Table 2.1: Tolerances requirements for dies and moulds Fallböhmer et al., 1996
Average Dimensional Error mm
Average from Error mm
Injection Molds
0.020 0.015
Die Casting Dies
0.046 0.041
Stamping Dies
0.061 0.043
Forging Dies
0.028 0.023
These results were used to recommend machining practices with reduce the tolerance of product for improved surface finish quality and hence minimizing cycle time, thus
improving productivity. Basically finishing process is a critical part in industry to producing a product based on mould and die. According to Lee et al. 2006 the
requirements surface roughness in finishing process for plastic moulding is 0.1 µm or smaller than the value.
2.10 HIGH SPEED MACHINING
High speed machining HSM is not simply as high cutting speed, it should be regarded as a process where the operations are performed with very specific methods and
production equipment. According to Coromant 1994, the requirements high speed machining for die and mould which is:
Cutting data
Typical cutting data for solid carbide end mills with a TiC,N or TiAlN-coating in hardened steel: 48-58 HRC.
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Semi-finishing
True vc: 150-200 mmin, ap: 3-4 of the cutter diameter, ae: 20-40 of the cutter diameter, fz: 0,05-0,15 mmz
Finishing and super-finishing
True vc: 200-250 mmin, ap: 0,1-0,2 mm, ae: 0,1-0,2 mm, fz: 0,02-0,2 mmz
High speed machining process enable manufactures to reduce the time machining and to achieve a higher surface quality. According to Fallböhmer et al. 2000 machining of alloy
steel usually hardness more than 30 HRc will result the cost effective technology by using advance machining tools. In addition machining of alloys steel in hardened state at high
cutting speeds will leads to elimination of distortion and reduction of finishing operations, if the part is finish-machined after heat treatment, achievement of high metal removal
rates, Lower machining costs and improved surface integrity Tönshoff et al., 1986
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Figure 2.9: Explanation of chip formation during machining of hard steel König et al., 1993
The machining of hard material basically producing continuous chip formation is observed at conventional due to high cutting speeds and minimum to moderate of feed
rates, Figure 2.9 a. However, at maximum of feed rates “saw-tooth” chips are produced, figure 2.9 b K.Nakayama 1974. based on figure b, the chip pattern can cause cyclic
variations of both cutting and thrust forces and the result in high frequency vibrations that affect tool life and failure Davies et al., 1996. Recent study by Elbestawi et al. 1996
the fracture on surface of the work pieces spread inside the chip until the stress state is change from a low to high compressive stress region. Based on the findings by the
researchers discussed above it can be concluded that common chip type observed in hard part machining are continuous chip at low undeformed chip thickness and saw-tooth shape
at high undeformed chip thickness. The cutting edge is dependent to a high frequency force variations and also the chip formation absolutely affects the cutting forces.
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2.11 RESEARCH GAP
