Cú đấm thường có thể cần phải được thực hiện nhỏ hơn kích thước yêu cầu của lỗ, như mở thường đóng cửa vào hồi của nó. Khoảng 0,001 inch (0,03 mm) cho mỗi giảm đường kính trong đục lỗ kích thước được khuyến khích. Trong trường hợp các cạnh thô của việc mở đấm thu được, một hoạt động cạo râu có thể là cần thiết. Đôi khi một phương pháp loại bỏ các vật liệu thay thế nên được lựa chọn để làm giảm bớt một vấn đề | BLANKING AND PIERCING OPERATIONS BLANKING AND PIERCING OPERATIONS 287 PUNCHING AFTERWARDS WITH THIS TOOL WILL PRODUCE A LOOSE CHIP SHEET METAL MATERIAL FIGURE 6-42 Chips within the die. The punch may often need to be made slightly smaller than the required size of the hole as the opening often closes up on its retrieval. Approximately in. mm per diameter reduction in punch size is advisable. Where rough edges of the punched opening are obtained a shaving operation may be needed. Sometimes an alternative material-removing method should be chosen to alleviate such a problem. Downloaded from Digital Engineering Library @ McGraw-Hill Copyright 2004 The McGraw-Hill Companies. All rights reserved. Any Use is subject to the Terms of Use as given at the website. BLANKING AND PIERCING OPERATIONS Downloaded from Digital Engineering Library @ McGraw-Hill Copyright 2004 The McGraw-Hill Companies. All rights reserved. Any Use is subject to the Terms of Use as given at the website. Source HANDBOOK OF DIE DESIGN __CHAPTER 7 BLANK CALCULATION OR FLAT LAYOUT 7-1 THE IMPORTANCE OF FLAT LAYOUT OR BLANK LAYOUT The importance of an accurate flat layout has been stressed throughout the preceding text. In die work and any sheet-metal work in general the importance of an accurate and dimensionally correct flat layout cannot be overemphasized. Many problems may be avoided if a full-sized or scaled layout is made first and the part s manufacture is evaluated on the basis of it instead of referring to the bent-up drawing which after all may or may not be manufacturable. 7-1-1 Flat Layout Development and Calculation When making a flat layout of a complex part it always helps to start from a certain side one that seems to be basic or the most complex and unfold the remaining portions bend after bend. A bracket shown in Fig. 7-1 is simple enough to serve as an example of the unfolding technique. First the A .
