluminum jig to fasten the guide bushing.
- 2) redesigning the shape of the jig to ensure the direction of deformation is the same.
- 3) employing a floating clamp that follows the displacement of the jig.
(2) Cutting tool lubrication technology
To replace the coolant and lubricate the cutting edge, we employed a system that delivers a tiny quantity of atomized biodegradable oil in a jet of air. Used oil is generally disposed of, but Mazda also introduced a collection and recycling system. However, when the oil is collected, it inevitably becomes mixed with other oils, such as machine lubricating oil. To enable recycling we developed a special oil, in collaboration with a grease manufacturer, that can be used for both purposes.
(3) Swarf removal technology
To ensure efficient machining of holes, high pressure coolant is conventionally delivered from the tip (cutting edge) of drill bits. It also functions to wash away waste metal. To ensure an equivalent efficiency of swarf removal without the coolant, we redesigned the shape of the cutting edges and optimized cutting conditions.
The figure below shows a comparison of power consumption under conventional and optimized conditions. Under the optimized conditions, the waveform is more stable and the process time is shorter since energy is more efficiently applied. In addition, the need to cool the cutting edge is eliminated because heating effects are reduced with such a short process time.
1) The adoption of the semi-dry system for 90 percent of processes resulted in an 84 percent reduction in the amount of coolant required.
2) Mazda has reduced electricity consumption by 40 percent on its machining lines. Two-thirds of the reduction is derived from the semi-dry process.
3) By recycling oil used for cutting and lubrication, the volume of oil-based waste liquid has been reduced.
The total amount of waste liquid produced by the machining lines has been cut by 80 percent.