Induction Coil Design to Enhance Heating Performance on Curve-Shaped Mold Surface Using Magnetic Shielding Materials

Abstract

[[abstract]]模具溫度是影響射出成形品質的一項重要參數，高的模具溫度設定有助於熔膠的模內充填及成形品質 的提升，卻也造成冷卻時間的大幅增加。高週波感應加熱具有高加熱效率、環保綠能等優點，是應用 於射出成形模面快速升溫的一項重要技術。感應加熱係利用感應線圈產生之磁場對模具表面進行感應 加熱，但感應加熱中相鄰線圈的電流方向相反時會造成磁場相斥的鄰近效應，易造加熱效率的大幅下 降及區域加熱溫度不均，因此如何有效地控制感應線圈之磁場均勻分布就顯得格外重要。影響模具表 面感應加熱性能（主要是升溫效率、均溫性及耗能）的關聯因子有：(1) 受加熱件的模具材料、模仁/ 模穴表面形狀；(2) 感應電流頻率、加熱距離；(3) 感應線圈形式、位置；(4) 磁屏蔽技術的運用等。 其中，以感應線圈的設計與製作及磁屏蔽技術的運用為技術的重點，由於不同型式的線圈在加熱速率 與模面溫差等品質指標上會有明顯的差異，尤其應用在曲面形狀的模面溫度控制時，如何保持小的模 面溫差控制的品質，須在感應線圈的設計與製作上著手。而感應磁場本身若線圈電流方向相反將會產 生磁場相斥的鄰近效應，導致溫度的不均勻分佈，增加線圈設計之困難及加熱效能的降低。目前解決 磁場分布不均的做法皆以加裝磁場集中器的方式進行磁場分布控制，而磁場集中器的主要功用為局部 增加磁場大小，但對於線圈電流方向所導致磁場相互抵銷時，卻無法有效的改善，導致感應加熱的效 能降低。因此，本「使用磁屏蔽材料於曲形模面快速加熱之感應線圈設計」，擬運用磁屏蔽材料區隔 相斥磁場之方式配合感應線圈設計進行感應加熱改善，增進感應加熱之效能及溫度均勻性，尤其探討 使用磁屏蔽方式對對曲形模面感應加熱的升溫速率、均溫性及耗能等重要性質的影響。[[abstract]]Mold temperature plays a significant role to the quality of injection molding process. A high mold temperature setting is feasible to enhance the molding quality but prolongs the cooling time. Use of induction heating to heat the mold surface only has advantages of rapid heating and cooling, good controllability, energy saving, and allowing local heating, seems to provide a feasible solution without scarifying the molding cycle. Still, there exist some problems to be resolved in induction heating such as proximity effect. Proximity appears as two nearby coils with inverse current directions to cause significant decrease of heating efficiency. Further non-uniform heating occurs. Factor that affects the performance of induction heating such as heating rate, temperature uniformity, and energy consumption includes: (1) material property and curvature of processed workpiece; (2) currency frequency and heating distance; (3) type and position of induction coil; (4) use of magnetic shielding method. To assure the temperature uniformity of induction heating, especially applying to curve-shaped mold surface, coil design and use of magnetic shielding method becomes critical. Therefore, this study proposes a novel magnetic shielding induction heating method by employing ferrite materials to enhance both the heat efficiency and uniformity of induction coil. The performance of proposed using magnetic shielding technique is evaluated and compared with conventional magnetic concentrator to depict the proposed method being applicable to efficiently eliminate the influence of proximity effect, especially on curve-shaped processed workpiece.[[note]]NSC102-2221-E327-00