Quality improvement, lead time reduction and cost reduction are major issues in the manufacturing of die mold industry. On the other hand, the complexity and diversification of product design has led to very high shape accuracy and surface quality requirements for die mold. In the die mold manufacturing, the skillful know-how necessary for hand finish work such as polishing and mold matching is being lost, while high quality and improvement of production efficiency are required.
The thermal displacement, which is the main cause of deterioration of machining accuracy. It is difficult to reduce thermal displacement and perform heavy cutting with high-speed spindle. Conventionally, there has been the spindle cooling technology which cooling oil is poured into the rotating spindle to directly cool the spindle. However, for this technology, it is the completely new spindle cooling technology that achieve the low cost structure and high cooling performance by efficiently cooling only the necessary parts.
Structure and Features
The spindle cooling structure of spindle device (20,000 min-1 specification) efficiently cooling only the most necessary front bearings (Fig. 1). The cooling oil is supplied from between the front bearing and motor. After cooling the front bearings, it is discharged from the tip of spindle.
High Precision
To machine the die mold with high precision, it is necessary to minimize the thermal displacement of the spindle and tools. In the general spindle device, the cooling of the spindle which is rotating body, is only heat dissipation to atmosphere, and the cooling effect is slight. The spindle and tools are cooled before operation (Fig. 2 (a)), but when operating, heat generate from bearings and motor is accumulated, resulting in thermal expansion (Fig. 2 (d)). So far, there is a technique of cooling the entire spindle to reduce thermal expansion (Fig. 2 (b)). By the way, the main spindle is supported by 5 bearings (4 bearings on the front side). Therefore, if the area around front bearing is cooled, the displacement of the tool tip can be effectively reduced (Fig. 2 (c)). The spindle thermally expands to the rear side regardless of the tool tip position. Therefore, it does not affect the machining accuracy. Based on this concept, we have developed the cooling structure with large thermal displacement reduction effect that intensively cool the area around the most necessary front bearings.
High Efficiency
To eliminate displacement during finish machining. Sufficient warm-up operation is required every time when machine is started, tools are changed, and the number of revolutions is changed. 10 or more tools are often used when manufacturing one mold, productivity reduction an d energy loss due to warm-up operation are enormous. According to our technology, as shown in Fig. 3, the time until the thermal displacement stabilizes can be significantly reduced. Therefore, the energy loss due to the warm-up operation can be minimized. By further applying the thermal displacement compensation system, the warm-up operation can be shortened to within 5 minutes.
Machining Ability
The new spindle cooling technology is used as the spindle device of our vertical machining center “MP-46V” for high precision parts and die mold machining (Fig. 4).
In order to improve the quality of die mold, reduce cost and shorten lead time, many items are required for machining centers for die mold machining. The new spindle structure is developed by repeating trial and error checking. The cooling circuit examination, the analysis of reliable delivery for coolant at high speed were experimented, manufactured and verified. Eventually, it was possible to make the simple spindle with high cooling efficiency. The performance of the “MP-46V” equipped with the new spindle cooling technology has significantly improved compare to the conventional model in all items (Table 1) (Fig. 5). The “MP-46V” for high-precision parts and die mold machining equipped with the new spindle cooling technology has been launched to the market and has been highly evaluated by customers.
Article by: Okuma Techno (Thailand) Ltd. & MEGA Tech