Essay: Analysis of the influence parameters on the energy demand of manufacturing processes

I Table of contents
I Table of contents II
II List of figures IV
III List of tables VI
IV Symbols VII
1 Introduction 8
1.1 Classification according to DIN 8580 9
1.2 Specific energy consumption of manufacturing processes 10
2 Primary Shaping 11
2.1 Liquid initial material state 11
2.1.1 Gravity Die Casting 12
2.1.2 Pressure Casting 12
2.1.3 Low Pressure Casting 13
2.1.4 Centrifugal Casting 13
2.1.5 Continuous Casting 14
2.1.6 Parameters influencing energy consumption in Casting processes 14
2.2 Primary shaping fibre-reinforced plastic 16
2.2.1 Press Moulding 16
2.2.2 Injection Moulding 17
2.2.3 Parameters influencing energy consumption in Injection Moulding Process 18
2.2.4 Extrusion 19
2.2.5 Blow Moulding 19
2.3 Granular or powder initial material state 20
2.3.1 Sand Moulding 20
3 Forming (DIN 8582) 22
3.1 Pressure Forming 23
3.1.1 Rolling Process 23
3.1.2 Ring Rolling 24
3.1.3 Parameter influencing the energy consumption in ring rolling process 25
3.2 Tension Compression Forming 25
3.2.1 Drawing 25
3.2.2 Deep Drawing 26
3.3 Bending 27
3.3.1 Parameter influencing the energy consumption in Bending process 28
4 Separating 29
4.1 Separating 30
4.2 Cutting with geometrically defined edges 30
4.2.1 Turning 30
4.2.2 Drilling 32
4.2.3 Milling 35
4.3 Cutting with geometrically non-defined edges 39
4.3.1 Grinding 39
4.3.2 Honing 42
4.3.3 Lapping 42
4.4 Non-conventional Machining 43
4.4.1 Thermal removing 43
4.4.1.1 Parameter influencing the energy consumption in EDM Process 44
5 Joining 45
5.1 Welding 46
5.1.1 Parameter influencing the energy consumption in welding process 48
6 Coating and Finishing 49
7 Change of Material Properties 50
8 Conclusion 51
References 52
Matrikelnummer 56
II List of figures
Fig. 1: Classification of manufacturing processes (DIN 8580) 9
Fig. 2: Classification of primary shaping processes according to the material initial state 11
Fig. 3: A typical permanent mould 12
Fig. 4 Breakdown of energy use in a Foundry 15
Fig. 5: Comparison of SEC in Casting Processes 16
Fig. 6: Injection Moulding process 17
Fig. 7: Comparison of SEC in Injection Moulding Process 18
Fig. 8: Extrusion Process 19
Fig. 9: Blow Moulding 20
Fig. 10: Sand Moulding Process 21
Fig. 11: Classification of Forming process (DIN 8582) 22
Fig. 12: Rolling Process 23
Fig. 13: Ring Rolling Process 24
Fig. 14: Drawing Process 25
Fig. 15: Deep Drawing Process 26
Fig. 16: Bending Process 27
Fig. 17: Classification of the Separating Process 29
Fig. 18: Turning Process 31
Fig. 19: Comparison of SEC in Turning Process 32
Fig. 20: Radial Drilling machine 33
Fig. 21: Common operations in Drilling 34
Fig. 22: Comparison of SEC for Drilling Process 35
Fig. 23: Principle of Up Milling 36
Fig. 24: Principle of Down Milling 36
Fig. 25: Types of milling cutters 37
Fig. 26: Horizontal Knee Type Milling Machine 38
Fig. 27: Comparison of SEC in Milling Process 39
Fig. 28: Plain Cylindrical Grinder 40
Fig. 29: Internal Grinding 41
Fig. 30: Surface Grinding 41
Fig. 31: Honing 42
Fig. 32: Lapping 43
Fig. 33: Classification of Joining Process 45
Fig. 34: Gas Welding 47
Fig. 35: Electric Arc Welding 48
Fig. 36: Classification of Coating and Finishing Processes 49
Fig. 37: Classification of the group “Change of material properties” processes 50
III List of tables
Table 1: Specific Energy Consumption in Casting Process 15
Table 2: Specific Energy Consumption in Injection Moulding Process 18
Table 3: Specific Energy Consumption in Turning Process 31
Table 4: Specific Energy Consumption in Drilling Process 34
Table 5: Specific Energy Consumption in Milling Process 38
IV Symbols
m metre
mm millimetre
s second
MPa megapascal
Kg kilogram
°C Celsius
KWh kilowatt hour
KPa kilopascal
J Joules
Π pi
KHz kilo hertz
A Ampere
V Volt
+ve positive
-ve negative
1 Introduction
For the planning and control of machines and processes, few established methods and tools of the Digital Factory are implemented by companies. The standard tools are utilized for various purposes like process simulation, material flow, hall layout and logistics. Therefore, these methods and tools of the Digital Factory play a significant role in the planning and control phase of the production systems. By the integration of energy data in the planning phase, an energy oriented dimensioning and operation of the production is made possible. In planning phase, the energy demand of the new production machines has been determined only with the help of diversity factor and connected load so far. Hence the real energy demand of the production machines has been derived less accurately.
The aim of this student research project is to identify and examine the existing energy demand analysis of various manufacturing processes. Empirical models and simulation approaches are also considered. The main emphasis of the project is to identify the machine or process parameters that are proportional to the energy demand of the respective processes and to portray the relationship between those parameters and energy demand. DIN – “Deutsches Institut für Normung” meaning German Institute of Standardization develops market-oriented standards and specifications that promote global trade and innovations, assure efficiency and quality, and help protect the environment and society. The manufacturing processes are considered according to DIN 8580, the standard that specifies the requirements for the processes.
The project is carried out at the Institute of Machine Tools and Production Technology at the Technical University of Braunschweig under the Sustainable Manufacturing and Life Cycle Engineering division where diverse methods, tools and technologies are developed to cope with different challenges over the whole life cycle while considering the triple bottom line – “People, Planet, Profit”, towards a more sustainable development. Life Cycle Engineering deals with life cycle related disciplines and methods over the whole life cycle of products and services. Sustainability in Production specializes in environmentally oriented objectives where energy and material efficiency of machines and processes are evaluated and improved and environmental friendly lubricant oils are developed for production machines.
1.1 Classification according to DIN 8580
The manufacturing process according to DIN 8580 are classified into six main groups as the following:
Fig. 1: Classification of manufacturing processes (DIN 8580)
The main groups are classified on the basis of three characteristics achievement of a form from a formless substance (Primary Shaping); change of form (Forming, Separating, Joining, Coating & Finishing) and by change of material properties. Each main group is further classified into groups and within the groups the manufacturing processes distinguish themselves by forming subgroups according to the process types and material properties. There are numerous manufacturing processes that considered to be a combination of processes. A combination of processes is possible when two separate processes are put into effect simultaneously.
1.2 Specific energy consumption of manufacturing processes
Specific energy is the energy consumed in production of a material unit. It facilitates the comparison of energy consumption of various processes. It could be considered as a standard unit of measure for the energy consumption of manufacturing processes and is used when the energy consumption is compared to the process parameters or characteristics. The specific energy consumption is not constant for a unit manufacturing process. The specific energy consumption varies according to different process parameters, workpiece materials because of its dynamic nature. The relationship between specific energy consumption and the process parameters is characterized by a model which should provide a reliable prediction of the specific energy consumption of the processes.
2 Primary Shaping
Primary shaping is the manufacturing process in which a geometrically defined object is obtained from formless substances. The primary shaping processes are classified based on the initial physical state of the materials utilized in the processes. The main group primary shaping is thus classified into groups as the following:
Fig. 2: Classification of primary shaping processes according to the material initial state
2.1 Liquid initial material state
The manufacturing processes under this group are defined by the liquid state of the initial material. The processes are namely: Gravity Die Casting, Pressure Casting, Low-pressure casting, Centrifugal Casting, Continuous Casting, Foaming Casting, Painting Casting, Moulding with fibre reinforced plastics, Formation of Crystals. These processes are discussed below and the process parameter proportional to the energy demand is identified.
2.1.1 Gravity Die Casting
In this process, the filling of the molten metal in the hollow die takes place under the influence of gravity. A typical permanent mould is shown in the Fig 3. Apart from these main operations, in order to achieve a qualitative casting, the die is coated with a fire-resistant protective layer and the mould is also heated or cooled to a predetermined working temperature.
Fig. 3: A typical permanent mould
2.1.2 Pressure Casting
Under Pressure Casting, the molten metal is pressed under high pressure (10-200 MPa) and high speeds (till 120m/s). Due to the high pressure, sand cores cannot be used in this process and the casting parts can be very thin-walled and have a very complicated geometry. Immediately after the filling the mould, the kinetic energy of the press piston is converted into pressure energy, resulting in a so called Hydraulic Impulse. The die-casting process is predominately used for aluminium, magnesium, zinc and tin alloys as well as to a small extent for copper alloys. In case of the iron alloys, the permanent moulds would not withstand the high thermal and mechanical stresses. The process sequence is characterized by short cycles and a few individual steps.
Pressure Casting Machines are generally divided into the machines with cold and warm filling chambers, where the cold chamber pressure casting machines are classified according to horizontal and vertical arrangements.
a) Cold chamber casting
The molten metal is filled in the filling chamber and with the horizontally moving pressure piston, the filling of the mould is done and solidified under pressure. After the mould is opened, the piston is moved back so that the cast component could be removed.
b) Hot chamber casting
In the die-casting machines with a hot chamber, the molten metal is heated in a crucible and the furnace is connected to the die-casting mould. In this process, the molten metal is sucked in upwardly by the moving pressure piston. During the downward movement, the inlet port is closed and the molten metal is forced into the die. As a result of the high inflow velocities of the molten metal, the air from the mould cavity cannot escape quickly and porosities are found on the inner part of the castings.
2.1.3 Low Pressure Casting
In low pressure casting, the mould is directly set up over the molten metal or the furnace. It is connected to the furnace chamber through an ascending pipe, which is closed by a pressure seal. Air or other gas is injected into the furnace chamber at a low pressure (0.12-0.40 bar). As a result, the molten metal moves upwards in the ascending pipe and moves into the mould cavity. The pressure is applied until the molten metal in the mould is solidified. The remaining molten metal flows back into the furnace vessel once the pressure is lowered. The permanent mould could be opened and the cast component could be removed. This process could also be carried out with sand moulds because it is carried out at lower pressures.
2.1.4 Centrifugal Casting
Central casting plays a significant role in mass production of circular castings as the cast components produced from this process are free from impurities. This process involves the filling of the mould cavity with the molten metal and its solidification and partial cooling under the effect of centrifugal force. A force field could be built up by rotating the mould along a horizontal, vertical or inclined axis. Usually metallic moulds are used in this process, but sand moulds could also be used. The molten metal is fed into the mould by means of a special trough which could be moved in the case of long tubular moulds. Before the filling of the molten metal, the moulds are heated to a certain temperature. In order to avoid the adherence of the solidified cast component, the inner surface of the mould is provided with a ceramic coating. The external diameter of the cast component corresponds to the inner diameter of the permanent metal mould.
The components produced by this process have a high density and are free from porosities and non-metallic impurities. The process is preferably used for the casting of rollers and pipes.
2.1.5 Continuous Casting
In this process, the molten metal is continuously poured into the mould cavity around a facility for quick cooling the molten metal to solidify it. The solidified metal is then continuously extracted from the mould at a predetermined rate. This process is divided
into two categories namely Asarco and Reciprocating. In reciprocating process, molten metal
is poured into a holding furnace. At the bottom of this furnace, there is a valve by which the
quantity of flow can be changed. The molten metal is poured into the mould at a uniform
speed. The water cooled mould is reciprocated up and down. The solidified portion of the
casting is withdrawn by the rolls at a constant speed. The movement of the rolls and the
reciprocating motion of the rolls are fully mechanized and properly controlled by means of cams and follower arrangements.
2.1.6 Parameters influencing energy consumption in Casting processes
On breaking down the energy consumption of casting process, the metal melting process is found to the major energy consuming process. The melting process constitutes about 55% of the total energy consumption. The specific energy consumption values are reproduced from the Yoon et al. (2014) and Lazzarin & Noro (2015) which ranges over various metal casting processes and materials. These values are accumulated values of the total energy consumption in a foundry or industry. A comparison of values between the different authors is made. The process parameter according to the given papers is throughput (kg) or productivity.
Fig. 4 Breakdown of energy use in a Foundry
Metal Casting
Type SEC (kWh kg-1) Author
Aluminium 4.44 Sutherland et al.
Cast Iron 7.78 Boustead and Hancock
Steel 4.72 Boustead and Hancock
Iron (Company) 0.62 Arasu and Jeffrey
Company Average 3.12-4.63 Jones
Company Average 2.69 Dalquist and Gutowski
Foundary Company Average 4.13 Hasanbeigi et al
Foundary Company Average 1.597 Lazzarin & Noro
Table 1: Specific Energy Consumption in Casting Process
Fig. 5: Comparison of SEC in Casting Processes
2.2 Primary shaping fibre-reinforced plastic
Under this group, there are various important processes such as Press forming, Injection Moulding, Extrusion, Extrusion Moulding, Rod pulling or wire drawing, Calandriering/ Bowl glancing, Blow forming, Modelling. The initial state of the material used in these processes is plastic.
2.2.1 Press Moulding
Press Moulding, otherwise known as compression moulding, is the process where pre-shaped charge of material, premeasured volume of powder, or viscous mixture of liquid-resin and filler material is placed directly into a heated mould cavity. The temperature in this set -up typically is around 200°C but can be much higher. Forming is done under pressure from a plug or from the upper half of the die which ranges from about 10 to 150 MPa. There is a flash formed, which subsequently is removed by trimming or by some other means. The typical parts manufactured by this process are dishes, handles, container caps, fittings, electrical and electronic components, washing-machine agitators, and housings. Fibre-reinforced parts with chopped fibres also are formed exclusively by this process. Compression moulding is used for producing with thermosetting plastics and the material initial state is partially polymerized. Depending on the material and part thickness and shape, curing times range from about 0.5 to 5 minutes. The curing time is directly proportional to the thickness of the material.
2.2.2 Injection Moulding
In injection moulding process, the pellets and granules are filled into a hopper connected to a cylinder-piston mechanism. The cylinder is heated externally to melt the polymer and a greater portion of the heat transferred to the polymer is due to frictional heating. The cylinder is heated so that the plastic powder gets heated to a temperature between 175–275°C. As the piston withdraws, some plastic powder is inducted into the cylinder and the piston then moves it forward by exerting pressure on it. Under the action of heat and pressure, the plastic softens and is forced through a nozzle into a water-cooled die. This process is used for large scale production of thermoplastics components.
Fig. 6: Injection Moulding process
2.2.3 Parameters influencing energy consumption in Injection Moulding Process
The injection moulding process could be classified as hydraulic, hybrid and electric based on the type of the injection unit. The values of specific energy consumption is reproduced in this table and a comparison is drawn between the different models. Throughput (kg) is the parameter to be considered in injection moulding process as well.
Type SEC (kWh kg-1) Author
Hydraulic 1.47 Duflou et al.
Hydraulic 0.64-5.82 Thiriez
Hydraulic 3.63 Thiriez
Hydraulic 0.48-0.94 Gutowski et al.
Hydraulic 0.19 Mattis et al.
Hydraulic 0.28-1.94 Krishnan et al.
Hydraulic 0.65-2.53 Chien and Dornfeld
Hybrid 0.47-2.04 Thiriez
Electric 0.11-0.37 Kanungo and Swan
Electric 1.86 Thiriez
Electric 0.33-1.27 Thiriez
Table 2: Specific Energy Consumption in Injection Moulding Process
Fig. 7: Comparison of SEC in Injection Moulding Process
2.2.4 Extrusion
Extrusion also known as extrusion moulding, is used to produce solid rods, pipes, tubing and different sections. A hopper feeds polymer material into a heated chamber. The polymer material is fed forward by a rotating screw in the middle of the chamber. Under the action of heat and pressure, it starts flowing. A heated die is fitted in the front portion of the chamber and it is the only way out for the material. More material is screw fed and a continuous stream of material is squeezed out from the die. The cross section of the outcoming material acquires the shape of the die, which is cooled and carried off by a suitable belt conveyer. The scheme of extrusion process is shown in Fig. 8.
Fig. 8: Extrusion Process
2.2.5 Blow Moulding
In blow moulding, a tube or preform, usually oriented so that it is vertical, is first extruded. lt is then clamped into a mould with a cavity much larger than the tube diameter and blown outward to fill the mould cavity. The blow ratio may be as high as 7:1 depending on the material. Blowing is performed with the help of a hot air blast at a pressure ranging from 350 to 700 kPa. Steel, aluminum, and beryllium copper are the typical die materials. In some operations, the extrusion is continuous and the moulds move with the tubing. The moulds close around the tubing, sealing off one end, breaking the long tube into individual sections, and moving away as air is injected into the tubular piece. The part is then cooled and ejected from the mold. Corrugated-plastic pipe and tubing are made by continuous blow moulding in which the pipe or tubing is extruded horizontally and blown into moving moulds.
Fig. 9: Blow Moulding
2.3 Granular or powder initial material state
The next major group under primary shaping is granular or powder initial material state, which is further divided into subgroups such as Pressing, Sand moulding and Thermal injection.
2.3.1 Sand Moulding
Sand Moulding is a process where a pattern is placed in sand to create a mould. The pattern is incorporated with the sand with the help of a gating system. The pattern is then removed and the mould cavity is filled with molten metal. The molten metal is cooled to produce the cast component. The sand mould is broken and the metal casting is removed. The casting must be then cleaned and inspected, and sometimes heat treatment is necessary for better metallurgical properties. If the casting has internal surfaces, a core is to be included in the mould. Since the sand is broken to remove the casting, a new sand mould has to be made for each component that has to be produced.
Fig. 10: Sand Moulding Process
3 Forming (DIN 8582)
The main group Forming is further subdivided into processes such as Pressure Forming, Tension Compression Forming, Tension Forming, Bending and Shear Forming.
Fig. 11: Classification of Forming process (DIN 8582)
The forming processes are carried out at different temperatures depending on the respective material properties. The primary goal of forming could also be the change in surface quality and material properties. The forming processes are classified on the basis of the following aspects: deformation temperature, predominant stress, semi-finished state and operation principle.
3.1 Pressure Forming
The group pressure forming consists of processes such as rolling process, forming under compression conditions, open die forming, die forming, pressing with compression, transformation blasting and surface refinement blasting.
3.1.1 Rolling Process
In rolling process, alloys and metals are deformed plastically by being pressed between two rotating rolls into semi-finished or finished products. Initially the metal is inserted in between the rolls, once the edge of the material enters the roll, the material gets pulled in by the friction between the surfaces of the rolls and the material. The material is squeezed and it is subjected to high compressive force and pulled inside by the rolls. During the process, the length of the material is increased and its cross section is reduced. The final cross-section is determined by the impression cut in the roll surface through which the material passes and into which it is compressed. The rolling process is shown in the Fig.8.
Rolling is performed both hot and cold. In a rolling mill, the beginning point is a cast ingot of steel which is broken down progressively into blooms, billets and slabs. The main objective of rolling is to convert larger sections such as ingots into smaller sections which can be used either directly in as rolled state or as stock for working through other processes. The slabs are further hot rolled into plate, sheet, rod, bar, rails and other structural shapes like angles, channels etc.
Fig. 12: Rolling Process
3.1.2 Ring Rolling
Seamless (i.e., without a joint) rings find wide application in industry. The inner and outer races of ball and roller bearings, steel tyres for railway wheel are some such applications. These rings are made by a special rolling process called ring rolling. The starting work piece is a thick walled circular piece of metal in whose centre a hole has been made by drifting and piercing. The work piece is heated until it becomes red hot and then placed between two rolls A and B which rotate in opposite directions. The arrangement of rolls and the ring is shown in Fig. 9.
Fig. 13: Ring Rolling Process
The pressure roll B exerts pressure on the material from inside. Caught between rolls A and B, the ring rotates. At the sametime, the inside and outside diameter of ring progressively increase and the wall thickness keeps on reducing. In order to ensure that the ring is circular, two guide rolls are suitably placed on the outer surface of the ring. When the outer and inner diameter of the ring increase to the size required, the rolling is stopped.
3.1.3 Parameter influencing the energy consumption in ring rolling process
According to Giorleo (2013), the upset height (mm) of the ring influences the energy consumption of the piercing and ring rolling process. Therefore the upset height is the parameter that influences the energy consumption in a ring rolling process.
3.2 Tension Compression Forming
The processes like drawing, deep drawing, compressing, collar compressing, upset bulging and internal large compression falls under the group tension compression forming.
3.2.1 Drawing
In drawing, the cross section of a long rod or wire is reduced or changed by pulling (hence the term drawing) it through a die called a draw die (Fig. 14). Thus, the difference between drawing and extrusion is that in extrusion the material is pushed through a die, whereas in drawing it is pulled through it. A very wide range of applications, including shafts for power transmission, machine and structural components, blanks for bolts and rivets, electrical wiring, cables, tension-loaded structural members, welding electrodes, springs, paper clips, spokes for bicycle wheels, and stringed musical instruments are covered by rod and wire products.
The major processing variables in drawing are reduction in cross-sectional area, die angle, friction along the die-workpiece interface, and drawing speed. The die angle influences the drawing force and the quality of the drawn product.
Fig. 14: Drawing Process
3.2.2 Deep Drawing
In deep drawing process, a flat metal plate or sheet is converted it into cup shape by pressing the sheet in the centre with a circular punch fitting into a cup shaped die. If the depth of cup is more than half its diameter, the process is termed as deep drawing and with a lesser depth to diameter ratio, it is called shallow drawing. Parts of various geometries and shape are made by drawing process. The deep drawing process is illustrated in Fig. 15.
Fig. 15: Deep Drawing Process
During the drawing process, a complicated pattern of stress is applied to the sheet metal part. The portion of the blank between the die wall and punch surface is subjected to pure tension, whereas the portion lower down near the bottom is subject both to tension and bending. The portion of metal blank, which forms the flange at the top of the cup is subjected to circumferential compressive stress and buckling and as a result becomes thicker.
The flange has therefore to be held down by a pressure pad, otherwise, its surface will become buckled and uneven like an orange peel. Deep drawing is a difficult operation and the material used should be specially malleable and ductile, otherwise it will crack under the induced stresses. The wall thickness of a deep drawn component does not remain uniform. The vertical walls become thinner due to tensile stresses. But the thinnest portion is around the bottom corner of the cup all around. This thinning of sheet at these locations is called “necking”. After deep drawing, the component may be subjected to certain finishing operations like “irowing”, the object of which is to obtain more uniform wall thickness.
3.2.2.1 Parameter influencing the energy consumption in Stamping process
Among various metal forming processes, stamping plays a significant role in the metal industry. According to Ingarao (2012), the thickness of the material influences the specific energy consumption. The material AA-1050 of two different thicknesses 1mm and 1.5mm, is deformed into a cone shape and the energy consumed is 243J and 372J respectively.
3.3 Bending
Bending is an important process under the main group forming. Bending means deforming a flat sheet along a straight line to form the required angle. Various sections like angles, channels etc., are formed by bending, which may then be used for fabrication of steel structures. Three common methods of bending are illustrated in Fig.16.
Fig. 16: Bending Process
The operation of bending is done with the help of a V-shaped punch, a die and press specially designed for such work. The stroke of such presses can be controlled at operator’s will and such presses are called press brakes.
In V-bending, a V-shaped punch forces the metal sheet or a flat strip into a wedge-shaped die. The bend angle will depend upon the distance to which the punch depresses. Bends of 90° or obtuse as well at acute angle, may be produced.
Wiper bending is used only for 90° bends. Here the sheet is held firmly down on the die, while the extended portion of sheet is bent by the punch. Spring back: At the end of the bending operation, after the punch exerting the bending force is retrieved, due to elasticity, there is a tendency for the bend angle to open out. This is called “spring back”. The effect of spring back may be offset by slight overbending in the first place. Other methods to prevent spring back are bottoming and ironing. For low carbon steels spring back is 1– 2°, while for medium carbon steel it is 3–4°.
3.3.1 Parameter influencing the energy consumption in Bending process
According to Duflou et al and Kalla D (2009), the energy consumption of the bending process is dependent on the bending force, where energy is the product of the bending force and the die closed depth.
4 Separating
Separating is the most significant main group under which there are groups that consists of various manufacturing processes. The main group separating is divided as the following:
Fig. 17: Classification of the Separating Process
Separating is manufacturing by changing the shape of a solid body by abolishing the material cohesion locally. Separating is classified into separating, cutting with geometrically defined edges, cutting with geometrically non-defined edges, non-conventional machining, disassembly and cleaning. The further classification of each group is dependent on the processes.
4.1 Separating
Cutting is the most frequently used method in sheet metal processing. For each part to be produced either the blank of sheet metal is produced by cutting, or the finished part is trimmed after the forming. Cutting is a process of separation, so it does not belong to the forming process. However, the cutting operation is always associated with a plastic deformation before the material tears in the shearing surface after reaching its cohesion strength. The processes under this group are heavy cutting, knife cutting, cutting, splitting, ripping/tear cutting and breaking.
4.2 Cutting with geometrically defined edges
The tools used under this group whose number of cutting edges, the geometry of the cutting parts and the position of the cutting edges are relative to the workpiece. This group consists of many significant material removal processes such as turning, milling, drilling, planing, countersink, sawing, rasping, brush machining and broaching.
4.2.1 Turning
In this operation, the work piece is rotated at a suitable r.p.m., so that metal cutting may take place at the recommended cutting speed. If ‘d’ is the diameter of work piece and N the r.p.m., the cutting speed can be calculated as π.d.N. A cutting tool is clamped in the tool post taking care that the tip of the tool is at the same height as the centre of job. In the turning operation, the job rotates and the cutting tool is inserted in the surface of work piece by moving the cross slide, starting at the right-hand end of the work piece. The depth of cut of 1–1.5 mm may be taken and then the tool is steadily moved from right to left by sliding the carriage on the machine bed. The operation of turning is shown in Fig. 18.
Feed is given to the tool. Feed is measured in mm/rev of work piece. Since work piece r.p.m. is N , feed per minute will be N × feed/revolution (mm). Obviously, it may not be possible to achieve the desired reduction of diameter in one pass of the tool, the tool will have to be brought back to the right side, again advanced by 1–1.5 mm by moving the cross slide and then traversed again from right to left side. This process will have to be repeated several times until the desired diameter is reached. In the process of turning, a cylindrical shape is generated as a result of the combined movement of the work piece and the tool.
Fig. 18: Turning Process
4.2.1.1 Parameter influencing the energy consumption in Turning process
The specific energy consumption values from various papers are reproduced and a comparison is made among them. The parameter that influences the energy consumption in a turning process is the material removal rate (MRR). Here the specific energy consumption is denoted as J mm-3.
Table 3: Specific Energy Consumption in Turning Process
Material SEC (J mm-3) Author
Brass 9.8 Kara and Li
Mild Steel 7 Kara and Li
Brass 2.7-9.8 Li et al
Steel (EN8) 12.9-36.2 Mativenga and Rajemi
42CrMo4 7.1-14.5 Neugebauer et al.
Carbon Steel(C45) 5.191 Tang (2016)
Carbon Steel(C45) 4.770 Tang (2016)
Ductile Iron 5.029 Tang (2016)
Steel 7.9 Lauwers
Fig. 19: Comparison of SEC in Turning Process
4.2.2 Drilling
Hole making is among the most important operations in manufacturing, and drilling is a major and common hole-making process. This is the operation of making a circular hole by removing a volume of metal from the job by a rotating cutting tool called drill. Drilling removes solid metal from the job to produce a circular hole. Before drilling, the hole is located by drawing two lines at right angle and a centre punch is used to make an
indentation for the drill point at the centre to help the drill in getting started. A suitable drill is held in the drill machine and the drill machine is adjusted to operate at the correct cutting speed. The drill machine is started and the drill starts rotating. Cutting fluid is made to flow liberally and the cut is started. The rotating drill is made to feed into the job. The hole, depending upon its length, may be drilled in one or more steps. After the drilling operation is
complete, the drill is removed from the hole and the power is turned off.
Core drilling: Holes made in castings by use of cores, are rough and require a special kind of drill, called core drill to clean up the holes. This operation is called core drilling.
Step drilling: More than one diameter can be ground on the drill body which saves an extra operation.
Counter boring: Often a flat surface is needed around a hole to provide a good seating area for washer and nuts/head of a bolt. The counter boring tool has a pilot, which ensures that the counterbore is concentric with the hole.
Counter sinking: Counter sinking provides a tapered entrance to the hole.
Reaming: Reaming is an operation of sizing and improving the geometry and finish of a previously drilled hole. Hand, machine and shell reamers are used for this purpose. Machine reamers are used with a drilling machine. To work efficiently, proper stock allowance is very important. Reamers cannot remove much material, but at the same time, enough material should be available all round. For holes up to 12.5 mm in diameter, about 0.38–0.4 mm of material is left as reaming allowance. A reamer follows the original hole and cannot shift its centre.
Fig. 20: Radial Drilling machine
Fig. 21: Common operations in Drilling
4.2.2.1 Parameter influencing the energy consumption in Drilling process
Material removal rate is the parameter that influences the energy consumption in drilling process like the other material removal processes. A comparison is drawn between the two energy consumption models.
Table 4: Specific Energy Consumption in Drilling Process
Material SEC ( J mm-3) Author
Gray Cast Iron 65 He et al
Gray Cast Iron 9-38 Neugebauer et al
Fig. 22: Comparison of SEC for Drilling Process
4.2.3 Milling
Milling is a machining process which is performed with a rotary cutter with several cutting edges arranged on the periphery of the cutter. It is a multiple point cutting tool which is used in conjunction with a milling machine. This process is used to generate flat surfaces or curved profile and many other intricate shapes with great accuracy and having very good surface finish. Milling machines are one of the essential machines in any modern machine shop.
Generally, there are two types of milling processes. These are called (a) Up milling or conventional milling process, and (b) Down milling or climb milling process. Both these processes are illustrated in Fig 23 & 24.
In upmilling, the direction of rotation of milling cutter and the direction of work piece feed are opposite to each other; whereas in down milling, they move in the same direction at the point of contact of the cutter and the workpiece. In upmilling, the thickness of chip at the start is nil and is maximum when the cutting teeth leave the surface of the work piece.
Fig. 23: Principle of Up Milling
In down milling, it is vice-versa. In up milling, the cutting teeth try to up root and lift the work piece from the machine table, in down milling, reverse happens. Technically, down milling is a superior process, but up milling is commonly used.
Fig. 24: Principle of Down Milling
Down milling is not used unless the milling machine is fitted with a backlash eliminator. The milling cutter is circular and a large number of cutting edges (or teeth) are arranged along its circumference. The cutter is rotated at a speed of N r.p.m. If the cutter diameter is D, then cutting speed at the tip of teeth can be calculated as πDN metres/minute and it should conform to the recommended values. The depth of cut is clearly shown in the figure and the thickness of the work piece will reduce by this amount in one pass. Usually, the width of the milling cutter is more than the width of the work piece, hence one pass is all that is required.
Feed of the work piece is measured in terms of mm/minute. Actually, the correct measure of feed is movement of work piece per revolution of cutter per teeth. If a milling cutter has z number of teeth and if the table feed is ‘f’ mm/minute, feed per rev per teeth will be f/NZ mm. It should therefore be clear that metal removal rate in milling operation is much higher than in shaping or planing operations.
However, as in shaping or planing operation, the stroke length is always a little more than the
length of the job, in milling operation also, the minimum table traverse required is L + D, where L is the length of job and D is the milling cutter diameter. D/2 is the minimum overlap required on either side of job, so that the cutter becomes clear of the job.
Unlike turning, the milling process involves intermittent cutting and the chip cross-section is
not uniform. The high impact loads at entry as well as fluctuating cutting force make milling process subject to vibration and chatter. This aspect has great influence on design of milling cutters. The various kinds of milling cutters are illustrated in the figure.
Fig. 25: Types of milling cutters
All the milling cutters described above are used in conjunction with milling machines, which provide rotary movement to the cutters, and feed to the workpiece and arrangement for clamping, automatic feed etc. Milling machines come in three basic models:
1. Horizontal milling machines,
2. Vertical milling machines, and
3. Universal milling machines
The most common type of milling machine is the horizontal knee type shown in figure
Fig. 26: Horizontal Knee Type Milling Machine
4.2.3.1 Parameter influencing the energy consumption in the Milling process
Various number of energy consumption models are available for the milling processes. The specific energy consumption is compared among the various energy models.