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TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
TALAT Lecture 3803: Process Technologies
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TALAT Lecture 3803: Process Technologies

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This lecture describes fabrication processes for superplastic forming, i.e. female and male die forming, and the criteria for selecting the correct process. General background in production …

This lecture describes fabrication processes for superplastic forming, i.e. female and male die forming, and the criteria for selecting the correct process. General background in production engineering and material science is assumed.

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  • 1. TALAT Lecture 3803 Process Technologies 15 pages, 21 figures Advanced Level prepared by K. Siegert and T. Werle, Institut für Umformtechnik, Universität Stuttgart Objectives: − to describe fabrication processes for superplastic forming, i.e. female and male die forming, and the criteria for selecting the correct process Prerequisites: − General background in production engineering and material science Date of Issue: 1994 © EAA – European Aluminium Association TALAT 3803 1
  • 2. 3803 Process Technologies Table of Contents 3803 Process Technologies ...................................................................................2 3803.01 Superplastic Fabrication Methods ............................................................ 2 3803.02 Female Die Superplastic Forming ............................................................. 4 3803.03 Superplastic Forming with Male Dies....................................................... 7 3803.04 Criteria for the Choice between Male Die and Female Die Forming... 11 3803.05 List of Figures............................................................................................ 15 3803.01 Superplastic Fabrication Methods Figure 3803.01.01 defines in general terms the application of superplastic forming of sheets metals. Superplastic Forming of Sheets Manufacturing complex shaped components in small and medium series using simple tools and alloys having a special fine-grained microstructure alu Training in Aluminium Application Technologies Superplastic Forming of Sheets 3803.01.01 In principle, superplastic forming of metals can be subdivided into bulk metal and sheet metal forming, see Figure 3803.02.02. Hot die forging, precision forging and isothermal forging are examples for bulk superplastic forming. Bulk forming, however, shall not be treated in this lecture. TALAT 3803 2
  • 3. Forming Superplastic Materials Superplastic Superplastic sheet forming bulk forming Air injection Precision forging process process -Female die forming - Isothermal forging -Male die forming - Hot die forging alu Forming Superplastic Materials 3803.01.02 Training in Aluminium Application Technologies Processes for superplastic forming of sheet metals are subdivided further into three main pneumatic forming processes: die forming, patrizen forming and membrane forming, see Figure 3803.01.03. The economy of female die forming and male die forming can be increased by using a number of tool inserts assembled in one tool so as to produce a number of parts simultaneously. Superplastic Forming Processes for Sheet Male Die Forming Female Die Forming Membrane Forming Female Die Forming Male Die Forming with Inserts with Inserts alu Training in Aluminium Application Technologies Superplastic Forming Processes for Sheet 3803.01.03 Fields of application for the different manufacturing processes are shown in Figure 3803.01.04. Superplastic forming can best be applied for producing medium series of parts and for complicated shaped components. The field of application of superplastic forming is limited by conventional process technologies. Small series of complicated parts generally have to be produced as single-parts. Classical sheet forming technologies are suitable for parts which are not so complicated. The relatively expensive pressure die casting is most suitable for producing large series of complicated parts. TALAT 3803 3
  • 4. Fields of Application for the Different Manufacturing Processes 3 1 Single-piece production 4 2 Deep drawing and stretch forming Complexity 3 Pressure die casting 4 Superplastic forming 1 2 100 101 102 103 104 105 Series size alu Fields of Application for the Different 3803.01.04 Training in Aluminium Application Technologies Manufacturing Processes 3803.02 Female Die Superplastic Forming Female die forming utilises a concave form, see Figure 3803.02.01. During the whole forming process, the flange of the sheet blank is clamped tight between the top and lower pressure chambers. A flow-in of the material into the tool interior is thus not possible. The forming zone, therefore, consists of the blank membrane area within the tool. The pressure difference applied in the first phase, causes free forming (pneumatic sinking) of the blank membrane in the direction of the lower pressure. In the second phase, the gradually increasing doming leads to contact between tool and blank. The gas membrane then divides into sub membranes, leading to varying flow rate conditions and consequently to non-homogeneous material flow. Furthermore, the locally varying frictional conditions result in an unfavourable wall thickness distribution. TALAT 3803 4
  • 5. Female Die Forming po po 1st process step Process start Free forming of Tightly clamped blank pu pu a dome 2nd process step End of process Hindering of po material flow Formed part due to tool contact starts pu alu Training in Aluminium Application Technologies Female Die Forming 3803.02.01 Figure 3803.02.02 illustrates the forming steps during female die forming, described in Figure 3803.02.01, using a photographic technique. The first phase of undisturbed free forming can be seen clearly. In the second phase, two sub membranes exist. Forming Steps During Female Die Forming Source: Photographic Art, R. Häselich alu Forming Steps During Female Die Forming 3803.02.02 Training in Aluminium Application Technologies Figure 3803.02.07 shows a tool insert for a Landrover front part. The complicated internal design with very narrow webs is clearly visible. The use of die inserts reduces the cost significantly. TALAT 3803 5
  • 6. Tool for a Landrover Front Part Source: Superform Metal Ltd. alu Tool for a Landrover Front Part 3803.02.03 Training in Aluminium Application Technologies Figure 3803.02.04 shows a complete equipment for female die forming. One sees a rather simple machine construction which is, however, equipped with a complicated control and regulation system for gas and heat flow. Equipment for Female Die Forming Source: Superform Metal Ltd. alu Equipment for Female Die Forming 3803.02.04 Training in Aluminium Application Technologies The rear wheel housing of an ASTON MARTIN LAGONDA is a typical component produced with female die forming, see Figure 3803.02.05 TALAT 3803 6
  • 7. Superplastically Formed Wheel Housing with the Female Die Forming Process Rear Wheel Housing - ASTON MARTIN - - LAGONDA - Source: Superform Metals Ltd. alu Superplastically Formed Wheel Housing 3803.02.05 Training in Aluminium Application Technologies . 3803.03 Superplastic Forming with Male Dies The male forming process works with a convex form, see Figure 3803.03.01. During the whole forming process, the flange of the sheet blank is clamped tight between the top and lower pressure chambers. A flow-in of the material into the tool interior is thus not possible. The forming zone, therefore, consists of the blank membrane area within the tool. The pressure difference applied in the first phase, causes free forming (pneumatic sinking) of the blank membrane in the direction of the lower pressure. In the second phase, when the doming is large enough, the punch with the positive form is moved in and the material pressed on to the form by changing the pressure direction. Frictional contact and local thinning of the membrane occurs much later than in female die forming. As a result, the wall thickness distribution is more favourable than in female die forming. TALAT 3803 7
  • 8. Superplastic Male Die Forming Process Start 1st 2nd End Process Step Process Step of Process pO pO pO pU pU Tightly Form punch moved clamped blank Free forming Formed part in and air pressure direction reversed alu Superplastic Male Die Forming 3803.03.01 Training in Aluminium Application Technologies Figure 3803.02.11 shows the complete equipment used for superplastic male die forming: preheating furnace, machine and regulation and control systems for gas and heat flow. Equipment for Superplastic Male Die Forming Source: Superform Metal Ltd. alu Equipment for Superplastic Male Die Forming 3803.03.02 Training in Aluminium Application Technologies Figure 3803.03.03 shows an opened malew die forming machine where the material flanges are visible. The punch is at the top-end of the stroke. TALAT 3803 8
  • 9. Machine for Male Die Forming Source: Superform Metal Ltd. alu Machine for Male Die Forming 3803.03.03 Training in Aluminium Application Technologies Figure 3803.03.04 shows the tool for male die forming. One can clearly see the crimped seam, running around the periphery, used to seal the gas pressure cavities as well as the connections for heating the tool. The punch has moved to the top-end of the stroke. Tool for Male Die Forming Source: Superform Metal Ltd. alu Tool for Male Die Forming 3803.03.04 Training in Aluminium Application Technologies Figure 3803.03.05 illustrates the different stages in the manufacturing of a component using the male die forming process. The three intermediate stages of the left show the TALAT 3803 9
  • 10. initial phase of free forming. The last three stages show the steps of forming after pressure reversal. Stages in the Manufacturing of a Component Using the Male Die Forming Process Source: Superform Metals Ltd. alu Stages in the Manufacturing of a Component 3803.03.05 Training in Aluminium Application Technologies Using the Male Die Forming Process Figure 3803.03.06 shows a tool set, consisting of a punch, punch holder plate and blank holder, for male die forming of an external rear view mirror housing for a car together with an untrimmed and a trimmed component. Tool Set for Manufacturing a Car External Rear View Mirror Housing Tool for Manufacturing a Car External Rear View Mirror Housing Process: Male Die Forming Source: Superform Metal Ltd. alu Tool Set for Manufacturing a Car External 3803.03.06 Training in Aluminium Application Technologies Rear View Mirror Housing TALAT 3803 10
  • 11. Figure 3803.03.07 shows a head rest for a pilot seat. The characteristically high form of the part makes it most suitable for male die forming. A sectional view is shown on the left. A good wall thickness distribution exists above the trimming line. Wall Thickness Distribution in a Head Rest - Male Die Process - Starting sheet thickness s = 3 mm Section A - A Sectional line A-A 1,13mm 1,20mm 1,45mm 37,7% 1,45mm 48,3% 40,0% 48,3% 1,38mm 46,0% 48,0% 1,44mm 1,79mm 59,7% Cutting line 3,00mm 3,00mm Wall thickness along part Part: Head rest of a pilot seat Source: Schneider, K.E. alu Wall Thickness Distribution in a Head Rest 3803.03.07 Training in Aluminium Application Technologies 3803.04 Criteria for the Choice between Male Die and Female Die Forming Figure 3803.04.01 shows the criteria required in principle for choosing the male die forming process. The male die forming process allows an accurate replication of the interior contours. Due to local differences in material flow, the external contour do not exactly conform to the required geometry. Since the male die forming process exploits the material volume better than die forming, it is possible to work with thinner starting sheets in the former case. Secondary form elements protruding out of the basic form in the blowing direction have a positive effect on the male die forming. The maximum ratio for the surface increase is 0.6. TALAT 3803 11
  • 12. Criteria for Choosing Male Die Forming b l The ratio of surface area increase A0/A1 is greater than 0.4. A0 = l ⋅ b h A0 = l ⋅ b + 2 ⋅ h(b + l ) z Exact replication of contours on inside of part. External surface of part free from z Actual contour manufacturing blemishes (scratches etc.). Wavy external surface of part due to wall Required contour thickness variations. Weight of part and sheet thickness required to be s as low as possible. Secondary Secondary form elements make female die form element forming very difficult. alu Training in Aluminium Application Technologies Criteria for Choosing Male Die Forming 3803.04.01 Principle criteria for choosing the female die forming process are discussed in Figure 3803.04.02. The maximum ratio for the surface increase is 0.4. Criteria for Choosing Female Die Forming An exact form replication on the outside surface of the part is essential. z Part interior surface free from manufacturing blemishes (scratches etc.). Wavy interior Required contour surface of part due to variations in wall Actual contour thickness. Ribs divide the part. Secondary form elements make male die forming difficult. The blank size necessary is not conducive to male die forming. alu Training in Aluminium Application Technologies Criteria for Choosing Female Die Forming 3803.04.02 Figure 3803.04.03 compares the component requirements, blank dimensions, geometrical and dimensional requirements, economy and the controlling parameters as a help for selecting the right process for superplastic forming processes. TALAT 3803 12
  • 13. Choosing a Process for Superplastic Forming Part requirements Dimensional and geometrical Economy Control possibilities requirements Criterion Part size Defect-free Dimensional Part wall Economic Forming Control of (possible) surface accuracy thickness aspects ratio log. strain rate < 2300 x 1300 < 900 x 1300 Process Constant surfacce surfacce External External Multiple Internal forming Internal surface surface fk < 0,4 fk < 0,6 > 900 costs Tool ϕ Female die process -- + + -- --- +++ -- Female die process -- + + -- --- ++ -- with insets Male die + - - + + + + process Male die process + - - + + + + with insets Source: Superform Metals Ltd. alu Training in Aluminium Application Technologies Choosing a Process for Superplastic Forming 3803.04.03 Figure 3803.04.04 gives a method for estimating the required gas pressure for forming which can be calculated using the formula p = 2 ⋅ kf ⋅ s/r. This formula is based on the equilibrium principle of the strength theory: p ⋅ Aproj. = kf ⋅ Astressed Estimating the Required Gas Pressure dA cosα Hemisphere dA σl σu σr dFn α σu p σl α F s r = average sphere radius p = internal pressure kf = flow stress s = sheet thickness Equilibrium conditions p Aproj. = kf Astressed p = kf 2s r alu Training in Aluminium Application Technologies Estimating the Required Gas Pressure 3803.04.04 In order to obtain kf from the flow curves it is necessary to estimate the logarithmic strain rate, ϕ ,as outlined in Figure 3803.04.05, where vwzg is the tool velocity (see also ! TALAT 3300, Figure 3303.02.04). TALAT 3803 13
  • 14. Estimating the Log. Strain Rate (or True Strain Rate) Elongation of a tensile specimen element l ϕ = ln l0 l0 dl " dϕ dl vwzg ϕ= = = dt ldt l alu Estimating the Log. Strain Rate (or True Strain Rate) 3803.04.05 Training in Aluminium Application Technologies TALAT 3803 14
  • 15. 3803.05 List of Figures Figure No. Figure Title (Overhead) 3803.01.01 Superplastic Forming of Sheets 3803.01.02 Forming Superplastic Materials 3803.01.03 Superplastic Forming Processes for Sheet 3803.01.04 Fields of Application for the Different Manufacturing Processes 3803.02.01 Female Die Forming 3803.02.02 Forming Steps during Female Die Forming 3803.02.03 Tool for a Landrover Front Part 3803.02.04 Equipment for Female Die Forming 3803.02.05 Superplastically Formed Wheel Housing 3803.03.01 Superlastic Male Die Forming 3803.03.02 Equipment for Superplastic Male Die Forming 3803.03.03 Machine for Male Die Forming 3803.03.04 Tool for Male Die Forming 3803.03.05 Stages in the Manufacturing of a Component Using the Male Die Forming Process 3803.03.06 Tool Set for Manufacturing a Car External Rear View Mirror Housing 3803.03.07 Wall Thickness Distribution in a Head Rest 3803.04.01 Criteria for Choosing Male Die Forming 3803.04.02 Criteria for Choosing Female Die Forming 3803.04.03 Choosing a Process for Superplastic Forming 3803.04.04 Estimating the Required Gas Pressure 3803.04.05 Estimating the Log. Strain Rate (or True Strain Rate) TALAT 3803 15

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