Effect on Cutting Force during Hard Machining of AISI D2 Tool Steel Using AlCrN Coated Tool

*Ravikumar Dasharathlal Patel and Sanket N. Bhavsar* 

## **Abstract**

At present, milling is the most suitable process among other all process for making molds, dies, automotive parts and aerospace parts, which are manufactured from hard tool steel. Tool steel (D-Grade tool steel) materials are largely used in the manufacture of cold forming dies due to the excellent wear characteristics and deep hardening. AISI D2 tool steel is used as the work material for the current experiment. Many researchers demonstrated that AlCrN coating, which has been developed recently, provided better wear protection than TiAlN coating. The present paper provides the details of machining experiments of AISI D2 tool steel using an AlCrN coated end mill tool. The aim of the present study is to develop a relationship between cutting force and input parameters (cutting speed, feed, depth of cut and width of cut). First and second order models were developed using Response Surface Methodology (RSM). The predicted cutting force results are shown in terms of first and second order equations. Comparision of both models (1st and 2nd order) for the prediction of cutting force during machining of AISI D2 tool steel was performed during this research work.

**Keywords:** milling, hard machining, AISI D2 steel, AlCrN coated tool, RSM CCD, ANOVA

#### **1. Introduction**

In the global market, satisfaction of customer requirements without compromising quality is becoming a major issue to sustain in the competitive market. One of the most widely used manufacturing processes is the milling process, which is interrupted cutting process to remove chips to obtain the required shape [1]. In manufacturing industries, the milling process is widely used to manufacture dies, automobile parts and aerospace industries. The cutting circumstances are more adverse than in turning [2]. The milling process for hard materials has reduced lead time and machining costs compared to other traditional processes [3]. In die and mold-making industries, machining of hard material is a challenging task due to high tool wear, higher tooling and handling cost [4]. Gaitonde et al., undertook an experiment on AISI D2 tool steel to evaluate machinability with analysis of cutting temperature, tool wear and surface roughness [5]. For hard machining, tool wear and temperature at the tool tip were the major issues [6]. To overcome this, coating on the tool can effectively improve the tool life. Coating of a cutting tool enhances the wear resistance, oxidation resistance, reduces temperature variation in tool and improves lubricity of the tool [7]. Experiments were carried out on austenitic

 stainless steel using hard AlTiN, AlCrN PVD coated tool. The AlCrN-based coatings have superior oxidation resistance and hot hardness when compared to AlTiN ones [8]. Hard machining in dry conditions gave the best results and substantial advantages such as lower manufacturing costs, reduced time for finish machining and improved surface quality [9]. Some research work has proved that there is high tool flank wear in up-milling operations compared to down-milling operations [1]. Tongchao Ding et al. milled AISI H13 steel with optimal cutting parameters and analyzed the significant effect on cutting force and surface roughness [10]. Experimental investigations were carried out by end milling process on hardened Impax Hi hard tool steel (55 HRC) by Bala Murugan Gopalsamy et al. [11]. Experimental and theoretical study has been undertaken on heat flow when machining of AISI H13 and AISI D2 tool steel by using ball nose end mills (TiAlN and tipped with PCBN) [12]. Flank wear is the main type of tool wear. Chipping, adhesion and attrition were responsible for flank wear. Due to this, tool life is less than 40 m length of cut when end milling of AISI D2 tool steel (58 HRC) [13]. End milling of AISI D2 tool steel is analyzed to develop the tool life model using PVD TiAIN coated carbide end mill tool. Lajis et al. developed a mathematical model that indicates the relationship between tool life and machining variables by using the concept of RSM [4]. Researchers also developed a mathematical model to predict cutting forces during machining of complex surfaces [14].

No much work has been done on AISI D2 tool steel with AlCrN coated end mill tool. At present, hardened AISI D2 tool steel is mostly machined by AlCrN coated carbide. The aim of this paper is to develop the relationship between the output response (cutting force) and input parameters (cutting speed, feed, depth of cut and width of cut) when AISI D2 tool steel is machined by an AlCrN coated tool.

### **2. Experimental details**

As part of the current research work, AISI D2 tool steel with a hardness of 62 HRC was hard machined. The chemical composition of the cut material can be found in **Table 1**.

The hardness of 59 HRC of the testing samples was achieved by hardening (with oil quenching) at 970°C followed by 2 hours of tempering at 710°C.

Machining was done on 40 × 80 × 16 mm AISI D2 tool steel (59HRC). Cutting experiments were carried out by Jyoti CNC machining Centre PX10. Walter made AlCrN coated tool (MC232-10.0W4B-WJ30ED) with a 10 mm diameter and four flute flat end mills were used for experimental work (shown in **Figure 1**). A tool dynamometer (9272, Kistler made) was mounted on the table of the machine tool to measure the cutting force signals during machining as shown in **Figure 2**. The signals were amplified through a charge amplifier and analog signals were converted using A/D acquisition card (PCI-6-23E, NI) and stored in a computer. LabVIEW was employed for cutting force data acquisition.

For the performance of experiments with four factors at five levels, RSM CCD design of experiment was employed to conduct the milling experiments. The RSM is helpful for analyzing, developing, improving and optimizing a process [15].


**Table 1.** 

*Chemical composition (average %) of machined AISI D2 tool steel.* 

*Effect on Cutting Force during Hard Machining of AISI D2 Tool Steel Using AlCrN Coated Tool DOI: http://dx.doi.org/10.5772/intechopen.81083* 

**Figure 1.**  *AlCrN coated tool.* 

**Figure 2.**  *Experimental setup.* 


#### **Table 2.**

*Independent variable with levels.* 

 RSM CCD was chosen because of the minimum number of experimental trials required as well as it is more efficient in handling a large number of factor variables compared to traditional factorial design. As shown in **Table 2**, the four factors to be considered were cutting speed, feed, radial depth of cut, and axial depth of cut.
