McGraw-Hill Machining and Metalworking Handbook 3rd ed - R. Walsh_ D. Cormier (McGraw-Hill_ 2006) Episode 9 pdf

The basic die set consisting of top and bottom plates (die shoe), guide- posts, and guide bushings plus an optional top shank may be ordered in many different styles and sizes from suppliers such as Danly or Dieco and others. Photographs and illustrations of typical standard and special die sets are shown in other subsections. 8.3.3 EDM mold making (ram EDM) Molds that are machined from tool steels are presently being made using ram EDM machines. In this process, the cavity of the mold is produced in a positive shape from a carbon-type material. This form, or “positive,” is then used in the ram EDM process to machine the cav- ity of the mold by the electric-discharge process. The ram, or electrode (positive form), is placed under a cutting/cooling fluid with the tool- steel mold block and is moved downward into the tool steel block as the electric-discharge cutting operation progresses. A hollow or cavity with the exact shape of the ram or electrode thus is produced to great accuracy with a fine surface finish on the tool-steel mold block. Molds or dies are produced with this method for manufacturing plastic parts (injection or compression molding process), as well as for die casting and powder-metal processing. Large amounts of material are machined accurately at a relatively rapid rate in the newer ram EDM process. When the mold cavities have been cut, the die or mold maker must polish the mold and add gates, ejec- tors, and other requirements to complete the final mold assembly. The P-type special-purpose tool steels usually are selected for production of molds for plastic parts, whereas other types of tool steels are selected for die-casting dies, permanent steel molds, and powder-metal dies. 8.3.4 Samples of dies, drawings, and stamped or blanked parts A typical high-quality die set is shown in Fig. 8.9. This is a heavy- duty, long-production-run type of stamping die for producing heavy- gauge cold-rolled steel parts. The male and female die element tool-steel materials were selected and heat treated with great care and assembled accurately by the die maker. The tool-steel die ele- ments were cut on the wire EDM machine using a sophisticated CNC program designed by the tool engineering department. The CNC pro- gram was then loaded into the EDM machine’s controller and the dies accurately cut, with the tool-steel die elements having been heat treated previously. Tooling, Die Making, Molds, Jigs, and Fixtures 559 Walsh CH08 8/30/05 10:04 PM Page 559 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Tooling, Die Making, Molds, Jigs, and Fixtures Figure 8.10 shows another finished die set with its required pro- tective shield surrounding the die. Industry regulations call for protective shields on dies where an operator may accidentally come into hand contact with the moving parts of the die during the blanking, punching, forming, or drawing operations. The design and addition of the protective die shields are an important part of die design today and are necessary for worker safety. Figure 8.11 shows two typical blanked parts. The upper part in the figure is made of a low-strength aluminum alloy (3003-H14), and the 50 percent cut or burnished section can be seen over the shear-fractured section. The part below is made of C-1018 cold- rolled steel, and a double cut or burnish is evident. The double cut alternating between the shear-fractured areas is characteristic of a close die clearance per side of 1 to 2 percent of the total stock thick- ness. This type of blanked edge may not be suitable for certain types of applications, and a secondary operation such as shaving may be required to finish the part edges. In Sec. 8.5.1 figures will be presented for calculating the tonnage required on the press for stamping parts. To calculate the tonnage requirements, we must know the perimeter of the part in linear 560 Chapter Eight Figure 8.9 A typical high-quality blanking die set. Walsh CH08 8/30/05 10:04 PM Page 560 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Tooling, Die Making, Molds, Jigs, and Fixtures Tooling, Die Making, Molds, Jigs, and Fixtures 561 Figure 8.10 Finished die set with required hand protection shield (clear Lexan plastic). Figure 8.11 Typical blanked parts, edge characteristics. Walsh CH08 8/30/05 10:04 PM Page 561 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Tooling, Die Making, Molds, Jigs, and Fixtures inches or millimeters. Figure 8.12 shows a measuring tool used to determine the perimeter of irregularly shaped parts. This tool is sometimes called a map measuring tool. To use the tool, the scale is zeroed, and the small wheel at the end of the tool is placed at a starting point on the perimeter of the part to be measured. Trac- ing the tool around the perimeter of the part by rolling the wheel on the part outline will give a direct scale measurement in inches or millimeters on the dial of the tool. From this measurement, the ton- nage requirements may be calculated using procedures shown in a later section. The modern die-making and design processes use CNC and com- puter programs not only to control the EDM machines but also to produce the die drawings. A computer-generated drawing is possible using the various computer-aided design (CAD) systems available today. The CAD program sends the output information for the draw- ing to a plotter or laser printer, where a clean, neat drawing is pro- duced. Figure 8.13 presents an example of a CAD drawing produced by a modern tool and die design and engineering department. 8.3.5 Steel-rule dies Steel-rule dies make use of low-cost materials and are employed in many industrial applications. These are single-element tools that consist of a steel-rule cutting section only. Printers rule or similar steel strip is employed and bent to the shape of the part to be punched or cut. The sharp edges of the steel-rule members are operated against a flat metal platen or a hard wood or plastic block and produce the blanked part by a cutting or cleaving action. Steel-rule dies are used to blank paper, cardboard, fiber, rubber, felt, leather, and similar materials (gaskets are a good example). 562 Chapter Eight Figure 8.12 Linear measuring device. Walsh CH08 8/30/05 10:04 PM Page 562 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Tooling, Die Making, Molds, Jigs, and Fixtures Figure 8.14 shows an exploded view of steel-rule die construction. The steel rules that do the actual cutting should be hardened to Rockwell C 52 to C 55, although this high a hardness may not be required for some materials. The stripper portion of the die is usually 0.312 to 0.375 in thick, extending slightly above the height of the steel-rule cutters, and is made of neoprene, cork sheet, or rubber. Tooling, Die Making, Molds, Jigs, and Fixtures 563 Figure 8.13 Typical CAD drawing of a die set. Walsh CH08 8/30/05 10:04 PM Page 563 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Tooling, Die Making, Molds, Jigs, and Fixtures 8.4 Die Clearances and Stamping Data Figure 8.15 shows the different types of edges produced on punched and blanked parts with different die clearances. This figure is typ- ical of the low-carbon steels, which are used frequently for many types of die-stamped, pierced, or blanked parts. 564 Chapter Eight Figure 8.14 Typical steel-rule die. Walsh CH08 8/30/05 10:04 PM Page 564 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Tooling, Die Making, Molds, Jigs, and Fixtures 565 Figure 8.15 Edge characteristics. Walsh CH08 8/30/05 10:04 PM Page 565 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Tooling, Die Making, Molds, Jigs, and Fixtures Figure 8.16 shows samples of typical slugs produced in the pierc- ing or punching of hard copper (ETP 110, hard drawn). The figure clearly shows the effect of die clearance and the characteristic edges produced by the cutting (burnishing) and shear-fracture actions. (The cut or burnished section is indicated by a and the shear-fracture section by b in the figure.) These slugs are typical of type 1 and type 2 edges, as shown in Fig. 8.15. Figure 8.17 gives punch-to-die clearances for piercing or blanking various metals and alloys to produce the five types of edge character- istics shown in Fig. 8.15. Clearances shown in Fig. 8.17 are based on data published on piercing by Danly Machine Corporation and on blanking by the American Society of Tool and Manufacturing Engineers (ASTME). The tabular die-clearance data shown in Fig. 8.17 are given per side as a percentage of the stock thickness. For example, if we were punching stainless steel whose stock thickness was 0.050 in and we desired a type 3 edge, the total die clearance would be 0.05 ϫ (0.09 to 0.11) ϫ 2 ϭ 0.009 to 0.011 in in total die clearance, or 0.0045 to 0.0055 in in clearance per side. Another method that has been used for many years in industry for die clearances is outlined below. Die Clearances per Side as a Percentage of Stock Thickness (Group Method) Clearance per side, Material group percent of stock thickness t Group 1: 1100 and 5052 aluminum alloys (all tempers); 3003-0; etc. 4.5% t Group 2: 2024 and 6061 aluminum alloys (all tempers); brass (all tempers); cold- rolled steel, soft; stainless steel, soft; copper, soft; BeCu, soft 6.0% t Group 3: Cold-rolled steel, half hard; stain- less steel, half hard and full hard; copper, hard 7.5% t Group 4: Nonmetallic materials (general) 1.25% t Note: Angular side clearance (one side) ϭ 0.5 to 2 percent. Angular side clear- ance is cut below the die straight (see previous data for die-straight heights or thicknesses). 8.4.1 Calculation of punch dimensions Punch dimensions may be estimated from the following: When the diameter of a pierced round hole is equal to the stock thickness, the 566 Chapter Eight Walsh CH08 8/30/05 10:04 PM Page 566 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Tooling, Die Making, Molds, Jigs, and Fixtures unit compressive stress on the punch is four times the unit shear stress on the cut area of the stock from the equation where S c ϭ unit compressive stress on the punch, psi S s ϭ unit shear stress on the stock, psi t ϭ stock thickness, in d ϭ diameter of punched hole, in The diameters of most punched holes are greater than stock thick- ness, and a value for the ratio d/t of 1.1 is recommended. The maxi- mum allowable length of a punch can be calculated from the following equation: where d/t ϭ 1.1 or higher E ϭ modulus of elasticity of the punch material, psi Other terms were defined previously. The punching of holes with diameters less than stock thickness is generally achieved by using high-compressive-strength tool steels, guided punches, greater than average die clearances, shear added L dEd St s = π 8 1 4 = St Sd s c Tooling, Die Making, Molds, Jigs, and Fixtures 567 Figure 8.16 Typical die-punched slugs. Walsh CH08 8/30/05 10:04 PM Page 567 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Tooling, Die Making, Molds, Jigs, and Fixtures Figure 8.17 Die clearances for piercing of various metals and alloys (for five types of edge charac- teristics as shown in Fig. 8.15). 568 Walsh CH08 8/30/05 10:04 PM Page 568 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Tooling, Die Making, Molds, Jigs, and Fixtures [...]... identified as follows: a: Round series, back-post AS-31 b: Round series, center-post AS-32 c: Four-post series AS-37 d: Diagonal-post AS-35 e: Long, narrow series, two-post AS-41 and three-post AS-42 In Fig 8. 19, the die sets are identified as follows: a: Four-post series AS-67 b: Two-post AS-63 c: Demountable two-post AS- 39 or four-post AS-40 The top and bottom plates of a die set are called the top... Jigs, and Fixtures 593 Figure 8.32 (Continued) Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Walsh CH08 8/30/05 10:05 PM Page 594 Tooling, Die Making, Molds, Jigs, and Fixtures 594 Chapter Eight Figure 8.32 (Continued) Downloaded... Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Walsh CH08 8/30/05 10:05 PM Page 581 Tooling, Die Making, Molds, Jigs, and Fixtures Tooling, Die Making, Molds, Jigs, and Fixtures 581 Figure 8.26 Die-punched mild-carbon-steel part A simple progressive punching and blanking... is removed The harder the material, the greater is the amount of springback on the workpiece Quarter-hard cold-rolled steel will exhibit approximately 1° to 2° of springback, half-hard has approximately 3° to 4°, hard steels have more than 5°, and annealed spring steels Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies... Walsh CH08 8/30/05 10:05 PM Page 590 Tooling, Die Making, Molds, Jigs, and Fixtures 590 Chapter Eight Figure 8.31 Tooling plastics Epoxies are used for capped forming tools, metal-bonding tools, vacuum-forming tools, molding dies, and all plastic impact tools Drawing dies having a metallic core and capped with a working face of epoxy are used in the appliance, automotive, and aerospace industries Epoxy... cycloaliphatic resins, which are two-part epoxy systems Cycloaliphatic resins (epoxies) are now used widely for electrical insulators and support details and structures for live current-carrying parts in medium- and high-voltage applications in the switchgear industry In effect, epoxy materials are molded in specially formulated epoxy molds Special release agents are required to separate the cast epoxy part... was deburred by tumbling ■ Silver plating was then applied to the finished part Typical examples of punched, blanked, and formed sheet metal parts are shown in Figs 8.25 and 8.26 Figure 8.25 shows a stainless steel sheet metal part that required spring action The material selected for this application was AISI 301 spring-temper stainless steel This part was preslit to proper width, shear-cut to length,... 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Walsh CH08 8/30/05 10:04 PM Page 571 Figure 8. 19 Danly die sets, types Tooling, Die Making, Molds, Jigs, and Fixtures 571 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use... purchased to these gauge equivalents, and tools and dies are designed for this standard gauging system Manufacturers’ standard gauges for steel sheets 8.6 Bending, Forming, and Progressive Die Operations and Data Bending and forming dies are used to shape sheet metal parts by the action of bending or drawing the metal Of concern to the die designer are allowable inside bend radii for various materials and. .. Jigs, and Fixtures 587 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Walsh CH08 8/30/05 10:05 PM Page 588 Figure 8.30 (Continued) Tooling, Die Making, Molds, Jigs, and Fixtures 588 Downloaded from Digital Engineering Library @ McGraw-Hill . presents an example of a CAD drawing produced by a modern tool and die design and engineering department. 8.3.5 Steel-rule dies Steel-rule dies make use of low-cost materials and are employed. computer-aided design (CAD) systems available today. The CAD program sends the output information for the draw- ing to a plotter or laser printer, where a clean, neat drawing is pro- duced. Figure. either plain or ball-bearing types. Guide pins and guide bushings are produced in various diameters and lengths, which must be determined by the design of the die set and the press used for the die