Machinability Analysis of Grey Cast Iron

Abstract

Grey Cast iron is an Iron Carbon alloy and is known for its wide range of applications in manufacturing industry. It contains inclusions such as Manganese, silicon, nickel, vanadium and copper. Traces of impurities such as sulphur and phosphorous are also present which is one of the factors affecting Machinability leading to unpredictable process behavior.
This Master’s degree thesis is an Industrial Project and was conducted in ‘Industrial Production Machine Shop’ at ‘Department of Production and Materials Engineering, Faculty of Engineering, LTH’. The study was conducted on Grey Cast Iron to assess the Machinability based on tool wear analysis, process analysis based on segmentation frequency and Material analysis.
The tool wear was studied on worn inserts using Alicona and Optical microscopes and flank wear was recorded. Machining tests were performed using a set of cutting parameters on Boeringer turning machine and dynamic cutting forces were recorded during the experiment. SEM, XEDS were used for an in-depth micro structural and elemental composition analysis
Inserts used in manufacturer’s facility to machine the material were used for tool wear analysis using Alicona and Optical microscopes. Flank wear and Notch wear were frequently observed in roughing inserts. Also, material adhesion was seen in finishing inserts which was later confirmed in SEM. No plastic deformation was found for any material group. Combined wear mechanisms were also observed in few inserts.
The second part of this project was conducted by machining material specimens to measure dynamic cutting forces. A cutting force sensor was used for this purpose and forces were recorded using force measurement setup. The tests were performed for a combination of cutting parameters and chips were collected for analysis. Material specimens were prepared from material blanks in surface preparation lab where polishing was done to obtain a mirror like finish. SEM/XEDS microscopy was performed to study micro-structure and elemental composition on the polished specimens to evaluate the potential cause of machinability variation linked to material issues.
The tool wear analysis showed that resultant wear was a combination of multiple wears, occurring simultaneously. Flank wear was dominant in all cases. Chipping and notching was also observed in most of the inserts which hints at the presence of inclusions and hard phases which were later confirmed in SEM analysis. Thermal cracking was also noted which hints at the development of heat zones due to high temperature.
The cutting force analysis showed that materials with good machinability has high segmentation frequency. Microstructural analysis provided information about graphite form and distribution of phases. Material with uniform phase distribution had better machinability in all cases. Inclusions were also observed in few samples. It was found that specimens having more carbides inclusions and low sulphides had low machinability. The same material caused more wear on inserts provided by the manufacturer which supported the experiment and material analysis.

Metal cutting
Machinability
Grey Cast Iron
Tool wear
Cutting forces in machining
Segmentation frequency
Microstructure
SEM/ XEDS

Popular Abstract

Machinability is the relative ease with which a workpiece material can be machined by a cutting tool to desired specifications. For the cutting tool, machinability is longer tool life. For a process, machinability is better control and less disturbances and for a workpiece material, a material which can be easily sheared without producing much abrasive and adhesive tool wear is better in machinability
The concept of machinability is complicated in nature with challenges associated with its effectiveness. Better understanding of cutting tools, process conditions including process parameters and workpiece material is necessary. The judgment cannot be made on a single entity. It is to find a best solution satisfying all three elements including tool, machining process and workpiece material.
In this context, Four specimens of Grey Cast Iron were investigated which were claimed to be of the same designation but varying in machining behavior. The analysis was conducted based on tool wear, machining process and workpiece material. During tool wear analysis, wear results were observed to be different for roughing and finishing inserts. To get more insights into machinability, machining of specimens were conducted on Boeringer turning machine with an uncoated cemented carbide insert and cutting forces generated during the process were recorded. Chips produced were also collected for every cutting data set. Fast Fourier Transform (FFT) analysis was performed on cutting force data to calculate segmentation frequency for each material and every cutting data set. Chips collected were examined to measure segmentation distance using ‘Image J’ software, which was used to calculate segmentation frequency. Segmentation frequency calculated from cutting forces analysis and chip segmentation analysis generated coherent results.
Material characterization was performed by SEM and XEDS analysis where material specimens were investigated for micro-structure and inclusions. Graphite form, distribution of phases and percentages of inclusions were observed to be responsible for adhesive and abrasive behavior on tool leading to unexpected cutting behavior. The specimens having high percentages of carbides and less sulphides showed more abrasive wear in tool wear analysis. Specimen with higher silicon was observed to have more adhesions in finishing inserts. Specimens having higher sulphides showed less cutting forces during machining and higher segmentation frequencies indicating better shearing.
The study concluded that machinability is a complex phenomenon as it changes by varying any of the element. The best way is to find an optimal solution satisfying tool, process and workpiece material.

• author: Chaudhry, Hassan
• supervisor: Fredrik Schultheiss
• organization: Production and Materials Engineering
• course: MMTM05 20231
• year: 2023
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Metal cutting Machinability Grey Cast Iron Tool wear Cutting forces in machining Segmentation frequency Microstructure SEM/ XEDS
• report number: LUTMDN/(TMMV-5357)/1-54/2023
• language: English
• id: 9136138
• date added to LUP: 2023-10-05 07:36:15
• date last changed: 2023-10-10 14:57:30