| 摘要 |
PURPOSE:To manufacture an upper plate for a speaker which has superior cm magnetic performance by using a bar material of iron containing less carbon by employing a forging method. CONSTITUTION:A plastic bar material 6 iron containing less carbon is cut to obtain a discoid raw material 7. The raw material 7 is placed in a die 9 which has a die hole 8 conforming to the external circumference shape of an upper plate for a speaker and cold forging is carried out with a press hammer 10 to obtain a discoid intermediate product 11. At the surface center part of this intermediate product 11, a recess 13 is formed with a press hammer 12 and after this product is turned over, a similar recess 14 is formed on its reverse side. Then, the center part is punched with a punch 15 to form a center hole 16, thus obtaining a product. Consequently, the upper plate for the speaker which has superior magnetic performance is obtained by using a material which contains less carbon. |
