Exercise 3 Lecture in the Subject: Manufacturing Technology II. The Forming System

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1 Lehrstuhl für Technologie der Fertigungsverfahren Laboratorium für Werkzeugmaschinen und Betriebslehre Exercise 3 Lecture in the Subject: Manufacturing Technology II The Forming System Werkzeugmaschinenlabor Lehrstuhl für Technologie der Fertigungsverfahren Prof. Dr. - Ing. F. Klocke RWTH - Aachen Steinbachstraße Aachen

2 Table of Contents Table of Contents 1...Introduction The forming system Classifying manufacturing processes Classifying the manufacturing processes as specified in DIN Classifying manufacturing processes...according to pre-forming geometry Classifying manufacturing processes... according to forming temperature Machine tools for forming technology Cooling and lubricating media used in forming technology Presentation and examples of commonly used forming processes Forming under compressive conditions Forming under combination of tensile and compressive conditions Forming under tensile conditions Forming under bending conditions Forming under shearing conditions Cutting Task 18 Manufacturing Technology II - Exercise 3 2

3 Einleitung 1 Introduction Forming and machining (cutting) are two of the most important groups of processes used in forming applications. The design and manufacture of formed parts always aim to ensure that the parts can be used without the need for any further cutting operations (i.e. the aim is to achieve net shape). This means that there must be very close tolerances and that a uniformly high level of surface quality is vital. The shape of the part, the material characteristics, the division of the forming cuts, the care with which intermediate steps such as annealing and lubrication are conducted, the condition of the tool and the machine and process management all have an effect on the level of dimensional and form accuracy which can be achieved. The levels of accuracy achieved in forming processes and in rival processes, are listed in Fig Fig. 1.1 Levels of accuracy which can be achieved in a range of manufacturing processes, König/Klocke Vol. 4, P. 145, Fig The volume of forged parts manufactured in one year in Germany, is approx. 930,000 tonnes. Some 150,000 tonnes of this, are cold-formed and a further 20,000 tonnes are formed in a warm forming operation. Cold extrusion is gaining Manufacturing Technology II - Exercise 3 3

4 Einleitung steadily in significance since this process still has considerable untapped potential. By way of comparison: Over 500,000 t of material are cold-formed in Japan every year. In North America alone, the forming industry records added value to the tune of around $32 billion per year. This exercise will focus on providing a graphic introduction to forming technology. The forming processes commonly used in industry will be presented. The forming system will also be discussed and important aspects such as forming temperature, classification of the processes and machine tools, will be examined.. Manufacturing Technology II - Exercise 3 4

5 The forming system 2 The forming system 2.1 Classifying manufacturing processes Classifying the manufacturing processes as specified in DIN DIN subdivides the group of manufacturing processes in six groups. These are primary forming and forming, cutting, joining, coating and changing material characteristics (Fig ). Primary forming is specified in DIN 8580 as the selective plastic modification of the shape of a, with control over the geometry. The mass and cohesion of the material remain unaltered. The forming processes are divided into five groups, which differ in terms of the state of stresses during the forming operation. Fig : Breakdown of the forming processes There is a further subdivision within these five groups, in terms of the process kinematics, tool and geometry, etc. One of the advantages of this classification is that no process is listed twice and that it is easy to classify new processes. However, a considerable disadvantage of this system is that it bears little relation to the classification in industrial practice Classifying manufacturing processes according to pre-forming geometry One of the methods of grouping forming processes in industrial practice, is by the shape of the part before machining. Basically, a distinction is drawn between solid and sheet forming, which bears no relation to the DIN classification. Manufacturing Technology II - Exercise 3 5

6 The forming system In solid forming operation, solid parts are formed in all dimensions, frequently including large cut surfaces or changes in wall thickness. Upsetting, rolling and extrusion are among the typical processes. In sheet metal forming operation, flat formed parts (sheet) are formed to produce hollow parts with a uniform wall thickness. Stretch drawing and deep drawing are among the typical processes. The forces required in solid forming operations are considerably higher than in sheet metal forming. The machine tools used in solid forming processes must, therefore be more rigid and larger than those used in sheet metal forming. The same applies to tools and tool materials Classifying manufacturing processes according to forming temperature Classification according to temperature is a further grouping criterion in forming technology. For a long time, the definition for hot forming was: Forming, when the part is heated above room temperature prior to forming. An alternative definition of hot forming is when the forming operation is conducted at a temperature above that of re-crystallisation. However, this means that forming operations conducted on lead at room temperature would be classified as hot forming. In warm forming operations the is heated, but not above the recrystallisation temperature as it is in hot forming operations. Whereas an unalloyed steel is heated to a temperature of 1200 C in hot forming operations, the temperature selected in warm forming operations is between 450 and 600 C. In cold forming operations, the parts are not heated before work begins. 2.2 Machine tools for forming technology In the case of machine tools for forming technology, there is one main criterion for differentiation, the relative tool movement which is either a) linear or b) non-linear (Fig ) Machine tools which do not fall into either of these categories, are special-purpose machines which are used for forming with media or with active energy. Manufacturing Technology II - Exercise 3 6

7 The forming system Fig : Machine tools used in forming processes A second subdivision can be made on the basis of the machine control system. Three of the basic options are: 1. Presses controlled by work (energy) 2. Presses controlled by force 3. Presses controlled by path (stroke). Fig shows the various types of machine tools in forming technology and their force gradients. Manufacturing Technology II - Exercise 3 7

8 The forming system Fig : Machine tools for forming technology: Work, force and path-related pressing 2.3 Cooling and lubricating media used in forming technology The primary function of lubricant in forming technology, is to reduce friction, thus minimising tool wear (Fig ). Various lubricants, which differ in terms of chemical composition, in their state of aggregation and in their function can be used, depending on the forming process and material involved. Manufacturing Technology II - Exercise 3 8

9 The forming system Fig : Requirements to be met by lubricant in solid and sheet material forming operations As a rule, oil and grease as well as watery suspensions, soap lubricants and solid lubricants such as molybdenum sulphide (MoS 2 ) and graphite are used in cold solid and sheet metal forming operations. Whereas solid lubricants or liquid lubricants on a carrier layer are generally used in solid forming operations, oil or water-miscible lubricants are usually used in sheet metal forming operations. In cold extrusion operations, the is initially coated with a layer of lubricant carrier in order to increase the adhesion of the lubricant layer. This carrier layer improves the adhesion of the lubricant to the and separates the material from the tool material, thus preventing cold welding. Zinc phosphates are used for these carrier coatings and iron oxalate is used for steel materials which are resistant to corrosion.. Manufacturing Technology II - Exercise 3 9

10 The forming system Reactive alkali soaps, mineral oils or solid lubricants such as molybdenum sulphide or graphite with additives are frequently used as lubricants on the carrier layer. One disadvantage of the soaps is that they cannot be used under extreme process conditions, e.g. temperatures in excess of 200 C. Oils with chlorine, sulphure or phosphorus additives (EP additives) are used in complex forming processes. These oils are also used in wire drawing operations for example. The functions of the lubricant in forging operations are different from those in cold solid forming operations: They are firstly, to provide thermal insulation in order to reduce the transfer of heat from the to the tool and secondly, to perform a carrier function for coolant and propellant agents. Lubricants in forging operations generally consist of a proportion of solid matter (graphite, MoS 2, Alkali phosphate, glass, potassium water glass + graphite), a lubricant carrier (water, oil, grease) and additives, for enhanced wettability, for example. Air, air-water mixtures, water or water with wetting agents (e.g. soap) are suitable. Lubricants are also required to reduce wear. Wear on forming tools is characterised by the combined effect of various wear mechanisms. In addition to the adhesive and abrasive wear which are the primary wear mechanisms, the tools also sustain wear as a result of fatigue (surface break-down) and tribooxidation. Manufacturing Technology II - Exercise 3 10

11 Presentation and examples of commonly used forming processes 3 Presentation and examples of commonly used forming processes 3.1 Compressive forming Fig : Manufacturing processes pressure forming: rolling Examples: Semi-finished products (sheet, rods, coil, wire, plates), gear tooth profiles, threads, rings. Manufacturing Technology II - Exercise 3 11

12 Presentation and examples of commonly used forming processes saddle upsetting web punch saddle punch streck forming perssure forging squeeze jowl squeeze jowl gathering by die stretching rotary swaging by the in feed method Fig : Examples: Manufacturing processes forging: free forming Free forming: flanged shafts, casings, crankshafts, cam shafts, turbine shafts. Forming under compressive conditions: Hollow flange, connecting rods, rear-axle shaft, gearwheels, levers, valves. Fig : Examples: Manufacturing processes pressure forming: grooving and stamping Coins, medals, buttons Manufacturing Technology II - Exercise 3 12

13 Presentation and examples of commonly used forming processes 3.2 Forming under combination of tensile and compressive conditions Fig : Manufacturing processes tenso-compressive forming: deep drawing and spinning Examples: deep drawing: Drinking cans, auto-body parts, cooking pots. spinning: Containers, reflectors, car and truck wheel rims Fig : Manufacturing processes tenso-compressive forming: slip-type drawing Examples: Pipes Manufacturing Technology II - Exercise 3 13

14 Presentation and examples of commonly used forming processes 3.3 Forming under tensile conditions punch drum drum girder prestressed pincers die evacuated stretch forming strech forming with magnetic field Fig : Examples: Manufacturing processes tensile forming: stretch forming Formed sheet steel parts for use in the aerospace, automotive and ship building industries. punch die piercer water rubber bag expending with piercer expending with rubber bag Fig : Manufacturing processes tensile forming: expending Examples: Bottles. Manufacturing Technology II - Exercise 3 14

15 Presentation and examples of commonly used forming processes 3.4 Forming under bending conditions blank holder punch punch bearing surface free bending bering surface off-hand rounding fixture punch snaker die bending Fig : Manufacturing processes forming by bending: free bending, off-hand rounding and die bending Examples: PC-casing, external parts for fridges. roll pair roll cross-section of the Fig : Examples: Manufacturing processes forming by bending: roll forming to shape Furniture, various profiles. Manufacturing Technology II - Exercise 3 15

16 Presentation and examples of commonly used forming processes 3.5 Forming under shearing conditions tool hob displacement by shear parallel to adjacent surfaces ψ lower die adjusting the position, push through M t twisting Fig : Manufacturing processes shear forming: push through and twisting Examples: Pre-forms for forging operations. Manufacturing Technology II - Exercise 3 16

17 Presentation and examples of commonly used forming processes 3.6 Cutting Fig : Examples: Manufacturing processes cutting: shear cutting A range of parts from the automotive industry, the electronics industry and the domestic appliance industry Fig : Examples: Manufacturing processes cutting: fine blanking Camera parts, domestic appliance parts. Manufacturing Technology II - Exercise 3 17

18 Task 4 Task The part shown in the diagram is to be manufactured in two stages in a cold forming process (solid forming). The starting diameter of the slug is D 0. D 0 D 1 Fig. 5.1 Workpiece (two-stage forming) 1. Name the two forming techniques which are used to manufacture this. 2. Where would you place these operations in terms of the DIN classification system? 3. What type of lubricant is generally used in this processes? 4. List the advantages and disadvantages of cold and hot forming operations. 5. Name the sheet forming processes which could, in principle, be used to manufacture this part. Manufacturing Technology II - Exercise 3 18