Seoul 2000 FISITA World Automotive Congress F2000G284 June 12-15, 2000, Seoul, Korea

Development of Alloy Cast Iron for Press Die

Masahiro Shinabe1) * Norihiko Nakagawa2) Toru Kato3) Eiji Nakade4) Jun Ogawa5) Tomohiro Matsumoto6)

1)2)3)4)5)Toyota Motor Corporation, 1 Motomachi Toyota-shi Aichi-ken, Japan 6)Kogi Corporation, 1-5-8 Nagata-ku Kobe-shi Hyogo-ken, Japan

This paper describes the development of alloy cast iron that can be used for the cutting edges of the trimming die of a press die. Usually, a block of tool steel or steel casting is inserted at the cutting edge of the trimming die of a press die. However, we unified the structure part and the cutting-edge part of a press die with alloy cast iron. As it can't bear as the cutting edge in this state, the cutting edge is processed by flame-hardening. After the flame-hardening, we developed the alloy cast iron so that enough hardness may be obtained by natural air-cooling. Thereby, the machining of the installation seat of the cutting edge decreased and the expense of dies has been reduced.

Keywords: Press Die, Alloy Cast Iron, Flame-hardening

INTRODUCTION EXPERIMENT

As customer preference diversifies, the number of vehicle A new alloy cast iron was designed to allow every operator models and the frequency of their revision are increasing. to consistently and easily perform hardening during die Conversely, total production is not growing as much, manufacture to obtain cutting edges whose characteristics making the volume per model shrink. Meanwhile, the ever- match those of tool steel, and hard-faced edges. changing market trend requires punctual response with appealing models. As a result, the plan and design of PLAN stamping dies for auto-manufacturing are faced with major challenges: The expenses on dies should be reduced to The following three objectives were required: prevent the growth of die-related cost per model, while the process of die production needs to be accelerated for shorter lead time. In view of the above, we looked into the 1.Hardenability possibility of a simpler die construction. In the � The alloy cast iron should be 50 HRC or harder by conventional construction, the cutting edges of a trimming die are made of tool steel or hard-facing, as Figure 1(a). natural air-cooling after flame-hardening. In the new construction, a trimming die including the � Penetration should be 2.5 mm or deeper in order for cutting edges is made of alloy cast iron, only the part of the cast iron to be usable as cutting edges. the cutting edge is processed by flame-hardening. The construction of the new cutting edge is shown in Figure 2.Weldability 1(b). The following is a report on a newly developed alloy � The new alloy cast iron should be as easily weldable cast iron, which is a key to the proposed die construction, as the conventional cast iron to enable easy on-site as well as its record of use and advantages. servicing. Upper die Tool steel Upper die 3.Impact resistance FC250 Flame-hardening Alloy cast or FC300 � The alloy cast iron should have an improved impact iron resistance to reduce chipping when used as cutting Lower die edges. Alloy cast Basic design Lower die iron FCD540 Hard-facing Flame-hardening In the new cast iron, graphite was precipitated in spherical forms, considering the high weldability and impact resistance necessary for use as cutting edges. In addition, (a) Conventional (b) New the composition included Cu, Ni and Mo to achieve the FCD540,FC250 and FC300 are provided by Japanese Industrial Standard. required hardness from flame-hardening. To attain high FCD540 is ductile cast iron which has more than 540MPa tensile strength. weldability and impact resistance combined with good FC250 is cast iron which has more than 250MPa tensile strength. hardenability, which is generally incompatible with the FC300 is cast iron which has more than 300MPa tensile strength. former, the chemical composition of the material, which Figure 1 - Cutting Edge Construction contained over 50% high-quality ductile pigs, was fine- tuned, and the casting plan was optimized to refine and uniformly distribute the graphite particles.

* Author. e-mail: [email protected]

1 DEVELOPED ALLOY CAST IRON Tensile Strength (MPa) 638 Table 1 shows the chemical composition of the alloy cast Alloy Cast Iron iron. Figure 2 is a microphotograph showing the FCD540 microstructure of the alloy cast iron. As can be seen in the 540 Charpy photograph, the alloy cast iron exhibits a fine pearlite Elongation 5.5 Absorbed structure. The graphite particles are refined to about 50 (%) μ m in diameter and spheroidized to more than 80%, 3.3 2.1 Energy presumably assuring sufficient toughness for use as cutting 2.0 (J ) edges.

Table 1 - Chemical Composition of Alloy Cast Iron <30 180 Chemical Composition(Wt%) 210 55 CSiMnPSMgCuNiMo Hardness (HB) Flame-Hardened 3.60 2.00 0.60 0.05 0.01 0.03 0.50 0.30 0.30 Hardness (HRC)

Fig 3 - Mechanical Properties Fig.3 Mechanical Properties

Graphite (80μm) 60 50 Pearlite 40 30 20 10 Ferrite Hardness(HRC) 0

00.5 11.522.53 depth from surface （mm）

Fig.4Fig Hardenability 4 - Hardenability of of the the Alloy Alloy CastCast IronIron Conventional cast iron (FCD540)

Graphite (50μm) machining Liquid Penetrate Test weld overlay

Pearlite

Welding material is hard-facing type. Ferrite Chemical composition of welding material: C:0.26wt% Si:0.33wt% Mn:1.43wt% Cr:11.05wt%

FigFig.5 5 - Weldability Weldability Test Test Procedure Procedure Developed alloy cast iron

Fig 2 - Photograph of the Edge on the Lower Die Figure 3 shows the mechanical properties of the alloy cast iron. It outperformed the reference FCD540 in all the test items. Weld overlay

Evaluation of hardenability crack

Figure 4 shows the hardenability of the alloy cast iron when tested as flame-hardened. The alloy cast iron had a hardness of 50 HRC to a depth of about 2.5 mm.

Evaluation of weldability crack Figure 5 shows the weldability test procedure. Figure 6 is a photograph showing the specimen after a liquid penetrate test. The photographed specimen exhibits Fig.6Fig 6 -Result Result ofof LiquidLiquid Penetrate Penetrant Test test

2 no cracking due to welding, probably because the RESULT expandability of the alloy cast iron was increased by the use of ductile pigs, and the graphite particles were highly refined. RECORD OF USE Evaluation of durability The alloy cast iron was put into practice for production in Figure 7 shows the test conditions for the durability of 1996. A preceding tryout for use as cutting edges started in the alloy cast iron when used as cutting edges. The 1995 in one set of dies. During the three and a half years upper and lower dies were furnished with cutting of tryout with 700,000 works, the tryout dies did not pose edges of the alloy cast iron, and examined for wear of any major trouble. the edges and the height of burrs on works after 300,000 cycles. Figure 8 is a photograph showing the edge of the lower die as it was worn. The degree of When progressing from the tryout, application was initially wear changed little after about 90,000 cycles, limited to models with a monthly production volume of presumably because the alloy composition and the 5,000 units or less, works with a thickness of 1 mm or less, refined graphite helped increase the toughness and and installation primarily on cutting edges, with some expandability. Figure 9 shows the height of burrs on exceptions in bending and drawing dies. These restrictions works. The maximum burr height after 300,000 cycles reflected the results of the foregoing durability test. While was about 0.03 mm, less than the maximum corporate operation under these conditions continued, the dies were standard of 0.08 mm, suggesting that the cutting edges evaluated and users' comments were sought. This year, were automatically refaced as they wore. based on the results of the research the limit on the production volume has been eliminated, and the scope of application has been significantly expanded.

Test method: Shearing test Feed Upper Die Test pieces: Alloy Cast Iron EXAMPLES OF APPLICATIONS OF ALLOY Heat treatment: Work CAST IRON TO DIES Flame-hardening Lower Work: Feed Pitch Figure 10 (a) and (b) show upper dies using the alloy cast iron and the conventional construction, designed for use in Tensile Strength 340MPa 7mm Test Piece Thickness: 0.75mm the same process for the same part. In the former, the outer （5×10×50mm） cutting edge, scrap cutter and piercing edges are integrated FigFig.7 The7 - Test Test Conditions Conditions for for Durability Durabilit y with the die block

0 cycle 10,000 cycles Piercing Edge Scrap Cutter

Cutting Edge

30,000 cycles 90,000 ˜ 300,000 cycles

Fig.8Fig 8 -Photograph Photograph of of the the Edge Edge on on the the Lower Lower Die Die (a) Alloy Cast Iron : New Construction

0.14 Work

0.12 Burr Height 0.1 Piercing Edge Allowable Limit (Tool Steel) 0.08 0.06 Scrap Cutter Cutting Edge Alloy Cast Iron 0.04 (Tool Steel) (Casting Steel) Burr Height(mm) Burr 0.02

0 0 5 10 15 20 25 30 Times(X10,000) (b) Tool Steel etc. : Conventional Construction Fig 9 - Height of Burrs on Works Fig 10 - Example of Application for Upper Die Fig.9 The Height of Burrs on Works

3 ADVANTAGES OF ALLOY CAST IRON

The alloy cast iron enables the die block to be manufactured in an integrated form, helping dramatically simplify the die construction. The following are specific advantages:

1. Expenses on the procurement and processing of tool steel (or cast steel) edges are saved.

2. Die blocks require no mounting face or bolting holes for installation of separate tool steel (or cast steel) edges and no hard-facing or finishing process.

3. Installation and adjustment of tool steel (or cast steel) edges are unnecessary.

CONCLUSION

The developed alloy cast iron helped simplify the die construction, thus reducing the cost of dies and the die manufacture time. For future prospects, we will continue to examine the tryout dies to prepare for a larger scale application to bending and drawing dies, seek a procedure for improved surface hardening and to further develop cast iron.

REFERENCES

[1]Noguchi,1989.Development of Flame-hardening Cast Iron for Press Dies: Toyota Engineering Society, Vol.38,No.1,pp.20-27. [2] H.Nakae,1995.Casting Engineering:Sangyo-Tosyo. [3]M.Megro A Suzuki 1983 Some Properties of Spheroidal Graphite Cast Iron Produced from High Purity Foundry Pig Iron:Casting,103th,p.15 [4]K.Nabekura,H.Fukazawa,etc,1979.A Study on the Weld-Heat Affected Structure of Spheroidal Graphite Cast Iron:Casting,96th,p.47 [5]T.Shiota,S.Komatsu,1979.The Influence of Graphite Size on the Impact Characteristics of Pearlitic Spheroidal Graphite Cast Iron:Casting,96th,p.41

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