In machining process, the common parameters that affect the surface roughness are cutting speed, feed rate, and type of lubricant, depth of cut and width of cut. Based on Liao et al.
2007, the milling parameters of feed rate and lubricating method have significant affected on quality of surface roughness and they discover that the quality of surface
roughness increased by increased the feed rate. There are several factors that contradict the feed rate in affecting the surface roughness where high cutting speed will reduced the
value of surface roughness. The previous research by Ozcelik and Bayramoglu 2006, the cutting parameter is the important part in producing a minimum surface roughness and
long tool life. the minimum surface roughness was obtained when the cutting parameters was set at the lowest of feed rate and highest of cutting speed Özel et al., 2007. The
differences of machining process parameters will impact the quality and specifications of the products surface. At the same time the result of the higher surface roughness can affect
the product performance in terms of friction, durability, operating noise, and energy consumption.
2.8 SURFACE FINISH PARAMETERS
Basically the surface parameter is used to determine the average surface finish. The surface finish may specify in several of machining operations. One of the parameters of
surface finish specifications is roughness average, Ra. This parameter also known as the arithmetic mean roughness value, arithmetic average AA or centreline average CLA
Lou et al., 1998. Ra is recognized widely used as the most common international parameter of roughness Standard and ISO, 1997. According to Gokkaya and NALBANT
2006 The average roughness Ra is the area between the roughness profile and its centre line, or the integral of the absolute value of the roughness profile height over the
evaluation length Figure 2.8. Therefore, the Ra is by the following equation: 20
Figure 2.8: Surface roughness profiles
The Roughness average Ra is also namely as the arithmetic mean roughness value, arithmetic average AA or centre line average CLA, see equation 4. Ra is basically
known and the most used international measurement of surface roughness. The equation of Ra is shown below.
Equation 2.3
L = Sampling length y = Ordinate profile curve.
21
Other than that, the Root-mean-square rms roughness or Rq, is root mean square parameter corresponding to Ra, see equation 2.4
Equation 2.4
Since Ra and Rq are the most widely used in determine the surface parameters in industry, Ra was selected to analyze the surface roughness in this study.
2.9 SURFACE QUALITY
The quality of surface machining can be defined as the accuracy of its manufacture with consideration to the dimension stated by the actual size of the part or products. During
machining operation there have characteristics information on the machined surface. This characteristics information included of finely spaced micro irregularities left by the cutting
tool. Every type of cutting tool leaves in various pattern of machining surface. This arrangement is known as surface irregularities or surface roughness. According to
Fallböhmer et al. 2000, Finishing process is a critical part in industry that contribute the highest share of manufacturing lead time for die casting, injection molds, and forging dies.
In the certain case of large automotive stamping dies, finish machining has significant part of the total production time Fallböhmer et al., 1996. Quality surface machining also give
the impact on benching time in polishing and grinding is about 15 percent for die casting and injection molds, 20 percent in sheet metal forming dies Fallböhmer et al., 1996.
With the finish the higher of surface quality it will allow a reduction of the benching time. In die and moulds manufactures, the main objective using high speed machining is to
minimize a polishing process and decrease the processing lead time time for finishing process. Table 2.1 is showing the averages values of dimensional and form error for dies
and mould 22
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
