Machining Different Metal Components - Report Example

Table of Contents Summary 2 Introduction 2 Discussion and Task Analysis 3 Task 1 3 Task 4 4 Tool wear 4 Conclusion 7 References 7 Table of Figures Figure 1: The regions of tool wear 4 Figure 2: Basic wear Mechanisms 5 Summary Machining is any of the various processes in which a piece of raw material is cut into a desired final shape and size by a controlled material removal process. These machining processes that have the component of controlled removal of material are referred to as subtractive manufacturing [MIT12]. Machining can be done on several materials, such as wood, ceramic, and plastic, but it forms a crucial part in the manufacture of most metal products [MTU17]. Hand and power tools have been used to create metal products for years. However, machining involves the use of machine tools, in conjunction with the hand and power tools, to produce work that is significantly more accurate and faster, increasing productivity while reducing waste. Introduction It is common practice that the principle machining processes result in the formation of swarf as a by-product. The machining processes can be broadly classified as follows;- 1. Turning operations: - Rotating the work-piece is the primary method of moving the metal against the working tool. The principal machine used in turning operations is the lathe. Some of the common turning processes include knurling, grooving, turning, and cutting. 2. Milling operations: - In milling operations, the cutting tool is rotated and the cutting edge brought close to bear against the workpiece, which is fastened down. The principle machines used in these processes are called milling machines 3. Drilling operations: - In the drilling processes, holes are produced or refined by bringing a rotating cutter, with the cutting edge at its farthest tip, into contact with the workpiece. Drill presses are the primary tool used for drilling operations, but lathes can also be used, where the workpiece is rotated instead of the cutting tool. 4. Miscellaneous operations: - These are operations that do not necessarily result in swarf formation, but require the use of a typical machining tool to be carried out. An example of this is burnishing, which refers to the deformation of the workpiece surface, due to sliding contact with the working tool. This report looks at the various processes used to machine different metal components, analyzing the tools used and the rationale behind the process. Discussion and Task Analysis Task 1 The first drawing shows a plumb bob. The making of the plumb bob can be done using a lathe machine. The machining processes that go into the making of the plumb bob are;- 1. Facing: - The metal is cut from the end to fit its dimensions with the finished product requirements, as well as removing any surface marks that might affect the appearance of the finished product. Facing is also done so that the ‘stock’ has the correct angle to fit into the axis of the lathe and the machining tool 2. Parallel turning: - This is done to cut the metal parallel to the rotating axis of the lathe machine. It has the effect of reducing the diameter of the workpiece. Parallel turning was done to reduce the diameter of the front 30mm from 20mm to 16mm 3. Taper turning: - Commonly referred to as tapering, the metal is machined into a nearly cone shape using the compound slide. This is necessary for the plumb bob as it need to have a sharp pointed edge at the tip. The cutting tool is set at an angle of 200 to taper the bit of the workpiece, forming a tip that has an overall angle of 400. 4. Drilling: - The plumb bob has a hole in its rear end, where the string and its supporting mechanism is attached, allowing it to dangle freely. The workpiece is secured within the lathe, and a series of drilling steps conducted. The first is centre drilling, to ensure the hole is right at the centre of the workpiece. The next is spot drilling, in which a hole is dug to act as a guide for other larger drill bits. This is done so that the larger drill bits cannot stray off from the centre position due to the stresses induced during the procedure. The final drilling process is then done using the drill bit whose diameter corresponds with the requirements of the finished product. The rear end of the plumb bob is drilled by an 8mm diameter drill bit for 19 mm, followed by a 10mm diameter drill bit for the first 4mm of the hole. This is done to create a countersink, so that the component to be placed in the hole flushes with the material and does not stick out 5. Chamfering: - The plumb bob has sections that have varying diameter, and chamfering is used to create a smooth transition between the different sections. This can be achieved by a process similar to taper turning, where the end of the taper is limited to the desired diameter, or by successive parallel turning and facing operations. The chamfering is also done at the rear end of the plumb bob at an angle of 450 6. Knurling: -The plumb bob has a section which has been knurled to provide better grip during usage. The process is achieved using very hard roller ’tools’ that have the reverse of the pattern to be imposed. To avoid deformation, and for accurate work, both the workpiece and the machining tool need to be firmly held in place Task 4 Tool wear This refers to the gradual failure of cutting tools due to regular operation, usually in reference to tipped tools, tool bits or drill bits used with machining tools. There are several types of tool wear, namely;- a. Flank wear – the portion of the tool in contact with the finished part erodes b. Crater wear – the contact of the chips erodes the rake face, which could lead to cutting edge failure c. Built-up edge – it occurs when working with soft metals with low melting points, the material tends to build up on the surface of the cutting edge, reducing its ability to work metals d. Glazing – this occurs due to the dulling of the exposed abrasive on grinding wheels Figure 1: The regions of tool wear Machining tools are subject to various load factors on the cutting edge, which strive to change the geometry of the cutting edge, determining its useful life. These load factors are;- i. Mechanical loading– The physical application of metal to the cutting edge at significant speeds takes a toll on the tolerance of the cutting tool, which could result in deformation, or even failure ii. Thermal loading – The constant contact between the material and the cutting edge causes a lot of friction, which generates heat. Some processes, such as milling, generate high amounts of energy, causing significant thermal loading. This also happens when the workpiece leaves the cutting edge, and comes into contact again iii. Chemical loading – The high temperatures generated at the contact of the cutting edge and the workpiece serve as catalysts, which provide an attractive environment for diffusion and chemical reaction of metals iv. Abrasive loading – Different workpieces are made up of different materials, and each workpiece is usually a combination of various components. Some of these components maybe harder than the cutting tool itself, causing a grinding, abrasive effect on the tool Tool wear in metal machining and cutting can be attributed to several principal mechanisms that are often considered, namely;- Figure 2: Basic wear Mechanisms 1. Abrasion Abrasion wear is caused by those hard particles embedded in the material of the workpiece. Hardness is the main material property that determines whether the cutting edge experiences abrasive wear or not. Tools that are harder than the hard particles in the workpiece material are able to machine the workpiece without abrasive failure. The hardness of the cutting tool can be increased by using a material with densely packed materials. However, increasing the hardness of the cutting tool reduces its tolerance to other causes of tool wear. 2. Diffusion Diffusion is caused by the chemical loading the cutting edge is subjected to while in operation. The chemical characteristics of the cutting tool and its affinity to the chemical composition of the workpiece material will dictate the development of diffusion wear of the cutting tool. Some cutting tools have an inert metallurgical relationship with most workpiece materials, but there are some exceptions which have a high chemical affinity. Such materials include steel and tungsten carbide, which have a high affinity for each other causing crater wear. Diffusion wear is accelerated by high temperatures, as it catalyzes the chemical reactions, thus is most prevalent at high machining speeds. The most common chemical reaction that takes place is oxidation, where either the workpiece or the cutting tool forms oxides. Some oxides are easily rubbed off, but others such as aluminium oxide, are harder and stronger. Oxidation mainly affects the interface part of the edge, leading to the formation of notches as air gains access to the cutting process. 3. Fatigue The dynamic loading on the cutting edge caused by the continuous imposition and removal of cutting stresses can result in the cracking and breaking of the edge. Intermittent cutting procedures also subjects the tool to temperature fluctuations, which cause internal shocks and stresses, due to the irregular heating and cooling of the cutting edge. This makes fatigue wear to be thermos-mechanical load combination. High rotational speeds could also subject the cutting edge to forces that exceed the tool’s material strength, causing deformations 4. Adhesion This refers to the build-up of long and short-chipping workpiece materials on the chip face of the cutting tool, which occurs when machining at low temperatures. This causes the chippings to be hardened and form part of the edge, which can be sheared off, but in some cases, this results in small pieces of the edge breaking away. Adhesion wear occurs as either flank wear or crater wear Conclusion In conclusion, it is evident that understanding machine operations is vital in producing high quality work. A balance has to be struck between the prevailing conditions and the precision required for the material being machined. The operator ought to have a detailed operational plan since it ensures no process is omitted or done before it time. References Dolinšek, S., Šuštaršič, B. and Kopač, J., 2001. Wear mechanisms of cutting tools in high-speed cutting processes. Wear, 250(1), pp.349-356. MIT12: , (MIT, 2012), MTU17: , (MTU, n.d.), Read More