3-1 The Necessity of General Knowledge This chapter provides the necessary background information to enable the reader to understand punches and dies, the tooling used in bending. The main section of this chapter deals with general subjects, such as the requirements for good tooling, material, and the manufacturing process. Usually, operators recognize the importance of tooling knowledge, but only within the limits of their job. Some operators do not take much interest in the general subjects noted above, and some think it is unnecessary to learn the extensive process involved in tooling. However, the precision, material, and hardness of a punch and die are directly related to the precision of the product which the operator must achieve. The more they know about tooling, the better chance they will have to attain their objective. Go to Top
3-2 Requirements for Good Tooling The requirements for good tooling must be examined when judging the quality of a punch and die. Moreover, we must know how these requirements are related to our bending work. Generally speaking, the following are essential requirements for good tooling:
In summary, good tooling consists of a punch and die which provide ease of handling, a long service life, high accuracy, and interchangeability. (The relationship between the length of tooling and its replacement will be described in subsection 3-4.) Go to Top
3-3 Tooling Materials, Heat Treatment, and Manufacturing Process During the bending operation, the tooling undergoes repetitive loads such as compressive loads and bending moments. Given the fact that the tooling may perform 3,000 processes a day, the frequency of repetitive load application could total 70,000 to 80,000 times per month and 800,000 to 1,000,000 times per year. The strength and wear resistance of tooling to withstand such repetitive loads can only be obtained by using a quality material and proper heat treatment. There are two methods of heat treatment: "hardening" and "thermal refining." The terms "hardened tooling" or "thermally refined tooling" comes from these methods of heat treatment. Generally, if it is called bending tooling, it refers to either hardened tooling or thermally refined tooling. There is other tooling which is made of so-called raw material which is not heat-treated. In a strict sense, however, this should not be considered tooling because the steel used for tooling is only effective when it is heat-treated (though the quality of material must be suitable for heat treatment).
3-3-1 Hardened Tooling
As previously stated, the purpose of heat-treating tooling is to increase its wear resistance and strength against bending force. The material commonly used in hardened tooling is alloy tool steel, though it varies with the tool manufacturer. The paragraphs that follow will describe chromium molybdenum steel (type 4) and DM. (i) Chromium molybdenum steel, type 4 (SCM4)
Chromium molybdenum steel is one of the structural alloy steels. It is a pearlitic steel containing chromium steel and a small amount of molybdenum. This steel, which is suited for tooling material, features toughness (tenacity), great wear resistance and superior hardenability by heat treatment. This tooling material is either completely or locally hardened (= overall or local hardening*') to obtain HRC43 to 48. HRC indicates the Rockwell hardness C scale. The Rockwell hardness test is used to measure the hardness of mechanical parts in many job sites because it is a simple method of measurement.
(ii) DM DM is the trade name for "Yasuki Steel" made by Hitachi Metal. This tooling material is equivalent to JIS alloy tool steel, SKT4. However, it contains more nickel for greater toughness. Like chromium molybdenum steel, DM provides excellent toughness and wear resistance, and its hardening strain (the tendency of bending, warping, or twisting after being hardened) is less than that of other material. Therefore, while SCM4 is used in general tooling, DM is utilized specifically for tooling whose sectional shapes have a greater hardening strain* 2 . Its hardness is identical to that of SCM4. Table 3-1 compares the heat treatment of tooling materials.
*1. Local hardening and overall hardening: Local hardening means heat-treating only part of the tooling such as a punch tip and a die V groove. This does not produce much hardening strain and the portion requiring grinding is small. However, sufficient strength cannot be obtained in the essential part of the tooling (for example, in the part of a punch where the maximum bending moment acts). Amada's tooling is treated by )overall hardening. *2. Sectional shapes having a large hardening strain: This refers to the sectional shapes of a gooseneck punch, straight sword punch, sash punch, and sash die. Shapes with large relief, slender shapes, and shapes with great changes in thickness are subject to develop hardening strain.
(iii) Manufacturing process
Fig. 3-1 shows the manufacturing process of hardened tooling. Hardened tooling is generally manufactured in the order shown below.
Material => Primary forming => Hardening => Correcting => Finishing
The formed workpiece, which has been hardened, is corrected prior to finishing. Then the workpiece is finished by grinding with a grinding machine.
Finishing work can best be performed by "profile grinding." Photo 3-1 shows a 2V die being ground by profile grinding. As seen from the photo, the contour including the V-grooves (each consists of groove face, shoulder R, and groove bottom R) and surfaces are ground simultaneously when using profile grinding. The grinding wheel used in profile grinding is dressed with a diamond dresser and finished with high accuracy by a crushing roll (Fig. 3-2). The job of the crushing roll is to smooth any roughness on the grinding wheel after dressing. This enables the wheel to function property.
3-3-2 Thermally Refined Tooling (i) Purpose of thermal refining The purpose of thermal refining is to unify the internal structure of the tooling material so that it will remain operable during use. The difference between thermal refining and hardening is that the tempering temperature in thermal refining is higher than in hardening. As indicated in Table 3-1, there is no difference between the two in hardening temperature (thermal refining may be considered a type of hardening). Thermal refining increases wear resistance and strength in its own way. Carbon steel (S45C) is used as thermally refined tooling material. (ii) Application of thermal refining
In general, thermal refining is employed in the following cases: Large, hard-to-harden tooling (This is related to the size of the electric furnace.) Complicated sectional shape, hard-to-grind tooling (This is often the case with special tooling.) Long, one-piece, hard-to-grind tooling (This is related to the workable length of the grinding machine.)
In general, thermal refining is employed in the following cases:
The hardness of thermally refined tooling is lower than that of hardened tooling, and is somewhere between HRC23 and 28. HRC28 is generally the maximum hardness that is workable with a bit (toot used with a lathe, shaper, and planer).
(iii) Manufacturing process The manufacturing process of thermally refined tooling differs between large and small tooling. As shown below, large tooling is produced in the same process as hardened tooling.
Material => Primary forming => Refining => Correcting => Finishing
Small tooling is fabricated of already-refined material (commercially available) in the following process.
Refined material => Primary forming => finishing
The difference in the manufacturing process of large and small tooling originates from the "mass effect" of heat treatment on each type of material. Generally, when a thin steel bar or a thin steel sheet is heat-treated, the effect of heat treatment penetrates completely through it. In thick steel bars or sheets, however, the outer part can be heat-treated to the desired hardness, but the inner part is not sufficiently hardened. This is because the cooling speed of the outer part is different from that of the inner part. Thus, the inner part is less hard than the outer part. This phenomenon is the mass effect. Since large tooling requires much working, the inner part with less hardness is exposed as a result of machining. For this reason, it is preferred that the tooling be refined after primary forming. Thermally refined tooling is finished with a planer or a profiling planer. A slow machining speed and a small amount of cut-in provide a high-precision surface finish. When working a complicated curve or arc such as those found in special tooling, an accurate template (profiling plate) should be prepared. The material is profiled by using the template and profiling planer .
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3-4 Length of Tooling With regard to length, tooling used in bending can be divided into one-piece tooling and split type tooling. One-piece tooling is simple tooling made in conformance with the required bending length. Split type tooling is tooling that can be split into individual sections. The length of the tooling greatly influences the efficiency of bending work. Now, we will examine how the length of tooling influences job efficiency in connection with tooling replacement, which is frequently performed in bending. The frequency of tooling replacement in a given day is between 5 and 20 times, with 10 being the average. Tooling replacement involves a series of preliminary operations as shown below.
Carrying => Mounting => Aligning => Accuracy adjusting => Removing => Storing
Table 3-2 compares both types of tooling with respect to this series of operations. The reader will be able to easily determine which type of tooling is more efficient.
Next, let us focus on how the type of tooling influences bending accuracy. The primary factor that affects bending accuracy is the parallelism of the tooling (tooling height). A comparison of parallelism between one-piece tooling and split type tooling is shown in Fig. 3-3. The limit of the working accuracy that a planer can achieve is 0.05 mm per meter of tooling. It is 0.02 mm in grinding work. In this example, the working accuracy of the one-piece tooling is 0.1 mm for an overall length of two meters, while the split type tooling is 0.02 mm. Thus, the split type is five times more accurate than the one- piece type.
So far, we have seen how the length of tooling influences job efficiency and bending accuracy. From the above facts, the reader will readily discover that split type tooling is superior. Fig. 3-4 shows the length of each tooling that can be mounted on various Amada machines. The tooling is available in two lengths: L (Long size) and S (Short size). L size is 835 mm (32.87") and S size is 415 mm (16.34").
3-5 Sectional Shape of Tooling A long shape which has an identical cross section from end to end is characteristic of tooling. Therefore, it is important for operators to remember the sectional shape and size of individual tooling for more accurate and speedy performance. It may be difficult for operators to remember them all because there are so many types. Some hints will be provided to help the reader remember.
3-5-1 Punches Fig. 3-5 shows an example of a punch sectional shape. The sectional shape of a punch can be classified by (1) tip angle, (2) relief shape, and (3) installed height. 'These should be memorized.
(i) Tip angle There are punches with a tip angle of 30°, 45°, 60°, 88°, or 90°. Punches with a 30° or 45° tip are used for acute-angled bending, and those with 60°, 88°, and 90° tips are used for 90° bending. The punch tip for 90° bending has a "punch tip R," which corresponds to the "punch tip flat width" in the 30° and 45° punches. In Fig. 3-6, (a) illustrates a 90° punch and (b) the tip of an acute-angled punch.
(ii) Relief shape Punches have a "relief" necessary for various bending. The shape of the relief is determined by the shape of the product. The relief shapes of major punches are shown in Fig. 3-7. As shown, punches can be divided into two types. One type has a relief at the rear. The other type has relieves of one or different shapes at the front and rear. Punches (a), (b), and (c) belong to the first type and (d) and (e) belong to the latter type. In Fig. 3-7, (a) is a bottoming punch for 90' bending and is the most commonly used type; (b) is a punch for acute-angled bending or air bending; (c) is a gooseneck punch; (d) is used for products having a symmetric shape and is called a straight-sword punch; and (e) is a sash punch that is widely used in the sash industry.
(iii) Installed height The height of a punch refers to its installed height (see Fig. 3-5). In the case of the radius ruler (R punch) or the coining ruler, note that the height E of the punch holder plus the ruler's height is the installed height (Fig. 3-8). There are seven different installed height: 65, 67, 70, 90, 95, 104, and 105
3-5-2 Dies Fig. 3-9 shows an example of a die sectional shape. Dies are classified by (1) the shape of the groove and (2) the number of grooves. A die with one V-groove is called a IV die and a die with two V-grooves is called a 2V die. Further, a die with three rectangular grooves is called a 3U die.
(i) IV die The IV dies having one V-groove can be divided into two types. One type is for bending work over 4 mm in thickness and the other type is used for making sashes. The first type has "working relief*" on each bank of the V-groove, as shown in Fig. 3-10. The sash die does not have such relief. As indicated in Fig. 3-11(a), the sash die is installed to thg sash die 'holder and used in combination with the sash,h punch.
*The working relief reduces forming time of the die and improves the surface precision of the groove. (;generally, dies with a large V-width are provided with working relief, but small V width dies are not.
(ii) 2V die
This is a bottoming die that can bend a maximum sheet thickness of 3.2 mm. It has two different V-grooves that have different V-widths but have identical V-groove angles. The 2V die is installed to a die holder when it is used [Fig. 3-11(b)]. Like sash dies, it has no working relief in the V-groove.
(iii) 3U die
As shown in Fig. 3-12, the 3U die consists of three different rectangular grooves and one flat surface. The die is used for partial bending in combination with a 45' punch. It is directly attached to the lower beam without using a die holder.
3-6 Sectionalized Type The sectionalized type mentioned here is different from the split type tooling we have discussed in the previous subsections. Split type tooling is a general term. The name is a classification term indicating that split tooling is distinct from one-piece type tooling. The term "sectionalized type" indicates a die or punch that is split into small, specific sizes.
3-6-1 Sectionalized Punch Photo 3-3 shows an example of a sectionalized punch. The shape of the sectionalized punch coincides with those of the L and S sizes. Accordingly, if sectionalized punches are used in a line, various combinations of sizes, including the total length of the beam can be created according to the operating requirements. This method is effective in making box-shaped products. The sectionalized sizes are 10, 15, 20, 40, 50, 100, 200, and 300 mm. There are two types of the 100 mm punch; an overhang called a horn at the left end and the other has a horn at the right end. The shape of the horn is identical among all Amada standard punches. They are ideal for box + pan forming when a return flange is involved. Amada offers a variety of sectionalized punches enabling you to purchase only those which best suit your needs.
3-6-2 Sectionalized Die The sectionalized die is attached to the die holder on the rail, as shown in Fig. 3-13. The size of H conforms to the flange height of the workpiece that can be bent with the tooling. That is, H = 10 mm indicates bending work can be performed up to a flange height of 10 mm, and similarly, H = 40 mm up to a flange height of 40 mm. The sectionalized dies which have an H size of 10 mm can be utilized in a row because they are 26 mm or the same height as the L and S sized 2V dies. With regard to a sectionalized die with the flange height of 40 mm, it is necessary to prepare several units of the same die or make a 2V die with an installed height of 56 mm as special tooling. Sectionalized dies are divided into eight lengths: 10, 15, 20, 40, 50, 100, 200, and 400 mm.
3-7 Holder There are two methods of attaching the tooling to the machine. One type fixes the punch or die directly on the upper or lower beam. The other type locks them by using holders. When using tooling holders, attach the punch to the punch holder and the die to the die holder.
3-7-1 Punch Holder As shown in Fig. 3-8, the use of a punch holder permits the desired shape punch to be attached as necessary, just as radius rulers of different radii or coining rulers can be attached thereto.
3-7-2 Die Holder Two types of die holders are utilized according to the type of die. One type is the die holder used in the bending of sashes [Fig. 3-11(a)]. The other type is the die holder used with 2V dies [Fig. 3-11(b)]. The die holder must be selected in conformance with the shape of the product. A detailed description of die holder selection is provided in subsection 4.3.
3-7-3 Die Base The lack of bending stroke commonly occurs in cases where a IV die (type not for sashes) is used with a machine having a large open height. The die base (Fig. 3-14) is set under the IV die to increase die height. (For the open height of the machine and the die height, refer to subsection 4. 1